Polishing carrier head with piezoelectric pressure control

Abstract

A support head for holding a substrate in a polishing system has a housing including a support plate, a first flexible membrane fastened to the housing, and a plurality of independently operable piezoelectric actuators fastened to the support plate. The first flexible membrane has an upper surface and a lower surface that provides a substrate mounting surface. The piezoelectric actuators are positioned above the first flexible membrane to independently adjust the compressive pressure on the upper surface of the first flexible membrane.

Description

Polishing carrier head with piezoelectric pressure control The present disclosure relates generally to profile control in polishing processes, and more particularly to a carrier head having a piezoelectric actuator. Integrated circuits are typically formed on a substrate (eg, a semiconductor wafer) by sequentially depositing conductive layers, semiconductor layers, or insulating layers on the silicon wafer and by sequentially processing the layers. One manufacturing 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. Alternatively, planarization can be used to flatten a substrate surface (e.g., a dielectric layer) for lithography. Chemical mechanical polishing (CMP) is a well-established planarization method. This planarization method typically requires mounting a substrate on a carrier head. The exposed surface of the substrate is placed against a rotating polishing pad. The carrier head applies a controllable load to the substrate, pushing it against the polishing pad. In some embodiments, the carrier head includes a membrane that forms multiple independent pressurizable chambers, where the pressure in each chamber controls the polishing rate in each corresponding area on the substrate. A polishing liquid, such as a slurry containing abrasive particles, is supplied to the surface of the polishing pad. In one aspect, a carrier head for holding a substrate in a polishing system comprises a housing including a carrier plate, a first flexible membrane secured to the housing, and a plurality of independently operable piezoelectric actuators secured to the carrier plate. The first flexible membrane has an upper surface and a lower surface providing a substrate mounting surface. The piezoelectric actuators are positioned above the first flexible membrane to independently adjust the compressive pressure on the upper surface of the first flexible membrane. In another embodiment, a polishing system includes a platform for supporting a polishing pad; a carrier head for holding a substrate against the polishing pad; an in-situ monitoring system for generating a signal that is dependent on the thickness of a layer on the substrate being polished; and a control system. The carrier head includes a housing secured to a drive shaft and rotatable by the drive shaft, the housing including a carrier plate, a first flexible membrane secured to the housing, and a plurality of independently operable piezoelectric actuators. The first flexible membrane has an upper surface and a lower surface that provides a substrate mounting surface. The piezoelectric actuator is secured to the carrier plate and positioned above the first flexible membrane so as to independently adjust the compressive pressure on the upper surface of the first flexible membrane. The plurality of piezoelectric actuators are arranged around a central axis of the carrier head at different angles. The control system is configured to control the voltage applied to the plurality of piezoelectric actuators based on the signal from the in-situ monitoring system so as to reduce the angular variation in the layer thickness. In another aspect, a polishing assembly includes a carrier head for holding a substrate in a polishing system, a drive shaft, a motor for rotating the drive shaft, a rotary coupling, a controller, a voltage supply line, and a data line. The carrier head includes a housing secured to the drive shaft and rotatable by the drive shaft, and includes a carrier plate, a plurality of independently operable piezoelectric actuators, and circuitry secured to the housing. The piezoelectric actuators are secured to the carrier plate and positioned to independently adjust pressure on the substrate. The voltage supply line and the data line connect the controller to the circuitry via the rotary coupling. The circuitry is configured to receive a voltage on the voltage supply line, receive data on the data line, and control the voltage applied to the plurality of piezoelectric actuators based on the data. In another embodiment, a carrier head for holding a substrate in a polishing system includes a housing; a first flexible membrane secured to the housing to form one or more pressurizable chambers for applying pressure to a central portion of a substrate through a central membrane portion of the first flexible membrane; and a plurality of independently operable piezoelectric actuators supported by the housing, the plurality of piezoelectric actuators being positioned radially outward from the central membrane portion and at different angles to independently adjust pressure on a plurality of angled regions of the substrate in an annular outer region of the substrate surrounding the central portion of the substrate. In another embodiment, a carrier head for holding a substrate in a polishing system includes a housing and a first flexible membrane secured to the housing to form one or more pressurizable chambers. The first flexible membrane has a lower surface that provides a substrate mounting surface for a central portion of a substrate. A plurality of independently operable piezoelectric actuators are supported by the housing, and the plurality of piezoelectric actuators are positioned radially outward from the first flexible membrane and at different angles. An edge control ring, which is stiffer than the first flexible membrane, is coupled to the plurality of piezoelectric actuators so that the plurality of piezoelectric actuators control the tilt angle of the edge control ring relative to the housing. The edge control ring is positioned to apply pressure to an annular area on the substrate surrounding the central portion of the substrate. In another aspect, a polishing system includes a platform supporting a polishing pad, a drive shaft, and a carrier head for holding a substrate in the polishing system. The carrier head includes a housing secured to and movable by the drive shaft; a plurality of independently operable piezoelectric actuators supported by the housing and positioned to control pressure on an edge portion of a back surface of a substrate held by the carrier head, the plurality of piezoelectric actuators being independently controllable. A control system is configured to control voltages applied to the plurality of piezoelectric actuators so that the position at which the highest pressure is applied to the edge portion of the back surface of the substrate experiences precession in conjunction with the precession of the substrate in the carrier head. Implementations of any of the above aspects may include one or more of the following features. The plurality of piezoelectric actuators may be arranged in a regular array (e.g., a rectangular grid). The plurality of piezoelectric actuators may be arranged in a plurality of arcuate regions, and the arcuate regions may be arranged at uniform or non-uniform angular spacings around the central axis of the carrier head. The plurality of piezoelectric actuators may be arranged in a plurality of hexagonal or trapezoidal regions. The plurality of piezoelectric actuators may include at least one piezoelectric actuator every 20° around the central axis of the carrier head. The plurality of piezoelectric actuators may include