Measurement of chemical mechanical abrasion vibrations using optical sensors

Abstract

A chemical mechanical polishing device comprises a platen for supporting a 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 upper layer on the substrate, an in-situ vibration monitoring system including a light source for emitting a light beam and a sensor for receiving a reflection of the light beam from the reflective surface of the polishing pad, and a controller configured to detect exposure of the lower layer due to polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system.

Description

Technology Field

[0001] This specification relates to chemical mechanical polishing, and more specifically, to measuring chemical mechanical polishing pad vibrations to detect layer transitions. Background Technology

[0002] Integrated circuits are typically formed on a substrate by the sequential deposition of conductive, semiconducting, or insulating layers on a silicon wafer. One fabrication step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of the patterned layer is exposed. To fill trenches or holes in the insulating layer, a conductive filler layer, for example, may be deposited on the patterned insulating layer. After planarization, portions of the metallic layer remaining between the raised patterns of the insulating layer form vias, plugs, and lines that provide conductive paths between thin-film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains on the non-planar surface. Additionally, planarization of the substrate surface is generally essential for photolithography.

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

[0004] One challenge in CMP is determining whether the polishing process is complete, for example, whether the 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 conditions, the relative speed between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate. In addition to these variations, variations in the initial thickness of the substrate layer also cause variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint generally cannot be determined solely 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 for a motor to rotate a platen or carrier head. However, existing monitoring techniques may not be able to meet the increasing demands of semiconductor device manufacturers.

[0006] In one aspect, the chemical mechanical polishing device comprises a platen for supporting a 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 upper layer on the substrate, an in-situ vibration monitoring system including a light source for emitting a light beam and a sensor for receiving a reflection of the light beam from the reflective surface of the polishing pad, and a controller configured to detect exposure of the lower layer due to polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system.

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

[0008] An apparatus and method for using an in-situ displacement monitoring system comprising a sensor and a light source for detecting vibrations in a polishing pad of a chemical mechanical polishing apparatus are disclosed herein. The detected vibrations correspond to motion induced by friction between a slurry and a substrate moving over a grooved upper surface of the polishing pad, for example, by the release of stress energy. Based on the detected vibrations, a vibration frequency domain analysis is determined, and the frequency domain analysis is monitored to determine a polishing endpoint, for example, to detect exposure of the underlying layer.

[0009] Monitoring displacement at high sampling rates provides wide spectral resolution to the vibration profile. For example, monitoring displacement at up to 350 kHz can provide vibration profile resolution in the range of less than 1 Hz to 175 kHz. Real-time frequency domain analysis enables precise and accurate detection of changes in the vibration profile corresponding to the exposure of underlying layers.

[0010] One or more of the following possible advantages can be realized. Exposure of the underlying layer can be detected more reliably. Polishing can be stopped more reliably, and wafer-to-wafer uniformity can be improved.

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

[0012] Figure 1 illustrates a schematic cross-sectional view of an example of a grinding device. FIG. 2a illustrates a schematic cross-sectional view of a vibration monitoring sensor that monitors the insert of a grinding pad. FIG. 2b illustrates a schematic cross-sectional view of another implementation of a vibration monitoring sensor that monitors an insert through a grinding pad. FIG. 2c illustrates a schematic cross-sectional view of another implementation of a vibration monitoring sensor engaged with a portion of a grinding pad. FIG. 3 illustrates a schematic plan view of a platen having an acoustic monitoring sensor. Figure 4 illustrates a flowchart of an acoustic monitoring method. Similar reference numbers and names in various drawings represent similar elements. Specific details for implementing the invention

[0013] In some semiconductor chip manufacturing processes, an upper layer, e.g., metal, silicon oxide, or polysilicon, is polished until an underlayer, e.g., a dielectric, e.g., silicon oxide, silicon nitride, or a high-K dielectric, is exposed. During the polishing of the upper layers, friction between the slurry, the substrate, and the polishing pad generates vibrations. In some applications, the vibration frequency spectrum changes when the underlayer is exposed. The polishing transition point can be determined by detecting these changes in vibration. For example, an acoustic sensor can be mechanically coupled to the polishing pad. However, such monitoring techniques may not meet the increasing 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.

[0014] By generating a light beam and measuring the reflection of the light beam from the polishing pad, it may be possible to measure the vibrations of the polishing pad with less attenuation and, therefore, reduced noise.

