Carrier head polishing with piezoelectric pressure control

Abstract

A carrier head for holding a substrate in a polishing system includes 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 of the upper surface of the first flexible membrane.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to profile control of a polishing process, and more particularly, to a carrier head having a piezoelectric actuator. [Background technology]

[0002] Integrated circuits are typically formed on a substrate (eg, a semiconductor wafer) by depositing successive conductive, semiconductive or insulating layers on the silicon wafer and then processing the layers.

[0003] One manufacturing step involves depositing a fill layer over a non-planar surface and planarizing the fill layer. In certain applications, the fill layer is planarized until the top surface of a patterned layer is exposed. In addition, planarization may be used to planarize a substrate surface, such as a dielectric layer, for lithography.

[0004] Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that a substrate be mounted on a carrier head. The exposed surface of the substrate is placed against a rotating polishing pad. The carrier head exerts a controllable load on the substrate to press the substrate against the polishing pad. In some cases, the carrier head includes a membrane that forms multiple independently pressurizable chambers, and the pressure in each chamber controls the polishing rate in each corresponding region on the substrate. A polishing fluid, such as a slurry containing abrasive polishing particles, is supplied to the surface of the polishing pad. Summary of the Invention

[0005] In one aspect, a carrier head for holding a substrate in a polishing system includes 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 for independently adjusting a compressive pressure on the upper surface of the first flexible membrane.

[0006] In another aspect, a polishing system includes a platen for supporting a polishing pad, a carrier head for holding a substrate against the polishing pad, an in-situ monitor system for generating a signal dependent on a thickness of a layer on the substrate being polished, and a control system. The carrier head includes a housing fixed to and rotatable by a drive shaft, the housing including a carrier plate, a first flexible membrane fixed to the housing, and a plurality of independently operable piezoelectric actuators. The first flexible membrane has an upper surface and a lower surface providing a substrate mounting surface. The piezoelectric actuators are fixed to the carrier plate and positioned above the first flexible membrane to independently adjust a compressive pressure on the upper surface of the first flexible membrane. The plurality of piezoelectric actuators are disposed at different angular positions around a central axis of the carrier head. The control system is configured to control voltages applied to the plurality of piezoelectric actuators based on a signal from the in-situ monitor system to reduce angular variations in the layer thickness.

[0007] 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 electric union, a controller, a voltage supply line, and a data line. The carrier head includes a housing secured to and rotatable by the drive shaft, the housing including a carrier plate, a plurality of independently operable piezoelectric actuators, and a circuit 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 circuit through the rotary electric union. The circuit is configured to receive a voltage on the voltage supply line, receive data on the data line, and control voltages applied to the plurality of piezoelectric actuators based on the data.

[0008] In another aspect, 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 to apply pressure to a center of the 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 independently operable piezoelectric actuators positioned radially outward of the central membrane portion and at different angular positions to independently adjust pressure on a plurality of angular zones within an annular outer region of the substrate surrounding the center of the substrate.

[0009] In another aspect, a carrier head for holding a substrate in a polishing system includes a housing and a first flexible membrane secured to the housing for forming one or more pressurizable chambers. The first flexible membrane has a lower surface that provides a substrate mounting surface at a center of the substrate. A plurality of independently operable piezoelectric actuators are supported by the housing, the plurality of piezoelectric actuators positioned radially outward of the first flexible membrane and at different angular positions. An edge control ring, which is stiffer than the first flexible membrane, is coupled to the plurality of piezoelectric actuators such that the plurality of piezoelectric actuators control the tilt of the edge control ring relative to the housing. The edge control ring is positioned to apply pressure to an annular region on the substrate surrounding the center of the substrate.

[0010] In another aspect, a polishing system includes a platen for 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 fixed to and movable by the drive shaft, and a plurality of independently operable piezoelectric actuators supported by the housing and positioned to control pressure on a backside edge portion of a substrate held by the carrier head, the plurality of independently controllable piezoelectric actuators. The polishing system is configured to control voltages applied to the plurality of piezoelectric actuators such that a location at which maximum pressure is applied to the backside edge portion of the substrate undergoes precession in conjunction with precession of the substrate in the carrier head.

[0011] 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, such as a rectangular grid. The plurality of piezoelectric actuators may be arranged in a plurality of arcuate zones, which may be arranged at uniform or non-uniform angular intervals around a central axis of the carrier head. The plurality of piezoelectric actuators may be arranged in a plurality of hexagonal or trapezoidal zones. The plurality of piezoelectric actuators may include at least one piezoelectric actuator for every 20° around a central axis of the carrier head. The plurality of piezoelectric actuators may include six or fewer actuators, for example consisting of three piezoelectric actuators.

