Determining substrate orientation with acoustic signals

Abstract

A chemical mechanical polishing apparatus includes a platform supporting a polishing pad, a carrier head securing a surface of a substrate against the polishing pad, a motor generating relative motion between the platform and the carrier head to polish a cover layer on the substrate, an in-situ acoustic monitoring system including an acoustic sensor receiving acoustic signals from the surface of the substrate, and a controller configured to determine an angular orientation of the substrate based on an acoustic signal received from the in-situ acoustic monitoring system.

Description

Technical Field

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

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers 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 may 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 grinding, the filler layer is flattened, for example, by grinding for a predetermined period of time to leave a portion of the filler layer on the non-planar surface. In addition, photolithography techniques typically require flattening of the substrate surface.

[0003] Chemical mechanical polishing (CMP) is a recognized planarization method. This planarization method usually requires the substrate to be mounted on a carrier or polishing head. The exposed surface of the substrate is usually placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. A polishing slurry is usually supplied to the surface of the polishing pad.

[0004] During grinding, the substrate may experience an "asymmetric" removal profile, i.e., the amount removed varies with angular position around the center of the substrate (rather than just with radial distance from the center of the substrate). Additionally, prior to grinding, the substrate may have an initial asymmetric, non-uniform thickness profile. Summary of the invention

[0005] A chemical mechanical polishing apparatus is disclosed herein, comprising an in-situ acoustic monitoring system disposed in a platform. A carrier head causes motion between a substrate and a polishing pad on the platform. The acoustic monitoring system receives an acoustic signal as the substrate sweeps across an acoustic sensor. The acoustic signal originates from an interface between the substrate surface and the polishing pad and varies over time depending on the polishing stage and the material exposed on the substrate surface. In some stages, the acoustic signal varies periodically depending on the angular orientation of the substrate relative to the acoustic sensor. Detecting such periodic variation helps determine the angular orientation of the substrate within the carrier head. The substrate angular orientation can be determined as a function of time and a predicted angular orientation generated at any point in time from the start of polishing.

[0006] In one aspect, a chemical mechanical polishing apparatus includes a platform supporting a polishing pad, a carrier head that secures a substrate surface against the polishing pad, a motor that generates relative motion between the platform and the carrier head to polish a cover layer on the substrate, an in-situ acoustic monitoring system including an acoustic sensor that receives an acoustic signal from the substrate surface, and a controller configured to determine an angular orientation of the substrate based on the acoustic signal received from the in-situ acoustic monitoring system.

[0007] In another aspect, a method includes contacting a substrate with a polishing pad, generating relative motion between the substrate and the polishing pad to polish an overlying layer on the substrate, monitoring acoustic signals from a surface of the substrate with an acoustic sensor, and determining an angular orientation of the substrate based on the monitored acoustic signals.

[0008] In another aspect, a chemical mechanical polishing system includes: a transfer station having a sensor that generates a signal that depends on the angular orientation of a substrate; a polishing station; a platform that supports a polishing pad; a carrier head that fixes a surface of the substrate against the polishing pad; a motor that generates relative motion between the platform and the carrier head to polish a cover layer on the substrate; an in-situ acoustic monitoring system including an acoustic sensor that receives an acoustic signal from the surface of the substrate; and a controller. The controller is configured to receive a signal from the sensor in the transfer station and determine an initial angular orientation of the substrate before polishing based on the signal, determine a rate of change of the angular orientation of the substrate based on the acoustic signal received from the in-situ acoustic monitoring system, and determine the angular orientation of the substrate based on the initial angular orientation and the rate of change.

[0009] In another aspect, a chemical mechanical polishing system includes: a polishing station having a platform supporting a polishing pad; a rotatable carrier head that fixes a surface of a substrate against the polishing pad; a motor that generates relative motion between the platform and the carrier head to polish a cover layer on the substrate; an in-situ acoustic monitoring system including an acoustic sensor that receives an acoustic signal from the surface of the substrate; and a controller. The controller is configured to determine a rate of change of an angular orientation of the substrate based on the acoustic signal received from the in-situ acoustic monitoring system to obtain a rotation rate of the carrier head, and determine an angular orientation difference between the substrate and the carrier head based on the rate of change of the angular orientation of the substrate and the rotation rate of the carrier head.

[0010] Implementations may include one or more of the following features.

[0011] The acoustic sensor may be a passive acoustic sensor. The acoustic sensor may receive acoustic signals with a frequency range from 10 kHz to 200 kHz.

