Multifunctional endpoint detection window

Abstract

To provide a multifunctional endpoint detection window.SOLUTION: There is provided a polishing pad having a window extending through the polishing pad from a polishing surface to a backside surface of the pad. The window includes a top window material separated from a polishing material, and a bottom window. Therein a 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 between a subpad material and the top window material and / or the bottom window material or a seal between the polishing layer and the bottom window material prevents particles or liquid used in chemical mechanical polishing from passing from above the polishing layer to below a subpad layer. The pad can be used for polishing with either optical or vibrational end-point detection.SELECTED DRAWING: Figure 2B

Description

[Technical Field]

[0001] The field of the invention is polishing pads used in chemical mechanical polishing. [Background technology]

[0002] Chemical mechanical planarization (CMP) is a type of polishing process widely used to flatten or planarize the building layers of integrated circuits or similar structures. Specifically, CMP is frequently used to produce flat, uniform layers of a specified thickness in the fabrication of three-dimensional circuit structures through additive deposition and planarization. CMP can remove excess material deposited on the substrate (e.g., wafer) surface to produce extremely flat layers of uniform thickness, with uniformity prevailing across the entire substrate (e.g., wafer) area. When uniform thickness prevails across the entire wafer, this is known as global uniformity.

[0003] CMP uses a liquid, often called a slurry, which may contain nano-sized particles. The slurry is dispensed onto the surface of a rotating multilayer polymer pad (sometimes called a polishing sheet), which is mounted on a rotating platen. The polishing pad includes a polishing layer and may include a subpad. A substrate (e.g., a wafer) is mounted on a separate fixture or carrier with a separate rotation mechanism and pressed against the pad surface under a controlled load. This can result in high relative motion between the substrate (e.g., wafer) and the polishing pad, resulting in high shear or wear rates on both the substrate and the pad surface. Slurry particles trapped at the shear and pad / substrate interface abrade the substrate (e.g., wafer) surface, removing material from the substrate surface. Removal rate control and uniformity are important. Additionally, it is useful to use metrology to determine when polishing has met its desired goals (e.g., film thickness, exposure of intended underlying structures, etc.). This is called endpoint detection.

[0004] Various types of film thickness metrology, along with real-time control software, can be used for endpoint detection. Endpoint detection processes periodic signals, such as collimated, non-collimated, or acoustic signals, to avoid wafer yield problems resulting from both under-polishing and over-polishing. For example, one approach to endpoint detection is an optical endpoint detection system that uses the transmission of light of a desired wavelength through a polishing pad. The light reflects off the polished substrate, and the reflected light signal is then returned to an interferometer. This requires that at least a portion of the polishing pad be sufficiently transparent to the light source used to obtain an acceptable signal-to-noise ratio. The metrology equipment can be located inside the body of the polishing machine or the platen that holds the pad.

[0005] For certain pad structures where optical detection is used, the pad material itself may be transparent to the desired optical wavelength and / or have a design that allows effective transmission of the signal wave. Alternatively, the pad may include an alternative structure that promotes wave transmission. For example, a transparent polymer may be provided, and an opaque material may be formed around such a polymer to create a transparent window. See, for example, U.S. Patent No. 5,623,999. As another example, an opening may be provided through the entire pad. See, for example, U.S. Patent No. 5,623,999 and U.S. Patent No. 5,623,999. A third approach is to form a pad with an opening into which a transparent window material is inserted and held in place with an adhesive. See, for example, U.S. Patent No. 5,623,999. Various versions of polishing pads with windows have been proposed. See, for example, Patent Documents 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, and 27.

[0006] Transmission of the signal wave through the boundary between the void (e.g., air) and the window surface can cause refraction or reflection of the signal wave, which can create noise or reduce the signal, thereby reducing the effectiveness of using the signal wave for endpoint detection. Therefore, in another approach, an optical fiber can be inserted into an opening in the subpad. See, for example, U.S. Patent No. 5,929,994.

[0007] For transmission of other vibrational waves, such as acoustic waves, non-porous windows are used, see, for example, U.S. Patent Nos. 5,211,999 and 5,211,999.

[0008] Additionally, because the window is typically formed from a material separate from the polishing layer, other problems can arise. Specifically, the modulus and resistance of the solid polymer window material are typically higher than those of the surrounding composite pad, resulting in differential compression during the polishing process, resulting in deformation near the window. The problem can be further exacerbated by differences in the coefficient of thermal expansion (CTE) and thermal conductivity (K) between the polishing material and the window. As the top surface of the pad and the window heat up due to friction during CMP, the differences in CTE and K cause additional overstress and overdeformation. This can cause the window region to protrude above the top surface of the pad's polishing area during use. The protruding window can scratch the polished substrate. Additionally, the voids in the surrounding area around the protruding area act as traps for slurry, conditioning debris, and other foreign contaminants, which can also increase the scratch defect rate. Furthermore, the pad is conditioned during use, and the conditioning wear rate is significantly higher in the raised areas due to increased contact pressure. Such differential window thinning can interfere with the optical signal and ultimately cause the window to break, a catastrophic failure that shortens the life of the pad.

