Monitoring of Acoustic Events on a Substrate

Abstract

A chemical mechanical polishing apparatus including a platen that supports a polishing pad, a carrier head for holding the surface of a substrate against the polishing pad, a motor for generating relative movement between the platen and the carrier head to polish an upper layer on the substrate, an array of acoustic sensors disposed within the carrier head for receiving an acoustic signal from the surface of the substrate, and a controller configured to detect the position of an acoustic event on the surface of the substrate based on the acoustic signal received by the array of acoustic sensors.

Description

Technical Field

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

Background Art

[0002] Integrated circuits are generally formed on a substrate by sequential deposition of conductive, semiconductive, or insulating layers on a silicon wafer. One manufacturing step involves depositing a fill layer on a non-planar surface and planarizing the fill layer. In some applications, the fill layer is planarized until the top surface of the patterned layer is exposed. A conductive fill layer can be deposited, for example, on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, the portions of the metal 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. In other applications, such as oxide polishing, the fill layer is planarized, for example, by polishing for a predetermined time period, to leave a portion of the fill layer on the non-planar surface. Further, planarization of the substrate surface is usually required for photolithography.

[0003] Chemical mechanical polishing (CMP) is an accepted method of planarization. This planarization method generally requires that the substrate be mounted on a carrier head 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 and presses the substrate against the polishing pad.

[0004] One problem in CMP is detecting the amount of material removed or the exposure of underlying layers of the substrate during the active polishing process. Various techniques for in-situ monitoring have been proposed. For example, the substrate in contact with the polishing pad can be monitored by an optical sensor as the substrate passes through a window in the polishing pad. As another example, acoustic monitoring techniques using acoustic sensors in the platen have been proposed.

SUMMARY OF THE INVENTION

[0005] A chemical mechanical polishing apparatus including an in-situ acoustic monitoring system disposed within a carrier head is disclosed herein. An acoustic signal varies periodically during a polishing operation based on an interface between a substrate and a pad. Variations in layer thickness result in an underlying layer being exposed during operation at different times. The acoustic monitoring system includes an array of acoustic sensors disposed within the carrier head that receive acoustic signals from the substrate interface.

[0006] The acoustic monitoring system processes the received acoustic signals to detect several acoustic events. For example, the location of a high amplitude acoustic event (e.g., an acoustic event having an intensity greater than a certain standard deviation from the average of the acoustic signal, or an acoustic event exceeding a threshold intensity value) can be detected by the acoustic monitoring system by comparing the time at which the acoustic signal is received with each acoustic sensor and calculating the time of flight to each sensor based on the received signal.

[0007] As a second example, the array of acoustic sensors can be used to monitor various regions of the substrate surface during the polishing process. The acoustic signal received by each acoustic sensor of the array can be shifted by a predetermined phase based on the region of the substrate surface to be monitored. The shifted signals are then added together to approximate the acoustic signal generated by the region of the substrate.

[0008] In a first aspect, a chemical mechanical polishing apparatus is disclosed herein that includes a platen supporting a polishing pad, a carrier head for holding a surface of a substrate against the polishing pad, a motor for generating relative movement between the platen and the carrier head to polish an overlying layer on the substrate, an array of acoustic sensors disposed within the carrier head for receiving acoustic signals from the surface of the substrate, and a controller configured to detect the location of an acoustic event on the surface of the substrate based on the acoustic signals received by the array of acoustic sensors.

[0009] The example can include the following features. The controller can be further configured to detect the position of an acoustic event on the surface of the substrate based on the time-of-flight calculation of the received acoustic signals by each of the acoustic sensors of the array. The array of acoustic sensors can include three or more acoustic sensors. The acoustic sensors can receive acoustic signals within a frequency range from 10 kHz to 200 kHz. The acoustic sensors can be passive acoustic sensors.

[0010] In a second aspect, a chemical mechanical polishing apparatus is disclosed herein, including a platen for supporting a polishing pad, a carrier head for holding the surface of the substrate against the polishing pad, a motor for generating relative movement between the platen and the carrier head to polish an upper layer on the substrate, an array of acoustic sensors disposed within the carrier head for receiving acoustic signals from the surface of the substrate, and a controller configured to detect a position on the substrate where a polishing endpoint has been reached based on the received acoustic signals.

