Monitoring acoustic events on substrate

Abstract

A chemical mechanical polishing apparatus includes: a table supporting a polishing pad; a carrier head for holding the surface of the substrate against the polishing pad; the motor is used for generating relative movement between the workbench and the carrying head so as to polish an overlying layer on the substrate; an acoustic sensor array disposed within the carrier head for receiving acoustic signals from a surface of the substrate; and a controller configured to detect a location of an acoustic event on the surface of the substrate based on the received acoustic signal from the acoustic sensor array.

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] Typically, integrated circuits are formed on a substrate by sequentially depositing a conductive layer, a semiconductive layer, or an insulating layer on a silicon wafer. One manufacturing step involves depositing a filler layer on a non-planar surface and flattening the filler layer. For some applications, the filler layer is flattened until the top surface of the patterned layer is exposed. For example, a conductive filler layer can be deposited on a patterned insulating layer to fill a groove or hole in the insulating layer. After flattening, the portion of the metal layer remaining between the raised patterns of the insulating layer forms 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 flattened, for example, by polishing for a predetermined period of time to retain a portion of the filler layer on the non-planar surface. In addition, photolithography generally requires flattening the substrate surface.

[0003] Chemical mechanical polishing (CMP) is a well-established planarization method. This planarization method typically requires mounting the substrate on a carrier head or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load to the substrate to push the substrate against the polishing pad.

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

[0005] A chemical mechanical polishing apparatus is disclosed herein, including an in-situ acoustic monitoring system disposed in a carrier head. An acoustic signal varies periodically during a polishing operation based on an interface between a substrate and a pad. Fluctuations in layer thickness cause an underlying layer to be exposed at different times during operation. The acoustic monitoring system includes an acoustic sensor array disposed on the carrier head, the acoustic sensor array receiving an acoustic signal from the substrate interface.

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

[0007] As a second example, an acoustic sensor array can be used to monitor various areas of a substrate surface during a polishing process. The acoustic signal received by each acoustic sensor in the array can be shifted by a predetermined phase based on the substrate surface area to be monitored. Each shifted signal is then summed to approximate the acoustic signal generated by the substrate area.

[0008] In a first aspect, a chemical mechanical polishing device is disclosed herein, comprising: a workbench 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 workbench and the carrier head so as to polish an overlying layer on the substrate; an acoustic sensor array arranged in the carrier head to receive an acoustic signal from the surface of the substrate; and a controller configured to detect a location of an acoustic event on the surface of the substrate based on the received acoustic signal from the acoustic sensor array.

[0009] Examples may include the following features. The controller may be further configured to detect the location of an acoustic event on the surface of the substrate based on a time-of-flight calculation of a received acoustic signal from each of the acoustic sensors in the array. The acoustic sensor array may include three or more acoustic sensors. The acoustic sensor may receive an acoustic signal in a frequency range of 10 kHz to 200 kHz. The acoustic sensor may be a passive acoustic sensor.

[0010] In a second aspect, the present invention discloses a chemical mechanical polishing device, comprising: a workbench for supporting 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 workbench and the carrier head so as to polish an upper layer on the substrate; an acoustic sensor array, which is arranged in the carrier head and is used to receive an acoustic signal from the surface of the substrate; and a controller, which is configured to detect a position on the substrate where a polishing end point has been reached based on the received acoustic signal.

[0011] Examples may include the following features. The controller may be configured to determine the position by beamforming the received acoustic signal. The controller may perform beamforming by applying a phase shift to each of the received acoustic signals and summing the phase-shifted received acoustic signals to detect the polishing endpoint in the zone. The controller may be configured to apply a set of corresponding phase shifts to the received acoustic signals and sum the phase-shifted received acoustic signals for each corresponding position in a plurality of positions on the substrate to generate a summed signal, the summed signal may be beamformed to selectively represent the acoustic activity at the corresponding position on the substrate, thereby generating a plurality of summed signals representing the plurality of positions. The controller may further include monitoring a change in the corresponding summed signal for each corresponding summed signal in the plurality of summed signals, the change representing the polishing endpoint at the corresponding position corresponding to the corresponding summed signal. The polishing endpoint may include removing the layer being polished to expose the underlying layer. The controller is further configured to denoise the received acoustic signal from the acoustic sensor array before detecting the polishing endpoint in the zone. The acoustic sensor array may include five or more acoustic sensors. Particular implementations of the subject matter described in this specification can be implemented to achieve one or more of the following technical advantages.