[0012] The controller may be configured to receive a carrier head rotation rate from a carrier head motor encoder to obtain a substrate precession rate, and to calculate a substrate rotation rate boundary condition based on the carrier head rotation rate and the precession rate. The carrier head may be rotatable and have a plurality of pressure actuators angularly positioned around a rotation axis of the carrier head. The controller may be configured to obtain an angular orientation of the carrier head, to compare the angular orientation of the carrier head with an angular orientation of the substrate, and to determine pressures of the plurality of actuators based on the comparison. A sensor may measure the angular orientation of the carrier head, and the controller may receive a signal from the sensor to obtain the angular orientation of the carrier head.

[0013] The controller may be further configured to de-noise the acoustic signal received from the in-situ acoustic monitoring system prior to determining the time-varying function representing the angular orientation distribution of the substrate. De-noising the acoustic signal received from the in-situ acoustic monitoring system may include sub-sampling, averaging, grouping, or windowing the received acoustic signal.

[0014] The controller may be configured to rotate the carrier head or the support of the substrate so as to move the area monitored by the sensor along the circumference of the edge of the substrate. The transfer station may include a substrate support. The sensor in the transfer station may be positioned to monitor the substrate while the substrate is positioned on the substrate. The controller may be configured to determine the orientation of the substrate before the substrate is loaded into the carrier head. The sensor in the transfer station may be positioned to monitor the substrate while the substrate is held by the carrier head when the carrier head is in the transfer station, and the controller may be configured to determine the orientation of the substrate after the substrate is loaded into the carrier head and before the carrier head is moved to the grinding station.

[0015] The controller may be configured to obtain a starting angular orientation of the carrier head as the angular orientation of the carrier head when the substrate is loaded into the carrier head at the transfer station. The controller may be configured to obtain a starting angular orientation of the carrier head as the angular orientation of the carrier head at the transfer station when the substrate is loaded into the carrier head and the angular orientation of the substrate is determined.

[0016] The controller may be configured to determine the angular orientation of the substrate during grinding based on the acoustic signal. The controller may be configured to reset the starting angular orientation every 1 to 10 seconds. The controller may be configured to reset the starting angular orientation whenever the angular orientation difference between the substrate and the carrier head exceeds a set value.

[0017] The controller may be configured to determine the angular orientation of the substrate based on a signal from a notch detector in the carrier head and an acoustic signal from the in-situ acoustic monitoring system.

[0018] Particular implementations of the subject matter described in this specification can be implemented to realize one or more of the following technical advantages.

[0019] Wafer to wafer (WTW) and within-wafer (WIW) polishing uniformity can be improved. Angle-dependent non-uniformity can be reduced. The software of an existing acoustic monitoring system can be updated to detect angle-oriented acoustic signals without requiring new hardware, which reduces the cost of ownership. Determining a time-varying function representing the angular orientation of a substrate allows for extrapolation of the angular orientation, which allows application of angle-dependent pressure to increase material removal accuracy.

[0020] 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

[0021] Figure 1 A schematic cross-sectional view of an exemplary grinding apparatus is shown.

[0022] Figure 2A A top view of the upper surface of the polishing pad on the platform and the carrier head holding the substrate is shown.

[0023] Figure 2B A bottom view of the carrier head is shown.

[0024] Figure 3A is a graph showing an exemplary acoustic signal.

[0025] Figure 3B yes Figure 3A Exploded view of a portion of the acoustic signal.

[0026] Figure 4A and Figure 4B An exemplary orientation of a substrate with parallel registration lines relative to the direction of travel of the acoustic sensor is shown.

[0027] FIG. 5A to FIG. 5E Example angular orientations of example substrates from the direction of travel of the acoustic sensor of FIG. 2 are shown.

[0028] Figure 6 Exemplary angular orientations of exemplary substrates having planar faces are shown.

[0029] Figure 7 A schematic cross-sectional view of a loading station is shown.

[0030] In the drawings, like reference numerals denote like elements. DETAILED DESCRIPTION

[0031] As described above, during grinding, the substrate may be subjected to an asymmetric removal profile, or may have an initially asymmetric, non-uniform thickness profile. It is assumed that the carrier head may include multiple chambers disposed at angles about a central axis, and different pressures may be applied to the angled chambers to compensate for the asymmetry. However, the problem is that during grinding, the substrate "precesses", i.e., rotates relative to the carrier head. Therefore, the degree to which the chamber needs to be pressurized to compensate for the asymmetry will change over time (because a given chamber will not always correspond to the same angular position on the substrate). Therefore, in order to correctly determine the grinding parameters to compensate for the asymmetry, it will be useful to determine the orientation of the substrate relative to the substrate.