no more than six actuators, for example, may consist of three piezoelectric actuators. The first flexible membrane may have an elastic modulus (Young's modulus) between 1 MPa and 20 MPa. The carrier head may include a first flexible membrane secured to the housing to form one or more pressurizable chambers for applying pressure to a central portion of a substrate surrounded by edge portions of the substrate via a central membrane portion of the first flexible membrane. The carrier head may include a second flexible membrane supported by the housing and extending below a plurality of independently operable piezoelectric actuators, such that the plurality of independently operable piezoelectric actuators provide an adjustable compressive pressure on an upper surface of the second flexible membrane. The second flexible membrane may extend below the first flexible membrane such that the first flexible membrane controls the compressive pressure on the upper surface of the second flexible membrane, and the second flexible membrane provides a mounting surface for the central portion and edge portions of the substrate. The circuit system may be secured to the housing to receive a voltage on a voltage supply line, receive data on a data line, and control a voltage applied to a plurality of piezoelectric actuators based on the data. The circuit system may be configured to receive a frame of data from a controller on the data line, the data comprising one or more control values. The circuit system may be configured to receive a data frame comprising a sequence of control values ​​within the frame and identify an actuator to which the control value in the sequence is applied based on the position of the control value within the sequence. The circuit system may be configured to receive a data frame comprising a pair of control values ​​and an identification value and identify the actuator to which the control value is applied based on the identification values. The control value may represent a voltage applied to the piezoelectric actuator. Certain implementations may include one or more of the following advantages. Pressure can be applied to the substrate in a manner that varies radially and angularly around the center of the substrate being polished. This allows profile control in a manner that can compensate for angular variations in the thickness of the incoming substrate and / or angular variations in the polishing rate of the polishing process. The pressure applied to an area can be controlled by causing the piezoelectric actuator to expand or contract to deform the membrane on top of the area. Thus, the polishing process for each area of ​​a layer on the substrate can be controlled independently and with high resolution. Furthermore, the use of piezoelectric actuators allows for expansion to a larger number of control areas in a more feasible manner than using pressure chambers. In particular, fewer rotational connections are required, and the number of rotational connections does not need to scale with the number of piezoelectric actuators. The details of one or more implementations of the present invention are set forth in the accompanying drawings and the following description. Other features, objectives, and advantages will be apparent from the detailed description and drawings, as well as from the claims. Variations in polishing rates between different regions of a substrate can cause different regions to reach their target thickness at different times. On the one hand, if polishing of different regions of the substrate is stopped simultaneously, those regions may not reach the desired thickness. On the other hand, stopping polishing of different regions at different times can lead to defects or reduced throughput of the polishing equipment. Therefore, it is necessary to be able to independently control the pressure on different regions. In an idealized process, the polishing rate across the substrate would be angularly symmetric about the substrate's axis of rotation due to the rotation of the carrier head and platform. However, in practice, the polishing process can result in angular variations in the polishing rate. Furthermore, the substrate to be polished may have a top layer with an initial thickness that varies angularly, i.e., exhibits angular non-uniformity. Finally, in some manufacturing processes, it may be necessary to introduce angular non-uniformity in the thickness of the polished layer in order to compensate for non-uniformities in later processing steps (e.g., deposition steps). Eliminating angular non-uniformity caused by the polishing process or when polishing a layer with an angularly non-uniform initial thickness, or intentionally providing angular variations in thickness when polishing a layer, remains challenging. However, using a carrier head with multiple piezoelectric actuators can solve this problem. The piezoelectric actuators can be angularly distributed around the carrier head, and each piezoelectric actuator can be independently controlled, allowing the introduction of angular non-uniformity to be reduced or minimized. FIG1 illustrates an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable, disc-shaped platform 120 on which a polishing pad 110 is positioned. The platform is operable to rotate about an axis 125. For example, a motor 121 can rotate a drive shaft 124 to rotate the platform 120. The polishing pad 110 can be removably secured to the platform 120, for example, by an adhesive layer. The polishing pad 110 can be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The polishing apparatus 100 may include a combined slurry / rinse arm 130. During polishing, the arm 130 is operable to dispense a polishing liquid 132 (e.g., an abrasive slurry) onto the polishing pad 110. Although only one slurry / rinse arm 130 is shown, additional nozzles may be used, such as one or more dedicated slurry arms per carrier head. The polishing apparatus may also include a polishing pad conditioner to abrade the polishing pad 110 so as to maintain the polishing pad 110 at a consistent abrasive state. The polishing apparatus 100 includes a carrier head 140 operable to hold the substrate 10 against the polishing pad 110. The carrier head 140 can be configured to independently control polishing parameters, such as pressure, for each of a plurality of regions on the substrate 10. The carrier head 140 may include a housing 141 that can be connected to the drive shaft 152, the membrane 182, and a retaining ring 142 to hold the substrate 10 beneath the flexible membrane 182. The lower surface of the membrane 182 provides a mounting surface for the substrate 10. The membrane 182 can be made of an elastic material, for example, a rubber such as silicone rubber or neoprene. The Young's modulus of the membrane 182 can range from 1 MPa to 20 MPa. Other materials (e.g., hydrogels and foams) are possible if they deform within the elastic range at a Young's modulus between 1 MPa and 10 MPa and have a relatively high shear modulus but low adhesion to avoid "sticking" to the membrane. The membrane 182 can be translucent to accommodate optical in-situ monitoring systems. The membrane 182 can be fastened to the housing 141. Carrier head 140 also includes a plurality of independently operable piezoelectric actuators 184 positioned above membrane 182 and secured to carrier plate 143. Carrier plate 143 may be provided as part of housing 141. Piezoelectric actuators 184 are positioned to contact the upper surface of membrane 182 so as to independently adjust the pressure on the upper surface of membrane 182. As depicted in FIG. 1 , five piezoelectric actuators 184a-184c are depicted (not individually numbered), but this number may be greater, for example, twenty to one hundred actuators. Alternatively, circuitry 189 (e.g., a circuit