Multifunctional Endpoint Detection Window

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 of three-dimensional circuit structures through additive stacking and planarizing. CMP can 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, that 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 subpad. Substrates (e.g., wafers) are mounted into a separate fixture, or carrier, that 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 for 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 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. As another example, an opening through the entire pad can be provided. See, e.g., U.S. Pat. Nos. 8,961,266 and 7,497,763. 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 polishing pads with windows have been proposed. See e.g., U.S. Pat. Nos. 7,621,798, 7,081,044, 7,195,539, 8,475,228, 10,569,383, U.S. 2021/0402556, U.S. 2022/0226956, U.S. 2020/164483, U.S. 2015/232549, U.S. Pat. No. 9,126,304, U.S.2008/0207089, U.S. 2017/0120417, U.S.2016/263721, U.S. Pat. Nos. 7,398,714, 7,435,161, U.S. 2005/064802, U.S. Pat. Nos. 9,475,168, 6,045,439, 6,716,085, 8,475,228, 7,264,536, JP5142866, and CN113478382.

Transmittance of a signal wave through a boundary between a gap (e.g., air) and a surface of the window can lead to refraction or reflection of the signal wave that can create noise or reduce the signal thereby lessening the effectiveness of using the signal wave for endpoint detection. Thus, in another approach, optical fibers can be inserted into openings in the subpad. See e.g., US2010/184357.

Transmittance of other vibrational waves such as acoustic waves can include non-porous windows. See e.g., US2023/0009737 and US2023/0009519.

In addition, since a window is typically formed of a material distinct from the polishing layer, other problems can arise. Particularly, since the modulus and stiffness of the solid polymer window material typically is higher than that of the surrounding composite pad, differential compression during the polishing process leads to deformation of the vicinity of the window. Differences in the coefficient of thermal expansion (CTE) and thermal conductivity (K) between the polishing material and the window can further exacerbate problems. Since the upper surfaces of the pad and window are frictionally heated during CMP, differences in CTE and K produce an additional transient stress and deformation. This can cause the window area to protrude above the upper surface of the pad polishing area during use. The protrusion of the window can cause scratching of the substrate being polished. In addition, a gap in the peripheral area around the protruding area acts as a trap for slurry, conditioning debris, and other foreign contaminates that can also lead to increased scratch defect rates. Furthermore, since the pad is conditioned during use, the conditioning wear rate is significantly higher in the raised area because of the increase in contact pressure. This differential thinning of the window can disturb the optical signal and, eventually, can lead to a break-through in the window, that is a catastrophic failure giving reduced pad lifetime.

CMP polishing pad windows are designed for use with specific endpoint detections systems for specific polishing equipment. For example, there is one window design used for optical endpoint detection systems and another type of window used for eddy current detection systems. This restricts usefulness of a specific pad to a specific endpoint detection system.

Thus, a need remains for an improved polishing pad with window region for use in end-point detection that is useful for multiple endpoint detection systems.

Disclosed herein is a polishing pad for chemical mechanical polishing comprising a polishing layer, a subpad, and a window region extending through the pad. The polishing layer has a polishing surface and a polishing layer interface surface opposite the polishing surface, the polishing layer comprising a polishing material. The subpad layer has a subpad interface surface adjacent to the polishing layer interface surface and a bottom surface opposite the subpad interface surface, the subpad layer comprising a subpad material. The window region includes (a) a top window material, which is transparent to light, the top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, wherein the top window peripheral surface forms a seal with the polishing material, with the subpad interface surface, or both; and (b) a bottom window portion, wherein the bottom window portion comprises a bottom window material having a bottom window interface surface adjacent the top window interface surface or the polishing layer interface surface, a bottom window peripheral surface, a bottom window bottom surface and a void space inward from the bottom window peripheral surface. The void space is aligned to allow light passing through the top window portion to pass through the polishing pad via the void space enabling optical end-point detection. Vibrational signals can be transmitted through the top window material or the polishing material and through the bottom window material enabling acoustic end-point detection.

