TW201742705A - Pad window insert - Google Patents

Abstract

A polishing pad includes a polishing layer having a polishing surface, an adhesive layer on a side of the polishing layer opposite the polishing layer, and a solid light-transmitting window extending through and molded to the polishing surface. The solid light-transmitting window has an upper portion with a first lateral dimension and a lower portion with a second lateral dimension that is smaller than the first lateral dimension. A top surface of the solid light-transmitting window coplanar with the polishing surface and a bottom surface of the solid light-transmitting window coplanar with a lower surface of the adhesive layer.

Description

Plug-in window

A windowed polishing pad, a system incorporating the polishing pad, and a process for making and using the polishing pad are described.

In the fabrication of modern semiconductor integrated circuits (ICs), it is often desirable to planarize the outer surface of the substrate. For example, planarization may be required to throw away the conductive fill layer until the top surface of the underlying layer is exposed, leaving a conductive material between the raised patterns of the insulating layer to form vias, plugs, and wires while on the substrate A conductive path is provided between the thin film circuits. In addition, planarization may be required to level and thin the oxide layer to provide a flat surface for lithographic etching.

One of the methods for achieving planarization or surface topography removal of a semiconductor substrate is chemical mechanical polishing (CMP). Conventional chemical mechanical polishing (CMP) processes involve pressing a substrate against a rotating polishing pad in the presence of a slurry.

Generally, in order to decide whether or not to stop polishing, it is necessary to detect when the desired surface flatness or layer thickness is achieved, or when the underlying layer is exposed. Many techniques have been developed to perform in situ detection of the endpoint during the CMP process. For example, an optical monitoring system for measuring the uniformity of layers on a substrate in situ during polishing of the layer has been applied. The optical monitoring system can include: a light source that directs the light beam toward the substrate during polishing; a detector that measures light reflected from the substrate; and a computer that can analyze the image from the detector Signal and calculate if the end point has been detected. In some CMP systems, the light beam is directed through the window in the polishing pad toward the substrate.

A window can be attached to the underside of the polishing pad such that a portion of the window is supported in a recess in the platform. This allows for a large surface area contact between the window and the polishing pad to increase the bond strength between the window and the polishing pad.

In one aspect, the polishing apparatus includes a platform having a flat upper surface, a groove formed in the upper surface, the groove having a bottom surface, and the channel is coupled to the bottom surface of the groove, the polishing apparatus also including a polishing pad, The polishing pad includes a polishing layer, a polishing surface, a lower side, and an opening through the lower side, the opening having a smaller lateral dimension than the groove, the opening aligning the channel. The solid light transmission window has a first portion, the first portion being at least partially disposed in the opening in the polishing pad, the solid light transmitting window having a second portion, the second portion being at least partially disposed in the groove in the platform, the second portion The portion has a larger lateral dimension than the first portion and extends below the polishing layer, and the second portion of the window is adhesively attached to the underside of the polishing pad.

Implementations of the invention may include one or more of the following features. The first portion of the window blocks the opening in the polishing pad. The top surface of the first portion of the window may be coplanar with the upper surface of the platform. The bottom surface of the groove may be parallel to the upper surface of the platform. The lower surface of the second portion of the window can contact the lower surface of the recess. The lower surface of the second portion of the window may not adhere to the lower surface of the recess. The polishing apparatus can also include an adhesive layer across the polishing layer. The adhesive layer can include a double-sided adhesive tape. The adhesive layer can be adjacent to the polishing layer. The underside of the polishing pad can be attached to the upper surface of the platform by adhesive adhesion. The top surface of the second portion of the window may be adhesively attached to the underside of the polishing pad by an adhesive layer. The top surface of the second portion of the window is adhesively attached to the underside of the polishing pad. The polishing pad can include a polishing layer. The polishing pad can include a polishing layer and a lower layer, the lower layer being more incompressible than the polishing layer. The second portion may have a second to ten times greater than the first portion, for example about eight times the lateral dimension. The second portion of the window can laterally fill the grooves in the platform. The polishing pad can have a thickness of less than 1 mm. The polishing apparatus can also include the optical fiber being disposed in the channel and positioned to receive or receive light through the first portion of the window. The optical fiber can be wider than the first portion of the window. The sides of the groove may be sloped and the second portion of the window may be sloped.

