Chemical mechanical polishing vibration measurement using optical sensors

Abstract

The chemical mechanical polishing apparatus includes a platen supporting a polishing pad, a carrier head holding a substrate against a polishing surface of the polishing pad, a motor generating relative motion between the platen and the carrier head to polish an overlying layer of the substrate, an in-situ vibration monitoring system including a light source emitting a light beam and a sensor receiving reflection of the light beam from a reflective surface of the polishing pad, and a controller configured to detect exposure of an underlying layer due to polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system.

Description

[Technical Field]

[0001] This disclosure relates to chemical mechanical polishing, and more particularly to measuring vibrations of a chemical mechanical polishing pad to detect layer transitions. [Background technology]

[0002]

[0002] Integrated circuits are typically formed on substrates by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. One manufacturing step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. For example, a conductive filler layer can be deposited over a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, portions of the metal layer remaining between the raised insulating layer patterns form vias, plugs, and lines that become conductive paths between thin-film circuits on the substrate. In other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains over the non-planar surface. In addition, planarization of the substrate surface is typically required for photolithography.

[0003] Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires the substrate to be mounted on a carrier or polishing head. The exposed surface of the substrate is usually positioned against a rotating polishing pad. The carrier head applies a controllable load to the substrate, pressing it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

[0004] One problem in CMP is determining whether the polishing process is complete (e.g., whether a substrate layer has been planarized to a desired flatness or thickness) or when a desired amount of material has been removed. Variations in slurry distribution, polishing pad condition, relative velocity between the polishing pad and the substrate, and load on the substrate can cause variations in material removal rate. These variations, as well as variations in the initial thickness of the substrate layer, cause variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint cannot usually be determined simply as a function of polishing time.

[0005] In some systems, the substrate is monitored in situ during polishing, for example, by monitoring the torque required by a motor to rotate the platen or carrier head. However, existing monitoring techniques may not meet the growing demands of semiconductor device manufacturers. Summary of the Invention

[0006]

[0006] In one aspect, a chemical mechanical polishing apparatus includes a platen supporting a polishing pad, a carrier head holding a substrate against the polishing surface of the polishing pad, a motor generating relative motion between the platen and the carrier head to polish an overlying layer of the substrate, an in-situ vibration monitoring system including a light source that emits a light beam and a sensor that receives reflections of the light beam from the reflective surface of the polishing pad, and a controller configured to detect exposure of an underlying layer due to polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system.

[0007] Advantages of implementations may include, but are not limited to, one or more of the following.

[0008] Disclosed herein are apparatus and methods for using an in-situ displacement monitoring system that includes a light source and a sensor to detect vibrations of a polishing pad of a chemical mechanical polishing apparatus. The detected vibrations correspond to motion induced by friction, e.g., release of stress energy, between a substrate and a slurry moving across the grooved upper surface of the polishing pad. A vibration frequency domain analysis is determined based on the detected vibrations, and the frequency domain analysis is monitored to determine a polishing endpoint, such as to detect exposure of an underlying layer.

[0009]

[0009] Displacement monitoring at high sampling rates provides broad spectral resolution of the vibration profile. For example, monitoring displacements up to 350 kHz provides vibration profile resolution ranging from below 1 Hz to 175 kHz. Real-time frequency domain analysis allows for precise and accurate detection of changes in the vibration profile corresponding to exposure of the underlying layer.

[0010]

[0010] One or more of the following possible advantages may be realized: Exposure of the underlying layer may be detected more reliably; Polishing may be stopped more reliably, resulting in improved wafer-to-wafer uniformity.

[0011] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of an example of a polishing apparatus. [Figure 2A]

[0013] 1 is a schematic cross-sectional view of a vibration monitoring sensor for monitoring an insert in a polishing pad. [Figure 2B]

[0014] 10 is a schematic cross-sectional view of another implementation of a vibration monitoring sensor for monitoring an insert passing through a polishing pad. [Figure 2C]

[0015] 10 is a schematic cross-sectional view of another implementation of a vibration monitoring sensor engaging a portion of a polishing pad. [Figure 3]

[0016] FIG. 1 is a schematic top view of a platen having an acoustic monitoring sensor. [Figure 4]

[0017] 1 is a flowchart of a method for acoustic monitoring. DETAILED DESCRIPTION OF THE INVENTION

[0013]

[0018] Like reference numbers and designations in the various drawings indicate like elements.

