WO2002077705A1

WO2002077705A1 - Methods and apparatus for polishing and planarization

Info

Publication number: WO2002077705A1
Application number: PCT/US2002/011262
Authority: WO
Inventors: Michael A. Labunsky; Guangwei Wu
Original assignee: Thomas West, Inc.
Priority date: 2001-03-23
Filing date: 2002-03-21
Publication date: 2002-10-03
Also published as: TW544371B

Abstract

A pad (15) for processing substrates (17) such as a pad (15) for CMP and methods of using the pad (15): the pad (15) is capable of allowing the substrate (17) to be optically monitored during the process. In one embodiment, at least a portion of the pad (15) includes an optical filter (25) for attenuating optical noise so that optical signals used for monitoring the substrate (17) provide a more accurate representation of the process status. The optical filter (25) is capable of transmitting the optical signal while reducing the amount of optical noise. In another embodiment, the surface of the filter (25) is recessed from the polishing surface of the pad so that the filter surface (25) is subjected to less abrasion during polishing processes and during pad conditioning.

Description

METHODS AND APPARATUS FOR POLISHING AND PLANARIZATION

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of United States Provisional Patent Application No. 60/278498, filed on 23 March 2001, United States Provisional Patent Application No. 60/285634, filed on 20 April 2001, and United States Non-Provisional Patent Application No. 09/992568, filed on 17 November 2001; the entire contents of all of these applications are incorporated herein by this reference.

TECHNICAL FIELD

This invention relates to pads and methods of using and making the pads for applications such as chemical mechanical planarization (CMP) and polishing of substrates such as semiconductor substrates, wafers, metallurgical samples, memory disk surfaces, optical components, lenses, electronic devices, and wafer masks. More particularly, the present invention relates to CMP pads and pads for polishing that are capable of filtering optical signals used for process monitoring.

BACKGROUND

The removal of material from the surface of a substrate so as to polish or planarize the substrate is essential in numerous technologies. For example, electronic devices typically include a substrate, such as a silicon or group III-IV types of wafers, on which numerous integrated circuits have been formed. Integrated circuits are integrated into a substrate by patterning regions in the substrate and layers on the substrate. To achieve high yields, it is crucial to start with a substantially flat substrate; consequently, it is often necessary to planarize the substrate surface. If the process steps of device fabrication are performed on a substrate surface that is not planar, various problems can occur which may result in a large number of inoperable devices. For example, in fabricating modern semiconductor integrated circuits, it is necessary to form conductive lines or similar structures above a previously formed structure. However, prior surface formation often leaves the top surface topography of a wafer highly irregular, with bumps, trenches, and other similar types of surface irregularities. Global planarization of such surfaces is necessary for processes such as photolithography. Although several techniques exist for achieving substrate surface planarity, processes employing chemical mechanical planarization or polishing techniques have been widely used to planarize the surface of wafers during the various stages of device fabrication in order to improve yield, performance and reliability. In general, chemical mechanical polishing (CMP) involves moving a wafer under a controlled pressure with pre-defined velocity over the surface of a polishing pad, while the aforementioned surface is covered or saturated with polishing slurry. Some processes involve moving a pad over a stationary substrate.

An important part of processes such as CMP is the determination of process endpoint. In addition, it is often desirable to be able to monitor the surface of the substrate throughout the process. There are standard technologies for in-situ monitoring and endpoint determination for CMP. Typically, the standard technologies are based on laser interferometer, phase-shift optical thickness measurement, reflectance change measurements, and similar techniques. The standard techniques, typically, require a transparent window in the CMP pad so that emitted light from a signal source can reach the substrate surface and the reflected light or signal can reach a detector.

Although the standard processes and apparatus for monitoring and endpoint detection for process like CMP are in common use, the standard technology still has problems. The obstacles encountered for copper CMP processes exemplify some of the problems with standard CMP monitoring technologies. Specifically, copper CMP requirements present essentially all process problems typically for CMP plus some unique aspects that will also arise in other advanced CMP situations. One of the unique aspects of copper CMP is formation of water- soluble copper salts, copper compounds, and copper-rich precipitates. The salts, compounds, and precipitates result in polishing by-products having blue-green colors. In addition, copper CMP by-products have a maximum transmission of visible light in the same region. Consequently, the copper by-products can significantly interfere with the optical signals used as part of standard CMP monitoring and end pointing. In other words, the presence of the copper by-products can introduce additional optical noise for the optical signal detector used for monitoring the CMP process.