[0032] It has been suggested to use a carrier head with an optical sensor to monitor substrate orientation. However, such a technique is difficult to implement and would in any case require changes to the equipment. Thus, there is still room for improvement in the art of determining substrate orientation within a carrier head (even if used for purposes other than compensating for the asymmetry described above).

[0033] A technique that can determine substrate orientation is acoustic monitoring. Without being limited by theory, component substrates, i.e., substrates used for integrated circuit component manufacturing (as opposed to blank substrates or bare silicon wafers), typically have patterned features. Patterned features may include small-scale features (such as nanoscale platforms and grooves) and larger-scale features (such as circuit system dies aligned along a regular array). Still without being limited by theory, when the substrate precesses (e.g., undergoes precession), the features may be aligned or misaligned with the relative direction of travel of the polishing layer protrusions of the polishing pad. This may result in changes in the acoustic signal.

[0034] In operation, a platform including an acoustic sensor is rotated at a first speed to transport the sensor under a substrate at a scanning frequency, while the substrate is rotated at a second speed. Measurements received each time the acoustic sensor passes under the substrate provide periodic measurements taken when the substrate is in varying rotational positions (e.g., various orientations of the substrate precessing under the carrier head). The scanning frequency and the substrate rotation frequency generate a periodic signal based on a beat frequency of the two rotation rates. The peaks or troughs of the periodic signal correspond to the alignment of the patterned features and the direction of projection travel.

[0035] The precession rate, ie, the rate of rotation of the substrate relative to the carrier head, can be determined by detecting the signal and determining parameters of the periodic alignment signal.

[0036] Figure 1An example of a grinding apparatus 100 is shown. The grinding apparatus 100 includes a rotatable dish-shaped platform 120 on which a grinding pad 110 is located. The grinding pad 110 can be a double-layered grinding pad having an outer grinding layer 112 and a softer backing layer 114. The platform is operable to rotate about a rotation axis 125. For example, a motor 121, such as a DC induction motor, can rotate a drive shaft 124 to rotate the platform 120.

[0037] The polishing apparatus 100 may include a port 130 for dispensing a polishing liquid 132 (eg, polishing slurry) onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner to polish the polishing pad 110 so as to maintain the polishing pad 110 in a consistent polishing state.

[0038] The polishing apparatus 100 includes a carrier head 140 operable to secure the substrate 10 against the polishing pad 110. The carrier head 140 may include a retaining ring 142 to retain the substrate 10 beneath a 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 to 146c, which can apply independently controllable pressure to associated areas on the flexible membrane 144 and, therefore, to the substrate 10. Although for ease of description, the carrier head 140 may include a retaining ring 142 to retain the substrate 10 beneath a flexible membrane 144. Figure 1 Only three chambers are shown in FIG. 1 , but there may be one or two chambers, or four or more chambers, such as nine to thirteen chambers. Figure 1 The chambers are shown arranged radially, but Figure 2B As shown, the carrier head may include a plurality of chambers, such as chambers 146a to 146f, distributed at angles about the central axis of the carrier head. This allows the angle of applied pressure to be varied to compensate for asymmetries in the grinding.

[0039] The carrier heads 140 are suspended from a support structure 150 (e.g., a carousel 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 (e.g., on a slide on the support structure 150), either by rotational oscillation of the carousel itself, or by sliding along a track. In typical operation, the platform rotates about its rotation axis 125, and each carrier head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad.

[0040] A controller 190 (such as a programmable computer) is connected to the motors 121, 154 to control the rotation rate of the platform 120 and the carrier head 140. For example, each motor may include an encoder, such as a motor encoder, which measures the rotation rate of the associated drive shaft. Feedback control circuitry may be in the motor itself, part of the controller, or a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft matches the rotation rate received from the controller. The encoder may also provide orientation of the drive shaft and related components, for example, the encoder 156 of the drive shaft 152 may be used to determine the angular orientation of the carrier head 140.

[0041] 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 mounted on the upper platform 120 at one or more locations.

[0042] A position sensor, such as an optical interrupter or a rotary encoder attached to the edge of the platform, can be used to sense the rotational position of the platform 120. This allows only a portion of the signal to be measured when the acoustic sensor 162 is close to the substrate 10, such as when the acoustic sensor 162 is below the carrier head 140 or the substrate 10.

[0043] exist Figure 1 In the illustrated embodiment, the acoustic monitoring system 160 includes an acoustic sensor 162 supported and positioned by the platform 120 to receive acoustic signals from the substrate 10 through the polishing pad 110. The acoustic sensor 162 may be partially or fully located in a recess 164 in the top surface of the platform 120. In some embodiments, the top surface of the acoustic sensor 162 is coplanar with the top surface of the platform 120.

