US20250303516A1

US20250303516A1 - Multifunctional endpoint detection window

Info

Publication number: US20250303516A1
Application number: US18/621,430
Authority: US
Inventors: Hyunjin Kim; Joseph So; Michael E. Mills
Original assignee: Rohm and Haas Electronic Materials CMP Holdings Inc
Current assignee: DuPont Electronic Materials Holding Inc
Priority date: 2024-03-29
Filing date: 2024-03-29
Publication date: 2025-10-02
Also published as: JP2025156199A; KR20250146279A

Abstract

A polishing pad for chemical mechanical polishing includes a top window material, which is transparent to light, which forms a seal with polishing material, with subpad material, or both; a bottom window material, having a void space inward from a peripheral surface if the bottom window material. The void space is aligned to allow light passing through the top window portion to and 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.

Description

FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

Chemical Mechanical Planarization (CMP) is a variation of a polishing process that is widely used to flatten, or planarize, the layers of construction of an integrated circuit or similar structure. Particularly, CMP is frequently used to produce planar uniform layers of a defined thickness in the manufacture 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.

SUMMARY OF THE INVENTION

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).

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 is a top view of an example of a chemical mechanical polishing pad including a window.

FIGS. 2A-D are cross-sectional views through the thickness of a portion of chemical mechanical polishing pad around a window region showing examples of a pad structure including a two component window as disclosed herein.

FIGS. 3A-D are cross-sectional views through the thickness of a portion of chemical mechanical polishing pad around a window region showing examples of a pad structure including a two component window as disclosed herein.

FIGS. 4A-D are cross-sectional views through the thickness of a portion of chemical mechanical polishing pad around a window region showing examples of a pad structure including a two component window as disclosed herein.

FIG. 5 is a cross-sectional view parallel to the bottom surface through the subpad and bottom window portion of a polishing pad showing an example of an arrangement of the bottom window material as in FIG. 3B.

FIG. 6 is a cross-sectional view parallel to the bottom surface through the subpad and bottom window portion of a polishing pad showing an example of an arrangement of the bottom window material as in FIG. 3B.

FIG. 7 is a cross-sectional view parallel to the bottom surface through the subpad and bottom window portion of a polishing pad showing an example of an arrangement of the bottom window material as in FIG. 2D.