[0015] FIG. 1 illustrates an example of a polishing device (100). The polishing device (100) includes a rotatable disc-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), for example, a DC induction motor, can rotate a drive shaft (124) to rotate the platen (120).

[0016] The polishing pad (110) may be a two-layer polishing pad having an outer polishing layer (112) and a softer back layer (114). In some embodiments, a plurality of slurry transport grooves (116) (see FIG. 2a) are formed on the upper surface of the polishing layer (112) of the polishing pad (110). The grooves (116) extend through the thickness of the polishing layer (112) partially rather than completely. Generally, the grooves (116) have a depth ranging from 25 mil to 30 mil (e.g., 0.025" to 0.030") from the polishing surface of the polishing pad (110), e.g., the upper surface, which may be lower depending on wear of the polishing pad (110) after a number of polishing operations.

[0017] The polishing device (100) may include a port (130) for dispensing a polishing liquid (132), such as a polishing slurry, onto a polishing pad (110). The polishing device may also include a polishing pad conditioner for polishing the polishing pad (110) to maintain the polishing pad (110) in a consistent polishing state.

[0018] The polishing device (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) may have independent control of polishing parameters associated with each respective substrate, e.g., pressure.

[0019] The carrier head (140) may include a retaining ring (142) to hold the substrate (10) under the flexible membrane (144). The carrier head (140) may also include one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers (146a-146c), which can apply independently controllable pressures to associated zones on the flexible membrane (144) and thus on the substrate (10). For convenience of illustration, only three chambers are illustrated in FIG. 1, but there may be one or two chambers, or four or more chambers, e.g., five chambers.

[0020] The carrier head (140) is suspended from a support structure (150), for example, a carousel or a track, and is connected by a drive shaft (152) to a carrier head rotation motor (154), for example, a DC induction motor, so that the carrier head can rotate about an axis (155). Optionally, each carrier head (140) may vibrate laterally, for example, on sliders on the carousel (150), or by rotational vibration of the carousel itself, or by sliding along the track. In typical operation, the platen rotates about the central axis (125) of the platen, and each carrier head rotates about the central axis (155) of the carrier head and is translated laterally across the upper surface of the polishing pad.

[0021] A controller (190), such as a programmable computer, is connected to motors (121, 154) to control the rotational speed of the platen (120) and the carrier head (140). For example, each motor may include an encoder that measures the rotational speed of the associated drive shaft. A feedback control circuit, which may be in the motor itself, part of the controller, or a separate circuit, receives the rotational speed measured by the encoder and adjusts the current supplied to the motor to ensure that the rotational speed of the drive shaft matches the rotational speed received from the controller.

[0022] Vibrations of the polishing pad to be monitored may be caused by the release of acoustic energy when the slurry, polishing pad, or substrate material undergoes deformation during polishing, and the resulting vibration frequency spectrum is related to the material properties of the slurry, polishing pad, and / or substrate. Possible sources of this energy, also referred to as "stress energy," and their characteristic frequencies, without being limited to any specific theory, include the breaking of chemical bonds, characteristic phonon frequencies, slip-stick mechanisms, etc. Vibrations generated during polishing may include noise (sometimes also referred to as an acoustic signal) generated by friction of the substrate against the polishing pad, or noise generated by cracking, chipping, breakage, or similar occurrence of defects on the substrate.

[0023] Vibrations can be monitored by optically monitoring the displacement of a portion of the polishing pad. Measuring displacement using a light source (e.g., a laser) provides high accuracy and high-frequency monitoring of the vibrations. An optical monitoring system can detect small displacements of the surface of the polishing pad with a high sampling rate (e.g., over 300 kHz) to facilitate precise reconstruction of the polishing pad vibrations. Additionally, it allows for direct measurement of vibrations, with no intermediate medium or mechanical coupling between the projected light and the bottom surface of the insert (118), and with minimal loss from the air within the recess (117) or added noise.

[0024] A position sensor, for example, an optical interrupter or rotary encoder connected to the rim of the platen, can be used to detect the angular position of the platen (120). This allows only parts of the signal measured when the light source (162) is close to the substrate, for example, when the light source (162) is under the carrier head or substrate, to be used for endpoint detection.

[0025] The polishing device (100) includes at least one in-situ vibration monitoring system (160). In particular, the in-situ vibration monitoring system (160) may be configured to detect vibrations in the polishing pad (110) caused by stress energy when the material of the substrate (10) undergoes deformation. The vibrations are transmitted through the polishing layer (112) and the back layer (114) of the polishing pad (110) and can be detected by the in-situ pad vibration monitoring system (160).