board having one or more components such as a microcontroller) is secured to carrier head 140. For example, the circuitry can be mounted on top of housing 141 of carrier head 140. For another example, the circuitry can be mounted inside carrier head 140. Circuitry 189 can receive voltage from voltage source 181 on voltage supply line 183. Circuitry 189 can also receive data from controller 190 via data line 186. Voltage supply line 183 and data line 186 can be routed through drive shaft 152 and rotating electrical coupling 156 (e.g., slip rings) to stationary components of voltage source 181 and controller 190. Additionally, the circuitry can independently control the voltage applied to each piezoelectric actuator via voltage line 187 based on data. Data line 186 can carry a plurality of data frames, and each of the plurality of frames can include data representing a pressure signal or equivalent voltage signal for one or more of the piezoelectric actuators. In some implementations, the data frames transmitted by controller 190 include a control value for each piezoelectric actuator, and circuitry 189 is configured to determine which control value is associated with each piezoelectric actuator based on the order of the control values ​​within the frame. In some implementations, the data frames transmitted by controller 190 include a control value and an identification value for the piezoelectric actuator to which the control value is applied, and circuitry 189 is configured to determine the appropriate piezoelectric actuator for the control value based on the identification value. Only two wires, for example, voltage supply line 183 and data line 186, need to be routed through rotating electrical connection 156. Consequently, the assembly can be simpler and more reliable than a piezoelectric actuator requiring multiple rotating connections for fluid lines (e.g., pneumatic air lines). Furthermore, the number of piezoelectric actuators can be expanded without increasing the number of rotating connections by appropriately modifying the data provided by controller 190 and the functionality of circuitry 189 that interprets that data. Figures 2A and 2B illustrate, respectively, a cross-sectional view and a bottom view of an array 1841 of piezoelectric actuators 184 within carrier head 140. Each piezoelectric actuator 184 comprises a layer 1842 of piezoelectric material sandwiched between two electrodes 185a and 185b. To vertically displace the actuator, a voltage is applied between the two electrodes 185a and 185b. One of these electrodes (e.g., top electrode 185a) can be connected to ground. The other electrode (e.g., bottom electrode 185b) can serve as a control electrode, to which circuitry 189 applies a controllable voltage. In some implementations, the top electrode 185a is a common ground electrode for all piezoelectric actuators 184. In this case, the top electrode 185a can span the substrate 10. The individual bottom electrodes 185b can be the same size as the segments of the piezoelectric layer actuators. In some implementations, the piezoelectric actuators 184 have a uniform size across the carrier plate 143. In some implementations, the piezoelectric actuator 184 includes an insulating plate 1843 attached beneath the bottom electrode 185b. The insulating plate 1843 does not need to have the same shape as the rest of the actuator 184 (e.g., layer 1842). That is, the plate 1843 can have a different shape and size than the piezoelectric layer 1842. For example, the insulating plate 1843 can be larger (laterally) than the piezoelectric layer 1842. Furthermore, the insulating plate 1843 can have different shapes and sizes so that the shape of the area on the membrane 182 where pressure is applied by the piezoelectric actuator 184 can vary across the array 1841. The shape of the insulating plate 1843 can be selected based on the desired shape of the area on the substrate where pressure will be applied by the actuator. Alternatively, the entire piezoelectric actuator (e.g., piezoelectric layer 1842) and the insulating plate 1843 (if present) can be selected based on the desired shape of the area on the substrate where pressure will be applied by the actuator. In some implementations, more than one piezoelectric actuator 184 can be positioned above the same insulating plate 1843. In this case, the same voltage signal can be applied to the piezoelectric actuators 184 above the same plate 1843. In this configuration, the actuators 184 are relatively small compared to the area spanned by a single plate 1843. Adjacent piezoelectric actuators 184 can be separated by gaps 1844. In some implementations, the gaps between adjacent actuators 184 are uniform across the array 1841. The piezoelectric actuators can be arranged adjacent to each other to span the entire membrane 182. The gaps 1844 separating each piezoelectric actuator (e.g., separating insulating plates 1843) are sufficiently small to smooth the pressure applied by the membrane to the substrate. The gaps 1844 can range from 100 μm to 1 mm. The piezoelectric actuators 184 can be disposed at a plurality of different angular positions about the axis 159. In some implementations, the actuators 184 are disposed in a regular array (eg, a rectangular, hexagonal, or polar array). As an example shown in Figure 2B, the actuators 184 are arranged in a rectangular array. As an example shown in Figure 2E, the actuators 184 are arranged in a hexagonal array. Referring to FIG. 2F , as another example, the actuators can first be divided into concentric rings, and then each actuator within each ring spans a specific amount of arc length. The actuators within a given ring can be uniformly sized and / or evenly spaced around the ring. In some implementations, the actuators are uniformly sized and evenly spaced across multiple rings, so that there are a greater number of actuators in the rings farther from the center of the carrier head than in the rings closer to the center of the carrier head. In some implementations, the actuators in different rings span the same central angle (in degrees / radians), making the actuators in the rings farther from the center of the carrier head longer. In some implementations, the farther the rings are from the center of the carrier head, the narrower the actuators can become. In some implementations, the actuators in the first ring can span a smaller angle (in degrees / radians) than the actuators in the second ring closer to the center of the carrier head. The specific shape of the piezoelectric actuators 184 may depend on the array. For example, the size of the piezoelectric actuators 184 may be larger at the center of the substrate 10, having a piezo or trapezoidal shape, and gradually decrease in size toward the edge of the substrate, having an arc shape. The total number of piezoelectric actuators 184 is driven by the cost of the piezoelectric material. For example, a polishing head using piezoelectric pressure control may have 100 piezoelectric actuators, each of which is approximately 70 mm in size. 2 . In some implementations, the angular and radial arrangement of the piezoelectric actuators 184 around the central axis can be non-uniform. For example, if one or more regions of the substrate require higher-resolution control than other portions, finer (smaller) piezoelectric actuators can be arranged there. As shown in Figures 2B, 2E, and 2F, in some implementations, the piezoelectric actuators span the substrate 10, for example, so that the pressure applied to the substrate is fully controlled by the piezoelectric actuators 184 in all areas of the substrate. However, in some implementations, a hybrid approach may be used, where the pressure in one area of ​​the substrate is controlled by the piezoelectric actuators and in another area of ​​the substrate by a pressurized chamber. For example, the carrier head 140 may include a second flexible membrane 144, as shown in Figure 2C. The outer surface of the second flexible membrane is positioned to contact the upper surface of the first flexible membrane 182. The second membrane 144 is secured to the housing to form one or more independently controllable pressure chambers (e.g., three chambers 146a-146c), which can apply independently controllable pressure to associated areas 148a-148c on the flexible membrane 144 and, therefore, on the substrate 10 (see Figure 2D). These areas include the central portion of the substrate 10. 