[0044] In some embodiments, the portion of the polishing pad directly above the acoustic sensor 162 may include an acoustic window 119, e.g., an area having a lower acoustic impedance than the surrounding polishing material. The acoustic window 119 may extend through the polishing layer 112 or the backing layer 114, or both. However, if the acoustic transmission of the polishing pad is sufficiently high, the acoustic window 119 may not be necessary.

[0045] The acoustic sensor 162 is a contact acoustic sensor, the surface of which is connected to the grinding layer 112, the backing layer 114 or a part of the acoustic window 119 (for example, directly contacting therewith, or having only an adhesive layer for attaching thereto, or having only an acoustic gel for transmitting acoustic signals therefrom). For example, the acoustic sensor 162 may be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. The piezoelectric sensor may include a rigid (e.g., stainless steel, etc.) contact plate placed in contact with the subject to be monitored, and a piezoelectric component (e.g., a piezoelectric layer sandwiched between two electrodes on the back of the contact plate). The acoustic sensor 162 may be connected to a power supply and / or other signal processing electronics 166 by a circuit system 168 through a rotational coupling (e.g., a mercury slip ring).

[0046] In some implementations, the in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, the signal is monitored by the acoustic sensor 162 without generating a signal from the acoustic signal generator (or the acoustic signal generator may be omitted from the system entirely). The passive acoustic signal monitored by the acoustic sensor 162 may be in the range of 20 kHz to 1 MHz, such as 20 kHz to 50 kHz, or 200 kHz to 400 kHz, or 200 kHz to 1 MHz, depending on the application. For example, to monitor the polishing of inter-layer dielectrics (ILDs) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz may be monitored.

[0047] The signal from the acoustic sensor 162 can be amplified by a built-in internal amplifier. In some embodiments, the amplification gain is between 40 dB and 90 dB (e.g., 50 dB or 80 dB). If necessary, the signal from the acoustic sensor 162 can then be further amplified and filtered, and digitized to a high-speed data acquisition board (e.g., in the electronic device 166) through an A / D port. 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 MHz to 3 MHz or 6 MHz to 8 MHz. In an embodiment where the acoustic sensor 162 is a passive acoustic sensor, a frequency range from 100 kHz to 2 MHz can be monitored, such as 500 kHz to 1 MHz (e.g., 750 kHz).

[0048] If positioned in the platform 120, the acoustic sensor 162 may be located at the center of the platform 120, such as the rotation axis 125, an edge or a midpoint of the platform 120 (eg, 5 inches from the rotation axis for a 20 inch diameter platform).

[0049] View now Figure 2A, showing a top view of the polishing pad 110 on top of the platform 120. The substrate 10 is held within the retaining ring 142 of the carrier head 140. The controller 190 commands the carrier head 140 to move the chambers 146a to 146c (see Figure 1 ) presses the substrate 10 into contact with the polishing layer 112.

[0050] When the carrier head 140 presses the substrate 10 toward the polishing layer 112, the carrier head 140 rotates at a carrier head rotation rate ω. C The substrate 10 is restrained by the retaining ring 142 in an area below the carrier head 140 and can move, for example, rotate, within the enclosed area. Specifically, the friction between the substrate 10 and the inner surface of the retaining ring 142 and / or the friction of the film 144 on the substrate 10 causes the substrate 10 to rotate at a substrate rotation rate ω. S Rotation. Substrate rotation rate ω S The rotation rate ω of the carrier head 140 may be approximated but is not usually exactly equal to C . The rotation rate of the carrier head ω C The difference between the rotation rate provides the precession rate.

[0051] The platform 120 includes an acoustic window 119 that contacts the underlying acoustic sensor 162. When the platform 120 rotates at a platform rotation rate ω P While rotating, the acoustic sensor 162 is stationary within the recess 164 of the platform 120 and travels in a common direction of travel 200 as the platform 120 rotates. This causes the acoustic window 119 and associated acoustic sensor 162 to sweep beneath the substrate 10 within the retaining ring 142.

[0052] The acoustic sensor 162 receives an acoustic signal based on acoustic information received from an interface between the substrate 10 and the pad 110 . Figure 3A An exemplary acoustic signal 300 generated during a grinding process is depicted. The acoustic signal 300 compares the total power spectral density (PSD) over a frequency range on the y-axis to time in seconds (s). The acoustic signal 300 has different regions, such as a first region 302, a second region 304, and a third region 306 corresponding to a layer transition of the substrate 10.

