TW201817541A - Plug-in window - 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 polishing pad with a window, a system including the polishing pad, and a process for manufacturing and using the polishing pad are described.

In the manufacturing process of modern semiconductor integrated circuits (IC), it is often necessary to flatten the outer surface of the substrate. For example, planarization may be required to remove the conductive fill layer until the top surface of the underlying layer is exposed, leaving conductive material between the raised patterns of the insulating layer to form vias, plugs, and lines on the substrate Conductive paths are provided between the thin film circuits on the. In addition, planarization may be required to level and thin the oxide layer to provide a flat surface for lithographic etching.

One method for achieving planarization or removal of surface topography of a semiconductor substrate is chemical mechanical polishing (CMP). A conventional chemical mechanical polishing (CMP) process involves pressing a substrate against a rotating polishing pad in the presence of a polishing slurry.

Generally, in order to decide whether 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 for in situ detection of endpoints during the CMP process. For example, optical monitoring systems have been used to measure the uniformity of a layer on a substrate in situ during polishing of the layer. The optical surveillance system may include a light source that directs a light beam toward the substrate during polishing; a detector that measures light reflected from the substrate; and a computer that analyzes the light from the detector. Signal and calculate if the end point has been detected. In some CMP systems, the light beam is directed toward the substrate through a window in the polishing pad.

The window can be attached to the underside of the polishing pad so that a portion of the window is supported in a groove in the platform. This may allow large surface area contact between the window and the polishing pad to increase the bonding strength between the window and the polishing pad.

In one aspect, the polishing device includes a platform having a flat upper surface, a groove formed in the upper surface, the groove having a bottom surface, and the channel connected to the bottom surface of the groove. The polishing device also includes 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 has a lateral dimension smaller than the groove, and the opening is aligned with the channel. The solid-state light transmission window has a first portion, the first portion is at least partially disposed in an opening in the polishing pad, the solid-state light transmission window has a second portion, the second portion is at least partially disposed in a groove in the platform, The part has a larger lateral dimension than the first part and extends below the polishing layer. The second part 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 part of the window can block 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 may contact the lower surface of the groove. The lower surface of the second portion of the window may not adhere to the lower surface of the groove. The polishing apparatus may also include an adhesive layer across the polishing layer. The adhesive layer may include a double-sided adhesive tape. The adhesive layer may be adjacent to the polishing layer. The underside of the polishing pad can be adhesively attached to the upper surface of the platform by an adhesive layer. 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 may be adhesively attached to the underside of the polishing pad. The polishing pad may include a polishing layer. The polishing pad may include a polishing layer and a lower layer, and the lower layer is more incompressible than the polishing layer. The second part may have a lateral dimension that is two to ten times larger, such as about eight times, larger than the first part. The second part of the window may fill the groove in the platform laterally. The polishing pad may have a thickness of less than 1 mm. The polishing apparatus may also include an optical fiber positioned in the channel and positioned to direct or receive light through a first portion of the window. The optical fiber may be wider than the first portion of the window. Multiple sides of the groove may be inclined, and the second portion of the window may be inclined.

In another aspect, a method of assembling a window for a polishing device includes the following steps: forming an opening through a polishing pad, the polishing pad including a polishing layer, the polishing layer having a polishing surface and a lower side; and forming a solid light transmission window, the The solid-state light transmission window has a first portion and a second portion, and the second portion has a lateral dimension larger than the first portion; the first portion of the window is inserted into the opening of the polishing pad; and the top surface of the second portion of the window is attached to the The lower side; and placing the polishing pad and the window on the platform so that the second part of the window fits into a groove in the flat upper surface of the platform, and the lower side of the polishing pad is adhered to the flat upper surface of the platform.

Implementations of the invention may include one or more of the following features. The adhesive layer may be formed on the bottom of the polishing layer, and the liner is covered with the adhesive, a part of the liner is removed around the opening, and the top surface of the second part of the window may contact the adhesive in the removed part 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 possibility of slurry leakage and reducing the possibility of the window being pulled away from the polishing pad due to the shear force from the substrate being polished. In addition, polishing pads can improve wafer-to-wafer consistency 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 present invention will be apparent from the description and drawings and the scope of the patent application.

