US20240253176A1

US20240253176A1 - Polishing pad with endpoint window

Info

Publication number: US20240253176A1
Application number: US18/404,443
Authority: US
Inventors: Yu-Chung Su; Hyunjin Kim
Original assignee: Rohm and Haas Electronic Materials CMP Holdings Inc
Current assignee: Rohm and Haas Electronic Materials CMP Holdings Inc
Priority date: 2023-01-31
Filing date: 2024-01-04
Publication date: 2024-08-01
Also published as: JP2024109098A; KR20240120691A

Abstract

A polishing pad for chemical mechanical polishing comprising a porous polishing layer having a top polishing surface, a sub-pad located opposite from the top polishing surface, the sub-pad having a bottom sub-pad surface, and a window for transmitting a signal wave through the polishing pad to a substrate to be polished and back through the polishing pad for endpoint detection, the window having a top window surface, a bottom window surface, and side edges, wherein the top window surface is recessed from the top polishing surface, the bottom window surface is substantially coplanar with the bottom sub-pad surface, the window extending from the bottom sub-pad surface to the top window surface and the side edges are in contact with the polishing material and the sub-pad material and wherein the window is non-porous.

Description

FIELD OF THE INVENTION

The field of the invention is polishing pads used in chemical mechanical polishing.

BACKGROUND OF THE INVENTION

Chemical Mechanical Planarization (CMP) is a variation of a polishing process that is widely used to flatten, or planarize, the layers of construction of an integrated circuit or similar structure. Particularly, CMP is frequently used to produce planar uniform layers of a defined thickness in the manufacture build three-dimensional circuit structures by an additive stacking and planarizing process. CMP processes remove excess deposited material on the substrate (e.g., wafer) surface to produce an extremely flat layer of a uniform thickness, with uniformity extending across the entire substrate (e.g., wafer) area. When the uniform thickness is across the entire wafer, it is known as global uniformity.
CMP utilizes a liquid, often called slurry, which can contain nano-sized particles. The slurry is fed onto the surface of a rotating multilayer polymer pad (sometimes referred to as polishing sheet), the pad being mounted on a rotating platen. The polishing pad includes a polishing layer and can include a sub-pad. Substrates (e.g., wafers) are mounted into a separate fixture, or carrier, which has a separate means of rotation, and pressed against the surface of the pad under a controlled load. This can lead to a high rate of relative motion between the substrate (e.g., wafer) and the polishing pad and a resulting high rate of shear or abrasion at both the substrate and the pad surface. The shear and the slurry particles trapped at the pad/substrate junction abrade the substrate (e.g., wafer) surface, leading to removal of material from the substrate surface. Control of removal rate and the uniformity of removal are important. Also, it is useful to use metrology to determine when the polishing has met its desired goal (e.g., film thickness, intended reveal of an underlying structure, etc.). This is referred to as endpoint detection.
Various types of film thickness metrology, together with real time control software, can be used to achieve the device design goals, such as endpoint detection. Endpoint detection processes periodic signals, such as a collimated light wave, non-collimated light wave or an acoustic signal wave to avoid wafer yield issues from both under-polishing and over-polishing. For example, one approach for endpoint detection is an optical endpoint detection system that uses transmittance of desired wavelengths of light through the polishing pad, the light reflects from the substrate being polished, and the reflected light signal then passes back to the interferometer. This requires that at least a portion of the polishing pad be sufficiently transparent to the light source used to yield an acceptable signal to noise ratio. The endpoint detection metrology equipment can be located within the polishing equipment or the body of the platen that holds the pad.
For certain pad structures where optical detection is used, the pad material itself can be transparent to the desired optical wavelength and or have a design to allow effective transmittance of the signal waves. Alternatively, the pad can include alternate structures to facilitate transmittance of the waves. For example, a transparent polymer can be provided and opaque material molded around that to produce a transparent window. See e.g., U.S. Pat. No. 5,605,760. A third approach is to form a pad with an aperture into which a transparent window material is inserted and held in place with an adhesive. See, e.g., U.S. Pat. No. 5,893,796. Various versions of these pads with windows have been proposed. See e.g., U.S. Pat. Nos. 7,621,798, 8,475,228, U.S. 10,569,383, U.S. 2021/0402556, U.S. Pat. Nos. 9,475,168, 6,045,439, 6,716,085, and 8,475,228.
When a window is used in a chemical mechanical polishing pad to assist in end-point detection, the use of two distinct materials (the window material and the polishing layer material) can lead to problems during use. These problems can include one or more of scratching or defects of the substrate being polished, limited usable lifetime of the pad due to differences in rate of wear on the window as compared to the polishing layer, or adhesion issues between the transparent window material and the polishing pad material. Thus, a need remains for an improved polishing pad with window region for use in end-point detection.

