Patent Application
20070254485
So that the manner in which the above recited aspects of the present invention are attained and can be understood in detail, a more particular description of embodiments of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In general, aspects of the inventions provide compositions and methods for removing at least a conductive material from a substrate surface. The inventions are described below in reference to a planarizing process for the removal of conductive materials from a substrate surface by an electrochemical mechanical polishing (Ecmp) technique.
The words and phrases used herein should be given their ordinary and customary meaning in the art by one skilled in the art unless otherwise further defined. Chemical mechanical polishing should be broadly construed and includes, but is not limited to, planarizing a substrate surface using chemical activity and mechanical activity, or a concurrent application of chemical activity and mechanical activity. Electropolishing should be broadly construed and includes, but is not limited to, removing material from a substrate by eroding the substrate surface under application of electric current. Electrochemical mechanical polishing (Ecmp) should be broadly construed and includes, but is not limited to, planarizing a substrate by the application of electrochemical activity, mechanical activity, chemical activity, or a concurrent application of a combination of electrochemical, chemical, and/or mechanical activity to remove material from a substrate surface.
Anodic dissolution should be broadly construed and includes, but is not limited to, the application of an anodic bias to a substrate directly or indirectly which results in the removal of conductive material from a substrate surface and into a surrounding polishing composition. Polishing composition should be broadly construed and includes, but is not limited to, a composition that provides ionic conductivity, and thus, electrical conductivity, in a liquid medium, which generally comprises materials known as electrolyte components. The amount of each component in the polishing compositions can be measured in volume percent or weight percent. Volume percent refers to a percentage based on volume of a desired liquid component divided by the total volume of all of the liquid in the complete composition. A percentage based on weight percent is the weight of the desired component divided by the total weight of all of the liquid components in the complete composition. Abrading and abrasion should be broadly construed and includes, but is not limited to, contacting a material and displacing, disturbing, or removing all or a portion of the material.
The electrochemical mechanical polishing process may be performed in a process apparatus, such as a platform having one or more polishing stations adapted for electrochemical mechanical polishing processes. A platen for performing an electrochemical mechanical polishing process may include a polishing article, a first electrode, and a second electrode, wherein the substrate is in electrical contact with the second electrode. A first electrochemical mechanical polishing process may be performed on a first platen as described herein and the second electrochemical mechanical polishing process may be performed on the same or different platen adapted for electrochemical mechanical polishing, such as the second platen as described herein.
A controller 108 is provided to facilitate control and integration of the modules of the system 100. The controller 108 comprises a central processing unit (CPU) 110, a memory 112, and support circuits 114. The controller 108 is coupled to the various components of the system 100 to facilitate control of, for example, the planarizing, cleaning, and transfer processes.
The factory interface 102 generally includes a cleaning module 116 and one or more wafer cassettes 118. An interface robot 120 is employed to transfer substrates 122 between the wafer cassettes 118, the cleaning module 116 and an input module 124. The input module 124 is positioned to facilitate transfer of substrates 122 between the planarizing module 106 and the factory interface 102 by grippers, for example vacuum grippers or mechanical clamps (not shown).
The planarizing module 106 includes at least a first electrochemical mechanical planarizing (Ecmp) station 128, disposed in an environmentally controlled enclosure 188. Examples of planarizing modules 106 that can be adapted to benefit from the invention include MIRRA® Chemical Mechanical Planarizing Systems, MIRRA MESA™ Chemical Mechanical Planarizing Systems, REFLEXION® Chemical Mechanical Planarizing Systems, REFLEXION LK™ Chemical Mechanical Planarizing Systems, and REFLEXION LK Ecmp™ Chemical Mechanical Planarizing Systems, all available from Applied Materials, Inc. of Santa Clara, Calif. Other planarizing modules, including those that use processing pads, planarizing webs, or a combination thereof, and those that move a substrate relative to a planarizing surface in a rotational, linear or other planar motion may also be adapted to benefit from the invention.
In the embodiment depicted in
A conventional chemical mechanical planarizing process is performed at the planarizing station 132 after processing at the second Ecmp station 130 by the barrier removal process described herein. Alternatively, an example of a conventional CMP process on a chemical mechanical polishing station for the barrier removal is described in United States Patent Publication No. 2003-0013387, published Jan. 16, 2003, issued as U.S. Pat. No. 7,104,869, entitled “Barrier Removal At Low Pressure Polish,” which is incorporated by reference in its entirety. It is contemplated that other CMP processes may be alternatively performed. As the CMP stations 132 are conventional in nature, further description thereof has been omitted for the sake of brevity.
It is contemplated that more than one Ecmp station may be utilized to perform the multi-step removal process after the bulk removal process performed at a different station. Alternatively, each of the first and second Ecmp stations 128, 130 may be utilized to perform both the bulk and multi-step conductive material removal on a single station. It is also contemplated that all Ecmp stations (for example 3 stations of the module 106 depicted in
The exemplary planarizing module 106 also includes a transfer station 136 and a carousel 134 that are disposed on an upper or first side 138 of a machine base 140. In certain embodiments, the transfer station 136 includes an input buffer station 142, an output buffer station 144, a transfer robot 146, and a load cup assembly 148. The input buffer station 142 receives substrates from the factory interface 102 by means of the loading robot 104. The loading robot 104 is also utilized to return polished substrates from the output buffer station 144 to the factory interface 102. The transfer robot 146 is utilized to move substrates between the buffer stations 142, 144 and the load cup assembly 148.
In certain embodiments, the transfer robot 146 includes two gripper assemblies (not shown), each having pneumatic gripper fingers that hold the substrate by the substrate's edge. The transfer robot 146 may simultaneously transfer a substrate to be processed from the input buffer station 142 to the load cup assembly 148 while transferring a processed substrate from the load cup assembly 148 to the output buffer station 144. An example of a transfer station that may be used to advantage is described in U.S. Pat. No. 6,156,124, issued Dec. 5, 2000 to Tobin, which is herein incorporated by reference in its entirety.
The carousel 134 is centrally disposed on the base 140. The carousel 134 typically includes a plurality of arms 150, each supporting a planarizing head assembly 152. Two of the arms 150 depicted in
A conditioning device 182 is disposed on the base 140 adjacent each of the planarizing stations 128, 130, 132. The conditioning device 182 periodically conditions the planarizing material disposed in the stations 128, 130, 132 to maintain uniform planarizing results.
In certain embodiments, the planarizing head may be a TITAN HEAD™ or TITAN PROFILER™ wafer carrier manufactured by Applied Materials, Inc. Generally, the planarizing head 204 comprises a housing 214 and retaining ring 224 that defines a center recess in which the substrate 122 is retained. The retaining ring 224 circumscribes the substrate 122 disposed within the planarizing head 204 to prevent the substrate from slipping out from under the planarizing head 204 while processing. The retaining ring 224 can be made of plastic materials such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), and the like, or conductive materials such as stainless steel, Cu, Au, Pd, and the like, or some combination thereof. It is further contemplated that a conductive retaining ring 224 may be electrically biased to control the electric field during Ecmp. Conductive or biased retaining rings tend to slow the polishing rate proximate the edge of the substrate. It is contemplated that other planarizing heads may be utilized.
The first Ecmp station 128 generally includes a platen assembly 230 that is rotationally disposed on the base 140. The platen assembly 230 is supported above the base 140 by a bearing 238 so that the platen assembly 230 may be rotated relative to the base 140. An area of the base 140 circumscribed by the bearing 238 is open and provides a conduit for the electrical, mechanical, pneumatic, control signals and connections communicating with the platen assembly 230.
Conventional bearings, rotary unions and slip rings, collectively referred to as rotary coupler 276, are provided such that electrical, mechanical, fluid, pneumatic, control signals and connections may be coupled between the base 140 and the rotating platen assembly 230. The platen assembly 230 is typically coupled to a motor 232 that provides the rotational motion to the platen assembly 230. The motor 232 is coupled to the controller 108 that provides a signal for controlling for the rotational speed and direction of the platen assembly 230.
A top surface 260 of the platen assembly 230 supports a processing pad assembly 222 thereon. The processing pad assembly may be retained to the platen assembly 230 by magnetic attraction, vacuum, clamps, adhesives and the like.
A plenum 206 is defined in the platen assembly 230 to facilitate uniform distribution of electrolyte to the planarizing surface 126. A plurality of passages, described in greater detail below, are formed in the platen assembly 230 to allow electrolyte, provided to the plenum 206 from an electrolyte source 248, to flow uniformly though the platen assembly 230 and into contact with the substrate 122 during processing. It is contemplated that different electrolyte compositions may be provided during different stages of processing.
The processing pad assembly 222 includes an electrode 292 and at least a planarizing portion 290. The electrode 292 is typically comprised of a conductive material, such as stainless steel, copper, aluminum, gold, silver and tungsten, among others. The electrode 292 may be solid, impermeable to electrolyte, permeable to electrolyte or perforated. At least one contact assembly 250 extends above the processing pad assembly 222 and is adapted to electrically couple the substrate being processed on the processing pad assembly 222 to the power source 242. The electrode 292 is also coupled to the power source 242 so that an electrical potential may be established between the substrate and electrode 292.
A meter (not shown) is provided to detect a metric indicative of the electrochemical process. The meter may be coupled or positioned between the power source 242 and at least one of the electrode 292 or contact assembly 250. The meter may also be integral to the power source 242. In certain embodiments, the meter is configured to provide the controller 108 with a metric indicative of processing, such a charge, current and/or voltage. This metric may be utilized by the controller 108 to adjust the processing parameters in-situ or to facilitate endpoint or other process stage detection.
A window 246 is provided through the pad assembly 222 and/or platen assembly 230, and is configured to allow a sensor 254, positioned below the pad assembly 222, to sense a metric indicative of polishing performance. For example, the sensor 254 may be an eddy current sensor or an interferometer, among other sensors. The metric, provided by the sensor 254 to the controller 108, provides information that may be utilized for processing profile adjustment in-situ, endpoint detection or detection of another point in the electrochemical process. In certain embodiments, the sensor 254 an interferometer capable of generating a collimated light beam, which during processing, is directed at and impinges on a side of the substrate 122 that is being polished. The interference between reflected signals is indicative of the thickness of the conductive layer of material being processed. One sensor that may be utilized to advantage is described in U.S. Pat. No. 5,893,796, issued Apr. 13, 1999, to Birang, et al., which is hereby incorporated by reference in its entirety.
Embodiments of the processing pad assembly 222 suitable for removal of conductive material from the substrate 122 may generally include a planarizing surface 126 that is substantially dielectric. Other embodiments of the processing pad assembly 222 suitable for removal of conductive material from the substrate 122 may generally include a planarizing surface 126 that is substantially conductive. At least one contact assembly 250 is provided to couple the substrate to the power source 242 so that the substrate may be biased relative to the electrode 292 during processing. Apertures 210, formed through the planarizing portion 290 and the electrode 292 and the any elements disposed below the electrode, allow the electrolyte to establish a conductive path between the substrate 122 and electrode 292.