2C, a plurality of piezoelectric actuators 184 are arranged around the second flexible membrane 144 to apply pressure to the membrane 182 at the edge portion 148d of the substrate (see FIG. 2D). For example, the piezoelectric actuators 184 can be positioned at uniform angular spacing around the central axis 159. The piezoelectric actuators 184 may be relatively "dense," for example, at least one every 30° around the central axis 159 , or at least one every 20° around the central axis 159 , or at least one every 10° around the central axis 159 , or at least one every 5° around the central axis 159 . Referring to Figures 2C and 2D, central region 148a may be generally circular, the remaining chamber regions 148b-148c may be concentric annular regions surrounding central region 148a, and piezoelectric region 148d may be concentric annular regions surrounding outermost chamber region 148c. Although Figures 2C and 2D depict only three chamber regions and one piezoelectric region, two, four, or more chamber regions may be present, and two, four, or more piezoelectric regions may be present outside the chamber regions. Although piezoelectric region 148d is depicted as concentric rings on the edge of substrate 10 in Figures 2C and 2D, piezoelectric regions may replace other chamber regions. For example, the central circular chamber region may be replaced by a circular region controlled by a plurality of arranged piezoelectric actuators. The decision to use a combination of pressure chambers and piezoelectric actuators can be evaluated based on a number of factors. For example, factors may be overall cost, the availability or accuracy of the polishing head 140. For example, a hybrid carrier head may be less expensive than a carrier head using only piezoelectric actuators while still providing improved angular control of polishing rate at the substrate edge where angular non-uniformity is most likely to occur. Referring to Figures 6A and 6B, an example hybrid carrier head 140 is shown that is similar to the carrier head depicted in conjunction with Figures 2C and 2D. However, an edge control ring 202 is positioned between the piezoelectric element 184 and the membrane 182 or substrate 10. The edge control ring can be more rigid than the membrane 182, for example, a hard plastic or a thin metal ring. Furthermore, instead of having a large number of piezoelectric actuators closely spaced around the perimeter of the loading area, the hybrid carrier head 140 of Figures 6A and 6B includes a sufficient number of actuators to control the vertical position and tilt of the edge control ring 202, for example, along one axis (in which case only two piezoelectric actuators are required) or along two perpendicular axes (in which case only three piezoelectric actuators are required). However, additional piezoelectric actuators may be included, in which case the piezoelectric actuators can be used to bend the edge control ring 202 into a desired shape, as appropriate. For example, the hybrid carrier head 140 may have six piezoelectric actuators. This will set the vertical positioning of the edge control ring 202 at six locations, with the edge control ring flexing to accommodate different heights at adjacent actuators.The piezoelectric actuators 184 can be evenly spaced around the center of the carrier head. This example implementation effectively and economically reduces angle variation because the controller 190 can control the pressure distribution on the edge region using only a small number of piezoelectric actuators 184 located at different locations above the piezoelectric region. Specifically, by controlling the extension of the piezoelectric actuators (three piezoelectric actuators 184a-184c), the deflection or tilt of the edge control ring 202 can be controlled, thereby adjusting the pressure distribution on the substrate edge. During polishing of a substrate using the hybrid carrier head 140, the controller 190 can reduce the angular variation of the polishing profile at the substrate edge by selecting the vertical extension of the actuator 184 to select the location where the highest or lowest pressure is applied, as well as the magnitude of the highest and lowest pressures. That is, the selection of the vertical positioning of the three positions on the edge control ring 202 controls the deflection of the ring 202, with the highest pressure being applied at the lowest position of the ring 202. The lowest pressure is applied at the highest position of the ring, which is 180° from the point where the maximum pressure is applied, as long as the ring remains straight. The pressure should vary relatively uniformly along the perimeter from the location of highest pressure to the location of lowest pressure. Controller 190 can select the location 204 of maximum (or minimum) pressure and the magnitude of the pressure applied at that location 204 to reduce edge non-uniformity. Controller 190 can adjust the orientation of the specific edge location 204 where the highest localized pressure is applied (i.e., ϑ) by varying the pressure applied at the three locations of piezoelectric actuators 184a-184c. For example, if actuator 184a has the greatest extension, actuator 184b has the second greatest extension, and actuator 184c has the lowest extension, location 204 will be located in the arc-shaped region between the two locations of piezoelectric actuators 184a and 184b, as shown in FIG. 6B . The relative magnitude of the extensions of actuators 184a-184c will determine the magnitude of the highest and lowest pressures. 6C , the carrier head 140 includes a central pressure chamber control region 148a and a plurality of piezoelectric actuators 184. The controller 190 can reduce the angle variation at the edge of the substrate 10 when polishing the substrate by adjusting the location of the maximum or minimum pressure and the amount of the maximum and minimum pressure. Returning to FIG. 1 , carrier head 140 is suspended from a support structure 150 (e.g., a turntable) and is connected to a carrier head rotation motor 154 via a drive shaft 152 so that the carrier head can rotate about an axis 155. Optionally, carrier head 140 can oscillate laterally (e.g., on a slider on turntable 150) or by rotational oscillation of the turntable itself. In operation, the platform rotates about its central axis 125, and each carrier head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad. The polishing apparatus may include an in-situ monitoring system 160, which, as discussed below, can be used to determine whether or by how much to adjust the polishing rate. In some implementations, the in-situ monitoring system 160 may include an optical monitoring system, such as a spectroscopy monitoring system. In other implementations, the in-situ monitoring system 160 may include an eddy current monitoring system. In one embodiment, the monitoring system 160 is an optical monitoring system. An optical path through the polishing pad 110 can be provided via a window 118 in the polishing pad 110. The optical monitoring system 160 can include a light source 162, a light detector 164, and circuitry 166 for sending and receiving signals between a remote controller 190 (e.g., a