SUMMARY OF THE INVENTION

Disclosed herein is a polishing pad for chemical mechanical polishing comprising a porous polishing layer having a top polishing surface, a sub-pad located opposite from the top polishing surface, the sub-pad having a bottom sub-pad surface, and a window for transmitting a signal wave through the polishing pad to a substrate to be polished and back through the polishing pad for endpoint detection, the window having a top window surface, a bottom window surface, and side edges, wherein the top window surface is recessed from the top polishing surface, the bottom window surface is substantially coplanar with the bottom sub-pad surface, the window extending from the bottom sub-pad surface to the top window surface and the side edges are in contact with the polishing material and the sub-pad material and wherein the window is non-porous.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike.

FIG. 1 is a cross-sectional view of one example of polishing pad as disclosed herein.

FIG. 2 is a cross-sectional view of one example of polishing pad as disclosed herein.

FIG. 3 is a top-down view of the upper surface of an example of the inventive pad wherein the window is rectangular in shape.

FIG. 4 is a top-down view of the upper surface of an example of the inventive pad wherein the window is oval in shape.

FIG. 5 is a cross-sectional view of one example of polishing pad as disclosed herein.

FIG. 6 is a cross-sectional view of one example of polishing pad as disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is a polishing pad useful in chemical mechanical polishing that has a design that reduces the risk of defects to the substrate caused by using different materials for the polishing material and the window while also reducing adhesion issues between the window and the polishing material. Particularly, the polishing pad comprises a polishing layer and a window. The polishing layer has a top polishing surface and a thickness. The polishing layer comprises a polishing material. The top surface of the window is recessed from the top polishing surface. The window can be a monolithic shape. The window material is transmissive of a signal wave. The signal wave can be, for example, light wave(s) (e.g., columnated light or non-columnated light) or acoustic wave(s). By having a window that is recessed from a top polishing surface of the pad, the recess can prevent direct pressure transmission between the window and the substrate. the recessed window can extend the useable lifetime of the polishing pad and reduce defects created by the different properties of the window material and the polishing material as compared to windows that extend to the top polishing surface.
Particularly, many prior polishing pads with windows or plugs require that at least a portion of the window (or plug) be coplanar with the top polishing surface to ensure good transmittance of the waves through the window and to the surface of the substrate being polished. However, since the window materials are of different composition from the polishing material, different mechanical properties local differences in contact pressure and texture during use are observed that can cause uneven polishing rates and increased wafer-scale non-uniformity. Furthermore, since polishing pads are generally conditioned with a bonded diamond abrasive during use to maintain a constant polishing rate, differences in the conditioning wear rate between the polishing material and the window can lead to a protrusion of the window area during continued use. The development of this protrusion has been widely observed to lead to higher levels of scratching defects and often leads to the pad being replaced, with consequent increase in manufacturing cost.to scratching and defects on the substrate being polished. Differential thinning of the window during use can also disturb the wave signal. Differences in coefficients of thermal expansion between the polishing material and the window material can lead to additional stresses with sufficient force to result in deformation, such as the formation of a window protrusion.
Having a top window surface recessed below the top polishing avoids protrusion of the window material above the top polishing surface that can lead to defects or scratching. That the window is recessed window avoids or prevents direct pressure transmission between the window between the substrate (e.g., silicon wafer). Furthermore, having a window that has a thickness less than the total thickness of the pad can facilitate stress relief in the pad. The stress relief can be further enhanced by including a peripheral portion of polishing material around the window that peripheral portion is also recessed below the top polishing surface. The recessed regions provide enhanced flexibility.
FIGS. 1, 2, 5, and 6 show cross-sections of examples of the polishing pad 100 as disclosed herein and having an overall thickness, a. The polishing pad has a polishing layer 120 with a top polishing surface 110 and a window region 103. The polishing layer 120 is porous and comprises a porous polishing material 101. FIGS. 1 and 2 show optional macrotexture 102. The macrotexture can be grooves, protrusions, or raised features to enhance polishing and management of slurry fluid and removed materials. The macrotexture can be, for example, in the form of grooves having a depth, b, and a width, g. The window region 103 includes a window (or plug) 104 having a top surface 104 a and a bottom surface 104 b. The transparent window 104 is non-porous to facilitate the transmission of signals for detecting polishing endpoints. The top surface 104 a of the window 104 is recessed from the top polishing surface 110 by a distance, c. The window can be a monolithic shape (i.e., made from a single material with no internal interfaces). Referring to FIGS. 1, 2 and 5 , the transparent window 104 extends from top surface 104 a to the