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

[0013] The 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 A schematic cross-sectional view of an example of a polishing apparatus is shown.

[0015] Figure 2 A perspective cross-sectional view of a carrier head is shown.

[0016] Figure 3A This is a bottom view of the carrier head.

[0017] Figure 3B Shows Figure 3A Close-up view of two exemplary acoustic sensors.

[0018] Figure 3C and Figure 3DAn acoustic sensor mounted in a retractable waveguide is shown.

[0019] Figure 4A and Figure 4B are schematic diagrams of two arrangements of acoustic sensors in a carrier head.

[0020] Figure 5A and Figure 5B Detecting high intensity acoustic events is schematically illustrated.

[0021] Fig. 6A and Figure 6B Various embodiments are shown for dividing a substrate into a plurality of acoustic monitoring zones.

[0022] Figure 6C Monitoring of the acoustic monitoring zone using an acoustic sensor in the carrier head is shown.

[0023] Fig.6D and Fig. 6E Signal processing for monitoring an acoustic monitoring zone based on independently received acoustic signals is shown.

[0024] In the drawings, like reference numerals refer to like elements. DETAILED DESCRIPTION

[0025] In some semiconductor chip manufacturing processes, an overlying layer (e.g., metal, silicon oxide, or polysilicon) is polished until patterned features of an underlying layer are exposed, which is, for example, a dielectric such as silicon oxide, silicon nitride, or a high-K dielectric. Reliably detecting exposure of the underlying layer can be difficult and is subject to increasing precision and accuracy requirements.

[0026] The carrier head induces motion between the substrate and the polishing pad on top of the table. Acoustic emissions are generated as the substrate sweeps over the micro-protrusions of the polishing pad. The acoustic emissions originate from the interface between the substrate surface and the polishing pad and vary over time depending on the polishing stage and the materials exposed on the substrate surface.

[0027] It has been proposed to place an acoustic sensor in the table to monitor the signal propagating through the polishing pad. However, a polishing system including an acoustic sensor arranged in the table can effectively receive an acoustic signal only when the table is swept across the acoustic sensor under the substrate; when the sensor is not under the substrate, the signal needs to propagate laterally through the polishing pad, so that noise generally overwhelms any signal. Although such a system produces acoustic measurements at regular intervals, there are periods when no signal is available.

[0028] In contrast, an acoustic monitoring system including an acoustic sensor array within a carrier head can continuously receive acoustic signals corresponding to the acoustic emissions. The received acoustic signals from the sensor array can be processed individually to monitor the substrate surface in real time. Alternatively or additionally, the received acoustic signals can be processed in parallel to determine information about an endpoint (e.g., exposure of an underlying layer) during polishing of the substrate. In particular, the location where exposure of the underlying layer is occurring can be calculated based on the received acoustic signals.

[0029] Figure 1 An example of a polishing apparatus 100 is shown. The polishing apparatus 100 includes a rotatable dish-shaped table 120 on which a polishing pad 110 is mounted. The polishing pad 110 may be a double-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The table is operable 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 table 120.

[0030] 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 grinding state.

[0031] 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 may include a retaining ring 142 for holding the substrate 10 below the flexible membrane 144. The carrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, such as three chambers 146a-146c, which can apply independently controllable pressurization to associated areas on the flexible membrane 144, and thus to associated areas on the substrate 10 (see Figure 1 ). Although for ease of explanation, 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.

[0032] 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 oscillate laterally, such as on a slider on the turntable 150, or by rotational oscillation of the turntable itself or by sliding along a track. In typical operation, the table rotates about its central axis 125, and each carrier head rotates about its central axis 155 and translates laterally over the top surface of the polishing pad.

[0033] A controller 190 (such as a programmable computer) is connected to the motors 121, 154 to control the rotational rates of the table 120 and the carrier head 140. For example, each motor may include an encoder that measures the rotational rate of the associated drive shaft. Feedback control circuitry may be located in the motor itself, as part of the controller, or as a separate circuit, and the feedback control circuitry receives the measured rotational rate from the encoder and adjusts the current supplied to the motor to ensure that the rotational rate of the drive shaft matches the rotational rate received from the controller.