[0053] Without wishing to be bound by theory, layer transitions occur when the apparatus 100 removes layer topography. In some embodiments, regions 302, 304, and 306 correspond to layer transitions in the substrate 10. The grinding of the topography of the substrate 10 may correspond to Figure 6The first region 302 of the acoustic signal 300 is shown in FIG. 3. In a second region 304 of the signal 300, the acoustic signal 300 is substantially constant (although affected by noise). The grinding of the flat surface may correspond to the second region 304 of the acoustic signal 300. The second region 304 is continuous in time until the filler layer extending over the patterned layer is removed.

[0054] The patterned layer is composed of a different material than the filler layer, such as a dielectric, and interacts differently with the surface and material of the polishing layer 112, thereby generating a third region 306 of the acoustic signal 300. In addition, continued polishing will produce depressions, and this topography will again increase the acoustic signal. The third region 306 is not constant, for example, it can increase or decrease.

[0055] Figure 3B An enlarged view of the third region 306 enclosed by a box A is depicted. Figure 3B The acoustic signal 310 has undergone further processing (eg, averaging) to reduce noise in the acoustic signal 300, such as denoising. In other examples, the denoising process may include applying sub-sampling, averaging, grouping, or windowing to the received acoustic signal.

[0056] Without wishing to be bound by theory, each data point of the acoustic signal 310 corresponds to a different situation in which the platform 120 sweeps past the acoustic sensor 162 beneath the substrate 10. Between each data point, the platform 120 undergoes a full rotation during which the acoustic sensor 162 is not beneath the substrate 10. The data points of the acoustic signal 310 depict an oscillating periodic motion over time on the y-axis between a maximum value (G) and a minimum value (H). Without wishing to be bound by theory, in some embodiments, the maximum value (G) and the minimum value (H) correspond to structural features of the patterned layer, and in particular features that are aligned parallel or perpendicular to the direction of motion of the polishing pad beneath the substrate.

[0057] The patterned layer of substrate 10 is a non-uniform surface, including circuit system dies with complex patterns of dielectric platforms and conductor-filled grooves. The shape of the dies can be rectangular, such as rectangular or square, and arranged in a regular array on the semiconductor layer. The dies arranged in the array form a series of parallel alignment lines along the surface of the rectangular dies, such as the edges of the dies or the scribe lines between the dies.

[0058] Figure 4A and Figure 4BA substrate 10 is depicted with a regular arrangement of parallel registration lines 11 in two respective orientations relative to the movement of the acoustic sensor 162. The spacing of the registration lines 11 is exemplary. The acoustic sensor 162 is shown sweeping under the substrate 10 along a direction of travel 200. The direction of travel 200 is an approximation of the relative motion of the acoustic sensor 162 as the platform 120 sweeps the acoustic sensor 162 under the substrate 10. In some embodiments, the acoustic monitoring system 160 is configured to generate a measurement each time the acoustic sensor 162 passes under the substrate 10 (e.g., when the acoustic sensor 162 crosses the diameter of the substrate 10). In this manner, the acoustic signal 310 is a signal corresponding to the rotation rate ω of the platform 120. P The sampling rate corresponds to the time interval between consecutive measurements of the acoustic signal 310, for example, the sampling rate corresponds to ω P .

[0059] In some embodiments, the acoustic monitoring system 160 is configured to generate a single measurement per pass at one point along the diameter of the substrate 10. In alternative embodiments, the acoustic monitoring system 160 is configured to generate multiple measurements per pass at multiple points across the diameter of the substrate 10. In such embodiments, the acoustic monitoring system 160 may process the multiple generated measurements into an average measurement in the measurement sequence of the acoustic signal 310.

[0060] Figure 4A The registration line 11 is shown aligned parallel to the direction of travel 200, while Figure 4B The registration line 11 is shown aligned perpendicularly to the direction of travel 200. In general, the orientation of the registration line 11 relative to the direction of travel 200 will change as the platform 120 and substrate 10 are independently rotated.

[0061] The convex portion of the grinding layer 112 sweeps under the substrate 10 along the travel direction 200, generates friction on the contact surface of the substrate 10, and removes the portion of the substrate 10 material that is in contact with the pad 110. Figure 4A and Figure 4B The corresponding alignment of the direction of travel 200 shown in generates different acoustic signals received by the acoustic sensor 162. In other words, Figure 4A The arrangement of the acoustic window 119 and the substrate 10, wherein the registration line 11 is parallel to the direction of travel 200, produces a first acoustic signal amplitude. Figure 4B In the arrangement, the registration line 11 is perpendicular to the direction of travel 200, resulting in a second acoustic signal amplitude.

