Computer program products, polishing methods, and polishing systems that provide spatial resolution based on pressure signals during motor torque monitoring.

Abstract

A polishing method includes: holding a substrate against the polishing surface of a polishing pad using a carrier head; generating relative movement between the substrate and the polishing pad; applying a first pressure modulated by a first modulation function to a first region of the substrate; applying a second pressure modulated by a second modulation function orthogonal to the first modulation function to a second region of the substrate; monitoring the substrate with an in-situ friction monitoring system to generate a sequence of measurements during the polishing of the substrate; and determining the relative contribution of the first region and the second region to the sequence of measurements based on distinguishing between a first frequency and a second frequency.

Description

Technical Field

[0001] This disclosure relates to the monitoring of motor torque or motor current during chemical mechanical polishing. Background Technology

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. One fabrication step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For some applications, the filler layer is planarized 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 trenches or holes in the insulating layer. After planarization, portions of the metal layer remaining between the raised patterns of the insulating layer form vias, plugs, and lines that provide conductive paths between thin-film circuits on the substrate. For other applications (such as oxide polishing), the filler layer is planarized until a predetermined thickness is left on the non-planar surface. Furthermore, photolithography often requires planarization of the substrate surface.

[0003] Chemical mechanical polishing (CMP) is a widely accepted planarization method. This method typically requires mounting a substrate on a carrier head or polishing head. The exposed surface of the substrate is usually placed against a rotating polishing pad. The carrier head provides a controlled load on the substrate to push it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

[0004] One challenge in CMP is determining whether the polishing process is complete—that is, whether the substrate layer has been planarized to the desired flatness or thickness, or when the desired amount of material has been removed. Variations in slurry distribution, polishing pad condition, the relative speed between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate. These variations, along with variations in the initial thickness of the substrate layer, lead to variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint cannot typically be determined solely as a function of polishing time. In some systems, the substrate is monitored in situ during polishing, for example, by monitoring the torque or current required by the motor rotating the stage or bearing head. Summary of the Invention

[0005] In one aspect, a polishing method includes: holding a substrate against a polishing surface of a polishing pad using a carrier head; generating relative movement between the substrate and the polishing pad; applying a first pressure modulated by a first modulation function to a first region of the substrate; applying a second pressure modulated by a second modulation function orthogonal to the first modulation function to a second region of the substrate; monitoring the substrate with an in-situ friction monitoring system to generate a sequence of measurements during the polishing of the substrate; and determining the relative contribution of the first region and the second region to the sequence of measurements based on distinguishing between a first frequency and a second frequency.

[0006] In another aspect, instructions are stored on a non-transitory computer-readable medium, the instructions being executed by one or more computers to perform the operations in the methods described above.

[0007] In another aspect, a polishing system includes: a worktable for supporting a polishing pad; a bearing head for holding a substrate against the polishing pad, wherein the bearing head is configured to apply independently adjustable pressure to multiple different areas of the substrate; a motor for generating relative movement between the bearing head and the worktable; an in-situ friction monitoring system for generating a value sequence; and a controller configured to perform the operations described above.

[0008] The implementation may include one or more of the following features: The first frequency and the second frequency may not be integer multiples of each other. The first and second cyclic waveforms may be the same waveform with different frequencies. The first and second frequencies may not be the frequencies of another moving part of the polishing system. The first and second cyclic waveforms may be selected from sine waves, sawtooth waves, triangular waves, or square waves. Storing one or more parameters may include storing a single parameter indicating which of the upper and lower coatings has a higher coefficient of friction. Storing one or more parameters may include storing a first parameter indicating the coefficient of friction of the upper coating and a second parameter indicating the coefficient of friction of the lower coating. The first and second frequencies may be between 10 Hz and 100 Hz.

[0009] The implementation may include one or more of the following potential advantages: Spatial information regarding the relative coefficient of friction of the substrate on the polishing pad can be extracted from the motor torque signal. Polishing of the entire substrate can be stopped more reliably when the undercoat is exposed. Polishing uniformity can be improved, and pitting and residue can be reduced.

[0010] Details of one or more embodiments are set forth in the accompanying drawings and the following description. Other aspects, features, and advantages will become apparent from the specification, the drawings, and the claims. Attached Figure Description

[0011] Figure 1 A schematic cross-sectional view of an example of a polishing device.