[0026] The in-situ vibration monitoring system (160) includes a displacement sensor assembly comprising a light source (162) positioned to direct light to a position on the bottom surface of the polishing pad, and a detector (164) for detecting reflections of light from the polishing pad. In some embodiments, the in-situ vibration monitoring system (160) includes a plurality of displacement sensor assemblies, thereby allowing vibration to be monitored at a plurality of positions on the polishing pad, for example, positions located equidistant from the axis of rotation (125) and / or evenly spaced around the axis of rotation (125).

[0027] In the embodiment illustrated in FIGS. 1 and 2a, the polishing pad (110) includes an insert (118) that is fixed to the polishing layer (112) and extends through the polishing layer, so that the upper surface (119) of the insert (118) and the uppermost surface of the polishing layer (112), e.g., the polishing surface (112a), are coplanar, so that the upper surface (119) will come into contact with the substrate (10) during operation. In some embodiments, as illustrated in FIG. 2a, the insert (118) extends through both the polishing layer and the back layer (114). In some embodiments, e.g., the embodiment of FIG. 2b, the insert extends through the polishing layer (112) but does not extend into the back layer (114). Rather, a void (114a) of the back layer (114) is located beneath the insert (118).

[0028] The insert (118) is generally cylindrical, but other shapes are possible. As illustrated in FIG. 2a, the insert (118) may be drum-shaped, having a membrane (118a) and annular sidewalls (118b) extending downward from the outer edges of the membrane (118a). The membrane (118a) may be thinner than the polishing layer (112). The thickness of the membrane (118a) may be 20% to 90% of the thickness of the polishing layer (112). The bottom edges of the sidewalls (119b) may be positioned against the top of the platen (120).

[0029] Optionally, as illustrated in FIG. 2b, a flange (118c), for example, an annular flange, may extend radially outward from the bottom edge of the annular sidewall (118b). The annular flange (118b) may be trapped between the polishing layer (112) and the back layer (114), or between the back layer (114) and the platen (120). In some embodiments, the flange (118b) is attached to the back layer (114) with an adhesive or adhesive tape to increase the stability of the insert (118) to the back layer (114).

[0030] In some embodiments, the outer diameter of the insert (118) (e.g., edge-to-edge) is in the range of 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 lower than the outer diameter of the insert (118) and defines a void within the insert (118). The diameter of the recess (117) may be in the range of 8 mm to 18 mm (e.g., 10 mm, 12 mm, 14 mm, or 16 mm). The insert (118) is composed of a material having a hardness similar to that of the surrounding back layer (114) and / or polishing layer (112), which can reduce differential polishing when the substrate (10) passes over the insert (118) during a polishing operation. In some embodiments, the insert (118) is composed of a material of the same hardness as the back layer (114) and / or the polishing layer (112). In some embodiments, the insert (118) is composed of a material resistant to chemical interactions, such as chemicals present in the liquid (132).

[0031] In some embodiments, one or more layers of the polishing pad (110), such as the back layer (114) and / or the polishing layer (112), are porous. In such embodiments, the insert (118) is a substantially non-porous solid material so that vibrations induced on the upper surface (119) are transmitted to the reflective surface (115) without acoustic loss, such as vibrations transmitted through a porous medium.

[0032] The upper inner surface of the recess (117) comprises a coating that constitutes the reflective surface (115) or is composed of such a material. The reflective surface (115) may be provided on the upper inner surface of the recess (117) by a metallic foil, a metallized coating, etc. In some embodiments, the reflective surface (115) reflects at least 90% (e.g., at least 90%, at least 92%, at least 95%) of the light in contact with the reflective surface (115) within the optical wavelength range used by the in-situ vibration monitoring system (160). The configuration of the insert (118) structurally connects the upper surface (119) to the reflective surface (115) so that vibrations caused by stress energy are transmitted from the upper surface (119) to the reflective surface (115).

[0033] The thickness of the membrane (118a), for example, the distance between the upper surface (119) and the reflective surface (115), may be in the range of 10 mil to 30 mil (e.g., 0.010" to 0.030"). In some embodiments, the thickness of the upper surface (119) is 20 mil (e.g., 0.020"). A reduced thickness of the membrane (118a) increases vibration detection sensitivity, while an increased thickness increases the durability of the insert (118) and the product life.

