Patent Application
20090061743
1. Field of the Invention
Embodiments of the present invention generally relate to polishing a substrate, such as a semiconductor wafer, with a soft polishing pad.
2. Description of the Related Art
In the fabrication of integrated circuits and other electronic devices on substrates, multiple layers of conductive, semiconductive, and dielectric materials are deposited on or removed from a feature side, i.e., a deposit receiving surface, of a substrate. As layers of materials are sequentially deposited and removed, the feature side of the substrate may become non-planar and require planarization and/or polishing. Planarization and polishing are procedures where previously deposited material is removed from the feature side of the substrate to form a generally even, planar or level surface. The procedures are useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, and scratches. The procedures are also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even or level surface for subsequent deposition and processing.
Chemical mechanical polishing is one process commonly used in the manufacture of high-density integrated circuits to planarize or polish a layer of material deposited on a semiconductor wafer by moving the feature side of the substrate in contact with a soft polishing pad while in the presence of a polishing fluid. Material is removed from the feature side of the substrate that is in contact with the polishing surface through a combination of chemical and mechanical activity.
Soft polishing pads are commonly used as the final removal step in the copper CMP damascene process. The useful lifetime of soft pads is typically low, and the initial performance for film removal rate of a new pad is low and requires a pre-conditioning process in order to ramp up and stabilize the removal rate. This pre-conditioning process is time-consuming, which affects the throughput of the process. Further, the conventional pre-conditioning process may decrease the usable lifetime of the polishing pad.
Therefore, there is a need in the art for an improved pad break-in method that optimizes the polishing surface of a new soft polishing pad while minimizing pre-conditioning time.
Embodiments described herein generally provide a method and apparatus for pre-conditioning a new soft polishing pad. In some embodiments, a method and apparatus for processing a substrate on a soft polishing pad is described.
In one embodiment, a method for polishing a substrate is described. The method includes conditioning a processing surface of a soft polishing pad by rotating the soft polishing pad a first direction while contacting the soft polishing pad with a rotating diamond conditioning disk rotating a second direction, applying a pressure of about 1 pound-force to about 4 pound-force to the rotating diamond conditioning disk, and removing the diamond conditioning disk from contact with the rotating processing surface of the soft polishing pad. The method also includes contacting a first substrate with the rotating processing surface of the soft polishing pad to perform a polishing process on the first substrate, removing the first substrate from the rotating processing surface of the soft polishing pad, conditioning the rotating processing surface of the soft polishing pad with a brush-type conditioning element rotating in the second direction, and contacting a second substrate with the rotating processing surface of the soft polishing pad to perform a polishing process on the second substrate.
In another embodiment, a method for conditioning a soft polishing pad prior to polishing a substrate is described. The method includes coupling a soft polishing pad to a platen, the soft polishing pad having a contact angle of less than about 80°, rotating the platen in a first direction at a first speed, providing a pressure applied to a conditioning disk toward the soft polishing pad while simultaneously rotating the conditioning disk a second direction at a second speed, and applying a fluid to the soft polishing pad.
In another embodiment, a method for processing a substrate using a soft polishing pad is described. The method includes coupling a new, unused soft polishing pad to a platen, providing rotational movement to the platen, placing a rotating conditioning disk in contact with the polishing material at a downforce of about 1 pound-force to about 4 pound-force, removing the rotating conditioning disk from contact with the soft polishing pad, and then contacting a substrate with the soft polishing pad to perform a polishing process on the substrate.
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.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
For example, the first processing station 102 may be configured to perform an electrochemical mechanical planarization (ECMP) process, the second processing station 103 may perform a second ECMP process, and the third processing station 106 may perform a conventional chemical mechanical polishing (CMP) process. It is to be understood that the invention is not limited to this configuration and that any or all of the stations 102, 103, and 106 may be adapted to use a CMP process to remove various layers deposited on the substrate. Alternatively, the processing module 105 may include two stations that are adapted to perform a CMP process while another station may perform an ECMP process. In one embodiment of a process, a substrate having feature definitions formed therein and filled with a barrier layer and then a conductive material disposed over the barrier layer may have the conductive material removed. The removal can be in two steps in the first and second processing stations 102, 103, by an ECMP process, with the barrier layer processed in the third station 106 by a conventional CMP process to form a planarized surface on the substrate.