[0012] Figure 2 The illustration shows a schematic top view of the polishing equipment.

[0013] Figure 3 The illustration shows a schematic bottom view of the substrate.

[0014] Figures 4A to 4C The figure shows a curve of pressure versus time in different chambers of the bearing head.

[0015] Figure 5 The diagram shows a flowchart of a method for processing motor current signals.

[0016] Figure 6 The power spectrum of the sample is shown in the figure.

[0017] The same reference numerals in the various figures indicate the same elements. Detailed Implementation

[0018] In some semiconductor chip manufacturing processes, the top cover layer (e.g., silicon oxide or polysilicon) is polished until the bottom cover layer (e.g., a dielectric, such as silicon oxide, silicon nitride, or a high-k dielectric) is exposed. For many applications, the coefficient of friction of the bottom cover layer against the polished layer differs from that of the top cover layer. Therefore, when the bottom cover layer is exposed, the torque required for the motor to rotate the stage or bearing head at a specified rotational rate changes. The polishing endpoint can be determined by detecting this change in motor torque. Motor torque can be measured by measuring the motor's power consumption, for example, by measuring the motor current if the voltage remains constant, or by receiving a value reported by the motor driver.

[0019] Most polishing processes produce different polishing rates across the substrate, causing the undercoat at the substrate edges to be removed before the center, or vice versa. Unfortunately, in conventional motor torque monitoring techniques, torque is the result of the total frictional force across the entire wafer surface; the measurement lacks spatial resolution. Therefore, when the undercoat begins to be exposed in some areas of the substrate and the motor current signal begins to change, it is impossible to determine which part of the substrate is removed first.

[0020] However, by applying pressure to the substrate at different frequencies in different zones, it is possible to obtain information about the spatial distribution of friction on the substrate from the motor current signal. This allows for the determination of the cleaning distribution on the substrate.

[0021] Figures 1 to 2 The illustration shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable disc-shaped worktable 120, on which a polishing pad 110 is located. The polishing pad 110 may be a double-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The worktable is operable to rotate about axis 125. Figure 2 (See arrow A in the diagram). For example, motor 121 (e.g., a DC induction motor) can rotate drive shaft 124 to rotate table 120.

[0022] The polishing apparatus 100 may include a port 130 for dispensing polishing fluid 132 (such as abrasive slurry) onto the polishing pad 110. The polishing apparatus may also include a polishing pad adjuster for abrading the polishing pad 110, thereby keeping the polishing pad 110 in a consistent abrasive state.

[0023] 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. Each carrier head 140 can independently control polishing parameters, such as pressure, associated with each respective substrate.

[0024] The support head 140 is suspended from the support structure 150 (e.g., a rotating rack) and connected to the support head rotation motor 154 (e.g., a DC induction motor) via a drive shaft 152, allowing the support head to rotate about axis 155. Figure 2 (See arrow B in the image). Optionally, each bearing head 140 can oscillate laterally (see arrow B in the image). Figure 2 Arrow C) in the diagram, for example, on the slider on the rotating rack 150, or by the rotational oscillation of the rotating rack itself. In typical operation, the table rotates about its central axis 125, and each bearing head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad.

[0025] The support head 140 may include a retaining ring 142 to hold the substrate 10 below the flexible membrane 144. The support head 140 also includes one or more independently controllable pressurized chambers defined by the membrane 144, such as three chambers 146a to 146c, which can apply independently controllable pressure to associated areas on the flexible membrane 144, and thus to associated areas 12a to 12c on the substrate 10 (see [link to relevant documentation]). Figure 3 Apply independent and controllable pressure. Although for ease of explanation... Figures 1 to 2 The diagram only shows three chambers, but there could be two chambers, or four or more chambers, such as five chambers.

[0026] Figure 2 and Figure 3 The chambers and regions are illustrated as concentric, for example, a circular central chamber 146a and annular concentric chambers 146b and 146c, which apply pressure to the circular central region 12a and the annular concentric regions 12b and 12c, respectively. However, other configurations are possible. For example, the chambers may be distributed at an angle around the central axis 155 of the bearing head 140. Furthermore, as described above, different numbers of chambers and regions may be present.

[0027] The pressure in chambers 146a to 146c can be controlled by pressure regulators 148a to 148c. Pressure regulators 148a to 148c can be coupled to the respective chambers 146a to 146c via pneumatic lines 149, which pass through rotary joints and drive shafts 152.