[0011] Examples can include the following features. The controller can be configured to determine the position by performing beamforming on the received acoustic signal. The controller can be configured to perform beamforming by applying a phase shift to each of the received acoustic signals and adding the phase-shifted received acoustic signals to detect a polishing endpoint in the zone. The controller can be configured to generate an added signal that can be beamformed to selectively represent the acoustic activity at each respective position of a plurality of positions on the substrate, and thus to apply each respective set of phase shifts to the received acoustic signals and add the phase-shifted received acoustic signals to generate a plurality of added signals representing the plurality of positions. The controller can further include monitoring each respective added signal of the plurality of added signals for a change in each respective added signal that represents a polishing endpoint at the respective position corresponding to the respective added signal. The polishing endpoint can include removal of a layer being polished to expose a lower layer. The controller is further configured to remove noise from the received acoustic signals by an array of acoustic sensors prior to detecting a polishing endpoint in the zone. The array of acoustic sensors can include five or more acoustic sensors. Certain embodiments of the subject matter described herein can be implemented to realize one or more of the following technical advantages.

[0012] One or more of the following possible advantages may be realized. Wafer-to-wafer (WTW) and within-wafer (WIW) polishing uniformity can be improved. Detection of the location of high-amplitude acoustic events enables real-time monitoring of areas where the underlying layer is exposed, without the sensor actually having to pass beneath that area. Monitoring of various areas of the substrate surface enables in-situ pressure control to achieve higher planarization uniformity. Detection of the location of high-amplitude acoustic events also enables monitoring of the formation of defects on the substrate surface.

[0013] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

Brief Description of the Drawings

[0014]

Figure 1

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Figure 3A

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Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6A

Figure 6B

Figure 6C

Figure 6D

Figure 6E

[0015] In the figures, like reference numerals indicate like elements.

[0016] In some semiconductor chip manufacturing processes, an upper layer, such as metal, silicon oxide, or polysilicon, is polished until a patterned feature of a dielectric, such as silicon oxide, silicon nitride, or a high-k dielectric, in a lower layer is exposed. Reliable detection of the exposure of the lower layer is difficult and may have to meet increasingly growing requirements for accuracy and precision.

[0017] The carrier head induces movement between the substrate and a polishing pad on the platen. When the substrate is swept over the irregularities of the polishing pad, acoustic emissions are generated. The acoustic emissions originate from the interface between the substrate surface and the polishing pad and vary with time according to the polishing stage and the material exposed on the substrate surface.

[0018] It has been proposed to place an acoustic sensor on the platen to monitor signals propagating through the polishing pad. However, a polishing system including an acoustic sensor disposed on the platen can effectively receive an acoustic signal only when the platen sweeps the acoustic sensor under the substrate. When the sensor is not below the substrate, the signal has to propagate laterally through the polishing pad, and as a result, generally noise overwhelms the signal. Such a system generates acoustic measurements at regular intervals, but there are periods when the signal is not available.

[0019] In contrast, an acoustic monitoring system including an array of acoustic sensors in a carrier head can continuously receive acoustic signals corresponding to acoustic emissions. The acoustic signals received by the array of sensors can be individually processed to monitor the surface of the substrate in real time. Alternatively or additionally, the received acoustic signals can be processed in parallel during polishing of the substrate to determine information regarding an endpoint, for example, the exposure of an underlying layer. In particular, the locations where the exposure of the underlying layer occurs can be calculated based on the received acoustic signals.

[0020] FIG. 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable disk-shaped platen 120 with a polishing pad 110 thereon. The polishing pad 110 can be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The platen is operable to rotate about an axis 125. For example, a motor 121, such as a DC induction motor, can rotate a drive shaft 124 to rotate the platen 120.

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

[0022] 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. The carrier head 140 can include a retaining ring 142 for holding the substrate 10 below the flexible membrane 144. The carrier head 140 includes one or more independently controllable pressurizable chambers, such as three chambers 146a - 146c, defined by a membrane, that can apply independently controllable pressure to associated zones on the flexible membrane 144 and thus on the substrate 10 (see FIG. 1). For ease of explanation, only three chambers are shown in FIG. 1, but there can be one or two chambers, or four or more chambers, such as five chambers.

[0023] The carrier head 140 is suspended from a support structure 150, such as a carousel or track, and is connected by a drive shaft 152 to a carrier head rotation motor 154, such as a DC induction motor, so that the carrier head can rotate about an axis 155. Optionally, each carrier head 140 can vibrate laterally, for example, on a slider on the carousel 150, or by the rotational vibration of the carousel itself, or by sliding along the track. During normal operation, the platen is rotated about its central axis 125, each carrier head is rotated about its central axis 155, and is translated laterally across the upper surface of the polishing pad.

[0024] A controller 190, such as a programmable computer, is connected to motors 121, 154 to control the rotational speeds of the platen 120 and the carrier head 140. For example, each motor can include an encoder that measures the rotational speed of the associated drive shaft. A feedback control circuit, which can be part of the controller within the motor itself, or a separate circuit, receives the measured rotational speed from 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.

