Predictive filter for polishing pad wear rate monitoring

Abstract

An apparatus for chemical mechanical polishing is disclosed, the apparatus comprising: a platen having a surface to support a polishing pad; a carrier head to secure a substrate against a polishing surface of the polishing pad; a pad conditioner to secure a conditioning disk against the polishing surface; an in-situ polishing pad thickness monitoring system; and a controller configured to receive a signal from the monitoring system and generate a measure of a polishing pad wear rate by applying a predictive filter to the signal.

Description

Technical Field

[0001] The present disclosure relates to monitoring the wear rate of polishing pads used in chemical mechanical polishing. Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconducting, or insulating layers onto a silicon wafer. Various manufacturing processes require planarizing the layers on the substrate. For example, one manufacturing step involves depositing a conductive filler layer onto a patterned insulating layer to fill grooves or holes in the insulating layer. The filler layer is then polished until the raised pattern of the insulating layer is exposed. After planarization, the portion of the conductive filler layer that remains between the raised patterns of the insulating layer forms vias, plugs, and lines that provide conductive paths between the thin-film circuitry on the substrate.

[0003] Chemical mechanical polishing (CMP) is an accepted planarization method. This planarization method generally requires a substrate to be mounted on a carrier head. The exposed surface of the substrate is 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 liquid (e.g., a slurry containing abrasive particles) is supplied to the surface of the polishing pad.

[0004] After a period of CMP processing, the surface of the polishing pad may become glazed due to the accumulation of slurry byproducts and / or material removed from the substrate and / or polishing pad. Glazing may reduce the polishing rate or increase non-uniformity across the substrate.

[0005] Generally speaking, the polishing pad is maintained at the desired surface roughness (and smoothing is avoided) by conditioning it with a pad conditioner. The pad conditioner is used to remove unwanted buildup on the polishing pad and regenerate the surface of the polishing pad to the desired roughness. A typical pad conditioner includes an abrasive conditioning disk. Such a conditioning disk may, for example, be embedded with diamond abrasive particles that scrape the polishing pad surface to retexture the pad. However, conditioning also tends to wear away the polishing pad. Thus, after a certain number of polishing and conditioning cycles, the polishing pad needs to be replaced. Summary of the Invention

[0006] In one aspect, an apparatus for chemical mechanical polishing includes: a platen having a surface to support a polishing pad; a carrier head to secure a substrate against a polishing surface of the polishing pad; a pad conditioner to secure a conditioning disk against the polishing surface; an in-situ polishing pad thickness monitoring system; and a controller configured to receive a signal from the monitoring system and generate a polishing pad wear rate measurement by applying a predictive filter to the signal.

[0007] Implementations may include one or more of the following features.

[0008] The in-situ polishing pad thickness monitoring system may include an electromagnetic induction monitoring system. The electromagnetic induction monitoring system may include a magnetic core fixed to the platen to generate a magnetic field to induce a current in the metal layer in the conditioning disk. The electromagnetic induction monitoring system may include a magnetic core fixed to the pad conditioner to generate a magnetic field to induce a current in the platen.

[0009] The controller may be configured to generate an alarm if the pad wear rate measurement exceeds a threshold.The controller may be configured to adjust the downforce of the pad adjuster on the adjustment disk based on the pad wear rate measurement to maintain a substantially constant wear rate.

[0010] The controller may be configured to apply the predictive filter to the signal to generate a filtered signal, the filtered signal including a sequence of adjustment values. The controller may be configured to generate the filtered signal for each adjustment value in the sequence of adjustment values ​​by: generating at least one predicted value from the sequence of measurement values; and calculating the adjustment value from the sequence of measurement values ​​and the predicted value.