[0034] 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 sensors 162. Each acoustic sensor 162 is mounted at a corresponding 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, such as when removing material of the substrate 10 to expose features of the underlying overburden.

[0035] In such Figure 1 In the illustrated embodiment, the acoustic monitoring system 160 includes an acoustic sensor 162 positioned within and supported by the carrier head 140 to receive an acoustic signal from the substrate 10. In some embodiments, the acoustic monitoring system 160 includes an array of acoustic sensors 162, such as more than one acoustic sensor 162. In such examples, each acoustic sensor 162 in the array receives a corresponding acoustic signal. For example, the acoustic monitoring system 160 may include three or more, or five or more acoustic sensors 162, each of which receives an acoustic signal that varies based on the position of the acoustic sensor 162 within the carrier head 140.

[0036] The acoustic sensors 162 of the acoustic monitoring system 160 are connected to a wireless transmitter 164. The acoustic sensors 162 each receive an acoustic signal and transmit the signal to the transmitter 164. The acoustic sensors 162 may be connected to the transmitter 164 by wire or wirelessly.

[0037] The transmitter 164 transmits the received acoustic signal to a wireless receiver 165, which is disposed, for example, in a recess 167 of the table 120, and which is in turn connected to the controller 190. The receiver 165 may be disposed in an alternative location within the signal range of the transmitter 164. For example, the receiver 165 may be supported by the support structure 150, located on the drive shaft 124, or located within the polishing chamber of the device 100. The transmitter 164 and the receiver 165 may operate on any functional wireless frequency, such as Bluetooth. TMOr Wi-Fi, such as 2.4 GHz or 5 GHz. Alternatively, the acoustic sensor 162 may be connected through circuitry to the controller 190, a power source, and / or to other signal processing electronics 166 via a rotational coupling (eg, a mercury slip ring).

[0038] The acoustic sensor 162 is a contact acoustic sensor 162 having a surface coupled to (e.g., in direct contact with) the back side 12 of the substrate 10 (i.e., the surface on the side of the substrate farther from the pad 110). The acoustic sensor 162 may be, for example, an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. The piezoelectric sensor may include: a rigid contact plate (e.g., of stainless steel or similar material) placed in contact with the subject to be monitored; and a piezoelectric component on the back side of the contact plate, e.g., a piezoelectric layer sandwiched between two electrodes.

[0039] In some embodiments, the in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, the acoustic sensor 162 monitors the signal 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 10 kHz to 200 kHz, 200 kHz to 400 kHz, or 200 kHz to 1 MHz. For example, for monitoring the polishing of an interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz may be monitored.

[0040] The signal from the sensor 162 can be amplified by a built-in internal amplifier. In some embodiments, the amplification gain is between 40 dB and 60 dB (e.g., 50 dB). The signal from the acoustic sensor 162 can then be further amplified and filtered if necessary, and digitized via an A / D port to a high-speed data acquisition board, such as a high-speed data acquisition board in the electronic component 166. The data from the acoustic sensor 162 can be recorded in a range similar to that of the generator 163, or in a different (e.g., higher) range, such as from 1 MHz to 10 MHz, such as 1-3 MHz or 6-8 MHz. In an embodiment in which the acoustic sensor 162 is a passive acoustic sensor, a frequency range of 100 kHz to 2 MHz can be monitored, such as 500 kHz to 1 MHz (e.g., 750 kHz).

[0041] The acoustic sensor 162 positioned in the carrier head 140 may be attached to or embedded in the retaining ring 142 or the chamber membrane 144. Positioning the acoustic sensor 162 on the membrane 144, but at substantially the maximum possible radial distance from the central axis 155, may increase the time of flight of the acoustic signal generated from the surface of the substrate 10 (relative to a sensor positioned closer to the central axis 155). The increased time of flight may make it easier to distinguish signals from the individual acoustic sensors 162, thereby improving the positional accuracy of the detected acoustic events.