[0062] For example, in some embodiments, Figure 4A The arrangement corresponds to a signal maximum (e.g., maximum G), and Figure 4BThe arrangement of corresponds to a signal minimum (e.g., minimum H). Between the periodic maximum and minimum values ​​(e.g., between G and H), the acoustic signal 310 consists of a series of measurements (e.g., Figure 3B points), each measurement value corresponds to a measurement generated at various angular orientations of the substrate 10.

[0063] When the acoustic window 119 is P When the substrate 10 is swept under the substrate 10 at given regular intervals, the substrate 10 will be oriented at an angle relative to the direction of travel 200. The platform 120 and the substrate 10 within the holding ring 142 are rotated at two speeds ω P and S When the acoustic window 119 is located below the substrate 10, the acoustic sensor 162 receives an acoustic signal from the interface between the polishing layer 112 and the substrate 10. When the acoustic sensor 162 is not located below the substrate 10, no signal is received from the interface.

[0064] Without wishing to be bound by theory, when the platform 120 rotates at a speed ω P While rotating, the acoustic monitoring system 160 generates acoustic measurements at the above sampling rate. Between measurements, the substrate 10 is rotated by a rotation distance Δθ S ∝(ω S –ω P ) / 2π. FIG. 5A to FIG. 5E A substrate 10 is shown including parallel registration lines 11 in an exemplary sequence of angular orientations corresponding to measurements of an acoustic signal 310 collected at a sampling rate.

[0065] In some implementations, when the registration line 11 is parallel to the direction of travel 200, Figure 5A The angular orientation may correspond to Figure 3B The maximum signal G and Figure 3B The substrate 10 is oriented as shown. S The acoustic sensor 162 receives the acoustic signal at the sampling rate. FIG. 5A to FIG. 5E In the example, ω S >ω P , which results in a positive (e.g., counterclockwise) Δθ S In each measurement (e.g., in measurements performed when the sampling rate r is an integer value), as the substrate 10 is processed, Δθ S Increase.

[0066] When the substrate 10 passes through FIG. 5B to FIG. 5D When the received acoustic signal is processed in the direction shown, the received acoustic signal is processed according to Δθ corresponding to the change of the acoustic signal 310 between the maximum value G and the minimum value H S And changes.

[0067] exist Figure 5EIn the embodiment, the registration line 11 is parallel to the travel direction 200, and the measurement signal, such as the acoustic signal 310, is returned to Figure 5A The acoustic signal amplitude. Therefore, FIG. 5A to FIG. 5E The example of shows an exemplary periodic fluctuation of the acoustic signal 310 .

[0068] See again Figure 3B , the controller 190 receives the acoustic signal 310 and processes the measurements to determine one or more parameters of the acoustic signal 310. For example, the controller 190 processes the received acoustic signal 310 and calculates the oscillation frequency F of the acoustic signal 310. B For example, a sine or similar function may be fitted to the sequence of values ​​in the acoustic signal 310, with an oscillation frequency F B The determined parameters of the acoustic signal 310 can be used to obtain characteristics of the orientation of the substrate 10, for example, an estimate of the rotation rate (ω S ), the variance of the rotation rate estimate, and the rotation orientation (θ S ).

[0069] The controller 190 determines the substrate rotation rate and a continuous time-varying function representing the orientation of the substrate 10 over time, such as θ based on the determined parameters. S Specifically, assuming that the rotation speeds of the platform, the carrier head, and the substrate are not much different (for example, the difference is greater than two times), then FIG. 5A to FIG. 5E As shown, the oscillation frequency F B It should be twice the beat frequency. Assuming the platform rotates faster than the carrier head, and the carrier head rotates faster than the substrate, then ω P >ω P Therefore, the beat frequency should be (ω P –ω S )=F B / 2. Therefore, the substrate rotation rate can be calculated as ω S =ω P –F B / 2. The precession rate can be calculated as ω S –ω C Thus, the orientation of the substrate relative to the carrier head can be calculated as a function of time T, for example, as a function including (ω S –ω C )*T. Using this data, the appropriate chamber 146a-146i to cover a given angular region of the substrate can be calculated over time, and the pressure can be selected over time to reduce asymmetric polishing.

[0070] In addition, the orientation of the substrate can be periodically measured based on the acoustic signal, and the measured orientation can be used to compensate for potential differences between actual precession and calculated precession. In general, the peaks and / or valleys should correspond to a specific orientation of the substrate relative to the direction of motion. The specific orientation(s) of the substrate corresponding to the peaks and / or valleys can be determined empirically, for example, by loading a substrate with a known orientation into the carrier head prior to grinding and then monitoring the acoustic signal during a test grinding operation. The orientation of the substrate can be expressed as the angle between the direction of travel 200 and the notch or flat surface 14 on the edge 12 of the substrate 10. Assuming that the correspondence between the peaks and the angular orientations is known, the angular difference between the carrier head and the substrate can be reset periodically.

