Acoustic monitoring of CMP retaining rings

Abstract

A chemical mechanical polishing apparatus includes: a platform supporting a polishing pad; the bearing head is used for fixedly holding the surface of the substrate to abut against the polishing pad; an acoustic sensor, which is supported on the platform; and the motor generates relative movement between the platform and the bearing head so as to polish the substrate. The carrier head includes a retaining ring for holding the substrate, and the acoustic sensor travels in a path below the carrier head and the retaining ring. A controller is configured to analyze a signal from the acoustic sensor and determine a characteristic of the retaining ring based on the signal.

Description

Technical Field

[0001] The present disclosure relates to in-situ monitoring of chemical mechanical polishing, and in particular, to acoustic monitoring. Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing a conductive layer, a semiconductor layer, or an insulating layer on a silicon wafer. One manufacturing step involves depositing a fill layer on a non-planar surface and planarizing the fill layer. For some applications, for example, a conductive fill material is used to fill a trench or hole in an insulating layer, and the fill layer is planarized until the top surface of the patterned layer is exposed. For other applications (such as oxide polishing), the fill layer is planarized, for example, by polishing for a predetermined period of time to leave a portion of the fill layer on the non-planar surface. In addition, photolithography generally requires planarization of the substrate surface.

[0003] Chemical mechanical polishing (CMP) is an accepted planarization method. This planarization method generally requires mounting the substrate on a carrier or polishing head. The exposed surface of the substrate is generally placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. The carrier head generally includes a retaining ring to surround the substrate and hold the substrate under the carrier head. The lower surface of the retaining ring can be pressed against the polishing pad and can wear as polishing progresses. Therefore, the retaining ring may need to be replaced periodically.

[0004] In some systems, the substrate is monitored in situ during polishing.Acoustic monitoring of the substrate during polishing has been proposed. Summary of the invention

[0005] In one aspect, a chemical mechanical polishing apparatus includes: a platform supporting a polishing pad; a carrier head holding a surface of a substrate against the polishing pad; an acoustic sensor supported on the platform; and a motor generating relative motion between the platform and the carrier head to polish the substrate. The carrier head includes a retaining ring for holding the substrate, and the acoustic sensor travels in a path under the carrier head and the retaining ring. A controller is configured to analyze a signal from the acoustic sensor and determine a characteristic of the retaining ring based on the signal.

[0006] In another aspect, a chemical mechanical polishing apparatus includes: a platform supporting a polishing pad; a carrier head holding a surface of a substrate against the polishing pad; an acoustic sensor supported on the platform; and a motor generating relative motion between the platform and the carrier head for polishing the substrate. The carrier head includes a retaining ring for holding the substrate, and the acoustic sensor travels in a path under the carrier head and the retaining ring. A controller is configured to select a portion of a signal from the acoustic sensor corresponding to the acoustic sensor under the retaining ring, and is configured to generate an alarm or modify a polishing parameter based on the selected portion of the signal from the acoustic sensor.

[0007] One or more of the following possible advantages may be achieved. The retaining ring may be monitored in real time and in situ. In situ monitoring may be used to determine if the retaining ring is "broken in", thereby reducing the time required for polishing system qualification. The wear state of the retaining ring may be monitored. The signal from the acoustic monitoring system may depend on the flatness or taper angle of the bottom surface of the retaining ring, which may be used as a basis for adjusting other polishing parameters to improve wafer-to-wafer (WTW) and within-wafer (WIW) polishing uniformity.

[0008] The details of one or more embodiments are set forth in the accompanying drawings and the description below.Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A schematic cross-sectional view of an example of a polishing system is illustrated.

[0010] Figure 2 A top view of the polishing system is shown.

[0011] Figure 3 A schematic cross-sectional view of an acoustic monitoring sensor beneath a retaining ring of a carrier head is illustrated.

[0012] In the drawings, like reference numerals denote like elements. DETAILED DESCRIPTION

[0013] During polishing, the polishing pad wears away the bottom surface of the retaining ring. Typically, wear does not occur at a uniform rate radially across the retaining ring, so the bottom surface exhibits a non-flat geometry. However, the wear of the retaining ring eventually reaches equilibrium, such that the bottom surface of the retaining ring maintains substantially the same geometry as the ring wears until the process or polishing conditions change. Due to the constant change in the geometry of the retaining ring, the polishing rate profile will drift until the retaining ring reaches equilibrium.