[0042] Positioning the acoustic sensors 162 in the membranes of the chambers 146a-146c helps increase the density of the acoustic sensors 162 and improve the positional accuracy of the detected acoustic events. Figure 2 , shows an exemplary carrier head 140 including an acoustic monitoring system 160. The carrier head 140 includes a retaining ring 142 that encloses the substrate 10, and a flexible membrane 144 that contacts the back side of the substrate 10.

[0043] The membrane 144 is composed of a chemically and water-resistant flexible material, and contacts the surface of the substrate 20 on the side of the substrate farther from the pad 110. For example, the membrane 144 may be composed of a polymer material such as silicone, polycarbonate, or polyurethane.

[0044] The membrane 144 divides the volume between the carrier body 248 and the membrane 244 into a plurality of chambers, such as chambers 246a-246i. The carrier body 248 may be fixed relative to the drive shaft, or may be vertically movable relative to a housing fixed to the drive shaft. The chambers may be radially symmetrical around the central axis 155. The air pressure within each of the chambers 246a-246i may be independently controlled by a connected controller 190. The membrane 144 is fixed to the carrier head 140, for example, by a clamping ring that clamps the flap of the membrane to the carrier body 248. The controller 190 modulates the air pressure applied by one or more pressure sources to each of the chambers 246a-246i to apply positive or negative pressure to the substrate 10 in a specific annular region. Specifically, a positive pressure causes the substrate 10 to be pressed against the pad 110 in the annular region of each of the chambers 246a-246i, while a negative pressure causes the substrate 10 to be pulled against the carrier head 140 in the annular region.

[0045] Figure 2The acoustic monitoring system 160 in includes a transmitter 164 connected to an acoustic sensor 162. The acoustic sensor 162 is illustrated as being mounted in a chamber 246a, with a central axis 255 passing through the chamber 246a. The acoustic sensor 162 can receive an acoustic signal from the substrate 10 when mounted. In some embodiments, the acoustic sensor 162 contacts the inner surface of the membrane 244 (i.e., the surface of the membrane that is farther from the substrate 10) to receive an acoustic signal transmitted from the substrate 10 through the membrane. For example, the sensor 162 can be supported on a support structure 248, which can be attached to a support plate within a carrier head or a part of a support plate within a carrier head, and the flaps of the membrane are clamped to the support structure 248. In an alternative embodiment, the acoustic sensor 162 is molded into the membrane 244. The sensor 162 can be embedded in the membrane 244 and covered by the membrane 244, or can be disposed in the membrane 244 with an exposed surface to directly contact the substrate 10.

[0046] In a further alternative embodiment, the membrane is made with a transmissive element that increases the transmission of the acoustic signal through the membrane 244 to the acoustic sensor 262 in contact with the transmissive element. Examples of transmissive elements may include wire or foil antennas.

[0047] 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 a connected transmitter 164. The transmitter 164 transmits the acoustic signal to the receiver 265. The receiver 265 is connected to signal processing electronics 266, which performs functions on the received acoustic signal. The electronics 266 may 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 is located within the controller 190.

[0048] Figure 2 Also shown is the receiving circuitry of the acoustic monitoring system 260, including a receiver 265 and electronic components 266. The receiver 265 is connected to signal processing electronic components 266 that perform functions on the received acoustic signals. The electronic components 266 may include, for example, an oscilloscope, a spectrum analyzer, a data acquisition system (DAQ), or other components for processing the received acoustic signals. In some embodiments, the electronic components 266 are located within the controller 190. Generally, the electronic components 266 may include a general purpose programmable computer, a dedicated circuit system, or a combination of the above.

[0049] The electronic component 266 performs signal processing of the received acoustic signal and / or calculations based on the received acoustic signal. The calculations may include determining one or more parameters of the acoustic signal. Examples of parameters of the acoustic signal may include phase, arrival time, frequency spectrum, or power spectrum. The electronic component 266 is connected to the controller 190 and transmits information to the controller 190. The electronic component 266 may transmit the acoustic signal, one or more parameters of the acoustic signal, or both to the controller 190. In some embodiments, the calculations are performed directly by the controller 190.

[0050] In some embodiments, controller 190 controls one or more components of apparatus 100 based on the received acoustic signals, such as a motor that controls the rotation rate of carrier head 140 or stage 220, or a pressure controller that controls the pressure within chambers 246a-246i.