[0071] For example, see Figure 6 , assuming that the peak indicates that the substrate is in an oriented (A peak or valley may correspond to the die edge being aligned with the die in the direction of motion, in which case Typically 0° or 90°). Assuming the controller detects the presence of the peak at time t1, the controller can calculate the orientation of the substrate as +ω S *(T – t1). In addition, the controller can obtain the carrier head orientation at time t1, for example from the motor encoder data In this case, the controller can calculate the precession Δ, which is the difference between the carrier head orientation and the substrate orientation, as The controller can then intermittently reset the calculation of the precession based on the most recently detected peak, thereby obtaining t1, and Although the above discussion focuses on peaks, the techniques can also be used for valleys, midline crossings, or inflection points. The calculation of precession can be reset periodically, for example, about every 1 to 10 seconds, or each time the precession Δ exceeds a set value (e.g., 90°, 180°, or 360°).

[0072] In some implementations, the initial orientation angle between the substrate 10 and the carrier head 140 can be measured before grinding begins. For example, the initial orientation can be measured at a transfer station.

[0073] See also Figure 7, a substrate may be loaded into the carrier head 140 at a transfer station 400 including a loading cup 410. The loading cup 410 may include a support 412, such as a pedestal, lift pins, or an edge support ring, to hold the substrate 10 before loading the substrate 10 into the carrier head 140 and / or after unloading the substrate 10 from the carrier head 140. The support 412 may be rotatable and / or vertically actuatable, such as by a motor 414. The loading cup 410 may also include one or more nozzles 420 to spray a cleaning fluid 422 (e.g., deionized water) onto the substrate 10 while the substrate is on the support 412 and / or held by the carrier head 140 at the transfer station 400.

[0074] The transfer station 400 also includes a sensor 450 (e.g., an optical sensor) for determining the substrate orientation, such as an angle relative to the loading cup 410. For example, the sensor 450 can generate a light beam 452 that is directed toward the edge of the substrate 10 when the substrate is positioned on the support 412, and detects the reflection of the light beam from the substrate 10. The support 412 can rotate; the notches or flat surfaces will generate different reflected light intensities, so the controller can determine the initial substrate orientation based on the signal from the sensor 450. When the carrier head is lowered or the substrate is raised to be attracted to the carrier head 140, the initial angular orientation of the carrier head 140 can also be measured. (eg, relative to the loading cup.) For example, the angular orientation of the carrier head may be monitored by a motor encoder 460 that is part of the motor 154 .

[0075] Alternatively, the angular orientation of the substrate 10 may be measured after the substrate 10 is loaded onto the carrier head. For example, the sensor 450 may direct the light beam 452 onto the substrate 10 while the substrate is held by the carrier head 140, and the motor 154 may rotate the carrier head 140 so that the controller detects the notch and thus the initial substrate orientation. To this end, the initial angular orientation of the carrier head 140 may be measured. The substrate can be in the initial orientation Orientation, for example, the notch is aligned with the light beam.

[0076] Through the measurement, the controller 190 can calculate the initial angle difference Δ0, that is, Thereafter, during grinding, the angular difference may be calculated based on the precession rate determined from the acoustic signal as described above, ie, Δ = Δ0 + (ω S –ω C )*(T-t0), where t0 is the time when the substrate descends to contact the rotating platform. The controller 190 may also intermittently reset the calculation of the precession based on the most recently detected peak as described above, thereby obtaining t1, and The new value of .

[0077] Although this specification contains many details, the details should not be viewed as limitations on the claims, but rather as descriptions of specific features of specific examples. Certain features described in this specification in the context of independent implementations may also be combined. Conversely, various features described in the context of a single implementation may also be implemented in multiple embodiments alone or in any suitable subcombination.

[0078] Various embodiments have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the present disclosure. Therefore, other embodiments are also within the scope of the following claims.

Claims

1. A chemical mechanical polishing device, comprising: A platform for supporting a polishing pad; a carrier head for fixing the surface of the substrate against the polishing pad; a motor for generating relative motion between the platform and the carrier head to grind the cover layer on the substrate; an in-situ acoustic monitoring system comprising an acoustic sensor for receiving an acoustic signal from said surface of said substrate; as well as A controller is configured to determine an angular orientation of the substrate based on acoustic signals received from the in-situ acoustic monitoring system.

2. The apparatus of claim 1 , wherein the platform is rotatable and the acoustic sensor is supported by the platform and rotates with the platform, and wherein the in-situ acoustic monitoring system is configured to generate a measurement each time the sensor passes over the substrate such that a first sequence of measurements is generated at a sampling rate equal to an integer multiple of the rotation rate of the platform.

