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, 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 subpad. 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 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. Sec, 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, which 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.

An aspect of the invention provides a polishing pad for chemical mechanical polishing comprising: a polishing layer having a polishing surface, a polishing layer interface surface opposite the polishing surface, and a polishing window region surface extending from the polishing surface to the polishing interface 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, and a bottom window regions interface surface extending from the bottom surface to the polishing layer interface surface, the subpad layer comprising a subpad material, a window extending through the polishing pad from the polishing surface to a backside surface of the pad, the window comprising: a top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, the top window peripheral surface being adjacent to the top window regions surface and separated from the top window region surface such that the top window peripheral surface does not have direct contact with the window region surface, and a bottom window material having a bottom window interface surface bonded to the top window interface surface a bottom window peripheral surface, a bottom window bottom surface wherein the bottom window material is elastomeric and can deform into a void space adjacent to the bottom window material when the pad is under pressure during polishing, wherein a seal is formed (a) between subpad material and the top window material, the bottom window material, or a combination of the top window material and the bottom window material form a seal with the subpad material or (b) between the bottom window material and the polishing material to prevent particles or liquid used in the chemical mechanical polishing from passing from above the polishing layer to below the subpad layer, and wherein the pad includes a path in the window region for transmitting columnated or non-columnated light through the thickness of the pad and wherein vibrational signals can be transmitted through the top window material and the bottom window material enabling acoustic end-point detection.

Another aspect of the invention provides a method of polishing comprising: providing a substrate to be polished; providing the polishing pad as in claim; providing a slurry on the polishing pad; polishing by moving the substrate relative to the polishing pad; and 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.

Disclosed herein is a polishing pad for chemical mechanical polishing comprising a polishing layer, a subpad layer, and window. The polishing layer comprises a polishing material and has a polishing surface, a polishing layer interface surface opposite the polishing surface, and a polishing window region surface extending from the polishing surface to the polishing interface surface. The subpad layer comprises a subpad material and has a subpad interface surface adjacent to the polishing layer interface surface and a bottom surface opposite the subpad interface surface, and a bottom window regions interface surface extending from the bottom surface to the polishing layer interface surface. The window extends through the polishing pad from the polishing surface to a backside surface of the pad. The window comprises a top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, the top window peripheral surface being adjacent to the top window regions surface and separated from the top window region surface such that the top window peripheral surface does not have direct contact with the window region surface, and a bottom window material having a bottom window interface surface bonded to the top window interface surface a bottom window peripheral surface, a bottom window bottom surface wherein the bottom window material is elastomeric and can deform into a void space adjacent to the bottom window material when the pad is under pressure during polishing. A seal is formed (a) between subpad material and the top window material, the bottom window material, or a combination of both the top window material and the bottom window material or (b) between the bottom window material and the polishing material 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. The pad includes a path in the window region for transmitting columnated or non-columnated light through the thickness of the pad. Vibrational signals can be transmitted through the top window material and the bottom window material enabling acoustic end-point detection.

The multifunctional window of the invention allows polishing methods 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).

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

As shown, for example, in-B, 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, and a polishing window-region surfaceextending from the polishing surfaceto the polishing layer interface surface. The padalso include a subpad layercomprising a subpad materialand having a subpad bottom surfaceand a subpad interface surfaceand a subpad layer window region surfaceextending from the subpad bottom surfaceto the 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 peripheral surfaceis adjacent to the polishing window-region surface, but the top window peripheral surfacedoes not contact the polishing window-region surface. There is a gapbetween the top window peripheral surfaceand the polishing window-region surface. The window region can include a recesssuch that the polishing face surfaceis recessed relative to the polishing surface. As an alternative the polishing face surfaceand the polishing surfacecan be coplanar (not shown). The polishing layercan have a reduced thickness in the window regionrelative to the remainder of the polishing layer (excluding macrotexture such as grooves) as shown in. Alternatively, the thickness of the polishing layerin the window regionmay be the same as the thickness of the polishing layer away from the window region (excluding macrotexture such as grooves) as shown for example in.