Also disclosed herein is a method comprising providing a substrate to be polished, providing the polishing pad as described herein, providing a slurry on the polishing pad, polishing by moving the substrate relative to the polishing pad, monitoring polishing by (a) transmitting a light wave through the top window material and the void and detecting the light wave reflected from the substrate, (b) transmitting a vibrational signal through the top window material, the polishing layer material or both and through the bottom window material, or both (a) and (b).

Disclosed herein is a polishing pad useful in chemical mechanical polishing. The polishing pad can be used with end-point detection using a variety of types of signal waves. Particularly, the polishing pad can be used with optical detection using columnated or non-columnated light and the polishing pad can be used with vibrational detection using, for example, acoustic waves. This is accomplished by the window region including a path for transmission of light through the pad and also materials for transmitting vibrational signals (e.g., acoustic waves) through the pad.

Referring to, the polishing pad, for example, includes a polishing surfaceand can include grooves. A window regionis found in the pad. As shown inthe window region has a circular-shaped perimeter. However, other perimeter shapes such as ovals, rectangles (including rectangular shapes with curved corners), and the like could be used.

As shown, for example, in, showing cross-sections through the thickness of the padin the area around the window region, the padincludes a polishing layercomprising a polishing materialhaving a polishing surface, a polishing layer interface surface. The padalso include a subpad layercomprising a subpad materialand having a subpad bottom surfaceand a subpad interface surface. The subpad interface surfacecan be in direct contact with the polishing layer interface surfaceor an adhesive or tie layer (not shown) could be used to connect the polishing layerto the subpad layer.

The window regionincludes a top portion comprising a top window material. The top window has a polishing face surfaceand a top window interface surfaceopposite from the polishing face surface, and a top window peripheral surfaceextending from the polishing face surfaceto the top window interface surface. The top window materialforms a seal with the polishing layer material, with the subpad interface surface(as in for example), or both. A seal is formed to prevent particles or liquid used in the chemical mechanical polishing from passing from above the polishing layer to below the subpad layer or below the window. Slurry below the subpad provides a negative impact on polishing uniformity. Slurry under the window interferes with and decreases intensity of the endpoint signal strength. Preferably, the window materialforms a seal with the polishing layer material. For example, the top window peripheral surfacecan be in direct contact with the polishing layer material, or an adhesive (not shown) can be used to hold the top window materialin place. The top window materialcan be in direct contact with a portion of the subpad materialor an adhesive (not shown) can bond the subpad materialwith the top window material(See, e.g.,where the top window interface surfacecan form a seal with the subpad interface surface). Alternatively, the top window materialcan have no contact with the subpad material(See, e.g.,). The polishing face surfacecan be coplanar with the polishing surface, but is preferably recessed from the polishing face surface as shown inwhere there is a recess.

The window further includes a bottom portion comprising a bottom window material. The bottom window materialhas a bottom window interface surface, a bottom window bottom surfaceand a bottom window peripheral surfaceextending from the bottom window interface surfaceto the bottom window bottom surface.

The bottom window materialhas a void regioninward of the bottom window materialthat extends from the bottom window interface surfaceto the bottom window interface surface. This void facilitates transmission of light through the window region. The bottom window materialfacilitates transmission of vibrational signals through the pad. As shown for example, inand, the bottom window peripheral surfacecan contact the subpad material. Preferably, however, there is a gapbetween at least a portion of the bottom window peripheral surfaceand the subpad material. Furthermore, there are channels between the four bottom window material regionsthat connect the perimeter gapto the central void region. More preferably, as shown, for example, in,A-D,A-D,andthere is a gapbetween the bottom window peripheral surfaceand the subpad materialsuch that there is no contact between the bottom window peripheral surfaceand the subpad material.