In certain embodiments, the planarizing portion 290 of the processing pad assembly 222 is a dielectric, such as polyurethane. Examples of processing pad assemblies that may be adapted to benefit from the invention are described in U.S. Pat. No. 6,991,528, issued Jan. 31, 2006, entitled “Conductive Planarizing Article For Electrochemical Mechanical Planarizing”, and United States Patent Publication No. 2004-0020789, published Feb. 5, 2004, entitled “Conductive Planarizing Article For Electrochemical Mechanical Planarizing,” both of which are hereby incorporated by reference in their entireties.
The contact assemblies 250 are generally electrically coupled to the power source 242 through the platen assembly 230 and are movable to extend at least partially through respective apertures 368 formed in the processing pad assembly 222. The positions of the contact assemblies 250 may be chosen to have a predetermined configuration across the platen assembly 230. For predefined processes, individual contact assemblies 250 may be repositioned in different apertures 368, while apertures not containing contact assemblies may be plugged with a stopper 392 or filled with a nozzle 394 (as shown in
Although the embodiments of the contact assembly 250 described below with respect to
In certain embodiments, each of the contact assemblies 250 includes a hollow housing 302, an adapter 304, a ball 306, a contact element 314 and a clamp bushing 316. The ball 306 has a conductive outer surface and is movably disposed in the housing 302. The ball 306 may be disposed in a first position having at least a portion of the ball 306 extending above the planarizing surface 126 and at least a second position where the ball 306 is substantially flush with the planarizing surface 126. It is also contemplated that the ball 306 may move completely below the planarizing surface 126. The ball 306 is generally suitable for electrically coupling the substrate 122 to the power source 242. It is contemplated that a plurality of balls 306 for biasing the substrate may be disposed in a single housing 358 as depicted in
The power source 242 generally provides a positive electrical bias to the ball 306 during processing. Between planarizing substrates, the power source 242 may optionally apply a negative bias to the ball 306 to minimize attack on the ball 306 by process chemistries.
The housing 302 is configured to provide a conduit for the flow of electrolyte from the source 248 to the substrate 122 during processing. The housing 302 is fabricated from a dielectric material compatible with process chemistries. A seat 326 formed in the housing 302 prevents the ball 306 from passing out of the first end 308 of the housing 302. The seat 326 optionally may include one or more grooves 348 formed therein that allow fluid flow to exit the housing 302 between the ball 306 and seat 326. Maintaining fluid flow past the ball 306 may minimize the propensity of process chemistries to attack the ball 306.
The contact element 314 is coupled between the clamp bushing 316 and the adapter 304. The contact element 314 is generally configured to electrically connect the adapter 304 and ball 306 substantially or completely through the range of ball positions within the housing 302. In certain embodiments, the contact element 314 may be configured as a spring form.
In the embodiment depicted in
Returning to FIGS. 4A and 5A-5B, the clamp bushing 316 includes a flared head 424 having a threaded post 426 extending therefrom. The clamp bushing 316 may be fabricated from either a dielectric or conductive material, or a combination thereof, and in certain embodiments, is fabricated from the same material as the housing 302. The flared head 424 maintains the flexures 344 at an acute angle relative to the centerline of the contact assembly 250 so that the flexures 344 of the contact elements 314 are positioned to spread around the surface of the ball 306 to prevent bending, binding and/or damage to the flexures 344 during assembly of the contact assembly 250 and through the range of motion of the ball 306.
The ball 306 may be solid or hollow and is typically fabricated from a conductive material. For example, the ball 306 may be fabricated from a metal, conductive polymer or a polymeric material filled with conductive material, such as metals, conductive carbon or graphite, among other conductive materials. Alternatively, the ball 306 may be formed from a solid or hollow core that is coated with a conductive material. The core may be non-conductive and at least partially coated with a conductive covering.
The ball 306 is generally actuated toward the planarizing surface 126 by at least one of spring, buoyant or flow forces. In the embodiment depicted in
In certain embodiments, the processing pad assembly 604 includes interposed pad 612 sandwiched between a conductive pad 610 and an electrode 614. The conductive pad 610 is substantially conductive across its top processing surface and is generally made from a conductive material or a conductive composite (i.e., the conductive elements are dispersed integrally with or comprise the material comprising the planarizing surface), such as a polymer matrix having conductive particles dispersed therein or a conductive coated fabric, among others. The conductive pad 610, the interposed pad 612, and the electrode 614 may be fabricated into a single, replaceable assembly. The processing pad assembly 604 is generally permeable or perforated to allow electrolyte to pass between the electrode 614 and top surface 620 of the conductive pad 610. In the embodiment depicted in
A conductive foil 616 may additionally be disposed between the conductive pad 610 and the interposed pad 612. The foil 616 is coupled to a power source 242 and provides uniform distribution of voltage applied by the source 242 across the conductive pad 610. In embodiments not including the conductive foil 616, the conductive pad 610 may be coupled directly, for example, via a terminal integral to the pad 610, to the power source 242. Additionally, the pad assembly 604 may include an interposed pad 618, which, along with the foil 616, provides mechanical strength to the overlying conductive pad 610. Examples of suitable pad assemblies are described in the previously incorporated U.S. Pat. No. 6,991,528 and United States Patent Publication No. 2004-0020789.
Methods are provided for polishing a substrate to remove residues and minimize dishing within features, while increasing throughput with a decrease in polishing time. The methods may be performed by an electrochemical polishing technique, which includes a combination of chemical activity, mechanical activity and electrical activity to remove conductive materials and planarize a substrate surface. The polishing compositions described herein form passivation layers on the substrate surface. The passivation layer may chemically and/or electrically insulate material disposed on a substrate surface.
In one aspect, the method may include processing a substrate having a conductive material layer disposed over features, supplying a first polishing composition, or bulk polishing composition, to the surface of the substrate, applying a first pressure between the substrate and a polishing article, providing relative motion between the substrate and the polishing article, applying a first bias between a first electrode and a second electrode in electrical contact with the substrate, removing a portion, such as at least about 50%, of the conductive material, supplying a second polishing composition, or residual polishing composition, to the surface of the substrate, applying a second pressure between the substrate and a polishing article, providing relative motion between the substrate and the polishing article, applying a second bias between a first electrode and a second electrode in electrical contact with the substrate, and removing residual conductive material from the substrate surface.
The removal of excess copper may be performed in one or more processing steps, for example, a single copper removal step or a first removal step, such as a bulk conductive material (e.g., copper) removal step and a second removal step, such as a residual conductive material removal step. Bulk material, or bulk conductive material, is broadly defined herein as any material deposited on the substrate in an amount more than sufficient to substantially fill features formed on the substrate surface. Residual material, or residual conductive material, is broadly defined as any material remaining after one or more bulk or residual polishing process steps. Generally, in a two step process, the first conductive material removal step, the bulk removal step, is performed by a first electrochemical mechanical polishing process to remove at least about 50% of the conductive layer, preferably at least about 70%, more preferably at least about 80%, for example, at least about 90%. The second conductive material removal step, the residual removal step, is performed by a second electrochemical mechanical polishing process that removes most, if not all, of the remaining conductive material disposed on the barrier layer to leave behind the filled plugs.
The first removal electrochemical mechanical polishing process may be performed on a first polishing platen and the second removal electrochemical mechanical polishing process on a second polishing platen of the same or different polishing apparatus as the first platen. In certain embodiments of the two-step process, the second removal electrochemical mechanical polishing process may be performed on the same platen with the bulk removal process. Any barrier material may be removed on a separate platen, such as the third platen in the apparatus described in
While the following processes and compositions are described for removing copper, the invention contemplates that the compositions and processes herein also may be used for the removal of other conductive materials, such as aluminum, platinum, tungsten, tungsten nitride, titanium, titanium nitride, tantalum, tantalum nitride, cobalt, gold, silver, ruthenium and combinations thereof.
The terms narrow and wide feature definitions may vary depending on the structures formed on the substrate surface, but can generally be characterized by the respective deposition profiles of excessive material deposition (or high overburden) formed over narrow feature definitions and minimal or low material deposition (minimal or low overburden), over wide feature definitions. For example narrow feature definitions may be about 0.13 μm in size and may have a high overburden as compared to wide feature definitions that may be about 10 μm in size and that may have minimal or insufficient overburden. However, high overburdens and low overburdens do not necessarily have to form over features, but may form over areas on the substrate surface between features.
The dielectric layer 810 may comprise one or more dielectric materials conventionally employed in the manufacture of semiconductor devices. For example, dielectric materials may include materials such as silicon dioxide, phosphorus-doped silicon glass (PSG), boron-phosphorus-doped silicon glass (BPSG), and silicon dioxide derived from tetraethyl orthosilicate (TEOS) or silane by plasma enhanced chemical vapor deposition (PECVD). The dielectric layer may also comprise low dielectric constant materials, including fluoro-silicon glass (FSG), polymers, such as polyamides, carbon-containing silicon oxides, such as Black Diamond™ dielectric material, silicon carbide materials, which may be doped with nitrogen and/or oxygen, including BLOK™ dielectric materials, available from Applied Materials, Inc. of Santa Clara, Calif.
A barrier layer 840 is disposed conformally in the feature definitions 820 and 830 and on the substrate 800. The barrier layer 840 may comprise metals or metal nitrides, such as tantalum, tantalum nitride, tantalum silicon nitride, titanium, titanium nitride, titanium silicon nitride, tungsten, tungsten nitride and combinations thereof, or any other material that may limit diffusion of materials between the substrate and/or dielectric materials and any subsequently deposited conductive materials.
A conductive material layer 860 is disposed on the barrier layer 840. The term “conductive material layer” as used herein is defined as any conductive material, such as copper, tungsten, aluminum, and/or their alloys used to fill a feature to form lines, contacts or vias. While not shown, a seed layer of a conductive material may be deposited on the barrier layer prior to the deposition of the conductive material layer 860 to improve interlayer adhesion and improve subsequent deposition processes. The seed layer may be of the same material as the subsequent material to be deposited.
One type of conductive material layer 860 comprises copper containing materials. Copper containing materials include copper, copper alloys (e.g., copper-based alloys containing at least about 80 weight percent copper) or doped copper. As used throughout this disclosure, the phrase “copper containing material,” the word “copper,” and the symbol “Cu” are intended to encompass copper, copper alloys, doped copper, and combinations thereof. Additionally, the conductive material may comprise any conductive material used in semiconductor manufacturing processing.