Furthermore, the standard technologies for determining CMP endpoints are usually directed toward very advanced methods of transmitting optical signals to the polishing surface and receiving reflected optical signals from the surface being polished. However, the standard methods and apparatus fail to recognize the fact that the material for conveying the optical signal plays a crucial role in the quality of the signal. The standard methods and apparatus for monitoring CMP processes have neglected to improve the optical transmission characteristics of the materials used in optical process monitoring.

The standard technology also has other problems. In the standard technology, it is preferable to have the window flushed or substantially flushed with the polishing pad surface. Examples of the standard technology can be found in US Patent 5,605,760, US Patent 6,171,181, and US Patent 6,0454,39. A problem with the standard technology is that during the polishing process, abrasive particles in the polishing slurry abrade the surface of the window material used for process monitoring and end-point-detection.

Another problem is that, during pad conditioning, diamond particles in the conditioning disk abrade the surface of the window for process monitoring and end-point-detection. The surface roughness of the window increases with operation time. In other words, the transmittance of the window decreases with increasing operation time. The end-point-detection system fails when the transmittance of the window becomes very low. The transmittance value caused end-point-detection failure may also depend on the polishing equipment. Specifically, the lifetime of window material can determine the lifetime of the polishing pad.

Although pads for processes such as polishing and planarization are in extensive use, a need remains for improved pads which provide effective planarization across substrates such as electronic devices and that are capable of allowing improved process monitoring. Specifically, pads are needed that are suitable for using optical signals that are higher in absolute value and more accurate for monitoring CMP processes. Improved CMP processes are needed so that optically monitoring the CMP process can be done with less signal loss and with reduced optical noise. Furthermore, there is a need for pads that have high durability in addition to allowing in situ process monitoring for CMP processes. Pads are needed that can be used for longer periods of time before the pad must be replaced. Improved processes are needed so that processes such as CMP processes can be effectively performed for longer periods of time before signal transmission properties of the window material become unsatisfactorily low. There is a need for pads that have high durability in addition to allowing in situ process monitoring for polishing processes.

SUMMARY

This invention pertains to improved methods and apparatus for monitoring and processing substrates such as for polishing processes and for CMP processes. Embodiments of the present invention are particularly suited for continuous film thickness monitoring as well as endpoint detection of CMP processes. The present invention seeks to overcome one or more of the deficiencies of the standard technologies for optically monitoring and processing surfaces.

An aspect of the present invention is a pad for processing substrates such as, for example, CMP of substrates. The pad is capable of allowing the substrate to be optically monitored during the CMP process. At least a portion of the pad includes an optical filter for attenuating optical noise so that optical signals used for monitoring the substrate provide a more accurate representation of the CMP process status. The optical filter is capable of transmitting the optical signal while substantially reducing the amount of optical noise.

Another aspect of the present invention is a method of monitoring CMP processes. In one embodiment, the method is carried out with a CMP pad capable of filtering predetermined frequencies of light so as to remove optical noise. The method includes the step of polishing a substrate surface with the pad using chemical mechanical polishing. The method also includes the step of directing an original optical signal toward the substrate surface and generating a reflected optical signal from the substrate surface. The method further includes the step of using the pad to filter optical noise from at least one of the original optical signal and the reflected optical signal. After the step of filtering the optical noise is the step of measuring the reflected optical signal to determine the status of the CMP process.

Another aspect of the present invention is a pad for processing substrates such as for example CMP of substrates. The pad is capable of allowing the substrate to be optically monitored during the CMP process for longer periods of time. The pad includes a window material. The surface of the window material has a recess relative to the polishing surface of the polishing pad instead of being flushed with the surface.

Yet, another aspect of the present invention includes electronic devices and other products made using the methods and apparatus of the present invention.

It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out aspects of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed descriptions of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section diagram of an embodiment of the present invention.