[0011] The controller may be configured to generate the at least one predicted value from the sequence of measurements using linear prediction. The prediction filter may be a Kalman filter. The prediction filter may calculate the pad rate measurement, the pad rate measurement conforming to the following formula:

[0012] x k =(Th k , CR k ) T

[0013]

[0014] y k =Th k +v k

[0015] y k =[1 0]x k +v k

[0016] where x k Is including pad thickness Th k and pad wear rate CR k is the state vector, α indicates the amount of conditioning time between each pad thickness measurement, ΔdF is the change in downforce on the conditioning disk, β is the ratio between pad wear rate and downforce, and y k is the pad thickness measurement, while v k represents the measurement noise.

[0017] Certain embodiments may include one or more of the following advantages. A wear rate can be calculated and the thickness of the polishing pad can be detected. Noise in the pad thickness measurement can be reduced, and the effects of pad thickness sensors measuring different areas on the polishing pad can be compensated for. A conditioning disk can be replaced as it nears the end of its useful life without unnecessarily replacing the conditioning disk. Similarly, a polishing pad can be replaced as it nears the end of its useful life without unnecessarily replacing the polishing pad. Thus, the life of the conditioning disk and polishing pad can be increased while avoiding uneven polishing of the substrate. The pressure on the conditioning disk can be adjusted so that the pad wear rate is maintained substantially constant.

[0018] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A is a schematic side view of a portion of a cross-section of a chemical mechanical polishing system including a sensor configured to detect pad thickness.

[0020] Figure 1B is a schematic side view, partially in cross-section, of another embodiment of a chemical mechanical polishing system including a sensor to detect pad thickness.

[0021] Figure 2 Schematic top view of a chemical mechanical polishing system.

[0022] Figure 3 A schematic circuit diagram of a drive system for an electromagnetic induction monitoring system.

[0023] Figure 4 is a graph illustrating the signal strength from the sensor over a number of platen rotations.

[0024] Like reference numbers in the various drawings indicate like elements. DETAILED DESCRIPTION

[0025] As mentioned above, conditioning also tends to wear away the polishing pad. Polishing pads typically have grooves that hold the slurry, and as the pad wears away, these grooves become increasingly shallow and polishing effectiveness degrades. Consequently, after a certain number of polishing and conditioning cycles, the polishing pad needs to be replaced. This is typically accomplished by replacing the polishing pad after a set number of substrates have been polished (e.g., after 500 substrates).

[0026] Unfortunately, the rate at which pads wear isn't always consistent, so a polishing pad may last longer or shorter than the set amount, which can result in wasted pad life or uneven polishing, respectively. Specifically, over the life of a polishing pad, the abrasive (e.g., diamond) on the conditioning disk gradually wears away. As a result, the disk's conditioning efficiency can decrease over time. Consequently, the conditioning effect of the surface texture changes and can decrease over the life of the polishing pad and from pad to pad. This alters the polishing behavior.

[0027] Similarly, conditioning discs tend to lose effectiveness over time. While not wishing to be bound by any particular theory, the abrasive particles on the conditioner also wear out and lose their sharpness. Therefore, the pad conditioner also needs to be replaced periodically. Again, this step is accomplished by replacing the conditioning disc after a set number of substrates have been polished (e.g., after 1,000 substrates). (The replacement rate of the pad and conditioning disc depends on the consumables and the process.)

[0028] The polishing pad thickness can be measured in situ (e.g., using a sensor mounted on the conditioner system, carrier head, or platen). If the measured pad thickness drops below a threshold, the polishing pad can be replaced. Furthermore, the pad wear rate can be calculated from the pad thickness measurement, and if the measured pad wear rate drops below a threshold, the conditioning disk can be replaced.

[0029] One difficulty is that thickness measurements can be susceptible to significant noise. Some contributions to the noise may be periodic, for example, caused by the sensor passing over different parts of the polishing pad. Other contributions to the noise are due to the "wet idle" problem: when the polishing system begins operating after a wet idle, the inductive sensor will tend to measure pad thickness with an unnaturally exaggerated value. This results in an inaccurate estimate of the pad's cut rate.