In another aspect, a method of assembling a window for use in a polishing apparatus includes the steps of: forming an opening through a polishing pad, the polishing pad comprising a polishing layer having a polishing surface and a lower side; forming a solid light transmission window, The solid light transmission window has a first portion and a second portion, the second portion having a lateral dimension greater than the first portion; inserting the first portion of the window into the opening of the polishing pad; attaching the top surface of the second portion of the window to the polishing pad a lower side; and placing the polishing pad and window on the platform such that the second portion of the window fits into a recess in the flat upper surface of the platform and the underside of the polishing pad adheres to the flat upper surface of the platform.

Implementations of the invention may include one or more of the following features. An adhesive layer may be formed on the bottom of the polishing layer, and the liner covers the adhesive, a portion of the liner is removed around the opening, and the top surface of the second portion of the window is contactable with the adhesive in the removed portion of the liner .

Implementations of the invention may include the following potential advantages. A strong bond can be formed between the window and the thin polishing pad, reducing the likelihood of slurry leakage and reducing the likelihood that the window will be pulled away from the polishing pad due to shear forces from the substrate being polished. In addition, the polishing pad enhances wafer-to-wafer uniformity of the spectrum reflected from the substrate, especially at short wavelengths.

Details of one or more embodiments will be set forth in the accompanying drawings and the description below. Other aspects, features, and advantages of the invention will be apparent from the description and drawings.

A window can be attached to the underside of the polishing pad such that a portion of the window is supported in a recess in the platform. This allows for a large surface area contact between the window and the polishing pad to increase the bond strength between the window and the polishing pad.

As shown in FIG. 1, CMP apparatus 10 includes a polishing head 12 for gripping semiconductor substrate 14 against polishing pad 18 on platform 16. The CMP apparatus can be constructed as described in U.S. Patent No. 5,738,574, the entire disclosure of which is incorporated herein by reference.

The substrate can be, for example, a product substrate (eg, including a plurality of memory or processor dies), a test substrate, a bare substrate, and a gating substrate. The substrate can be at various stages of integrated circuit fabrication, such as the substrate can be a bare wafer, or the substrate can include one or more deposited and/or patterned layers. The term substrate can include circular discs and rectangular sheets.

The active portion of the polishing pad 18 can include a polishing layer 20 having a polishing surface 24 and a bottom surface 22 that can contact the substrate and the bottom surface 22 secured to the platform by an adhesive layer 28 (eg, an adhesive tape) 16. Adhesive layer 28 can be a pressure sensitive adhesive. In addition to the adhesive tape and any liner, the polishing pad can be constructed, for example, from a single layer of pad, wherein the polishing layer 20 can be formed from a thin, durable material suitable for use in a chemical mechanical polishing process. Thus, the layer of polishing pad can be comprised of a single layer of polishing layer 20 and an adhesive layer 28 (and optionally a liner that can be removed when the polishing pad is mounted to the polishing platform).

Polishing layer 20 can be constructed, for example, of foamed polyurethane with at least some openings in polishing surface 24. Adhesive layer 28 can be a double-sided adhesive tape, for example, a thin layer of polyethylene terephthalate (PET) having an adhesive (eg, a pressure sensitive adhesive) on both sides (eg, Mylar®). This polishing pad is available from Fujibo, Tokyo, Japan, and the polishing pad is marketed under the trade name H7000HN.

Referring to Figure 2, in some implementations, polishing pad 18 has a radius R of 15.0 inches (381.00 mm) to 15.5 inches (393.70 mm) and has a corresponding diameter of 30 inches to 31 inches. In some implementations, the polishing pad 18 can have a radius of 21.0 inches (533.4 mm) to 21.5 inches (546.1 mm) and a corresponding diameter of 42 inches to 43 inches.