computer) and the light source 162 and light detector 164. One or more optical fibers 170 can be used to transmit light from the light source 162 to the optical path in the polishing pad and to transmit light reflected from the substrate 10 to the detector 164. The output of the circuit system 166 can be a digital electronic signal that is transmitted through a rotary coupler 129 (e.g., a slip ring) in the drive shaft 124 to the controller 190 for use in the optical monitoring system. Similarly, the power supply can be turned on or off in response to a control command in the digital electronic signal from the controller 190 through the rotary coupler 129 to the optical monitoring system 160. Alternatively, the circuit system 166 can communicate with the controller 190 via wireless signals. Light source 162 can be operable to emit white light, and light detector 164 can be a spectrometer. As described above, light source 162 and light detector 164 can be connected to a computing device (e.g., controller 190) that is operable to control the operation of light source 162 and light detector 164 and receive signals therefrom. The computing device can include a microprocessor, such as a programmable computer, located near the polishing apparatus. Regarding control, the computing device can, for example, synchronize the activation of the light source with the rotation of platform 120. In some implementations, the light source 162 and detector 164 of the in-situ monitoring system 160 are mounted within the platform 120 and rotate with the platform 120. In this case, the movement of the platform causes the sensor to scan across each substrate. Specifically, as the platform 120 rotates, the controller 190 can cause the light source 162 to emit a series of flashes that begin just before and end just after each substrate 10 passes through the optical path. Alternatively, the computing device can cause the light source 162 to emit light continuously, beginning just before and ending just after each substrate 10 passes through the optical path. In either case, the signal from the detector can be integrated over a sampling period to generate a spectral measurement at the sampling frequency. In operation, the controller 190 may receive, for example, a signal carrying information describing the spectrum of light received by the light detector for a particular flash of the light source or a time frame of the detector. This spectrum is thus the spectrum measured in situ during polishing. As shown in FIG. 3A , if the detector is mounted on a platform, then due to the rotation of the platform (indicated by arrow 304), as the viewing window 108 travels beneath the carrier head, the optical monitoring system will take spectral measurements at a sampling frequency such that the spectral measurement is taken at a location 301 in an arc across the substrate 10. For example, each of points 301a-301k represents a location at which a spectral measurement is taken by the monitoring system of the substrate 10 (the number of points is illustrative; more or fewer measurements than shown may be taken depending on the sampling frequency). Due to the rotation of the carrier head 140 as the viewing window 108 is scanned, spectra are acquired from different radial and angular locations on the substrate 10. Thus, for any given scan of the optical monitoring system across a substrate, the controller 190 can calculate the radial position (relative to the center of the particular substrate 10 being scanned) and the angular position (relative to a reference angle for the particular substrate 10 being scanned) for each measured spectrum from that scan based on the timing, motor encoder information, optical detection of the substrate edge and / or retaining ring, and optical detection or calculation of the precession of the substrate 10 relative to the retaining ring 142. Under many operating conditions, the rate of precession of the substrate relative to the carrier head is slow enough to allow the controller 190 sufficient time to change and apply a new pressure in a particular angular region on the substrate. Thus, in some cases, for example, if the substrate's precession rate is less than 10° per minute (e.g., less than 5° per minute), the optical monitoring system can optionally ignore the difference in the substrate's angular position relative to the carrier head's angular position and still accurately polish the substrate to obtain the desired post-polishing profile. In cases where polishing a substrate requires a non-uniform angular profile, the monitoring system can align the initial angular position of the substrate and carrier head (e.g., based on the notch) and calculate the substrate's precession rate based on the substrate's outer diameter, the inner diameter of the retaining ring, and the carrier head's rotation rate (e.g., rotations per minute). The system can thus precisely vary the pressure applied to the substrate to achieve the target angular position. In some embodiments, the controller 190 can adjust the pressure to counteract the observed precession rate of the substrate 10 to reduce angular changes during polishing. As an example, in conjunction with FIG. 6B or FIG. 6C , the controller 190 can continuously adjust the corresponding pressure applied at different locations in the piezoelectric region 148 d (e.g., corresponding to the locations of the piezoelectric actuators 184 a-184 c) to change the angular location of the location 204 where the highest (or lowest) effective local pressure is applied. The orientation of a particular location 204 (e.g., ϑ) can be changed at a particular angular velocity to counteract the precession rate of the substrate 10 relative to the carrier head 140, so that the effective local pressure applied at the particular region 204 of the substrate 10 appears static relative to the substrate 10, as if the substrate 10 is not experiencing precession. The polishing system may also include a rotary positioning sensor (e.g., a flange attached to the edge of the platform that passes through the fixed photointerrupter) to provide additional information for determining which substrate and position on the substrate the spectrum is measured. The controller can thus associate each measured spectrum with an area 188 or 148d on the substrate 10 (see Figures 2B and 2D). In some implementations, the time of the spectrum measurement can be used instead of a precise calculation of the radial position. For angular positioning, the motor encoder of motor 154 can provide the angular position of the drive shaft 152 and the carrier head 140. This angular position, combined with the platform angular position provided by the encoder for motor 121 or the rotary photointerrupter, can be used to determine the angular position of each measurement. As an example, referring to FIG. 3B , during one rotation of the platform, spectra corresponding to different positions 303 a - 303 o are collected by light detector 164. Each spectrum collected at position 303 a - 303 o is associated with a piezoelectric region 188 a - 188 o based on their radial and angular positioning. While this example shows each region associated with the same number of spectra, these regions may also be associated with a different number of spectra based on in-situ measurements. The number of spectra associated with each region may vary from one rotation of the platform to another. Of course, the number of positions given above is merely illustrative, as the actual number of spectra associated with each region will depend at least on the sampling rate, the rotation rate of the platform, and the radial width of each region. Without being bound by any particular theory, due to variations in the thickness of the outermost layer, the spectrum of light reflected from substrate 10 evolves