[0030] However, by applying a predictive filter (e.g., a Kalman filter) to the pad thickness measurement, this noise can be reduced, and the pad wear rate can be calculated more accurately. Consequently, when comparing the wear rate to a threshold, the likelihood of replacing the conditioning disk too early or too late is reduced. Furthermore, the actual pad thickness can be more accurately measured, reducing the likelihood of replacing the polishing pad too early or too late. Furthermore, the controller can sense when the wear rate indicates a problem with the polishing process.

[0031] FIG1 illustrates an example of a polishing system 20 of a chemical mechanical polishing apparatus. Polishing system 20 includes a rotatable, disc-shaped platen 24 on which a polishing pad 30 is positioned. Platen 24 can be rotated about axis 25. For example, motor 22 can rotate drive shaft 28 to rotate platen 24. Polishing pad 30 can be a two-layer polishing pad having an outer layer 34 and a softer backing layer 32.

[0032] The polishing system 20 can include a supply port or combined supply and rinse arm 39 to dispense a polishing liquid 38 (eg, slurry) onto the polishing pad 30 .

[0033] The polishing system 20 may also include a polishing pad conditioner 60 to abrade the polishing pad 30 to maintain the polishing pad 30 in a consistent abrasive state. The polishing pad conditioner 60 includes a base, an arm 62 that can sweep laterally across the polishing pad 30, and a conditioner head 64 connected to the base by an arm 64. The conditioner head 64 brings an abrasive surface (e.g., the lower surface of a disk 66 held by the conditioner head 64) into contact with the polishing pad 30 to condition the polishing pad. The abrasive surface can be rotatable, and the pressure of the abrasive surface against the polishing pad can be controllable.

[0034] In some embodiments, arm 62 is pivotally attached to the base and sweeps back and forth to move conditioner head 64 in an oscillating, sweeping motion across polishing pad 30. The motion of conditioner head 64 can be synchronized with the motion of carrier head 70 to prevent collisions.

[0035] Vertical movement of the conditioner head 64 and pressure control of the conditioning surface on the polishing pad 30 may be provided by a vertical actuator 68 above or in the conditioner head 64 (e.g., a pressurizable chamber positioned to apply downward pressure to the conditioner head 64). Alternatively, vertical movement and pressure control may be provided by a vertical actuator in the base that raises and lowers the entire arm 62 and conditioner head 64, or by a pivot connection between the arm 62 and the base that allows for controllable tilt of the arm 62 and, therefore, a controllable height of the conditioner head 64 above the polishing pad 30.

[0036] The adjustment disk 66 may be a metal disk coated with abrasive particles (eg, diamond particles). Specifically, the adjustment disk 66 may be a conductive body.

[0037] The carrier head 70 is operable to secure the substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 72 (e.g., a turntable or track) and is connected by a drive shaft 74 to a carrier head rotation motor 76 so that the carrier head can rotate about an axis 71. Optionally, the carrier head 70 can oscillate laterally, for example, on a slider on the turntable or track 72, or by rotational oscillation of the turntable itself. During operation, the platen rotates about its central axis 25, and the carrier head rotates about the carrier head's central axis 71 and translates laterally across the top surface of the polishing pad 30.

[0038] The carrier head 70 may include a flexible membrane 80 having a substrate mounting surface for contacting the backside of the substrate 10 and a plurality of pressurizable chambers 82 for applying different pressures to different zones (e.g., different radial zones) on the substrate 10. The carrier head may also include a retaining ring 84 to secure the substrate.

[0039] The polishing system 20 includes an in-situ polishing pad thickness monitoring system 100 that generates a signal indicative of the thickness of the polishing pad. Specifically, the in-situ polishing pad thickness monitoring system 100 may be an electromagnetic induction monitoring system. Electromagnetic induction monitoring systems operate by generating eddy currents in a conductive layer or current in a conductive loop. During operation, the polishing system 20 may use the monitoring system 100 to determine whether the conditioning disk and / or polishing pad needs to be replaced.