In the first electrochemical mechanical polishing step, a first passivation layer 885 is formed from exposure of the conductive material to the first polishing composition. The first passivation layer 885 forms on the exposed conductive material 860 on the substrate surface including the high overburden 870, peaks, and minimal overburden 880, valleys, formed in the deposited conductive material 860. The first passivation layer 885 chemically and/or electrically insulates the surface of the substrate from chemical and/or electrical reactions.
The process begins with a substrate being positioned in a polishing apparatus, such as the apparatus descried herein and shown in
An example of the first polishing composition for the bulk removal step includes between about 1 wt. % and about 10 wt. % of phosphoric acid, between about 0.1 wt. % and about 6 wt. % of the at least one chelating agent, between about 0.01 wt. % and about 1 wt. % of the corrosion inhibitor, between about 0.5 wt. % and about 10 wt. % of an inorganic or organic salt, between about 0.2 wt. % and about 5 wt. % of an oxidizer, and between about 0.05 wt. % and about 1 wt. % of abrasive particulates. The first polishing composition has a conductivity of between about 30 milliSiemens/centimeter (mS/cm) and about 70 mS/cm, for example, between about 60 mS/cm and about 64 mS/cm. Alternatively, first electrochemical mechanical polishing step may comprise the second electrochemical mechanical polishing composition as described herein. The process may also be performed with a composition temperature between about 20° C. and about 60° C.
A polishing article coupled to a polishing article assembly containing a second electrode is then physically contacted and/or electrically coupled with the substrate through a conductive polishing article. The substrate surface and polishing article are contacted at a pressure less than about 2 pounds per square inch (lb/in2 or psi) (13.8 kPa). The contact pressure may include a pressure of about 1 psi (6.9 kPa) or less, for example, between about 0.01 psi (69 Pa) and about 1 psi (6.9 kPa), such as between about 0.1 (0.7 kPa) psi and about 0.8 psi (5.5 kPa) or between about 0.1 (0.7 kPa) psi and less than about 0.5 psi (3.4 kPa). In one aspect of the process, a pressure of about 0.3 psi (2.1 kPa) or less is used.
Relative motion is provided between the substrate surface and the conductive article to reduce or remove the first passivation layer 885. Relative motion is provided between the substrate surface and the conductive pad assembly 222. The conductive pad assembly 222 disposed on the platen is rotated at a platen rotational rate of between about 7 rpm and about 80 rpm, for example, about 28 rpm, and the substrate disposed in a carrier head is rotated at a carrier head rotational rate between about 7 rpm and about 80 rpm, for example, about 37 rpm. The respective rotational rates of the platen and carrier head are believed to provide reduced shear forces and frictional forces when contacting the polishing article and substrate. Both the carrier head rotational speed and the platen rotational speed may be between about 7 rpm and less than 40 rpm. In one aspect of first polishing process, the carrier head rotational speed may be greater than a platen rotational speed by a ratio of carrier head rotational speed to platen rotational speed of greater than about 1:1, such as a ratio of carrier head rotational speed to platen rotational speed between about 1.5:1 and about 12:1, for example between about 1.5:1 and about 3:1, to remove material from the substrate surface.
A first bias from a power source 242 is applied between the two electrodes. The bias may be transferred from a conductive pad and/or electrode in the polishing article assembly 222 to the substrate 122. The bias may be applied by an electrical pulse modulation technique providing at least anodic dissolution.
The first bias is generally provided to produce anodic dissolution of the conductive material from the surface of the substrate at a current density up and about 100 mA/cm2 which correlates to an applied current of about 40 amps to process substrates with a diameter up and about 300 mm. For example, a 200 mm diameter substrate may have a current density between about 0.01 mA/cm2 and about 50 mA/cm2, which correlates to an applied current between about 0.01 A and about 20 A. The invention also contemplates that the bias may be applied and monitored by volts, amps and watts. For example, in certain embodiments, the power supply may apply a power between about 0.01 watts and 100 watts, a voltage between about 0.01 V and about 10 V, and a current between about 0.01 amps and about 10 amps. The bias between about 1.6 volts and about 3.5 volts, such as 3 volts, may be used as the applied bias in the first electrochemical processing step.
The first bias may be varied in power and application depending upon the user requirements in removing material from the substrate surface. For example, increasing power application has been observed to result in increasing anodic dissolution. The bias may also be applied by an electrical pulse modulation technique. Pulse modulation techniques may vary, but generally include a cycle of applying a constant current density or voltage for a first time period, then applying no current density or voltage or a constant reverse current density or voltage for a second time period. The process may then be repeated for one or more cycles, which may have varying power levels and durations. The power levels, the duration of power, an “on” cycle, and no power, an “off” cycle” application, and frequency of cycles, may be modified based on the removal rate, materials to be removed, and the extent of the polishing process. For example, increased power levels and increased duration of power being applied have been observed to increase anodic dissolution.
In one pulse modulation process for electrochemical mechanical polishing, the pulse modulation process comprises an on/off power technique with a period of power application, “on”, followed by a period of no power application, “off”. The on/off cycle may be repeated one or more times during the polishing process. The “on” periods allow for removal of exposed conductive material from the substrate surface and the “off” periods allow for polishing composition components and by-products of “on” periods, such as metal ions, to diffuse to the surface and complex with the conductive material. During a pulse modulation technique process it is believed that the metal ions migrate and interact with the corrosion inhibitors and/or chelating agents by attaching to the passivation layer in the non-mechanically disturbed areas. The process thus allows etching in the electrochemically active regions, not covered by the passivation layer, during an “on” application, and then allowing reformation of the passivation layer in some regions and removal of excess material during an “off” portion of the pulse modulation technique in other regions. Thus, control of the pulse modulation technique can control the removal rate and amount of material removed from the substrate surface.
The “on”/“off” period of time may be between about 1 second and about 60 seconds each, for example, between about 2 seconds and about 25 seconds, and the invention contemplates the use of pulse techniques having “on” and “off” periods of time greater and shorter than the described time periods herein. In one example of a pulse modulation technique, power is applied between about 16% and about 66% of each cycle.
Non-limiting examples of pulse modulation technique with an on/off cycle for electrochemical mechanical polishing of materials described herein include: applying power, “on”, between about 5 seconds and about 10 seconds and then not applying power, “off”, between about 2 seconds and about 25 seconds; applying power for about 10 seconds and not applying power for 5 seconds, or applying power for 10 seconds and not applying power for 2 seconds, or even applying power for 5 seconds and not applying power for 25 seconds to provide the desired polishing results. The cycles may be repeated as often as desired for each selected process. One example of a pulse modulation process is described in commonly assigned U.S. Pat. No. 6,379,223, issued Apr. 30, 2002, which is incorporated by reference herein to the extent not inconsistent with the claimed aspects and disclosure herein. Further examples of pulse modulation processes are described in co-pending United States Patent Publication No. 2004-0072445, entitled “Effective Method To Improve Surface Finish In Electrochemically Assisted Chemical Mechanical Polishing”, published on Apr. 15, 2004, which is incorporated by reference herein to the extent not inconsistent with the claimed aspects and disclosure herein.
A removal rate of conductive material of up and about 15,000 Å/min can be achieved by the processes described herein. Higher removal rates are generally desirable, but due to the goal of maximizing process uniformity and other process variables (e.g., reaction kinetics at the anode and cathode) it is common for dissolution rates to be controlled between about 100 Å/min and about 15,000 Å/min. In certain embodiments of the invention where the copper material to be removed is less than 5,000 Å thick, the voltage (or current) may be applied to provide a removal rate between about 100 Å/min and about 5,000 Å/min. The substrate is typically exposed to the polishing composition and power application for a period of time sufficient to remove at least a portion or all of the desired material disposed thereon.
The first passivation layer is formed from the exposure of the substrate surface to the corrosion inhibitor and/or other materials capable of forming a passivating or insulating film, for example, chelating agents. The thickness and density of the passivation layer can dictate the extent of chemical reactions and/or amount of anodic dissolution. For example, a thicker or denser passivation layer 885 has been observed to result in less anodic dissolution compared to thinner and less dense passivation layers. Thus, control of the composition of passivating agents, corrosion inhibitors and/or chelating agents, allow control of the removal rate and amount of material removed from the substrate surface.
During anodic dissolution under application of the bias, the substrate surface, i.e., the conductive material layer 860 may be biased anodically above a threshold potential of the conductive material, for example, a metal material, on the substrate surface to “oxidize”. When a metal material oxidizes, a metal atom gives up one or more electrons to the power source and forms metal ions or cations. The metal ions may then leave the substrate surface and dissolve into the electrolyte solution. In the case where copper is the desired material to be removed, cations can have the Cu1+ or Cu2+ oxidation state.
The metal ions may also contribute to the formation of the thickness and/or density of the first passivation layer 885. For example, the inhibitors and/or chelating agents found in the polishing composition may complex with the metal ions and the metal ions become incorporated into the first passivation layer 885. Thus, the presence of the inhibitors and/or chelating agents found in the polishing composition limit or reduce the electrochemical dissolution process of the metal ions into the electrolyte, and further incorporate such metal ions into the first passivation layer 885. It has been observed that the thickness and/or density of the undisturbed portion of the first passivation layer 885 may increase after periods of applied bias for anodic dissolution of conductive materials on the substrate surface. It is believed that the increase in the thickness and/or density of the undisturbed portion of the first passivation layer 885 is related to the total applied power and is a function of time and/or power levels. It has also been observed that the undisturbed portion of the passivation layer 885 incorporates metal ions and that the metal ions may contribute to the thickness and/or density of the passivation layer.
Mechanical abrasion by a conductive polishing article removes the first passivation layer 885 that insulates the conductive material chemically and/or electrically. For example, the first passivation layer suppresses the current for anodic dissolution so that areas of high overburden is preferentially removed over areas of minimal overburden as the passivation layer is retained in areas of minimal or no contact with the conductive polishing article. The removal rate of the conductive material 860 covered by the first passivation layer 885 is less than the removal rate of conductive material without the first passivation layer 885. As such, the excess material disposed over narrow feature definitions 820 and the substrate field 850 is removed at a higher rate than over wide feature definitions 830 still covered by the first passivation layer 885.
The polishing pressures used herein reduce or minimize damaging shear forces and frictional forces for substrates containing low k dielectric materials. Reduced or minimized forces can result in reduced or minimal deformations and defect formation of features from polishing. Further, the lower shear forces and frictional forces have been observed to reduce or minimize formation of topographical defects, such as erosion of dielectric materials and dishing of conductive materials as well as reducing delamination, during polishing. Contact between the substrate and a conductive polishing article also allows for electrical contact between the power source and the substrate by coupling the power source to the polishing article when contacting the substrate.