as polishing proceeds (e.g., over multiple rotations of the platform, rather than during a single sweep across the substrate), resulting in a series of time-varying spectra. Furthermore, a specific spectrum is exhibited by a specific thickness of the layer stack. For each measured spectrum, controller 190 can calculate a characteristic value. This characteristic value is typically the thickness of the outer layer, but can also be a related feature, such as the thickness removed. Alternatively, the characteristic value can be a physical property other than thickness, such as metal line resistance. Furthermore, the characteristic value can be a more general representation of the substrate's progress through the polishing process, such as an index value representing the time or number of stage rotations at which a spectrum is expected to be observed during a polishing process following a predetermined schedule. One technique for calculating eigenvalues ​​involves identifying a matching reference spectrum from a library of reference spectra for each measured spectrum. Each reference spectrum in the library may have an associated eigenvalue, such as a thickness value or index value indicating the time or number of platform rotations at which the reference spectrum is expected to occur. By determining the associated eigenvalues ​​for the matching reference spectra, an eigenvalue can be generated. This technique is described in U.S. Patent Publication No. 2010-0217430. Another technique involves fitting an optical model to a measured spectrum. Specifically, the parameters of the optical model are optimized to provide the best fit between the model and the measured spectrum. The parameter values ​​generated for the measured spectrum generate feature values. This technique is described in U.S. Patent Publication No. 2013-0237128. Possible input parameters for the optical model may include thickness, refractive index and / or extinction coefficient of each layer, and the spacing and / or width of repeating features on the substrate. The difference between the output spectrum and the measured spectrum can be calculated as the sum of the absolute differences between the measured spectrum and the output spectrum of the entire spectrum, or as the sum of the squared differences between the measured spectrum and the reference spectrum. Other techniques for calculating the difference are possible, for example, a cross-correlation between the measured spectrum and the output spectrum can be calculated. Another technique is to analyze the characteristics of a spectral feature from a measured spectrum, for example, the wavelength or width of a peak or valley in the measured spectrum. The wavelength or width value of the feature from the measured spectrum provides a characteristic value. This technique is described in U.S. Patent Publication No. 2011-0256805. Pressure Control Based on In-Situ Measurement Generally speaking, at the end of the polishing process (or at the endpoint when the polishing process is stopped), the substrate will have a desired thickness profile. This desired thickness profile may include the same predetermined thickness for all regions of the substrate 10, or different predetermined thicknesses for different regions of the substrate 10. When polishing multiple substrates having non-uniform initial thicknesses simultaneously, the multiple substrates may have the same desired thickness profile or different desired thickness profiles. In some implementations, to maintain the measured thickness relationship between the control and reference regions throughout the polishing process similar to or identical to the thickness relationship indicated by the desired thickness profile(s) at the endpoint time, the controller and / or computer may schedule adjustments to the polishing rate of the control region at a predetermined rate, for example, every given number of revolutions (e.g., every 5-50 revolutions) or every given number of seconds (e.g., every 2-20 seconds). In some ideal cases, the adjustment may be zero at the pre-scheduled adjustment time. In other implementations, such adjustments may be made at a rate determined in situ. For example, if the measured thickness relationship between different regions differs significantly from the desired thickness relationship, the controller and / or computer may decide to adjust the polishing rate more frequently. During polishing, the pressure applied to each area of ​​the layer on the substrate is caused by the deformation of the membrane 182, and the membrane deformation is controlled by the vertical displacement of the corresponding piezoelectric actuator above that area. By calculating the Young's modulus of the membrane, a static formula describing the relationship between the actuator displacement and the pressure applied to the substrate can be obtained via Hooke's law. As shown in Figure 4, when the number of displacement types D1 of the actuator is given as input, the static formula 403 can output the number of pressure types P1 applied to the areas in the layer, and vice versa. Although shown as a straight line, when the membrane has nonlinear elasticity, the formula function can be a nonlinear curve. Given the membrane material properties and the range of motion of the piezoelectric actuator, this formula can be used as a plausibility check to know in advance the pressure range that can be applied to multiple areas in the layer. In addition, a series of lookup tables can also be used here. For example, when the membrane is 2 mm thick and has a Young's modulus of 2 MPa, given a target pressure of 2 Psi applied to a control region in the layer, the desired piezoelectric actuator movement distance can be found to be, for example, 14 μm downward. For another example, when the membrane is 2 mm thick and has a Young's modulus of 5 MPa, if the piezoelectric actuator movement distance for a certain voltage change is a fixed 5 μm downward, the actual pressure applied to the control region can be found to be, for example, 1.8 Psi. For another example, instead of using actuator displacement and membrane thickness, the membrane deformation strain caused by the compressive motion of the piezoelectric actuator can be used to generate another lookup table. FIG5 shows a flow chart (500) of a control method using a piezoelectric actuator, which includes determining the expected thickness of each control region at a planned time (502), determining the measured thickness of the control region (504), determining an adjustment to the pressure applied to the control region (506), determining an adjustment to the voltage applied to the piezoelectric actuator above the control region (508), applying the adjusted voltage to actuate the piezoelectric actuator and thereby modifying the pressure applied to the membrane above the control region (510). Steps 502 to 506 can be implemented using an in-situ monitoring system and controller, and step 510 can be executed on the circuit system 189. A signal representing the expected pressure (or the voltage to be applied) for each control region is transmitted from the monitoring system 160 to the circuit system 189. As shown in FIG6, the control method using a piezoelectric actuator is fast enough to adjust the pressure given the current frame of signal data before receiving the next frame of signal data. As used in this specification, the term substrate can include, for example, production substrates (e.g., including multiple memory or processor dies), test substrates, bare substrates, and gated substrates. A substrate can be at various stages of integrated circuit fabrication; for example, a substrate can be a bare wafer, or it can include one or more deposited and / or patterned layers. The term substrate can also include circular disks and rectangular