[0025] The grinding apparatus 100 includes at least one in-situ acoustic monitoring system 160. The in-situ acoustic monitoring system 160 includes one or more acoustic sensors 162. Each acoustic sensor 162 is installed at each respective location in the carrier head 140. The in-situ acoustic monitoring system 160 can be configured to detect acoustic emissions caused by the interface between the substrate 10 and the pad 110, for example, when underlying features are exposed when the material of the substrate 10 is removed.

[0026] In the embodiment shown in FIG. 1, the acoustic monitoring system 160 includes acoustic sensors 162 that are disposed within and supported by the carrier head 140 to receive acoustic signals from the substrate 10. In some embodiments, the acoustic monitoring system 160 includes an array of acoustic sensors 162, for example, two or more acoustic sensors 162. In such an example, each acoustic sensor 162 of the array receives a respective acoustic signal. For example, the acoustic monitoring system 160 can include three or more, or five or more, acoustic sensors 162, and each sensor receives an acoustic signal that varies based on the location of the acoustic sensor 162 within the carrier head 140.

[0027] The acoustic sensors 162 of the acoustic monitoring system 160 are connected to a wireless transmitter 164. Each acoustic sensor 162 receives an acoustic signal and transmits that signal to the transmitter 164. The acoustic sensors 162 can be wired or wirelessly connected to the transmitter 164.

[0028] The transmitter 164 transmits the received acoustic signal to, for example, a wireless receiver 165 disposed within the recess 167 of the platen 120, and the wireless receiver 165 is connected to the controller 190. The receiver 165 can be disposed at an alternative location within the signal range of the transmitter 164. For example, the receiver 165 can be supported by the support structure 150 on the drive shaft 124 or within the polishing chamber of the apparatus 100. The transmitter 164 and the receiver 165 can operate on any functional wireless frequency, such as Bluetooth (trademark), or Wi-Fi, for example, 2.4 gigahertz (GHz), or 5 GHz. Alternatively, the acoustic sensor 162 can be circuit-connected to the controller 190, to the power supply, and / or to other signal processing electronics 166 through a rotary joint, such as a mercury slip ring.

[0029] The acoustic sensor 162 is a contact acoustic sensor 162 having a surface bonded (e.g., in direct contact therewith) to the back surface 12 of the substrate 10, i.e., the surface on the side of the substrate farther from the pad 110. The acoustic sensor 162 can be, for example, an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. The piezoelectric sensor can include a rigid contact plate, such as stainless steel, placed in contact with the body to be monitored, and a piezoelectric assembly on the back side of the contact plate, such as a piezoelectric layer sandwiched between two electrodes.

[0030] 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 an acoustic signal generator (or the acoustic signal generator can be completely omitted from the system). The passive acoustic signal monitored by the acoustic sensor 162 can be in the range of 50 kHz to 1 MHz, for example, 10 kHz to 200 kHz, 200 to 400 kHz, or 200 KHz to 1 MHz. For example, in the monitoring of the polishing of the interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0031] The signal from the sensor 162 can be amplified by a built-in internal amplifier. In some embodiments, the amplification gain is between 40 and 60 dB (e.g., 50 dB). The signal from the acoustic sensor 162 can then be further amplified, filtered if necessary, and digitized, for example, in the electronic device 166, through an A / D port to a high-speed data acquisition board. The data from the acoustic sensor 162 can be recorded in a range similar to that of the generator 163, or in a different, for example, higher range, such as 1 - 10 MHz, for example, 1 - 3 MHz or 6 - 8 MHz. In embodiments where the acoustic sensor 162 is a passive acoustic sensor, a frequency range up to 100 kHz - 2 MHz, such as 500 kHz - 1 MHz (e.g., 750 kHz), can be monitored.

[0032] When disposed within the carrier head 140, the acoustic sensor 162 can be attached to the retaining ring 142 or the chamber membrane 144, or embedded within the retaining ring 142 or the chamber membrane 144. Placing the acoustic sensor 162 on the membrane 144, but at a substantially maximum possible radial distance from the central axis 155, can increase the flight time of the acoustic signal generated from the surface of the substrate 10 (relative to sensors placed closer to the central axis 155). The increased flight time can make it easier to distinguish signals from individual acoustic sensors 162, and thus increase the location accuracy of the detected acoustic events.

