Patent Application
20080020682
1. Field of the Invention
Embodiments of the present invention generally relate to the fabrication of integrated circuits and more particularly to the removal of conductive material from a substrate.
2. Description of the Related Art
In VLSI and ULSI semiconductor manufacturing, reliable formation of multilevel interconnects is important to the continued effort to increase circuit density and quality of individual substrates and die. Multilevel interconnects are formed using sequential material deposition and material removal techniques on a substrate surface to form features therein. As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization prior to further processing. Planarization, or “polishing,” is a process in which material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing excess deposited material, undesired surface topography, and surface defects, such as surface roughness, agglomerated materials, crystal lattice damage, scratches, and the like. Planarization also provides an even surface for subsequent photolithography and other semiconductor manufacturing processes.
Electrochemical mechanical polishing (ECMP) is one method of planarizing a surface of a substrate. ECMP is a method that removes conductive materials, such as copper, from a substrate surface by electrochemical “anodic” dissolution while polishing the substrate with a reduced mechanical abrasion and pressure compared to conventional chemical mechanical planarization (CMP) processes. The greatly reduced down-pressure required for ECMP allows the planarization of substrates having delicate low-k materials deposited thereon. Electrochemical dissolution is performed by applying an electrical bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte, such as a polishing composition. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. The polishing material may be, for example, a processing pad disposed on a rotating platen. The polishing composition may be disposed in the processing pad and the metal ions on the substrate surface dissolve into the surrounding polishing composition.
A typical ECMP system includes a substrate support and two electrodes disposed within an electrolyte containment basin. The substrate is in electrical contact with one of the electrodes, and in effect, the substrate becomes an anode during processing for material removal. A mechanical component of the polishing process is performed by providing a relative motion between the substrate and the processing pad while in contact with each other that enhances the removal of the conductive material from the substrate.
The removal rate of conductive material from a substrate surface is an important metric for the performance of an ECMP processing system. Lower removal rate results in a longer processing time, thereby increasing the production cost per substrate. Process parameters used to affect removal rate during ECMP include voltage applied between the electrodes, makeup of electrolyte/polishing composition, substrate pressure against the processing pad, polishing head rpm, and processing pad rpm.
Conventionally an abrasive conditioning element, such as a diamond conditioning disk, or a brush conditioner, such as a Nylon™ brush, is periodically used to refurbish the processing pad surface to improve polishing results. A conditioning element is applied to the processing pad, often in conjunction with a suitable cleaning fluid, using a spinning conditioning disc that also translates laterally across the surface of the processing pad. After such conditioning, the removal rate of the processing pad is increased and fewer substrate surface defects are formed by the processing pad. A conditioning process is also typically performed on unused processing pads in order to remove native oxides and other passivation layers formed on the conductive materials therein in order to “break-in” the processing pad.
ECMP processing station 100 performs both substrate processing and processing pad conditioning. In operation, a substrate is mounted on polishing head 101 and is processed face-down, i.e., production side down, during the ECMP process. Polishing head 101 and processing pad 103 rotate continuously in one direction, in this example counterclockwise. Polishing head 101 may also translate linearly across the surface of processing pad 103. During processing pad conditioning, processing pad 103 continues to rotate in the same direction as during the ECMP process, and conditioning head 104 rotates continuously in that same direction. Conditioning head 104 is also displaced along path 120 in a sweeping motion during the conditioning process to uniformly and completely condition the entire surface of processing pad 103.
While the processing pad conditioning method described above improves the removal rate of ECMP processing pads, even higher removal rates are desirable in the ECMP process. Higher ECMP removal rates result in higher throughput and, and hence, lower processing cost per substrate. In addition, higher ECMP removal rates for a given processing pad allow more substrates to be processed before reconditioning of the pad is necessary. Because the reconditioning process is generally time-consuming, a longer period between such reconditioning significantly reduces ECMP system downtime, which also lowers processing cost per substrate.
The present invention provides a method of conditioning processing pads that increases the removal rate. According to embodiments of the present invention, conductive material removal rates will be increased during the ECMP process if the direction of rotation of the processing pad relative to the conditioning disc is opposite the direction of rotation of the processing pad relative to the substrate.
According to a first embodiment, the relative rotation between the conditioning element and the processing pad is produced by rotating both the conditioning element and the processing pad in a first rotational direction. The relative rotation between the substrate and the processing pad during polishing is produced by rotating both the substrate and the processing pad in a second rotational direction, wherein the second rotational direction is opposite to the first rotational direction.
According to a second embodiment, the relative rotation between the conditioning element and the processing pad is produced by rotating the processing pad in a first rotational direction and the relative rotation between the substrate and the processing pad is produced by rotating the processing pad in a second rotational direction, wherein the second rotational direction is opposite to the first rotational direction.