[0028] Alternatively, other actuators, such as piezoelectric actuators, can be used instead of pneumatically controlling the pressure on a region of the substrate.

[0029] A control system 190 (such as a programmable computer) is connected to motors 121 and 154 to control the rotational speed of the table 120 and the carrier head 140. For example, each motor may include an encoder that measures the rotational speed of the associated drive shaft. A feedback control circuit, which may be located within the motor itself, part of the controller, or in a separate circuit, receives the measured rotational speed from the encoder and adjusts the current supplied to the motor to ensure that the rotational speed of the drive shaft matches the rotational speed received from the controller.

[0030] The control system 190 is also connected to pressure regulators 148a to 148c to control the pressure applied to chambers 146a to 146c in the bearing head 140.

[0031] The polishing equipment also includes an in-situ monitoring system 160, which can be used to determine the polishing endpoint. The in-situ monitoring system 160 generates a signal dependent on the friction between the substrate and the polishing pad. In some embodiments, the in-situ system provides a motor current or motor torque monitoring system. In this case, the in-situ monitoring system 160 includes a sensor for measuring motor torque. The measurement of motor torque can be a direct measurement of torque and / or a measurement of the current supplied to the motor.

[0032] For example, torque meter 160 may be mounted on drive shaft 124, and / or torque meter 162 may be mounted on drive shaft 152. The output signals of torque meters 160 and / or 162 are directed to controller 190.

[0033] Alternatively or additionally, current sensor 170 may monitor the current supplied to motor 121, and / or current sensor 172 may monitor the current supplied to motor 154. The output signals of current sensors 170 and / or 172 are directed to control system 190. Although the current sensor is illustrated as part of the motor, the current sensor may be part of the controller (if the controller itself outputs the drive current of the motor) or a separate circuit.

[0034] Alternatively or additionally, in-situ monitoring systems can perform more direct measurements of frictional forces. For example, an in-situ monitoring system may include sensors to measure the deflection of the flexural elements in the bearing head caused by friction on the substrate and / or retaining ring.

[0035] The sensor's output can be a digital electronic signal (if the sensor's output is an analog signal, it can be converted into a digital signal by an ADC in the sensor or controller). A digital signal consists of a sequence of signal values, where the time intervals between the signal values ​​depend on the sensor's sampling frequency. This sequence of signal values ​​can be called a signal-to-time curve. The sequence of signal values ​​can be represented as a set of values ​​x. n .

[0036] See Figures 4A to 4C Instead of applying a constant pressure to the associated region in each chamber during polishing, each chamber applies a pressure modulated (e.g., cyclic pressure) around a specified set point. Each chamber in a multi-chamber bearing head will utilize a modulation function orthogonal to the modulation functions of the other chambers. For example, each chamber may modulate the pressure at a frequency different from each of the other chambers. For a bearing head with N chambers, these frequencies may be labeled F1, F2, ..., FN. In some implementations, no frequency is an integer multiple of another frequency.

[0037] Each modulation function can be orthogonal to other disturbances that cause friction to other components of the polishing system. For example, each frequency can also be different from some or all other frequencies associated with the moving parts during polishing in a chemical mechanical polishing system, such as the head sweep frequency, pad regulator sweep frequency, table rotation speed per minute, or head rotation speed per minute.

[0038] Modulation functions can be mutually orthogonal over a suitable time interval (e.g., ten to twenty seconds). An example of mutually orthogonal modulation functions is a sine function with different frequencies. Other possible mutually orthogonal modulation functions include Legendre polynomials or various orthogonal wavelet bases, such as Haar wavelets.

[0039] The pressure applied to chamber 146a can be generated by Figure 4A As shown in the diagram, the pressure applied to the intermediate chamber 146b can be generated by... Figure 4B The diagram shows that the pressure applied to the outer chamber 146c can be generated by... Figure 4C The diagram illustrates this. In this example, the pressure in the outer chamber 146c varies at the highest frequency F3, and the pressure in the central chamber 146a varies at the lowest frequency F1, but this is not necessary. The frequencies F1, ..., FN can each be between 1 Hz and 1 kHz, for example, between 10 Hz and 100 Hz.