[0040] Reference Figure 1A and Figure 2 In some embodiments, the monitoring system includes a sensor 102 mounted in a recess 26 in the deck. The sensor 102 may include a magnetic core 104 positioned at least partially in the recess 26 and at least one coil 106 wound around the core 104. A drive and sense circuit system 108 is electrically connected to the coil 106. The drive and sense circuit system 108 generates a signal that can be sent to the controller 90.

[0041] In some embodiments, the monitoring system includes a plurality of sensors 102 mounted in recesses in the deck. The sensors 102 may be spaced about the axis of rotation 25 at equal angular intervals.

[0042] Although shown outside of the platen 24, some or all of the drive and sense circuitry 108 may be mounted within the platen 24. A rotational coupler 29 may be used to electrically connect elements in the rotatable platen (e.g., the coil 106) to elements external to the platen (e.g., the drive and sense circuitry 108).

[0043] For an inductive monitoring system with the sensor 102 in the platen, the conductor 130 is positioned in contact with the top surface (i.e., polishing surface) of the polishing pad 30. Thus, the conductor 130 is positioned on the far side of the polishing pad 30 relative to the sensor 102. In some embodiments, the conductor is the conditioning disk 66 (see Figure 1A In some embodiments, the conductor 130 may have one or more holes passing through it, for example, the body may be a loop. In some embodiments, the conductor is a solid sheet without holes. Any of these conductors may be part of the adjustment disk 66.

[0044] As platen 24 rotates, sensor 102 sweeps under conductor 130. By sampling the signal from circuitry 108 at a particular frequency, monitoring system 100 generates measurements at multiple locations across conductor 130 (e.g., across dial 66). During each sweep, measurements at one or more of these locations may be selected or combined.

[0045] Reference Figure 3 , the coil 106 generates a magnetic field 120. When the magnetic field 120 reaches the conductor 130, the magnetic field 120 can pass through the conductor 130 and generate a current (for example, if the conductor 130 is a loop) and / or eddy currents (for example, if the conductor 130 is a sheet of material). This creates an effective impedance that can be measured by the circuit system 108, thereby generating a signal representing the thickness of the polishing pad 30.

[0046] Various configurations are possible for the drive and sense circuitry 108. For example, the drive and sense circuitry 108 may include a marginal oscillator and use the drive current used to maintain a constant amplitude for the marginal oscillator as the signal. Alternatively, the drive coil 106 may be driven at a constant frequency and the amplitude or phase of the current from the sense coil (relative to the drive oscillator) may be used for the signal.

[0047] As an alternative or in addition to sensors in the platen, e.g. Figure 1B , the monitoring system 100 may include a sensor 102' positioned above the polishing pad 30. For example, the pad thickness sensor 102' may be positioned in the conditioner head 64, on the conditioner arm 62, or on the carrier head 70. The sensor 102' may be biased, for example, by a spring 103, into contact with the polishing surface 34 of the polishing pad 30.

[0048] The pad thickness sensor 102' can also be an electromagnetic induction monitoring system. In this case, the sensor 102' can be similar to the sensor 120 and include a magnetic core 104, at least one coil 106 wound around the core 104, and a drive and sense circuit system 108 electrically connected to the coil 106. The magnetic field 120 from the core 104 can pass through the polishing pad and induce eddy currents in the underlying conductor (e.g., the platen 24). The effective impedance depends on the distance between the sensor 102 and the platen 24, and this can be sensed by the circuit system 108, thereby providing a measurement of the thickness of the polishing pad 30.

[0049] Alternatively, the sensor 102' may be a contact profilometer.

[0050] The controller 90 (e.g., a general-purpose programmable digital computer) receives signals from the in-situ polishing pad thickness monitoring system 100 and can be configured to generate measurements of the thickness of the polishing pad 30 from the signals. As described above, the thickness of the polishing pad changes over time (e.g., over the course of polishing tens or hundreds of substrates) due to the conditioning process. Thus, selected or combined measurements from the in-situ polishing pad thickness monitoring system 100 provide a time-varying sequence of values ​​indicative of changes in the thickness of the polishing pad 30 over the course of multiple substrates.