DETAILED DESCRIPTION OF THE INVENTION

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 FIG. 1 , the polishing pad 1, for example, includes a polishing surface 11 and can include grooves 12. A window region 100 is found in the pad 1. As shown in FIG. 1 the 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 FIGS. 2A-2D, 3A-3D, and 4A-4D, showing cross-sections through the thickness of the pad 1 in the area around the window region 100, the pad 1 includes a polishing layer 10 comprising a polishing material 14 having a polishing surface 11, a polishing layer interface surface 13. The pad 1 also include a subpad layer 20 comprising a subpad material 24 and having a subpad bottom surface 21 and a subpad interface surface 23. The subpad interface surface 23 can be in direct contact with the polishing layer interface surface 13 or an adhesive or tie layer (not shown) could be used to connect the polishing layer 10 to the subpad layer 20.
The window region 100 includes a top portion comprising a top window material 30. The top window has a polishing face surface 31 and a top window interface surface 33 opposite from the polishing face surface 31, and a top window peripheral surface 32 extending from the polishing face surface 31 to the top window interface surface 33. The top window material 30 forms a seal with the polishing layer material 14, with the subpad interface surface 23 (as in for example FIG. 2A), 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 material 30 forms a seal with the polishing layer material 14. For example, the top window peripheral surface 32 can be in direct contact with the polishing layer material 14, or an adhesive (not shown) can be used to hold the top window material 30 in place. The top window material 30 can be in direct contact with a portion of the subpad material 24 or an adhesive (not shown) can bond the subpad material 24 with the top window material 30 (See, e.g., FIG. 2A where the top window interface surface 33 can form a seal with the subpad interface surface). Alternatively, the top window material 30 can have no contact with the subpad material 24 (See, e.g., FIG. 2C). The polishing face surface 31 can be coplanar with the polishing surface 11, but is preferably recessed from the polishing face surface as shown in FIGS. 2A-2D, 3A-3D, and 4A-4D where there is a recess 15.
The window further includes a bottom portion comprising a bottom window material 40. The bottom window material 40 has a bottom window interface surface 43, a bottom window bottom surface 41 and a bottom window peripheral surface 42 extending from the bottom window interface surface 43 to the bottom window bottom surface 41.
The bottom window material 40 has a void region 44 inward of the bottom window material 40 that extends from the bottom window interface surface 43 to the bottom window interface surface 41. This void facilitates transmission of light through the window region. The bottom window material 40 facilitates transmission of vibrational signals through the pad. As shown for example, in FIG. 2D and FIG. 7 , the bottom window peripheral surface 42 can contact the subpad material 24. Preferably, however, there is a gap 45 between at least a portion of the bottom window peripheral surface 42 and the subpad material 24. Furthermore, there are channels between the four bottom window material regions 40 that connect the perimeter gap 45 to the central void region 44. More preferably, as shown, for example, in FIGS. 2A-C, 3A-D, 4A-D, 5 and 6 there is a gap 45 between the bottom window peripheral surface 42 and the subpad material 24 such that there is no contact between the bottom window peripheral surface 42 and the subpad material 24.
The top window material 30 can have a larger dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window material 40 and the void 44. (See, e.g., FIGS. 2A and 4C). Alternatively, the top window material 30 can have the same dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window material, the void 44, and the optional gaps 45. (See, e.g., FIG. 2B). In yet another alternative, the top window material 30 can have a smaller dimension (e.g., diameter or width and length) than the bottom window portion comprising the bottom window material 40 and the void 44. (See, e.g., FIGS. 2C, 3B-D, 4A-B and 4D).
The bottom window material 40 is located solely under and adjacent to the top window material 30 as shown, for example, in FIGS. 2A-D and 3A, and such that the top window interface surface 33 contacts the bottom window interface surface 43, or those surfaces are bonded together with an adhesive (not shown). Alternatively, the bottom window material 40 is located solely under and adjacent to the polishing material 14, as shown, for example, in FIGS. 3B and 3C, and such that the polishing layer interface surface 13 contacts the bottom window interface surface 43, or those surfaces are bonded together with an adhesive (not shown). As another alternative, a portion of the bottom window material 40 is located under and adjacent to the polishing material 14 with another portion of the bottom window material 40 located under and adjacent to the top window material 30. For example in FIGS. 3D, 4A, 4B and 4D a portion of the bottom window interface surface 43 contacts the polishing layer interface surface 13 or those surfaces are bonded together with an adhesive (not shown) and a portion of the bottom window interface surface 43 contacts the top window interface surface 33 or those surfaces are bonded together with an adhesive (not shown).
The bottom window material 40 can be a monolithic material having a void (or through hole) 44 extending from the bottom window interface surface 43 to the bottom window bottom surface 41. For example, as shown in FIG. 5 , the bottom window material 40 could 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 material 24 could comprise individual columnar structures, such as rectangles as shown in FIG. 6 , or arcs, wedges, cylinders, and the like.