[0040] refer to Figure 4A If the nominal pressure to be applied to the central chamber 146a is P1, the control system 190 can cyclically vary the pressure applied to the central chamber 146a between high pressure P1H and low pressure P1L, such that the average pressure applied to the chamber 146a throughout the cycle is P1. Similarly, the pressure applied to the intermediate chamber 146b can cyclically vary between high pressure P2H and low pressure P2L to provide an average pressure P2, and the pressure applied to the outer chamber 146c can cyclically vary between high pressure P3H and low pressure P3L to provide an average pressure P3.

[0041] although Figures 4A to 4CThe diagram illustrates a square wave signal, but this is not necessary. The pressure applied to the chamber can be a sine wave, sawtooth wave, etc. Although different chambers can have the same pressure waveform (with different frequencies), different pressure waveforms can also be applied to different chambers.

[0042] The pressure difference between high and low pressure (e.g., between P1H and P1L) should be large enough to be detectable in subsequent signal analysis, but otherwise as small as possible to limit fluctuations in the polishing rate. For example, the difference between high and low pressure (e.g., P1H-P1L) can be 10-50% of the average pressure (e.g., P1), such as 15-33%.

[0043] The frictional variation associated with the modulation of each zone can be determined by calculating the scalar projection of the signal values ​​onto the modulation function. In the case where the mutually orthogonal functions are sinusoidal curves, this projection can be performed via a discrete Fourier transform, such as a Fast Fourier Transform (FFT). Therefore, the sequence of signal values, i.e., the motor torque measurements taken during polishing (whether direct measurements or as motor current measurements), is analyzed to determine the power corresponding to each of the frequencies F1, F2, ..., FN. In the case of sinusoidal modulation, the power associated with each frequency can also be calculated by passing the signal through different bandpass filters centered at the modulation frequency in its passband and subsequently calculating the energy content of the output signal.

[0044] Figure 6 The figure shows the power spectrum 600 generated by the Fourier transform of the signal value sequence, where peaks 610a, 610b, and 610c are located at frequencies F1, F2, and F3, respectively. The power spectrum 600 may also contain peaks due to other cyclic behaviors. For example, peak 620 at frequency FX may correspond to the carrier head sweep frequency.

[0045] The relative amplitudes of peaks 610a, 610b, and 610c in the power spectrum can be tracked over time to provide information about the amount of friction in each region 12a to 12c on the substrate, and thus information about whether the undercoating has been exposed in this region. Specifically, changes in the peak amplitude at a particular frequency (absolute peak amplitude or peak amplitude relative to other peaks) can indicate exposure of the undercoating in the region of the pressure chamber where a pressure waveform with a corresponding frequency is applied. For example, if the amplitude of peak 610a changes, this can indicate that region 12a is exposed.

[0046] For example, the coefficient of friction between the undercoat and the polishing pad may be lower than that between the overcoat and the polishing pad. In this case, the motor torque will decrease when the undercoat is exposed. If peak 610a experiences a decrease in amplitude, for example from amplitude A1 to amplitude A2, while other peaks 610b and 620c remain constant, this may indicate that the central region 12a is exposed, while the intermediate region 12b and the outer region 12c have not yet been exposed.

[0047] On the other hand, if the coefficient of friction between the undercoat and the polishing pad is higher than that between the overcoat and the polishing pad, the motor torque will increase when the undercoat is exposed. Furthermore, if peak 610a experiences an increase in amplitude, for example from amplitude A1 to amplitude A3, while other peaks 610b and 620c remain constant, this can indicate that the central region 12a is exposed, while the intermediate region 12b and the outer region 12c have not yet been exposed.

[0048] If peaks 610b or 620c change while other peaks remain constant, similar logic applies. By evaluating the power spectrum during the polishing process and observing which frequencies change and when, the control system 190 can determine when each zone is cleared to the undercoat. For example, the control system 190 can determine whether the peak amplitude exceeds a threshold, such as decreasing to below a threshold (if the undercoat has a lower coefficient of friction than the overcoat) or exceeding a threshold (if the undercoat has a higher coefficient of friction than the overcoat). The threshold can be a preset value determined empirically or can be generated based on initial motor torque measurements, such as a change of at least a certain percentage (e.g., 10%) of the average power at the stated frequency during an initial period (e.g., polishing for 1-2 minutes).

[0049] although Figure 6 The diagram illustrates the power spectrum generated by the Fourier transform, but the technique can be extended to scalar projections of the execution signal value onto the modulation function. The value obtained from the scalar projection can be monitored to determine whether the value is increasing or decreasing. For example, control system 190 can determine whether the value exceeds a threshold, or, for example, decreases below or exceeds the threshold.