[0009] CMP polishing pad windows are designed for use with specific endpoint detection 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 limits the usefulness of a particular pad to a specific endpoint detection system. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 5,605,760 [Patent Document 2] U.S. Patent No. 8,961,266 [Patent Document 3] U.S. Patent No. 7,497,763 [Patent Document 4] U.S. Patent No. 5,893,796 [Patent Document 5] U.S. Patent No. 7,621,798 [Patent Document 6] U.S. Patent No. 7,081,044 [Patent Document 7] U.S. Patent No. 7,195,539 [Patent Document 8] U.S. Patent No. 8,475,228 [Patent Document 9] U.S. Patent No. 10,569,383 [Patent Document 10] U.S. Patent Application Publication No. 2021 / 0402556 [Patent Document 11] US Patent Application Publication No. 2022 / 0226956 [Patent Document 12] US Patent Application Publication No. 2020 / 164483 [Patent Document 13] US Patent Application Publication No. 2015 / 232549 [Patent Document 14] U.S. Patent No. 9,126,304 [Patent Document 15] US Patent Application Publication No. 2008 / 0207089 [Patent Document 16] US Patent Application Publication No. 2017 / 0120417 [Patent Document 17] US Patent Application Publication No. 2016 / 263721 [Patent Document 18] U.S. Patent No. 7,398,714 [Patent Document 19] U.S. Patent No. 7,435,161 [Patent Document 20] US Patent Application Publication No. 2005 / 064802 [Patent Document 21] U.S. Patent No. 9,475,168 [Patent Document 22] U.S. Patent No. 6,045,439 [Patent Document 23] U.S. Patent No. 6,716,085 [Patent Document 24] U.S. Patent No. 8,475,228 [Patent Document 25] U.S. Patent No. 7,264,536 [Patent Document 26] Japanese Patent No. 5142866 [Patent Document 27] Chinese Patent Application Publication No. 113478382 [Patent Document 28] US Patent Application Publication No. 2010 / 184357 [Patent Document 29] US Patent Application Publication No. 2023 / 0009737 [Patent Document 30] US Patent Application Publication No. 2023 / 0009519 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, there remains a need for an improved polishing pad having a window area for use in endpoint detection that is useful for multiple endpoint detection systems. [Means for solving the problem]

[0012] One aspect of the present invention provides a polishing pad for chemical mechanical polishing, the polishing pad comprising: a polishing layer having a polishing surface, a polishing-layer interface opposite the polishing surface, and a polishing window region surface extending from the polishing surface to the polishing interface, the polishing layer comprising an abrasive; a subpad layer having a subpad interface adjacent the polishing-layer interface, a bottom surface opposite the subpad interface, and a bottom window region interface extending from the bottom surface to the polishing-layer interface, the subpad layer comprising a subpad material; and a window extending through the polishing pad from the polishing surface to a back surface of the pad, the window comprising: an upper window material having a polishing surface, an upper window peripheral surface, and an upper window interface, the upper window peripheral surface being adjacent to the upper window region surface and separated from the upper window region surface so as not to directly contact the window region surface; and a bottom window material having a bottom window interface, a bottom window peripheral surface, and a bottom window bottom surface bonded to the bottom window material, the bottom window material being elastic and capable of deforming into a gap space adjacent to the bottom window material when the pad is under pressure during polishing, wherein a seal is formed (a) between the subpad material and the top window material, the bottom window material, or a combination of the top window material and the bottom window material, forming a seal together with the subpad material, or (b) between the bottom window material and the polishing material to prevent particles or liquids used in chemical mechanical polishing from passing from above the polishing layer to below the subpad layer, the pad including a passage in the window region for transmitting cylindrical or non-cylindrical light through the thickness of the pad, and a vibration signal can be transmitted through the top and bottom window materials, enabling acoustic endpoint detection.

[0013] Another aspect of the present invention provides a polishing method, comprising: providing a substrate to be polished; providing a polishing pad according to claim 1; providing a slurry on the polishing pad; polishing the substrate by moving it relative to the polishing pad; and monitoring the polishing by (a) transmitting light waves through the top window material and the void and detecting light waves reflected from the substrate; (b) transmitting a vibration signal through the top window material, the polishing layer material, or both, and through the bottom window material, or by both (a) and (b).

[0014] Reference will now be made to the drawings of exemplary embodiments, wherein like elements are numbered alike. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a top view of an example chemical mechanical polishing pad including a window. [Figure 2A] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 2B] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 3A] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 3B] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 3C] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 3D]1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 4A] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 4B] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 4C] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window region showing an example of a pad structure including a two-component window as disclosed herein. [Figure 5] 4C is a cross-sectional view parallel to the bottom plane through the subpad and bottom window portion of the polishing pad showing an example of the placement of the bottom window material as in FIG. 4B. [Figure 6] 4C is a cross-sectional view parallel to the bottom plane through the subpad and bottom window portion of the polishing pad showing an example of the placement of the bottom window material as in FIG. 4B. [Figure 7] 3A-3D are cross-sectional views taken parallel to the bottom plane through the subpad and bottom window portion of the polishing pad, showing an example of a bottom window material arrangement such as that in FIGS. 3A-3D. [Figure 8A] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window area showing an example of a pad structure including a component window. [Figure 8B] 1 is a cross-sectional view through the thickness of a portion of a chemical mechanical polishing pad around a window area showing an example of a pad structure including a component window. DETAILED DESCRIPTION OF THE INVENTION

[0016] Disclosed herein is a polishing pad useful for chemical mechanical polishing. The polishing pad can be used for endpoint detection using various types of signal waves. Specifically, the polishing pad can be used for optical detection using cylindrical or non-cylindrical light, and the polishing pad can be used for vibration detection using, for example, acoustic waves. This is achieved by a window region that includes a path for transmitting light through the pad and a material for transmitting a vibration signal (e.g., acoustic wave) through the pad.