[0051] Reference now Figure 3A , shows a bottom view of an example carrier head 140 having a support structure 250 disposed in the carrier head 140 (see Figure 2 and Figure 3B ) are two acoustic sensors of two different configurations, acoustic sensor 362a and acoustic sensor 362b. Although Figure 3A A carrier head is shown with two sensors, but a carrier head may have only one of the sensors, or multiple sensors of one type but not another (e.g., multiple sensors with a configuration of acoustic sensor 362a). Figure 3A Three chambers are shown, but there may be one or two chambers, or four or more chambers. Figure 3A Sensors 362a, 362b are shown in the middle chamber, but the sensors can be located in different chambers, such as the innermost or outermost chambers. Figure 3A The sensors 362a, 362b are shown in the same chamber, but the sensors may be located in a number of different chambers.

[0052] The carrier head 140 includes a retaining ring 142 that surrounds the internal components. The support structure 346 is a rigid structure of the carrier head 140 that supports and houses additional components. The support structure 346 holds one or more membrane supports 348 to which the membrane 144 is secured. Figure 3A and Figure 3B The membrane 144 is not shown, but reference Figure 3C and Figure 3D The membrane 144 will be described.

[0053] Figure 3B2 is a schematic perspective view of two acoustic sensors 362a, 362b. Acoustic sensor 362a is a direct contact acoustic sensor that extends from the surface of support structure 250. Acoustic sensor 362a includes two springs 361 that push acoustic sensor 362a against membrane 144 (not shown, but in the drawings). Figure 3B The spring 361 may be positioned between the support structure 250 and a flange extending from the sensor 362a.

[0054] The extension force is large enough to maintain contact with the membrane 144 when positive atmospheric pressure within whichever chamber the sensor is positioned has pressed the membrane 144 away from the support structure 346 and against the substrate 10 / carrier head 140. On the other hand, the extension force is small enough that when negative atmospheric pressure within the chamber pulls the membrane 144 against the support structure 346, the acoustic sensor 362a retracts so that the contact surface 363 is coplanar with the support structure 346.

[0055] Acoustic sensor 362b is a second acoustic sensor arrangement in which an associated acoustic sensor is movable between a recessed position and an extended position, such as in Figure 3C and Figure 3D Now refer to Figure 3C and Figure 3D , the acoustic sensor 362b includes a contact sensor 366 mounted on a waveguide 367. The waveguide 367 pivots at a corner fixed to a base 368 disposed within the support structure 346. The spring 369 provides a force that extends the waveguide 367 to an extended state ( Figure 3D ), and retracting the waveguide 367 to a retracted state ( ) when the membrane 144 contacts the support structure 346 (e.g., such as during vacuum suction of the substrate to the carrier head 140). Figure 3C ).

[0056] The waveguide 367 being movable between the first position and the second position provides flexibility to the polishing process. During the step where the sensor 362b is retracted, for example, due to the application of a vacuum within the chamber to bring the membrane 144 into contact with the waveguide 367 and pivot the waveguide 367 upward, 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 small surface area, thereby reducing the overall pressure of the waveguide 367 across the membrane 144 and reducing the possibility of uneven polishing. This can also increase the spatial resolution of the received acoustic signal.

[0057] Waveguide 367 includes a contact surface 370 and a sensing surface 371. Contact sensor 366 contacts contact surface 370. When in the extended position, sensing surface 371 contacts membrane 144. Acoustic signals from within carrier head 140 generated by substrate polishing travel through membrane 144 and are received by sensing surface 371. The signal is transmitted through waveguide 367 to contact surface 370 and is received by contact sensor 366.

[0058] Two acoustic sensors, acoustic sensor 362a and acoustic sensor 362b, are positioned at exemplary locations within support structure 346. Acoustic sensors within carrier head 140 may be arranged at locations for monitoring different areas of carrier head 140, such as at Figure 4A and Figure 4B The arrangement is further described in .

[0059] Figure 4A and Figure 4B Two exemplary configurations of an acoustic sensor array disposed within a carrier head are shown. Figure 4A An array of three acoustic sensors is depicted, including acoustic sensors 462a-462c. The array of acoustic sensors 462a-462c is arranged in a triangular arrangement, wherein the distances between the acoustic sensors 462a-462c are approximately equal, such as an equilateral triangle.