Referring to FIG. 3A, in some implementations, a trench 26 can be formed in the polishing surface 24. The grooves may present a "waffle" pattern, for example, a cross hatch pattern of vertical grooves with slanted sidewalls dividing the polished surface into a plurality of rectangular (eg, square) regions.

Returning to Fig. 1, typically, the polishing pad material can be wetted by chemical polishing liquid 30, which can include abrasive particles. For example, the slurry can include potassium hydroxide (KOH) and fumed-silica particles. However, some polishing processes can be "abrasive-free."

As the platform rotates about its central axis, the polishing head 12 presses against the substrate 14 against the polishing pad 18. In addition, the polishing head 12 typically rotates about its central axis and translates across the surface of the platform 16 through the drive shaft or translation arm 32. The pressure and relative motion between the substrate and the polishing surface, together with the polishing solution, results in polishing of the substrate.

Optical apertures 34 are formed in the top surface of the platform 16. An optical monitoring system including a light source 36 (such as a laser) and a detector 38 (such as a photodetector) can be positioned below the top surface of the platform 16. For example, the optical monitoring system can be positioned in a chamber within the platform 16 that optically communicates with the optical aperture 34 and can rotate with the platform. One or more optical fibers 50 can carry light from source 36 to the substrate and from the substrate to detector 38. For example, the optical fiber 50 can be a bifurcated optical fiber having a stem portion 52 proximate (eg, abutting) a window 40 in the polishing pad; a first foot portion 54 coupled to the light source 36; and a second leg portion 56 coupled to Detector 38.

The optical opening 34 can be filled with a transparent solid body (such as a quartz block) (in this case, the optical fiber does not abut the window 40, but can abut the solid body in the optical opening), or the optical opening 34 can be a void . In one implementation, the optical monitoring system and optical apertures can form part of the module, and the module fits into corresponding recesses in the platform. Alternatively, the optical monitoring system can be a stationary system located below the platform and the optical aperture can extend through the platform. Light source 36 can utilize any wavelength from far infrared to ultraviolet, such as red light (although broadband spectrum such as white light can also be used), and detector 38 can be a spectrometer.

A solid state window 40 is formed in the upper polishing pad 18 and aligned with the optical opening 34 in the platform. The window 40 and the opening 34 can be positioned such that the window 40 and the opening 34 can see the substrate 14 held by the polishing head 12 during at least a portion of the rotation of the platform, regardless of the translational position of the polishing head 12.

At least during the period in which the window 40 is adjacent to the substrate 14, the light source 36 projects through the apertures 34 and the window 40 to strike the surface of the substrate 14 above. Light reflected from the substrate forms a composite beam that can be detected by detector 38. The light source and the detector are coupled to a computer not shown, and the computer receives the measured light intensity from the detector and uses the measured light intensity to determine the polishing end point, for example, by detecting the exposure of the new layer. A sudden change in the reflectivity of the substrate; the thickness removed from the outer skin (such as the transparent oxide layer) is calculated by using the principle of interference; by monitoring the spectrum of the reflected light and detecting the target spectrum; The measurement spectrum matches the reference spectrum from the database and determines where the linear function of the index value of the fitted reference spectrum reaches the target value; or by monitoring the signal that meets the predetermined endpoint criteria.

One of the problems of loading a generally large rectangular window (eg, a 2.25 inch by 0.75 inch window) into a very thin polishing layer is peeling during polishing. In particular, the lateral friction from the substrate during polishing can be greater than the adhesion of the molding window to the sidewalls of the polishing pad.

Returning to Figure 2, a small window 40 can be used, such as less than about 3 mm in diameter, to reduce the friction applied by the substrate during polishing. For example, the upper portion of the window 40 can be a circular region about 3 mm wide with a center distance D of about 7.5 inches (190.50 mm) from the center of the polishing pad 18 of 30 to 31 inches in diameter, or The distance D from the center of the polishing pad 18 having a center distance of 42 to 43 inches is about 9 inches to 11 inches.