[0051] The output of the sensor 102 can be a digital electronic signal (if the output of the sensor is an analog signal, the analog signal can be converted to a digital signal by an ADC in the sensor or controller). A digital signal consists of a sequence of signal values, where the time interval between signal values ​​depends on the sampling frequency of the sensor. This sequence of signal values ​​can be referred to as a signal versus time plot. The sequence of signal values ​​can be represented as a set of values ​​S N .

[0052] To relate signal strength to polishing pad thickness, a polishing pad of known thickness (as measured by a profilometer, pin gauge, or similar device) can be placed on the platen and the signal strength measured.

[0053] In some embodiments, the signal strength from sensor 102 is linearly related to the thickness of the polishing layer. In this case, in the following equation, the value Th=S or Th=A*S, where A is a constant used to fit the function to data of known polishing pad thickness.

[0054] However, the signal strength from sensor 102 is not necessarily linearly related to the thickness of the polishing layer. For example, the signal strength can be an exponential function of the thickness of the polishing layer.

[0055] An exponential function of thickness can then be fitted to the data. For example, the function can be of the form:

[0056] S=Ae -B*Th

[0057] Where S is the signal intensity, Th is the polishing pad thickness, and A and B are constants adjusted to fit the function to data of known polishing pad thickness.

[0058] For a polishing pad subsequently used for polishing, the controller 90 may use this function to calculate the polishing pad thickness from the signal intensity. More specifically, the controller may be configured to generate a measure of the polishing pad thickness Th from an equivalent logarithmic function of the signal intensity, such as from the following function:

[0059]

[0060] However, other functions can be used, such as a second or higher order polynomial function, or a piecewise linear function. Thus, the signal value sequence S N may be converted to a thickness value sequence Th N .

[0061] The controller 90 is also configured to generate a measure of the wear rate of the polishing pad 30 from the signal. The wear rate can be calculated by fitting a linear function to the pad thickness values S N measured over time. For example, the function can be fitted to the thickness values from a running window (e.g., the last N wafers), where N is selected depending on whether one wants the pad wear rate to be closer to the instantaneous wear rate or closer to the average pad wear rate. A smaller N value is more responsive to noise. A larger N value is less responsive but also less instantaneous. In some embodiments, the running window is the last 3-30 measurements.

[0062] However, as noted above, the pad thickness measurements are susceptible to noise. In particular, noise can be introduced each time a new substrate is started and each time the polishing system enters a wet idle mode. However, a filter incorporating linear prediction can be used to smooth the series of thickness measurements. This same filter can be used to calculate the current pad wear rate. Linear prediction is a statistical technique that uses current and past data to predict future data. Linear prediction can be implemented with a set of equations that keep track of the autocorrelation of current and past data, and is able to predict further into the future than would be possible with a simple polynomial extrapolation.

[0063] The thickness and wear rate can be represented as follows:

[0064] Th k+1 = Th k - aCR k

[0065] CR k+1 = CR k + ω k

[0066]

[0067] where Th is the pad thickness, CR is the instantaneous pad wear rate (or reduction rate), a indicates the amount of conditioning time between each pad thickness measurement (which can be set by the operator), and ω is a white noise parameter. If the pad is measured once per substrate, then a is the same as the conditioning time for one substrate. The reduction rate of the thickness can be measured in units of hours, but the time between measurements can be measured in units of seconds, so a conversion by dividing by 3600 can be performed. For example, CR can be expressed in mils / hr, while the conditioning time for each wafer is specified in seconds in the CMP polishing recipe.