The top window materialcan have a larger dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window materialand the void. (See, e.g.,). Alternatively, the top window materialcan have the same dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window material, the void, and the optional gaps. (See, e.g.,). In yet another alternative, the top window materialcan have a smaller dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window materialand the void. (See, e.g.,-D,A-B andD).

The bottom window materialis located solely under and adjacent to the top window materialas shown, for example, inandA, and such that the top window interface surfacecontacts the bottom window interface surface, or those surfaces are bonded together with an adhesive (not shown). Alternatively, the bottom window materialis located solely under and adjacent to the polishing material, as shown, for example, in, and such that the polishing layer interface surfacecontacts the bottom window interface surface, or those surfaces are bonded together with an adhesive (not shown). As another alternative, a portion of the bottom window materialis located under and adjacent to the polishing materialwith another portion of the bottom window materiallocated under and adjacent to the top window material. For example ina portion of the bottom window interface surfacecontacts the polishing layer interface surfaceor those surfaces are bonded together with an adhesive (not shown) and a portion of the bottom window interface surfacecontacts the top window interface surfaceor those surfaces are bonded together with an adhesive (not shown).

The bottom window materialcan be a monolithic material having a void (or through hole)extending from the bottom window interface surfaceto the bottom window bottom surface. For example, as shown in, the bottom window materialcould have an annular shape. However, other shapes such as ovals, rectangles, hexagons, and the like with through holes could be used. In an alternative structure, the bottom window materialcould comprise individual columnar structures, such as rectangles as shown in, or arcs, wedges, cylinders, and the like.

As shown in, an optional encapsulating layercan be under the bottom window bottom surface. Alternatively, no encapsulating layeris required (See, e.g.,). The optional encapsulating layercan be located only adjacent to (under) the bottom window material(See, e.g.,). Alternatively, the optional encapsulating layercan extend from the voidto the subpad materialas shown, for example, in. Alternatively, the optional encapsulating layercan extend continuously from the subpad materialacross any gap, the bottom window bottom surfaceand the voidas shown in. Alternatively, the optional encapsulating layercan extend across the entire bottom of the pad forming a bottom pad surface as in. This encapsulating layer is optional in all configurations and disclosed herein are included configurations like those ofbut with no encapsulating layerwith the bottom window bottom surfacebeing coplanar with the subpad bottom surfaceas if. Further disclosed herein (but not illustrated) are configurations like those ofbut with the encapsulating layerextending from the voidto the subpad materialas in. Further disclosed herein (but not illustrated) are configurations like those ofbut with the encapsulating layerextending across the entire window region including the voidfrom subpad materialto subpad material as in. Further disclosed herein (but not illustrated) are configurations like those ofbut with the encapsulating layerextending across the entire bottom of the pad forming a bottom pad surface as in. For structures where the encapsulating layerextends across the void, the encapsulating layer is transparent to the light intended to be used for optical signaling.

The overall thickness of the polishing pad (e.g., polishing layer plus subpad) 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 subpad can have a thickness of from 0.5 up to 3, from 0.7 up to 2.5, from 1 to 2 mm. The thickness of the top window material can have a thickness of, for example, from 0.3 up to 3.2, from 0.4 up to 2.7, from 0.8 up to 2.2, or 1 to 1 mm, while the thickness of the bottom window material can be from 0.3 up to 3.2, from 0.4 up to 2.7, from 0.8 up to 2.2, or 1 to 1 mm, provided that the overall thickness of the window does not exceed the overall thickness of the pad. The top window material can have a diameter (or length and width) of from 2, from 3, or from 4 up to 30, up to 25, up to 20, up to 15, or up to 10 mm. The distance from a bottom window peripheral surfaceto an opposite bottom window peripheral surfacecan be from 1.5, from 2, from 3, from 4, from 5, from 6, from 7, from 8, from 9, or from 10 up to 75, up to 70, up to 60, up to 50, up to 40, up to 30, or up to 20 mm. The voidbeing inward from the bottom window peripheral surfacenecessarily has a smaller dimension that the distance from a bottom window peripheral surfaceto an opposite bottom window peripheral surface, but can have a dimension in the direction parallel to the polishing surfaceof from 1, 2, from 3, from 4, from 5, from 6, from 7, from 8, from 9, or from 10 up to 40, up to 38, up to 35, up to 30, up to 25, or up to 20 mm. The gapfrom the bottom window peripheral surfaceto the subpad material can be 0 or can be from 0.1, from 0.2 from 0.3, from 0.4, or from 0.5 up to 40, up to 35, up to 30, up to 25, up to 20, up to 15, up to 10, or up to 5 mm.