[0014]

[0019] In some semiconductor chip manufacturing processes, an overlying layer (e.g., metal, silicon oxide, or polysilicon) is polished until an underlying layer (e.g., silicon oxide, silicon nitride, or a dielectric such as a high-k dielectric) is exposed. During polishing of the overlying layer, friction between the slurry, substrate, and polishing pad creates vibrations. In some applications, the vibration frequency spectrum changes when the underlying layer is exposed. The polishing transition point can be determined by detecting this change in vibration. For example, an acoustic sensor can be mechanically coupled to the polishing pad. However, such monitoring techniques may not meet the growing demands of semiconductor device manufacturers. In particular, consistent, low-loss acoustic coupling between the polishing pad and the acoustic sensor can be difficult or expensive.

[0015]

[0020] By generating a light beam and measuring the reflection of the light beam from the polishing pad, it may be possible to measure the vibration of the polishing pad with less damping and therefore less noise.

[0016]

[0021] 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable, disk-shaped platen 120 on which a polishing pad 110 is positioned. The platen is operable to rotate about an axis 125. For example, a motor 121 (e.g., a DC induction motor) can turn a drive shaft 124 to rotate the platen 120.

[0017]

[0022] The polishing pad 110 may be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. In some implementations, a plurality of slurry-delivery grooves 116 (see FIG. 2A ) are formed in the top surface of the polishing layer 112 of the polishing pad 110. The grooves 116 extend partially, but not completely, through the thickness of the polishing layer 112. The grooves 116 have a depth ranging from 25 mils to 30 mils (e.g., 0.025" to 0.030") from the polishing surface (e.g., top surface) of the polishing pad 110, and may become lower as the polishing pad 110 wears following several polishing operations.

[0018]

[0023] The polishing apparatus 100 may include a port 130 for dispensing a polishing liquid 132 (e.g., a polishing slurry) onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner that polishes the polishing pad 110 to maintain the polishing pad 110 in a consistent polishing condition.

[0019]

[0024] The polishing apparatus 100 includes at least one carrier head 140. The carrier head 140 is operable to hold the substrate 10 against the polishing pad 110. Each carrier head 140 can have individual control of polishing parameters (e.g., pressure) associated with the respective substrate.

[0020]

[0025] Carrier head 140 may include a retaining ring 142 that holds substrate 10 beneath a flexible membrane 144. Carrier head 140 also includes one or more individually controllable pressurizable chambers (e.g., three chambers 146a-146c) defined by the membrane. These chambers may apply individually controllable pressures to associated zones of flexible membrane 144 (and thus on substrate 10). For ease of illustration, only three chambers are shown in FIG. 1, but there may be one or two chambers, or four or more chambers, e.g., five chambers.

[0021]

[0026] Carrier heads 140 are suspended from support structure 150 (e.g., a carousel or track) and connected by drive shaft 152 to carrier head rotation motors 154 (e.g., DC induction motors), which may rotate the carrier heads about axis 155. Optionally, each carrier head 140 may reciprocate laterally, for example, on a slider in carousel 150, either by rotational oscillation of the carousel itself or by sliding along a track. In typical operation, the platen rotates about its central axis 125, and each carrier head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad.

[0022]

[0027] A controller 190 (e.g., a programmable computer) is connected to the motors 121, 154 to control the rotational speed of the platen 120 and carrier head 140. For example, each motor may include an encoder that measures the rotational speed of an associated drive shaft. A feedback control circuit, which may be within the motor itself, part of the controller, or a separate circuit, receives the measured rotational speed from the encoder and adjusts the current supplied to the motor to ensure that this rotational speed of the drive shaft matches the rotational speed received from the controller.