sub-pad bottom surface 106 b. This extension from top surface 105 a to sub-pad bottom surface 106 b results in increased contact that increases frictional forces holding the window in place during polishing. Typically, there are no chemical bonds between the transparent window 104 and the polishing layer 120. This lack of chemical bonds between the materials makes it critical that the transparent window extend the entire length from the top surface 104 a to the sub-pad bottom surface 106 b. Furthermore, transparent window 104 preferably has the same thickness measured from top surface 104 a to bottom surface 104 b as measured across the transparent window 104. This reduces signal variation and renders bottom surface 104 b of transparent window 104 coplanar with bottom surface 106 b of sub-pad 106. The polishing pad 100 includes a sub-pad 106 below the polishing layer 120. The bottom surface 104 b of the window 104 is coplanar or substantially coplanar with a bottom surface 106 b of the sub-pad 106. “Substantially coplanar” as used herein is meant that the surface of the window and the surface of the adjacent material (e.g., the bottom surface of the sub-pad or the top surface of the peripheral region as discussed below) are at a vertical distance from each other of less than 0.02, less than 0.01 or less than 0.005 mm.
As shown in FIG. 2 , the window region can include a peripheral portion 105 of the polishing material 101. The peripheral portion can have a top surface 105 a. The top surface 104 a of the window 104 and the top surface 105 a of the peripheral portion can both be recessed from the top polishing surface 110. For example, as shown in FIG. 2 , the top window surface 104 a and the top peripheral portion surface 105 a are both recessed from the top polishing surface 110 by a distance c. The peripheral portion can be formed of polishing material 101. The top surface 105 a of the peripheral portion can form a ledge having a dimension d. Advantageously, dimension “d” (peripheral portion or ledge width) is greater than or equal to dimension “c” (window recess depth) to reduce stresses that originate from compressing porous polishing layer 120 adjacent non-porous window 104. Most advantageously, dimension “d” (peripheral portion or ledge width) is greater than dimension “c” (window recess depth) to reduce stresses that originate from compressing porous polishing layer 120 adjacent non-porous window 104. Because window 104 is non-porous, it has less compressibility over scales of at least 1 mm²as compressed with a flat circular surface with a thickness equal to the thickness of the polishing layer 120. A portion of the top surface 104 a of the window and the top surface 105 a or curved 109 can be coplanar. Particularly, at least where the window meets the polishing material the top window surface 104 a and the top peripheral portion surface 105 a are coplanar. FIG. 2 shows the peripheral portion being formed with right angles. However, the transition from vertical to horizontal could alternatively be a curved transition.
As shown in FIG. 5 , the polishing pad 100 can include an encapsulating layer 108 in contact with the bottom surface 104 b or the window 104 and the bottom surface 106 b of the sub-pad 106. The encapsulating layer 108 can facilitate adhesion of the pad 100 to the platen. The encapsulating layer 108 can facilitate insertion of the window 104 into the pad with proper alignment. The encapsulating layer 108 can provide an even surface on the bottom of the pad. The encapsulating layer 108 prevent any adhesive between the side edges of the window and the polishing layer or sub-pad from leaking out. The encapsulating layer 108 can assist in holding the window 104 in place. The encapsulating layer 108 can prevent any leakage of slurry to the bottom side of the polishing pad 100. In another alternative, an encapsulating layer 108 could also be added to the polishing pad 100 as shown in FIG. 2 .
As shown in FIG. 6 , the window 104 can include a top window portion 104 t that defines the top surface 104 a and a bottom encapsulating layer 104 el that defines bottom surface 104 b of the window 104. The bottom encapsulating layer 104 el can facilitate adhesion of the pad 100 to the platen. The bottom encapsulating layer 104 el can facilitate insertion of the window 104 into the pad with proper alignment. The bottom encapsulating layer 104 el can provide an even surface on the bottom of the pad. The bottom encapsulating layer 104 el prevent any adhesive between the side edges of the window and the polishing layer or sub-pad from leaking out to the bottom side of the pad 100. The bottom encapsulating layer 104 el can assist in holding the window 104 in place. The bottom encapsulating layer 104 el can prevent any leakage of slurry to the bottom side of the polishing pad 100. In another alternative, a bottom encapsulating layer 104 el could also be added to the polishing pad 100 as shown in FIG. 1 .
The encapsulating layer 108 or bottom encapsulating layer 104 el or a portion of the encapsulating layer 108 or bottom encapsulating layer 104 el can be transparent to light if light is used for end-point detection. The encapsulating layer 108 or bottom encapsulating layer 104 el can be opaque, such as when acoustic signal waves are used for end-point detection.
The encapsulating layer can comprise a polymer film, such as for example a polyester film.
The macrotexture 102 can be isolated from the window region 103. Alternatively, the macrotexture can intersect with the recessed peripheral portion 105 of the window region 103.