sheets. The polishing apparatus and methods described above can be applied to a variety of polishing systems. The polishing pad, the carrier head, or both can be movable to provide relative motion between the polishing surface and the substrate. For example, the platform can orbit rather than rotate. The polishing pad can be a round (or some other shaped) pad secured to the platform. Some aspects of the endpoint detection system can be applied to linear polishing systems, such as those in which the polishing pad is a continuous or linearly moving roll-to-roll conveyor belt. The polishing layer can be a standard (e.g., polyurethane with or without fillers) polishing material, a soft material, or a fixed abrasive material. When relative positioning terms are used, it should be understood that the polishing surface and substrate can be maintained in a vertical orientation or some other orientation. Although the above description has focused on the control of a chemical mechanical polishing system, the sequential metrology station may be applicable to other types of substrate processing systems, such as etching or deposition systems. Embodiments of the subject matter and functional operations described in this specification (such as control systems) can be implemented in digital electronic circuitry, tangibly embodied computer software or firmware, computer hardware (including the structures disclosed in this specification and their structural equivalents), or a combination of one or more of the foregoing. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible, non-transitory storage medium for execution by data processing equipment or for controlling the operation of the data processing equipment. Alternatively or additionally, the program instructions can be encoded on an artificially generated propagated signal, such as a computer-generated electrical, optical, or electromagnetic signal, generated to encode information for transmission to appropriate receiver equipment for execution by the data processing equipment. The computer storage medium can be a computer-readable storage medium, a computer-readable storage substrate, a random or serial access memory element, or a combination of one or more thereof. The term "data processing equipment" refers to data processing hardware and encompasses all types of equipment, devices, and machines used to process data, including, for example, a programmable digital processor, a digital computer, or multiple digital processors or computers. The equipment may also be or further include special-purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). In addition to hardware, the equipment may optionally include code that creates an execution environment for computer programs, such as code constituting processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of the foregoing. A computer program (which may also be referred to or described as a program, software, software application, module, software module, script, or code) may be written in any programming language, including compiled or interpreted languages, or declarative or procedural languages, and may be implemented in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program may be stored as part of a file that stores other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., a file storing one or more modules, subroutines, or portions of code). A computer program may be deployed to execute on one or more computers located at a single site, or distributed across multiple sites interconnected by a data communication network. The processes and logic flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows may also be performed by special-purpose logic circuitry, and the device may also be implemented as a special-purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). A system of one or more computers "configured to" perform specific operations or actions means that the system has installed thereon software, firmware, hardware, or a combination thereof that, when executed, causes the system to perform the operations or actions. One or more computer programs configured to perform specific operations or actions means that the one or more programs include instructions that, when executed by data processing equipment, cause the equipment to perform the operations or actions. A computer suitable for executing computer programs includes (for example, it may be based on) a general-purpose or special-purpose microprocessor, or both, or any other type of central processing unit. Generally, the central processing unit will receive instructions and data from read-only memory or random access memory, or both. The essential elements of a computer are a central processing unit for executing or running instructions and one or more memory elements for storing instructions and data. Generally, a computer will also include one or more mass storage elements (e.g., magnetic disks, magneto-optical disks, or optical disks) for storing data, or be operatively coupled to receive data from or transfer data to, or both, such mass storage elements. However, a computer need not have these elements. Additionally, a computer may be embedded in another device such as a cellular phone, a personal digital assistant (PDA), a mobile audio or video player, a game joystick, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name a few. Computer-readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media, and memory devices, including, for example, semiconductor memory devices (e.g., EPROM, EEPROM, and flash memory devices); magnetic disks (e.g., internal hard disks or removable disks); magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory can be supplemented by, or incorporated in, special purpose logic circuitry. Control of the various systems and processes described in this specification, or portions thereof, may be implemented as a computer program product comprising instructions stored on one or more non-transitory computer-readable storage media and executable on one or more processing elements. The systems described in this specification, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing elements and memory to store executable instructions for performing the operations described in this specification. Although this specification contains many specific implementation details, they should not be interpreted as limiting the scope of any invention or the scope of what may be claimed, but rather as descriptions of features that may be specific to a particular embodiment of a particular invention. Certain features described in this specification in the context of separate embodiments may also be implemented in combination with a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any appropriate subcombination. Furthermore, although features may be described above as working in certain combinations, or even initially claimed as such, in some cases one or more features from the combination may be deleted from the claimed combination, and the claimed combination may point to a subcombination or a variant of the subcombination. Similarly, although operations are depicted in a particular order in the figures, this should not be construed as requiring that the operations be performed in the particular order shown or in a sequential order, or that all depicted operations be performed to achieve the desired result. In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system modules and components in the above-described embodiments should not be construed as requiring such separation in all embodiments, and it should be understood that the program components and systems generally may be integrated together in a single software product or packaged in multiple software products. Specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions described in the claims can be performed in a different order and still achieve the desired results. As an example, the processes depicted in the accompanying drawings do not necessarily require the particular order shown or sequential order to achieve the desired results. In some situations, multitasking and parallel processing may be advantageous. Other embodiments are within the scope of the following claims. 