The window can be attached to the underside of the polishing pad so that a portion of the window is supported in a groove in the platform. This may allow large surface area contact between the window and the polishing pad to increase the bonding strength between the window and the polishing pad.

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

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

The effective portion of the polishing pad 18 may include a polishing layer 20 having a polishing surface 24 and a bottom surface 22. The polishing surface 24 may contact the substrate, and the bottom surface 22 is fixed to the platform by an adhesive layer 28 (eg, an adhesive tape). 16. The adhesive layer 28 may be a pressure-sensitive adhesive. In addition to the adhesive tape and any liner, the polishing pad may be composed of, for example, a single-layer pad, wherein the polishing layer 20 may be formed of a thin and durable material suitable for a chemical mechanical polishing process. Therefore, the layers of the polishing pad can be composed of a single polishing layer 20 and an adhesive layer 28 (and optionally a liner that can be removed when the polishing pad is mounted on a polishing platform).

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

Referring to FIG. 2, in some implementations, the 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 may 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, grooves 26 can be formed in the polished surface 24. The grooves can present a "waffle" pattern, for example, a cross hatch pattern of vertical grooves with inclined sidewalls divides the polished surface into a plurality of rectangular (eg, square) regions.

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

When the platform is rotated about its central axis, the polishing head 12 is pressed to the substrate 14 against the polishing pad 18. In addition, the polishing head 12 generally rotates around its central axis and translates across the surface of the platform 16 through a transmission shaft or translation arm 32. The pressure and relative movement between the substrate and the polishing surface, combined with the polishing solution, results in polishing of the substrate.

Optical openings 34 are formed in the top surface of the platform 16. An optical surveillance system including a light source 36 (such as a laser) and a detector 38 (such as a light detector) can be positioned below the top surface of the platform 16. For example, the optical surveillance system may be located in a chamber within the platform 16, which is in optical communication with the optical opening 34 and may rotate with the platform. One or more optical fibers 50 can carry light from the light source 36 to the substrate and from the substrate to the detector 38. For example, the optical fiber 50 may be a bifurcated optical fiber with the trunk 52 approaching (eg, adjoining) the window 40 in the polishing pad; the first leg 54 is connected to the light source 36; and the second leg 56 is connected to Detector 38.

The optical openings 34 may be filled with a transparent solid sheet (such as a quartz block) (in this case, the optical fibers will not abut the window 40 but may adjoin the solid sheets in the optical openings), or the optical openings 34 may be hollow . In an implementation, the optical monitoring system and the optical opening can form components of the module, and the module is installed in a corresponding groove in the platform. Alternatively, the optical surveillance system may be a fixed system located below the platform, and the optical opening may extend through the platform. The light source 36 can use any wavelength from far infrared to ultraviolet, such as red light (however, a broadband spectrum such as white light can also be used), and the detector 38 can be a spectrometer.

The solid state window 40 is formed in the polishing pad 18 above, and is aligned with the optical opening 34 in the platform. The window 40 and the opening 34 may be positioned so 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 translation position of the polishing head 12.

At least while the window 40 is adjacent to the substrate 14, the light source 36 projects the light beam through the opening 34 and the window 40 to hit the surface of the substrate 14 above. The light reflected from the substrate forms a composite beam that can be detected by the detector 38. The light source and the detector are coupled to an unillustrated computer. 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 a new layer Sudden change in the reflectivity of the substrate; calculating the thickness removed from the outer surface layer (such as a transparent oxide layer) by using the principle of interference; 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 achieves the target value; or by monitoring signals that meet predetermined endpoint criteria.

One of the problems with 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 detail, the lateral frictional force from the substrate during polishing may be greater than the adhesion of the molding window to the sidewall of the polishing pad.

Returning to FIG. 2, a small window 40 may be used, such as having a diameter less than about 3 mm, in order to reduce the frictional force exerted by the substrate during polishing. For example, the upper portion of the window 40 may be a circular area that is approximately 3 mm wide with a center distance D from the center of the 30- to 31-inch diameter polishing pad 18 of approximately 7.5 inches (190.50 mm), or The center distance D from the center of the polishing pad 18 having a diameter of 42 to 43 inches is about 9 inches to 11 inches.