[0017] Disclosed herein is a polishing pad for chemical mechanical polishing, comprising a polishing layer, a subpad layer, and a window. The polishing layer comprises an abrasive and has a polishing surface, a polishing-layer interface opposite the polishing surface, and a polishing window region surface extending from the polishing surface to the polishing interface. The subpad layer comprises a subpad material and has a subpad interface adjacent to the polishing-layer interface, a bottom surface opposite the subpad interface, and a bottom window region interface extending from the bottom surface to the polishing-layer interface. The window extends through the polishing pad from the polishing surface to the back surface of the pad. The window comprises a top window material having a polishing surface, an upper window peripheral surface, and an upper window interface, the upper window peripheral surface being adjacent to the upper window area surface and separated from the upper window area surface so that the upper window peripheral surface does not directly contact the window area surface; and a bottom window material having a bottom window interface bonded to the top window interface, a bottom window peripheral surface, and a bottom window bottom surface, the bottom window material being elastic and capable of transforming into a void section adjacent to the bottom window material when the pad is under pressure during polishing. A seal is formed (a) between the subpad material and the top window material, the bottom window material, or a combination of both the top and bottom window materials, or (b) between the bottom window material and the polishing material to prevent particles or liquids used in chemical mechanical polishing from passing from above the polishing layer to below the subpad layer or below the window. Slurry below the subpad negatively impacts polishing uniformity. Slurry below the window interferes with and reduces the intensity of the endpoint signal. The pad includes a path in the window area for transmitting cylindrical or non-cylindrical light through the thickness of the pad. Vibration signals can be transmitted through the top and bottom window materials, enabling acoustic endpoint detection.

[0018] The multi-functional window of the present invention enables a polishing method that includes providing a substrate to be polished, providing a polishing pad described herein, providing a slurry on the polishing pad, polishing the substrate by moving it relative to the polishing pad, and monitoring the polishing by (a) transmitting light waves through the top window material and the void and detecting light waves reflected from the substrate, (b) transmitting a vibration signal through the top window material, the polishing layer material, or both, and through the bottom window material, or both (a) and (b).

[0019] 1, polishing pad 1 includes polishing surface 11 and may include grooves 12. Window areas 100 are visible in pad 1. As shown in FIG. 1, the window areas are circular; however, oval, rectangular (including rectangular shapes with curved corners), etc. may be used.

[0020] 2A-2B, 3A-3D, 4A-4C, and 8A-8B, which show cross sections through the thickness of pad 1 in the area around window area 100, pad 1 includes polishing layer 10 with polishing material 14 having polishing surface 11, polishing-layer interface 13, and polishing window area surface 16 extending from polishing surface 11 to polishing-layer interface 13. Pad 1 also includes subpad layer 20 with subpad material 24 and having subpad bottom surface 21 and subpad interface 23, and subpad layer window area surface 25 extending from subpad bottom surface 21 to subpad interface 23. Subpad interface 23 can be in direct contact with polishing layer interface 13, or an adhesive or bonding layer (not shown) can be used to connect polishing layer 10 to subpad layer 20.

[0021] The window region 100 includes an upper portion that includes an upper window material 30. The upper window has a polishing surface 31, an upper window interface 33 opposite the polishing surface 31, and an upper window peripheral surface 32 extending from the polishing surface 31 to the upper window interface 33. The upper window peripheral surface 32 is adjacent to the polishing window region surface 16, but the upper window peripheral surface 32 does not contact the polishing window region surface 16. A gap 44 exists between the upper window peripheral surface 32 and the polishing window region surface 16. The window region may include a recess 15 such that the polishing surface 31 is recessed relative to the polishing surface 11. Alternatively, the polishing surface 31 and the polishing surface 11 may be coplanar (not shown). The polishing layer 10 may have a reduced thickness in the window region 100 relative to the remainder of the polishing layer (excluding macrotexture, such as grooves), as shown in FIGS. 2A-2B, 3A-3D, 4A-4C, and 8A. Alternatively, the thickness of the polishing layer 10 in the window region 100 can be the same as the thickness of the polishing layer away from the window region (excluding macrotexture such as grooves), for example as shown in FIG. 8B.

[0022] The window further includes a bottom portion comprising a bottom window material 40. The bottom window material 40 has a bottom window interface 43, a bottom window bottom surface 41, and a bottom window peripheral surface 42 extending from the bottom window interface 43 to the bottom window bottom surface 41. The bottom window interface 43 is adjacent to the top window interface 33. Specifically, the bottom window interface 43 may be in direct contact with the top window interface 33. Alternatively, a bonding or adhesive layer (not shown) may connect the top window interface 33 to the bottom layer interface 43. The bonding or adhesive layer may be, for example, a pressure-sensitive adhesive. If the pad 1 is to be used in optical detection, the bonding or adhesive layer is preferably transparent to the wavelengths of light used for such optional detection, as light passes through the top window material 30 and air gap 44, unless an optional air gap 44 is present below the top window material 30, as shown in Figures 3A-3D and 4A-4B.

[0023] The bottom window material 40 is elastic and reversibly compressible. The window region 100 includes a void 44 adjacent the bottom window material 40 that allows the bottom window material to deform into a void region when the pad is under pressure during polishing. See FIG. 2B.

[0024] The void 44 may be (i) the same as the void 44 between the polishing window area surface 16 and the upper window peripheral surface 32, for example, as shown in Figures 2A-2B and 3A-3D, or (ii) between areas of the bottom window material 40, for example, as shown in Figures 3A-3D, 4A-4B and 5-7, or (iii) between the subpad material 24 and the bottom window material 40, as shown in Figures 4B-4C, 5, 6 and 8A-8B, or a combination of two or more of (i), (ii) and (iii), as shown in Figures 3A-3D, 4B, 5, 6 and 8A-8B.