[0014] In order to reduce polishing variations between or across substrates, the retaining ring may be "broken in" prior to use in the polishing process. One method of breaking in the retaining ring is to simulate substrate polishing, for example, by pressing the retaining ring against a moving polishing pad, causing the ring to wear until an equilibrium geometry is achieved. However, the disadvantage of "breaking in" is that it is time consuming and requires the use of a polishing apparatus. As a result, the breaking in process is downtime for the polishing apparatus, during which polishing cannot be performed, thereby increasing the cost of ownership.

[0015] By acoustically monitoring the retaining ring, it is possible to determine in real time and in situ when the retaining ring is breached. Thus, the time required for breach can be reduced.

[0016] As another problem, the impact of the substrate on the inner surface of the retaining ring can cause grooves on the inner surface. The grooves in turn affect the pressure applied to the edge of the substrate, thereby affecting the polishing uniformity.

[0017] By acoustically monitoring the retaining ring, the formation of grooves on the inner surface of the retaining ring can be detected. This allows for quick replacement of the retaining ring, thereby reducing the possibility of polishing non-uniformity.

[0018] More generally, acoustic monitoring of the retaining ring can be used to improve the polishing process. For example, signals from the acoustic monitoring system can indicate the geometry and / or smoothness of the lower surface of the retaining ring, which can affect the polishing profile of the substrate, particularly near the edge of the substrate. Thus, these signals can be used as input to control various polishing parameters, such as the pressure applied in different areas of the substrate, to improve polishing performance.

[0019] Any of these problems may be addressed independently of the others, or the system may address multiple problems.

[0020] Figure 1 An example of a polishing apparatus 100 is illustrated. The polishing apparatus 100 includes a rotatable dish-shaped platform 120 on which a polishing pad 110 is disposed. The polishing pad 110 may be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The platform may be operated to rotate about an axis 125. For example, a motor 121 (e.g., a DC induction motor) may rotate a drive shaft 124 to rotate the platform 120.

[0021] The polishing apparatus 100 may include a port 130 for dispensing a polishing liquid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner for grinding the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.

[0022] The polishing apparatus 100 includes a carrier head 140. The carrier head 140 is operable to hold the substrate 10 against the polishing pad 110. The carrier head 140 includes a retaining ring 170 to hold the substrate 10 below the flexible membrane 144. The retaining ring 170 may include a lower portion 172 formed of a wear-resistant plastic (e.g., PPS) that is compatible with the polishing process, and an upper portion 174 formed of a more rigid material (e.g., metal). Alternatively, the entire retaining ring may be formed of plastic. The retaining ring 170 is typically fixed to the carrier head 140 using screws so that the retaining ring 170 can be removed and replaced.

[0023] The carrier head 140 also includes one or more independently controllable pressurizable chambers (e.g., three chambers 146a to 146c) defined by the membrane, which can apply independently controllable pressure to associated areas on the flexible membrane 144 and thus to the substrate 10 (see Figure 1 ). Although for the sake of convenience in Figure 1 Only three chambers are shown in FIG, but there may be one or two chambers, or four or more chambers, for example five chambers.

[0024] The carrier heads 140 are suspended from a support structure 150 (e.g., a turntable or track) and are connected to a carrier head rotation motor 154 (e.g., a DC induction motor) via a drive shaft 152 so that the carrier heads can rotate about an axis 155. Optionally, each carrier head 140 can swing laterally, such as on a slider on the turntable 150, or by rotational swinging of the turntable itself, or by sliding along a track. In typical operation, the platform rotates about its central axis 125, and each carrier head rotates about its central axis 155 and translates the top surface laterally across the top surface of the polishing pad.

[0025] A controller 190 (eg, a programmable computer) is coupled to the motors 121, 154 to control the rotational rates of the platform 120 and carrier head 140. For example, each motor may include an encoder that measures the rotational rate of the associated drive shaft.

