Patent Application
20240253175
The field of the invention is polishing pads used in chemical mechanical polishing.
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 for achieving global uniformity.
Various types of film thickness metrology, together with real time control software, can be used to achieve the device design goals. One approach for endpoint detection 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, which processes the reflectance signal to determine if the polishing has reached its desired goal (e.g., film thickness, intended reveal of an underlying structure). The metrology equipment can be located within the body of the platen that holds the pad. 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.
For certain pad structures the pad material itself can be transparent to the desired optical wavelength. Alternatively, a plug of 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, 10,569,383, U.S. 2021/0402556, U.S. Pat. No. 9,475,168.
The use of two distinct materials in the pad can lead to problems in use including 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 a transparent window.
Disclosed herein is a polishing pad for chemical mechanical polishing comprising a polishing layer having a top polishing surface, a bottom surface and a thickness, the polishing layer comprises a porous polishing material and a window region, wherein the window region comprises a transparent window that has an exposed top surface and an exposed bottom surface to enable light to transmit through the polishing pad in the window region, the exposed top surface of the transparent window is recessed from the top polishing surface, the transparent window extending from the recess region to the bottom surface of the polishing pad, the window region further comprises a peripheral portion of the polishing material in contact with side edges of the transparent window, the peripheral portion of polishing material has a top surface that is recessed from the top surface of the top polishing surface and wherein the transparent window is non-porous and wherein a portion of the top surface of the peripheral portion adjacent to the transparent window is coplanar with the top surface of the transparent window and wherein the exposed bottom surface of the transparent window is coplanar with the bottom surface of the polishing layer.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike.
Disclosed herein is a polishing pad useful in chemical mechanical polishing that has a design that minimizes the risk of defects to the substrate caused by the use of different materials for the polishing material and the transparent window while also minimizing adhesion issues between the transparent window and the polishing material. Particularly, the polishing pad comprises a polishing layer and a window region. The polishing layer has a top polishing surface and a thickness. The polishing layer comprises a polishing material. The window region is recessed from the top polishing surface. The window region comprises a transparent window that has an exposed top surface and an exposed bottom surface to enable light to transmit through the polishing pad in the window region. The window region further comprises a peripheral portion of the polishing material in contact with side edges of the transparent window where the peripheral portion of polishing material also has a top surface that is recessed from the top surface of the top polishing surface. The peripheral portion can be a ledge. By having a window region that is recessed from a top polishing surface of the pad and that comprises both the transparent window and a peripheral portion (or ledge) of polishing material the useable lifetime of the polishing pad can be increased and defects created by the different properties of the transparent window material and the polishing material are reduced.
Particularly, many prior polishing pads with transparent window require that at least a portion of the window be coplanar with the top polishing surface to ensure good transmittance of the light 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 dressed with a bonded diamond abrasive during use to maintain a constant polishing rate, differences in the dressing wear rate between the upper pad 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 optical signal. Differences in coefficients of thermal expansion between the polishing material and the window material can lead to additional stress and deformation.
Having a recessed window region with a top window surface recessed below the top polishing surface together with a peripheral portion of polishing material also recessed below the top polishing surface facilitates stress relief in the pad and also avoids protrusion of the window material above the top polishing surface that can lead to defects or scratching.
Transparent window 104 preferably has the same thickness measured from top surface 104a to bottom surface 104b as measured across the transparent window 104. This reduces light distortion and renders top surface 104a of transparent window 104 coplanar with top surface 105a of the peripheral region 105. In addition, it renders bottom surface 104a of transparent window 104 coplanar with bottom surface 105b of polishing layer 120. The top surface 104a of the window 104 and the top surface 105a of the peripheral portion are recessed from the top polishing surface 110 by a distance c. The peripheral portion can be formed of polishing material 101. The top surface 105a of the peripheral portion can form a ledge having a width dimension d. Advantageously, dimension “d” (peripheral portion or ledge width) is greater than or equal to dimension “a” (polishing layer thickness) minus dimension “c” (window recess depth) or window thickness 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 “a” (polishing layer thickness) minus dimension “c” (window recess depth) or window thickness 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 mm2 as compressed with a flat circular surface with a thickness equal to the thickness of the window 104.
The polishing pad 100 can include an optional sub-pad 106 below the polishing layer 120. The sub-pad 106 also includes an opening 107 having a dimension f to expose the bottom surface 104b of the window 104. In
In
In an additional example, as shown in
The thinness of the polishing layer in the peripheral portion of the polishing layer relative to overall polishing layer thickness can enable flexibility during use without negatively affecting the optical signal (e.g., signal to noise ratio remains acceptable) or pad lifetime. In fact 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. Similarly the width of the peripheral portion can be adjusted to provide the desired mechanical response for the pad materials and design. 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, or up to 0.6 mm. 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, or up to 0.6 mm. To further adjust effective flexibility of the pad the width f of the opening 107 can be adjusted to controllably alter flexibility in the window region without affecting operation of the endpoint system. By moving the sub pad 106 away from the interface of the window 104 with the polishing material 101, stress on the junction can be reduced, further improving window integrity.
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 thickness of the window can be less than overall thickness, a, of the polishing layer 120 to provide the recess in the window region 103. For example, a thickness of the window can be 0.3 to 3, 0.4 to 2.5, 0.5 to 2 mm, or 0.6 to 1.5 mm, provided it is not thicker than the overall pad thickness and preferably not thicker than the polishing layer.
The polishing layer can have a thickness, a, of 1 up to 4, up to 3, or up to 2.5 mm. The overall thickness of the polishing pad (e.g., polishing layer plus sub-pad) is preferably no greater than 4 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 or 20 to 50, or 30 to 40% of polishing layer 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, a, 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 a polymer or polymer blends desired so long as it has sufficient transmission at the wavelengths 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 co-polymers (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 100 as disclosed here can be made by providing a plug of window material in a mold and injection molding the polishing layer around the plug. According to one approach a thick slab of polishing layer with a thick plug is formed and then sliced into the desired thickness, a, of the polishing layer 120. The recess of the window region 103 is then cut into the polishing layer 120 in the area around the plug of window material. The polishing layer can also be cut to provide the macrotexture 102. Alternatively, single pads may be cast around a window material 104 in a mold having the depth, a, of the desired polishing layer. When casting around a window material, the polishing pad material penetrates the irregular or rough surface of the window to provide a secure bond that allows additional processing such as skiving a polymer cake into polishing pads. After removal from the mold, the recess is then cut into the polishing layer in the region of the window to a desired recess depth c to form the window region 103. In this latter approach the macrotexture 102 can be formed from a top surface of the mold or a flat top surface can again be cut to provide the macrotexture. 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 100 as disclosed herein comprises providing a substrate to be polished, providing the polishing pad 100 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 light through the transparent window 104 and detecting light reflected from the substrate back through the transparent window 104 to determine when polishing is complete. Preferably a semi-transparent slurry is used.
This disclosure further encompasses the following aspects.
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 “5wt. % 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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18162442 | Jan 2023 | US |
| Child | 18404415 | US |