FIG. 2 is a graph of optical transmission characteristics for an optical filter according to an embodiment of the present invention.

FIG. 3 is a cross section diagram of an embodiment of the present invention.

FIG. 4 is a cross section diagram of an embodiment of the present invention.

FIG. 5 is a cross section diagram of an embodiment of the present invention.

FIG. 6 is a cross section diagram of an embodiment of the present invention.

DESCRIPTION

The operation of embodiments of the present invention will be discussed below, primarily, in the context of planarizing and/or polishing substrates such as substrates used for fabrication of electronic devices. However, it is to be understood that embodiments in accordance with the present invention may be used for applications such as planarizing and/or polishing substrates such as metallurgical samples, memory disk surfaces, optical components, lenses, electronic devices, and wafer masks. Further, it us to be understood that embodiments in accordance with the present invention may be used for applications such as offline and non-in- situ optical metrology applications where optical losses are critical factors in system performance.

In the following description of the figures, identical reference numerals have been used when designating substantially identical elements or steps that are common to the figures.

One embodiment of the present invention is a pad for CMP. The pad is capable of substantially transmitting an optical signal for monitoring a CMP process. The pad is also capable of optical filtering so that optical noise is substantially prevented from causing inaccuracies in the optical signal measurements used for monitoring the CMP process.

Reference is now made to Fig. 1 wherein there is shown a cross-section diagram of a portion of a CMP pad 15 according to one embodiment of the present invention. Pad 15 includes a polymer sheet 20 and an optical filter 25. Polymer sheet 20 has chemical and physical properties for performing chemical mechanical polishing. Polymer sheet 20 has a hole 22 extending from a first side of sheet 20 through to the opposite side of sheet 20.

Optical filter 25 is capable of transmitting optical signals for monitoring the CMP process. Optical filter 25 is also capable of attenuating selective wavelengths of light corresponding to the wavelengths of optical noise. Preferably, optical filter 25 is substantially impermeable to fluid transfer.

Polymer sheet 20 and optical filter 25 are connected so that optical filter 25 substantially prevents fluid communication through hole 22 from the first side of polymer sheet 20 to the second side of polymer sheet 20. Optical filter 25 allows transmission of an original optical signal for monitoring the CMP process so that the optical signal can impinge upon the surface of a substrate during CMP. Optical filter 25 also allows transmission of a reflected optical signal from the surface of the substrate during CMP.

Polymer sheet 20 can be made using a variety of techniques such as those typically used for making CMP polishing pads. Methods of making standard CMP polishing pads are well known in the technical and patent literature. For more information about polishing pads, see WIPO Publication W096/15887, the specification of which is incorporated herein by reference. Other representative examples of polishing pads are described in U.S. Patents 4,728,552, 4,841,680, 4,927,432, 4,954,141, 5,020,283, 5,197,999, 5,212,910, 5,297,364, 5,394,655 and 5,489,233, the specifications of which are also each incorporated herein in their entirety by reference.

In one configuration, polymer sheet 20 comprises a molded composite plastic that includes an embedded matrix, such as polyester fibers. The matrix is impregnated with a polymer resin such as polyurethane. In another embodiment, the polymer sheet includes a non- woven felt and a polymer resin; the felt is impregnated with the resin to form the polymer sheet.

In one embodiment of the present invention, optical filter 25 is made of a cast plastic such as polyurethane. In a preferred embodiment, optical filter 25 is made from cast polyether urethane. In a further embodiment, the thickness of the filter is held in the range of about 0.040 to about 0.042 inch (1.0 mm to about 1.1 mm).

Generally, preferred embodiments of the present invention use materials that are capable of withstanding substantially all chemical and physical rigors associated with CMP process. Some of the typical conditions that the materials may need to withstand are pH range from 2 to 14 and abrasion resistance < 0.0005 inch (12 micrometers) thickness loss after 1000 wafer buffs. Optical filter 25 may operate according to a variety of well-known techniques for optical filtering. For instance, optical filter 25 may operate on the principle of selectively absorbing predetermined wavelengths of light, or optical filter 25 may operate on the principle of selectively enhancing optical transmission of predetermined wavelengths. Alternatively, optical filter 25 may operate on the principle of selectively reflecting predetermined wavelengths of light. In addition, a combination of optical filtering techniques maybe used in some embodiments of the present invention.