The depth of the recesscan be, for example, 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 a peripheral portion of the polishing layer adjacent to the top window materialthan in the other areas of the padas shown in, andA-D can enable flexibility during use. Similarly, a width of the peripheral portion can be adjusted to provide the desired mechanical response for the pad materials and design. The width 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 top window materialcan comprise a polymer or a blend of polymers. For optical detection systems the top materialshould have sufficient transmission at the wavelengths of light used by the optical metrology. It can be helpful if that top window materialhas 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, etc.).

The top window materialcan be 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, methylene bis 4,4′ cyclohexyl isocyanate, 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.

The curing agent can be 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 bottom window materialcan be a polymeric material. The bottom window materialpreferably comprises an elastomeric material. As used herein, “elastomeric material” means one that deforms when under force, but which returns substantially to its original form when the force is removed. The voidand the preferred gapallow the elastomeric material of the bottom portion of the window to deform into the gap when the pad is under downforce (but returns substantially to its original shape when the downforce is removed). Particularly, the thickness of the bottom portion will be reduced under the downforce, but the perimeter may expand in a direction perpendicular to the downforce. This compression reduces deformation forces in the polishing layer, particularly at the polishing surface. The compressibility of the bottom portion can be selected to substantially match that of the surrounding subpad material, the surrounding polishing material or both. Because the window extends to the bottom edge of the pad, reflection and refraction of the signal wave at a solid/gas or solid/vacuum interface is avoided.

The elastomeric material of the bottom window materialpreferably has an elastic modulus that is lower than that of the first window material. Desirably the elastomeric material can have a similar refractive index and optical transmittance to the upper window layer. A wide variety of transparent elastomers can be used, such as, for example, polyurethanes, polyolefins, polyamides, polyacrylates, styrenic block copolymers, and silicone elastomers. A preferred material family are silicone elastomers. An elastomeric material that can be easily cast or molded into appropriate shapes is desirable.

The polishing layercan have, for example, a tensile storage modulus of 300 to 400 MPa, while the subpad layercan have, for example, a tensile storage modulus can be 5 to 30 MPa. The overall composite compressibility is highly affected by the relative layer thickness. The design of pads of the present invention allows simple methods for selecting an appropriate lower window layer material. For example, standard compressibility testing methods can be used on test samples of the pad stack and the window stack to allow rapid compressibility matching prior to any pad fabrication.

The polishing layer materialcan comprise a polymer. The polishing material can be opaque at the thickness of the polishing layer. 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 to 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 subpad materialcan comprise a polymeric material. The subpad material can be more compliant (or more elastic) than the polishing material. The subpadcan comprise a porous layer. Examples of polymeric materials for the subpad 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 optional encapsulating layercan provide one or more of the following benefits: facilitate insertion of the windowinto the pad with proper alignment; provide an even surface on the bottom of the pad; prevent any adhesive between the side edges of the windowand the polishing layer, the subpad, or both, from leaking out; assist in holding the windowin place; prevent any leakage of slurry to the bottom side of the polishing pad. The encapsulating layer can be a polymer, such as, for example, a polyester. The encapsulating layer can be a non-adhesive layer. The encapsulating layer can have a thickness of, for example from 0.025, from 0.05, from 0.1 up to 1 mm.