[0068] In some embodiments, the linear prediction filter is a Kalman filter. An example of a Kalman filter can be represented in the following matrix format:

[0069] x k =(Th k ,(R k ) T

[0070]

[0071]

[0072] where x k is a state vector that includes pad thickness and pad wear rate as two axis components in the state space, ΔdF is the change in downforce on the dial, β is the ratio between pad wear rate and downforce (β may vary with the life of the dial), and y k is the pad thickness output (e.g. this is measured using an inductive sensor), v k represents the measurement noise, and ω k is a white noise parameter. Note that the system and measurement model above are stochastic formulations, not deterministic ones. ω indicates that the pad wear rate (CR) can drift by a random amount from one substrate to the next. C k is the matrix relating the measured outputs to the state vector.

[0073] The state estimation time extrapolation of the Kalman filter can be expressed as

[0074]

[0075] Among them A k-1 is the state matrix

[0076]

[0077] And the error covariance extrapolation of the Kalman filter can be expressed as

[0078]

[0079] where Pk is the covariance of the error in the state estimate and Qk is the covariance matrix of the noise vector W w / ω. The measurement update of the Kalman filter can be expressed as:

[0080]

[0081] For the various equations above, the following matrix format values ​​can be used:

[0082]

[0083] When the measurement of the thickness of the polishing pad 30 meets a threshold, the controller 90 can generate an alert to the operator of the polishing system 20 that the polishing pad 30 needs to be replaced. Alternatively or additionally, the measurement of the thickness of the polishing pad can be fed to the in-situ substrate monitoring system 40, for example, to be used by the in-situ substrate monitoring system 40 to adjust the signal from the substrate 10.

[0084] When the measure of the wear rate of the polishing pad 30 meets a threshold, the controller 90 can generate an alert to the operator of the polishing system 20 that the conditioning disk 66 needs to be replaced. Alternatively or additionally, the controller 90 can adjust the downforce from the conditioner head 64 on the conditioning disk 66 to maintain a constant polishing pad wear rate. It can be assumed that the wear rate is proportional to the downforce on the conditioning disk 66.

[0085] In some embodiments, if the wear rate measurement falls outside of a predetermined range, this may indicate a problem with the polishing process (other than with the conditioning disk) and the controller 90 may generate an alarm.

[0086] If the sensor 102 is positioned above the polishing pad 30 and measures the distance to the platen 24, the sensor 102 will produce an effectively continuous signal that does not require extensive processing.

[0087] However, if the sensor 102 is mounted in the platen 24 and rotates with the platen and measures the distance to the conductor 130 , the sensor 102 may generate data even when the sensor is not beneath the conductor 130 . Figure 4 The "raw" signal 150 from the sensor 102 is depicted over the course of two rotations of the platen 24. A single rotation of the platen is indicated by the time period R.

[0088] The sensor 102 can be configured so that the closer the conductors 130 are (and therefore the thinner the polishing pad 30), the stronger the signal strength. Figure 4 As shown in FIG, initially, sensor 102 may be below carrier head 70 and substrate 10. Because the metal layer on the substrate is thin, it produces only a weak signal (indicated by region 152). In contrast, when sensor 102 is below conductor 130, sensor 102 produces a strong signal (indicated by region 154). Between those times, sensor 102 produces an even lower signal (indicated by region 156).

[0089] Several techniques can be used to filter out portions of the signal from sensor 102 that do not correspond to conductor 130. Polishing system 20 can include a position sensor to sense when sensor 102 is beneath conductor 130. For example, an optical interrupter can be mounted at a fixed location, and a marker can be attached to the perimeter of platen 24. The attachment point and length of the marker are selected so that it generates a signal that sensor 102 is sweeping beneath substrate conductor 130. As another example, polishing system 20 can include an encoder to determine the angular position of platen 24 and use this information to determine when sensor 102 is sweeping beneath conductor 130. In either case, controller 90 can exclude portions of the signal from periods when sensor 102 is not beneath conductor 130.