The window 40 may have a nearly circular shape (and may have other shapes, such as a rectangle). If the window is extended, the longer dimension of the window may be substantially parallel to the radius of the polishing pad passing through the center of the window. The window 40 may have an uneven outer edge 42, for example, the outer edge may be longer than a similarly shaped circle or rectangle, such as (from the top) a zigzag or other zigzag pattern. This can increase the surface area of the window in contact with the sidewalls of the polishing pad, and can thereby improve 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 an integral single piece of a homogeneous material. The upper portion 40a is aligned longitudinally with the lower portion 40b, but its lateral direction (ie, in one or two directions parallel to the polishing surface) is smaller than the lower portion 40b. Therefore, a part of the polishing layer 20 protrudes above the lower portion 40b, so that the edge protruding beyond the lower portion 40b of the upper portion 40a forms a window sill 49. The lower portion 40b may laterally protrude beyond the upper portion 40a on all sides of the window 40, or the lower portion 40b may laterally protrude beyond the upper portion 40a on two opposite sides of the window 40 as appropriate, but along other portions of the window 40 Align the sides. The upper surface of the lower portion 40b protruding beyond the upper portion 40a may be a substantially flat surface. The upper portion 40a may be located in the center of the lower portion 40b, for example, concentrically 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, for example, approximately 8 times larger. For example, if the window 40 is circular, the upper portion 40a may have a diameter of 3 mm, and the lower portion 40b may have a diameter of 25 mm.

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

The upper portion 40 a of the window 40 may protrude into an opening in the adhesive layer 28. An edge of the adhesive layer 28 (eg, an adhesive tape) may abut the side of the upper portion 40 a of the window 40. The lower portion 40b of the window may protrude into a 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 polished surface 24. The bottom of the upper portion 40 a of the window 40 may be coplanar with the bottom surface of the adhesive layer 28.

The upper surface of the lower portion 40 b is fixed to the lower side of the polishing layer 20 by a part of the adhesive layer 28. The outer edge of the upper portion 40a of the window 40 may be fixed to the inner side wall edge 48 of the polishing layer 20 as appropriate, for example, with additional adhesive.

The increased surface area of the connection between the window 40 and the polishing layer 20 provided by the connection on the window sill 49 can provide a strong joint, reduce the possibility of slurry leakage, and reduce the window caused by the shear force from the polished substrate 40 is the possibility of being pulled away from the polishing pad 18. The trunk portion 52 of the optical fiber abuts or almost abuts the lower portion 40b. In some implementations, the trunk portion 52 may be wider than the upper portion 40 a 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 (eg, supported on the bottom of the groove 78 in the upper surface 76 of the platform 16), or may It is 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 groove 78.

Referring to FIG. 3B, before being mounted on the platform 16, the polishing pad 18 may also include a lining 70. In addition to the block covered by the adhesive lower portion 40 b of the window 40, the lining 70 spans the bottom surface 22 of the polishing pad 18.上 的 胶层 28。 On the adhesive layer 28. The liner 70 may be a thin flexible material (such as paper) and has a release coating so that it can be peeled from the adhesive layer 28. In some implementations, the liner may 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 peeled from the adhesive layer 28, and the polishing layer 20 can be applied to the platform 16 using the adhesive layer 28. However, the lining 70 does not span the window 40, but is removed in a block (e.g., a block of about 25 cm wide) of the lower portion 40b of the window 40 and immediately adjacent to the block to form a hole 72, The lower portion 40 b of the window 40 can be fitted into the hole 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 may be about 0.8 or 0.9 mm. The polishing layer 20 may 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 may be about half the thickness of the polishing pad, for example, almost 0.5 mm.

In order to manufacture 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 grooves 26 may be formed in the polishing layer 20 as part of the pad forming process before the pressure-sensitive adhesive layer 28 is attached, or the grooves 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 FIG. 5, in some implementations, the window 40 may be formed by casting and hardening a polymer in the shape of the window 40. In one implementation, the polymer is 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 may be degassed, for example for 15 to 30 minutes, before being placed in the openings. The polymer may be hardened at room temperature for about 24 hours, or a heating lamp or oven may be used to shorten the hardening time. In some implementations, the polymer can be poured into a mold and hardened or solidified to form the window 40 in its final shape. In some implementations, the window 40 may be hardened into a large solid block, and then the solid block of the polymer is processed to form the window 40 in a final shape.

