Patent Application
20110014858
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a polishing pad having a grooved pattern for a chemical mechanical polishing system.
Compositions and methods for chemical-mechanical polishing of the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for CMP of surfaces of semiconductor substrates (e.g., integrated circuits) typically contain an abrasive, various additive compounds, and the like.
Chemical-mechanical polishing (CMP) involves the concurrent chemical and mechanical abrasion of surface, e.g., abrasion of an overlying first layer to expose the surface of a non-planar second layer on which the first layer is formed. One such process is described in U.S. Pat. No. 4,789,648 to Beyer et al. Briefly, Beyer el al., discloses a CMP process using a polishing pad and a slurry to remove a first layer at a faster rate than a second layer until the surface of the overlying first layer of material becomes coplanar with the upper surface of the covered second layer. More detailed explanations of chemical mechanical polishing are found in U.S. Pat. No. 4,671,851, No. 4,910,155 and No. 4,944,836.
In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents, acids, bases, or other additives present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide.
One problem in CMP relates to polishing slurry distribution over the polishing pad. The CMP process requires the interaction of the polishing pad, abrasive particles and any reactive agent or chemical in the polishing composition with the substrate to obtain the desired polishing results. Ineffective distribution of the slurry across the surface of the polishing pad can lead to diminished polishing efficiency. Polishing pads generally include some feature such as perforations or textures (e.g., grooves, surface depressions, and the like) to aid in distributing the abrasive polishing slurry relatively uniformly across the pad. Grooves are often a preferred texturing feature, because they can be designed to directly channel the excess slurry to where it is needed. Grooved polishing pads are often characterized by the dimensions (e.g., width and depth) of the grooves and the spacing between the grooves (known as “pitch”). Examples of grooved pads include those disclosed in U.S. Pat. No. 5,921,855 to Osterheld et al., U.S. Pat. No. 6,520,847 to Osterheld et al., and U.S. Pat. No. 6,736,847 to James et al.
While conventional grooved CMP pads have certain preferred performance characteristics over, for example, perforated pads, there is still a need in the art for improved pad performance features, such as improved pad lifetime (e.g., due to reduced wear rates). The present invention addresses this need.
The present invention provides polishing pads for use in CMP processes. In one embodiment, a pad comprises a surface defining a plurality of grooves with landing surfaces separating the grooves, the landing surfaces together defining a substantially planar polishing surface, each groove having a depth of at least about 10 mil and a width, WG, with any two adjacent grooves being separated from each other by a landing surface having a width, WL, wherein the quotient WL/WG is less than or equal to 3. In a preferred embodiment, the surface of the pad defines a series of concentric, substantially circular grooves. Preferably, each groove has the same WG, and each landing surface has the same WL.
In an alternative embodiment, the surface of the pad defines a spiral groove having a depth of at least about 10 mil and a width WG, and a spiral landing surface outlining the spiral groove. The spiral landing surface has a width, WL, and defines a substantially planar publishing surface. As in the previously described embodiment, the quotient WL/WG is less than or equal to 3.
The polishing surface of the polishing pads of the present invention can be formed from any substance suitable for use in CMP pad construction. In some preferred embodiments the polishing surface of the pad is formed from a thermoplastic polyurethane material. The pads can be constructed from a single layer of pad material or from multiple layers (e.g., a base layer and a surface layer).
The polishing pads of the present invention provide an unexpected improvement in polishing removal rate uniformity over extended use (e.g., polishing of up to 650 semiconductor wafers) compared to a conventional grooved pad of similar construction, but with WL/WG equal to about 7.
In one embodiment, a polishing pad of the present invention comprises a surface defining a plurality of grooves, preferably concentric and substantially circular grooves, with landing surfaces separating the grooves. The landing surfaces together define a substantially coplanar polishing surface. Each groove has a depth of at least about 10 mil and a width, WG, with any two adjacent grooves being separated by a landing surface having a width, WL, wherein the quotient WL/WG, is less than or equal to 3. Preferably, each of the plurality grooves has substantially the same depth, and/or substantially the same WG. Each of the landing surfaces preferably has substantially the same WL, as well. The width of each groove preferably is substantially uniform throughout the majority of the groove depth, although the bottom of the groove may be rounded, resulting in a decreasing width near the bottom of the groove.
In an alternative embodiment, a polishing pad of the present invention comprises a surface defining a spiral groove having a depth of at least about 10 mil with a spiral landing surface outlining the spiral groove. The spiral landing surface defines a substantially planar polishing surface. The groove has a width, WG, and the landing surface has a width, WL, wherein the quotient WL/WG is less than or equal to 3.
In each of the embodiments of the present invention, each groove in the surface of the polishing pad preferably has a depth of not more than about 50 mil. In some preferred embodiments, the depth of each groove is in the range of about 10 to about 50 mil, more preferably about 15 to about 40 mil.
If desired, the quotient WL/WG in any given embodiment of the polishing pad of the present invention can less than or equal to about 2, or less than or equal to about 1.