[0012] The first flexible membrane may have a modulus of elasticity (Young's modulus) between 1 MPa and 20 MPa.

[0013] The carrier head may include a first flexible membrane secured to the housing to form one or more pressurizable chambers to apply pressure through a central membrane portion of the first flexible membrane to a center of the substrate surrounded by an edge portion of the substrate. The carrier head may include a second flexible membrane supported by the housing and extending beneath 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 beneath 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 center and edge portions of the substrate.

[0014] A circuit may be secured to the housing to receive a voltage on the voltage supply line and data on the data line and to control voltages applied to the plurality of piezoelectric actuators based on the data. The circuit may be configured to receive a frame of data from the controller on the data line, the data including one or more control values. The circuit may be configured to receive a frame of data including a sequence of control values ​​in the frame and to identify an actuator to which a control value in the sequence applies based on a position of the control value in the sequence. The circuit may be configured to receive a frame of data including a pair of control value and identification value and to identify an actuator to which the control value applies based on the identification value. The control value may represent a voltage to apply to the piezoelectric actuators.

[0015] Certain implementations may include one or more of the following advantages: Pressure may be applied to the substrate in a manner that varies both radially and angularly around the center of the substrate being polished. This allows for profile control to 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 across an area may be controlled by expanding and contracting the piezoelectric actuators to deform the membrane on top of the area. Thus, the polishing process of each area of ​​a layer on the substrate may be controlled independently and with fine definition. Furthermore, compared to using pressure chambers, using piezoelectric actuators allows for scaling to much more areas of control in a more feasible manner. In particular, fewer rotational connections are required, eliminating the need to scale the number of rotational connections to the number of piezoelectric actuators.

[0016] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0017] [Figure 1]1 is a schematic cross-sectional view of an embodiment of a polishing apparatus. [Figure 2A] 3 illustrates an example cross-sectional view of a portion of a carrier head, a substrate, and a polishing pad, showing a piezoelectric actuator within the carrier head. [Figure 2B] 1 shows a schematic bottom view of a carrier head with piezoelectric actuators arranged in a rectangular array. [Figure 2C] 1 shows an exemplary cross-sectional view of a hybrid carrier head including both piezoelectric and pressure chamber control zones. [Figure 2D] 1 shows a schematic bottom view of a hybrid carrier head with corresponding zones. [Figure 2E] A schematic bottom view of a carrier head with piezoelectric actuators arranged in a hexagonal array is shown. [Figure 2F] FIG. 1 shows a schematic bottom view of a carrier head with piezoelectric actuators arranged in a polar array. [Figure 3A] A top view of the polishing pad is shown, indicating where in situ measurements are taken on a first substrate. [Figure 3B] 1 shows a schematic top view of the distribution of locations where in-tu measurements are taken relative to a pixelate zone of a substrate. [Figure 4] 1 is a schematic diagram of a static formula for determining the pressure applied on a substrate based on a piezoelectric actuator displacement with an elastic membrane between the actuator and the substrate. [Diagram 5] FIG. 1 is a flow diagram illustrating an exemplary profile control process during polishing of a conductive layer having a non-uniform initial thickness. [Figure 6A] 1 shows an exemplary cross-sectional view of another embodiment of a hybrid carrier head including both multiple piezoelectric edge control zones and pressure chamber control zones. [Figure 6B] 6B shows a schematic bottom view of the hybrid carrier head of FIG. 6A with an exemplary pressure control scenario. [Figure 6C]A schematic bottom view of a hybrid carrier head including multiple piezoelectric edge control zones and one central pressure chamber control zone is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Due to variations in polishing rate among different regions of the substrate, different regions of the substrate may reach their target thickness at different times. On the one hand, different regions of the substrate may not reach the desired thickness if polishing of the regions is stopped at the same time. On the other hand, stopping polishing for different zones at different times may cause defects in the polishing apparatus or reduce throughput. Therefore, it is necessary to be able to control the pressure for different regions independently.

[0019] In an idealized process, due to the rotation of the carrier head and platen, the polishing rate on the substrate would be angularly symmetric about the axis of rotation of the substrate. However, in reality, the polishing process may introduce angular variations in the polishing rate. In addition, the substrate being polished may have a top layer whose initial thickness varies angularly, i.e., includes angular non-uniformity. Finally, in some manufacturing processes, it may be desirable to induce angular non-uniformity in the thickness of the layer being polished to compensate for non-uniformity in a later processing step, e.g., a deposition step. It remains a challenge to eliminate angular non-uniformity induced by the polishing process or when polishing a layer with an initial thickness with angular non-uniformity, or to intentionally introduce angular thickness variations when polishing a layer.