[0026] The polishing apparatus 100 includes at least one in-situ acoustic monitoring system 160. The in-situ acoustic monitoring system 160 includes one or more acoustic signal sensors 162. Each acoustic signal sensor may be mounted at one or more locations on the platform 120. In particular, the in-situ acoustic monitoring system may be configured to detect an acoustic signal from the retaining ring 170.

[0027] A position sensor (e.g., an optical interrupter or a rotary encoder attached to the platform rim) may be used to sense the angular position of the platform 120. This allows only the portion of the signal measured when the sensor 162 is close to the retaining ring 170 (e.g., when the sensor 162 is below the retaining ring) to be used in subsequent signal processing as an indication of the state of the retaining ring.

[0028] exist Figure 1 and Figure 3 In the embodiment shown in FIG. 1 , the acoustic monitoring system 160 includes an acoustic sensor 162 supported and positioned by the platform 120 to receive acoustic signals from the substrate 10 through the polishing pad 110. The acoustic sensor 162 may be partially or completely located in a recess 164 in the top surface of the platform 120. In some embodiments, the top surface of the acoustic sensor 162 is coplanar with the top surface of the platform 120.

[0029] In some embodiments, the portion of the polishing pad directly above the acoustic sensor 162 may include an acoustic window 119, e.g., a region having a lower acoustic impedance than the surrounding polishing material. The acoustic window 119 may extend through the polishing layer 112, or the backing layer 114, or both. However, if the acoustic transmission of the polishing pad is sufficiently high, the acoustic window 119 may not be necessary.

[0030] The acoustic sensor 162 is a contact acoustic sensor having a portion of the polishing pad, such as the polishing layer 112, or the backing layer 114, or the acoustic window 119, connected to (e.g., in direct contact, or with only an adhesive layer for attachment, or with only an acoustic gel for transmitting an acoustic signal therefrom) a portion of the polishing pad, such as the polishing layer 112, or the backing layer 114, or the acoustic window 119. For example, the acoustic sensor 162 may be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. The piezoelectric sensor may include: a rigid contact plate, such as stainless steel, etc., which is placed in contact with the subject to be monitored; and a piezoelectric component on the back side of the contact plate, such as a piezoelectric layer sandwiched between two electrodes.

[0031] In some embodiments, the acoustic sensor 162 is positioned within a recess 169 in the housing 163. An optional spring 165 can be disposed between the housing 163 and the support 167, providing pressure against the housing 163. The pressure on the housing 163 forces the acoustic sensor 162 to contact a portion of the polishing pad 110. Alternatively, the spring 165 can be pressed directly against the acoustic sensor 162, for example, if no housing is used. In some embodiments, the spring 165 is a long travel spring 165 to supply similar pressure to the strong spring 165 over a larger compression range.

[0032] The acoustic sensor 162 may be connected to a power source and / or other signal processing electronics 166 via circuitry 168 through a rotational coupling (eg, a mercury slip ring).

[0033] In some embodiments, the in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, the signal is monitored by the acoustic sensor 162 without generating a signal from the acoustic signal generator (or the acoustic signal generator may be omitted from the system entirely). The passive acoustic signal monitored by the acoustic sensor 162 may be in the range of 50 kHz to 1 MHz, such as 200 to 400 kHz, or 200 KHz to 1 MHz. For example, to monitor the polishing of an interlayer dielectric (ILD) in a shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz may be monitored.

[0034] The signal from the sensor 162 may be amplified by a built-in internal amplifier or by an external amplifier. In some embodiments, the amplification gain is between 40 and 60 dB (e.g., 50 dB). If necessary, the signal from the acoustic sensor 162 may then be further amplified and filtered and digitized through an A / D port to, for example, a high-speed data acquisition board in the electronic device 166. The data from the acoustic sensor 162 may be recorded in a similar range to that of the generator 163 or in a different range, such as a higher range, such as from 1 to 10 MHz, such as 1 to 3 MHz or 6 to 8 Mz. In embodiments where the acoustic sensor 162 is a passive acoustic sensor, a frequency range from 100 kHz to 2 MHz, such as 500 kHz to 1 MHz (e.g., 750 kHz) may be monitored.