[0025] Air gaps 44 in the subpad layer and beneath the top window material 30, such as those shown in Figures 3A-3D and 4A-4C, can facilitate light transmission through the window region even if the bottom window material 40 is not opaque or otherwise enhances light transmission. In the absence of such air gaps beneath the top window material 30, the bottom window material 40 (and any adhesive that may optionally be used between the top and bottom window materials 30, 40) must be transparent to light to allow light transmission for use in optical endpoint detection. Thus, a pad having a window region 100, such as that shown in Figures 2A-2B, can include a transparent bottom window material 40 to facilitate optical endpoint detection. In contrast, pads having a window region 100, such as those shown in Figures 3A-3D and 4A-4C, can be used for optical endpoint detection using a transparent, partially transparent, translucent, or opaque bottom member.

[0026] The polishing pad as disclosed herein can also be used for vibration (e.g., acoustic) endpoint detection. Specifically, vibration can be transmitted through the top window material 30 and the bottom window material 40 below the bottom window material.

[0027] The arrangement of the bottom window material 40 and the top window material 30 relative to the polishing layer 10 and subpad 20 is such that a seal is formed to prevent slurry and particles on top of the polishing layer from leaking through the window area 100 to the opposite side of the pad. For example, the bottom window material 40, which is continuous with the subpad material 24, can form a seal, as shown, for example, in FIGS. 2A-2B. As another example, the bottom window material 40 can form a seal with both the top window material 30 and the subpad material 24, as shown, for example, in FIGS. 3A-3D. In yet another example, the top window material 30 can form a seal with the subpad material, as shown, for example, in FIGS. 4A-4C. In yet another example, as shown, for example, in FIGS. 8A-8B, the bottom window material 40 forms a seal with the polishing layer material 14. The seal can be formed by direct contact with the adhesive surfaces or by using a tie or adhesive layer, such as a hot melt adhesive or pressure-sensitive adhesive, between the surfaces to strengthen the seal.

[0028] The pad may include an optional encapsulation layer 50 below the bottom window material 40. For example, in FIGS. 2A-2B and 3A, the encapsulation layer 50 is located only below the bottom window material 40. This approach is also shown in FIGS. 4A-4C. As another example, in FIG. 3B, the encapsulation layer 50 extends across the entire window area that is located both below the bottom window material and below the cavity 44. Pads having window areas such as those in FIGS. 4A-4C or 8A-8B can also be formed with the encapsulation layer 50 extending across the entire window area, including below the optional cavity 44. FIG. 3C shows a pad design that does not include the optional encapsulation layer 50. Pad designs that include variations of the pad designs of FIGS. 2A-2B, 4A-4C, and 8A-8B that do not include an encapsulation layer are also disclosed herein (not shown). The bottom window bottom surface 41 can define the bottom surface of the pad, the bottom window bottom surface 41 can be coplanar with the subpad bottom surface 21, or both. Figures 3D and 8A-8B show pad designs in which the optional encapsulation layer 50 extends across the entire bottom of the pad. Also disclosed herein (not shown) are pad designs having variations of the pad designs of Figures 2A-2B and 4A-4C in which the encapsulation layer is modified to extend across the entire bottom of the pad instead of directly underneath the bottom window material 40 as shown. Also disclosed herein (not shown) are pad designs having variations of the pad designs of Figures 8A-8B in which the encapsulation layer is present only underneath the bottom window material 40.

[0029] The dimension of the top window portion perpendicular to the pad thickness (e.g., diameter, width, and length, or distance from polishing window area surface 16 to the opposing polishing window area surface 16) can be longer than the dimension of the bottom window portion perpendicular to the pad thickness (e.g., diameter, width, and length, or distance from subpad layer window area surface 25 to the opposing subpad layer window area surface 25, including bottom window material 40 and any subpad layer area void 44) ​​(see, e.g., FIGS. 4A-4C). Alternatively, the dimension of the top window portion perpendicular to the pad thickness can be the same as the dimension of the bottom window portion perpendicular to the pad thickness. In yet another alternative, the dimension of the top window portion perpendicular to the pad thickness can be smaller than the dimension of the bottom window portion perpendicular to the pad thickness (see, e.g., FIGS. 2A-2B, 3A-3D, and 8A-8B).

[0030] The bottom window material 40 can be a monolithic material, for example, as shown in Figures 2A-2D, 5, 7, and 8A-8B. A monolithic window material 49 having a void (or through-hole) 44 extends from the bottom window interface 43 to the bottom window bottom surface 41. See, for example, Figures 3A-3D, 4A-4B, 5, and 7. For example, as shown in Figure 5, the bottom window material 40 can have an annular shape. However, other shapes, such as an oval, rectangle, or hexagon with a through-hole, can be used. In alternative configurations, the bottom window material 24 can include a rectangle, as shown in Figure 6, or individual cylindrical structures, such as an arc, wedge, or cylinder.

[0031] 8A and 8B, the void 44 improves the manufacturability of the window area 100. In particular, the void 44 allows the top window material 30 and the bottom window material 40 to be aligned and centered within the recess 15. In FIG. 8A, the bottom window material is secured to the polishing layer 10 and the encapsulation layer 50. The encapsulation layer is then secured to a polishing platen (not shown).