[0034] The reflective surface (115) is flat and extends over at least a portion of the upper surface of the recess (117) parallel to the lower surface of the polishing layer and the polishing pad (110). The reflective surface (115) may extend over the upper surface of the recess (117) in a range of 10% to 100% of the surface area (e.g., more than 10%, more than 30%, more than 50%, more than 70%, less than 90%, less than 70%, less than 50%, less than 30%, less than 20%, or 100%). In some embodiments, the reflective surface (115) may have a width in the range of 8 mm to 18 mm (e.g., 10 mm, 12 mm, 14 mm, or 16 mm).

[0035] A light source (162) emits a light beam (163) directed toward a reflective surface (115). In some embodiments, the light beam (163) is continuous, and in alternative embodiments, the light beam (163) is discontinuous, for example, pulsed. In some embodiments, the light source (162) emits a collimated light beam (163) of a single wavelength, for example, the light source (162) is a laser. An in-situ vibration monitoring system (160) includes a sensor (164) positioned to receive 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 where the light (163) is received by the sensor (164). The sensor (164) generates a signal based on the received beam (163). The sensor (164) communicates electronically with the circuit (168) and transmits a signal to the circuit (168).

[0036] The sensor (164) may be connected by circuit (168) to a power supply and / or other signal processing electronic circuit (166) via a rotary coupling, e.g., a mercury slip ring. The signal processing electronic circuit (166) may, in turn, be connected to a controller (190). In some implementations, the signal from the sensor (164) may be amplified by a built-in internal amplifier. Then, the signal from the sensor (164) may be further amplified and filtered as needed, and may be digitized, for example, via an A / D port to a high-speed data acquisition board of the electronic circuit (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 higher rates (e.g., above 100 kHz) provides information about higher frequency vibrations and increases the reproduction of lower frequency components in the vibrations.

[0037] In some implementations, the light source (162), sensor (164), circuit (168), and / or signal processing electronic circuit (166) are included in a single device, e.g., an LK-G5000 sensor head and controller manufactured by Keyence.

[0038] In FIG. 2c, a recess (117) is formed in the polishing layer (112) itself rather than in a separate insert. A reflective surface (115) is provided on the upper inner surface of the recess (117). In such embodiments, the polishing layer (112) over the recess (117) and the reflective surface (115) is continuous. The depth of the recess (117) is 10% to 80% of the thickness of the polishing layer (112). Lower values ​​increase the durability of the polishing layer (112) over the recess (117), whereas higher values ​​increase the signal from the light beam (163), as detected by the sensor (164). In some embodiments, the polishing pad (110) includes a portion over the recess (117) composed of a non-porous material to reduce vibration signal noise, for example, through reflection and attenuation.

[0039] Additionally, referring to FIG. 3, a plan view of a polishing pad (110) is shown, comprising grooves (116), an insert (118), and a portion (180) of the polishing layer (112) surrounding the insert (118). In some embodiments, the portion (180) is flat, that is, without grooves, and is coplanar with the top surface of the surrounding polishing layer (112). Embodiments including a portion (180) around the insert (118) can reduce vibrations transmitted through the insert (118) due to interaction with the edges of the grooves (116) of the rest of the polishing pad (110). In some embodiments, the portion (180) is composed of the same material as the insert (118). In some alternative embodiments, the portion (180) is composed of a non-porous material, e.g., the material of the insert (118).

[0040] The insert (118) and the in-situ pad vibration monitoring system (160) underneath it may be positioned at the center of the platen (120), for example, on the axis of rotation (125), at the edge of the platen (120), or at an intermediate point (for example, 5 inches from the axis of rotation in the case of a 20-inch diameter platen).

[0041] When the portion (180) of the polishing pad rotates under the substrate (10), referring to FIGS. 1 and 3, stick / slip operation between the portion (180) and the substrate (10), for example, stress energy release, will cause vibration characteristics. However, since the portion (180) and the sensor (162) are independent of the rest of the platen (120) and the polishing pad (110), the sensor can selectively pick up vibration behavior from the pad portion (180).

[0042] For example, the signal received by the sensor (164) from the light source (162) after amplification, preliminary filtering, and digitization may receive data processing from, for example, a controller (190) for endpoint detection or feedback or feedforward control. In some implementations, the controller (190) determines the exposure of the lower layer.

[0043] In some implementations, 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 the frequency band exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint. Alternatively, if the width of a local maximum or minimum in a selected frequency range exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint.

[0044] As another example, wavelet packet transform (WPT) can be performed on the signal to decompose it into low-frequency and high-frequency components. If necessary, the decomposition can be repeated to divide the signal into smaller components. The intensity of one of the frequency components can be monitored, and if the intensity of the component exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint.