In one embodiment of the present invention, the optical filtering characteristics for filter 25 are created by adding a dye to a plastic body included in optical filter 25. The addition of the dye causes the plastic to transmit a band of wavelengths that includes the wavelengths for the original optical signal and the reflected optical signal used for monitoring the CMP process. Examples of suitable dyes that can be used are diazo type colorants such as those available from GAP Corporation, phthalocyanine type green and blue colorants such as those made by E.I.DuPont, Inc. In some embodiments of the present invention, the amount of dye ranges from about 1% to about 5% by volume and have optical transmission greater than about 85% in a specified wavelength region.

Fig. 2 shows the optical transmission characteristics of one embodiment of the present invention. This embodiment includes a cast plastic with a dye added to enhance the optical transmission properties of an optical filter in the range of about 600 nanometers. Specifically, addition of the dye causes the plastic to behave as a bandpass optical filter. It is to be understood that factors such as the optical properties of the CMP by-products and the choice of light source and/or detector combination influence the selection of the dyes for embodiments of the present invention. It is well understood that different dyes can be added to cast plastic or other materials so as to cause optical transmission blocking or optical transmission enhancement for essentially any predetermined optical wavelength from the UN band down to the far infra-red end of the visible spectra.

In a further embodiment, optical filter 25 may also include microfibers 30 (shown Fig. 1) made of materials such as nylon, kevlar, kapton, and capron. The core density, individual diameters of filaments, filament spacing, and other properties are selected in such a way that the optical quality of filter 25 shows substantially no noticeable degradation while maintaining mechanical properties having the following values: Tensile strength >8000 pounds per square inch, Elongation at break < 400%, Tear resistance > 700 pounds per inch. Furthermore, the increased strength of the filter material yields increased resistance to abrasion and increased resistance to cyclical stresses associated with CMP processes. Preferably, microfibers 30 are suspended in the cast plastic so as to form a composite material having greater strength than that of the cast plastic without the reinforcing microfibers. Other well known techniques can be used to increase the strength of the plastic. For example, the strength can also be increased by methods such as adding microspheres and analogous methods.

The durability of the filter can also be increased by increasing the hardness of the filter. The hardness of some of the plastics suitable for embodiments of the present invention can be increased by adding hardeners to the plastic. For instance, hardeners such as 1,4-butanediol, 2,3-butanediol, ethylene diamine, and trimethylol propane can be added to the polyurethane to produce a final material hardness in the range of 60 to 60D on the Shore D scale. The higher hardness of the filter reduces susceptibility of the filter to scratching by the slurry and/or scratching during processes such as pad conditioning.

Reference is now made to Fig. 3 wherein there is shown a cross section diagram of a portion of a CMP pad 15 according to the present invention. CMP pad 15 shown in Fig. 3 is substantially the same as that described for the CMP pad presented in Fig. 1. The CMP pad shown in Fig. 3 also includes an antireflection coating 35. Anti-reflection coating 35 is applied to optical filter 25 to reduce losses of optical signal intensity at the surface of optical filter 25 caused by changes in the refractive index. Without antireflection coatings, the signal loss due to refractive index changes can equal about 4 percent of the signal intensity. However, use of the anti-reflection coating reduces the 4 percent loss due to reflection. Embodiments of the present invention include anti-reflection capabilities so that that reflection losses of the optical signal is less than 4%. Because of the selection of the antireflection properties, some embodiments of pads according to the present invention can have reflection losses in the range of about 0% to about 3.8% and all subranges subsumed therein. Preferably, the reflection losses are less than about 3.5%, and more preferably less than about 3 % for the optical signal used for monitoring the process.

Optical filters according to some embodiments of the present invention are strong and mechanically stable. These characteristics allow the optical filters to be used in embodiments of the present invention in a variety of shapes and sizes. Particularly advantageous is that the smallest size is limited only by the choice of optical source and detector combination.