[0032] The overall thickness of the polishing pad (e.g., the polishing layer plus the subpad) is preferably 4 mm or less. For example, the overall thickness of the polishing pad can be 1 to a maximum of 4 mm, 1.5 to a maximum of 4 mm, 1.7 to a maximum of 3.5 mm, or 2 to a maximum of 3 mm. The polishing layer can have a thickness of 0.5 to a maximum of 3 mm, 0.7 to a maximum of 2.5 mm, 1.2 to a maximum of 2.2 mm, or 1 to 2 mm. The subpad can have a thickness of 0.5 to a maximum of 3 mm, 0.7 to a maximum of 2.5 mm, or 1 to 2 mm. The thickness of the top window material can be, for example, 0.3 to a maximum of 3.2 mm, 0.4 to a maximum of 2.7 mm, 0.8 to a maximum of 2.2 mm, or 1 to 1 mm, while the thickness of the bottom window material can be 0.3 to a maximum of 3.2 mm, 0.4 to a maximum of 2.7 mm, 0.8 to a maximum of 2.2 mm, or 1 to 1 mm, as long as the overall thickness of the window does not exceed the overall thickness of the pad.

[0033] The top window material may have a diameter (or length and width) of from 2, 3, or 4 up to 60 mm, up to 50 mm, up to 40 mm, up to 30 mm, up to 25 mm, up to 20 mm, up to 15 mm, or up to 10 mm. The gap 44 between the top window peripheral surface 32 and the polished window area surface 16 may be from 1, 2, 3, 4, 5, 7, 10, 15, or 20 up to 40 mm or up to 35 mm. The distance from the bottom window peripheral surface 42 to the opposing bottom window peripheral surface 42 may be from 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10 up to 75 mm, up to 70 mm, up to 60 mm, up to 50 mm, up to 40 mm, up to 30 mm, or up to 20 mm.

[0034] Any gap 44 present inward from the bottom window peripheral surface 42 will necessarily have a dimension smaller than the distance from the bottom window peripheral surface 42 to the opposing bottom window peripheral surface 42, but may have a dimension in a direction parallel to the polished surface 11 that is greater than 0 mm, greater than 0.5 mm, greater than 1 mm, greater than 2 mm, greater than 3 mm, greater than 4 mm, greater than 5 mm, greater than 6 mm, greater than 7 mm, greater than 8 mm, greater than 9 mm, or greater than 10 mm, up to 40 mm, up to 38 mm, up to 35 mm, up to 30 mm, up to 25 mm, or up to 20 mm. Any gap 44 from the bottom window peripheral surface 42 to the subpad layer window area surface 25 can be 0 mm or can be from 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm up to 40 mm, up to 35 mm, up to 30 mm, up to 25 mm, up to 20 mm, up to 15 mm, up to 10 mm, or up to 5 mm.

[0035] The depth of recess 15 can be, for example, greater than 0.1 millimeters (mm), greater than 0.2 mm, or at least 0.3 mm and up to 1.1 mm, 1 mm, 0.8 mm, 0.6 mm, or 0.4 mm. Having a thinner abrasive material in the peripheral portion of the polishing layer adjacent to upper window material 30 than in other areas of pad 100, as shown in FIGS. 2A-2D, 3A-3D, and 4A-4D, can facilitate flexibility during use. Similarly, the width of the peripheral portion can be tailored to provide the desired mechanical response for the pad material and design. The width of the peripheral region can be, for example, at least 0.05 millimeters (mm), at least 0.1 mm, at least 0.2 mm, or at least 0.3 mm and up to 1.1 mm, 1 mm, 0.8 mm, 0.6 mm, or 0.4 mm.

[0036] The top window material 30 can include a polymer or a blend of polymers. For optical detection systems, the top material 30 must have sufficient transmittance at the wavelength of light used for optical metrology. It can be useful if the 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 polyurethane, acrylic polymers, and cyclic olefin copolymers (e.g., TOPAS 8007).

[0037] The upper window material 30 can be made from an aliphatic polyisocyanate-containing material ("prepolymer"). The prepolymer is the reaction product of an aliphatic polyisocyanate (e.g., diisocyanate) and a hydroxy-containing material. The prepolymer is then cured with a curing agent. Preferred aliphatic polyisocyanates include methylene bis-4,4'cyclohexyl isothiocyanate, 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-isocyanate-3,3, Preferred aliphatic polyisocyanates include, but are not limited to, 5-trimethyl-5-isocyanatomethylcyclohexane, methylcyclohexylene 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. Preferred aliphatic polyisocyanates have less than 10% by weight of unreacted isocyanate groups.

[0038] The curing agent may be a polydiamine. Preferred polydiamines include diethyltoluenediamine (DETDA), 3,5-dimethylthio-2,4-toluenediamine and their isomers, 3,5-diethyltoluene-2,4-diamine and their isomers, 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'-dialkyldiaminodiphenylmethane, p,p'-methylene Examples of suitable curing agents include, but are not limited to, toluene-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'-dimethyldiphenylmethane, 2,2',3,3'-tetrachlorodiaminodiphenylmethane, 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 curing agents include both primary and secondary amines.

[0039] In addition, other curing agents, such as diols, triols, tetraols, or hydroxy-terminated curing agents, may be added to the polyurethane compositions described above. Suitable diol, triol, and tetraol groups include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, low 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-(β-hydroxyethyl)ether, hydroquinoline-di-(β-hydroxyethyl)ether, and mixtures thereof. Preferred hydroxy-terminated curing agents 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 curing agent and the amine curing agent may contain one or more saturated, unsaturated, aromatic, and cyclic groups. Furthermore, the hydroxy-terminated curing agent and the amine curing agent may contain one or more halogen groups. The polyurethane composition may be formed using a blend or mixture of curing agents. However, if desired, the polyurethane composition may be formed using a single curing agent.