[0023]

[0028] The monitored vibrations of the polishing pad may be caused by the release of acoustic energy when the slurry, polishing pad, or substrate material deforms during polishing, and the resulting vibration frequency spectrum is related to the material properties of the slurry, polishing pad, and / or substrate. Without being limited to a particular theory, the source of this energy, also referred to as "stress energy," and its characteristic frequencies may include chemical bond scission, characteristic phonon frequencies, slip-stick mechanisms, etc. Vibrations generated during polishing may include noise generated by friction of the substrate against the polishing pad (which may also be referred to as an acoustic signal), or noise generated by the occurrence of cracks, chips, cuts, or similar defects on the substrate.

[0024]

[0029] Vibrations can be monitored by optically monitoring the displacement of a portion of the polishing pad. Measuring the displacement using a light source (e.g., a laser) provides high-precision, high-frequency vibration monitoring. Optical monitoring systems can detect small displacements on the surface of the polishing pad at high sampling rates (e.g., 300 kHz or higher), which facilitates precise reconstruction of the vibration of the polishing pad. In addition, because there is no intervening medium or mechanical coupling between the projected light and the bottom surface of the insert 118, vibrations can be measured directly with little loss or added noise due to air in the recess 117.

[0025]

[0030] A position sensor (e.g., an opto-isolator or rotary encoder connected to the rim of the platen) can be used to sense the angular position of the platen 120. This allows only the portion of the signal measured when the light source 162 is close to the substrate (e.g., when the light source 162 is below the carrier head or substrate) to be used for endpoint detection.

[0026]

[0031] The polishing apparatus 100 includes at least one in-situ vibration monitoring system 160. Specifically, the in-situ vibration monitoring system 160 can be configured to detect vibrations in the polishing pad 110 caused by stress energy when the material of the substrate 10 deforms. The vibrations pass through the backing layer 114 and the polishing layer 112 of the polishing pad 110 and can be detected by the in-situ pad vibration monitoring system 160.

[0027]

[0032] The in-situ vibration monitoring system 160 includes a displacement sensor assembly including a light source 162 positioned to direct light to a location on the bottom surface of the polishing pad and a detector 164 that detects reflection of the light from the polishing pad. In some implementations, the in-situ vibration monitoring system 160 includes multiple displacement sensor assemblies so that vibrations can be monitored at multiple locations on the polishing pad, for example, multiple locations equidistant from the axis of rotation 125 and / or multiple locations equispaced around the axis of rotation 125.

[0028]

[0033] 1 and 2A, the polishing pad 110 includes an insert 118 secured within and extending through the polishing layer 112 such that an upper surface 119 of the insert 118 is flush with the top surface (e.g., polishing surface 112a) of the polishing layer 112, and thus the upper surface 119 contacts the substrate 10 during operation. In some implementations, as shown in FIG. 2A, the insert 118 extends through both the polishing layer and the backing layer 114. In some implementations, such as the implementation of FIG. 2B, the insert extends through the polishing layer 112 but does not extend into the backing layer 114. Rather, a void 114a in the backing layer 114 is positioned below the insert 118.

[0029]

[0034] The insert 118 is generally cylindrical, although other shapes are possible. As shown in FIG. 2A , the insert 118 may be drum-shaped having a membrane 118a and an annular sidewall 118b extending downward from the outer edge of the membrane 118a. The membrane 118a may be thinner than the polishing layer 112. The thickness of the membrane 118a may be between 20% and 90% of the thickness of the polishing layer 112. The lower end of the sidewall 118b may rest on top of the platen 120.

[0030]

[0035] 2B, a flange 118c (e.g., an annular flange) may extend radially outward from the lower end of the annular sidewall 118b. The annular flange 118b may be sandwiched between the polishing layer 112 and the backing layer 114, or between the backing layer 114 and the platen 120. In some implementations, the flange 118b is affixed to the backing layer 114 with an adhesive or adhesive tape to increase the stability of the insert 118 relative to the backing layer 114.