[0050] In response to the detection that a specific area on the substrate has been cleared, the control system 190 can reduce the pressure in the chamber. This can reduce pitting and erosion.

[0051] exist Figure 5The method employed is summarized below. During polishing (502), pressure waveforms with mutually orthogonal modulation functions (e.g., different frequencies) are applied to different regions of the substrate by a bearing head (504). Friction of the substrate against the pads is monitored, for example as motor torque or direct friction measurement (506), and a scalar projection of the friction measurement results onto the modulation function is performed (508). For example, in the case of sinusoidal modulation at different frequencies, a power spectrum can be generated from the motor torque signal, for example by Fourier transform. Regions with power spectra corresponding to different frequencies are compared (510), and the system can determine whether a region has been cleared before another region by detecting whether the power of one modulation changes relative to the power of another modulation (512). For example, again, in the case of sinusoidal modulation at different frequencies, whether the power of one frequency changes relative to another frequency can be detected.

[0052] The embodiments and all functional operations described herein (e.g., control system 190) can be implemented in digital electronic circuit systems or in computer software, firmware, or hardware (including the structural means and their equivalents disclosed herein) or combinations thereof. The embodiments described herein can be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage device for execution by or control of a data processing device (e.g., a programmable processor, a computer, or multiple processors or computers).

[0053] Computer programs (also known as programs, software, software applications, or code) can be written in any programming language, including compiled or interpreted languages, and can be deployed in any form, including as standalone programs or as modules, components, subroutines, or other units suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored as part of a file that holds other programs or data, as a single file dedicated to the program in question, or as multiple collaborating files (e.g., files storing portions of one or more modules, subroutines, or code). A computer program can be deployed to execute on one or more computers at one location, or on one or more computers distributed across multiple locations and interconnected by a communication network.

[0054] The process and logic flow described in this specification can be executed by one or more programmable processors, which execute one or more computer programs to perform functions by manipulating input data and producing outputs. The process and logic flow can also be executed by a dedicated logic circuit system, and the device can also be implemented as a dedicated logic circuit system, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit).

[0055] The term "data processing device" encompasses all devices, apparatuses, and machines used for processing data, including, for example, programmable processors, computers, or multiple processors or computers. In addition to hardware, the device may also contain code that creates an execution environment for the computer program in question, such as code constituting processor firmware, protocol stacks, database management systems, operating systems, or combinations thereof. For example, processors suitable for executing computer programs include both general-purpose and special-purpose microprocessors, as well as any one or more processors of any kind of digital computer.

[0056] Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and memory devices, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and memory may be supplemented by or incorporated into a dedicated logic circuit system.

[0057] The polishing equipment and methods described above can be applied to various polishing systems. The polishing pad or carrier head, or both, can be movable to provide relative movement between the polished surface and the wafer. The stage can run around a track instead of rotating. The endpoint detection system can be applied to linear polishing systems (e.g., where the polishing pad is a linearly moving continuous strip or roll-to-roll). The polishing layer can be a standard (e.g., polyurethane with or without filler) polishing material, a soft material, or a fixed abrasive material. The method can be applied to other combinations of overlay and underlay materials, such as metal over a dielectric, or a dielectric over a metal, etc.

[0058] The terminology of relative positioning is used; it should be understood that polished surfaces and wafers may be held in a vertical orientation or some other orientation.

[0059] Although this specification contains many details, these details should not be construed as limiting the scope of the claims, but rather as descriptions of features characteristic of particular embodiments of the particular invention.

Claims

1. A computer program product comprising a non-transitory computer-readable medium having instructions for causing one or more computers to perform the following operations: During the polishing of the substrate, the bearing head of the polishing system applies a first pressure modulated by a first modulation function to a first region of the substrate; The bearing head of the polishing system applies a second pressure modulated by a second modulation function to different second regions of the substrate, the second modulation function being orthogonal to the first modulation function; Receive measurement value sequences from the in-situ friction monitoring system; as well as The relative contributions of the first region and the second region to the measurement sequence are determined by distinguishing between the first modulation function and the second modulation function.

2. The computer program product of claim 1, comprising instructions for performing the following operations: Determine which of the first or second regions the overlying layer is removed first to expose the underlying layer; and The polishing parameters are adjusted based on which of the first or second regions is cleared first.