Residual material is removed with a second electrochemical mechanical polishing process. The second electrochemical mechanical polishing process provides a reduced removal rate compared to the first electrochemical mechanical polishing process step in order to prevent excess metal removal from forming topographical defects, such as concavities or depressions known as dishing D, as shown in
In the second electrochemical mechanical polishing step, a second passivation layer 890 is formed from exposure of the conductive material to the second, residual, polishing composition. The second passivation layer 890 forms on the exposed conductive material 860 on the substrate surface. The second passivation layer 890 chemically and/or electrically insulates the surface of the substrate from chemical and/or electrical reactions.
A second, or residual removal, polishing composition as described herein for residual material removal is provided to the substrate surface. The polishing composition may be provided at a flow rate between about 50 and about 800 milliliters per minute, such as about 300 milliliters per minute, to the substrate surface.
An example of the second, residual, polishing composition includes between about 1 wt. % and about 10 wt. % of an acid based electrolyte, such as between about 3 wt. % and about 8 wt. %, between about 0.1 wt. % and about 6 wt. % of a chelating agent, such as between about 1 wt. % and about 3 wt. %, between about 0.01 wt. % and about 1 wt. % of a corrosion inhibitor, such as between about 0.1 wt. % and about 0.3 wt. %, between about 0.001 vol. % and about 2 vol. % of a passivating polymeric material, such as between about 0.015 vol. % and about 0.6 wt. %, between about 1 wt. % and about 20 wt. % of a pH adjusting agent, such as between about 2 wt. % and about 5 wt. %, between about 0.025 wt. % and about 1 wt. % of anionic polymeric abrasive particles, such as between about 0.01 wt. % and about 0.5 wt. %, a solvent, and a pH between about 4 and about 7, and optionally, between about 0.01 wt. % and about 0.05 wt. % of leveler. The residual composition has a conductivity of between about 20 and about 80 milliSiemens/centimeter (mS/cm), for example, between about 30 and about 60 milliSiemens/centimeter (mS/cm).
A further example of the second polishing composition includes about 4.25 vol. % of phosphoric acid, about 2 wt. % of ammonium hydrogen citrate, about 0.2 wt. % of benzotriazole, about 0.5 vol. % of L-2001, about 0.025 vol. % of 750000 molecular weight. Polyethylene imine (PEI), 0.05 wt. % of XECP-7 abrasive particles, deionized water, and sufficient ammonium hydroxide, about 2.6 wt. %, to provide a pH of about 5.75, and a conductivity of about 54 mS/cm.
The mechanical abrasion in the above second electrochemical mechanical polishing process step for residual removal is performed at the first electrochemical mechanical polishing process step contact pressure of less than about 2 pounds per square inch (lb/in2 or psi) (13.8 kPa) between the polishing pad and the substrate. Removal of the conductive material 860 may be performed with a process having a pressure of about 1 psi (6.9 kPa) or less, for example, between about 0.01 psi (69 Pa) and about 1 psi (6.9 kPa), such as between about 0.1 (0.7 kPa) psi and about 0.8 psi (5.5 kPa). In one aspect of the process, a pressure of about 0.3 psi (2.1 kPa) or less is used. Alternatively, the pressure of the second electrochemical mechanical polishing step may be reduced compared to the first electrochemical mechanical polishing step to further reduce the removal rate of the copper material. Contact between the substrate and a conductive polishing article also allows for electrical contact between the power source and the substrate by coupling the power source to the polishing article when contacting the substrate.
Relative motion is provided between the substrate surface and the conductive pad assembly 222, preferably a fully conductive pad assembly should be assembly 602 as shown in
The bias applied for the second electrochemical mechanical polishing step, or residual polishing step, includes a power application is a current density of between about 3 W/cm2 and about 20 W/cm2. A voltage of between about 1.4 volts and about 3 volts, such as between about 1.9 volts and about 2.4 volts, may be used as the applied bias in the second electrochemical processing step. Alternatively, the bias may be applied a current range between 1 amp and about 20 amps, for example, between about 3 amps and about 6 amps. The second bias may be less than the bias of the first electrochemical polishing step, the bulk polishing step. The substrate is typically exposed to the polishing composition and power application for a period of time sufficient to remove at least a portion or all of the desired material disposed thereon. The process may also be performed at a temperature between about 20° C. and about 60° C.
The polymeric inhibitor of the second polishing composition is believed to form a second passivation layer 890 on the surface of the exposed copper material as shown in
Mechanical abrasion by a conductive polishing article removes or disturbs the second passivation layer 890 that insulates or suppresses the current for anodic dissolution, such that areas of high overburden are preferentially removed over areas of minimal overburden as the second passivation layer 890 is retained in areas of minimal or no contact with the conductive pad assembly 222. The removal rate of the conductive material 860 covered by the second passivation layer 890 is less than the removal rate of conductive material without the second passivation layer 890. As such, the excess material disposed over narrow feature definitions 820 and the substrate field 850 is removed at a higher rate than over wide feature definitions 830 still covered by the second passivation layer 890.
The thickness and density of the second passivation layer 890 can dictate the extent of chemical reactions and/or amount of anodic dissolution. For example, a thicker or denser second passivation layer 890 has been observed to result in less anodic dissolution compared to thinner and less dense passivation layers. Thus, control of the composition of pH of the composition, i.e., polymeric inhibitors and additional compounds, allow control of the removal rate and amount of material removed from the substrate surface.
Referring to
After conductive material and barrier material removal processing steps, the substrate may then be buffed to minimize surface defects. Buffing may be performed with a soft polishing article, i.e., a hardness of about 40 or less on the Shore D hardness scale as described and measured by the American Society for Testing and Materials (ASTM), headquartered in Philadelphia, Pa., at reduced polishing pressures, such as about 2 psi or less.
Optionally, a cleaning solution may be applied to the substrate after each of the polishing processes to remove particulate matter and spent reagents from the polishing process as well as help minimize metal residue deposition on the polishing articles and defects formed on a substrate surface. An example of a suitable cleaning solution is Electra Clean™, commercially available from Applied Materials, Inc., of Santa Clara, Calif.
Finally, the substrate may be exposed to a post polishing cleaning process to reduce defects formed during polishing or substrate handling. Such processes can minimize undesired oxidation or other defects in copper features formed on a substrate surface. An example of such a post polishing cleaning is the application of Electra Clean™, commercially available from Applied Materials, Inc., of Santa Clara, Calif.
It has been observed that substrate planarized by the processes described herein have exhibited reduced topographical defects, such as dishing and erosion, reduced residues, improved planarity, and improved substrate finish.
Suitable polishing compositions that may be used with the processes described herein are as follows. A first polishing composition for bulk conductive material polishing may include an acid based electrolyte, a chelating agent, an oxidizer, a corrosion inhibitor, an inorganic or organic acid salt, abrasive particles, a pH adjusting agent, a pH between about 3 and about 10, and a solvent. A second polishing composition for residual conductive material polishing may include an acid based electrolyte, a chelating agent, a corrosion inhibitor, a passivating polymeric material, a pH adjusting agent, a pH between about 3 and about 10, and a solvent. The second polishing composition may also include an oxidizer and/or abrasive particulates.
Although the polishing compositions are particularly useful for removing copper, it is believed that the polishing compositions also may be used for the removal of other conductive materials, such as aluminum, platinum, tungsten, titanium, titanium nitride, tantalum, tantalum nitride, cobalt, gold, silver, ruthenium and combinations thereof.
A first polishing composition, the bulk polishing composition, may be used as a first electrochemical mechanical polishing step composition. The first polishing composition may include an acid based electrolyte, a chelating agent, an oxidizer, a corrosion inhibitor, an inorganic or organic acid salt, abrasive particles, a pH adjusting agent, a pH between about 3 and about 10, and a solvent.
The first polishing composition includes an acid based electrolyte system for providing electrical conductivity. Suitable acid based electrolyte systems include, for example, phosphoric acid based electrolytes, sulfuric acid, nitric acid, perchloric acid, acetic acid, citric acid, salts thereof and combinations thereof. Suitable acid based electrolyte systems include an acid electrolyte, such as phosphoric acid, boric acid and/or citric acid, as well as acid electrolyte derivatives, including ammonium, potassium, sodium, calcium and copper salts thereof. The acid based electrolyte system may also buffer the composition to maintain a desired pH level for processing a substrate.
Examples of suitable acid based electrolytes include compounds having a phosphate group (PO4−3), such as, phosphoric acid, copper phosphate, potassium phosphates (KXH(3-X)PO4) (x=1, 2 or 3), such as potassium dihydrogen phosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4), ammonium phosphates ((NH4)XH(3-X)PO4) (x=1, 2 or 3), such as ammonium dihydrogen phosphate ((NH4)H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), compounds having a nitrite group (NO31−), such as, nitric acid or copper nitrate, compounds having a boric group (BO33−), such as, orthoboric acid (H3BO3) and compounds having a sulfate group (SO42−), such as sulfuric acid (H2SO4), ammonium hydrogen sulfate ((NH4)HSO4), ammonium sulfate, potassium sulfate, copper sulfate, derivatives thereof and combinations thereof. The invention also contemplates that conventional electrolytes known and unknown may also be used in forming the composition described herein using the processes described herein.
The acid based electrolyte system may contains an acidic component that can take up about 1 and about 30 percent by weight (wt. %) or volume (vol. %) of the total composition of solution to provide sufficient conductivity as described herein for practicing the processes described herein. Examples of acidic components include dihydrogen phosphate and/or diammonium hydrogen phosphate and may be present in the first polishing composition in amounts between about 15 wt. % and about 25 wt. %. Alternately, phosphoric acid may be present in concentrations up to 30 wt. %, such as between about 1 wt. % and about 10 wt. %. For example, phosphoric acid may be between about 3 wt. % and about 8 wt. %, such as about 4.25 wt. %. The acid based electrolyte may also be added in solution, for example, the 4.25 wt. % of phosphoric acid may be from 85% aqueous phosphoric acid solution for an actual phosphoric acid composition of about 3.6 wt. %.
One aspect or component of the present invention is the use of one or more chelating agents to complex with the surface of the substrate to enhance the electrochemical dissolution process. In any of the embodiments described herein, the chelating agents can bind to a conductive material, such as copper ions, increase the removal rate of metal materials and/or improve dissolution uniformity across the substrate surface. The metal materials for removal, such as copper, may be in any oxidation state, such as 0, 1, or 2, before, during or after ligating with a functional group. The functional groups can bind the metal materials created on the substrate surface during processing and remove the metal materials from the substrate surface. The chelating agents may also be used to buffer the first polishing composition to maintain a desired pH level for processing a substrate. The chelating agents may also form or enhance the formation of the second passivation layer on the substrate surface.