[0031]

[0036] In some implementations, the outer diameter (e.g., edge-to-edge) of the insert 118 ranges from 10 mm to 20 mm (e.g., 12 mm, 14 mm, 16 mm, or 18 mm). The insert 118 includes a recess 117. The diameter of the recess 117 is smaller than the outer diameter of the insert 118, defining a void within the insert 118. The diameter of the recess 117 can range from 8 mm to 18 mm (e.g., 10 mm, 12 mm, 14 mm, or 16 mm). The insert 118 is made of a material having a durometer similar to that of the surrounding backing layer 114 and / or polishing layer 112, which can reduce differential polishing as the substrate 10 passes over the insert 118 during the polishing operation. In some implementations, the insert 118 is made of a material with the same durometer as the backing layer 114 and / or polishing layer 112. In some implementations, the insert 118 is made of a material that is resistant to chemical interactions, such as those present in the liquid 132 .

[0032]

[0037] In some implementations, one or more layers of the polishing pad 110 are porous, such as the backing layer 114 and / or the polishing layer 112. In such implementations, the insert 118 is a solid material that is substantially non-porous so that vibrations induced at the top surface 119 are transmitted to the reflective surface 115 without acoustic losses, such as vibrations passing through a porous medium.

[0033]

[0038] The upper inner surface of recess 117 includes a coating or is made of a material that constitutes reflective surface 115. Reflective surface 115 can be provided on the upper inner surface of recess 117 by a metal foil, a metallization coating, or the like. In some implementations, reflective surface 115 reflects at least 90% of light that contacts reflective surface 115 in the optical wavelength range used by in situ vibration monitoring system 160 (e.g., at least 90%, at least 92%, at least 95%). The structure of insert 118 structurally connects upper surface 119 to reflective surface 115 such that vibrations caused by stress energy are transmitted from upper surface 119 to reflective surface 115.

[0034]

[0039] The thickness of the membrane 118a (e.g., the distance between the top surface 119 and the reflective surface 115) can range from 10 mils to 30 mils (e.g., 0.010" to 0.030"). In some implementations, the thickness of the top surface 119 is 20 mils (e.g., 0.020"). A thinner membrane 118a improves vibration detection sensitivity, while a thicker membrane 118a improves durability and product life of the insert 118.

[0035]

[0040] The reflective surface 115 is planar and spans at least a portion of the upper surface of the recess 117 that is parallel to the lower surface of the polishing layer and polishing pad 110. The reflective surface 115 can span between 10% and 100% of the surface area of ​​the upper surface of the recess 117 (e.g., 10% or more, 30% or more, 50% or more, 70% or more, 90% or less, 70% or less, 50% or less, 30% or less, 20% or less, or 100%). In some implementations, the reflective surface 115 can have a width of 8 mm to 18 mm (e.g., 10 mm, 12 mm, 14 mm, or 16 mm).

[0036]

[0041] The light source 162 emits a beam of light 163 directed toward the reflective surface 115. In some implementations, the beam of light 163 is continuous, while in alternative implementations, the beam of light 163 is not continuous (e.g., pulsed). In some implementations, the light source 162 emits a parallel beam of light 163 of a single wavelength, for example, the light source 162 is a laser. The in-situ vibration monitoring system 160 includes a sensor 164 positioned to receive the light 163 scattered from the reflective surface 115. Vibrations from the membrane 118a are converted into displacement of the reflective surface 115. The displacement changes the position at which the light 163 is received by the sensor 164. The sensor 164 generates a signal based on the received beam 163. The sensor 164 is in electronic communication with and transmits the signal to the circuit 168.

[0037]

[0042] The sensor 164 may be connected by circuitry 168 through a rotary coupling (e.g., a mercury slip ring) to a power supply and / or other signal processing electronics 166. The signal processing electronics 166 may be connected to a controller 190. In some implementations, the signal from the sensor 164 may be amplified by an internal amplifier. The signal from the sensor 164 may then be further amplified, filtered, and digitized through an A / D port, if necessary, before reaching a high-speed data acquisition board (e.g., within the electronics 166). Data from the sensor 164 may be recorded at 100 to 400 kHz. In some implementations, data from the sensor 164 is collected at 392 kHz. Data collected at a higher rate (e.g., 100 kHz or higher) provides information about higher frequency vibrations and improves the repeatability of low-frequency components in the vibrations.