According to a third embodiment, the relative rotation between the conditioning element and the processing pad is produced by rotating the conditioning element in a first rotational direction and rotating the processing pad in a second rotational direction, wherein the first rotational direction is the opposite of the second rotational direction. The relative rotation between the substrate and the processing pad during polishing is produced by rotating the substrate in the second rotational direction and the processing pad in the first rotational direction.
According to a fourth embodiment, the relative rotation between the conditioning element and the processing pad is produced by rotating one of the conditioning element or the processing pad in a first rotational direction while the other remains rotationally stationary. The relative rotation between the substrate and the processing pad during polishing is produced by rotating one of the substrate or the processing pad in a second rotational direction while the other remains rotationally stationary, wherein the first rotational direction is the opposite of the second rotational direction.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of 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.
For clarity, identical reference numerals have been used, where applicable, to designate identical elements that are common between figures.
The processing pad assembly 222 generally includes a processing pad 203 coupled to a backing 207. The backing 207 may also be coupled to an electrode 209. The processing pad 203 and the backing 207 have a plurality of holes or pores formed therein to allow the polish composition to make contact with, and thus provide a conductive path between the substrate 208 and the electrode 209. The processing pad 203 is used to apply a uniform bias to the substrate surface by use of a conductive surface that makes contact with the surface of the substrate.
Processing pad 203 is a conductive pad that has a working surface adapted to polish the production side, i.e., the electronic device side, of substrate 208 during ECMP processing. The working surface may be smooth or patterned to facilitate distribution of a polishing composition and/or electrolyte over the surface of the processing pad assembly 222. Patterns may include grooves, cutouts, perforations, and the like.
Processing pad 203 may be fabricated from polymeric materials compatible with the process chemistry and includes conductive material or conductive contact elements extending therefrom. Examples of suitable polymeric materials include polyurethane, polycarbonate, fluoropolymers, PTFE, PTFA, polyphenylene sulfide (PPS), or combinations thereof. For example, processing pad 203 may be fabricated from a conductive composite, i.e., the conductive elements are dispersed integrally with or make up the material of the polishing surface. Conductive composites include a polymer matrix having conductive particles dispersed therein or a conductive-coated fabric, among others.
Alternatively, processing pad 203 may consist of a fabric layer having a conductive layer disposed thereover, wherein the conductive layer has an exposed surface adapted to polish substrate 208. The fabric layer may be woven or non-woven. The conductive layer may be comprised of a soft metal and, in one example, the exposed surface may be planar. Examples of processing pad 203 that may be adapted to benefit from the invention are described in commonly assigned U.S. Pat. No. 6,979,248, U.S. Pat. No. 6,988,942, and U.S. Pat. No. 6,991,528, each of which is hereby incorporated by reference in its entirety.
Alternatively, processing pad 203 may include one or more intervening layers (not shown). For example, a conductive foil may be disposed below processing pad 203 to promote uniform power distribution thereacross. In addition, an interposed pad may be provided below the conductive foil to increase mechanical attributes of processing pad 203. Lastly, a subpad may be provided to tailor the compliance of the processing pad 203.
The substrate 208 and the processing pad assembly 222 disposed in the basin 204 are moved relative to each other to provide a desired polishing motion. The polishing motion includes at least one motion defined by an orbital, rotary, or curvilinear motion, or combinations thereof, to provide a relative rotational motion between the surface of substrate 208 and the processing surface of processing pad assembly 222. In one example, the polishing motion may be achieved by rotating polishing head 202, basin 204, or both. Additional components to the polishing motion may be included by linearly or curvilinearly translating polishing head 202 relative to basin 204. In the example depicted in
A power source 224 is coupled to the processing pad assembly 222 by electrical leads 223A, 223B. The power source 224 applies an electrical bias to the processing pad assembly 222 to drive an electrochemical process described herein. During ECMP, substrate 208 is exposed to the polishing composition and is in electrical contact with processing pad 203. A bias from power source 224 is then applied between substrate 208 and processing pad 203. The bias is generally provided to produce anodic dissolution of the conductive material from the surface of substrate 208 at a current density up to about 55 mA/cm2, which correlates to an applied current of up to about 40 amps to process substrates with a diameter of about 300 mm. The bias may be varied in power and duration depending on numerous factors, including the thickness and type of conductive material to be removed from the substrate surface. Substrate 208 is typically exposed to the power application and polishing composition (described below) for a period of time sufficient to remove at least a portion or all of the desired material disposed thereon. For example, the substrate may be exposed to the polishing composition and power between about 5 seconds and about 300 seconds, but may vary depending on the thickness and type of conductive material to be removed.