[0045] Detection of the polishing endpoint triggers the cessation of polishing, but 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 subsequent processing operations, e.g., processing of a substrate during polishing at a subsequent station, or fed back to control processing of a subsequent substrate at the same polishing station.

[0046] FIG. 4 is a flowchart illustrating steps for determining the exposure of the lower layer of a substrate using reflected optical signals. The substrate is polished by a polishing pad (step (402)). This may include holding the substrate on a carrier head and bringing the substrate into contact with a polishing surface, and, for example, generating relative motion between the substrate and the polishing pad by rotating the platen and the carrier head. As the substrate undergoes relative motion with the polishing pad, energy is released between the slurry, the polishing pad, or the substrate material during polishing, causing deformation, and the resulting vibration frequency spectrum is transmitted from the polishing surface to the lower side of the polishing layer.

[0047] The light source generates a light beam directed toward a reflective surface (115) on the bottom 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.

[0048] The controller (190) determines the exposure of the lower layer of the substrate (10) based on the vibration frequency spectrum (step (408)). The determination may include performing a Fast Fourier Transform (FFT) or Wavelet Packet Transform (WPT) on the signal to determine the vibration frequency spectrum. For example, the total power of 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 lower layer. In response to the signal, the controller (190) modifies the processing process, for example, by stopping the polishing, changing the pressure applied to the substrate, or modifying the supplied polishing fluid. The in-situ pad vibration monitoring system (160) and / or the controller (190) may perform additional or alternative data processing on the vibration frequency spectrum or on the signal as described herein.

[0049] All of the implementations and functional operations described herein may be implemented as digital electronic circuits comprising the structural means and their structural equivalents disclosed herein, or as computer software, firmware, or hardware, or combinations thereof. The implementations described herein may be implemented as one or more non-transient computer program products, that is, as one or more computer programs (tangibly embodied in a machine-readable storage device for execution by a data processing device, e.g., a programmable processor, a computer, or a plurality of processors or computers, or for controlling the operation thereof).

[0050] A computer program (also known as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, and may be distributed in any form, including as a standalone 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 may be stored in other programs or in part of a file holding data, in a single file dedicated to the program, or in multiple co-working files (e.g., files storing one or more modules, subprograms, or parts of code). A computer program may be distributed to be executed on a single computer, or on multiple computers located in one place or distributed across multiple locations and interconnected by a communication network.

[0051] The processes and logic flows described herein may be performed by one or more programmable processors that execute one or more computer programs to perform functions by manipulating input data and generating outputs. The processes and logic flows may also be performed by special-purpose logic circuits, for example, a Field Programmable Gate Array (FPGA) or an Application-Specific Integrated Circuit (ASIC), and the device may also be implemented as such special-purpose logic circuits.

[0052] The term “data processing device” includes all devices, devices, and machines for processing data, including, for example, a programmable processor, a computer, or a number of processors or computers. In addition to hardware, a device may include code that creates an execution environment for the computer program, for example, processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of these. Processors suitable for executing the computer program include, for example, both general-purpose and special-purpose microprocessors, and any one or more processors of any type of digital computer.

[0053] Computer-readable media suitable for storing computer program instructions and data include, for example, semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; optomagnetic disks; and all forms of non-volatile memory, media, and memory devices, including CD-ROM and DVD-ROM disks. Processors and memory may be complemented by or included therein by special-purpose logic circuits.

[0054] The polishing devices and methods described above can be applied to various polishing systems. The polishing pad, or the carrier head, or both, may move to provide relative motion between the polishing surface and the wafer. For example, the platen may orbit instead of rotating. The polishing pad may be a circular (or any other shaped) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems (e.g., a continuous or reel-to-reel belt in which the polishing pad moves linearly). The polishing layer may be a standard (e.g., polyurethane with or without fillers) abrasive material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and the wafer may be maintained in a vertical orientation or any other orientation.

[0055] Although this specification contains many specific implementation details, they should not be interpreted as limitations on the scope of any invention or the scope of the subject matter to be claimed, but rather as descriptions of features that may be specific to specific embodiments of specific inventions. Specific features described in this specification in the context of separate embodiments may also be combined and implemented in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments. Furthermore, although features may be described above as operating in specific combinations and may even be initially claimed as such, one or more features from the claimed combination may, in some cases, be omitted from the combination, and the claimed combination may relate to a sub-combination or a variation of a sub-combination.