[0020] However, a carrier head using multiple piezoelectric actuators can address this issue: the piezoelectric actuators can be angularly distributed around the carrier head, and each piezoelectric actuator can be independently controlled, allowing angular non-uniformity to be reduced or intentionally introduced.

[0021] 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable, disk-shaped platen 120 on which a polishing pad 110 is positioned. The platen is operable to rotate about an axis 125. For example, a motor 121 can turn a drive shaft 124 to rotate the platen 120. The polishing pad 110 can be removably secured to the platen 120, for example, by a layer of adhesive. The polishing pad 110 can be a dual-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114.

[0022] The polishing apparatus 100 may include a mixed slurry / rinse arm 130. During polishing, the arm 130 is operable to dispense a polishing fluid 132, such as a polishing slurry, onto the polishing pad 110. Although only one slurry / rinse arm 130 is shown, additional nozzles, such as one or more dedicated slurry arms per carrier head, may be used. The polishing apparatus may also include a polishing pad conditioner that abrades the polishing pad 110 to maintain it in a consistent abrasive state.

[0023] 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 multiple zones on the substrate 10.

[0024] The carrier head 140 may include a housing 141 that may be connected to the drive shaft 152, the membrane 182, and a retaining ring 142 for holding the substrate 10 under the flexible membrane 182. The underside of the membrane 182 provides a mounting surface for the substrate 10. The membrane 182 may be made of an elastic material, for example, a rubber such as silicone rubber or neoprene. The Young's modulus of the membrane 182 may range from 1 to 20 MPa. Other materials, for example, hydrogels and foams, are permissible if they deform in the elastic range with a Young's modulus of 1 to 10 MPa and have a relatively high shear modulus but low adhesion to avoid "sticking" to the membrane. The membrane 182 may be translucent to be compatible with an optical in situ monitor system. The membrane 182 may be secured to the housing 141.

[0025] The carrier head 140 also includes a plurality of independently operable piezoelectric actuators 184 positioned above the membrane 182 and secured to a carrier plate 143. The carrier plate 143 may be provided by a portion of the housing 141. The piezoelectric actuators 184 are positioned to contact an upper surface of the membrane 182 for independently adjusting the pressure on the upper surface of the membrane 182. As shown in FIG. 1, five piezoelectric actuators 184a-184e (not individually numbered) are illustrated, although this number may be much higher, for example, between 20 and 100 actuators. Alternatively,

[0026] Circuitry 189, e.g., a circuit board having one or more elements such as a microcontroller, is secured to carrier head 140. For example, the circuitry may be mounted on top of housing 141 of carrier head 140. In another example, the circuitry may be mounted inside carrier head 140.

[0027] Circuitry 189 may receive voltage on voltage supply line 183 from voltage source 181. Circuitry 189 may also receive data over data line 186 from controller 190. Voltage supply line 183 and data line 186 may be routed through drive shaft 152 and rotating electrical union 156, e.g., slip rings, to fixed components of voltage source 181 and controller 190.

[0028] Additionally, the circuitry can independently control the voltage applied to each piezoelectric actuator based on the data through voltage lines 187. Data lines 186 can transfer multiple frames of data, with each frame of the multiple frames including data representing a pressure signal or equivalent voltage signal for one or more of the piezoelectric actuators. In some implementations, the frame of data transmitted by controller 190 includes a control value for each piezoelectric actuator, and circuitry 189 is configured to determine which control value is associated with each piezoelectric actuator by the order of the control values ​​within the frame. In some implementations, the frame of data transmitted by controller 190 includes both a control value and an identification value of the piezoelectric actuator to which the control value applies, and circuitry 189 is configured to determine the appropriate piezoelectric actuator for the control value based on the identification value.

[0029] Only two electrical lines, e.g., a voltage supply line 183 and a data line 186, need to be routed through the rotary electrical union 156. As a result, assembly can be simpler and more reliable than pressure actuators, which require rotary connections of multiple fluid lines, e.g., pneumatic air lines. Additionally, the number of piezoelectric actuators can be scaled up by appropriate modification of the data provided by the controller 190 and the functionality of the circuitry 189 to interpret the data, without the need to increase the number of rotary connections.