The polishing head 202 retains the substrate 208 during processing. In one embodiment, the polishing head 202 includes a housing 214 enclosing a bladder 216. Bladder 216 may be deflated when contacting the substrate to create a vacuum therebetween, thus securing the substrate to the polishing head 202 to allow placement and removal of the substrate. The bladder 216 may additionally be inflated and pressurized to assure contact between the substrate and the processing pad assembly 222 retained in basin 204. A retaining ring 238 is coupled to housing 214 and circumscribes substrate 208 to prevent the substrate from slipping from polishing head 202 while being processed. During ECMP, substrate 208 and processing pad 203 contact each other at a pressure of less than about 2 psi (13.8 kPa). For example, a contact pressure between the substrate and polishing pad between about 0.01 psi (69 Pa) and about 1.5 psi (10.2 kPa), may be used for polishing the surface of substrate 208. The optimal contact pressure therebetween is dependent on the underlying non-conductive materials on the surface of the substrate, what conductive material is being removed, the makeup of the polishing composition, and other factors.
The basin 204 is generally fabricated from a plastic such as fluoropolymers, TEFLON® polymers, or other materials that are compatible or non-reactive with the polishing composition or other chemicals used in ECMP station 200. The basin 204 is rotationally supported above a base 206 by bearings 234. A drive system 236 is coupled to the basin 204 and rotates the basin 204 during processing. A catch basin 228 is disposed on the base 206 and circumscribes the basin 204 to collect processing fluids, such as polishing composition, that flow out of port 218 disposed through the basin 204 during and/or after processing. An outlet drain 219 and outlet valve 219A are incorporated in the invention to allow the polishing composition in the catch basin to be sent to a reclaim system (not shown) or a waste drain (not shown).
A polishing composition delivery system 232 is generally disposed adjacent basin 204. Polishing composition delivery system 232 includes a nozzle or outlet 230 coupled to a polishing composition source 242. The outlet 230 delivers polishing composition or other processing fluids from the polishing composition source 242 into the basin 204, typically at a rate between about 0.1 and 2.0 liters per minute, depending on the specific ECMP process. The polishing composition source 242 schematically shown here includes a source of all of the chemicals required to supply and support the polishing composition during processing. The polishing composition may contain abrasive particles to assist in the mechanical removal of conductive materials from substrate 208. The abrasive content of the polishing composition is selected based on the particular ECMP process. In addition, the abrasive content of the polishing composition may be varied during the ECMP process, for example from about 0 wt % to 0.4 wt. %. Examples of polishing compositions and methods of varying the abrasive content thereof are described in detail in commonly assigned U.S. patent application Ser. No. 10/957,199, filed Oct. 1, 2004 by Rashid et al., which is hereby incorporated by reference herein.
A conditioning apparatus 250 is disposed proximate basin 204 to periodically condition or regenerate processing pad 203 of processing pad assembly 222. Typically, conditioning apparatus 250 includes an arm 252 coupled to a stanchion 254 that is adapted to position and sweep a conditioning element 258 across processing pad assembly 222. Conditioning element 258 is coupled to the arm 252 by a shaft 256 to allow clearance between the arm 252 and sidewalls 246 of basin 204 while the conditioning element 258 is in contact with processing pad assembly 222.
Conditioning element 258 is typically a diamond or silicon carbide disk, which may be patterned to enhance the process of conditioning the surface of processing pad 203. Alternatively, the conditioning element 258 may be made of a Nylon™ brush or similar conditioner for in-situ conditioning of processing pad 203. One conditioning element 258 that may be adapted to benefit from aspects of the invention is described in U.S. patent application Ser. No. 09/676,280, filed Sep. 28, 2000 by Li, et al, which is incorporated herein by reference to the extent not inconsistent with the claimed invention.
In operation, conditioning element 258 contacts processing pad 203 with a down-force in the range of about 0.01 to about 10 lbs, the optimal pressure depending on factors such as the composition of the conditioning element 258 and the processing pad 203. A cleaning fluid may be dispensed onto processing pad 203, either through conditioning element 258 or via a nozzle external thereto. Alternatively, an electrolyte for polishing is dispensed onto processing pad 203 to maintain a liquid film between conditioning element 258 and the pad surface. Cleaning fluid or electrolyte is generally supplied at a rate between about 10 ml/min to about 500 ml/min. The conditioning element 258 may be rotated at a speed between about 5 to about 100 rpm. The conditioning element 258 may be swept across the surface of processing pad 203 over a range between about 0.1 and 14 inches. The frequency of the sweep may be in the range of about 2 to about 40 cycles/minute.