In certain preferred embodiments, WL for each landing surface is not more than about 80 mil. In other preferred embodiments, WL for each landing surface is in the range of about 30 to about 60 mil. WG for each groove preferably is not more than about 50 mil. In some preferred embodiments, WG for each groove is in the range of about 20 mil to about 40 mil.
Table 1 illustrates some specific examples of different grooving dimensions suitable for polishing pads of the present invention.
The polishing pads of the present invention are particularly suited for use in conjunction with a chemical-mechanical polishing apparatus. Typically, the CMP apparatus comprises a platen, which, when in use, is in motion and has a velocity that results from orbital, linear, and/or circular motion, a polishing pad in contact with the platen and moving relative to the platen when in motion, and a carrier that holds a substrate to be polished by contacting and moving relative to the surface of the polishing pad. The polishing of the substrate takes place by the substrate being placed in contact with the polishing pad of the invention and then moving the polishing pad relative to the substrate, so as to abrade at least a portion of the substrate to polish the substrate.
Suitable materials for forming at least a portion of a polishing pad of the invention polishing pads include, for example, polymers of varying density, hardness, thickness, compressibility, ability to rebound upon compression, and compression modulus. Non-limiting examples of such polymers include polyvinylchloride, polyvinyl fluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, coformed products thereof, and mixtures thereof. The surface of the polishing pad defining the plurality of grooves can comprise any such material. In a preferred embodiment, the surface defining the plurality of grooves or spiral groove comprises a thermoplastic polyurethane. If desired the pads of the present invention can be composed of a single layer of material or can include two or more layers of material, e.g., a base layer and a surface layer.
Desirably, the CMP pads of the invention can further comprise at least one light-or other radiation-transmitting window region for in situ inspecting and monitoring a polishing process by analyzing the light or other radiation reflected from a surface of a workpiece being polished with the pad. Many in situ polishing endpoint detection systems and techniques for inspecting and monitoring the polishing process by analyzing light or other radiation reflected from a surface of the workpiece are known in the art. Such methods are described, for example, in U.S. Pat. No. 5,196,353 to Sandhu et al., U.S. Pat. No. 5,433,651 to Lustig el al., U.S. Pat. No. 5,949,927 to Tang, and U.S. Pat. No. 5,964,643 to Birang et al. Desirably, the inspection or monitoring of the progress of the polishing process with respect to a workpiece being polished enables the determination of the polishing end-point, i.e., the determination of when to terminate the polishing process with respect to a particular workpiece.
The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.
This example illustrates the superior removal rate stability and removal uniformity stability obtainable in copper CMP utilizing a polishing pad of the present invention.
A polishing pad comprising a thermoplastic polyurethane surface layer including a series of concentric circular grooves each having a width, WG, of about 30 mil, separated by concentric landing surfaces having a width, WL, of 30 mil (pitch of 60 mil), with WL/WG equal to about 1. The polishing was repeatedly performed with the same pad on copper blanket wafers using the commercial polishing slurry C8800 (Cabot Microelectronics Corporation, Aurora, Ill.) on Mirra polisher under the following polishing conditions: down-force of 1 pounds-per-square inch (psi), platen speed of 93 revolutions-per-minute (rpm), carrier speed of 87 rpm, and a slurry feed rate of 100 milliliters-per-minute (mL/min). For comparison, copper blanket wafers were also polished under the same conditions with a similar polyurethane polishing pad having concentric annular grooves separated by concentric annular landing surfaces, but having WL of about 70 mil and WG of about 10 mil (pitch of about 80 mil), with WL/WG of about 7.
The observed removal uniformity stability percentage, defined as WIWNU or with-in-wafer non-uniformity (i.e., relative standard deviation of Cu removal across 49 point diameter scan of entire wafer with 5 mm edge exclusion), obtained with each pad is graphed in
This example illustrates the effect of the grooving configuration on pad wear rate.
Three polishing pads of the invention comprising a thermoplastic polyurethane surface layer including a series of concentric circular grooves were used for relative pad wear test. The test was performed on an IPEC polisher with 7 ft-lb conditioning down force, 105 rpm platen speed, and 100 rpm conditioner rotational speed. Conditioner was from 3M Co (Model A188). D.I. water was used and the test last for 40 minutes. Wear rate was calculated using data from minute 10 to minute 40, and normalized to mil-per-hour by times 2. The pads had the following dimensions: Pad 60/20−WG=20 mil, WL=40 mil, pitch=60 mil, WL/WG=2; Pad 60/30−WG=30 mil, WL=30 mil, pitch=60 mil, WL/WG=1; and Pad 40/20−WG=20 mil, WL=20 mil, pitch=40 mil, WL/WG=1. For comparison, a similar polyurethane polishing pad having concentric annular grooves separated by concentric annular landing surfaces, but having WL of about 70 mil and WG of about 10 mil (pitch of about 80 mil), with WL/WG of about 7 (Pad 80/10) was tested.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This application claims the benefit of U.S. Provisional Application for Patent Ser. No. 61/271,068, filed on Jul. 16, 2009, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61271068 | Jul 2009 | US |