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

A hole 82 can be punched out that penetrates the entire polishing pad 18 including the polishing layer 20, the adhesive layer 28, and the liner 70. The size of the hole 82 may be determined to accommodate the upper portion 40 a of the window 40. In some implementations, the upper portion 40 a substantially blocks the hole 82 of the polishing pad 18. The hole 82 may be punched from the top of the polishing pad (ie, the side with the polishing surface), for example, by a machine press. This allows the positioning and sizing of the portion of the hole 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, it is not necessary to completely peel off the liner 70 from the polishing pad 18. This portion of the peeling liner 70 may expose a portion of the bottom surface 22 of the adhesive layer 28 around the hole 82. The stripped portion can also be cut off, for example, in a block of a window sill 49 that is sized to accommodate the bottom portion 40b of the window 40, but this step can also be performed later.

Referring to FIGS. 5 and 6, the window 40 is fixed to the polishing pad 18 such that the upper portion 40 a extends into the hole 82 and the upper surface of the bottom portion 40 b (eg, the window sill 49) contacts the adhesive layer 28. In some embodiments, the size of the upper portion 40a may be determined to extend substantially through and substantially fill the hole 82, so that when the window sill 49 is adhered to the adhesive layer 28, the upper surface 44 and the polishing surface 24 of the polishing layer 20 share flat.

In addition to the lining 70, a window support sheet 74 spanning the window 40 may be provided as appropriate. For example, the window support sheet 74 may be fixed to a part of the adhesive layer 28 immediately surrounding the window 40. The thickness of the support sheet body 74 may be the same as or less than that of the liner 70. The supporting sheet body 74 may be polytetrafluoroethylene (PTFE), such as Teflon®, or another non-adhesive material. The combined polishing pad 18 and window 40 may then be ready to be shipped to the customer, for example, in a sealed plastic bag.

Referring now to FIG. 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 place the polishing pad 18 Attached to the platform 16. The lower portion 40b of the window 40 is inserted into a recess 78 in the upper surface 76 of the platform 16. In some methods, the lining 70 in the surrounding area of the window 40 can be partially peeled, the lower portion 40b of the window 40 is inserted into the groove, and then the remaining portion of the lining is peeled off and the rest of the polishing pad is fixed Go to platform 16.

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

In some implementations, the bottom plate 88 of the groove 78 may 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 groove 78 is perpendicular to the polishing surface 75. Referring to FIG. 8, in some implementations, the side wall 84 of the lower portion 40 b may be formed at an angle that is not perpendicular to the bottom surface 46, such as between 20 ° and 80 °, such as 45 °, and the groove The side walls 86 of 78 may be formed at substantially similar angles, so that when the lower portion 40b is inserted into the groove 78, the side walls 84 and the side walls 86 are substantially in contact with each other. For example, the side wall 84 may be inclined inward from the window sill 49 to the bottom surface 46, so that the lower portion 40b forms a tapered section. Similarly, a side wall 86 may be formed to engage the tapered section. In this regard, when the window 40 is inserted into the groove 78 in the inclined sidewall 86, the inclined sidewall 84 may cause the window 40 and the polishing pad 18 to exhibit self-centering characteristics.

In this regard, the polishing pad 18 is adhered to the platform 16 by the adhesive layer 28 so that the window 40 is held in the groove 78 in the platform 16. The window 40 may be vertically supported by the bottom plate 88 of the groove 78 and may be held laterally by the side wall 86 of the groove 78. The window 40 can be attached to the polishing pad by contacting the top surface of the window sill 49 with the same adhesive layer, which fixes the lower side of the polishing pad to the platform 16.