The one or more chelating agents can include compounds having one or more functional groups selected from the group of amine groups, amide groups, carboxylate groups, dicarboxylate groups, tricarboxylate groups, hydroxyl groups, a mixture of hydroxyl and carboxylate groups, and combinations thereof. The one or more chelating agents may also include salts of the chelating agents described herein. The first polishing composition may include one or more chelating agents at a concentration between about 0.1% and about 15% by volume or weight, but preferably utilized between about 0.1% and about 4% by volume or weight. For example, about 2% by volume of ethylenediamine may be used as a chelating agent.
Examples of suitable chelating agents having one or more carboxylate groups include citric acid, tartaric acid, succinic acid, oxalic acid, amino acids, salts thereof, and combinations thereof. For example, chelating agents may include ammonium hydrogen citrate, potassium citrate, ammonium succinate, potassium succinate, ammonium oxalate, potassium oxalate, potassium tartrate, and combinations thereof. The salts may have multi-basic states, for example, citrates have mono-, di- and tri-basic states. Other suitable acids having one or more carboxylate groups include acetic acid, adipic acid, butyric acid, capric acid, caproic acid, caprylic acid, glutaric acid, glycolic acid, formaic acid, fumaric acid, lactic acid, lauric acid, malic acid, maleic acid, malonic acid, myristic acid, plamitic acid, phthalic acid, propionic acid, pyruvic acid, stearic acid, valeric acid, derivatives thereof, salts thereof and combinations thereof. Further examples of suitable chelating agents include compounds having one or more amine and amide functional groups, such as ethylenediamine (EDA), diethylenetriamine, diethylenetriamine derivatives, hexadiamine, amino acids, glycine, ethylenediaminetetraacetic acid (EDTA), methylformamide, derivatives thereof, salts thereof and combinations thereof. For example, EDTA includes the acid as well as a variety of salts, such as sodium, potassium and calcium (e.g., Na2EDTA, Na4EDTA, K4EDTA or Ca2EDTA).
In any of the embodiments described herein, the inorganic or organic acid salts may be used to perform as a chelating agent. The first polishing composition may include one or more inorganic or organic salts at a concentration between about 0.1% and about 15% by volume or weight of the composition, for example, between about 0.1% and about 8% by volume or weight. For example, about 2% by weight of ammonium hydrogen citrate may be used in the first polishing composition. The chelating agent may also be added in solution or in a substantially pure form, for example, ammonium hydrogen citrate may be added in a 98% pure form.
Examples of suitable inorganic or organic acid salts include ammonium and potassium salts or organic acids, such as ammonium oxalate, ammonium hydrogen citrate, ammonium succinate, monobasic potassium citrate, dibasic potassium citrate, tribasic potassium citrate, potassium tartarate, ammonium tartarate, potassium succinate, potassium oxalate, and combinations thereof. Additionally, ammonium and potassium salts of the carboxylate acids may also be used.
In any of the embodiments described herein, the corrosion inhibitors can be added to reduce the oxidation or corrosion of metal surfaces by enhancing the formation of the second passivation layer 890 that minimizes the chemical interaction between the substrate surface and the surrounding electrolyte. The layer of material formed by the corrosion inhibitors thus tends to suppress or minimize the electrochemical current from the substrate surface to limit electrochemical deposition and/or dissolution. The first polishing composition may include between about 0.001% and about 5.0% by weight of the organic compound from one or more azole groups. The commonly preferred range being between about 0.2% and about 0.4% by weight. The corrosion inhibitor may also be added in solution or in a substantially pure form, for example, benzotriazole may be added in a 99% pure form.
Suitable corrosion inhibitors include compounds having a nitrogen atom (N), such as organic compounds having azole groups. Examples of suitable compounds include benzotriazole (BTA), mercaptobenzotriazole, 5-methyl-1-benzotriazole (TTA), and combinations thereof. Other suitable corrosion inhibitors include film forming agents that are cyclic compounds, for example, imidazole, benzimidazole, triazole, and combinations thereof. Derivatives of benzotriazole, imidazole, benzimidazole, triazole, with hydroxy, amino, imino, carboxy, mercapto, nitro and alkyl substituted groups may also be used as corrosion inhibitors.
Alternatively, polymeric inhibitors, for non-limiting examples, polyalkylaryl ether phosphate or ammonium nonylphenol ethoxylate sulfate, may be used in replacement or conjunction with azole containing corrosion inhibitors in an amount between about 0.002% and about 1.0% by volume or weight of the composition.
One or more pH adjusting agents is preferably added to the first polishing composition to achieve a pH between about 2 and about 10, and preferably between a pH of about 3 and about 7. The amount of pH adjusting agent can vary as the concentration of the other components is varied in different formulations, but in general the total solution may include up and about 70 wt. % of the one or more pH adjusting agents, but preferably between about 0.2% and about 25% by volume. Different compounds may provide different pH levels for a given concentration, for example, the composition may include between about 0.1% and about 10% by volume of a base, such as potassium hydroxide, ammonium hydroxide, sodium hydroxide or combinations thereof, providing the desired pH level. The pH adjusting agent may also be added in solution or in a substantially pure form, for example, potassium hydroxide may be added in a 45% aqueous potassium hydroxide solution.
The one or more pH adjusting agents can be chosen from a class of organic acids, for example, carboxylic acids, such as acetic acid, citric acid, oxalic acid, phosphate-containing components including phosphoric acid, ammonium phosphates, potassium phosphates, and combinations thereof, or a combination thereof. Inorganic acids including phosphoric acid, sulfuric acid, hydrochloric, nitric acid, derivatives thereof and combinations thereof, may also be used as a pH adjusting agent in the first polishing composition.
The balance or remainder of the first polishing compositions described herein is a solvent, such as a polar solvent, including water, preferably deionized water. Other solvents may be used solely or in combination with water, such as organic solvents. Organic solvents include alcohols, such as isopropyl alcohol or glycols, ethers, such as diethyl ether, furans, such as tetrahydrofuran, hydrocarbons, such as pentane or heptane, aromatic hydrocarbons, such as benzene or toluene, halogenated solvents, such as methylene chloride or carbon tetrachloride, derivatives, thereof and combinations thereof.
The first polishing composition may further include one or more surface finish enhancing and/or removal rate enhancing materials including abrasive particles, one or more oxidizers, and combinations thereof.
Abrasive particles may be used to improve the surface finish and removal rate of conductive materials from the substrate surface during polishing. The addition of abrasive particles to the first polishing composition can allow the final polished surface to achieve a surface roughness of that comparable with a conventional CMP process even at low pad pressures. Surface finish, or surface roughness, has been shown to have an effect on device yield and post polishing surface defects. Abrasive particles may comprise up and about 30 wt. % of the first polishing composition during processing. A concentration between about 0.001 wt. % and about 5 wt. % of abrasive particles may be used in the first polishing composition.
Suitable abrasives particles include inorganic abrasives, polymeric abrasives, and combinations thereof. Inorganic abrasive particles that may be used in the electrolyte include, but are not limited to, silica, alumina, zirconium oxide, titanium oxide, cerium oxide, germania, or any other abrasives of metal oxides, known or unknown. For example, colloidal silica may be positively activated, such as with an alumina modification or a silica/alumina composite. The typical abrasive particle size used in certain embodiments of the current invention is generally between about 1 nm and about 1,000 nm, preferably between about 10 nm and about 100 nm. Generally, suitable inorganic abrasives have a Mohs hardness of greater than 6, although the invention contemplates the use of abrasives having a lower Mohs hardness value.
The polymer abrasives described herein may also be referred to as “organic polymer particle abrasives”, “organic abrasives” or “organic particles.” The polymeric abrasives may comprise abrasive polymeric materials. Examples of polymeric abrasives materials include polymethylmethacrylate, polymethyl acrylate, polystyrene, polymethacrylonitrile, and combinations thereof.
The polymeric abrasives may have a Hardness Shore D of between about 60 and about 80, but can be modified to have greater or lesser hardness value. The softer polymeric abrasive particles can help reduce friction between a polishing article and substrate and may result in a reduction in the number and the severity of scratches and other surface defects as compared to inorganic particles. A harder polymeric abrasive particle may provide improved polishing performance, removal rate and surface finish as compared to softer materials.
The hardness of the polymer abrasives can be varied by controlling the extent of polymeric cross-linking in the abrasives, for example, a higher degree of cross-linking produces a greater hardness of polymer and, thus, abrasive. The polymeric abrasives are typically formed as spherical shaped beads having an average diameter between about 0.1 micron and about 20 microns or less.
The polymeric abrasives may be modified to have one ore more functional groups that can bind to the conductive material or conductive material ions, thereby facilitating the electrochemical mechanical polishing removal of material from the surface of a substrate. For example, if copper is to be removed in the polishing process, the organic polymer particles can be modified to have an amine group, a carboxylate group, a pyridine group, a hydroxide group, ligands with a high affinity for copper, or combinations thereof, to bind the removed copper as substitutes for or in addition to the chemically active agents in the first polishing composition, such as the chelating agents or corrosion inhibitors. The substrate surface material, such as copper, may be in any oxidation state, such as 0, 1+, or 2+, before, during or after ligating with a functional group. The functional groups can bind to the metal material(s) on the substrate surface to help improve the uniformity and surface finish of the substrate surface.
Additionally, the polymeric abrasives have desirable chemical properties, for example, the polymer abrasives are stable over a broad pH range and are not prone to aggregating to each other, which allow the polymeric abrasives to be used with reduced or no surfactant or no dispersing agent in the composition.
Alternatively, inorganic particles coated with the polymeric materials described herein may also be used with the first polishing composition. It is within the scope of the current invention for the first polishing composition to contain polymeric abrasives, inorganic abrasives, the polymeric coated inorganic abrasives, and any combination thereof depending on the desired polishing performance and results.
The optional oxidizer can be present in the first polishing composition in an amount ranging between about 0.01% and about 100% by volume or weight, for example, between about 0.1% and about 20% by volume or weight. In an embodiment of the first polishing composition, between about 0.1% and about 15% by volume or weight of hydrogen peroxide is present in the first polishing composition. In certain embodiments, the oxidizer is added to the rest of the first polishing composition just prior to beginning the electrochemical mechanical polishing process. The oxidizer may be added to the composition in a solution, such as a 30% aqueous hydrogen peroxide solution or a 40% aqueous hydrogen peroxide solution.
Examples of suitable oxidizers include peroxy compounds, e.g., compounds that may disassociate through hydroxy radicals, such as hydrogen peroxide and its adducts including urea hydrogen peroxide, percarbonates, and organic peroxides including, for example, alkyl peroxides, cyclical or aryl peroxides, benzoyl peroxide, peracetic acid, and ditertbutyl peroxide. Sulfates and sulfate derivatives, such as monopersulfates and dipersulfates may also be used including for example, ammonium peroxydisulfate, potassium peroxydisulfate, ammonium persulfate, and potassium persulfate. Salts of peroxy compounds, such as sodium percarbonate and sodium peroxide may also be used.