As shown in FIGS. 2A-2D, 3A-3D, and 4B-4D, an optional encapsulating layer 50 can be under the bottom window bottom surface 41. Alternatively, no encapsulating layer 50 is required (See, e.g., FIG. 4A). The optional encapsulating layer 50 can be located only adjacent to (under) the bottom window material 40 (See, e.g., FIGS. 2A-2D, 3A-3D). Alternatively, the optional encapsulating layer 50 can extend from the void 44 to the subpad material 24 as shown, for example, in FIG. 4B. Alternatively, the optional encapsulating layer 50 can extend continuously from the subpad material 24 across any gap 45, the bottom window bottom surface 41 and the void 44 as shown in FIG. 4C. Alternatively, the optional encapsulating layer 50 can extend across the entire bottom of the pad forming a bottom pad surface as in FIG. 4D. This encapsulating layer is optional in all configurations and disclosed herein are included configurations like those of FIGS. 2A-2D and 3A-3D but with no encapsulating layer 50 with the bottom window bottom surface 41 being coplanar with the subpad bottom surface 21 as if FIG. 4A. Further disclosed herein (but not illustrated) are configurations like those of FIGS. 2A-2D and 3A-3D but with the encapsulating layer 50 extending from the void 44 to the subpad material 24 as in FIG. 4B. Further disclosed herein (but not illustrated) are configurations like those of FIGS. 2A-2D and 3A-3D but with the encapsulating layer 50 extending across the entire window region including the void 44 from subpad material 24 to subpad material as in FIG. 4C. Further disclosed herein (but not illustrated) are configurations like those of FIGS. 2A-2D and 3A-3D but with the encapsulating layer 50 extending across the entire bottom of the pad forming a bottom pad surface as in FIG. 4D. For structures where the encapsulating layer 50 extends across the void 44, 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 surface 42 to an opposite bottom window peripheral surface 42 can 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 void 44 being inward from the bottom window peripheral surface 42 necessarily has a smaller dimension that the distance from a bottom window peripheral surface 42 to an opposite bottom window peripheral surface 42, but can have a dimension in the direction parallel to the polishing surface 11 of 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 gap 45 from the bottom window peripheral surface 42 to 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 recess 15 can 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 material 30 than in the other areas of the pad 100 as shown in FIGS. 2A-2D, 3A-3D, and 4A-4D 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 material 30 can comprise a polymer or a blend of polymers. For optical detection systems the top material 30 should have sufficient transmission at the wavelengths of light used by the optical metrology. It can be helpful if that top window material 30 has a hardness or thermal expansion coefficient similar to that of the material used in the polishing layer. Examples of window materials include polyurethanes, acrylic polymers, cyclic olefin copolymers (e.g., TOPAS 8007, etc.).
The top window material 30 can 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 material 40 can be a polymeric material. The bottom window material 40 preferably 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 void 44 and the preferred gap 45 allow 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 material 40 preferably has an elastic modulus that is lower than that of the first window material 30. 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 layer 10 can have, for example, a tensile storage modulus of 300 to 400 MPa, while the subpad layer 20 can 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 material 14 can comprise a polymer. The polishing material can be opaque at the thickness of the polishing layer 101. 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 material 24 can comprise a polymeric material. The subpad material can be more compliant (or more elastic) than the polishing material. The subpad 102 can 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 layer 50 can provide one or more of the following benefits: facilitate insertion of the window 103 into the pad with proper alignment; provide an even surface on the bottom of the pad; prevent any adhesive between the side edges of the window 103 and the polishing layer 101, the subpad 102, or both, from leaking out; assist in holding the window 103 in place; prevent any leakage of slurry to the bottom side of the polishing pad 100. 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 material 30 can be placed in a mold and polishing layer material 14 molded 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 recess 15 is 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 30, the mold can include a shape to provide the recess 15. A layer comprising the subpad material 24 can have a window opening punched through it. The subpad material can be laminated to the polishing layer material. The bottom window material 40 and any optional encapsulating layer 50 can 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.
Aspect 11: The polishing pad of any of the previous Aspects wherein there is an adhesive between the top window interface surface and the bottom window interface surface.
Aspect 12: The polishing pad of any of Aspects 1-10 wherein the top window interface surface is in direct contact with the bottom window interface surface.
Aspect 13: The polishing pad of any one of the previous Aspects wherein the bottom window material is elastomeric.
Aspect 14: The polishing pad of any one of the previous Aspects wherein the subpad material is different from the bottom window material.
Aspect 15. A method of polishing comprising providing a substrate to be polished, providing the polishing pad as in any one of the previous Aspects, providing a 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).
All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). Moreover, stated upper and lower limits can be combined to form ranges (e.g., “at least 1 or at least 2 weight percent” and “up to 10 or 5 weight percent” can be combined as the ranges “1 to 10 weight percent”, or “1 to 5 weight percent” or “2 to 10 weight percent” or “2 to 5 weight percent”).
The disclosure may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The disclosure may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function or objectives of the present disclosure.
All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.
Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

Claims

What is claimed is:

1. A polishing pad for chemical mechanical polishing comprising:

a 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.

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

3. The polishing pad of claim 1 wherein the pad comprises an encapsulating layer adjacent to the bottom window bottom surface.

4. The polishing pad of claim 1 wherein there is a gap between the bottom window peripheral surface and the subpad material.

5. The polishing pad of claim 3 wherein the encapsulating layer extends across the subpad bottom surface.

6. The polishing pad of claim 3 wherein the encapsulating layer defines a bottom surface coplanar with the subpad bottom surface.

7. The polishing pad of claim 3 wherein the encapsulating layer is transparent to light and encloses the void.

8. The polishing pad of claim 1 wherein the bottom window material is elastomeric.

9. The polishing pad of claim 1 wherein the subpad material is different from the bottom window material.

10. A method of polishing comprising:

providing a substrate to be polished;

providing the polishing pad as in claim 1;

providing a slurry on the polishing pad;

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).