[0030] 2A and 2B respectively show an example cross-sectional view and a bottom view of an array 184c of piezoelectric actuators 184 in a carrier head 140. Each piezoelectric actuator 184 includes a layer 184a of piezoelectric material sandwiched between two electrodes 185a, 185b. To vertically displace the actuator, a voltage is applied between the two electrodes 185a and 185b. Also, one of the electrodes, e.g., the top electrode 185a, can be connected to ground. The other electrode, e.g., the bottom electrode 185b, can function as a control electrode to which a voltage is controllably applied by a circuit 189.

[0031] In some implementations, the top electrode 185a is a common ground electrode for all of the piezoelectric actuators 184. In this case, the top electrode 185a may straddle the substrate 10. The individual bottom electrodes 185b may be the same size as a segment of the piezoelectric layer actuator. In some implementations, the piezoelectric actuators 184 are of uniform size across the carrier plate 143.

[0032] In one embodiment, the piezoelectric actuator 184 includes an insulating plate 184d attached below the bottom electrode 185b. The insulating plate 184d need not have the same shape as the rest of the actuator 184, e.g., layer 184a. That is, the plate 184d can be a different shape and size than the piezoelectric layer 184a. For example, the insulating plate 184d can be larger (laterally) than the piezoelectric layer 184a. In addition, the insulating plate 184d can have different shapes and sizes such that the shape of the area on the membrane 182 to which pressure is applied by the piezoelectric actuator 184 can vary across the array 184c. The shape of the insulating plate 184d can be selected based on the desired shape for the zone on the substrate to which pressure is to be applied by the actuator. Alternatively, the entire piezoelectric actuator (e.g., the piezoelectric layer 184a and, if present, the insulating plate 184d) can be selected based on the desired shape for the zone on the substrate to which pressure is to be applied by the actuator.

[0033] In some implementations, multiple piezoelectric actuators 184 can be positioned above the same insulating plate 184d, in which case the same voltage signal can be applied to the piezoelectric actuators 184 above the same plate 184d, in which case the actuators 184 are relatively small compared to the area spanned by a single plate 184d.

[0034] Adjacent piezoelectric actuators 184 may be separated by a gap 184b. In some implementations, the gap between adjacent actuators 184 is uniform across the array 184c. The piezoelectric actuators may be positioned adjacent to one another across the membrane 182. The gap 184b separating each piezoelectric actuator, e.g., separating the insulating plates 184d, is small enough so that the pressure exerted by the membrane on the substrate is smoothed. The gap 184b may be in the range of 100 um to 1 mm.

[0035] The piezoelectric actuators 184 can be positioned at a number of different angular positions about the axis 159. In some implementations, the actuators 184 are arranged in a regular array, for example, a rectangular, hexagonal, or polar array.

[0036] 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.

[0037] Referring to FIG. 2F, as another example, the actuators may first be divided into concentric rings, and then each actuator in each ring spans a certain amount of arc length. The actuators in a given ring may have a uniform size and / or may be uniformly spaced around the ring. In some implementations, since the actuators are uniformly sized and uniformly spaced across the rings, there are more actuators in rings further away from the center of the carrier head compared to rings closer to the center of the carrier head. In some implementations, the actuators in different rings span the same central angle (degrees / radius), so that the actuators in rings further away from the center of the carrier head are longer. In some implementations, the actuators may become progressively narrower the further the ring is from the center of the carrier head. In some implementations, the actuators in a first ring may span a smaller angle (degrees / radius) than the actuators in a second ring closer to the center of the carrier head.

[0038] The particular shape of the piezoelectric actuators 184 may depend on the array. For example, the piezoelectric actuators 184 may be larger in size in a pie or trapezoid shape at the center of the substrate 10 while gradually decreasing in size in a bow shape towards the substrate edge. The total number of piezoelectric actuators 184 is determined by the cost of the piezoelectric material. For example, polishing heads using piezoelectric pressure control may each have a size of about 70 mm. 2 The piezoelectric actuator may comprise 100 piezoelectric actuators of size 100 mm.

[0039] In some implementations, the angular and radial placement of the piezoelectric actuators 184 about the central axis may be non-uniform. For example, if one or more regions within the substrate require finer control than the remaining regions, finer (smaller) piezoelectric actuators may be placed therein.

[0040] As shown in Figures 2B, 2E and 2F, in some implementations, the piezoelectric actuator spans the substrate 10, e.g., pressure applied to the substrate is controlled in all regions of the substrate entirely by the piezoelectric actuator 184. However, in some implementations, a hybrid approach can be used in which pressure in one region of the substrate is controlled by the piezoelectric actuator and pressure in another region of the substrate is controlled by a pressurized chamber. For example, the carrier head 140 can 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 pressures to associated zones 148a-148c on the flexible membrane 144 and thus on the substrate 10 (see Figure 2D). The zones include the center of the substrate 10.