The oxidizer can also be an inorganic compound or a compound containing an element in its highest oxidation state. Examples of inorganic compounds and compounds containing an element in its highest oxidation state include but are not limited to periodic acid, periodate salts, perbromic acid, perbromate salts, perchloric acid, perchloric salts, perbonic acid, nitrate salts (such as cerium nitrate, iron nitrate, ammonium nitrate), ferrates, perborate salts and permanganates. Other oxidizers include bromates, chlorates, chromates, iodates, iodic acid, and cerium (IV) compounds such as ammonium cerium nitrate.
One or more oxidizers may be used herein to enhance the removal or removal rate of the conductive material from the substrate surface. An oxidizer is generally an agent that reacts with a material by accepting an electron(s). In the current embodiment the oxidizer is used to react with the surface of the substrate that is to be polished, which then aids in the removal of the desired material. For example, an oxidizer may be used to oxidize a metal layer to a corresponding oxide or hydroxide, for example, copper to copper oxide. Existing copper that has been oxidized, including Cu1+ ions, may further be oxidized to a higher oxidation state, such as Cu2+ ions, which may then promote the reaction with one or more of the chelating agents. Also, in some instances the oxidizer can be used in some chemistries (e.g., low pH) that can enhance the chemical etching of the surface of the substrate to further increase the removal rate from the anode surface. In cases where no bias is applied to the surface of the substrate the inhibitors and chelating agents will complex with the metal ions on the surface that become dislodged from the surface due to the relative motion and pressure applied by the conductive article. The addition of abrasives can further improve the removal rate of the complexed metal ions due to the abrasive particles ability to increase that contact area between the conductive article and the substrate surface.
In the case of electrochemical mechanical polishing, the conductive layer on the substrate surface is biased anodically above a threshold potential, by use of the power source 242 and the electrode 292, thus causing the metal on the substrate surface to “oxidize” (i.e., a metal atom gives up one or more electrons to the power source 242). The ionized or “oxidized” metal atoms thus dissolve into the electrolyte solution with the help of components in the electrolyte. In the case where copper is the desired material to be removed, it can be oxidized to a Cu1+ or a Cu2+ oxidation state. Due to the presence of the inhibitors and/or chelating agents found in the first polishing composition, the electrochemical dissolution process of the metal ions into the electrolyte is more limited than a polishing composition which does not contain these components. The presence of the inhibitors and/or chelating agents also appears to have an effect on the attachment strength of the metal ion(s) and inhibitor and/or chelating agent complex to the surface of the substrate. It has been found that in one embodiment that the removal rate in an electrochemical mechanical polishing process can be increased by the addition of an oxidizer. It is thought that the oxidizer tends to further oxidize the metal ions formed due to the anodic bias, which in the case of copper brings it to the more stable Cu2+ oxidation state. The inhibitors and/or chelating agents found in the first polishing composition complex with the oxidized metal ions which tend to have a lower attachment, or bond, strength due to the way the inhibitor bonds to the oxidized metal ion and metal surface. The lower attachment strength allows the complexed metal ion to be more easily and efficiently removed due to the interaction of the substrate surface and the conductive article. The addition of abrasives to the electrochemical mechanical polishing first polishing composition can further improve the removal rate of the complexed metal ions due to the abrasive particles' ability to increase contact area between the conductive article and the substrate surface.
Further, controlling the amounts and types of constituents of the first polishing composition, such as corrosion inhibitors and oxidizers, can result in tuning the desired removal rate of the process. For example reduced amounts of corrosion inhibitor will result in an increase in the material removal rate as compared to compositions having higher corrosion inhibitor concentrations. In cases where the first polishing composition does not contain corrosion inhibitors the electrochemical mechanical polishing material removal rate is greatly increased over a polishing composition which contains a corrosion inhibitor due to the formation of the metal ions and inhibitor complex which tends to shield the surface of the substrate to the electrolyte. Likewise reduced amounts of oxidizers will generally result in lower removal rates compared to compositions having higher oxidizer compositions. It has been suggested that at low concentrations of the oxidizer, the corrosion inhibitor and/or chelating agent can complex with a metal ion before it becomes oxidized further by the oxidizer due to kinetic effects limiting the supply of the oxidizer to the surface of the substrate. The corrosion inhibitor and metal ion complex can thus affect the removal efficiency due to the formation of the stronger attachment strength complexed metal ions.
An example of a first polishing composition described herein includes about 2% by volume ethylenediamine, about 2% by weight ammonium hydrogen citrate, about 0.3% by weight benzotriazole, between about 0.1% and about 3% by volume or weight, for example, about 0.45% hydrogen peroxide, and/or about between about 0.01% and 1% by weight, for example 0.15% by weight, of abrasive particles, and about 6% by volume phosphoric acid. The pH of the composition is about 5, which may be achieved by, for example, the composition further including potassium hydroxide to adjust the pH to the preferred range. The remainder of the first polishing composition is deionized water.
The first polishing composition may include one or more additive compounds. Additive compounds include electrolyte additives including, but not limited to, suppressors, enhancers, brighteners, stabilizers, and stripping agents to improve the effectiveness of the first polishing composition in polishing of the substrate surface. For example, certain additives may decrease the ionization rate of the metal atoms, thereby inhibiting the dissolution process, whereas other additives may provide a finished, shiny substrate surface. The additives may be present in the first polishing composition in concentrations up and about 15% by weight or volume, and may vary based upon the desired result after polishing.
Further examples of additives to the first polishing composition are more fully described in U.S. patent application Ser. No. 10/141,450, filed on May 7, 2002, which is incorporated by reference herein to the extent not inconsistent with the claimed aspects and disclosure herein.
The second polishing composition for residual conductive material polishing may include an acid based electrolyte, a chelating agent, a corrosion inhibitor, a passivating polymeric material, a pH adjusting agent, a pH between about 3 and about 10, and a solvent. Alternatively, the second polishing composition may comprise a leveler. The second polishing composition may be an abrasive free polishing composition and optionally, may further include an oxidizer, abrasive particles, or a combination of the two.
The second polishing composition includes an acid based electrolyte system for providing electrical conductivity. Suitable acid based electrolyte systems include, for example, phosphoric acid based electrolytes, sulfuric acid, nitric acid, perchloric acid, acetic acid, citric acid, salts thereof and combinations thereof. Suitable acid based electrolyte systems include an acid electrolyte, such as phosphoric acid, boric acid and/or citric acid, as well as acid electrolyte derivatives, including ammonium, potassium, sodium, calcium and copper salts thereof. The acid based electrolyte system may also buffer the composition to maintain a desired pH level for processing a substrate.
Examples of suitable acid based electrolytes include compounds having a phosphate group (PO43−), such as, phosphoric acid, copper phosphate, potassium phosphates (KXH(3-X)PO4) (x=1, 2 or 3), such as potassium dihydrogen phosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4), ammonium phosphates ((NH4)XH(3-X)PO4) (x=1, 2 or 3), such as ammonium dihydrogen phosphate ((NH4)H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), compounds having a nitrite group (NO31−), such as, nitric acid or copper nitrate, compounds having a boric group (BO33−), such as, orthoboric acid (H3BO3) and compounds having a sulfate group (SO42−), such as sulfuric acid (H2SO4), ammonium hydrogen sulfate ((NH4)HSO4), ammonium sulfate, potassium sulfate, copper sulfate, derivatives thereof and combinations thereof. The invention also contemplates that conventional electrolytes known and unknown may also be used in forming the composition described herein using the processes described herein.
The acid based electrolyte system may contains an acidic component that can take up about 1 and about 30 percent by weight (wt. %) or volume (vol. %) of the total composition of solution to provide suitable conductivity for practicing the processes described herein. Examples of acidic components include dihydrogen phosphate and/or diammonium hydrogen phosphate and may be present in the polishing composition in amounts between about 15 wt. % and about 25 wt. %. Alternately, phosphoric acid may be present in concentrations up to 30 wt. %, for example, between about 2 wt. % and about 6 wt. %. The acid based electrolyte may also be added in solution, for example, the 6 wt. % of phosphoric acid may be from 85% aqueous phosphoric acid solution for an actual phosphoric acid composition of about 5.1 wt. %.
One aspect or component of the present invention is the use of one or more chelating agents to complex with metal ions and/or the surface of the substrate to enhance the electrochemical dissolution process. The chelating agents may also be used to buffer the polishing composition to maintain a desired pH level for processing a substrate. The chelating agents may also enhance the formation of the second passivation layer 890 on the substrate surface.
In any of the embodiments described herein, the inorganic or organic acid salts may be used to perform as a chelating agent. The polishing composition may include one or more inorganic or organic salts at a concentration between about 0.1% and about 15% by volume or weight of the composition, for example, between about 0.1% and about 8% by volume or weight. For example, about 2% by weight of ammonium hydrogen citrate may be used in the polishing composition. The chelating agent may also be added in solution or in a substantially pure form, for example, ammonium hydrogen citrate may be added in a 98% pure form.
Examples of suitable inorganic or organic acid salts include ammonium and potassium salts or organic acids, such as ammonium oxalate, ammonium hydrogen citrate, ammonium succinate, monobasic potassium citrate, dibasic potassium citrate, tribasic potassium citrate, potassium tartarate, ammonium tartarate, potassium succinate, potassium oxalate, and combinations thereof. Additionally, ammonium and potassium salts of the carboxylate acids may also be used.
Alternatively, and additionally, one or more chelating agents can include compounds having one or more functional groups selected from the group of amine groups, amide groups, carboxylate groups, dicarboxylate groups, tricarboxylate groups, hydroxyl groups, a mixture of hydroxyl and carboxylate groups, and combinations thereof. The polishing composition may include one or more chelating agents at a concentration between about 0.1% and about 15% by volume or weight, but preferably utilized between about 0.1% and about 4% by volume or weight. For example, about 2% by volume of ethylenediamine may be used as a chelating agent.
Examples of suitable chelating agents having one or more carboxylate groups include citric acid, tartaric acid, succinic acid, oxalic acid, amino acids, salts thereof, and combinations thereof. For example, chelating agents may include ammonium hydrogen citrate, potassium citrate, ammonium succinate, potassium succinate, ammonium oxalate, potassium oxalate, potassium tartrate, and combinations thereof. The salts may have multi-basic states, for example, citrates have mono-, di- and tri-basic states. Other suitable acids having one or more carboxylate groups include acetic acid, adipic acid, butyric acid, capric acid, caproic acid, caprylic acid, glutaric acid, glycolic acid, formaic acid, fumaric acid, lactic acid, lauric acid, malic acid, maleic acid, malonic acid, myristic acid, plamitic acid, phthalic acid, propionic acid, pyruvic acid, stearic acid, valeric acid, derivatives thereof, salts thereof and combinations thereof. Further examples of suitable chelating agents include compounds having one or more amine and amide functional groups, such as ethylenediamine (EDA), diethylenetriamine, diethylenetriamine derivatives, hexadiamine, amino acids, glycine, ethylenediaminetetraacetic acid (EDTA), methylformamide, derivatives thereof, salts thereof and combinations thereof. For example, EDTA includes the acid as well as a variety of salts, such as sodium, potassium and calcium (e.g., Na2EDTA, Na4EDTA, K4EDTA or Ca2EDTA).