[0056] Similarly, although operations are illustrated in the drawings and enumerated in the claims in a specific order, this should not be understood as requiring that such operations be performed in the specific order illustrated or in a sequential order, or that all illustrated operations be performed, in order to achieve desired results. In certain situations, multitasking and parallel processing may be advantageous. Furthermore, the distinction between the various system modules and components in the embodiments described above should not be understood as requiring such distinction in all embodiments, and it should be understood that the described program components and systems may generally be integrated together into a single software product or packaged into multiple software products.

[0057] Specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the operations described in the claims may be performed in different orders and still achieve desired results. As an example, the processes illustrated in the accompanying drawings do not necessarily require the specific order or sequential order illustrated to achieve desired results. In some cases, multitasking and parallel processing may be advantageous.

Claims

Claim 1 A chemical mechanical polishing device comprising: a platen for supporting a polishing pad, wherein the polishing pad comprises a recessed area, the uppermost surface of the recessed area extends from and is coplanar with the peripheral polishing surface of the polishing pad, and the bottom surface of the recessed area is parallel to the lower surface of the polishing pad and comprises a reflective surface recessed from the lower surface, wherein the reflective surface is more reflective than the remainder 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 upper layer on the substrate; an in-situ pad vibration monitoring system comprising a light source for emitting a light beam and a sensor for receiving a reflection of the light beam from the reflective surface; and a controller configured to detect exposure of the lower layer due to polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system, wherein the measurements represent vibration of the reflective surface in a direction perpendicular to the lower surface of the polishing pad. Claim 2 delete Claim 3 A device according to claim 1, wherein the polishing pad includes an insert, the upper surface of the insert is coplanar with the upper surface of the polishing pad, and the reflective surface is received within the insert. Claim 4 A device according to paragraph 3, wherein the polishing pad comprises a porous material and the insert comprises a non-porous material. Claim 5 In paragraph 3, the device wherein the distance between the upper surface of the insert and the reflective surface received within the insert is in the range of 10 mil to 30 mil. Claim 6 In paragraph 3, the device wherein the reflective surface accommodated within the insert has a width ranging from 8 mm to 18 mm. Claim 7 delete Claim 8 In paragraph 3, the polishing pad has a polishing layer and a plurality of slurry transport grooves on the polishing surface of the polishing layer, and the insert is positioned in a portion of the polishing pad that is not a slurry transport groove. Claim 9 In claim 1, the controller is configured to perform frequency domain analysis of the measurements received from the sensor of the in-situ pad vibration monitoring system. Claim 10 In claim 9, the device is configured such that the controller detects a polishing endpoint based on the frequency domain analysis. Claim 11 In claim 1, the device is configured such that the controller, in response to measurements from a sensor of the in-situ pad vibration monitoring system: adjusts the current pressure of the carrier head; or adjusts the baseline pressure of subsequent polishing of a new substrate. Claim 12 A device according to claim 1, wherein the sensor is configured to receive the reflected light beam at a frequency of 250 kHz or higher. Claim 13 In claim 1, the device is configured such that the sensor receives the reflected light beam at a frequency of 395 kHz. Claim 14 A method comprising: generating relative motion between a polishing pad of a chemical mechanical polishing device and a substrate, wherein the polishing pad comprises a recessed area, the uppermost surface of the recessed area extends from a peripheral polishing surface of the polishing pad and lies coplanarly therewith, and the bottom surface of the recessed area is parallel to a lower surface of the polishing pad and includes a reflective surface recessed from the lower surface; generating a light beam, wherein the light beam is reflected from the reflective surface of the polishing pad, and the reflective surface is more reflective than the rest of the polishing pad; receiving the reflected light beam by a sensor of the chemical mechanical polishing device; detecting a change in vibration in a direction perpendicular to the lower surface of the polishing pad; and determining a polishing endpoint of a substrate supported by the chemical mechanical polishing device based on the change in vibration. Claim 15 A method according to claim 14, further comprising the step of determining the frequency domain analysis of the reflected light beam. Claim 16 In paragraph 15, the step of determining the polishing endpoint is a method based on the frequency domain analysis. Claim 17 In claim 15, the step of determining the frequency domain analysis comprises the step of performing a Fast Fourier Transform (FFT) or a Wavelet Packet Transform (WPT). Claim 18 A method according to claim 15, further comprising the step of adjusting the current pressure of the carrier head; or the step of adjusting the baseline pressure of subsequent polishing of a new substrate based on the frequency domain analysis.

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