FIGS. 3 and 4 show top views of two examples of the polishing pad 100 as disclosed herein where 110 is the top polishing layer, 102 are optional grooves, 104 is the window and 105 is the optional peripheral portion of the window region. In FIG. 3 the window 104 is substantially oval while in FIG. 4 the window 104 and peripheral portion 105 are substantially rectangular. Other shapes such as squares, circles, other polygons (not shown) could be used as well. Furthermore, the top polishing layer can optionally contain multiple windows (not shown), such as three or more equidistantly spaced windows. Multiple equidistant windows decrease the time between signal measurements. This decreasing the time between signal measurements can increase the accuracy of polishing endpoint detection.
The window is preferably a monolithic structure made of a single material to avoid interfaces that can interfere with or inhibit the transmission of the signal wave. The window material is a non-flowable material at room temperature and at temperature and conditions of use. The window material, for example, can be a solid or a gel. The window material can be homogeneous in that it is free of internal interfaces. For example, the window can be non-porous. The window can have a cross-section defined by the side edges that is constant or substantially same at each distance through the thickness of the window. In other words the cross-section does not expand or contract throughout the thickness of the window.
The recess of the window region can extend pad lifetime. The depth of the window region recess (e.g., 103) can be adjusted to accommodate the characteristics of the materials used in the pad (e.g., the polishing material, the window material) to provide desired flexibility without undue, harmful deformation during use. For example, the recess depth, c, can be greater than 0.1, greater than 0.2, or at least 0.3 millimeters (mm) up to 1.1, up to 1, up to 0.8, up to 0.6 mm, or up to 0.4 mm.
Having a thinner polishing material in the peripheral portion of the polishing layer relative to overall polishing layer thickness can enable flexibility during use. Similarly, the width of the peripheral portion can be adjusted to provide the desired mechanical response for the pad materials and design. The width, d, of the peripheral region can be, for example, at least 0.05, at least 0.1, at least 0.2, or at least 0.3 millimeters (mm) up to 1.1, up to 1, up to 0.8, up to 0.6 mm, or up to 0.4 mm.
The major dimension, e, of the window material in a direction parallel to the top polishing surface can be dimensions that are commonly used for windows in CMP pads. Further example, the dimensions of the window in a direction parallel to the top polishing surface about 8 to 18 mm. The window can have dimensions in the sub-pad region (e.g., dimension f) that are the same or substantially the same as the dimension (e.g., dimension e) in the polishing layer region. For example, a cross section of the window in a horizontal direction can be constant throughout the thickness of the window.
Having the window extend substantially to the bottom of the sub-pad avoids additional interfaces that can disrupt the transmission of a signal wave through the pad toward the substrate to be polished. For example, a window with a bottom surface recessed above the bottom of the sub-pad can create a reflective surface that can create noise and interference with the wave transmission. Note that, since during use of the pad, a slurry is present in the recess 103, the disruption of the wave signals in that region is reduced. Particularly, with an optical system a semi-transparent slurry can be used.
The overall thickness of the polishing pad (e.g., polishing layer plus sub-pad) is preferably no greater than 4 mm. For example, the overall thickness of the polishing pad can be from 1 up to 4 mm, from 1.5 up to 4 mm, from 1.7 up to 3.5 mm, or from 2 up to 3 mm. The polishing layer can have a thickness of from 0.5 up to 3, from 0.7 up to 2.5, from 1.2 up to 2.2, or from 1 to 2 mm. The sub-pad can have a thickness of from 0.5 up to 3, from 0.7 up to 2.5, from 1 to 2 mm. The window by virtue of the recess at the top side and being substantially coplanar with the bottom of the sub-pad has a thickness that is less than the overall thickness of the polishing pad. The thickness of the window can be from 0.6 up to 3.9, from 0.7 up to 3.8, from 0.8 up to 3.7, from 0.9 up to 3.5, from 1 up to 3, or from 1.5 up to 2.5 mm.
As noted the polishing layer can include optional macrotexture (e.g., grooves). Since the macrotexture can impact effective modulus, variable adjustment of the window area recess depth, c, peripheral portion width, d, relative to macrotexture or groove depth b and overall polishing layer thickness, a, can be done to provide the desired flexibility that is a feature of the pad design disclosed herein. For example, window recess depth, c, can be from 20 to 50, or 30 to 40% of overall pad thickness, a. As another example, window recess depth, c, can be from 50 to 90, or 60 to 80% of macrotexture depth b. As another example, the peripheral portion width, d, can be 40 to 60% of the macrotexture (e.g., groove) width, g. Due to the manufacturing process for the disclosed pad as discussed below, these ratios can be easily adjusted during manufacture.
An additional advantage of the inventive design is that it can provides a simple means for determining the end of life of the pad. Since the window recess depth can be proportionately lower than the groove depth, pad conditioning wear over time is expected to produce a change in endpoint signal as the window recess depth approaches zero. Since this change can occur before the macrotexture is fully removed, the pad can be taken out of service before there is significant change in polishing performance, such that non-uniformity and defects may be prevented.