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 interface surfaceis adjacent the top window interface surface. Particularly, the bottom window interface surfacecan be in direct contact with the top window interface surface. Alternatively, a tie layer or an adhesive layer (not shown) can connect the top window interface surfaceto the bottom layer interface surface. The tie or adhesive layer can be, for example, a pressure sensitive adhesive. If the padis to be used with optical detection, the tie or adhesive layer preferably is transmissive to the wavelength of light used in such optional detection unless an optional gapunderlies the top window materialas shown in-B, in which case light can pass through the top window materialand the gap.

The bottom window materialis elastomeric and reversibly compressible. The window regionincludes a voidadjacent to the bottom window materialenabling the bottom window material to deform into the void region when the pad is under pressure during polishing. See.

The voidcan be (i) the same as the gapbetween the polishing window-region surfaceand the top window peripheral surfaceas shown, for example, inandA-D; (ii) between regions of the bottom window materialas shown, for example, in,, and; (iii) between the subpad materialand the bottom window materialas shown, for example, in,,, andA-B; or a combination of two or more of (i), (ii), and (iii), as shown in,B,,, andA-B.

A voidin the subpad layer and underlying the top window material, such as shown inand-A-C, can facilitate transmission of light through the window region even if the bottom window materialis opaque or not highlight transmissive of light. In the absence of such a void underlying the top window material, the bottom window material(and any adhesive that may optionally be used between the top window materialand bottom window material) must be transparent to light to enable transmission of light for use in optical end point detection. Thus, a pad having a window regionas shown, for example, incan include a transparent bottom window materialto facilitate optical end point detection. In contrast, in a pad having a window regionas shown, for example, inandA-C, can be used for optical end point detection with a bottom material that is transparent, partially transparent, translucent, or opaque.

The polishing pads as disclosed herein can also be used with vibrational (e.g., acoustic) end point detection. Particularly, vibrations can be transmitted through the top window materialand the bottom window materialunderlying such bottom window material.

The arrangement of the bottom window materialand the top window materialrelative to the polishing layerand the subpadare such that a seal is formed to prevent slurry and particulates above the polishing layer from leaking to the opposite side of the pad through the window region. For instance, a continuous bottom window materialtogether with the subpad materialcan form a seal as shown, for example, in. As another instance, the bottom window materialcan form seals with both the top window materialand the subpad material, as shown, for example, in. In yet another instance, the top window materialcan form a seal with the subpad material as shown, for example, in. In yet another instance as shown, for example, in, the bottom window materialforms a seal with the polishing layer material. The seal can be formed by direct contact of the adjacent surfaces or with a tie or adhesive layer, such as hot melt adhesive or pressure sensitive adhesive between the surfaces to strengthen the seal.

The pad can include an optional encapsulating layerunder the bottom window material. For example, in, andA, the encapsulating layeris located only under the bottom window material. This approach is also shown in. As another example, in, the encapsulating layerextends across the entire window region, being located both under the bottom window material and under the void. A pad having a window region as inorA-B could also be formed with an encapsulating layeringextending across the entire window region including under any void., shows a pad design without the optional encapsulating layer. Also disclosed herein (but not illustrated) are pad designs with are variations of the pad designs of,A-C. andA-B without an encapsulating layer. The bottom window bottom surfacecan define a bottom surface of the pad, bottom window bottom surfacecan be coplanar with the subpad bottom surface, or both.-B, show a pad designs where an optional encapsulating layerextends across the entire bottom of the pad. Also disclosed herein (but not illustrated) are pad designs with are variations of the pad designs of, andA-C modified such that an encapsulating layer extends across the entire bottom of the pad instead of just under the bottom window materialas shown. Also disclosed herein (but not illustrated) are variations of the pad designs ofwith the encapsulating layer underlying only the bottom window material.