[0033] Placing the acoustic sensor 162 within the membranes of the chambers 146a - 146c facilitates an increase in the density of the acoustic sensors 162 and an increase in the location accuracy of the detected acoustic events. Referring now to FIG. 2, an exemplary carrier head 140 including an acoustic monitoring system 160 is shown. The carrier head 140 includes a retaining ring 142 surrounding the substrate 10 and a flexible membrane 144 in contact with the back surface of the substrate 10.

[0034] The film 144 is composed of a chemical and water resistant flexible material that contacts the surface of the substrate 10 on the side of the substrate farther from the pad 110. For example, the film 144 can be composed of a polymeric material such as silicone, polycarbonate, or polyurethane.

[0035] The film 144 divides the volume between the carrier body 248 and the film 244 into a plurality of chambers, such as chambers 246a - 246i. The carrier body 248 can be fixed to the drive shaft or can be vertically movable relative to a housing fixed to the drive shaft. These chambers can be radially symmetric about the central axis 155. The air pressure within each of the chambers 246a - 246i can be independently controlled by the connected controller 190. The film 144 is attached to the carrier head 140, for example, by a clamping ring that clamps a flap of the film to the carrier body 248. The controller 190 adjusts the air pressure applied to each of the chambers 246a - 246i by one or more pressure sources so as to apply a positive or negative pressure to the substrate 10 within a specific annular region. Specifically, a positive pressure causes the annular region of each of the chambers 246a - 246i to push the substrate 10 against the pad 110, and a negative pressure causes the annular region to pull the substrate 10 against the carrier head 140.

[0036] The acoustic monitoring system 160 of FIG. 2 includes a transmitter 164 connected to an acoustic sensor 162. The acoustic sensor 162 is shown to be installed in a chamber 246a through which the central axis 155 passes. The acoustic sensor 162 can receive an acoustic signal from the substrate 10 when installed. In some embodiments, the acoustic sensor 162 contacts the inner surface of the membrane 244, i.e., the surface of the membrane farther from the substrate 10, in order to receive the acoustic signal transmitted through the membrane from the substrate 10. For example, the sensor 162 can be supported on a support structure 250, and the support structure 250 can be attached to a support plate within a carrier head where a flap of the membrane is clamped or can be part of the support plate. In an alternative embodiment, the acoustic sensor 162 is formed within the membrane 244. The sensor 162 can be embedded within the membrane 244 and covered by the membrane 244, or can be provided within the membrane 244 having a surface exposed to directly contact the substrate 10.

[0037] In a further alternative embodiment, the membrane is manufactured with a transmissive element that increases the transmission of the acoustic signal through the membrane 244 to the acoustic sensor 162 in contact with the transmissive element. Examples of the transmissive element can include a wire or a foil antenna.

[0038] The acoustic signal generated by the interface between the substrate 10 and the polishing layer 112 of the pad 110 travels through the substrate 10 and is received by the acoustic sensor 162. The acoustic sensor 162 transmits the received acoustic signal to the connected transmitter 164. The transmitter 164 transmits the acoustic signal to a receiver 265. The receiver 265 is connected to signal processing electronics 266 that perform functions on the received acoustic signal. The electronics 266 can include, for example, an oscilloscope, a spectrum analyzer, a data acquisition system (DAQ), or other components for processing the received acoustic signal. In some embodiments, the electronics 266 are within the controller 190.

[0039] FIG. 2 also shows the receiving circuit of an acoustic monitoring system 260 that includes a receiver 265 and an electronic device 266. The receiver 265 is connected to a signal processing electronic device 266 that performs functions on the received acoustic signal. The electronic device 266 can include, for example, an oscilloscope, a spectrum analyzer, a data acquisition system (DAQ), or other components for processing the received acoustic signal. In some embodiments, the electronic device 266 is within the controller 190. Generally, the electronic device 266 can include a general-purpose programmable computer, a dedicated circuit, or a combination thereof.

[0040] The electronic device 266 performs signal processing of the received acoustic signal and / or calculations based on the received acoustic signal. The calculations can include determining one or more parameters of the acoustic signal. Examples of parameters of the acoustic signal can include phase, arrival time, frequency spectrum, or power spectrum. The electronic device 266 is connected to the controller 190 and transmits information to the controller 190. The electronic device 266 can transmit to the controller 190 the acoustic signal, one or more parameters of the acoustic signal, or both. In some embodiments, the calculations are performed directly by the controller 190.

[0041] In some embodiments, the controller 190 controls one or more components of the apparatus 100, such as a motor that controls the rotational speed of the carrier head 140 or the platen 120, or a pressure controller that controls the pressure within the chambers 246a - 246i based on the received acoustic signal.