The mechanical strength of the filter and high light-transmission characteristics allows a user to reduce the physical size of the filter, thus, reducing the "parasitic zone" within polishing region of the substrate. Furthermore, the superior optical signal transmission capabilities of the filter can enable the use of a reduced power light source for the optical signal. The lower power light source can, in some cases, reduce the parasitic photochemical effects that can occur within the polishing zone.

Reference is now made to Figure 4 wherein there is shown a cross section view of an embodiment of the present invention. A frequency-tuned optical filter 25 is physically incorporated in a polishing pad 17. The location of the filter is essentially a matter of designer choice and only depends on choice of optical signal source and detector combination (the optical signal source and detector are not shown in Figure 4). In order to minimize physical interactions between the surface of filter 25 and the semiconductor wafer that is being polished, filter 25 is recessed about 0.001 inch (0.025 mm) to about 0.002 inch (0.050 mm) in reference to polymer sheet 20. In other embodiments, filter 25 could be flush with the surface of sheet 20 or recessed further depending on desired results. An example of a suitable polymer sheet is a TWI 813 pad, commercially available from Thomas West, Inc. Use of a pad and sub-pad combination allows easy installation of filter 25, particularly where there is a 1 mm to 1.5 mm ledge remaining on a sub-pad 40 such as the TWI 817 sub-pad, commercially available from Thomas West, Inc. An adhesive 38 such as PSA-C and the sub-pad 40 are capable of providing full circumferential support of the optical filter 25. An adhesive 42, such as PSA-C or equivalent from companies such as Avery Dennison Company of Plainsville, Ohio, provides a substantially leak-tight seal between the CMP slurry media and electro-optical components located below the polishing pad environment. (Slurry media and electro-optical components are not shown in Fig. 4.) Sub-pad 40 is an optional feature; essentially the same type of installation can be accomplished with substantially any type of pad that includes a backing adhesion layer.

In other embodiments, the pad includes a window material. As an option, the window material may not have optical filtering capabilities such as those described for the embodiments in Figures 1-3. The surface of the window material is positioned to be recessed relative to the polishing surface of the polishing pad instead of being flushed with the surface like the standard technology. By creating the recess, pad maintenance processes such as pad conditioning cause less damage to the window material. Specifically, the conditioning disk will have less or no contact with the window material and cause less scratching of the window material. In addition, there will be less abrasion of the window material during polishing processes. Consequently, the transmittance of the window material can be retained for longer operation times. To avoid excessive accumulation of slurry particles, it is preferable for the recess to not be too large. A suitable recess range is about equal to or smaller than about three fourths of the thickness of the pad. A preferred recess range should be about equal to or smaller than about half of the thickness of the pad. Reference is now made to Fig. 5 wherein there is shown a cross-section view of a section of a polishing pad 15 according to one embodiment of the present invention. Pad 15 includes a polymer sheet 20 and a window material 26. Polymer sheet 20 has chemical and physical properties for performing chemical mechanical polishing. Polymer sheet 20 has a hole 22 extending from a first side of sheet 20 through to the opposite side of sheet 20. Window material 26 is capable of transmitting optical signals for monitoring the CMP process. In preferred embodiments, window material 26 is substantially impermeable to fluid transfer.

Polymer sheet 20 and window material 26 are connected so that window material 26 substantially prevents fluid communication through hole 22 from the first side of polymer sheet 20 to the second side of polymer sheet 20. Window material 26 allows transmission of an original optical signal for monitoring the CMP process so that the optical signal can impinge upon the surface of a substrate during CMP. Window material 26 also allows transmission of a reflected optical signal from the surface of the substrate during CMP. The surface of window material 26 is positioned to be recessed relative to the polishing surface of polishing pad 15 instead of being flushed with the surface like the standard technology. The window material is recessed so as to substantially minimize contact between the window material and a conditioning disk during pad conditioning processes. Therefore, the transmittance of the window material can be retained for longer operation times. To avoid excessive accumulation of slurry particles, it is preferable for the recess to not be too large. The preferred recess range should be equal to or smaller than about half of the thickness of the pad. For some embodiments of the present invention, the amount of the recess is in the range of about 5% to about 75% of the thickness of the polishing pad or top pad in a stacked pad configuration. The preferred amount of the recess is in the range of about 5% to about 50% of the thickness of the polishing pad or the top pad in a stacked pad configuration.