[0040] The bottom window material 40 is an elastomeric material. As used herein, "elastomeric material" means a material that deforms when subjected to a force but substantially returns to its original shape when the force is removed. One or more voids 44 allow the elastomeric material of the bottom window material 40 to deform into the voids 44 when the pad is under downforce during polishing. The bottom window material 40 can substantially return to its original shape when the downforce is removed. In particular, although the thickness of the bottom window material 40 will decrease under downforce during polishing, a portion of the bottom window material 40 may deform into the void spaces 44. For example, as shown in FIG. 2B, when subjected to downforce, the bottom window material 40 may deform into void spaces 44 above and adjacent to the bottom window material 40. As another example, when subjected to downforce, the bottom window material may deform into void spaces 44 inward from the bottom window peripheral surface 42, as shown in FIGS. 3A-3D, 4A-4B, and 5. As yet another example, the bottom window material 40 can deform into a gap 44 between the bottom window peripheral surface 42 and the subpad window area surface 25, as shown in Figures 4B, 4C, and 5. This compression reduces deformation forces on the polishing layer, specifically the polishing surface. The compressibility of the bottom can be selected to substantially match the compressibility of the surrounding subpad material, the surrounding abrasive material, or both. Because the window extends to the bottom edge of the pad, reflection and refraction of the signal wave at solid / gas or solid / vacuum interfaces is avoided.

[0041] The elastomeric material of the bottom window material 40 preferably has a lower modulus of elasticity than the top window material 30. Desirably, the elastomeric material will have a refractive index and optical transmittance similar to that of the top window layer. A wide variety of transparent elastomers may be used, such as, for example, polyurethanes, polyolefins, polyamides, polyacrylates, styrenic block copolymers, and silicone elastomers. A preferred family of materials is silicone elastomers. Elastomeric materials that can be easily cast or molded into the appropriate shape are desirable.

[0042] The polishing layer 10 may have a tensile storage modulus of, for example, 300-400 MPa, while the subpad layer 20 may have a tensile storage modulus of, for example, 5-30 MPa. The overall composite compressibility is significantly affected by the relative layer thicknesses. The pad design of the present invention allows for a simple method for selecting an appropriate lower window layer material. For example, standard compressibility test methods can be used on test samples of the pad stack and window stack, allowing for rapid compressibility matching prior to any pad manufacturing.

[0043] The abrasive layer material 14 may include a polymer. The abrasive may be opaque through the thickness of the abrasive layer 101. Pores may be provided, for example, by the addition of hollow flexible polymer elements (e.g., hollow microspheres), blowing agents, frothing, or supercritical carbon dioxide. Examples of polymeric materials for the abrasive layer include polyurethane, polycarbonate, polysulfone, nylon, polyether, polyester, polystyrene, acrylic polymers, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, polybutadiene, polyethyleneimine, polyethersulfone, polyamide, polyetherimide, polyketone, epoxy resin, silicone, copolymers thereof (e.g., polyether-polyester copolymers), and combinations or blends thereof. The abrasive layer may include a polymer that is a polyurethane formed by the reaction of one or more polyfunctional isocyanates with one or more polyols. For example, a polyisocyanate-terminated urethane prepolymer may be used. The polyfunctional isocyanate used in forming the polishing layer of the chemical mechanical polishing pad of the present invention can be selected from the group consisting of aliphatic polyfunctional isocyanates, aromatic polyfunctional isocyanates, and mixtures thereof. For example, the polyfunctional isocyanate used in forming 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, cyclohexane diisocyanate, and mixtures thereof. The polyfunctional isocyanate can be an isocyanate-terminated urethane prepolymer formed by reacting a diisocyanate with a prepolymer polyol. The isocyanate-terminated urethane prepolymer may have 2 to 12 weight percent, 2 to 10 weight percent, 4 to 8 weight percent, or 5 to 7 weight percent unreacted isocyanate (NCO) groups.

[0044] 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 may be selected from the group consisting of polytetramethylene ether glycol (PTMEG), ester-based polyols (ethylene adipate, butylene adipate, etc.), polypropylene ether glycol (PPG), polycaprolactone polyols, copolymers thereof, and mixtures thereof. For example, the prepolymer polyol may be selected from the group consisting of PTMEG and PPG. When the prepolymer polyol is PTMEG, the isocyanate-terminated urethane prepolymer may have an unreacted isocyanate (NCO) concentration of 2 to 10 wt % (more preferably 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., e.g., PET-80A, PET-85A, PET-90A, PET-93A, PET-95A, PET-60D, PET-70D, and PET-75D); Adiprene® prepolymers (available from Chemtura, e.g., LF800A, LF900A, LF910A, LF930A, LF931A, LF939A, LF950A, LF952A, LF600D, LF601D, LF650D, LF667, LF700D, LF750D, LF751D, LF752D, LF753D, and L325); and Andur® prepolymers (available from Anderson Development Available from Polypropylene Glycol Company, for example, 70APLF, 80APLF, 85APLF, 90APLF, 95APLF, 60DPLF, 70APLF, and 75APLF. When the prepolymer polyol is PPG, the isocyanate-terminated urethane prepolymer may have an unreacted isocyanate (NCO) concentration of 3 to 9 wt % (more preferably 4 to 8 wt %, and most preferably 5 to 6 wt %). Examples of commercially available PPG-based isocyanate-terminated urethane prepolymers include PPT-80A, PPT-90A, PPT-95A, PPT-65D, and PPT-75D available from COIM USA, Inc.; Adiprene® prepolymers (LFG963A, LFG964A, and LFG740D available from Chemtura); and Andur® prepolymers (8000APLF, 9500APLF, 6500DPLF, and 7501DPLF available from Anderson Development Company). The isocyanate-terminated urethane prepolymer may be a low-free isocyanate-terminated urethane prepolymer having a free toluene diisocyanate (TDI) monomer content of less than 0.1% by weight. Non-TDI-based isocyanate-terminated urethane prepolymers can also be used.For example, isocyanate-terminated urethane prepolymers such as those formed by reacting a polyol such as 4,4'-diphenylmethane diisocyanate (MDI) and polytetramethylene glycol (PTMEG) with an optional diol 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 (e.g., 27-85A, 27-90A, 27-95A, etc., available from COIM USA, Inc.); Andur® prepolymers (e.g., IE75AP, IE80AP, IE 85AP, IE90AP, IE95AP, IE98AP, etc., available from Anderson Development Company); and Vibrathane® prepolymers (e.g., B625, B635, B821, etc., available from Chemtura).