[0042] Next, referring to FIG. 3A, a bottom view of an exemplary carrier head 140 is shown having two acoustic sensors, acoustic sensor 362a and acoustic sensor 362b, of two different configurations disposed on a support structure 250 (see FIGS. 2 and 3B) within the carrier head 140. FIG. 3A shows a carrier head having both sensors, although the carrier head may have only one of those sensors, or may have multiple sensors of one type and not the other (e.g., multiple sensors of the configuration of acoustic sensor 362a). Further, FIG. 3A shows three chambers, although there may be one or two, or four or more chambers. Further, FIG. 3A shows sensors 362a, 362b in the middle chamber, although those sensors may be located in different chambers, such as the innermost or outermost chamber. Further, FIG. 3A shows sensors 362a, 362b in the same chamber, although those sensors may be disposed in different chambers.

[0043] The carrier head 140 includes a retaining ring 142 that surrounds internal components. The support structure 250 is a rigid structure of the carrier head 140 that supports and houses additional components. The support structure 250 holds one or more membrane supports to which a membrane 144 is attached. The membrane 144 is not shown in FIGS. 3A and 3B and will be described with reference to FIGS. 3C and 3D.

[0044] FIG. 3B is a schematic perspective view of the two acoustic sensors 362a, 362b. Acoustic sensor 362a is a direct contact acoustic sensor that extends from the surface of the support structure 250. Acoustic sensor 362a includes two springs 361 that move acoustic sensor 362a (not shown in FIG. 3B but above) relative to a membrane 144. Springs 361 may be disposed between the support structure 250 and a flange extending from sensor 362a.

[0045] The extension force is high enough to maintain contact with the membrane 144 when positive atmospheric pressure presses the membrane 144 away from the support structure 346 and against the substrate 10 and the carrier head 140 in any chamber in which the sensor is disposed. On the other hand, the extension force is low enough such that when negative atmospheric pressure in the chamber pulls the membrane 144 toward the support structure 346, the acoustic sensor 362a retracts so that the contact surface 363 is coplanar with the support structure 346.

[0046] The acoustic sensor 362b is a second acoustic sensor arrangement in which the associated acoustic sensors are each movable between a recessed position and an extended position as shown in FIGS. 3C and 3D. Referring now to FIGS. 3C and 3D, the acoustic sensor 362b includes a contact sensor 366 mounted on a waveguide 367. The waveguide 367 pivots at a corner attached to a base 368 disposed within the support structure 346. A spring 369 provides a force to extend the waveguide 367 to an extended state (FIG. 3D) when the membrane 144 moves away from the support structure 346, such as during vacuum chucking of the substrate to the carrier head 140, and to contract the waveguide 367 to a contracted state (FIG. 3C) when the membrane 144 is brought into contact with the support structure 346.

[0047] The waveguide 367, which is movable between a first position and a second position, provides flexibility to the polishing process. For example, when a vacuum is applied within the chamber such that the membrane 144 contacts the waveguide 367 and drives the waveguide 367 to pivot upward, during the step in which the sensor 362b is contracted, the sensing surface 371 is no longer in direct contact with the membrane. When the waveguide 367 is in the extended state, the sensing surface 371 has a low surface area, which reduces the overall pressure of the waveguide 367 through the membrane 144 and reduces the potential for polishing non-uniformities. This may also increase the spatial resolution of the received acoustic signal.

[0048] The waveguide 367 includes a contact surface 370 and a sensing surface 371. The contact sensor 366 contacts the contact surface 370. When in the extended position, the sensing surface 371 contacts the membrane 144. Acoustic signals generated from the polishing of the substrate within the carrier head 140 travel through the membrane 144 and are received by the sensing surface 371. The signals are transmitted through the waveguide 367 to the contact surface 370 and received by the contact sensor 366.

[0049] Two acoustic sensors, acoustic sensor 362a and acoustic sensor 362b, are disposed at exemplary positions within the support structure 346. The acoustic sensors within the carrier head 140 can be disposed at positions for monitoring different areas of the carrier head 140, such as the arrangements further described in FIGS. 4A and 4B.

[0050] FIGS. 4A and 4B show two exemplary configurations of an array of acoustic sensors disposed within a carrier head. FIG. 4A shows an array of three acoustic sensors including acoustic sensors 462a - 462c. The array of acoustic sensors 462a - 462c is arranged in a triangular configuration where the distances between the acoustic sensors 462a - 462c are approximately equal, for example, an equilateral triangle.