[0060] Figure 4B A second exemplary array of six acoustic sensors is depicted, including acoustic sensors 462d-462i. Acoustic sensors 462d and acoustic sensor 462e are spaced apart from acoustic sensors 462f-462i. Acoustic sensors 462f-462i are arranged along a common centerline, for example, linearly. The arrangement of acoustic sensors 462d-462i can provide independent functions based on the arrangement. For example, acoustic sensors 426d, 462e, and 462i are close to the arrangement of acoustic sensors 462a-462c. In such embodiments, acoustic sensors 426d, 462e, and 462i can provide information for triangulation of acoustic events, while acoustic sensors 426f-h can provide local information related to the acoustic monitoring area below the sensors. Typically, the process of triangulation includes locating an acoustic event by accurately calculating the time difference of arrival (TDOA) of signals emitted from an object to three or more receivers.

[0061] 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. The high amplitude acoustic events may include. In some embodiments, the acoustic monitoring system 160 may receive acoustic signals corresponding to the acoustic events at the plurality of acoustic sensors 162 and determine an estimated location where the acoustic signals are generated, such as a location where an acoustic event is detected.

[0062] refer to Figure 5A and Figure 5B , shows a carrier head 540 having a substrate 500 located within a retaining ring 542. The carrier head 540 includes Figure 4A The acoustic sensors 562a-562c are connected to a transmitter 564 and a receiver 565 of the acoustic monitoring system 560. Figure 5A As shown, substrate 500 includes a defect 580 that generates a high amplitude acoustic event 582. Acoustic event 582 propagates outward from defect 580.

[0063] Figure 5B An acoustic event 582 is shown propagating outward from a defect 580. The defect 580 is located at a distance d from each of the acoustic sensors 562a-562c. a d b and d c Each acoustic sensor 562a-562c is detected at a different time t a ,t b and t c An acoustic event 582 is received. The distance that the acoustic event 582 propagates to each of the acoustic sensors 562a-562c varies based on the location of the acoustic sensors 562a-562c within the carrier head 540, for example, d a ≠d b ≠d c Therefore, the acoustic sensors 562a-562c receive the acoustic event 582 at different times, for example, t a ≠t b ≠t c .

[0064] The acoustic sensors 562a-562c send the received acoustic signals to the transmitter 564, which transmits the acoustic signals to the receiver 565. The receiver 565 transmits the acoustic signals to the electronic components 566 and the controller 590.

[0065] The electronic component 566 receives the acoustic signal and performs calculations on the signal. In some embodiments, the electronic component 566 calculates the location of the defect 580 on the substrate 500 based on the received acoustic signal. For example, the electronic component 566 performs a triangulation (e.g., triangulation) calculation using the time at which the acoustic sensors 562a-562c receive the acoustic event 582 to determine the location of the defect 580.

[0066] Given a defect 580 at a known location (e.g., P i =P x , P y , P z ) n The acoustic event 582 is generated at an unknown location (e.g., E = (x, y, z)) on the substrate 500 within the range of the receivers (e.g., acoustic sensors 562a-562c). Without wishing to be bound by theory, the distance R from the transmitter to one of the receivers, expressed in Cartesian coordinates, is m for

[0067] Distance R m is the wave speed c multiplied by the transit time from defect 580 to one of acoustic sensors 562a-562c. The time difference for acoustic event 582 to hit each of acoustic sensors 562a-562c, for example, T=t i -t o , calculated by the electronics 566 based on the receiver. The distance to each of the acoustic sensors 562a-562c is then calculated based on the time difference. The distance to each of the acoustic sensors 562a-562c is used to calculate the location of the defect 580 on the substrate 500. Locating the defect 580 helps with wafer-to-wafer and intra-wafer quality control of the polishing process.

[0068] 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 that is applied to received acoustic signals to monitor the spatial location of acoustic activity or events at a distance from the array of acoustic sensors 162.

[0069] In some embodiments, a phase shift, such as a time delay, is applied to each of the acoustic signals received by the acoustic sensor 162 so that the phase shift is related to the distance of the acoustic sensor 162 from the area to be monitored. The phase shifted signals are then summed to produce a summed signal. Applying a phase shift to each received acoustic signal to detect acoustic activity at a particular area is called "beamforming." This can amplify the acoustic signal generated at the selected area, whether it is an acoustic event or acoustic activity.

