Patent Application
20160121453
Embodiments of the disclosure relate to polishing systems for polishing a substrate, such as a semiconductor substrate. More particularly, embodiments relate to a retaining ring usable in a chemical mechanical planarization (CMP) system.
Chemical mechanical polishing (CMP) is a process commonly used in the manufacture of high-density integrated circuits to planarize or polish a layer of material deposited on a substrate. A carrier head may provide the substrate retained therein to a polishing station of the CMP system and controllably urge the substrate against a moving polishing pad. CMP is effectively employed by providing contact between a feature side of the substrate and moving the substrate relative to the 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. Particles removed from a substrate while polishing become suspended in the polishing fluid. The suspended particles are removed while polishing the substrate by the polishing fluid.
The carrier head typically includes a retaining ring that circumscribes the substrate and may facilitate holding of the substrate in the carrier head. A bottom surface of the retaining ring is typically made of a sacrificial plastic material that is generally in contact with the polishing pad during polishing. The sacrificial plastic material is designed to progressively wear over sequential runs.
The retaining rings are typically manufactured using conventional CNC machining methods. However, the surface of the sacrificial plastic material produced by conventional machining methods is typically too rough and must be conditioned to produce a smoother surface and an acceptable flatness. One method for “break in” conditioning of a new retaining ring involves installing the retaining ring on a fully functional CMP system and running a recipe with numerous dummy wafers. However, this approach is inefficient due to high capital and labor costs.
Therefore, there is a need for a simplified method and apparatus for producing retaining rings having a desired roughness and surface flatness.
A retaining ring, a retaining ring conditioning method, and a conditioning fixture are disclosed. In one embodiment, a fixture for forming a sacrificial surface on a retaining ring includes a fixture plate sized to substantially match an outside diameter of the retaining ring, and a clamp device adapted to provide a lateral load to one of an inside diameter sidewall or an outer diameter sidewall of a lower portion of the retaining ring.
In another embodiment, a retaining ring for a polishing process is disclosed. The retaining ring includes a body comprising an upper portion and a lower portion, and a sacrificial surface disposed on the lower portion, the sacrificial surface comprising a negative tapered surface having a taper height that is about 0.0003 inches to about 0.00015 inches.
In another embodiment, a retaining ring for a polishing process is disclosed. The retaining ring includes a ring shaped body comprising an upper portion and a lower portion, the upper portion having a planar surface disposed in a first plane, and a sacrificial surface disposed on the lower portion, the sacrificial surface disposed in a second plane that is negatively angled relative to first plane and having a taper height that is about 0.0003 inches to about 0.00015 inches.
In another embodiment, a method for forming a retaining ring for a polishing process is provided. The method includes coupling a fixture plate to an upper portion of a ring-shaped body, providing a lateral load to one of an inside diameter sidewall or an outer diameter sidewall of a lower portion of the ring-shaped body, and urging the lower portion of the ring-shaped body toward a rotating polishing pad.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure 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 disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other 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.
A retaining ring, and a method for conditioning and/or refurbishing a retaining ring, utilized for polishing a substrate are described herein. Apparatus for implementing the method includes a fixture assembly that is coupled to the retaining ring facilitating the conditioning and/or refurbishing.
The CMP system 100 may include a chemical delivery system 138 and a pad rinse system 140. The chemical delivery system 138 includes a chemical tank 142 which holds a polishing fluid 144, such as a slurry or deionized water. The polishing fluid 144 may be sprayed by a spray nozzle 146 onto the polishing surface 120. A drain 148 may collect the polishing fluid 144 which may flow off of the polishing pad 125. The polishing fluid 144 that is collected may be filtered to remove impurities, and transported back to the chemical tank 142 for reuse.