[0035] If positioned in the platform 120, the acoustic sensor 162 may be located at the center of the platform 120, for example, at the rotation axis 125, at an edge of the platform 120, or at a midpoint (eg, 5 inches from the rotation axis for a 20 inch diameter platform).

[0036] refer to Figure 2, due to the motion of the platform 120 (as shown by arrow A), the sensor 162 sweeps in a path (as shown by dashed arrow B) traveling under the retaining ring 170 and the substrate 10. The acoustic monitoring system 160 (e.g., the controller 190) can be configured to sample the signal from the sensor 162 as the sensor passes under the retaining ring 170. For example, the controller 190 can determine the angular position of the sensor 162 based on input from a motor encoder or a platform position sensor and compare it to the position of the carrier head 140 and the retaining ring 170 (e.g., based on the sweep information). The determination of the position of the sensor relative to the substrate is discussed in U.S. Pat. No. 6,159,073 and U.S. Pat. No. 6,296,548. This allows the portion of the signal received when the sensor 162 is under the retaining ring 170 to be identified and selected. Portions of the signal corresponding to the sensor in other positions (e.g., under the substrate 10 or not under the carrier head 140 at all) can be used for other monitoring purposes, such as detecting defects on the substrate 10, but are not necessarily used for the retaining ring monitoring discussed below.

[0037] Back to Figure 1 and 3 , the acoustic signal generated by the interface between the retaining ring 174 and the polishing layer 112 of the pad 110 travels through the polishing pad 110 and is received by the acoustic sensor 162. The acoustic sensor 162 transmits the received signal to the signal processing electronics 166 to perform functions on the received acoustic signal. The electronics 166 may include, for example, filters, amplifiers, spectrum analyzers, data acquisition systems (DAQ), or other components for processing received acoustic signals. Typically, the electronics 166 may include a general purpose programmable computer, a dedicated circuit system, or a combination thereof. In some embodiments, the electronics 166 is within the controller 190, for example, implemented by the controller 190.

[0038] The signal from the acoustic sensor 162 (e.g., after amplification, preliminary filtering, and digitization) may be subjected to data processing, for example, in the controller 190, for use in detecting various stages of the retaining ring (e.g., the retaining ring is damaged or a groove is formed on the inner surface of the retaining ring), or for feedback or feedforward control of polishing parameters. The controller 190 may generate an alarm indicating the type of event, for example, the alarm may indicate which of the retaining ring damage or groove formation (or other possible events, such as unclassified events) has occurred.

[0039] In some embodiments, the controller 190 is configured to monitor changes in acoustic signal strength. For example, for an active acoustic monitoring system (where the sensor 162 transmits acoustic energy), the received signal strength is compared to the transmitted signal strength to produce a normalized signal, and the normalization can be monitored over time to detect changes. As another example, for a passive acoustic monitoring system, the received signal strength is compared to a measured initial signal strength (e.g., obtained when the retaining ring is newly installed on the carrier head) to produce a normalized signal, and the normalization can be monitored over time to detect changes. The change may indicate that the retaining ring is damaged.

[0040] In some embodiments, a frequency analysis of the signal is performed. For example, frequency domain analysis can be used to determine changes in the relative power of spectral frequencies and determine when a membrane transformation occurs at a specific radius. Information about the time of transformation by radius can be used to trigger an endpoint. As another example, a fast Fourier transform (FFT) can be performed on the signal to produce a frequency spectrum. Specific frequencies can be monitored, and if the intensity in a frequency band exceeds a threshold, this can indicate a change in the retaining ring, for example, the retaining ring is damaged or a groove is formed on the inner surface of the retaining ring. Alternatively, if the location (e.g., wavelength) or bandwidth of a local maximum or minimum in a selected frequency range exceeds a threshold, this can indicate a change in the retaining ring.

[0041] In some embodiments, the spectrum of the signal (e.g., power, wavelength, or frequency spectrum) can be compared to a reference spectrum. If the difference (e.g., the sum of the squares of the differences in power, wavelength, or frequency range) exceeds or falls below a threshold, this can indicate a change in the retaining ring, such as damage to the retaining ring or the formation of grooves on the inner surface of the retaining ring.