[0051] FIG. 4B shows a second exemplary array of six acoustic sensors, including acoustic sensors 462d-462i. Acoustic sensors 462d and 462e are spaced apart from acoustic sensors 462f-462i. Acoustic sensors 462f-462i are arranged, for example, linearly along a common centerline. The arrangement of acoustic sensors 462d-462i can provide independent functions based on that arrangement. For example, acoustic sensors 462d, 462e, and 462i approximate the arrangement of acoustic sensors 462a-462c. In such embodiments, acoustic sensors 462d, 462e, and 462i can provide information for triangulation of an acoustic event, and acoustic sensors 462f-h can provide local information related to the acoustic monitoring zone under those sensors. Generally, the process of triangulation involves determining the location of an acoustic event by accurately calculating the time difference of arrival (TDOA) of signals emitted from an object to three or more receivers.

[0052] The acoustic monitoring system 160 receives acoustic signals generated by the substrate 10 (e.g., the interface between the substrate 10 and the pad 110) from the acoustic sensors 162. During some polishing operations, high amplitude acoustic events may occur and be received by the acoustic monitoring system 160. High amplitude acoustic events can be included. In some embodiments, the acoustic monitoring system 160 receives acoustic signals corresponding to acoustic events at a plurality of acoustic sensors 162 and determines the estimated location where the acoustic signals were generated, for example, detecting the location of the acoustic event.

[0053] Referring to FIGS. 5A and 5B, a carrier head 540 having a substrate 500 therein is shown within a retaining ring 542. The carrier head 540 includes, for example, three acoustic sensors 562a - 562c arranged in a triangular array in the array of FIG. 4A. The acoustic sensors 562a - 562c are connected to a transmitter 564 and a receiver 565 of an acoustic monitoring system 560. As shown in FIG. 5A, the substrate 500 includes a defect 580 that generates a high - amplitude acoustic event 582. The acoustic event 582 propagates outwardly from the defect 580.

[0054] FIG. 5B shows the acoustic event 582 propagating outwardly from the defect 580. The location of the defect 580 is at distances, respectively, d a d b and d c from each of the acoustic sensors 562a - 562c. Each acoustic sensor 562a - 562c receives the acoustic event 582 at different times, t a t b and t c . The distances that the acoustic event 582 propagates to each of the acoustic sensors 562a - 562c are different based on the locations of the acoustic sensors 562a - 562c within the carrier head 540, e.g., d a ≠d b ≠d c . Thus, the times at which the acoustic sensors 562a - 562c receive the acoustic event 582 are different, e.g., t a ≠t b ≠t c .

[0055] The acoustic sensors 562a - 562c send the received acoustic signals to the transmitter 564, and the transmitter 564 sends the acoustic signals to the receiver 565. The receiver 565 sends the acoustic signals to an electronic device 566 and a controller 590.

[0056] The electronic device 566 receives an acoustic signal and performs calculations on the signal. In some embodiments, the electronic device 566 calculates the location of a defect 580 on the substrate 500 based on the received acoustic signal. For example, the electronic device 566 uses the times at which the acoustic sensors 562a - 562c receive an acoustic event 582 to perform calculations of triangulation, for example, triangulation, to determine the location of the defect 580.

[0057] At a known location (e.g., P i =P x ,P y ,P z ), P n receivers, for example, acoustic sensors 562a - 562c, are provided with a defect 580 that generates an acoustic event 582 at an unknown location (e.g., E=(x,y,z)) on the substrate 500 within range. Without wishing to be bound by theory, for Cartesian coordinates, the distance R m from the emitter to one of the receivers is TIFF2025521167000002.tif10170.

[0058] The distance R m is the wave speed c times the transit time from the defect 580 to one of the acoustic sensors 562a - 562c. The time difference of the acoustic event 582 reaching each of the acoustic sensors 562a - 562c, for example, T=t i -t o is calculated by the electronic device 566 based on the receivers. Then, based on that time difference, the distances to each of the acoustic sensors 562a - 562c are calculated. The distances to each of the acoustic sensors 562a - 562c are used to calculate the location of the defect 580 on the substrate 500. Identifying the location of the defect 580 aids in quality control between and within wafers for the polishing process.

[0059] In some embodiments, the acoustic monitoring system 160 monitors an area of the substrate 10 using an array of acoustic sensors 162. The acoustic monitoring system 160 beamforms the acoustic signals received by the acoustic sensors 162 to acoustically isolate the acoustic signals generated by the area of the substrate 10. Beamforming is an acoustic technique applied to the received acoustic signals to monitor the spatial location of acoustic activity or events at a distance from the array of acoustic sensors 162.