The pad rinse system 140 may include a nozzle 152 that delivers deionized water 154 to the polishing surface 120 of the polishing pad 125. The nozzle 152 is coupled to a deionized water tank (not shown). After polishing, the deionized water 154 from the nozzle 152 may rinse debris and excess polishing fluid 144 from the substrate 110, the carrier head 105 and the polishing surface 120. Although the pad rinse system 140 and the chemical delivery system 138 are depicted as separate elements, it should be understood that a single delivery tube may perform both functions of delivering the deionized water 154 delivery and the polishing fluid 144.
The carrier head 105 is coupled to a shaft 156. The shaft 156 is coupled to a motor 158, which may be coupled to an arm 160. The motor 158 may be utilized to move the carrier head 105 laterally in a linear motion (X and/or Y direction) relative to the arm 160. The carrier head 105 also includes an actuator 162 configured to move the carrier head 105 in a Z direction relative to arm 160 and/or the polishing pad 125. The carrier head 105 is also coupled to a rotary actuator or motor 164 that rotates the carrier head 105 about a centerline 166 (which may also be a rotational axis) relative to the arm 160. The motors 158, 164 and actuator 162 position and/or move the carrier head 105 relative to the polishing surface 120 of the polishing pad 125. In one embodiment, the motors 158, 164 rotate the carrier head 105 relative to the polishing surface 120 and provide a down-force to urge the substrate 110 against the polishing surface 120 of the polishing pad 125 during processing.
The carrier head 105 includes a body 168 which houses a flexible membrane 170. The flexible membrane 170 provides a surface on the underside of the carrier head 105 that contacts the substrate 110. The body 168 and the flexible membrane 170 are circumscribed by the retaining ring 115. The retaining ring 115 may have a plurality of grooves 172 (one is shown) that facilitates slurry transportation.
The carrier head 105 may also contain one or more bladders, such as an outer bladder 174 and an inner bladder 176, that are adjacent to the flexible membrane 170. As discussed above, the flexible membrane 170 contacts a backside of the substrate 110 when the substrate 110 is retained in the carrier head 105. The bladders 174, 176 are coupled to a first variable pressure source 178A that selectively delivers a fluid to the bladders 174, 176 to apply force to the flexible membrane 170. In one embodiment, the bladder 174 applies force to an outer zone of the flexible membrane 170 while the bladder 176 applies force to a central zone of the flexible membrane 170. Forces applied to the flexible membrane 170 from the bladders 174, 176 are transmitted to portions of the substrate 110 and may be used to control the edge to center pressure profile that is translated to the substrate 110 and against the polishing surface 120 of the polishing pad 125. The first variable pressure source 178A is configured to deliver fluids to each of the bladders 174, 176 independently in order to control forces through the flexible membrane 170 to discrete regions of the substrate 110. Additionally, vacuum ports (not shown) may be provided in the carrier head 105 to apply suction to the backside of the substrate 110 facilitating retention of the substrate 110 in the carrier head 105. Examples of a carrier head 105 that may be adapted to benefit from the disclosure include the TITAN HEAD™, the TITAN CONTOUR™ and the TITAN PROFILER™ carrier heads, which are available from Applied Materials, Inc. of Santa Clara, Calif., among other carrier heads available from other manufacturers.
In one embodiment, the retaining ring 115 is coupled to the body 168 by an actuator 180. The actuator 180 is controlled by a second variable pressure source 178B. The second variable pressure source 178B provides or removes fluid from the actuator 180 which causes the retaining ring 115 to move relative to the body 168 of the carrier head 105 in the Z direction. The second variable pressure source 178B is adapted to provide the Z directional movement of the retaining ring 115 independent of movement provided by the motor 162. The second variable pressure source 178B may provide movement of the retaining ring 115 by applying negative pressure or positive pressure to the actuator 180 and/or the retaining ring 115. In one aspect, pressure is applied to the retaining ring 115 to urge the retaining ring 115 toward the polishing surface 120 of the polishing pad 125 during a polishing process.