[0041] Returning to FIG. 2C, a plurality of piezoelectric actuators 184 are disposed around the second flexible membrane 144 and apply pressure to the membrane 182 at the edge of the substrate 148d (see FIG. 2D). For example, the piezoelectric actuators 184 may be positioned at uniform angular intervals around the central axis 159. The piezoelectric actuators 184 may be relatively "high density" (e.g., 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, etc.).

[0042] 2C and 2D, the central zone 148a may be substantially circular, the remaining chamber zones 148b-148c may be concentric annular zones around the central zone 148a, and the piezoelectric zone 148d may be a concentric annular zone around the outermost chamber zone 148c. Although only three chamber zones and one piezoelectric zone are shown in FIGS. 2C and 2D, there may be two chamber zones, or four chamber zones, or more, and there may be two piezoelectric zones, or more than four piezoelectric zones outside the chamber zones. In FIGS. 2C and 2D, the piezoelectric zone 148d is plotted as a concentric ring on the edge portion of the substrate 10, but the piezoelectric zone may replace other chamber zones. For example, the central circular chamber zone may be replaced by a circular zone controlled by multiple arranged piezoelectric actuators. The use of a combination of pressure chambers and piezoelectric actuators may be evaluated by multiple factors. For example, the factors may be the total cost, efficiency, or accuracy of the polishing head 140. For example, a hybrid carrier head can be less costly than a carrier head that uses exclusively piezoelectric actuators, while still providing improved angular control of polishing rate at the edge of the substrate where angular non-uniformity is most likely to occur.

[0043] 6A and 6B, an exemplary hybrid carrier head 140 is shown that is similar to the carrier head shown in connection with FIGS. 2C and 2D. However, an edge control ring 202 is placed between the piezoelectric element 184 and the membrane 182 or substrate 10. The edge control ring may be more rigid than the membrane 182, for example, a hard plastic or thin metal ring. In addition, rather than a large number of closely spaced piezoelectric actuators around the periphery of the loading area, the hybrid carrier head 140 of FIGS. 6A and 6B includes a sufficient number of actuators to control both the vertical position and tilt of the edge control ring 202, for example, along one axis (in which case only two piezoelectric actuators would be required) or in two orthogonal axes (in which case only three piezoelectric actuators would be required). However, additional piezoelectric actuators may be included, in which case the piezoelectric actuators may be optionally used to deflect the edge control ring 202 into a desired shape. For example, the hybrid carrier head 140 may have six piezoelectric actuators. This would allow the edge control ring 202 to bend to six vertical positions to accommodate different heights at adjacent actuators. The piezoelectric actuators 184 may be evenly spaced around the center of the carrier head.

[0044] This exemplary embodiment is efficient and economical in reducing the angular variation because the controller 190 can control the pressure distribution over the edge region using only a few piezoelectric actuators 184 located at different locations above the piezoelectric zone. In particular, by controlling the extension of the piezoelectric actuators, the three piezoelectric actuators 184a-c can control the distortion or tilt of the edge control ring 202, thus adjusting the distribution of pressure on the substrate edge.

[0045] 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 and the magnitude of the highest and lowest pressure. That is, the selection of the vertical position of the three positions on the edge control ring 202 controls the distortion of the ring 202, with the highest pressure being applied where the ring 202 is at its lowest. The lowest pressure will be applied where the ring is at its highest, which is 180° from where the highest pressure is applied as long as the ring remains flat. The pressure should vary relatively uniformly along the circumference from the location of highest pressure to the location of lowest pressure.

[0046] The controller 190 can select a location 204 for maximum (or minimum) pressure and the magnitude of pressure applied at that location 204 to reduce edge non-uniformity. The controller 190 can adjust the orientation (i.e., θ) of the particular edge location 204 to apply the highest local pressure by varying the pressure applied at the three locations of the piezoelectric actuators 184a-c. For example, if actuator 184a has the largest extension, actuator 184b has the second largest extension, and actuator 184c has the smallest extension, then the location 204 will be located within the arc region between the two locations of the piezoelectric actuators 184a, 184b, as shown in FIG. 6B. The relative sizes of the extensions of the actuators 184a-c will set the maximum and minimum pressure magnitudes.

[0047] 6C, carrier head 140 includes one central pressure chamber control zone 148a and multiple piezoelectric actuators 184. Controller 190 can adjust the location where maximum or minimum pressure is applied and the magnitude of the maximum and minimum pressure when polishing substrate 10 to reduce angular variation at the substrate edge.