[0060] In some embodiments, a phase shift, such as a time delay, is applied to each of the acoustic signals received by the acoustic sensors 162, and thus the phase shift correlates with the distance from the acoustic sensors 162 of the area to be monitored. The phase-shifted signals are then added together to create an added signal. Applying a phase shift to each received acoustic signal to detect acoustic activity in a particular area is referred to as "beamforming". This can amplify the acoustic signals generated in the selected area, whether it is an acoustic event or acoustic activity.

[0061] The amount of phase shift applied to each of the acoustic signals can vary over time. In particular, the phase shift can be varied such that the spatial area provided by beamforming is "scanned" over all or an area of the wafer at a given interval.

[0062] FIGS. 6A and 6B show an exemplary substrate 600, such as substrate 10 or substrate 500, divided into a number of monitoring zones. The dashed lines shown on the substrate 600 in FIGS. 6A and 6B represent an exemplary example of dividing independent acoustic monitoring zones.

[0063] FIG. 6A shows a substrate 600 divided into monitoring zones A - I. Monitoring zones A - H are radial sections of a portion of the circumference of the substrate 600, and monitoring zone I is a circular section around the center of the substrate 600. FIG. 6B shows the substrate 600 divided into monitoring zones J - M. Monitoring zones K - M are concentric annular rings around the center of the substrate 600, and monitoring zone J is a circular section around the center of the substrate 600, such as monitoring zone I.

[0064] The monitoring zones of FIGS. 6A and 6B are exemplary, and alternative monitoring zone divisions can be achieved through appropriate signal processing of the received acoustic signals. The signal processing can be performed in the controller 190 or the signal processing electronics 166. In embodiments where the signal processing electronics 166 performs beamforming, the signal processing electronics 166 can send the summed signals to the controller 190 for modification of one or more polishing parameters of the polishing operation, such as the pressure in one or more of the chambers 146a - 146c. In alternative embodiments, the monitoring zones can be regular or irregular arrays of shapes that cover at least a portion of the surface of the substrate 600, such as a rectangular grid (= lattice).

[0065] FIG. 6C shows the substrate 600 within the retaining ring 642 of the carrier head 640. Each acoustic monitoring zone of the substrate 600 is disposed at a certain distance from each of the acoustic sensors 662a - 662c. For example, acoustic monitoring zone E is shown in FIG. 6C, and arrows representing acoustic signals φ1 - φ3 indicate the respective paths that the acoustic signal φ follows to reach the acoustic sensors 662a - 662c.

[0066] The acoustic signal φ is generated in the acoustic monitoring zone E. The acoustic signal φ travels from the acoustic monitoring zone E to each of the acoustic sensors 662a to 662c along different paths having respective lengths. The acoustic sensor 662b receives the acoustic signal φ1 at a first time based on the distance of the acoustic sensor 662b from the acoustic monitoring zone E, and the acoustic sensors 662c and 662a receive the acoustic signals φ2 and φ3, respectively, at times based on the distance from the acoustic monitoring zone E.

[0067] The acoustic sensors 662a to 662c transmit the received acoustic signals φ1 to φ3 to the transmitter 664 of the acoustic monitoring system 660, which are sent to the receiver 665 and the electronic device 666. FIG. 6D is a chart showing the acoustic signals φ1 to φ3 received by the electronic device 666 at different times. The acoustic signals φ1 to φ3 are shown along the y-axis and time is shown along the x-axis. The acoustic signal φ1 is received at the first time, the acoustic signal φ2 is received at a second time having a phase offset of Δ1, and the acoustic signal φ3 is received at a third time having a phase offset of Δ2.

[0068] The electronic device 666 receives the acoustic signals φ1 to φ3 and applies phase offsets of Δ1 and Δ2 to the acoustic signal φ2 and the acoustic signal φ3, respectively, so as to approximate that the acoustic signals φ1 to φ3 generated in the acoustic monitoring zone E are received simultaneously at the acoustic sensors 662a to 662c. Then, the phase-shifted acoustic signals, for example, (φ2 + Δ1) or (φ3 + Δ2) are added to obtain an added signal representing the acoustic signal φ generated in the acoustic monitoring zone E, for example, φ = φ1+(φ2 + Δ1)+(φ3 + Δ2).

[0069] The added signal can include constructive or destructive interference based on the received acoustic signals φ1 to φ3. Such interference can represent various acoustic events or acoustic activities from the acoustic monitoring zone, such as detection of layer transitions, defects, or scratches. In some embodiments, the controller 690 can vary the polishing parameters of the carrier head 640 based on the detected acoustic events. For example, the controller 690 can vary the pressure within the chambers 146a to 146c or the rotational speed of the controller 690 based on the detected acoustic events such as layer transitions.