The polishing material 101 of the polishing layer 120 can comprise a polymer. The polishing material 101 can be opaque at the thickness of the polishing layer 120. Pores can be provided, for example, by addition of hollow flexible polymer elements (e.g., hollow microspheres), blowing agents, frothing or supercritical Carbon Dioxide. Examples of polymeric materials for the polishing layer include polyurethanes, polycarbonates, polysulfones, nylons, polyethers, polyesters, polystyrenes, acrylic polymers, polymethyl methacrylates, polyvinylchlorides, polyvinyl fluorides, polyethylenes, polypropylenes, polybutadienes, polyethylene imines, polyether sulfones, polyamides, polyether imides, polyketones, epoxy resins, silicones, copolymers thereof (such as, polyether-polyester copolymers), and combinations or blends thereof. The polishing layer can comprise a polymer that is a polyurethane formed by reaction of one or more polyfunctional isocyanates and one or more polyols. For example, a polyisocyanate terminated urethane prepolymer can be used. The polyfunctional isocyanate used in the formation of the polishing layer of the chemical mechanical polishing pad of the present invention can be selected from the group consisting of an aliphatic polyfunctional isocyanate, an aromatic polyfunctional isocyanate and a mixture thereof. For example, the polyfunctional isocyanate used in the formation of the polishing layer of the chemical mechanical polishing pad of the present invention can be a diisocyanate selected from the group consisting of 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4′-diphenylmethane diisocyanate; naphthalene-1,5-diisocyanate; tolidine diisocyanate; para-phenylene diisocyanate; xylylene diisocyanate; isophorone diisocyanate; hexamethylene diisocyanate; 4,4′-dicyclohexylmethane diisocyanate; cyclohexanediisocyanate; and, mixtures thereof. The polyfunctional isocyanate can be an isocyanate terminated urethane prepolymer formed by the reaction of a diisocyanate with a prepolymer polyol. The isocyanate-terminated urethane prepolymer can have 2 to 12 wt %, 2 to 10 wt %, 4-8 wt % or 5 to 7 wt % unreacted isocyanate (NCO) groups. The prepolymer polyol used to form the polyfunctional isocyanate terminated urethane prepolymer can be selected from the group consisting of diols, polyols, polyol diols, copolymers thereof and mixtures thereof. For example, the prepolymer polyol can be selected from the group consisting of polyether polyols (e.g., poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and mixtures thereof); polycarbonate polyols; polyester polyols; polycaprolactone polyols; mixtures thereof; and, mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butanediol; 1,3-butanediol; 2-methyl-1,3-propanediol; 1,4-butanediol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; and, tripropylene glycol. For example, the prepolymer polyol can be selected from the group consisting of polytetramethylene ether glycol (PTMEG); ester based polyols (such as ethylene adipates, butylene adipates); polypropylene ether glycols (PPG); polycaprolactone polyols; copolymers thereof; and mixtures thereof. For example, the prepolymer polyol can be selected from the group consisting of PTMEG and PPG. When the prepolymer polyol is PTMEG, the isocyanate terminated urethane prepolymer can have an unreacted isocyanate (NCO) concentration of 2 to 10 wt % (more preferably of 4 to 8 wt %; most preferably 6 to 7 wt %). Examples of commercially available PTMEG based isocyanate terminated urethane prepolymers include Imuthane® prepolymers (available from COIM USA, Inc., such as, PET-80A, PET-85A, PET-90A, PET-93A, PET-95A, PET-60D, PET-70D, PET-75D); Adiprene® prepolymers (available from Chemtura, such as, LF 800A, LF 900A, LF 910A, LF 930A, LF 931A, LF 939A, LF 950A, LF 952A, LF 600D, LF 601D, LF 650D, LF 667, LF 700D, LF750D, LF751D, LF752D, LF753D and L325); Andur® prepolymers (available from Anderson Development Company, such as, 70APLF, 80APLF, 85APLF, 90APLF, 95APLF, 60DPLF, 70APLF, 75APLF). When the prepolymer polyol is PPG, the isocyanate terminated urethane prepolymer can have an unreacted isocyanate (NCO) concentration of 3 to 9 wt % (more preferably 4 to 8 wt %, most preferably 5 to 6 wt %). Examples of commercially available PPG based isocyanate terminated urethane prepolymers include Imuthane® prepolymers (available from COIM USA, Inc., such as, PPT-80A, PPT-90A, PPT-95A, PPT-65D, PPT-75D); Adiprene® prepolymers (available from Chemtura, such as, LFG 963A, LFG 964A, LFG 740D); and Andur® prepolymers (available from Anderson Development Company, such as, 8000APLF, 9500APLF, 6500DPLF, 7501DPLF). The isocyanate terminated urethane prepolymer can be a low free isocyanate terminated urethane prepolymer having less than 0.1 wt % free toluene diisocyanate (TDI) monomer content. Non-TDI based isocyanate terminated urethane prepolymers can also be used. For example, isocyanate terminated urethane prepolymers include those formed by the reaction of 4,4′-diphenylmethane diisocyanate (MDI) and polyols such as polytetramethylene glycol (PTMEG) with optional diols such as 1,4-butanediol (BDO) are acceptable. When such isocyanate terminated urethane prepolymers are used, the unreacted isocyanate (NCO) concentration is preferably 4 to 10 wt % (more preferably 4 to 10 wt %, most preferably 5 to 10 wt %). Examples of commercially available isocyanate terminated urethane prepolymers in this category include Imuthane® prepolymers (available from COIM USA, Inc. such as 27-85A, 27-90A, 27-95A); Andur® prepolymers (available from Anderson Development Company, such as, IE75AP, IE80AP, IE 85AP, IE90AP, IE95AP, IE98AP); and Vibrathane® prepolymers (available from Chemtura, such as, B625, B635, B821).
The window 104 can comprise, for example, a polymer or polymer blends. For optical detection systems the window material should have sufficient transmission at the wavelengths of light used by the optical metrology. It can be helpful if that window material has a hardness or thermal expansion coefficient similar to that of the material used in the polishing layer. Examples of window materials include polyurethanes, acrylic polymers, cyclic olefin copolymers (e.g., TOPAS 8007, etc.). Use of polyurethane materials can be helpful in pads where the polishing layer and sub-pad layer(s) are also polyurethanes.