Window 40 can have a nearly circular shape (and possibly other shapes, such as a rectangle). If the window is extended, the longer dimension of the window can be substantially parallel to the radius of the polishing pad passing through the center of the window. The window 40 can have a jagged outer edge 42, for example, the outer edge can be longer than a similarly shaped circle or rectangle, such as (in top view) in a zigzag or other meandering pattern. This increases the surface area of the window in contact with the sidewalls of the polishing pad and can thereby enhance the adhesion of the window to the polishing pad.

Referring to FIG. 3A, the window 40 includes an upper portion 40a and a lower portion 40b. The window 40, including the upper portion 40a and the lower portion 40b, may be a unitary single piece of homogeneous material. The upper portion 40a is longitudinally aligned with the lower portion 40b, but is laterally smaller (i.e., in one or two directions parallel to the polishing surface) than the lower portion 40b. Therefore, a portion of the polishing layer 20 protrudes above the lower portion 40b, so that the edge projecting beyond the lower portion 40b of the upper portion 40a forms the window sill 49. The lower portion 40b can project laterally beyond the upper portion 40a at all sides of the window 40, or the lower portion 40b can laterally project beyond the upper portion 40a from the opposite sides of the window 40, but other along the window 40 Side alignment. The upper surface that protrudes beyond the lower portion 40b of the upper portion 40a may be a substantially flat surface. The upper portion 40a can be located within the center of the lower portion 40b, for example, concentric with the lower portion 40b. The lateral dimension of the lower portion 40b may be 2 to 10 times larger than the lateral dimension of the upper portion 40a, such as about 8 times larger. For example, if the window 40 is circular, the upper portion 40a can have a diameter of 3 mm and the lower portion 40b can have a diameter of 25 mm.

The thickness of the upper portion 40a may be approximately the same as the lower portion 40b. Alternatively, the upper portion 40a may be thicker or thinner than the lower portion 40b.

The upper portion 40a of the window 40 can project into the opening in the adhesive layer 28. The edge of the adhesive layer 28 (e.g., adhesive tape) can abut the side of the upper portion 40a of the window 40. The lower portion 40b of the window can project into the recess 78 in the top surface 76 of the platform 16.

The upper portion 40a of the window is as thick as the combination of the polishing layer 20 and the adhesive layer 28. The top surface 44 of the upper portion 40a of the window 40 is coplanar with the polishing surface 24. The bottom of the upper portion 40a of the window 40 can be coplanar with the bottom surface of the adhesive layer 28.

The upper surface of the lower portion 40b is fixed to the lower side of the polishing layer 20 by a portion of the adhesive layer 28. The outer edge of the upper portion 40a of the window 40 can optionally be secured to the inner sidewall edge 48 of the polishing layer 20, for example, by an additional adhesive.

The increased joint surface area between the window 40 and the polishing layer 20 provided by the connection on the sill 49 provides a strong bond, reduces the likelihood of slurry leakage, and reduces windowing due to shear from the substrate being polished. 40 is the possibility of being pulled away from the polishing pad 18. The trunk portion 52 of the optical fiber abuts or nearly abuts the lower portion 40b. In some implementations, the trunk portion 52 can be wider than the upper portion 40a of the window 40.

The bottom surface of the lower portion 40b of the window may non-adhesively abut the bottom of the groove 78 in the upper surface 76 of the platform 16 (e.g., supported on the bottom of the groove 78 in the upper surface 76 of the platform 16), or may Fixed to the bottom of the groove 78 in the upper surface 76 of the platform 16. In some implementations, the lower portion 40b of the window fills the recess 78.