The top window portion dimension perpendicular to the thickness of the pad (e.g., the diameter or width and length or a distance from a polishing window region surfaceto an opposing polishing window surface) can be larger than the bottom window portion dimension perpendicular to the thickness of the pad (e.g., the diameter or width and length or a distance from a subpad layer window region surfaceto an opposing subpad layer window region surfaceand comprising the bottom window materialand any subpad layer region void). (See, e.g.,). Alternatively, such top window portion dimension perpendicular to the thickness of the pad can be the same as such bottom window portion dimension perpendicular to the thickness of the pad dimension. In yet another alternative, such top window portion dimension perpendicular to the thickness of the can be smaller dimension than the bottom window portion dimension perpendicular to the thickness of the pad. (See, e.g.,,A-D, andA-B).

The bottom window materialcan be a monolithic material as shown, for example, in-B. The monolithic window materialhaving a void (or through hole)extending from the bottom window interface surfaceto the bottom window bottom surface. See, e.g.,-B,, and. 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.

Referring to, the voidimproves the manufacturability of the window region. In particular, voidallows top window materialand bottom window materialto be aligned and centered within recess. In, bottom window material is secured to polishing layerand encapsulating layer. The encapsulating layer in turn is secured to a polishing platen (not shown).

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 60, up to 50, up to 40, up to 30, up to 25, up to 20, up to 15, or up to 10 mm. The voidbetween the top window peripheral surfaceand the polishing window region surfacecan be from 1, from 2, from 3, from 4, from 5, from 7, from 10, from 15, or from 20 up to 40, or up to 35 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.

Any 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 greater than 0, from 0.5, from 1, from 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. Any voidfrom the bottom window peripheral surfaceto the subpad layer window region surfacecan 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 co-polymers (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 materialis an elastomeric material. As used herein, “elastomeric material” means one that deforms when under force, but which returns substantially to the original its original form when the force is removed. The void(s)allow the elastomeric material of the bottom window materialto deform into the voidwhen the pad is under downforce during polishing. The bottom window materialcan return substantially to its original shape when the downforce is removed. Particularly, the thickness of the bottom window materialwill be reduced under the downforce during polishing but a portion of the bottom window materialmay deform into the void. For example, as shown in, when under downforce, the bottom window materialmay deform into the void spaceabove and adjacent to the bottom window material. As another example, when under down force bottom window material may deform into a voidthat is inward from the bottom window peripheral surfaceas shown in,A-B, and. As yet another example, the bottom window materialmay deform into a voidthat is between the bottom window peripheral surfaceand the subpad window region surfaceas shown in. 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 top 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, poly acrylates, 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 top window materialto a partially assembled pad that already has a cast in place bottom window materialin the subpad layer, or insertion of the window assembly into a net shape mold used to prepare a bottom layer blank followed by lamination of the polishing layer.

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.

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, a polishing layer interface surface opposite the polishing surface, and a polishing window region surface extending from the polishing surface to the polishing interface 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, and a bottom window regions interface surface extending from the bottom surface to the polishing layer interface surface, the subpad layer comprising a subpad material, a window extending through the polishing pad from the polishing surface to a backside surface of the pad, the window comprising: a top window material having a polishing face surface, a top window peripheral surface, and a top window interface surface, the top window peripheral surface being adjacent to the top window regions surface and separated from the top window region surface such that the top window peripheral surface does not have direct contact with the window region surface, and a bottom window material having a bottom window interface surface bonded to the top window interface surface a bottom window peripheral surface, a bottom window bottom surface wherein the bottom window material is elastomeric and can deform into a void space adjacent to the bottom window material when the pad is under pressure during polishing, wherein a seal is formed (a) between subpad material and the top window material, the bottom window material, or a combination or (b) between the bottom window material and the polishing material prevent particles or liquid used in the chemical mechanical polishing from passing from above the polishing layer to below the subpad layer, and wherein the pad includes a path in the window region for transmitting columnated or non-columnated light through the thickness of the pad and wherein vibrational signals can be transmitted through the top window material and 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 having a void located inward from the bottom window peripheral surface that extends from the bottom window interface surface to the bottom window bottom surface.