[0038]

[0043] In some implementations, the light source 162, the sensor 164, the circuitry 168, and / or the signal processing electronics 166 are included in a single device, such as, for example, a Keyence LK-G5000 sensor head and controller.

[0039]

[0044] 2C , rather than being a separate insert, recess 117 is fabricated in polishing layer 112 itself. A reflective surface 115 is provided on the upper inner surface of recess 117. In such implementations, reflective surface 115 and polishing layer 112 above recess 117 are continuous. The depth of recess 117 is between 10% and 80% of the thickness of polishing layer 112. A lower value increases the durability of polishing layer 112 above recess 117, while a higher value increases the signal from light beam 163 detected by sensor 164. In some implementations, polishing pad 110 includes a portion above recess 117 made of a non-porous material to reduce vibration signal noise, for example, by reflection and damping.

[0040]

[0045] 3 , a top view of the polishing pad 110 is shown, including the grooves 116, the inserts 118, and a portion 180 of the polishing layer 112 surrounding the inserts 118. In some implementations, the portion 180 is flat, i.e., without grooves, and is flush with the top surface of the surrounding polishing layer 112. Implementations that include the portion 180 around the inserts 118 may reduce vibrations transmitted through the inserts 118 due to interaction with the edges of the grooves 116 in the rest of the polishing pad 110. In some implementations, the portion 180 is made of the same material as the inserts 118. In some alternative implementations, the portion 180 is made of a non-porous material, such as the material of the inserts 118.

[0041]

[0046] The insert 118 and in-situ pad vibration monitoring system 160 can be positioned at the center of the platen 120 (e.g., at the axis of rotation 125), at the edge of the platen 120, or at a midpoint (e.g., 5 inches from the axis of rotation for a 20-inch diameter platen).

[0042]

[0047] 1 and 3, when portion 180 of the polishing pad rotates under substrate 10, stick / slip action (e.g., stress energy release) between portion 180 and substrate 10 causes vibration characteristics. However, because portion 180 and sensor 162 are independent of the rest of polishing pad 110 and platen 120, the sensor can selectively acquire vibration behavior from portion 180 of the pad.

[0043]

[0048] The signal received by the sensor 164 from the light source 162 may undergo data processing, e.g., after amplification, pre-filtering, and digitization, for either endpoint detection or feedback or feed-forward control, e.g., in the controller 190. In some implementations, the controller 190 determines the exposure of the underlying layer.

[0044]

[0049] In some implementations, a frequency analysis of the signal is performed. For example, a fast Fourier transform (FFT) may be performed on the signal to generate a frequency spectrum. A specific frequency band may be monitored, and if the intensity of this frequency band exceeds a threshold, it may indicate that an underlying layer has been exposed, which may be used to trigger an endpoint. Alternatively, if the local maximum or minimum width of a selected frequency range exceeds a threshold, it may also indicate that an underlying layer has been exposed, which may be used to trigger an endpoint.

[0045]

[0050] As another example, a wavelet packet transform (WPT) may be performed on the signal to decompose it into low- and high-frequency components. This decomposition can be repeated as necessary to decompose the signal into smaller components. The intensity of one of the frequency components may be monitored; if the intensity of this component exceeds a threshold, this may indicate exposure of the underlying layer and can be used to trigger an endpoint.

[0046]

[0051] Detection of the polishing endpoint triggers a halt to polishing, although polishing may continue for a predetermined amount of time after the endpoint is triggered. Alternatively or additionally, the collected data and / or the endpoint detection time may be fed forward to control processing of the substrate in a subsequent processing operation (e.g., polishing at a subsequent station) or may be fed back to control processing of a subsequent substrate at the same polishing station.