Referring to FIG. 3B, the polishing pad 18 can also include a liner 70 that spans the bottom surface 22 of the polishing pad 18 except for the block covered by the underlying portion 40b of the window 40 prior to mounting on the platform 16. Adhesive layer 28 on top. The liner 70 can be a thin flexible material (e.g., paper) and has a release coating that can be stripped from the adhesive layer 28. In some implementations, the liner can be a non-compressible and generally fluid impermeable layer, such as polyethylene terephthalate (PET), such as Mylar®. In use, the liner 70 can be manually stripped from the adhesive layer 28 and the polishing layer 20 applied to the platform 16 using the adhesive layer 28. However, the liner 70 does not span the window 40, but is removed in the block of the lower portion 40b of the window 40 (e.g., a block about 25 cm wide) and immediately adjacent the block to form the aperture 72, The lower portion 40b of the window 40 can be received in the aperture 72.

The polishing pad 18 is very thin, such as less than 2 mm, such as less than 1 mm. For example, the total thickness of the polishing layer 20, the adhesive layer 28, and the liner 70 can be about 0.8 or 0.9 mm. The polishing layer 20 can be about 0.7 or 0.8 mm thick, while the adhesive layer 28 and the liner 70 provide a thickness of about 0.1 mm. The thickness of the grooves 26 can be about half the thickness of the polishing pad, for example, almost 0.5 mm.

To make a polishing pad, a polishing layer 20 is initially formed, and the bottom surface of the polishing layer 20 is covered with a pressure-sensitive adhesive layer 28 and a liner 70, as shown in FIG. The trench 26 may be formed in the polishing layer 20 as part of the pad forming process prior to attachment of the pressure sensitive adhesive layer 28, or the trench 26 may be cut in the polishing layer 20 after the polishing pad is formed. The grooves 26 may be formed before or after the liner 70 is attached.

Referring now to Figure 5, in some implementations, window 40 can be formed by casting and hardening a polymer in the shape of window 40. In one implementation, the polymer was a mixture of 2 parts Calthane A 2300 and 3 parts Calthane B 2300 (available from Cal Polymers, Inc., Long Beach, California). The liquid polymer mixture can be degassed, such as for 15 to 30 minutes, prior to placement in the opening. The polymer can be hardened at room temperature for about 24 hours, or a heat lamp or oven can be used to shorten the hardening time. In some implementations, the polymer can be poured into the mold and hardened or solidified to form a window 40 in its final shape. In some implementations, the window 40 can be hardened into a large solid block, and then the window 40 in its final shape is formed by processing the solid block of polymer.

In some implementations, the sidewalls 84 of the lower portion 40b can be substantially perpendicular to the bottom surface 46 of the window 40. In some implementations, sidewalls 84 can be formed at an angle to the bottom surface 46, as discussed further in the description of FIG.

The aperture 82 can be punched through the entire polishing pad 18 including the polishing layer 20, the adhesive layer 28, and the liner 70. The aperture 82 can be sized to receive the upper portion 40a of the window 40. In some implementations, the upper portion 40a substantially blocks the aperture 82 of the polishing pad 18. The hole 82 can be punched out from the top of the polishing pad (i.e., the side with the polishing surface), for example, by a machine press. This allows for the positioning and size determination of the portion of the aperture 82 to be highly accurate and repeatable.

A portion of the liner 70 can be stripped or removed from the adhesive layer 28. At this time, the liner 70 does not have to be completely stripped from the polishing pad 18. This portion of the strip liner 70 can expose a portion of the bottom surface 22 of the adhesive layer 28 around the aperture 82. This portion that is stripped may also be cut, for example, in a block of window sill 49 that is sized to accommodate bottom portion 40b of window 40, although this step may be performed thereafter.

Referring to Figures 5 and 6, the window 40 is secured to the polishing pad 18 such that the upper portion 40a extends into the aperture 82 and the upper surface of the bottom portion 40b (e.g., window sill 49) contacts the adhesive layer 28. In certain embodiments, the upper portion 40a can be sized to extend substantially through and substantially fill the aperture 82 such that when the sill 49 is adhered to the adhesive layer 28, the upper surface 44 is associated with the polishing surface 24 of the polishing layer 20. flat.