The window is advantageously made from an aliphatic polyisocyanate-containing material (“prepolymer”). The prepolymer is a reaction product of an aliphatic polyisocyanate (e.g., diisocyanate) and a hydroxyl-containing material. The prepolymer is then cured with a curing agent. Preferred aliphatic polyisocyanates include, but are not limited to, methlene bis 4,4′ cyclohexylisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, tetramethylene-1, 4-diisocyanate, 1,6-hexamethylene-diisocyanate, dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, methyl cyclohexylene diisocyanate, triisocyanate of hexamethylene diisocyanate, triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate, uretdione of hexamethylene diisocyanate, ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and mixtures thereof. The preferred aliphatic polyisocyanate has less than 10 wt. % unreacted isocyanate groups.
Advantageously, the curing agent is a polydiamine. Preferred polydiamines include, but are not limited to, diethyl toluene diamine (“DETDA”), 3,5-dimethylthio-2,4-toluenediamine and isomers thereof, 3,5-diethyltoluene-2,4-diamine and isomers thereof, such as 3,5-diethyltoluene-2,6-diamine, 4,4′-bis-(sec-butylamino)-diphenylmethane, 1, 4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline), 4, 4′-methylene-bis-(3-chloro-2,6-diethylaniline) (“MCDEA”), polytetramethyleneoxide-di-p-aminobenzoate, N,N′-dialkyldiamino diphenyl methane, p,p′-methylene dianiline (“MDA”), m-phenylenediamine (“MPDA”), methylene-bis 2-chloroaniline (“MBOCA”), 4,4′-methylene-bis-(2-chloroaniline) (“MOCA”), 4,4′-methylene-bis-(2,6-diethylaniline) (“MDEA”), 4,4′-methylene-bis-(2,3-dichloroaniline) (“MDCA”), 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane, 2,2′,3,3′-tetrachloro diamino diphenylmethane, trimethylene glycol di-p-aminobenzoate, and mixtures thereof. Preferably, the curing agent of the present invention includes 3, 5-dimethylthio-2,4-toluenediamine and isomers thereof. Suitable polyamine curatives include both primary and secondary amines.
In addition, other curatives such as, a diol, triol, tetraol, or hydroxy-terminated curative may be added to the aforementioned polyurethane composition. Suitable diol, triol, and tetraol groups include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, lower molecular weight polytetramethylene ether glycol, 1,3-bis(2-hydroxyethoxy) benzene, 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene, 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, resorcinol-di-(beta-hydroxyethyl) ether, hydroquinone-di-(beta-hydroxyethyl) ether, and mixtures thereof. Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy) benzene, 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene, 1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene, 1,4-butanediol, and mixtures thereof. Both the hydroxy-terminated and amine curatives can include one or more saturated, unsaturated, aromatic, and cyclic groups. Additionally, the hydroxy-terminated and amine curatives can include one or more halogen groups. The polyurethane composition can be formed with a blend or mixture of curing agents. If desired, however, the polyurethane composition may be formed with a single curing agent.
The sub-pad 106 can comprise a polymeric material. The sub-pad material can be more compliant than the polishing material 101 of the polishing layer 102. The sub-pad 106 can comprise a porous layer. Examples of polymeric materials for the sub-pad layer(s) include polyurethanes, polycarbonates, polysulfones, nylons, epoxy resins, polyethers, polyesters, polystyrenes, acrylic polymers, polymethyl methacrylates, polyvinylchlorides, polyvinyl fluorides, polyethylenes, polypropylenes, polybutadienes, polyethylene imines, polyether sulfones, polyamides, polyether imides, polyketones, silicones, copolymers thereof (such as, polyether-polyester copolymers), and combinations or blends thereof.
The polishing pad as disclosed here can be made by providing a plug of window material in a mold with a recess in the mold to hold a bottom portion of the window material and molding the polishing layer around the portion of the plug protruding into the mold cavity. This forms a polishing layer with an embedded plug where a portion of the plug protrudes beyond the polishing layer. To form the sub-pad portion of the pad, the sub-pad can be molded in a second molding step in a separate mold around the bottom portion of the plug. Alternatively, these steps could be reversed with the sub-pad being molded first around a portion of the window material plug followed by molding of the polishing layer. According to another approach, a subpad material can be pre-formed and adhered to the bottom of the polishing layer with an aperture formed to receive the bottom portion of the window. With both approaches, the recess of the window region 103 is cut into the window 104 and, optionally, if a recessed peripheral portion 105 is desired, into the polishing layer 120 in the area around the plug of window material. The polishing layer 120 can also be cut to provide the macrotexture 102. Cutting to form the recess can be done, for example, by milling. A commercially available example of a mill that could be used can be by a CNC mill.
A method of using the polishing pad as disclosed herein comprises providing a substrate to be polished, providing the polishing pad as disclosed herein, optionally providing a slurry on the polishing pad, contacting the polishing pad to the substrate and moving the substrate and the polishing pad relative to each other (e.g., in a rotational movement), and transmitting a signal wave through the window and detecting the signal wave reflected from the substrate back through the window to determine when polishing is complete. When an optical detection is used, use of a semi-transparent slurry is preferred.
This disclosure further encompasses the following aspects.