[0090] Alternatively or additionally, the controller may simply compare the signal 150 to a threshold value T (see Figure 4 ) and excludes the part of the signal that does not meet the threshold T (for example, is lower than the threshold T).

[0091] Due to the sweep of conditioner head 64 across polishing pad 30, sensor 102 may not pass completely under the center of conductor 130. For example, sensor 102 may pass only along the edge of the conductor. In this case, because less conductive material is present, the signal strength will be lower (e.g., as shown by region 158 of signal 150) and this is not a reliable indicator of the thickness of polishing pad 30. An advantage of excluding portions of the signal that do not meet threshold T is that controller 90 can also exclude these unreliable measurements caused by sensor 102 passing along the edge of conductor 130.

[0092] In some embodiments, for each sweep, the non-excluded portions of the signal 150 may be averaged to produce an average signal strength for the sweep.

[0093] If the polishing system 20 includes an in-situ substrate monitoring system 40, the in-situ polishing pad monitoring system 100 can be a first electromagnetic induction monitoring system (e.g., a first eddy current monitoring system), and the substrate monitoring system 40 can be a second electromagnetic induction monitoring system (e.g., a second eddy current monitoring system). However, due to the different components being monitored, the first and second electromagnetic induction monitoring systems are configured to have different resonant frequencies.

[0094] The in-situ polishing pad thickness monitoring system can be used in various polishing systems. The polishing pad or the carrier head or both can be movable to provide relative movement between the polishing surface and the substrate. The polishing pad can be a circular (or some other shape) pad fixed to the platen, a narrow belt extending between a supply roller and a take-up roller, or a continuous belt. The polishing pad can be fixed to the platen, progressively advanced on the platen between polishing operations, or continuously driven across the platen during polishing. The pad can be fixed to the platen during polishing, or a fluid bearing can be present between the platen and the polishing pad during polishing. The polishing pad can be a standard (e.g., polyurethane with or without filler) rough pad, a soft pad, or a fixed abrasive pad.

[0095] Furthermore, while the above description focuses on monitoring during polishing, measurements of the polishing pad may be obtained before or after polishing the substrate (eg, while the substrate is being transported to the polishing system).

[0096] The embodiments of the present invention and all functional operations described in this specification may be implemented using digital electronic circuit systems, or using computer software, firmware, or hardware (including the structural components disclosed in this specification and their structural equivalents), or using a combination of the above items. The embodiments of the present invention may be implemented as one or more computer program products (i.e., one or more computer programs tangibly implemented in an information medium (e.g., a non-transitory machine-readable storage medium or a propagated signal)) for execution by a data processing device (e.g., a programmable processor, a computer, or multiple processors or computers) or for controlling the operation of the data processing device. Computer programs (also referred to as programs, software, software applications, or code) may be written in any form of programming language (including compiled or interpreted languages) and may be deployed in any form (including as stand-alone programs, or as modules, elements, subroutines, or other units suitable for use in a computing environment). A computer program does not necessarily correspond to a file. A program may be stored in a portion of a file that contains other programs or data, in a single file dedicated to the program in question, or in multiple collaborative files (e.g., files that store one or more modules, subroutines, or code portions). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0097] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes or logic flows can also be performed by, and the apparatus can be implemented as, special purpose logic circuitry such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0098] A number of embodiments of the present invention have been described. Nevertheless, it will be appreciated that various modifications can be made without departing from the spirit and scope of the present invention. Accordingly, other embodiments are within the scope of the appended claims.