[0047]

[0052] 4 is a flowchart illustrating steps for determining exposure of an underlying layer of a substrate using a reflected optical signal. A substrate is polished by a polishing pad (step 402). This may include holding the substrate on a carrier head, contacting the substrate with a polishing surface, and generating relative motion between the substrate and the polishing pad by, for example, rotating the platen and carrier head. As the substrate moves relative to the polishing pad, energy is released during deformation of the slurry, polishing pad, or substrate material during polishing, and the resulting vibration frequency spectrum is transmitted from the polishing surface to the underside of the polishing layer.

[0048]

[0053] The light source generates a light beam that is directed toward the bottom reflective surface 115 of the polishing pad 110 (step 404). The sensor receives the reflected light beam (step 406) and generates a signal based on the received reflected light beam.

[0049]

[0054] The controller 190 determines the exposure of the underlying layer of the substrate 10 based on the vibration frequency spectrum (step 408). The determination may include performing a fast Fourier transform (FFT) or a wavelet packet transform (WPT) on the signal to determine the vibration frequency spectrum. For example, the total power over a preset wavelength range may be monitored. If the controller 190 detects that the monitored power exceeds a preset threshold, the controller 190 may generate a signal indicating the exposure of the underlying layer. In response to the signal, the controller 190 modifies the process (e.g., stops polishing, changes the applied pressure to the substrate, or modifies the polishing fluid supplied). The in-situ pad vibration monitoring system 160 and / or the controller 190 may perform additional or alternative data processing on the signal or the vibration frequency spectrum, as described herein.

[0050]

[0055] All of the implementations and functional operations described herein can be implemented as digital electronic circuitry, or as computer software, firmware, or hardware, including the structural means disclosed herein and their structural equivalents, or as combinations of these. The implementations described herein can also be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage device for execution by or to control the operation of a data processing apparatus (e.g., a programmable processor, a computer, or multiple processors or computers).

[0051]

[0056] A computer program (also known as a program, software, software application, or code) can be written in any programming language, including compiled or translated languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored as part of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple cooperative files (e.g., files that store one or more modules, subprograms, or portions of code). A computer program can be deployed to be executed on one or more computers, or on multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

[0052]

[0057] The processes and logic flows described herein may be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows may also be performed by, and apparatus may be implemented as, special purpose logic circuitry (e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit)).

[0053]

[0058] The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including, by way of example, a programmable processor, computer, or multiple processors or computers. In addition to hardware, an apparatus may include code that creates the execution environment for the computer program in question (e.g., code comprising processor firmware, a protocol stack, a database management system, an operating system, or any combination of one or more of these). Processors suitable for executing computer programs include, by way of example, both general-purpose and special-purpose microprocessors, and any one or more processors of any kind of digital computer.

[0054]

[0059] Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and memory devices, including, by way of example, semiconductor memory devices (e.g., EPROM, EEPROM, and flash memory devices), magnetic disks (e.g., internal or removable disks), magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0055]

[0060] The polishing apparatus and method described above can be applied to a wide variety of polishing systems. The polishing pad, the carrier head, or both can move to provide relative motion between the polishing surface and the wafer. For example, the platen can orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems, for example, when the polishing pad is a linearly moving continuous belt or a reel-to-reel belt. The polishing layer can be a standard abrasive material (e.g., polyurethane with or without fillers), a soft material, or a fixed abrasive material. It should be understood that the term relative positioning is used, and the polishing surface and wafer can be held in a vertical orientation or in several other orientations.

[0056]

[0061] While this specification contains numerous details of specific implementations, these should not be construed as limiting on any scope of the invention or the scope of the claims, but rather as descriptions of features that may be specific to particular embodiments of a particular invention. Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as operative in particular combinations and initially claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and a claimed combination may be subject to subcombinations or various subcombinations.

[0057]

[0062] Similarly, although acts may be shown in the figures or recited in the claims in a particular order, it should not be understood that performing such acts in the particular order shown, or in any sequential order, or that performing all of the shown acts is necessary to achieve desirable results. Multitasking and parallel processing may be advantageous in certain situations. Furthermore, the separation of various system modules and components in the above-described embodiments should not be understood as requiring such separation in all embodiments. It should also be understood that the program components and systems described may generally be integrated into a single software product or packaged into multiple software products.