- Aspect 1: A polishing pad for chemical mechanical polishing comprising a porous polishing layer having a top polishing surface, a sub-pad located opposite from the top polishing surface, the sub-pad having a bottom sub-pad surface, and a window for transmitting a signal wave through the polishing pad to a substrate to be polished and back through the polishing pad for endpoint detection, the window having a top window surface, a bottom window surface, and side edges, wherein the top window surface is recessed from the top polishing surface, the bottom window surface is substantially coplanar with the bottom sub-pad surface, the window extending from the bottom sub-pad surface to the top window surface and the side edges are in contact with the polishing material and the sub-pad material and wherein the window is non-porous.
- Aspect 2: The polishing pad of Aspect 1 wherein the window comprises a top window portion defining the top window surface and an encapsulating layer portion defining the bottom window surface.
- Aspect 3: The polishing pad of Aspect 1 or 2 wherein the window is opaque.
- Aspect 4: The polishing pad of Aspect 2 wherein the window comprises, a top window portion defining the top window surface; and an encapsulating layer portion defining the bottom window surface.
- Aspect 5: The polishing pad of Aspect 1 further comprising an encapsulating layer in contact with the bottom window surface and the bottom sub-pad surface.
- Aspect 6: The polishing pad of Aspect 5 wherein the window is transparent to light and the encapsulating layer comprises a transparent portion in contact with the window.
- Aspect 7: The polishing pad of Aspect 5 wherein the encapsulating layer is opaque.
- Aspect 8: The polishing pad of any one of the previous Aspects wherein the top polishing surface comprises grooves.
- Aspect 9: The polishing pad of any of the previous Aspects wherein a portion of the polishing layer in contact with the side edges of the window forms a peripheral region that is recessed from the top polishing surface.
- Aspect 10: The polishing pad of Aspect 9 wherein the recessed peripheral portion of polishing layer has a top surface that is recessed 0.1 to 1.1 mm from the top surface of the top polishing surface and the top recessed surface has a width of 0.1 to 1.1 mm.
- Aspect 11: The polishing pad of Aspect 9 or 10 wherein the top polishing surface comprises grooves and the grooves intersect with a recessed peripheral portion of the window region.
- Aspect 12: The polishing pad of any one of the Aspects 9-11 wherein a top surface of the peripheral portion adjacent to the window is coplanar with the top surface of the window.
- Aspect 13: The polishing pad of any one of the previous Aspects wherein the top surface of the window is recessed below the polishing surface to a depth of 0.1 to 1.1 mm.
- Aspect 14: The polishing pad of any one of the previous Aspects wherein the window is substantially transparent to light.
- Aspect 15: The polishing pad of any one of Aspects 1 and 4-14 wherein the window is monolithic.
- Aspect 16: The polishing pad of any one of the previous Aspects wherein the window has a cross-section of constant area through the thickness of the window.
- Aspect 17: The polishing pad of any one of the previous Aspects wherein the window comprises a window material that is non-flowable.
- Aspect 18: The polishing pad of Aspect 11 wherein the window material is incompressible at the conditions of storage and use.
- Aspect 19: The polishing pad of Aspect 11 wherein the window material comprises a solid or a gel.
- Aspect 20: The polishing of any one of the previous Aspects wherein the window is a plug.
- Aspect 21: The polishing pad of any one of the previous Aspects wherein the recess prevents direct pressure transmission between the window and a substrate being polished.
- Aspect 22: The polishing pad of any one of the previous Aspects wherein the polishing layer comprises a polishing material.
- Aspect 23: The polishing pad of any one of the previous Aspects wherein the sub-pad comprises a sub-pad material.
- Aspect 24: The polishing pad of any one of the previous Aspects wherein the window comprises a window material.
- Aspect 25: The polishing pad of Aspect a wherein there are no chemical bonds between the window and the polishing layer.
- Aspect 26: A method of polishing comprising providing a substrate to be polished providing the polishing pad as in any one of the previous Aspects, providing a between the polishing pad and the substrate, moving the substrate relative to the polishing pad, transmitting a signal wave through the window material and slurry and detecting the signal wave reflected from the substrate back through the window and slurry to determine when polishing is complete.
- Aspect 27: The method of Aspect 26 wherein the signal wave comprises a columnated light wave, a non-columnated light wave, or an acoustic wave.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). Moreover, stated upper and lower limits can be combined to form ranges (e.g., “at least 1 or at least 2 weight percent” and “up to 10 or 5 weight percent” can be combined as the ranges “1 to 10 weight percent”, or “1 to 5 weight percent” or “2 to 10 weight percent” or “2 to 5 weight percent”).
The disclosure may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The disclosure may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function or objectives of the present disclosure.
All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.
Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