10: Substrate 100: Polishing device 108: Viewing window 110: Polishing pad 112: Outer polishing layer 114: Backing layer 118: Viewing window 120: Platform 121: Motor 124: Drive shaft 125: Axis 128: Selector coupler 129: Rotary coupler 130: Slurry / rinse arm 132: Polishing liquid 140: Carrier head 141: Housing 142: Retaining ring 143: Carrier plate 144: Second flexible membrane 146a: Chamber 146b: Chamber 146c: Chamber 148a: Central region 148b: Chamber region 148c: Chamber region 148d : Edge portion 150: Support structure 152: Drive shaft 154: Carrier head rotation motor 156: Rotational coupling 159: Axis 160: In-situ monitoring system 162: Light source 164: Light detector 166: Circuit system 170: Optical fiber 181: Voltage source 182: Membrane 183: Voltage supply line 184: Piezoelectric actuator 184a~e: Piezoelectric actuator 1841: Array 1842: Piezoelectric layer / layer of piezoelectric material 1843: Insulating plate 1844: Gap 185: Electrode 185a: Top electrode 185b: Bottom electrode 186: Data line 187: Voltage Line 188a: piezoelectric region 188b: piezoelectric region 188c: piezoelectric region 188d: piezoelectric region 188e: piezoelectric region 188f: piezoelectric region 188g: piezoelectric region 188h: piezoelectric region 188i: piezoelectric region 188j: piezoelectric region 188k: piezoelectric region 188l: piezoelectric region 188m: piezoelectric region 188n: piezoelectric region 188o: piezoelectric region 189: circuit system 190: controller 202: edge control ring 204: position 301: position 301a: point 301b: point 301c: point 301d: point 3 01e: point 301f: point 301g: point 301h: point 301i: point 301j: point 301k: point 303a: position 303b: position 303c: position 303d: position 303e: position 303f: position 303g: position 303h: position 303i: position 303j: position 303k: position 303l: position 303m: position 303n: position 303o: position 304: arrow 403: static formula 500: flow chart 502: step 504: step 506: step 508: step 510: step FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus. FIG. 2A illustrates an example cross-sectional view of a portion of a carrier head, substrate, and polishing pad showing a piezoelectric actuator in the carrier head. FIG. 2B shows a schematic bottom view of a carrier head having a rectangular array of piezoelectric actuators. FIG. 2C illustrates a cross-sectional view of an example of a hybrid carrier head including a piezoelectric control region and a pressure chamber control region. FIG. 2D shows a schematic bottom view of the hybrid carrier head with corresponding regions. FIG. 2E shows a schematic bottom view of a carrier head having piezoelectric actuators arranged in a hexagonal array. FIG. 2F shows a schematic bottom view of a carrier head having piezoelectric actuators in a polar array. FIG. 3A shows a top view of the polishing pad and illustrates the location of in-situ metrology on the first substrate. FIG. 3B is a schematic top view showing the distribution of multiple locations for in-situ measurement relative to the unitized area of ​​the substrate. FIG. 4 is a schematic graph illustrating a static formula for determining the pressure applied to a substrate based on the displacement of a piezoelectric actuator in conjunction with an elastic film between the actuator and the substrate. FIG. 5 is a flow chart illustrating an example profile control process during polishing a conductive layer having a non-uniform initial thickness. FIG. 6A illustrates a cross-sectional view of another example implementation of a hybrid carrier head including multiple piezoelectric edge control regions and pressure chamber control regions. FIG. 6B illustrates a schematic bottom view of the hybrid carrier head of FIG. 6A with an example pressure control scenario. FIG. 6C illustrates a schematic bottom view of a hybrid carrier head including multiple piezoelectric edge control regions and a central pressure chamber control region. Domestic deposit information (please note in the order of deposit organization, date, and number) None Foreign deposit information (please note in the order of deposit country, organization, date, and number) None 10:Substrate 100: Polishing equipment 182: Membrane 184: Piezoelectric actuator 1841: Array 1842: Piezoelectric layer / layer of piezoelectric material 1843:Insulation Board 1844: Gap 185: Electrode 185a: Top electrode 185b: bottom electrode 187: Voltage line 189:Circuit System

Claims

1. A polishing assembly, comprising: A voltage source; One drive shaft; A support head for holding a substrate in a polishing system, the support head comprising: a housing secured to and movable by a drive shaft, the housing including a support plate; a plurality of independently operable piezoelectric actuators secured to the support plate for independently adjusting pressure on the substrate held by the support head; and a circuit system secured to the housing, the circuit system including a microcontroller; a motor for rotating the drive shaft; a rotary coupling; and a controller configured to generate data on a data line, the data comprising a plurality of frames, each frame including both a control value and an identification value for the piezoelectric actuator to which the control value is applied. A voltage supply line, wound through the rotary coupling and the drive shaft to connect the voltage source to the circuit system; and a data line, separate from the voltage supply line and wound through the rotary coupling and the drive shaft to connect the controller to the microcontroller, wherein the circuit system is configured to receive a voltage on the voltage supply line, and wherein the microcontroller is configured to receive the data on the data line, and the microcontroller is configured to determine an appropriate piezoelectric actuator for the control value based on the identification value so as to control the voltage applied to the plurality of piezoelectric actuators based on the data.

2. The polishing assembly as claimed in claim 1, wherein the microcontroller is configured to determine at least one control voltage for each frame based on data in the frame to be applied to at least one of the plurality of piezoelectric actuators.

3. The polishing assembly as described in claim 1, wherein the circuitry is mounted on top of the housing.

4. The polishing assembly as described in claim 1, wherein the circuitry is mounted inside the carrier head.

5. The polishing assembly as claimed in claim 1, wherein the plurality of independently operable piezoelectric actuators are positioned at different angles around one of the central axes of the carrier head.

6. The polishing assembly as claimed in claim 5, wherein the plurality of independently operable piezoelectric actuators are positioned to control pressure on an edge portion of a back surface of the substrate.

7. The polishing assembly as claimed in claim 6, wherein the plurality of piezoelectric actuators includes at least one piezoelectric actuator at 30° intervals around the central axis of the carrier head.

8. The polishing assembly as claimed in claim 6, wherein the controller is configured to control the voltage applied to the plurality of piezoelectric actuators such that rotation of the substrate in a positioning head that applies a maximum pressure to the edge portion of the back surface of the substrate undergoes rotation relative to the carrier head.

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