Reference is now made to Figure 6 wherein there is shown a cross-section view of a section of a polishing pad. Window material 26 is an integral part of polishing pad 17. The location of the window material is essentially independent and only depends on choice of optical signal source and detector combination (the optical signal source and detector are not shown in Figure 6). In order to minimize physical interactions between the surface of window material 26 and the semiconductor wafer that is being polished, window material 26 is recessed about 5% to about 75% of the thickness of polymer sheet 20 in reference to polymer sheet 20. An example of a suitable polymer sheet is a TWI 813 pad, commercially available from Thomas West, Inc. Use of a pad and sub-pad combination allows easy installation of the window material 26, particularly where there is a 1 mm to 1.5 mm ledge left on a sub-pad 40 such as the TWI 817 sub-pad, commercially available from Thomas West, Inc. An adhesive 38 such as PSA-C and the sub-pad 40 are capable of providing full circumferential support of the window material 26. An adhesive 42 such as PSA-C or equivalent by Avery Dennison Company of Plainsville, Ohio provides a substantially leak-tight seal between the slurry media and electro-optical components located below the polishing pad environment (slurry and electro-optical components not shown in Fig. 6). Sub-pad 40 is an optional feature; essentially the same type of installation can be accomplished with substantially any type of pad that includes a backing adhesion layer.

Experiments have been done comparing the performance of CMP pads according to embodiments of the present invention and CMP pads of the standard technology. Under analogous operating conditions, the CMP pads according to the standard technology can be operated for about 5-6 hours before they need to be replaced. However, CMP pads, according to embodiments of the present invention where the window is recessed about 300 micrometers, can be operated for about 9 hours or longer before the pads need to be replaced.

Clearly, there is a significant improvement in the operating lifetime of pads according to embodiments of the present invention compared to pads of the standard technology. The longer operating lifetimes of pads according to embodiments of the present invention, consequently, are expected to provide a lower cost of ownership for polishing processes such as CMP processes. Furthermore, substrates, electronic devices, and other products produced using embodiments of the present invention are expected to have lower production costs as a result of the present invention. Still further, production facilities using embodiments of the present invention are expected to have higher overall production efficiencies as a result of the longer operating times for CMP processes using embodiments of the present invention.

While there have been described and illustrated specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims and their legal equivalents.

Claims

CLAIMSWhat is claimed is:

1. A pad for optically monitoring and processing the surface of a substrate, at least a portion of the pad comprising an optical filter for attenuating optical noise; the optical filter being capable of transmitting an optical signal for optically monitoring the substrate.

2. The pad of claim 1 wherein the optical filter is capable of enhanced optical transmission for frequencies near the frequencies of the optical signal.

3. The pad of claim 1 wherein the optical filter comprises a bandpass filter having a frequency transmission band so that the optical signal is substantially transmitted by the filter.

4. The pad of claim 3 wherein the bandpass filter has peak transmission in the wavelength range of about 450 nanometers to about 700 nanometers.

5. The pad of claim 4 wherein the bandpass filter has peak transmission at a wavelength of about 580 nanometers.

6. The pad of claim 1 wherein the optical filter comprises a dye suspended in an optically transmissive material, wherein the dye alters the optical transmission properties of the optically transmissive material.

7. The pad of claim 6 wherein the optically transmissive material comprises a cast plastic.

8. The pad of claim 6 wherein the optically transmissive material comprises a polyurethane.

9. The pad of claim 8 wherein the dye is present at concentrations of 1% to 5% by volume and provides optical transmission greater than about 85% in a specified region.

10. A CMP pad for optically monitoring CMP processes using an optical signal, the pad comprising: a) a polymer sheet having a first side and a substantially parallel second side, the polymer sheet having a hole extending from the first side to the second side; b) an optical filter, the optical filter being substantially impermeable to fluid transport, the optical filter being connected with the polymer sheet to substantially prevent fluid communication through the hole from the first side to the second side, the optical filter being capable of attenuating optical noise so that measurements of the optical signal have reduced interference from optical noise.