[0042] Determination of appropriate characteristics of the signal to monitor and appropriate criteria for triggering an indication of a change in the retaining ring may be determined empirically. For example, polishing may be performed using a worn retaining ring known to be in balance, and the spectrum of the signal from the retaining ring may be used as a reference spectrum. As another example, polishing may be performed using both a new retaining ring and a worn retaining ring known to be in balance. The spectra of the signals may be compared to empirically determine the power, wavelength, or frequency band for monitoring, and whether a worn retaining ring has a higher or lower signal strength within the band. Criteria for generating a signal indicating an alarm that the retaining ring is breached may be derived, and the controller 190 may be configured to test whether the signal meets the criteria.

[0043] As another example, polishing may be performed using a retaining ring known to have grooves on the inner surface, and the spectrum of the signal from the retaining ring may be used as a reference spectrum. As another example, polishing may be performed using both a new retaining ring and a retaining ring known to have grooves on the inner surface. The spectra of the signals may be compared to empirically determine the power, wavelength, or frequency band to monitor, and whether the retaining ring with the grooves has a higher or lower signal strength within the band. Criteria for generating a signal indicating an alarm that the retaining ring has grooves may be derived, and the controller 190 may be configured to test whether the signal meets the criteria.

[0044] In operation, acoustic signals are collected from the in-situ acoustic monitoring system 160. The signals are monitored to detect changes in the retaining ring. Detection of a change may trigger an alarm to an operator, or the polishing operation may be automatically stopped. In the event that the retaining ring is damaged, the retaining ring may be used again. The retaining ring may be removed from the polishing system for use in another polishing system, or the polishing system may be converted from polishing of a dummy substrate to polishing of an equipment substrate for actual integrated circuit production. In the event that the retaining ring has grooves on its interior surface, the operator may replace the retaining ring.

[0045] In some embodiments, controller 190 controls one or more components of apparatus 100, such as a motor that controls the rotation rate of carrier head 140 or platform 120 or a pressure controller that controls the pressure within chambers 146a-c based on received acoustic signals.

[0046] Acoustic monitoring signals collected from the retaining ring can be used for feed-forward to control substrate processing in subsequent processing operations, such as polishing at a subsequent station, or for feedback to control processing of subsequent substrates at the same polishing station. For example, signal strength in one or more powers, wavelengths, or frequency bands can be correlated to polishing rates in one or more regions (e.g., radial zones) of the substrate. A control algorithm can receive the acoustic monitoring signals and determine adjustments to one or more pressures applied to the polishing head in order to improve polishing uniformity.

[0047] In some embodiments, a portion of the signal obtained from the sensor below the substrate may be used. For example, a groove on the inner surface of a retaining ring may generate vibrations in the substrate that may be sensed by an acoustic sensor. Likewise, a retaining ring known to have grooves on the inner surface may be used to perform polishing, and the spectrum of the signal (including the portion of the signal corresponding to the sensor below the substrate) may be used as a reference spectrum or for determining criteria for generating an alarm. In operation, the portion of the signal corresponding to the sensor located below the substrate may be comparatively analyzed to determine whether the criteria are met, or may be subjected to a Fourier transform and compared to a reference spectrum.

[0048] The embodiments and all functional operations described in this specification can be implemented in a digital electronic circuit system, or in computer software, firmware or hardware, including the structural components disclosed in this specification and their structural equivalents, or a combination thereof. The embodiments described herein can be implemented as one or more non-transitory computer program products, that is, one or more computer programs tangibly embodied in a machine-readable storage device for execution or control of its operation by a data processing apparatus (e.g., a programmable processor, a computer, or multiple processors or computers).

[0049] A computer program (also referred to as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted 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 may be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store portions of one or more modules, subroutines, or codes). A computer program may be deployed to execute on multiple computers at one computer or one site, or distributed across multiple sites and interconnected by a communication network.