[0070] The amount of phase shift applied to each of the acoustic signals may vary over time. In particular, the phase shift may be varied so that the spatial region provided by the beamforming "sweeps" across all of the wafer or a region of the wafer at predetermined intervals.

[0071] Fig. 6A and Figure 6B An example substrate 600 , such as substrate 10 or substrate 500 , is shown, the example substrate 600 being divided into a plurality of monitoring zones. Fig. 6A and Figure 6B The dashed lines shown on the substrate 600 in FIG. 6 represent an illustrative example of dividing independent acoustic monitoring zones.

[0072] Fig. 6A A substrate 600 is shown divided into monitoring zones AI. Monitoring zones AH are radial segments that are part of the circumference of the substrate 600, whereas monitoring zone I is a circular segment around the center of the substrate 600. Figure 6B A substrate 600 is shown divided into monitoring zones JM. The monitoring zones KM are concentric rings around the center of the substrate 600, while the monitoring zones J are circular segments around the center of the substrate 600 (such as monitoring zone I).

[0073] Fig. 6A and Figure 6B The monitoring zones are exemplary only, and alternative monitoring zone divisions may be achieved by appropriate signal processing of the received acoustic signals. Signal processing may 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 may send a summed signal to the controller 190 to modify one or more polishing parameters of the polishing operation, such as pressure in one or more chambers 146a-146c. In alternative embodiments, the monitoring zone may be a regular or irregular array of shapes, such as a rectangular grid, covering at least a portion of the surface of the substrate 600.

[0074] Figure 6C The substrate 600 is shown positioned within the retaining ring 642 of the carrier head 640. Each acoustic monitoring area of ​​the substrate 600 is arranged at a distance from each of the acoustic sensors 662a-662c. For example, Figure 6CThe acoustic monitoring zone E is shown in , and the arrows representing acoustic signals Φ1-Φ3 show the respective paths that the acoustic signals Φ follow to reach the acoustic sensors 662a-662c.

[0075] 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-662c along different paths having corresponding 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 sensor 662c and the acoustic sensor 662a receive the acoustic signals Φ2 and Φ3 at times based on the distances from the acoustic monitoring zone E, respectively.

[0076] Acoustic sensors 662a - 662c transmit received acoustic signals Φ1 -Φ3 to a transmitter 664 of an acoustic monitoring system 660 , and the received acoustic signals Φ1 -Φ3 are sent to a receiver 665 and electronic components 666 . Fig.6D 6 is a graph depicting acoustic signals Φ1-Φ3 received by electronic element 666 at different times. Acoustic signals Φ1-Φ3 are shown along the y-axis, and time is shown along the x-axis. Acoustic signal Φ1 is received at a first time, acoustic signal Φ2 is received at a second time with a phase shift Δ1, and acoustic signal Φ3 is received at a third time with a phase shift Δ2.

[0077] The electronic component 666 receives the acoustic signals Φ1-Φ3 and applies phase shifts of Δ1 and Δ2 to the acoustic signals Φ2 and Φ3, respectively, to approximate the acoustic signals Φ1-Φ3 generated at the acoustic monitoring zone E and simultaneously received at the acoustic sensors 662a-662c. The phase-shifted acoustic signals (e.g., (Φ2+Δ1) or (Φ3+Δ2)) can then be summed into a summed signal representing the acoustic signal Φ generated at the acoustic monitoring zone E, e.g., Φ=Φ1+(Φ2+Δ1)+(Φ3+Δ2).

[0078] The summed signal may include constructive or destructive interference based on the received acoustic signals Φ1-Φ3. The interference may represent various acoustic events or acoustic activities in the acoustic monitoring area, such as detection of layer transitions, defects, or scratches. In some embodiments, the controller 690 may change the polishing parameters of the carrier head 640 based on the detected acoustic events. For example, the controller 690 may change the pressure within the chambers 146a-146c or the rotation rate of the controller 690 based on the detected acoustic events (such as layer transitions).