The cleaning fluid is formulated to dissolve polishing by-products and is generally used to clean processing pad 203. For example, for cleaning processing pads utilized for copper polishing, the cleaning fluid may include amine solutions, carboxylic acid solutions, combinations thereof, and the like. The pH value of the cleaning solution may be adjusted to substantially match that of the ECMP processing fluid. In this way, in the event that the cleaning fluid mixes with the polishing fluid, chemical incompatibility issues therebetween are avoided that would otherwise affect polishing performance. Acid-based, base-based, and neutral cleaning solutions may be applied by conditioning apparatus 250, depending on the conductive material to be removed by ECMP and on the composition of processing pad 203. Examples of cleaning solutions suitable for use by conditioning apparatus 250 are described in detail in commonly assigned U.S. patent application Ser. No. 11/209,167, filed Aug. 22, 2005 by Wang et al., which is hereby incorporated by reference herein.
The ECMP station 200 described above may be disposed on a polishing platform, such as the planarization platform illustrated in
Platform 300 generally includes a base 308 that supports the one or more ECMP stations 200, the one or more polishing stations 306, a transfer station 310, and a carousel 312. A loading robot 316 transfers substrates 314 to and from the transfer station 310 of the apparatus 300 and a factory interface 320. The factory interface 320 may include a cleaning module 322, a metrology device 304, and one or more substrate storage cassettes 318. The carousel 312 has a plurality of arms 338, each respectively supporting one of a plurality of polishing heads 208. Each polishing head 208 retains one substrate 314 during processing. Substrates are loaded and unloaded from the polishing heads 208 by the load cup assembly 328. The carousel 312 moves the polishing heads 208 between the load cup assembly 328 of the transfer station 310, the one or more ECMP stations 200 and the one or more polishing stations 306. The polishing head 208 retains the substrate 314 against the ECMP station 200 or polishing station 306 during processing. The arrangement of the ECMP stations 200 and polishing stations 306 on the apparatus 300 allows for the substrate 314 to be sequentially polished by moving the substrate between stations while being retained in the same polishing head 208.
According to a first embodiment of the invention, processing pad 203 rotates counterclockwise and polishing head 202 rotates counterclockwise during ECMP processing, and during the conditioning and/or break-in process, processing pad 203 rotates clockwise and conditioning element 258 rotates clockwise. According to a second embodiment of the invention, processing pad 203 rotates clockwise and polishing head 202 rotates clockwise during ECMP processing, and during the conditioning and/or break-in process, processing pad 203 rotates counterclockwise and conditioning element 258 rotates counterclockwise. In a third embodiment, the direction of rotation of the polishing pad during polishing is opposite the direction of rotation of the polishing pad during conditioning, while the direction of rotation of the substrate and the conditioning head are the same. In each embodiment, the relative rotational motion produced between processing pad 203 and conditioning element 258 is substantially the opposite that of the relative rotational motion produced between processing pad 203 and substrate 208 during ECMP processing.
In
Referring back to
Referring to
The invention may be applied to an ECMP process in which the processing pad and the substrate are rotated in opposite directions, e.g., clockwise and counterclockwise, respectively. During the conditioning process, the processing pad is rotated clockwise and the conditioning element is rotated counterclockwise, so that the relative rotational motion produced between the processing pad and the conditioning element is opposite to the relative rotational motion between the processing pad and the substrate. In another aspect, the processing pad rotates in the same direction in both the ECMP process and the conditioning process, and a substantially different relative rotation motion is provided during the conditioning process by rotating the conditioning element in the opposite direction that the substrate is rotated during the ECMP process.
An ECMP process, wherein a relative rotational motion between a substrate and a processing pad is produced by rotating only the substrate or only the processing pad, may also benefit from the application of an aspect of inventive method. For example, if the processing pad remains rotationally stationary during the ECMP process and only the substrate is rotated, then during the conditioning process, the conditioning head may be rotated in the opposite direction, to provide a substantially different relative rotational motion. In so doing, the resultant removal rate of the processing pad can be improved.
Aspects of the invention further contemplate the application of different conditioning processes on different regions of a processing pad. By conditioning a processing pad differently in different regions, a single processing pad may provide a different removal rate in each region. In effect, this provides an additional process parameter, i.e., which region of the pad is being used, for modulating removal rates during the ECMP process. It may be desirable in some applications for the removal rate to vary during an ECMP process, but typical process parameters affecting removal rate, e.g., down-pressure, polishing composition abrasive content, etc., may have been optimized to a certain value and need to be kept constant during the ECMP process. This aspect of the invention allows removal rate of a conductive material from a substrate to be varied during the ECMP process even when conventional process parameters are fixed.
Any number of different processing regions may be prepared on the surface of processing pad 203A, limited only by the ratio of the diameter of processing pad 203A to the diameter of a substrate to be processed therewith. For example, if the diameter of processing pad 203A is at least three times the diameter of a substrate to be processed therewith, then up to three discrete concentric regions, each with a different associated removal rate, may be formed on processing pad 203A during the conditioning process.
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.