Polishing pads as disclosed herein can be prepared via a variety of processes, including insertion of a discrete window assembly into a pad having a matching opening, addition of the lower window component to a pad that already has a cast in place upper window component in the upper pad layer, or insertion of the window assembly into a net shape mold used to prepare a top pad layer blank followed by lamination of the subpad.

For example, a plug comprising the top window materialcan be placed in a mold and polishing layer materialmolded into a block or cake around the plug. The block or cake can then be sliced into layers having the desired thickness of the polishing layer. If recessis desired that can be machined in after slicing of the block. Alternatively, if an individual layer is molded around a window comprising the top window material, the mold can include a shape to provide the recess. A layer comprising the subpad materialcan have a window opening punched through it. The subpad material can be laminated to the polishing layer material. The bottom window materialand any optional encapsulating layercan be inserted before or after lamination. Adhesive can be used to facilitate bonding during the lamination. An optional pressure sensitive adhesive can be applied on the bottom of the pad to facilitate adhesion of the pad to the platen during polishing.

Alternatively, a window assembly having a top portion and bottom portion as described herein can be placed in a mold and the polishing layer formed around the relevant portions. The subpad can then be applied by lamination.

As another example, a polishing pad as disclosed here can be made by providing a window assembly in a mold with a recess in the mold to hold at least part of the bottom portion of the window and molding the polishing layer around the portion of the window 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 subpad portion of the pad, the subpad can be molded in a second molding step in a separate mold provided the mold includes a spacer to provide for the gap.

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. According to a preferred method, during polishing both optical detection (e.g., a columnated or non-columnated light wave) and vibrational detection (e.g., acoustic waves) are used during polishing of a single substrate.

This disclosure further encompasses the following aspects.

Aspect 1: A polishing pad for chemical mechanical polishing comprising: a polishing layer having a polishing surface and a polishing layer interface surface opposite the polishing surface, the polishing layer comprising a polishing material, a subpad layer having a subpad interface surface adjacent to the polishing layer interface surface and a bottom surface opposite the subpad interface surface, the subpad layer comprising a subpad material, a top window material, which is transparent to light, the top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, wherein the top window peripheral surface forms a seal with the polishing material, with the subpad interface surface, or both, a bottom window portion, wherein the bottom window portion comprises a bottom window material having a bottom window interface surface adjacent the top window interface surface or the polishing layer interface surface, a bottom window peripheral surface, a bottom window bottom surface and a void space inward from the bottom window peripheral surface, wherein the void space is aligned to allow light passing through the top window portion to pass through the polishing pad via the void space enabling optical end-point detection and vibrational signals can be transmitted through the top window material or the polishing material and through the bottom window material enabling acoustic end-point detection.

Aspect 2: The polishing pad of Aspect 1 wherein the top window polishing face surface is recessed below the polishing surface.

Aspect 3: The polishing pad of Aspect 1 or 2 wherein the pad comprises an encapsulating layer adjacent to the bottom window bottom surface.

Aspect 4: The polishing pad of Aspect 3 wherein the encapsulating layer extends across the subpad bottom surface.

Aspect 5: The polishing pad of Aspect 3 wherein the encapsulating layer defines a bottom surface coplanar with the subpad bottom surface.

Aspect 6: The polishing pad of any one of Aspects 3-5 wherein the void extends through the encapsulating layer.

Aspect 7: The polishing pad of any one of Aspects 3-5 wherein the encapsulating layer is transparent to light and encloses the void.

Aspect 8: The polishing pad of any of the previous Aspects wherein there is a gap between the bottom window peripheral surface and the subpad material.

Aspect 9: The polishing pad of any of the previous Aspects wherein there is an adhesive between the polishing layer interface surface and the subpad interface surface.

Aspect 10: The polishing pad of any of Aspects 1-9 wherein the polishing layer interface surface is in direct contact with the subpad interface surface.