In any of the embodiments described herein, the corrosion inhibitors can be added to reduce the oxidation or corrosion of metal surfaces by enhancing the forming of the passivation layers that minimizes the chemical interaction between the substrate surface and the surrounding electrolyte. The layer of material formed by the corrosion inhibitors thus tends to suppress or minimize the electrochemical current from the substrate surface to limit electrochemical deposition and/or dissolution. The polishing composition may include between about 0.001% and about 5.0% by weight of the organic compound from one or more azole groups. The commonly preferred range being between about 0.2% and about 0.4% by weight. The corrosion inhibitor may also be added in solution or in a substantially pure form, for example, benzotriazole may be added in a 99% pure form.
Suitable corrosion inhibitors include compounds having a nitrogen atom (N), such as organic compounds having azole groups. Examples of organic compounds having azole groups include benzotriazole (BTA), mercaptobenzotriazole, 5-methyl-1-benzotriazole (TTA), and combinations thereof. Other suitable corrosion inhibitors include film forming agents that are cyclic compounds, for example, imidazole, benzimidazole, triazole, and combinations thereof. Derivatives of benzotriazole, imidazole, benzimidazole, triazole, with hydroxy, amino, imino, carboxy, mercapto, nitro and alkyl substituted groups may also be used as corrosion inhibitors.
The second polishing composition includes a polymeric inhibitor, including a combination of polymeric inhibitors, which by chemical or physical means, form a layer of material which minimizes the chemical interaction between the substrate surface and the surrounding electrolyte. The layer of material formed by the inhibitors may suppress or minimize the electrochemical current from the substrate surface to limit electrochemical deposition and/or dissolution. By a physical mechanism, the second passivation layer 885 may be of a viscous form that inhibits fluid flow to and from the conductive material, limiting the removal rate of material therefrom.
Suitable polymeric inhibitors include compounds having a nitrogen atom (N), an oxygen atom (O), or a combination of the two. Polymeric inhibitors include ethylene imine (C2H5N) based polymeric materials, such as polyethylene imine (PEI) having a molecular weight between about 400 and about 1000000 comprising (—CH2—CH2—NH—) monomer units, ethylene glycol (C2H6O2) based polymeric materials, such as polyethylene glycol (PEG) having a molecular weight between about 200 and about 100000 comprising (OCH2CH2)N monomer units, or combinations thereof. Polyamine and polyimide polymeric material may also be used as polymeric inhibitors in the composition. Other suitable polymeric inhibitors include oxide polymers, such as, polypropylene oxide and ethylene oxide/propylene oxide co-polymer (EOPO), with a Molecular Weight range between about 200 and about 100000.
Additionally, the polymeric inhibitors may comprise polymers of heterocyclic compounds containing nitrogen and/or oxygen atoms, such as polymeric materials derived from monomers of pyridine, pyrole, furan, purine, or combinations thereof. The polymeric inhibitors may also include polymers with both linear and heterocyclic structural units containing nitrogen and/or oxygen atoms, such as a heterocyclic structural units and amine or ethylene imine structural units. The polymeric inhibitors may also include carbon containing functional groups or structural units, such as homocyclic compounds, such as benzyl or phenyl functional groups, and linear hydrocarbons suitable as structural units or as functional groups to the polymeric backbone. A mixture of the polymeric inhibitors described herein is also contemplated, such as a polymeric mixture of a heterocyclic polymer material and an amine or ethylene imine polymeric material (polyethylene imine). An example of a suitable polymeric inhibitor includes XP-1296 (also known as L-2001), containing a heterocyclic polymer/polyamine polymer, commercially available from Rohm and Hass Electronic Materials of Marlborough, Mass., and Compound S-900, commercially available from Enthone-OMI Inc. of New Haven, Conn.
The polymeric inhibitor may be present in the composition of this invention in amounts ranging between about 0.001 wt. % and about 2 wt. %, such as between about 0.005 wt. % and about 1 wt. %, for example, between about 0.01 wt. % and about 0.5 vol %. A polymeric inhibitor of 2000 or 750000 molecular weight polyethylene imine in a concentration of about 0.025 wt. % may be used in the composition. More than one polymeric inhibitor may be included in the second polishing composition. Some polymeric inhibitor may be added the composition in a solution, for example, the second polishing composition may include 0.5 wt. % PEI with a 2000 molecular weight of a 5% aqueous PEI solution and/or 0.5 wt. % XP-1296 (or XP tradename family of compounds from Rohm and Haas) with a 2000 molecular weight of a 10% aqueous XP-1296 solution.
Polymeric inhibitors may be in a dilute form manufacturing, for example, polyethylene imine may be added to a composition from a 50% polyethylene imine solution, so the concentration of the solution may be 0.025 wt. % and the actual polyethylene imine concentration would be about 0.0125 wt. %. Thus, the invention contemplates that the percentages of all of the components, including the polymeric inhibitors, reflect both dilute compounds provided from their manufacturing source as well as the actual present amount of the component. For example, 6% phosphoric acid may also be present as 5.1%, or 6% of the 85% phosphoric acid solution available from phosphoric acid manufacturers. Where possible, the actual amount of the component of the composition has been provided.
The second polishing composition may include abrasive particles. Abrasive particles, referred to as abrasives, may comprise between about 0.001 wt. % and about 5 wt. % of the second polishing composition during processing, such as a concentration between about 0.0025 wt. % and about 1 wt. %, for example, between about 0.01 wt. % and about 0.5 wt. % of abrasive particles in the second polishing composition.
Suitable abrasives particles include polymeric abrasives. Suitable polymeric abrasives are anionic polymer abrasive. Anionic polymer abrasives include polymeric material having anionic functional groups. Anionic functional groups include amine functional groups. Examples of anionic polymer abrasive materials include polymer abrasive materials formed from polyethylene imine and derivatives thereof. An example of an anionic polymer material is a solution of a b-type anionic polymer, such as XECP-7 polymeric abrasive, commercially available from Mitsui & Co., Ltd., of New York, N.Y. The anionic polymeric abrasive is present in the composition at a concentration between about 0.01 wt. % and about 0.5 wt. %, for example, about 0.05 wt. %.
The anionic polymer abrasive is preferably used in combination with a passivating polymeric material as described herein, for example, high molecular weight, i.e., 750,000 molecular weight, polyethylene imine. A preferred combination includes XECP-7 mixed with 750,000 molecular weight, polyethylene imine. The anionic polymer abrasive is generally used in a composition having a pH between about 4 and about 8, such as a pH between about 5.5 and about 6.5, for example, a pH of about 6.25.
The polymeric abrasives may have a Hardness Shore D of between about 60 and about 80, but can be modified to have greater or lesser hardness value. The softer polymeric abrasive particles can help reduce friction between a polishing article and substrate and may result in a reduction in the number and the severity of scratches and other surface defects as compared to inorganic particles. A harder polymeric abrasive particle may provide improved polishing performance, removal rate and surface finish as compared to softer materials. The hardness of the polymer abrasives can be varied by controlling the extent of polymeric cross-linking in the abrasives, for example, a higher degree of cross-linking produces a greater hardness of polymer and, thus, abrasive. The polymeric abrasives are typically formed as spherical shaped beads having an average diameter between about 0.1 micron and about 20 microns or less.
Additionally, the polymeric abrasives have desirable chemical properties, for example, the polymer abrasives are stable over a broad pH range and are not prone to aggregating to each other, which allow the polymeric abrasives to be used with reduced or no surfactant or no dispersing agent in the composition.
Alternatively, inorganic particles coated with the anionic polymeric materials described herein may also be used with the second polishing composition. Additionally, inorganic abrasive particles may be used in addition to the polymeric abrasive particles described herein. Inorganic abrasives include, but are not limited to, silica, alumina, zirconium oxide, titanium oxide, cerium oxide, germania, or any other abrasives of metal oxides, known or unknown. For example, colloidal silica may be positively activated, such as with an alumina modification or a silica/alumina composite. The typical abrasive particle size used in one embodiment of the current invention is generally between about 1 nm and about 1,000 nm, preferably between about 10 nm and about 100 nm. Generally, suitable inorganic abrasives have a Mohs hardness of greater than 6, although the invention contemplates the use of abrasives having a lower Mohs hardness value.
One or more pH adjusting agents is preferably added to the polishing composition to achieve a pH between about 2 and about 10, and preferably an acidic pH between about 3 and less than about 7. The amount of pH adjusting agent can vary as the concentration of the other components is varied in different formulations, but in general the total solution may include up and about 70 wt. % of the one or more pH adjusting agents, but preferably between about 0.2% and about 25% by volume. Different compounds may provide different pH levels for a given concentration, for example, the composition may include between about 0.1% and about 10% by volume of a base, such as potassium hydroxide, ammonium hydroxide, sodium hydroxide or combinations thereof, providing the desired pH level. The one or more pH adjusting agents may be added the composition in a solution, for example, the second polishing composition may include ammonium hydroxide (NH4OH) of about 28 to about 30% ammonia in an aqueous solution.
The one or more pH adjusting agents can be chosen from a class of organic acids, for example, carboxylic acids, such as acetic acid, citric acid, oxalic acid, phosphate-containing components including phosphoric acid, ammonium phosphates, potassium phosphates, and combinations thereof, or a combination thereof. Inorganic acids including phosphoric acid, sulfuric acid, hydrochloric, nitric acid, derivatives thereof and combinations thereof, may also be used as a pH adjusting agent in the polishing composition.
The balance or remainder of the polishing compositions described herein is a solvent, such as a polar solvent, including water, preferably deionized water. Other solvent may be used solely or in combination with water, such as organic solvents. Organic solvents include alcohols, such as isopropyl alcohol or glycols, ethers, such as diethyl ether, furans, such as tetrahydrofuran, hydrocarbons, such as pentane or heptane, aromatic hydrocarbons, such as benzene or toluene, halogenated solvents, such as methylene chloride or carbon tetrachloride, derivatives, thereof and combinations thereof.