The embodiment described in system 100 includes a base 108 that supports the processing stations 102, 103 and 106, a transfer station 110, and a carousel 112. A plurality of conditioning devices 182 are shown coupled to the base 108 and are movable in the direction indicated by arrow 109 in order to selectively place the conditioning device 182 over each of the processing stations 102, 103, and 106. The transfer station 110 generally facilitates transfer of substrates 114 to and from the system 100 via a loading robot 116. The loading robot 116 typically transfers substrates 114 between the transfer station 110 and an interface 120 that may include a cleaning module 122, a metrology device 104 and one or more substrate storage cassettes 118.
The transfer station 110 comprises an input buffer station 124, an output buffer station 126, a transfer robot 132, and a load cup assembly 128. The loading robot 116 places the substrate 114 onto the input buffer station 124. The transfer robot 132 has two gripper assemblies, each having pneumatic gripper fingers that hold the substrate 114 by the substrate's edge. The transfer robot 132 lifts the substrate 114 from the input buffer station 124 and rotates the gripper and substrate 114 to position the substrate 114 over the load cup assembly 128, and then places the substrate 114 down onto the load cup assembly 128.
The carousel 112 supports a plurality of carrier heads 190, each of which retains one substrate 114 during processing. The carousel 112 moves the carrier heads 190 between the transfer station 110 and processing stations 102, 103 and 106. The carousel 112 is centrally disposed on the base 108 and includes a plurality of arms 138. Each arm 138 supports one of the carrier heads 190. Two of the arms 138 depicted in
The carrier head 190 retains the substrate 114 while the substrate 114 is disposed in the processing stations 102, 103, 106, which allows the substrate 114 to be sequentially processed by moving the substrate between stations while being retained in the same carrier head 190.
To facilitate control of the processing system 100 and processes performed thereon, a controller 140 comprising a central processing unit (CPU) 142, memory 144 and support circuits 146 is connected to the polishing system 100. The CPU 142 may be one of any form of computer processor that can be used in an industrial setting for controlling pressures and various drives disposed on the system 100. The memory 144 is connected to the CPU 142. The memory 144, or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits 146 are connected to the CPU 142 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like.
Power to operate the processing system 100 and/or the controller 140 is provided by a power supply 150. Illustratively, the power supply 150 is shown connected to multiple components of the polishing system 100, including the transfer station 110, the interface 120, the loading robot 116 and the controller 140.
In one embodiment, the soft polishing pad 226 is new or unused, i.e. no substrates have been polished or contacted the processing surface 125 of the soft polishing pad 226. The soft polishing pad 226 includes at least an upper surface comprised of a polishing material 228 having a plurality of microscopic pore structures and is coupled to a platen 230 that is rotationally mounted on the base 108. The soft polishing pad 226 may be comprised of other layers, such as sub pads, compliant layers, stiffening layers, and adhesives, between the polishing material 228 and the platen 230. The soft polishing pad 226 may be removably disposed on an upper surface of the platen 230 by binders, such as pressure sensitive adhesives or fasteners, which are configured to facilitate static placement and replacement of the soft polishing pad 226.
The spray bar 255 is rotatably coupled to the base 108 about a centerline A and provides a fluid 260 that is directed toward the processing surface 125. The fluid 260 may be a chemical solution, a cleaning solution, or a combination thereof. For example, the fluid 260 may be an abrasive containing or abrasive free polishing compound adapted to aid in removal of material from the feature side of the substrate. Reductants and oxidizing agents such as hydrogen peroxide may also be added to the fluid 260. Alternatively, the fluid 260 may be a rinsing agent, such as deionized water (DIW), that is used as a rinse or flush to remove polishing byproducts from the polishing material 228. In an alternative, the fluid 260 may be used to facilitate conditioning of the polishing surface 125 to open the microscopic pore structures of the processing surface 125.
The conditioning device 182 generally includes a conditioner carrier 212 coupled to the head assembly 202, which is coupled to a support member 204 by an arm 206. The support member 204 is disposed through the base 108 of the processing station 106. Bearings are provided between the base 108 and the support member 204 to facilitate rotation of the support member 204 about a centerline B relative to the base 108. An actuator (not shown) may be coupled between the base 108 and the support member 204 to control the rotational orientation of the support member 204 about the centerline B and laterally position the head assembly 202 relative to the processing station 106. The support member 204 may house drive components to selectively rotate the conditioning element 208 relative to the processing pad 226 about a centerline C. The support member 204 may also provide fluid conduits to control the vertical position of one of the conditioner carrier 212 or the head assembly 202.