[0048] 1, carrier head 140 is suspended from a support structure 150, e.g., a carousel, and is connected by a drive shaft 152 to a carrier head rotation motor 154 such that the carrier head can rotate about axis 155. Optionally, carrier head 140 can oscillate, e.g., laterally on a slider on carousel 150, or by rotational oscillation of the carousel itself. In operation, the platen rotates about its central axis 125, and each carrier head rotates about its central axis 155 and translates laterally across the upper surface of the polishing pad.

[0049] The polishing apparatus can include an in-situ monitoring system 160 that can be used to determine whether to adjust the polishing rate or make adjustments to the polishing rate, as described below. In some implementations, the in-situ monitoring system 160 can include an optical monitoring system, such as a spectroscopic monitoring system. In other embodiments, the in-situ monitoring system 160 can include an eddy current monitoring system.

[0050] In one embodiment, the monitoring system 160 is an optical monitoring system. Optical access through the polishing pad can be provided by 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 transmitting signals between a remote controller 190, e.g., a computer, and the light source 162 and the light detector 164. One or more optical fibers 170 can be used to transmit light from the light source 162 to the optical access in the polishing pad and transmit light reflected from the substrate 10 to the detector 164.

[0051] The output of circuitry 166 may be a digital electronic signal that passes through a rotary coupler 129, e.g., a slip ring, in drive shaft 124 to a controller 190 for the optical monitoring system. Similarly, the light source may be turned on or off in response to a control command in a digital electronic signal that passes from controller 190 through rotary coupler 129 to optical monitoring system 160. Alternatively, circuitry 166 could communicate with controller 190 by wireless signals.

[0052] The light source 162 can be operable to emit white light, and the light detector 164 can be a spectrometer. As mentioned above, the light source 162 and the light detector 164 can be connected to a computing device, e.g., a controller 190, operable to control their operation and receive their signals. The computing device can include a microprocessor, e.g., a programmable computer, located near the polishing apparatus. With respect to control, the computing device can, for example, synchronize activation of the light source with the rotation of the platen 120.

[0053] In some implementations, the light source 162 and the detector 164 of the in-situ monitor system 160 are mounted within the platen 120 and rotate with it. In this case, the movement of the platen causes the sensor to scan across each substrate. In particular, as the platen 120 rotates, the controller 190 can cause the light source 162 to start a series of flashes just before each substrate 10 passes over the optical access and end the series of flashes just after each substrate 10 passes over the optical access. Alternatively, the computing device can cause the light source 162 to start a series of light emissions just before each substrate 10 passes over the optical access and end the series of light emissions just after each substrate 10 passes over the optical access. In either case, the signal from the detector can be integrated over a sampling period to generate a spectral measurement at the sampling frequency.

[0054] During operation, the controller 190 may receive, for example, a signal carrying information describing the spectrum of light received by the photodetector for a particular flash of the light source or detector time frame, which is thus the spectrum measured in situ during polishing.

[0055] 3A, if the detector is placed in the platen, as window 108 moves under the carrier head, due to the rotation of the platen (indicated by arrow 304), the optical monitoring system will make spectral measurements at a sampling frequency such that the spectral measurements are at locations 301 in an arc across substrate 10. For example, each point 301a-301k represents a location of a spectral measurement by the monitoring system on substrate 10 (the number of points is exemplary and more or less measurements than shown may be taken depending on the sampling frequency). Due to the rotation of carrier head 140 as window 108 sweeps, spectra are obtained from different radial and angular positions on substrate 10.

[0056] Thus, based on timing, motor encoder information, optical detection of the edges of the substrate and / or retaining ring, and optical detection or calculation of the precession of the substrate 10 relative to the retaining ring 142, for any given scan of the optical monitoring system across the substrate, the controller 190 can calculate both the radial position (relative to the center of the particular substrate 10 being scanned) and the angular position (relative to a reference angle of the particular substrate 10 being scanned) for each measured spectrum from the scan.

[0057] In many operating conditions, the precession rate of the substrate relative to the carrier head is slow enough that the controller 190 may have enough time to apply new pressure changes at specific angular regions on the substrate. Thus, in some situations, for example, when the precession rate of the substrate is less than 10° per minute, e.g., less than 5° per minute, the optical monitoring system can optionally ignore differences in the angular position of the substrate relative to the angular position of the carrier head and still accurately polish the substrate to have a desired post-polishing profile.

[0058] In situations where a non-uniform angular profile is desired for polishing the substrate, the monitor system can align the initial angular positions of the substrate and carrier head (e.g., based on a notch) and calculate the precession rate of the substrate based on the outer diameter of the substrate, the inner diameter of the retaining ring, and the rotational speed of the carrier head (e.g., revolutions per minute). Thus, the system can precisely vary the pressure applied to a target angular position on the substrate.