11. The CMP pad of claim 10 wherein the optical filter comprises: a matrix of reinforcing fibers; and a cast plastic body, the fibers being integrated with the body so as to strengthen the body.

12. The CMP pad of claim 10 wherein the optical filter comprises: a dye; and a cast plastic body, the dye being suspended in the body, the dye having optical properties so that the presence of the dye in the body allows transmission of a band of optical wavelengths while attenuating transmission of optical noise.

13. The CMP pad of claim 10 wherein the optical filter comprises polyurethane.

14. The CMP pad of claim 10 wherein the polymer sheet comprises polyurethane.

15. The CMP pad of claim 12 wherein the dye concentration is from about 1% to about 5% by volume and has optical transmission greater than about 85% in a predetermined wavelength region.

16. The CMP pad of claim 10 wherein the optical filter comprises an antireflection coating for increasing the efficiency of transmitting the signal.

17. The CMP pad of claim 10 wherein the polymer sheet comprises a polishing surface and the filter is recessed below the polishing surface a distance of about 5% to about 75% of the thickness of the polymer sheet.

18. A method of process monitoring, the method being carried out with a pad capable of filtering predetermined frequencies of light, the method comprising the steps of: i. removing material from a substrate surface with the pad; ii. directing an original optical signal at the substrate surface and generating a reflected optical signal from the substrate surface; iii. filtering optical noise from at least one of the original optical signal and the reflected optical signal using the pad; iv. measuring the reflected optical signal to determine the status of the process.

19. The method of claim 18 wherein the step of filtering optical noise comprises at least one step of reducing the intensity of optical noise of wavelengths longer than about the wavelength of the original optical signal, reducing the intensity of optical noise of wavelengths shorter than about the wavelength of the original optical signal, and reducing the intensity of optical noise of wavelengths longer than and wavelengths shorter than about the wavelength of the original optical signal.

20. The method of claim 18 wherein the step of filtering optical noise comprises at least one step of reducing the intensity of optical noise of wavelengths longer than about the wavelength of the reflected optical signal, reducing the intensity of optical noise of wavelengths shorter than about the wavelength of the reflected optical signal, and reducing the intensity of optical noise of wavelengths longer than and wavelengths shorter than about the wavelength of the reflected optical signal.

21. The method of claim 18 further comprising the step of increasing the transmission of the original optical signal through the pad using an antireflection coating applied to the pad.

22. The method of claim 18 wherein the step of optical filtering involves using only a portion of the pad.

23. The method of claim 18 wherein the step of optical filtering substantially prevents transmission of optical noise having wavelengths shorter than about 450 nanometers and optical noise having wavelengths longer than about 700 nanometers.

24. A pad for optically monitoring and processing the surface of a substrate, the pad having a polishing surface; at least a portion of the pad comprising a window material; the window material being capable of transmitting an optical signal for optically monitoring the substrate; the window being capable of filtering predetermined optical wavelengths so as to attenuate optical noise; the window material having a surface recessed relative to the polishing surface of the pad.

25. The pad of claim 24 wherein the window material is recessed a distance of about 300 micrometers.

26. The pad of claim 24 wherein the window material is recessed a distance from about 5% to about 75% of the thickness of the pad.

27. The pad of claim 24 wherein the window material is recessed a distance from about 5% to about 50% of the thickness of the pad.

28. A pad for optically monitoring and processing substrates, the pad having a polishing surface; at least a portion of the pad comprising a window material; the window material being capable of transmitting an optical signal for optically monitoring the substrate; the window material having reflection losses of less than 4% for a wavelength of the optical signal.

29. The pad of claim 28 wherein the window material comprises an antireflection coating.

30. The pad of claim 28 wherein the window material comprises a surface having a texture for reduced optical reflection.

31. The pad of claim 28 wherein the window material has reflection losses of less than about 3.5%.

32. The pad of claim 28 wherein window material has reflection losses of less than about 3%.

33. A pad for optically monitoring CMP processes, the pad having a polishing surface; at least a portion of the pad comprising a window material; the window material being capable of transmitting an optical signal for optically monitoring CMP processes; the window material comprising a resin and at least one of a matrix of microfibers and a multiplicity of microspheres for increasing the strength of the window material.