A conditioning element 208 is coupled to the bottom surface of the conditioner carrier 212. The conditioner carrier 212 is coupled to the head assembly 202 and may be selectively pressed against the platen 230 while rotating about centerline C to condition the polishing material 228. Likewise, the platen 230 with the soft polishing pad 226 thereon rotates relative to the base 108 about a centerline D. The conditioning element 208 may be an abrasive disc, such as a diamond or ceramic material, both being configured to abrade and enhance the polishing material 228. Alternatively, the conditioning element 208 may be a brush-type conditioning disk, such as a disk having nylon bristles. The conditioning element 208 is adapted to be easily replaced to provide a new or different disk as desired by the user.
In one embodiment, the soft polishing pad 226 is a soft, compliant pad material, such as polymer based pad materials typically utilized in CMP. The polymer material may be a polyurethane, a polycarbonate, fluoropolymers, PTFE, PTFA, polyphenylene sulfide (PPS), or combinations thereof. The pad material may further comprise open or closed cell foamed polymers, elastomers, felt, impregnated felt, plastics, and like materials compatible with the processing chemistries. In another embodiment, the pad material is a felt material impregnated with a porous coating.
In one embodiment, the soft polishing pad 226 in a new or unused condition includes a thickness between about 0.38 mm to about 1.15 mm, for example about 0.77 mm and a density between about 0.25 g/cm3 to about 0.8 g/cm3, for example about 0.52 g/cm3. The soft polishing pad 226 in a new or unused condition also includes a compressibility between about 7% to about 21%, for example about 14% and an elasticity between about 75% to about 100%, for example about 92%. The soft polishing pad 226 in a new or unused condition also includes a tensile modulus at 100% elongation (100% modulus) between about 4 megapascals (MPa) and about 12 MPa, for example about 8.3 MPa and may exhibit a hardness between about 40 Shore A and about 80 Shore A. In one example, the hardness is between about 68 Shore A and 74 Shore A, such as about 70 Shore A. In another example, the hardness of the soft polishing pad 226 is about 63 Shore A.
The upper surface of the soft polishing pad 226 includes a plurality of microscopic pore structures that, when in a new or unused condition, are not fully and/or evenly open. In one embodiment, the soft polishing pad 226 in a new or unused condition includes an average pore size between about 20 microns (μm) to about 60 μm, for example, about 40 μm and a pore rate or porosity between about 10% to about 40%, for example about 20%. The upper surface of the soft polishing pad 226 in a new or unused condition also includes a nap thickness of between about 0.2 mm and about 1 mm, for example about 0.58 mm. Additionally, the soft polishing pad 226 includes an enhanced hydrophilicity. In one embodiment, the upper surface of the soft polishing pad 226 in a new or unused condition includes an enhanced wetability, having a contact angle less than about 80°, such as between about 35° and about 46°, for example about 38.2°.
Generally, the soft polishing pad 226 comprise a processing surface 125 which includes microscopic pore structures as described above. The pore structures effect material removal from the feature side of the substrate. Attributes such as polishing compound retention, polishing or removal activity, and material and fluid transportation affect the removal rate. In order to facilitate optimal removal of material from the substrate, these microscopic pores must be fully and evenly open to provide a relatively high and stable removal rate. These pore structures, when open, facilitate removal by enhancing pad surface wetability, maintaining pad surface roughness, and dispersing polishing compounds, such as, for example, abrasive particles supplied from the polishing compound.
When a new soft polishing pad is installed on the platen, the processing surface is clean, but the pores may not be fully open. For example, the processing surface may be embossed and/or comprise a thin layer or film that may partially or fully cover the pores. The embossment or film may cause portions of the processing surface to lay over and cover the pores and, until removed, block at least a portion of the pores, resulting in non-uniform surface roughness and/or low pad surface wetability. Although the processing surface of the soft polishing pad is nominal, a pre-conditioning process and/or a polishing process may commence using the new pad. In one method, the new soft polishing pad may be pre-conditioned with a brush-type conditioning device, which may not provide enough roughness to substantially open the pores and optimize the processing surface. In another method, the new soft polishing pad may be put into service by performing a polishing process on actual or dummy substrates without pre-conditioning, and the pad may be conditioned concurrently with the polishing process. In any of these methods, the pores disposed in the processing surface of the pad will eventually open and the processing surface will optimize over time and a number of substrates, as determined by a stabilized average removal rate.