Although certain embodiments have been described, the invention is not so limited. For example, although a window with a simple circle is described, the window can also be more complex, such as rectangular, oval, or star-shaped. The top portion of the window may protrude one or more sides beyond the bottom portion. It should be understood that various other modifications can be made without departing from the spirit and scope of the invention. Therefore, other embodiments also fall within the scope of the following patent applications.

10‧‧‧CMP equipment

12‧‧‧Polishing head

14‧‧‧ substrate

16‧‧‧ platform

18‧‧‧ polishing pad

20‧‧‧Polished

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‧‧‧ windows

40a‧‧‧upper

40b‧‧‧ lower part

42‧‧‧ (window)

44‧‧‧ (window) top surface

46‧‧‧ (window) bottom surface

48‧‧‧ inside wall edge

49‧‧‧ Windowsill

  50‧‧‧ Optical Fiber

52‧‧‧ Leader

54‧‧‧first foot

56‧‧‧ second foot

70‧‧‧lining

72‧‧‧ hole

74‧‧‧ (window) support sheet

76‧‧‧ (platform) top surface

78‧‧‧ groove

82‧‧‧hole

84‧‧‧ (the lower part of the window)

86‧‧‧ (groove) sidewall

88‧‧‧ (groove) floor

FIG. 1 is a cross-sectional view of a CMP apparatus including a polishing pad.

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

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

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

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

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

Similar element symbols in the multiple drawings indicate similar elements.

Domestic hosting information (please note in order of hosting institution, date, and number) None

Information on foreign deposits (please note in order of deposit country, institution, date, and number) None

Claims (10)

A polishing pad assembly includes: a polishing pad including 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 The adhesive layer spans the polishing pad, the adhesive layer has an opening aligned with the opening passing through the polishing pad; a solid-state light transmission window, the solid-state light transmission window is an integral single piece of homogeneous material and includes 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 larger than one of the upper portion, and the lower portion extending below the polishing pad A top surface of one of the lower portions of the window is adhesively attached to the lower side of the polishing pad, the lower portion has a bottom surface and a plurality of side walls, wherein the side walls extend to the bottom surface at a non-vertical angle . The polishing pad assembly according to claim 1, wherein the non-vertical angle is between 20º and 80º. The polishing pad assembly according to claim 2, wherein the non-vertical angle is about 45 °. The polishing pad assembly according to claim 1, wherein the bottom surface of the lower portion is parallel to a top surface of the upper portion. The polishing pad assembly according to claim 4, wherein the top surface of the upper portion of the window is coplanar with the polishing surface. The polishing pad assembly according to claim 1, wherein the upper portion of the window blocks the opening in the polishing pad. The polishing pad assembly according to claim 1, wherein the lower portion has a lateral dimension which is one to two to ten times larger than the upper portion. A chemical mechanical polishing system includes: a platform having an upper surface to support a polishing pad assembly, the platform having a groove formed in the upper surface to receive a window of the polishing pad assembly, the groove having A plurality of side walls extending to the upper surface at a non-vertical angle; a carrier head for contacting a substrate with a polishing surface of the polishing pad assembly; and an optical monitoring system configured to guide the light beam through The window of the polishing pad in the groove is configured to receive the reflection of the light beam from the substrate, and the reflection of the light beam passes through the window of the polishing pad in the groove. The system of claim 8, wherein the optical surveillance system includes an optical fiber disposed to abut the window in the groove. The system according to claim 8, comprising the polishing pad assembly, wherein the polishing pad assembly includes: a polishing pad having a polishing surface, a lower side, and an opening, the opening passing through the polishing pad, an adhesive layer Located on the lower side of the polishing pad, the adhesive layer fixes the polishing pad to the platform, the adhesive layer has an opening aligned with the opening passing through the polishing pad, and a solid-state light transmission window, The solid-state light transmission window is an integrated single piece of homogeneous material and includes an upper portion and a lower portion. The upper portion is at least partially disposed in the opening in the polishing pad, and the lower portion has a size larger than the upper portion. A lateral dimension of one portion, and the lower portion extends below the polishing pad and is disposed in the groove in the platform. A top surface of one of the lower portions of the window is adhesively attached to the The lower side, the lower portion has a bottom surface and a plurality of side walls, wherein the side walls extend at a non-vertical angle and abut the side walls of the groove.