Claims

1. A device for chemical mechanical polishing, comprising: a platen having a surface to support the polishing pad; a carrier head for securing the substrate against the polishing surface of the polishing pad at a first position; a pad adjuster for securing the adjustment disk against the polishing surface; an in-situ polishing pad thickness monitoring system for generating a plurality of signals dependent on pad thickness during polishing of a plurality of substrates; and a controller configured to receive the plurality of signals from the in-situ polishing pad thickness monitoring system during polishing of a plurality of substrates and generate polishing pad wear rate measurements during polishing of the plurality of substrates by applying a predictive filter to the plurality of signals, wherein the in-situ polishing pad thickness monitoring system comprises an electromagnetic induction monitoring system having a sensor located in the platen and a conductor positioned to contact the polishing surface of the polishing pad at a second position laterally spaced from the first position; The controller is further configured to: excluding portions of the plurality of signals that are from periods when the sensor is not beneath the conductor or excluding portions of the plurality of signals that are caused by the sensor passing along an edge of the conductor, If the polishing pad wear rate measurement exceeds a threshold, an alarm is generated indicating that the conditioning disk needs to be replaced, or the downforce of the pad conditioner on the conditioning disk is adjusted based on the polishing pad wear rate measurement to maintain a substantially constant wear rate.

2. The device of claim 1, wherein the conductor comprises the adjustment disk.

3. The apparatus of claim 1, wherein the electromagnetic induction monitoring system comprises a magnetic core fixed in the platen to generate a magnetic field to induce a current in the metal layer in the adjustment disk.

4. The apparatus of claim 1, wherein the electromagnetic induction monitoring system comprises a magnetic core fixed to the pad conditioner to generate a magnetic field to induce current in the platen.

5. The apparatus of claim 4, wherein the pad conditioner includes an arm extending above the platen, and the magnetic core is secured to the arm of the pad conditioner.

6. The apparatus of claim 5, wherein the arm is configured to perform an oscillatory sweeping motion across the polishing pad.

7. The apparatus of claim 1 , wherein the controller is configured to apply the predictive filter to the plurality of signals to generate a filtered signal, the filtered signal comprising a sequence of adjustment values, and wherein the controller is configured to generate the filtered signal for each adjustment value in the sequence of adjustment values ​​by: Producing at least one predicted value from the series of measured values, and The adjustment value is calculated from the series of measured values ​​and the predicted value. 8 . The apparatus of claim 7 , wherein the controller is configured to generate the at least one predicted value by generating the at least one predicted value from the sequence of measured values ​​using linear prediction.

9. The apparatus of claim 8, wherein the prediction filter comprises a Kalman filter.

10. A method of operating a chemical mechanical polishing apparatus, the method comprising the steps of: polishing the substrate with a polishing pad; Adjusting the polishing pad using an adjustment disk; monitoring a thickness of the polishing pad using an in-situ polishing pad thickness monitoring system and generating a plurality of signals dependent on the pad thickness from the in-situ polishing pad thickness monitoring system during polishing of a plurality of substrates, wherein the in-situ polishing pad thickness monitoring system comprises an electromagnetic induction monitoring system having a sensor located in a platen and a conductor positioned in contact with a polishing surface of the polishing pad, the platen having a surface for supporting the polishing pad; excluding portions of the plurality of signals resulting from periods when the sensor is not beneath the conductor or excluding portions of the plurality of signals resulting from the sensor passing along an edge of the conductor; generating a measure of pad wear rate during polishing of a plurality of substrates by applying a predictive filter to the signal; and If the pad wear rate measurement meets a threshold, an alarm is generated indicating that the conditioning disk needs to be replaced, or a downforce on the conditioning disk by a pad conditioner securing the conditioning disk against the polishing surface is adjusted based on the pad wear rate measurement to maintain a substantially constant pad wear rate.

11. The method of claim 10 , wherein applying the predictive filter to the plurality of signals generates a filtered signal, the filtered signal comprising a sequence of adjustment values, and wherein generating the filtered signal comprises performing the following steps for each adjustment value in the sequence of adjustment values: Producing at least one forecast value from the series of measurements, and The adjustment value is calculated from the series of measured values ​​and the predicted value.

12. The method of claim 11, wherein the step of generating the at least one predicted value comprises using linear prediction to generate the at least one predicted value from the sequence of measured values. The method of claim 12 , wherein the predictive filter comprises a Kalman filter.

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