[0058]

[0063] Specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. By way of example, the processes illustrated in the accompanying figures do not necessarily need to occur in the particular order shown to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.

Claims

1. 1. A chemical mechanical polishing apparatus, comprising: A platen, a polishing pad including a recessed region, an upper surface of the recessed region extending from and coplanar with the peripheral polishing surface of the polishing pad, and a lower surface of the recessed region having a reflective surface that is parallel to the polishing surface and the lower surface of the polishing pad and recessed from the lower surface of the polishing pad, the reflective surface reflecting light more than other portions of the polishing pad; a carrier head for holding a substrate against the polishing surface of the polishing pad; a motor for generating relative motion between the platen and the carrier head to polish an overlying layer of the substrate; an in-situ pad vibration monitoring system including a light source that emits a light beam and a sensor that receives a reflection of the light beam from the reflective surface; a controller configured to detect exposure of an underlying layer due to the polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system indicative of vibration of the reflective surface in a direction perpendicular to the underside of the polishing pad; and A chemical mechanical polishing apparatus comprising:

2. 10. The apparatus of claim 1, wherein the polishing pad comprises an insert, the top surface of the insert being flush with the top surface of the polishing pad, and the reflective surface being provided on the insert.

3. The apparatus of claim 2 , wherein the polishing pad comprises a porous material and the insert comprises a non-porous material.

4. 3. The apparatus of claim 2, wherein the distance between the top surface of the insert and the reflective surface ranges between 10 mils and 30 mils.

5. The apparatus of claim 2 , wherein the reflective surface has a width ranging between 8 mm and 18 mm.

6. 3. The apparatus of claim 2, wherein the polishing pad has a polishing layer and a plurality of slurry delivery grooves in a polishing surface of the polishing layer, and the insert is positioned in a portion of the polishing pad that does not have slurry delivery grooves.

7. The apparatus of claim 1 , wherein the controller is configured to perform a frequency domain analysis of the measurements received from the sensors of the in-situ pad vibration monitoring system.

8. The apparatus of claim 6 , wherein the controller is configured to detect a polishing endpoint based on frequency domain analysis.

9. In response to the measurements from the sensors of the in-situ pad vibration monitoring system, the controller: adjusting the current pressure of the carrier head; or Adjusting the base pressure for subsequent polishing of new substrates The apparatus of claim 1 configured to:

10. The apparatus of claim 1 , wherein the sensor is configured to receive the reflected light at a frequency of 250 kHz or greater.

11. The apparatus of claim 1 , wherein the sensor is configured to receive the reflected light at a frequency of 395 kHz.

12. generating relative motion between the substrate and a polishing pad of a chemical mechanical polishing apparatus, the polishing pad including a recessed region, an upper surface of the recessed region extending from and coplanar with a peripheral polishing surface of the polishing pad, and a lower surface of the recessed region having a reflective surface parallel to the polishing surface and lower surface of the polishing pad and recessed from the lower surface of the polishing pad; generating a light beam, the light beam being reflected from a reflective surface of the polishing pad, the reflective surface being more reflective than other surfaces of the polishing pad; receiving the reflected light beam with a sensor of the chemical mechanical polishing apparatus; detecting from the reflected light beam a change in vibration of the reflecting surface in a direction perpendicular to the lower surface of the polishing pad; determining a polishing endpoint of the substrate supported by the chemical mechanical polishing apparatus based on the change in vibration; A method comprising:

13. The method of claim 12 further comprising determining a frequency domain analysis of the reflected light beam.

14. The method of claim 13 , wherein the determining the polishing endpoint is based on the frequency domain analysis.

15. The method of claim 13 , wherein the determining a frequency domain analysis comprises performing a Fast Fourier Transform (FFT) or a Wavelet Packet Transform (WPT).

16. Adjusting the current pressure on the carrier head; or adjusting a baseline pressure for subsequent polishing of a new substrate based on said frequency domain analysis; The method of claim 13 further comprising:

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