[0045] The subpad material 24 may include a polymeric material. The subpad material may be more compliant (or more elastic) than the abrasive material. The subpad 102 may include a porous layer. Examples of polymeric materials for the subpad layer include polyurethane, polycarbonate, polysulfone, nylon, epoxy resin, polyether, polyester, polystyrene, acrylic polymer, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, polybutadiene, polyethyleneimine, polyethersulfone, polyamide, polyetherimide, polyketone, silicone, copolymers thereof (e.g., polyether-polyester copolymers), and combinations or blends thereof.

[0046] The optional encapsulation layer 50 can provide one or more of the following benefits: facilitating insertion of the window 103 into the pad with proper alignment; providing a uniform surface to the bottom of the pad; preventing any adhesive from leaking between the side edges of the window 103 and the polishing layer 101, the subpad 102, or both; helping to hold the window 103 in place; and preventing any slurry from leaking to the bottom side of the polishing pad 100. The encapsulation layer can be, for example, a polymer such as polyester. The encapsulation layer can be a non-adhesive layer. The encapsulation layer can have a thickness of, for example, from 0.025 mm, from 0.05 mm, from 0.1 mm, to a maximum of 1 mm.

[0047] Polishing pads as disclosed herein can be made by a variety of processes, including inserting a separate window assembly into a pad with a matching opening, adding a top window material 30 to a partially assembled pad that already has a cast in the bottom window material 40 in place in the subpad layer, or inserting the window assembly into a net-shaped mold that is used to make a bottom layer blank followed by lamination of the polishing layer.

[0048] An optional pressure sensitive adhesive may be applied on the bottom of the pad to promote adhesion of the pad to the platen during polishing.

[0049] A method for using a polishing pad as disclosed herein includes providing a substrate to be polished, providing a polishing pad as disclosed herein, and optionally providing a slurry on the polishing pad; contacting the polishing pad with the substrate, moving the substrate and the polishing pad relative to each other (e.g., in a rotational motion); transmitting a signal wave through a window and detecting the signal wave reflected from the substrate through the window to determine when polishing is complete. When optical detection is used, the use of a translucent slurry is preferred. According to a preferred method, during polishing, both optical detection (e.g., cylindrical or non-cylindrical light waves) and vibration detection (e.g., acoustic waves) are used during the polishing of a single substrate.

[0050] The present disclosure further includes the following aspects.

[0051] Aspect 1: A polishing pad for chemical mechanical polishing, comprising: a polishing layer having a polishing surface, a polishing-layer interface opposite the polishing surface, and a polishing window area surface extending from the polishing surface to the polishing interface, wherein the polishing layer comprises a polishing material, a subpad layer having a subpad interface adjacent to the polishing interface, a bottom surface opposite the subpad interface, and a bottom window area interface extending from the bottom surface to the polishing-layer interface, wherein the subpad layer comprises a subpad material and a window extending through the polishing pad from the polishing surface to a back surface of the pad, wherein the window comprises: an upper window material having a polishing surface, an upper window peripheral surface, and an upper window interface, wherein the upper window peripheral surface is adjacent to the upper window area surface and is separated from the upper window area surface so as not to directly contact the window area surface; a bottom window material having a bottom window interface, a bottom window peripheral surface, and a bottom window bottom surface bonded to the bottom window material, the bottom window material being elastic and capable of deforming 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 the subpad material and the top window material or between the combination, or (b) between the bottom window material and the polishing material to prevent particles or liquids used in chemical mechanical polishing from passing from above the polishing layer to below the subpad layer, the pad including a path in the window region for transmitting columnar or non-columnar light through the thickness of the pad, a vibration signal can be transmitted through the top window material, and the bottom window material enables acoustic endpoint detection.

[0052] Aspect 2: The polishing pad of aspect 1, wherein the upper window polishing surface is recessed below the polishing surface.

[0053] Aspect 3: The polishing pad of Aspect 1 or 2, having a void disposed inwardly from the bottom window peripheral surface, the void extending from the bottom window interface to the bottom window bottom surface.

[0054] Embodiment 4: The polishing pad of any one of embodiments 1-3, having a void disposed between the bottom window peripheral surface and the subpad layer window area surface.

[0055] Embodiment 5: The polishing pad of embodiment 4, having a void disposed between the bottom window peripheral surface and the subpad layer window area surface.

[0056] Embodiment 6: The polishing pad of any one of embodiments 1-5, comprising an encapsulation layer adjacent to the bottom surface of the bottom window.

[0057] Aspect 7: A polishing pad as described in aspect 6, wherein the encapsulant extends across a gap disposed between the bottom window peripheral surface and the subpad layer window area surface, across a gap disposed inward from the bottom window peripheral surface extending from the bottom window interface to the bottom window bottom surface 41, or both, and the encapsulant is transparent.