3. The apparatus of claim 2, wherein the controller is configured to obtain a substrate rotation rate boundary condition and determine an oscillation frequency in the first sequence of measurements. 4 . The apparatus of claim 3 , wherein the controller is configured to calculate the measured substrate rotation rate based on the sampling rate, the oscillation frequency, and the substrate rotation rate boundary condition.

5. The apparatus of claim 4, wherein the controller is configured to calculate, for each measurement in the sequence of measurements, a phase of a sinusoidal signal representative of the angular orientation of the substrate based on the sampling rate, the oscillation frequency, and the substrate rotation rate boundary conditions.

6. The apparatus of claim 5, wherein the frequency of the sinusoidal signal representative of the angular orientation of the substrate is twice the rotation rate of the substrate.

7. The apparatus of claim 1, wherein the controller is further configured to determine one or more parameters representing a time-varying function of the angular orientation of the substrate over time based on acoustic signals received from the in-situ acoustic monitoring system.

8. The apparatus of claim 7, wherein determining the time-varying function representative of the angular orientation of the substrate comprises determining a fast Fourier transform of the acoustic signal received from the in-situ acoustic monitoring system.

9. The apparatus of claim 7, wherein the controller is further configured to calculate the angular orientation of the substrate based on the time-varying function.

10. The apparatus of claim 7, the controller further configured to determine the time-varying function representative of the angular orientation of the substrate based on the received acoustic signal and an initial rotational position.

11. A chemical mechanical polishing system comprising: a transfer station including a sensor that generates a signal dependent on the angular orientation of the substrate; a lapping station including a platform for supporting a lapping pad; A carrier head, used to fix the surface of the substrate against the polishing pad; a motor for generating relative motion between the platform and the carrier head to grind the cover layer on the substrate; an in-situ acoustic monitoring system comprising an acoustic sensor for receiving an acoustic signal from said surface of said substrate; as well as a controller configured to receive a signal from the sensor in the transfer station and determine an initial angular orientation of the substrate before grinding based on the signal, determine a rate of change of the angular orientation of the substrate based on an acoustic signal received from the in-situ acoustic monitoring system, and determine the angular orientation of the substrate based on the initial angular orientation and the rate of change.

12. The system of claim 11, wherein the carrier head is rotatable, and wherein the controller is configured to obtain an angular orientation of the carrier head to determine a difference between the angular orientation of the carrier head and the angular orientation of the substrate.

13. The system of claim 12, wherein the carrier head includes a plurality of pressure actuators angularly positioned about a rotational axis of the carrier head, and wherein the controller is configured to determine the pressures of the plurality of actuators based on the difference.

14. The system of claim 11, wherein the sensor in the polishing station is configured to detect a notch or a flat surface of the substrate.

15. A chemical mechanical polishing system comprising: a lapping station including a platform for supporting a lapping pad; a rotatable carrier head for fixing the surface of the substrate against the polishing pad; a motor for generating relative motion between the platform and the carrier head to grind the cover layer on the substrate; an in-situ acoustic monitoring system comprising an acoustic sensor for receiving an acoustic signal from said surface of said substrate; as well as A controller is configured to determine a rate of change of the angular orientation of the substrate based on the acoustic signal received from the in-situ acoustic monitoring system to obtain a rotation rate of the carrier head, and determine an angular orientation difference between the substrate and the carrier head based on the rate of change of the angular orientation of the substrate and the rotation rate of the carrier head.

16. The system of claim 15, wherein the controller is configured to determine the angular orientation difference based on the rate of change of the angular orientation of the substrate, the rotation rate of the carrier head, a starting angular orientation of the substrate, and a starting angular orientation of the carrier head.

17. The system of claim 16, wherein the starting angular orientation of the substrate is an initial angular orientation of the substrate prior to grinding.

18. The system of claim 17, further comprising a transfer station, the transfer station comprising a sensor, the sensor generating a signal depending on the angular orientation of the substrate, and wherein the controller is configured to receive the signal from the sensor in the transfer station and determine the initial angular orientation of the substrate based on the signal.

19. The system of claim 16, wherein the starting angular orientation of the substrate is an angular orientation of the substrate during polishing.

20. The system of claim 19, wherein the controller is configured to store an association between a feature in the acoustic signal and a stored angular orientation, to detect the feature in the acoustic signal, and to set the starting angular orientation to the stored angular orientation.

21. The system of claim 20, wherein the controller is configured to repeatedly detect the feature in the acoustic signal and repeatedly reset the starting angular orientation to the stored angular orientation.

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