[0059] In some implementations, the controller 190 can adjust the pressure to reduce angular variations during polishing by compensating for the observed precessional velocity of the substrate 10. As an example related to FIG. 6B or 6C, the controller 190 can sequentially adjust the respective pressures applied at different locations (e.g., locations 184a-c) within the piezoelectric zone 148d to vary the angular position of the location 204 at which the highest (or lowest) effective local pressure is applied. The orientation (e.g., θ) of a particular location 204 can be changed at a particular angular velocity to compensate for the precessional velocity of the substrate 10 relative to the carrier head 140, such that the effective local pressure applied to a particular region 204 within the substrate 10 appears stationary relative to the substrate 10, as if the substrate 10 were not undergoing precession.

[0060] The polishing system may also include a rotational position sensor, such as a flange attached to the edge of the platen that will pass a stationary optical interrupter, to provide additional data for determining which substrate and the position on the substrate of the measured spectrum. In this way, the controller may associate the various measured spectra with zones 188 or 148d (see FIGS. 2B and 2D) on the substrate 10. In some implementations, the measurement time of the spectrum may be used as a proxy for precise calculation of the radial position. For angular position, the motor encoder for the motor 154 may provide the angular position of the drive shaft 152 and carrier head 140, which, in conjunction with the angular position of the platen provided by the encoder for the motor 121 or the rotary optical interrupter, may be used to determine the angular position of each measurement.

[0061] As an example, referring to FIG. 3B, in one rotation of the platen, spectra corresponding to different locations 303a-303o are collected by the photodetector 164. Based on the radial and angular positions of the locations 303a-303o, each spectrum collected at the locations 303a-303o is associated with a piezoelectric zone 188a-188o. Although this example shows that each zone is associated with the same number of spectra, the zones may also be associated with different numbers of spectra based on in situ measurements. The number of spectra associated with each zone may vary with each rotation of the platen. Of course, the number of locations given above is merely exemplary, as the actual number of spectra associated with each zone will depend at least on the sampling rate, the rotational speed of the platen, and the radial width of each zone. Without being limited to any particular theory, it is believed that the spectrum of light reflected from the substrate 10 evolves as polishing progresses (e.g., over multiple rotations of the platen rather than during a single sweep across the substrate) due to changes in the thickness of the outermost layer, thus resulting in a sequence of time-varying spectra. Furthermore, a particular spectrum is exhibited by a particular thickness of the layer stack.

[0062] For each measured spectrum, the controller 190 can calculate a characteristic value. The characteristic value is typically the thickness of the outer layer, but can be a relevant characteristic such as the thickness removed. In addition, the characteristic value can be a physical property other than thickness, for example, metal line resistance. In addition, the characteristic value can be a more general representation of the progress of the substrate through the polishing process (e.g., an index value representing the time at which the spectrum is expected to be observed in the polishing process according to a predetermined progress, or the number of platen rotations).

[0063] One technique for calculating the characteristic value is to identify, for each measured spectrum, a matching reference spectrum from a library of reference spectra. Each reference spectrum in the library may have an associated characteristic value, for example a thickness value or index value indicating the time or number of platen rotations during which the reference spectrum is expected to occur. By determining the associated characteristic value of the matching reference spectrum, the characteristic value can be generated. This technique is described in U.S. Patent Application Publication No. 2010-0217430.

[0064] Another technique is to fit an optical model to the measured spectrum. In particular, the parameters of the optical model are optimized to provide a best fit of the model to the measured spectrum. The parameter values ​​generated for the measured spectrum generate the characteristic values. This technique is described in US Patent Application Publication No. 2013-0237128. Possible input parameters for the optical model can include the thickness, refractive index, and / or extinction coefficient of each of the layers, the spacing and / or width of the repeating features on the substrate.

[0065] The calculation of the difference between the power spectrum and the measured spectrum can be the sum of the absolute differences between the measured spectrum and the power spectrum across the spectrum, or the sum of the squared differences between the measured spectrum and the reference spectrum. Other techniques for calculating the difference can be used, for example, calculating the cross-correlation between the measured spectrum and the power spectrum.

[0066] Another technique is to analyze the properties of spectral features from the 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 the property value. This technique is described in U.S. Patent Application Publication No. 2011-0256805.