[0070] In some embodiments, the electronic device 666 can apply additional signal processing to the received signals such as the acoustic signals φ1 to φ3. The received acoustic signal, or the added signal, can be added, filtered, amplified, correlated, noise removed, or transformed into a second dimension. For example, the received signal, or the added signal, can be transformed into the frequency dimension before or after other signal processing. A Fourier transform, such as a fast Fourier transform, can be applied to the received signal, or the added signal.

[0071] The electronic device 666 or the controller 690 can store an array of phase offsets Δ in memory or storage for each of the acoustic sensors 662a to 662c based on the distance to each of the acoustic monitoring zones such as the acoustic monitoring zones of FIGS. 6A or 6B. The electronic device 666 or the controller 690 can then receive acoustic signals from each of the acoustic sensors 662a to 662c and apply the phase offset Δ to each received acoustic signal based on the distance to the acoustic monitoring zone to be monitored. The acoustic monitoring zones can be monitored independently, continuously, or in parallel.

[0072] Although this specification contains many details, they should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular examples. Also, some of the features described herein in the context of separate embodiments may be combined. Conversely, the various features described in the context of a single embodiment may be implemented separately in multiple embodiments, or in any suitable sub-combination.

[0073] Some embodiments have been described. Nevertheless, it will be understood that various modifications may 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 platen for supporting a polishing pad, A carrier head for maintaining the surface of a substrate relative to the polishing pad, A motor for generating relative movement between the platen and the carrier head to polish an upper layer on the substrate, An array of acoustic sensors disposed within the carrier head for receiving acoustic signals from the surface of the substrate, A controller configured to detect the position of an acoustic event on the surface of the substrate based on the acoustic signals received by the array of acoustic sensors A chemical mechanical polishing apparatus comprising the same.

2. The apparatus according to claim 1, wherein the controller is further configured to detect the position of the acoustic event on the surface of the substrate based on the time-of-flight calculation of the acoustic signals received by each of the acoustic sensors of the array.

3. The apparatus according to claim 1, wherein the array of acoustic sensors includes three or more acoustic sensors.

4. The apparatus according to claim 1, wherein the acoustic sensors receive acoustic signals within a frequency range from 10 kHz to 200 kHz.

5. The apparatus according to claim 1, wherein the acoustic sensors are passive acoustic sensors.

6. A platen for supporting a polishing pad, A carrier head for maintaining the surface of a substrate relative to the polishing pad, A motor for generating relative movement between the platen and the carrier head to polish an upper layer on the substrate, An array of acoustic sensors disposed within the carrier head for receiving acoustic signals from the surface of the substrate, A controller configured to detect the position on the substrate where the polishing endpoint has been reached based on the received acoustic signals A chemical mechanical polishing apparatus comprising the same.

7. The apparatus according to claim 6, wherein the controller is configured to determine the position by performing beamforming of the received acoustic signals.

8. The apparatus according to claim 7, wherein the controller is configured to perform beamforming by applying a phase shift to each of the received acoustic signals and adding the phase-shifted received acoustic signals to detect the polishing endpoint in a zone.

9. The controller generates an added signal that is beamformed to selectively represent the acoustic activity at each of a plurality of positions on the substrate, and thus applies a respective set of phase shifts to the received acoustic signals to generate a plurality of added signals representing the plurality of positions, and adds the phase-shifted received acoustic signals, the apparatus according to claim 7.

10. monitoring each of the plurality of added signals for a change in the respective added signal that represents a polishing endpoint at the respective position corresponding to the respective added signal, the apparatus according to claim 9.

11. The apparatus according to claim 6, wherein the polishing endpoint includes removal of a layer being polished to expose a lower layer.

12. The apparatus according to claim 6, wherein the controller is further configured to remove noise from the received acoustic signals by the array of acoustic sensors prior to detecting a polishing endpoint in a zone.

13. The apparatus according to claim 6, wherein the array of acoustic sensors includes five or more acoustic sensors.

14. holding a substrate with a carrier head and contacting a surface of the substrate with a polishing pad; generating relative movement between the substrate and the polishing pad; monitoring acoustic signals from the substrate with a plurality of sensors within the carrier head; calculating a position of an acoustic event on the surface of the substrate based on the acoustic signals received by the plurality of sensors A method of polishing, comprising.

15. The method according to claim 14, wherein calculating the position is based on a time-of-flight calculation of acoustic signals received by each of an array of acoustic sensors.

16. The method according to claim 14, wherein the plurality of sensors monitor acoustic signals within a frequency range from 10 kHz to 200 kHz.

17. The method according to claim 14, wherein monitoring includes passive monitoring using passive acoustic sensors.

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