3. The computer program product of claim 1, wherein the first modulation function comprises a first cyclic waveform having a first frequency, and the second modulation function comprises a second cyclic waveform having a different second frequency.

4. The computer program product of claim 3, comprising instructions for: determining the power spectrum of the measurement value sequence, and identifying a first power in a first region of the spectrum corresponding to the first frequency and a second power in a first region of the spectrum corresponding to the second frequency.

5. The computer program product of claim 4, wherein determining the power spectrum comprises performing a Fourier transform on the sequence of measurements.

6. The computer program product of claim 2, comprising storing one or more parameters indicating the relative coefficient of friction of the upper and lower layers.

7. The computer program product of claim 6, comprising instructions for: determining a scalar projection of the measurement value sequence onto each of the first modulation function and the second modulation function to generate a first value and a second value.

8. The computer program product of claim 7, wherein one or more parameters indicate that the undercoat has a low coefficient of friction, and includes instructions for determining that the first region is cleared before the second region based on a decrease in the first value relative to the second value.

9. The computer program product of claim 7, wherein one or more parameters indicate that the undercoat has a high coefficient of friction, and includes instructions for determining that the first region is cleared before the second region based on an increase in the first value relative to the second value.

10. The computer program product of claim 7, wherein one or more parameters indicate that the undercoat has a low coefficient of friction, and includes instructions for determining that the second region is cleared prior to the first region based on a decrease in the second value relative to the first value.

11. The computer program product of claim 7, wherein one or more parameters indicate that the undercoat has a high coefficient of friction, and includes instructions for determining that the second region is cleared prior to the first region based on an increase in the second value relative to the first value.

12. The computer program product of claim 1, comprising instructions for receiving a first nominal pressure and a second nominal pressure from a polishing recipe, wherein the average value of the first pressure modulated by the first modulation function is equal to the first nominal pressure, and the average value of the second pressure modulated by the second modulation function is equal to the second nominal pressure.

13. The computer program product of claim 12, comprising instructions for: calculating a first high pressure value and a first low pressure value based on the first nominal pressure, and calculating a second high pressure value and a second low pressure value based on the second nominal pressure.

14. A polishing method comprising the following steps: Use the bearing head to hold the substrate against the polishing surface of the polishing pad; This generates relative movement between the substrate and the polishing pad; A first pressure modulated by a first modulation function is applied to a first region of the substrate; A second pressure modulated by a second modulation function is applied to a second region of the substrate, the second modulation function being orthogonal to the first modulation function; During the polishing of the substrate, the substrate is monitored using an in-situ friction monitoring system to generate a sequence of measurement values; as well as The relative contributions of the first region and the second region to the measurement sequence are determined by distinguishing between the first frequency of the first modulation function and the second frequency of the second modulation function.

15. The method of claim 14, wherein the in-situ friction monitoring system comprises a table torque monitoring system or a motor current monitoring system.

16. The method of claim 14, wherein the first region comprises a central region of the substrate, and the second region comprises an edge region of the substrate.

17. The method of claim 14, comprising the following steps: Determine which of the first or second regions the overlying layer is removed first to expose the underlying layer; and The polishing parameters are adjusted based on which of the first or second regions is cleared first.

18. The method of claim 14, wherein the first modulation function and the second modulation function are orthogonal to the modulation functions of other moving parts in the polishing system.

19. A polishing system comprising: A worktable for supporting a polishing pad; A support head for holding a substrate against the polishing pad, wherein the support head is configured to apply independently adjustable pressure to multiple different areas of the substrate; An electric motor, used to generate relative motion between the bearing head and the worktable; An in-situ friction monitoring system, wherein the in-situ friction monitoring system is used to generate value sequences; as well as The controller is configured to: During the polishing of the substrate, the bearing head applies a first pressure modulated by a first modulation function to a first region of the substrate; The bearing head applies a second pressure modulated by a second modulation function to different second regions of the substrate, the second modulation function being orthogonal to the first modulation function; Receive measurement value sequences from the in-situ friction monitoring system; as well as The relative contributions of the first region and the second region to the measurement sequence are determined by distinguishing between the first modulation function and the second modulation function.

20. The system of claim 19, wherein the in-situ friction monitoring system comprises a bearing head torque monitoring system, a worktable torque monitoring system, or a motor current monitoring system.

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