[0050] The processes and logic flows described in this specification 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 also be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0051] The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including, for example, a programmable processor, a computer, or a plurality of processors or computers. In addition to hardware, an apparatus may include code that creates an execution environment for the computer program in question, for example, code constituting processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of the foregoing. Processors suitable for executing a computer program include, for example, both general and special purpose microprocessors, and any one or more processors of any type of digital computer.

[0052] Computer-readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media, and memory devices, including, for example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[0053] Although this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of particular features of particular examples. Certain features described in this specification in the context of separate embodiments may also be combined. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.

[0054] Many embodiments have been described. However, it will be appreciated that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A chemical mechanical polishing device, comprising: a platform supporting a polishing pad; a carrier head that holds a surface of a substrate against the polishing pad, the carrier head including a retaining ring for holding the substrate; an acoustic sensor supported on the platform; a motor that produces relative motion between the platform and the carrier head to polish the substrate and causes the acoustic sensor to travel in a path beneath the carrier head and the retaining ring; as well as A controller is configured to analyze the signal from the acoustic sensor and determine a characteristic of the retaining ring based on the signal. 2 . The apparatus of claim 1 , wherein the controller is configured to detect that the retaining ring is broken based on the signal.

3. The apparatus of claim 2, wherein the controller is configured to generate an alarm in response to detecting that the retaining ring is breached. 4 . The apparatus of claim 1 , wherein the controller is configured to detect that a groove has been formed on the inner surface of the retaining ring based on the signal.

5. The apparatus of claim 4, wherein the controller is configured to generate an alarm in response to detecting that the groove has been formed on the inner surface of the retaining ring.

6. The apparatus of claim 1, wherein the controller is configured to generate a measured frequency spectrum of the signal. 7 . The apparatus of claim 6 , wherein the controller is configured to compare the measured spectrum with a reference spectrum.

8. The apparatus of claim 6, wherein the controller is configured to detect signal strength in a band in the measured frequency spectrum and compare the signal strength to a threshold value.

9. The apparatus of claim 1, wherein the controller is configured to select the portion of the signal corresponding to the acoustic sensor positioned below the retaining ring.

10. A chemical mechanical polishing device, comprising: a platform supporting a polishing pad; a carrier head that holds a surface of a substrate against the polishing pad, the carrier head including a retaining ring for holding the substrate; an acoustic sensor supported on the platform; a motor that produces relative motion between the platform and the carrier head to polish the substrate and causes the acoustic sensor to travel in a path beneath the carrier head and the retaining ring; as well as A controller is configured to select a portion of the signal from the acoustic sensor that corresponds to the acoustic sensor below the retaining ring and to generate an alarm or modify a polishing parameter based on the selected portion of the signal from the acoustic sensor.

11. The apparatus of claim 10, wherein the controller is configured to detect that the retaining ring is broken based on the selected portion of the signal.

12. The apparatus of claim 10, wherein the controller is configured to detect that a groove has been formed on the inner surface of the retaining ring based on the selected portion of the signal.

13. The apparatus of claim 10, wherein the controller is configured to modify the polishing parameter based on the selected portion of the signal.

14. A method for chemical mechanical polishing a device, comprising: contacting a surface of a substrate with a polishing pad; Producing relative motion between the substrate and the polishing pad to polish the substrate, and using a carrier head to hold the substrate relative to the lateral motion; sweeping an acoustic sensor in a path beneath the carrier head and the retaining ring during polishing; as well as Signals from the acoustic sensor are analyzed, and a characteristic of the retaining ring is determined based on the signals.

15. The method of claim 14, comprising: The retaining ring is detected to be broken based on the signal.

16. The method of claim 15, comprising: An alarm is generated in response to detecting that the retaining ring is breached.

17. The method of claim 14, comprising: It is detected based on the signal that a groove has been formed on the inner surface of the retaining ring.

18. The method of claim 17, comprising: An alarm is generated in response to detecting that the groove has been formed on the inner surface of the retaining ring.

19. The method of claim 14, comprising: Polishing parameters are modified based on the signal.

20. The method of claim 14, comprising: A portion of the signal is selected that corresponds to the acoustic sensor positioned below the retaining ring.

Images