As discussed above, the retaining ring 115 may contact the polishing surface 120 during polishing of the substrate 110. The chemical delivery system 138 may deliver polishing fluid 144 to the polishing surface 120 and substrate 110 during polishing. Grooves 172 formed in the retaining ring 115 facilitate transportation of the polishing fluid 144 and entrained polishing debris through the retaining ring 115 and away from the substrate 110. After processing a substrate 110, the substrate 110 may be removed from the carrier head 105.
The retaining ring 115 may be ring shaped and include a center line that shares the center line 166 of the carrier head 105 illustrated in
The body 235, or at least the upper portion 240, may be formed from a metallic material, such as stainless steel, aluminum, molybdenum, or another process-resistant metal or alloy, or a ceramic or a ceramic filled polymer plastic, or a combination of these or other suitable materials. In one example, the upper portion 240 of the body 235 may be formed from a metal, such as stainless steel. Additionally, the body 235, or at least the lower portion 245, may be fabricated from a plastic material such as polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, polybutylene naphthalate, ERTALYTE® TX, PEEK, TORLON®, DELRIN®, PET, VESPEL®, DURATROL®, or a combination of these or other suitable materials. In one example, the lower portion 245 of the body 235 may be fabricated from a ceramic material. In one embodiment, the upper portion 240 provides rigidity while the lower portion 245 provides a sacrificial surface 255 that contacts the polishing surface 120 of the polishing pad 125. The sacrificial surface 255 tends to wear during polishing processes and must be replaced after numerous cycles.
As described above, conventional retaining rings are manufactured using conventional CNC machining methods. The surface finish (average surface roughness (Ra)) and flatness achieved by these methods is typically about 16 Ra and 0.001 inches, respectively. The machine tolerance and finish at these levels do not yield a production worthy part as the as-machined retaining rings generate an unacceptable amount of particles during polishing. Furthermore, conventional retaining rings with a generally flat (0.001-inch) profile has been shown to inadequately control the polishing pad surface topology thus requiring an extensive break-in process prior to use in production.
It has been found that optimal polishing is achieved using a retaining ring 115 with a negative taper on the sacrificial surface 255 (i.e., where a thickness of the inside diameter sidewall 225 of the retaining ring 115 is slightly thinner than a thickness of the outer diameter sidewall 230). Additionally, it has been found that altering the roughness of the sacrificial surface 255 of the retaining ring 115 to a roughness much less than about 16 Ra reduces particles as well as enhances polishing.
The clamp device 605 may include two annular rings 620 and 625 that are fastened to each other and/or to the outer clamp ring 610 using fasteners 640. One of the fasteners may be an adjustment fastener while the other fastener may be a locking fastener. Another plurality of fasteners 645 may be used to couple the fixture plate 615 to the upper portion 240 of the retaining ring 115. The clamp device 605, specifically the annular ring 625, may rest on a shoulder 630 extending radially outward from the outer surface of the upper portion 240. Tightening of the fasteners 640 and the fasteners 645 facilitates the coupling of the fixture plate 615 and the outer clamp ring 610 such that the fixture 600 is integral with the retaining ring 115. Utilization of the outer clamp ring 610 keeps the lower portion 245 of the retaining ring 115 square with respect to a surface of a polishing pad (not shown) while forming the negative tapered surface 500. Adjustment of a lower surface 650 of the outer clamp ring 610 relative to the sacrificial surface 255 controls rebound of the polishing pad during the polishing process and influences taper of the sacrificial surface 255 and/or the outer diameter sidewall 230 of the lower portion 245 of the retaining ring 115. The fixture 600 may comprise an outer diameter fixture that is utilized to apply a controlled lateral load on the outer diameter sidewall 230 of the lower portion 245 of the retaining ring 115. The outer clamp ring 610 may be further utilized to maintain a fixed boundary on the outer diameter sidewall 230 of the lower portion 245 of the retaining ring 115. in the absence of a fixed boundary on the outer diameter sidewall 230 of the lower portion 245, lateral forces applied to the inner diameter sidewall 225 may adversely displace and enlarge the outer diameter of the lower portion 245 rather than inducing material deformation toward the lower surface 650 of the outer clamp ring 610.