[0079] In some embodiments, the electronic component 666 may apply additional signal processing to the received signal (such as the acoustic signals Φ1-Φ3). The received acoustic signal or the summed signal may be summed, filtered, amplified, correlated, denoised, or converted to a second dimension. For example, the received signal or the summed signal may be converted to a frequency dimension before or after other signal processing. A Fourier transform, such as a fast Fourier transform, may be applied to the received signal or the summed signal.

[0080] The electronic component 666 or the controller 690 may be based on the acoustic monitoring area (such as Fig. 6A or Figure 6B The array of phase shifts Δ for each of the acoustic sensors 662a-662c is stored in a memory or storage device based on the distance to each of the acoustic monitoring zones to be monitored. The electronics 666 or controller 690 can then receive the acoustic signals from each of the acoustic sensors 662a-662c and apply a phase shift 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, serially, or in parallel.

[0081] Although many details are included in this specification, these details should not be interpreted as limitations on the scope of the claimed protection, but should be understood as feature descriptions specific to a particular example. Certain features described in this specification in the context of different embodiments may be combined. Conversely, various features described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments.

[0082] A number of embodiments have been described. However, it will be appreciated 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 appended claims.

Claims

1. A chemical mechanical polishing device, comprising: a workbench supporting a polishing pad; a carrier head for holding a surface of a substrate against the polishing pad; a motor for generating a relative motion between the worktable and the carrier head so as to polish an upper covering layer on the substrate; an acoustic sensor array disposed within the carrier head for receiving acoustic signals from the surface of the substrate; as well as A controller is configured to detect a location of an acoustic event on the surface of the substrate based on received acoustic signals from the acoustic sensor array.

2. The apparatus of claim 1, wherein the controller is further configured to detect the location of the acoustic event on the surface of the substrate based on a time-of-flight calculation of a received acoustic signal from each of the acoustic sensors of the array.

3. The apparatus of claim 1, wherein the acoustic sensor array comprises three or more acoustic sensors.

4. The apparatus of claim 1, wherein the acoustic sensor receives acoustic signals within a frequency range of 10 kHz to 200 kHz.

5. The apparatus of claim 1, wherein the acoustic sensor is a passive acoustic sensor.

6. A chemical mechanical polishing device, comprising: a workbench supporting a polishing pad; a carrier head for holding a surface of a substrate against the polishing pad; a motor for generating a relative motion between the worktable and the carrier head so as to polish an upper covering layer on the substrate; an acoustic sensor array disposed within the carrier head for receiving acoustic signals from the surface of the substrate; as well as A controller is configured to detect a position on the substrate where a polishing endpoint has been reached based on the received acoustic signal.

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

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

9. An apparatus as claimed in claim 7, wherein the controller is configured to apply a set of corresponding phase shifts to the received acoustic signals for each corresponding position among a plurality of positions on the substrate and sum the phase-shifted received acoustic signals to produce a summed signal, the summed signal being beamformed to selectively represent the acoustic activity at the corresponding position on the substrate, thereby producing a plurality of summed signals representing the plurality of positions.

10. The apparatus of claim 9, comprising, for each respective summation signal of the plurality of summation signals, monitoring a change in the respective summation signal, the change indicating a polishing endpoint at the respective position corresponding to the respective summation signal.

11. The apparatus of claim 6, wherein the polishing endpoint comprises removing a layer being polished to expose an underlying overlying layer.

12. The apparatus of claim 6, the controller further configured to de-noise the received acoustic signal from the acoustic sensor array prior to a polishing endpoint in a detection zone.

13. The apparatus of claim 6, wherein the acoustic sensor array comprises five or more acoustic sensors.

14. A polishing method comprising the following steps: holding the substrate using a carrier head and contacting a surface of the substrate with a polishing pad; Producing relative motion between the substrate and the polishing pad; monitoring acoustic signals from the substrate from a plurality of sensors in the carrier head; Positions of acoustic events on the surface of the substrate are calculated based on the acoustic signals received from the plurality of sensors.

15. The method of claim 14, wherein the step of calculating the position is based on a time-of-flight calculation of the received acoustic signal from each of the acoustic sensors of the array.

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

17. The method of claim 14, wherein the step of monitoring comprises passive monitoring using a passive acoustic sensor.

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