While not being limited to any particular theory, it is believed that a lone pair of electrons in the polymer's functional groups which include nitrogen (n) atom or oxygen (O) atom interact with the copper material on the surface to form a passivation layer. A corrosion inhibitor having a nitrogen atom may also contribute to forming the passivation layer with the polymeric passivation material. Chelating agents that have a donor electron or a lone pair of electrons may also contribute to the formation of the passivation layer in a similar manner. The passivation layer formed from the second polishing composition may mechanically interact with the exposed conductive material by forming a viscous layer that inhibits fluid flow, or mass transportation, of polishing composition to and from the exposed conductive material. The viscous layer may be formed from a phosphoric acid or phosphoric acid derivative. This inhibiting flow can be effective in reducing removal of copper material in recessed areas.
An example of the second, residual, polishing composition includes between about 1 wt. % and about 10 wt. % of an acid based electrolyte, such as between about 3 wt. % and about 8 wt. %, between about 0.1 wt. % and about 6 wt. % of a chelating agent, such as between about 1 wt. % and about 3 wt. %, between about 0.01 wt. % and about 1 wt. % of a corrosion inhibitor, such as between about 0.1 wt. % and about 0.3 wt. %, between about 0.001 vol. % and about 2 vol. % of a passivating polymeric material, such as between about 0.015 vol. % and about 0.6 wt. %, between about 1 wt. % and about 20 wt. % of a pH adjusting agent, such as between about 2 wt. % and about 5 wt. %, between about 0.025 wt. % and about 1 wt. % of anionic polymeric abrasive particles, such as between about 0.01 wt. % and about 0.5 wt. %, a solvent, and a pH between about 4 and about 7, and optionally, between about 0.01 wt. % and about 0.05 wt. % of leveler. The residual composition has a conductivity of between about 20 and about 80 milliSiemens/centimeter (mS/cm), for example, between about 30 and about 60 milliSiemens/centimeter (mS/cm).
A further example of the second polishing composition includes about 4.25 vol. % of phosphoric acid, about 2 wt. % of ammonium hydrogen citrate, about 0.2 wt. % of benzotriazole, about 0.5 vol. % of L-2001, about 0.025 vol. % of 750000 molecular weight. Polyethylene imine (PEI), 0.05 wt. % of XECP-7 abrasive particles, deionized water, and sufficient ammonium hydroxide, about 2.6 wt. %, to provide a pH of about 5.75, and a conductivity of about 54 mS/cm.
In an alternative embodiment of the second polishing composition a leveler may be included in the composition. Levelers include compounds that suppress current at locations where mass transfer rate is most rapid, and in the case of an electrochemical mechanical polishing process, levelers reduce removal rates at protruding surfaces or corners to improve passivation layer formation. The differential mass transfer rates of levelers at different locations are a result of differences in diffusion rates to different geometrical locations and of higher electrostatic migration rates to points on the surface at a more negative voltage.
Suitable levelers are cationic compounds or are cationic compounds in the compositions described herein. The suitable levelers include protonated nitrogen-based functional groups. Examples of such levelers include a quaternary ammonium halide or a quaternary ammonium hydroxide. Quaternary ammonium halide or a quaternary ammonium hydroxide compounds include tetraalkylammonium compounds, such as a cetyltrimethylammonium cation and a halogen anion, for example, dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium chloride, or alternatively, cetyltrimethylammonium hydroxide. Another example of such a leveler is octadecylmethylpolyoxyethyleneammonium chloride. DTAB is cationic in acidic solution. Additional suitable levelers include an alkyltrimethylammonium halide where the alkyl group has at least twelve carbon atoms.
Other suitable levelers include those containing a functional group of the formula N—R—S, where N is nitrogen atom, S is a sulfur atom, and R is a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group. Typically the alkyl groups have from 1 to 6 carbon atoms, more typically from 1 to 4 carbon atoms. Suitable aryl groups include substituted or unsubstituted phenyl or napthyl. The substituents of the alkyl and aryl groups may be, for example, alkyl, halo and alkoxy. Levelers of this formula include 1-(2-hydroxyethyl)-2-imidazolidinethione, 4-mercaptopyridine, 2-mercaptothiazoline, ethylene thiourea, thiourea, alkylated polyalkyleneimine, and combinations thereof. Commercial leveler products are commercially available as a Liberty or Ultrafill Leveler from Shipley Inc, of Marlboro, Mass., and Booster 3 from Enthone OMI, of New Haven, Conn.
Additional levelers include polyoxyethylene ether or nonionic surfactants such as, for example, a dimethyl silicone ethylene oxide, or an alkyl polyethylene oxide.
The levelers may be present in an amount between about 0.005 vol. % and about 0.1 vol. %, such as between about 0.01 vol. % and about 0.05 vol. %, for example about 0.02 vol. % in the composition.
While the second polishing compositions may be described as oxidizer free polishing compositions, an alternative embodiment of the composition may include an oxidizer.
Optionally, the second polishing composition may include one or more oxidizers. The oxidizer can be present in the polishing composition in an amount ranging between about 0.01% and about 100% by volume or weight, for example, between about 0.1% and about 20% by volume or weight. In an embodiment of the polishing composition, between about 0.1% and about 15% by volume or weight of hydrogen peroxide is present in the polishing composition. The oxidizer may be added to the composition in a solution, such as a 30% aqueous hydrogen peroxide solution or a 40% aqueous hydrogen peroxide solution.
In certain embodiments, the oxidizer is added to the rest of the polishing composition just prior to beginning the electrochemical mechanical polishing process. Examples of suitable oxidizers include peroxy compounds, e.g., compounds that may disassociate through hydroxy radicals, such as hydrogen peroxide and its adducts including urea hydrogen peroxide, percarbonates, and organic peroxides including, for example, alkyl peroxides, cyclical or aryl peroxides, benzoyl peroxide, peracetic acid, and ditertbutyl peroxide. Sulfates and sulfate derivatives, such as monopersulfates and dipersulfates may also be used including for example, ammonium peroxydisulfate, potassium peroxydisulfate, ammonium persulfate, and potassium persulfate. Salts of peroxy compounds, such as sodium percarbonate and sodium peroxide may also be used.
The oxidizer can also be an inorganic compound or a compound containing an element in its highest oxidation state. Examples of inorganic compounds and compounds containing an element in its highest oxidation state include but are not limited to periodic acid, periodate salts, perbromic acid, perbromate salts, perchloric acid, perchloric salts, perbonic acid, nitrate salts (such as cerium nitrate, iron nitrate, ammonium nitrate), ferrates, perborate salts and permanganates. Other oxidizers include bromates, chlorates, chromates, iodates, iodic acid, and cerium (IV) compounds such as ammonium cerium nitrate.
The second polishing composition may include one or more additive compounds. Additive compounds include electrolyte additives including, but not limited to, suppressors, enhancers, brighteners, stabilizers, and stripping agents to improve the effectiveness of the second polishing composition in polishing of the substrate surface. For example, certain additives may decrease the ionization rate of the metal atoms, thereby inhibiting the dissolution process, whereas other additives may provide a finished, shiny substrate surface. The additives may be present in the second polishing composition in concentrations up and about 15% by weight or volume, and may vary based upon the desired result after polishing.
Electrochemical mechanical polishing compositions of varying compositions may be used to remove bulk material and residual material, such as copper and/or copper alloys, as well as to remove barrier materials, such as tantalum nitrides or titanium nitrides. Specific formulations of the polishing compositions are used to remove the particular materials. Polishing compositions utilized during embodiments herein are advantageous for electrochemical mechanical polishing processes. Generally, electrochemical mechanical polishing compositions are much more conductive than traditional CMP solutions. The electrochemical mechanical polishing compositions have a conductivity of about 10 mS/cm or higher, while traditional CMP solutions have a conductivity between about 3 mS/cm and about 5 mS/cm. The conductivity of the electrochemical mechanical polishing compositions greatly influences that rate at which the electrochemical mechanical polishing process advances, i.e., more conductive solutions have a faster material removal rate. For removing bulk material, the electrochemical mechanical polishing composition has a conductivity of about 10 mS/cm or higher, for example, between about 10 mS/cm and about 100 mS/cm, preferably in a range between about 30 mS/cm and about 70 mS/cm. For residual material, the electrochemical mechanical polishing composition has a conductivity of about 10 mS/cm or higher, for example, between about 10 mS/cm and about 100 mS/cm, preferably in a range between about 20 mS/cm and about 80 mS/cm.
It has been observed that a substrate processed with the polishing composition described herein has improved surface finish, including less surface defects, such as dishing, erosion (removal of dielectric material surrounding metal features), and scratches, as well as improved planarity.
The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all-inclusive and are not intended to limit the scope of the inventions described herein. The compositions described herein may be further disclosed by the examples as follows.
The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all-inclusive and are not intended to limit the scope of the inventions described herein.
Examples of residual compositions include:
about 3.6 vol. % of phosphoric acid;
about 2 wt. % of ammonium hydrogen citrate;
about 0.2 wt. % of benzotriazole;
about 0.5 vol. % of L-2001;
about 0.0125 vol. % of 750000 molecular weight polyethylene imine (PEI);
about 0.05 wt. % of XECP-7 polymeric abrasive;
deionized water; and
ammonium hydroxide to provide a pH of about 5.75.
about 4.25 vol. % of 85% aqueous phosphoric acid (H3PO4) solution;
about 2 wt. % of 98% ammonium hydrogen citrate;
about 0.2 wt. % of 99% benzotriazole;
about 0.5 vol. % of L-2001 (L-2001 has about <1% heterocyclic polymer/amine polymer solution);
about 0.025 vol. % of 750000 molecular weight 50% polyethylene imine (PEI) solution;
about 0.05 wt. % of XECP-7 polymeric abrasive;
deionized water; and
ammonium hydroxide to provide a pH of about 5.75 (approximately 2.6 wt. % of 45% NH4OH solution).
about 5.1 vol. % of phosphoric acid;
about 2 wt. % of ammonium citrate;
about 0.3 wt. % of benzotriazole;
about 0.5 vol. % of XP-1296;
about 0.025 vol. % of 750000 molecular weight polyethylene imine (PEI));
about 0.05 wt. % of XECP-7 polymeric abrasive;
deionized water; and
potassium hydroxide to provide a pH of about 5.75.
about 6 vol. % of 85% aqueous phosphoric acid (H3PO4) solution;
about 2 wt. % of 98% ammonium citrate;
about 0.3 wt. % of 99% benzotriazole;
about 0.5 vol. % of L-2001 (L-2001 has about <1% heterocyclic polymer/amine polymer solution);
about 0.025 vol. % of 750000 molecular weight 50% polyethylene imine (PEI) solution;
about 0.05 wt. % of XECP-7 polymeric abrasive; deionized water; and
potassium hydroxide to provide a pH of about 5.75 (approximately 9% of 45% KOH solution).
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 60/795,760 (APPM/010798L), filed Apr. 28, 2006, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60795760 | Apr 2006 | US |