After processing and removal of the deformed ring 935 from the fixture plate 615, the retaining ring 115 relaxes into a neutral state (sacrificial surface 255 has the negative tapered surface 500) as shown in
One theory of operation is, by mounting a retaining ring 115 to the rigid fixture plate 615, and applying a downforce (e.g., about 36-in/lb) using fasteners 645, induces a positive taper angle 938 at the sacrificial surface 255 of the lower portion 245 of the retaining ring 115 that is proportional to the positive taper 920 of the fixture plate 615. The induced positive taper angle 938 is characterized by a uniform displacement of the inside diameter sidewall 225 (e.g., a displacement of approximately 0.001-inch) relative to the plane defined by the outer diameter sidewall 230 of the lower portion 245 of the retaining ring 115. Note that the positive taper 920 can be modified in order to influence the magnitude of the positive taper angle 938. For example, a greater positive taper 920 on the fixture plate 615 would yield a greater positive taper angle 938 on the retaining ring 115 prior to conditioning. The displacement of the inside diameter sidewall 225 reduces to approximately zero during conditioning due to asymmetric material removal from the bottom surface 220. The retaining ring 115 relaxes to neutral state after removing fasteners 645 thus achieving a finished state with a negative taper surface 500.
The fixture 1000 may comprise an internal interference fit swage fixture that is utilized to apply a controlled lateral load on the inside diameter sidewall 225 of the lower portion 245 of the retaining ring 115. The fixture plate 615 utilized in the fixture 600 may also be used with the fixture 1000. However, a clamping device 1005 is an internal clamping device in this embodiment. The clamping device 1005 includes a plurality of fasteners 1007 (only one is shown in the partial cross-sectional view of
A conditioning method for producing a retaining ring 115 having a negative tapered surface 500 will be described. The conditioning method utilizes a stand-alone conditioning system 1100 such that CMP tools for polishing production substrates may remain on-line. The conditioning system 1100 mimics a full scale CMP system but at dramatically lower cost. Once the fixture 1115 is positioned such that the sacrificial surface 255 faces the polishing pad 1110, the platen 1105 may be rotated at about 65 rpm for about 15-30 minutes or until a mirror finish is achieved on the sacrificial surface 255. A slurry, such as a commercially available CMP slurry, may be dispersed at the center of the polishing pad 1110 at a rate of about 65 milliliters per minute during conditioning of the retaining ring 115. After conditioning, the retaining ring 115 may be disassembled from the fixture 1115 and then the profile of the negative tapered surface 500 may be verified by laser and coordinate measuring methods, for example. In order to refurbish a used retaining ring 115 that no longer conforms to taper specifications due to sacrificial surface consumption, the worn sacrificial surface 255 may be removed by a lathe such that the entire lower portion 245 of the retaining ring 115 is removed. The upper portion 240 of the retaining ring 115 may further be machined to expose virgin material of the upper portion 240. A new lower portion 245 may then be adhered to the upper portion 240 and the retaining ring 115 having the new lower portion 245 may be coupled to the fixture 1115 as described above. The conditioning regime described above may then be performed on the conditioning system 1100 to produce the negative tapered surface 500 as previously described. Alternatively, to refurbish a retaining ring 115 without replacing the whole lower portion 245, the worn sacrificial surface 255 may be reconditioned via lathe removal of 0.01 inches to 0.08 inches from the bottom surface 220. The retaining ring 115 then having a flat bottom surface (e.g., sacrificial surface 255) may be coupled to the fixture 1115 and the conditioning regime described above then performed on the conditioning system 1100 to produce the negatively tapered surface 500 as previously described.
While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 62/072,659 filed Oct. 30, 2014, which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62072659 | Oct 2014 | US |