In addition to the lining 70, a window support sheet 74 spanning the window 40 can be provided as appropriate. For example, the window support panel 74 can be secured to a portion of the adhesive layer 28 proximate the window 40. The support sheet 74 may be the same thickness as the liner 70 or thinner than the liner 70. The support sheet 74 may be polytetrafluoroethylene (PTFE) such as Teflon® or another non-adhesive material. The combined polishing pad 18 and window 40 can then be ready for shipment to the customer, for example, in a sealed plastic bag.

Referring now to Figure 7, when the customer receives the combined polishing pad 18 and window 40, the customer can remove the liner 70 (and the window support sheet 74, if present) and then use the adhesive layer 28 to polish the polishing pad 18. Attached to the platform 16. The lower portion 40b of the window 40 is inserted into the recess 78 in the upper surface 76 of the platform 16. In some methods, the liner 70 in the peripheral region of the window 40 can be partially stripped, the lower portion 40b of the window 40 can be inserted into the recess, and then the remainder of the liner can be stripped and the remainder of the polishing pad can be secured. To platform 16.

The shape and size of the lower portion 40b can be determined such that the lower portion 40b substantially fills the recess 78. For example, while the upper surface 76 of the platform 16 contacts the adhesive layer 28, the sidewall 84 of the lower portion 40b can substantially contact the recess 78. All of the side walls 86, and the bottom surface 46 of the window 40 substantially contacts the bottom plate 88 of the recess 78.

In some implementations, the bottom plate 88 of the recess 78 can be substantially parallel to the upper surface 76 of the platform 16. In some implementations, the sidewall 84 of the lower portion 40b is perpendicular to the bottom surface 46 and the sidewall 86 of the recess 78 is perpendicular to the polishing surface 75. Referring to Figure 8, in some implementations, the sidewalls 84 of the lower portion 40b can be formed at an angle that is not perpendicular to the bottom surface 46, such as between 20 and 80 degrees, such as 45 degrees, and the grooves The side walls 86 of 78 may be formed at substantially similar angles such that when the lower portion 40b is inserted into the recess 78, the side walls 84 and the side walls 86 substantially contact each other. For example, the side wall 84 can be angled inwardly from the sill 49 to the bottom surface 46 such that the lower portion 40b forms a tapered cross section. Similarly, sidewalls 86 can be formed to engage the tapered section. In this regard, the inclined sidewalls 84 can cause the window 40 and polishing pad 18 to exhibit self-centering characteristics when the window 40 is inserted into the recess 78 in the angled sidewall 86.

In this regard, the polishing pad 18 is adhered to the platform 16 by the adhesive layer 28 such that the window 40 is retained within the recess 78 in the platform 16. The window 40 can be vertically supported by the bottom plate 88 of the recess 78 and can be held laterally by the side walls 86 of the recess 78. The window 40 can be adhered to the polishing pad by contacting the top surface of the sill 49 with the same adhesive layer that secures the underside of the polishing pad to the platform 16.

Although certain embodiments have been described, the invention is not limited thereto. For example, although a window with a simple circle is described, the window can be more complex, such as rectangular, elliptical, or star shaped. The top portion of the window may protrude beyond one or more sides of the bottom portion. It will be appreciated that a variety of other modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are also within the scope of the following claims.