Claims

What is claimed is:

1. A polishing pad for chemical mechanical polishing comprising

a porous polishing layer having a top polishing surface,

a sub-pad located opposite from the top polishing surface, the sub-pad having a bottom sub-pad surface, and

a window for transmitting a signal wave through the polishing pad to a substrate to be polished and back through the polishing pad for endpoint detection, the window having a top window surface, a bottom window surface, and side edges, wherein the top window surface is recessed from the top polishing surface, the bottom window surface is substantially coplanar with the bottom sub-pad surface, the window extending from the bottom sub-pad surface to the top window surface and the side edges are in contact with the polishing material and the sub-pad material and wherein the window is non-porous.

2. The polishing pad of claim 1 wherein the window comprises, a top window portion defining the top window surface; and an encapsulating layer portion defining the bottom window surface.

3. The polishing pad of claim 1 further comprising an encapsulating layer in contact with the bottom window surface and the bottom sub-pad surface.

4. The polishing pad of claim 1 wherein a portion of the polishing layer in contact with the side edges of the window forms a peripheral region that is recessed from the top polishing surface.

5. The polishing pad of claim 4 wherein a top surface of the peripheral portion adjacent to the window is coplanar with the top surface of the window.

6. The polishing pad of claim 1 wherein the top polishing surface comprises grooves.

7. The polishing pad of claim 1 wherein the top surface of the window is recessed below the polishing surface to a depth of 0.1 to 1.1 mm.

8. The polishing pad of claim 4 wherein the recessed peripheral portion of polishing layer ha a top surface that is recessed 0.1 to 1.1 mm from the top surface of the top polishing surface and the top recessed surface has a width of 0.1 to 1.1 mm.

9. The polishing pad of claim 1 wherein there are no chemical bonds between the window and the polishing layer.

10. A method of polishing comprising

providing a substrate to be polished

providing the polishing pad as in claim 1

providing a slurry on the polishing pad,

moving the substrate relative to the polishing pad,

transmitting a signal wave through the window material and slurry and detecting the signal wave reflected from the substrate back through the window and slurry to determine when polishing is complete.