[0058] Embodiment 8: The polishing pad of any one of embodiments 1-7, having an adhesive between the top window material and the bottom window material.

[0059] Aspect 9: The polishing pad of any one of Aspects 1-8, wherein the top window interface is in direct contact with the bottom window interface.

[0060] Aspect 10: A polishing method comprising: providing a substrate to be polished; providing a polishing pad as described in claim 1; providing a slurry on the polishing pad; polishing by moving the substrate relative to the polishing pad; and monitoring the polishing by (a) transmitting light waves through the top window material and the void and detecting light waves reflected from the substrate; (b) transmitting a vibration signal through the top window material, the polishing layer material, or both, through the bottom window material, or by both (a) and (b).

[0061] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., the range "up to 25% by weight, more specifically 5% to 20% by weight" includes the endpoints and all intermediate values ​​in the range "5% to 25% by weight," etc.). Additionally, stated upper and lower limits can be combined to form ranges (e.g., "at least 1% by weight or at least 2% by weight" and "up to 10% or 5% by weight" can be combined to form the ranges "1 to 10% by weight," "1 to 5% by weight," "2 to 10% by weight," or "2 to 5% by weight").

[0062] The present disclosure can either comprise, consist of, or consist essentially of any suitable components disclosed herein. The present disclosure can additionally or alternatively be formulated to be free or substantially free of any components, materials, ingredients, adjuvants, or species used in prior art compositions or that are not necessary to achieve the function and purpose of the present disclosure.

[0063] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety, except that if a term in an incorporated reference conflicts or conflicts with a term in the present application, the term in the present application takes precedence over the conflicting term in the incorporated reference.

[0064] Unless otherwise specified herein, all test standards are the latest standards in effect as of the filing date of this application or, if priority is claimed, as of the filing date of the earliest priority application in which the test standard appears. [Explanation of symbols]

[0065] 1 pad 10 Polishing layer 11 Polished surface 12 grooves 13 Polishing layer interface 14 Abrasive layer material 15 recess 16 Polished window area surface 20 Subpad Layer 21 Bottom of subpad 23 Subpad interface 24 Sub-pad material 25 Subpad layer window area surface 30 Upper window material 31 Polished surface 32 Upper window periphery 33 Upper window interface 40 Bottom window material 41 Bottom window bottom 42 Bottom window periphery 43 Bottom window interface 44 void 49 Monolithic window material 50 Encapsulation Layer 100 Window Area 101 Polishing layer 102 Subpad 103 Window

Claims

1. 1. A polishing pad for chemical mechanical polishing, comprising: a polishing layer having a polishing surface, a polishing-layer interface facing the polishing surface, and a polishing window area surface extending from the polishing surface to the polishing interface, the polishing layer comprising an abrasive; a subpad layer having a subpad interface adjacent the polishing layer interface, a bottom surface opposite the subpad interface, and a bottom window region interface extending from the bottom surface to the polishing layer interface, the subpad layer comprising a subpad material; a window extending through the polishing pad from the polishing surface to a back surface of the pad, the window comprising: an upper window material having a polished surface, an upper window perimeter surface, and an upper window interface, the upper window perimeter surface being adjacent to the upper window area surface and separated from the upper window area surface so as not to directly contact the window area surface; a bottom window material having a bottom window interface bonded to the top window interface, a bottom window peripheral surface, and a bottom window bottom surface, the bottom window material being elastic and capable of deforming into a void space adjacent to the bottom window material when the pad is under pressure during polishing; Equipped with a seal is formed between (a) a subpad material and the top window material, the bottom window material, or a combination of the top and bottom window materials to form a seal with the subpad material, or (b) a subpad material is formed between the bottom window material and the polishing material to prevent particles or liquids used in the chemical mechanical polishing from passing from above the polishing layer to below the subpad layer; the pad includes passages in the window area for transmitting cylindrical or non-cylindrical light through the thickness of the pad, and a vibration signal can be transmitted through the top and bottom window materials, enabling acoustic endpoint detection; Polishing pad.

2. The polishing pad of claim 1 , wherein the upper window polishing surface is recessed below the polishing surface.

3. 10. The polishing pad of claim 1, further comprising a void disposed inwardly from the bottom window peripheral surface extending from the bottom window interface to the bottom window surface.

4. 10. The polishing pad of claim 1, further comprising a gap disposed between the bottom window peripheral surface and the subpad layer window area surface.

5. 5. The polishing pad of claim 4, further comprising an air gap disposed between the bottom window peripheral surface and the subpad layer window area surface.

6. 10. The polishing pad of claim 1, further comprising an encapsulation layer adjacent the bottom surface of the bottom window.

7. 7. The polishing pad of claim 6, wherein the encapsulant extends across a gap disposed between the bottom window peripheral surface and the subpad layer window area surface, across a gap disposed inward from the bottom window peripheral surface extending from the bottom window interface to the bottom window bottom surface 41, or both, and the encapsulant is transparent.

8. 10. The polishing pad of claim 1, further comprising an adhesive between the top window material and the bottom window material.

9. The polishing pad of claim 1 , wherein the top window interface is in direct contact with the bottom window interface.

10. Providing a substrate to be polished; Providing the polishing pad of claim 1; providing a slurry on the polishing pad; polishing the substrate by moving it relative to the polishing pad; (a) transmitting light waves through the top window material and the gap and detecting light waves reflected from the substrate; (b) transmitting vibration signals through the top window material, the polishing layer material, or both, and through the bottom window material, or both (a) and (b), thereby monitoring polishing. A polishing method comprising:

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