10‧‧‧CMP equipment
12‧‧‧ polishing head
14‧‧‧Substrate
16‧‧‧ platform
18‧‧‧ polishing pad
20‧‧‧ polishing layer
22‧‧‧ (polished layer) bottom surface
24‧‧‧ Polished surface
26‧‧‧ trench
28‧‧‧Adhesive layer
30‧‧‧ polishing liquid
32‧‧‧Drive shaft or translation arm
34‧‧‧ (optical) opening
36‧‧‧Light source
38‧‧‧Detector
40‧‧‧ window
40a‧‧‧ upper part
40b‧‧‧ below
42‧‧‧ (window) outer edge
44‧‧‧(window) top surface
46‧‧‧(window) bottom surface
48‧‧‧Inside sidewall edge
49‧‧‧ Window sill
50‧‧‧Optical fiber
52‧‧‧Main Department
54‧‧‧First foot
56‧‧‧Second foot
70‧‧‧ lining
72‧‧‧ hole
74‧‧‧(window) support sheet
76‧‧‧ (platform) top surface
78‧‧‧ Groove
82‧‧‧ hole
84‧‧‧ (lower part of the window) side wall
86‧‧‧ (groove) side wall
88‧‧‧ (groove) bottom plate

Figure 1 is a cross-sectional view of a CMP apparatus containing a polishing pad.

Figure 2 is a top plan view of one embodiment of a polishing pad having a window.

Figure 3A is a cross-sectional view of the polishing pad of Figure 2 mounted on the platform.

Figure 3B is a cross-sectional view of the polishing pad of Figure 2.

Figures 4 through 7 illustrate a method of forming a polishing pad.

Figure 8 is a cross-sectional view of another implemented polishing pad mounted on a platform.

Similar element symbols in the various figures indicate similar elements.

Domestic deposit information (please note according to the order of the depository, date, number)

Foreign deposit information (please note in the order of country, organization, date, number)

16‧‧‧ platform

18‧‧‧ polishing pad

20‧‧‧ polishing layer

24‧‧‧ Polished surface

26‧‧‧ trench

28‧‧‧Adhesive layer

40‧‧‧ window

40a‧‧‧ upper part

40b‧‧‧ below

44‧‧‧(window) top surface

46‧‧‧(window) bottom surface

48‧‧‧Inside sidewall edge

49‧‧‧ Window sill

52‧‧‧Main Department

76‧‧‧ (platform) top surface

78‧‧‧ Groove

Claims (10)

A polishing pad assembly comprising: a polishing pad comprising a polishing layer, a polishing surface, a lower side and an opening, the opening passing through the polishing pad; an adhesive layer on the lower side of the polishing pad Adhesive layer spanning the polishing pad, the adhesive layer having an opening aligned with the opening through the polishing pad; a solid light transmission window, the solid light transmission window being a monolithic monolithic body of homogeneous material and including An upper portion and a lower portion, the upper portion being at least partially disposed in the opening in the polishing pad, the lower portion having a lateral dimension greater than one of the upper portions, and the lower portion extending below the polishing pad a top surface of the lower portion of the window is adhesively attached to the lower side of the polishing pad through the adhesive layer; and a removable liner covering the adhesive layer on the lower side of the polishing pad a remaining portion of the window that is uncovered by the lower portion of the window, the adhesive layer being configured such that the liner is removable, and the polishing pad is disposed on a platform such that the polishing pad is the window Attached to the throw The same adhesive layer of the light pad is attached to the platform. The polishing pad assembly of claim 1, further comprising a removable window backing piece covering a bottom surface of the lower portion of the window. The polishing pad assembly of claim 1, wherein the removable liner has an opening to receive the lower portion of the window. The polishing pad assembly of claim 1, wherein the upper portion of the window blocks the opening in the polishing pad. A polishing pad assembly according to claim 4, wherein a top surface of the upper portion of the window is coplanar with the polishing surface. The polishing pad assembly of claim 1, wherein the adhesive layer comprises a pressure sensitive adhesive. The polishing pad assembly of claim 6, wherein the adhesive layer comprises a double-sided adhesive tape. The polishing pad assembly of claim 1, wherein the polishing pad is comprised of the polishing layer. The polishing pad assembly of claim 1, wherein the polishing pad is comprised of the polishing layer and a lower layer that is more incompressible than the polishing layer. The polishing pad assembly of claim 1, wherein the lower portion has a lateral dimension that is two to ten times greater than the upper portion.