In order to promote a faster stabilization in the average removal rate, a method is described herein where a pad conditioning method is implemented prior to processing substrates using a rough conditioning element. The method facilitates increased average removal rate and promotes stabilization of the average removal rate after a lesser number of substrates processed. The method also increases throughput by the enhanced average removal rate stabilization.
In one embodiment, the conditioning element 208 includes a rough contact surface, such as a contact surface comprising a diamond material. The conditioning element 208 may be a disk or element as is typically used to condition hard polyurethane polishing pads. Use of a rough conditioning element to condition a soft polishing pad may not be performed due to concerns regarding destruction of the pad surface by the rough conditioning element. A brush, such as a nylon brush with soft bristles can be used on a soft polishing pad for a determined amount of time. However, any rough conditioning element may be used, such as conditioning elements having embedded diamonds or ceramic particles, or diamond particles, polycrystalline diamonds, diamond matrices, or combinations thereof. A suitable diamond disk is described in U.S. patent application Ser. No. 11/775,533, filed Jul. 10, 2007, which is incorporated by reference herein.
In one embodiment, the platen 230 may be rotated in the first direction at a first speed, such as between about 40 RPM to about 130 RPM, for example about 50 RPM to about 75 RPM. The conditioning element may be rotated in the second direction at a second speed, such as about 60 RPM to about 120 RPM, for example about 90 RPM to about 110 RPM. The second direction may be the same direction as the first direction of the platen, or the second direction may be a rotational direction opposite the rotational direction of the platen. Step 340 includes applying pressure or down force to the conditioning element. A downward pressure in a range between about 0.1 lbf (pound-force) to about 10 lbf, for example about 0.5 lbf to about 8 lbf, such as between about 1.0 lbf to about 3 lbf may be applied to the head assembly 202 (
An optional step 350 provides applying a rinse from the spray bar 255 to the soft polishing pad, which may be a cleaning fluid, such as deionized water and/or a diluted chemical solution comprising complexing agents configured to avoid metal accumulation and contamination on the pad. The rinse may be applied at a pressure between about 25 psi to about 90 psi, for example about 40 psi to about 60 psi. After a period of time, while performing steps 310-340, and optionally, step 350, the pore structures may be optimized and a polishing process may commence at step 360 by providing a substrate and contacting the polishing surface with the substrate. The conditioning element 208, such as a diamond disk, may be used during steps 310-340, and optionally, step 350. As an option, the conditioning element 208 may be replaced with a brush-type conditioning element at 360. A suitable brush-type conditioning element is described in U.S. patent application Ser. No. 11/734,063, filed Apr. 11, 2007, which is incorporated herein by reference.
In one embodiment, a first conditioning process as described above at steps 310-340, and optionally, step 350, to perform a break-in or pre-conditioning process is performed on the processing surface 125 of the soft polishing pad. In a typical polishing process at 360, a substrate is coupled to a carrier head 190 (
In an embodiment, a second conditioning process to maintain or refresh the processing surface 125 of the pad 226 may additionally be performed simultaneously, or at user defined intervals, at or during the process at step 360. The second conditioning process includes rotating and controllably urging the conditioning element 208 relative to the soft polishing pad 226 to condition and clean the processing surface 125 of the soft polishing pad 226. The second conditioning process may be used ex-situ, which is conditioning when a substrate polishing process is not occurring, such as before or after a substrate is being polished. The second conditioning process cleans and frees the pore structures of polishing byproducts, such as previously removed material, spent portions of the polishing compound, and weakened portions of the processing surface 125 that may have clogged a portion of the pores.
The second conditioning process helps to optimize the pore structures and also maintain the pore structures to facilitate removal and is continued or repeated as needed to maintain an optimal processing surface 125 and thus a more stable removal rate. A high pressure rinse as described above at 350 may be performed before, during, or after the second conditioning process.
Diamond conditioning elements to perform the pre-conditioning process are not used on soft pads due to fear of destruction of the pad surface by the rough disk surface. The processing surface 125 of the new polishing pad 226 may be modified by the first conditioning method described above to a roughness that may be equal to a processing surface obtained by extensive conditioning using a brush-type conditioning element and/or with the use of dummy wafers. While not necessary, use of dummy wafers to achieve a targeted removal rate may be used with the first conditioning process. However, the number of dummy wafers and slurry consumption may be reduced, which lessens cost of ownership, time, and other factors.
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. 60/968,830 (Attorney Docket No. 11053L), filed Aug. 29, 2007, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60968830 | Aug 2007 | US |