[0067] Pressure control based on in situ measurements Generally, a desired thickness profile will be achieved for the substrate at the end of the polishing process (or at an endpoint where the polishing process stops). The desired thickness profile may include the same predetermined thickness for all zones of the substrate 10, or different predetermined thicknesses for different zones of the substrate 10. When multiple substrates having non-uniform initial thicknesses are polished simultaneously, the multiple substrates may have the same desired thickness profile or different desired thickness profiles.

[0068] In some embodiments, to keep the measured thickness relationship between the control zone and the reference zone similar or identical to the thickness relationship indicated by the desired thickness profile at the endpoint time throughout the polishing process, the controller and / or computer can schedule to adjust the polishing rate of the control zone 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 situations, the adjustment can be zero at the pre-scheduled adjustment time. In other embodiments, the adjustment can be made at a rate determined in situ. For example, if the measured thicknesses of different zones differ significantly from the desired thickness relationship, the controller and / or computer can decide to make frequent adjustments to the polishing rate.

[0069] During polishing, the pressure applied to each region of the layer on the substrate is due to the deformation of the membrane 182, which is controlled by the vertical displacement of the corresponding piezoelectric actuator above that region. By calibrating 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 through Hooke's law. As shown in FIG. 4, the static formula 403 can output a pressure type amount P1 applied on a zone in the layer given an actuator displacement type amount D1 as input, and vice versa. Although shown as a straight line, the formula function can be a nonlinear curve when the membrane is nonlinearly elastic. This formula can be used as a sanity check to know in advance what range of pressures can be applied to multiple zones in the layer, given the membrane material properties and the range of motion of the piezoelectric actuator. Furthermore, a series of look-up tables can be used here as well. For example, given a target pressure of 2 Psi to apply on a control zone in a layer, the desired piezoelectric actuator travel distance can be looked up as, for example, 14 um downwards if the Young's modulus is 2 MPa and the membrane is 2 mm thick. As another example, if the piezoelectric actuator travel distance is fixed at 5 um downwards for a voltage change, the actual pressure applied on the control zone can be looked up as, for example, 1.8 Psi if the membrane's Young's modulus is 5 MPa and the membrane is 2 mm thick. As another example, instead of using the actuator displacement and membrane thickness, the membrane deformation strain due to the compressive motion of the piezoelectric actuator can be employed to create another lookup table.

[0070] FIG. 5 shows a flow diagram of a control method using piezoelectric actuators (500) that includes determining an expected thickness of each control zone at a projected time (502), determining a measured thickness of the control zone (504), determining an adjustment to an applied pressure on the control zone (506), determining an adjustment to a voltage applied to a piezoelectric actuator above the control zone (508), and applying an adjusted voltage to actuate the piezoelectric actuator to change the pressure applied to the membrane above the control zone (510), where steps 502-506 can be accomplished using an in situ monitor system and controller, and step 510 can be performed on circuit 189. A signal representing the desired pressure (or applied voltage) for each control zone will be transferred from monitor system 160 to circuit 189. As shown in FIG. 6, the control method using piezoelectric actuators is fast enough to adjust the pressure given a current frame of signal data before the next frame of signal data is received.

[0071] The term substrate as used herein may include, for example, a product substrate (e.g., including multiple memory or processor dies), a test substrate, a bare substrate, and a gating substrate. The substrate may be at various stages of integrated circuit manufacturing, for example, the substrate may be a bare wafer, or the substrate may include one or more deposited and / or patterned layers. The term substrate may include a circular plate and a rectangular slab.

[0072] The polishing apparatus and method described above can be applied to a variety of polishing systems. Either the polishing pad or the carrier head, or both, can move to provide relative motion between the polishing surface and the substrate. For example, the platen can orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad fixed to the platen. Some aspects of the endpoint detection system can be applicable to linear polishing systems, for example, where the polishing pad is a continuous or linearly moving reel-to-reel belt. The polishing layer can be a standard (e.g., polyurethane with or without fillers) abrasive material, a soft material, or a fixed-abrasive material. Although the terminology of relative orientation is used, it should be understood that the polishing surface and the substrate can be held in a vertical orientation or in some other orientation.

[0073] Although the above description has focused on the control of a chemical mechanical polishing system, the in-sequence metrology station may also be applicable to other types of substrate processing systems, such as etch or deposition systems.

[0074] Embodiments of the subject matter described herein, such as the control system for functional operations, can be implemented in digital electronic circuitry, tangibly embodied computer software or firmware, computer hardware including the structures disclosed herein and their structural equivalents, or a combination of one or more of them. Embodiments of the subject matter described herein 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 or for controlling the operation of a data processing apparatus. Alternatively or additionally, the program instructions can be encoded in an artificially generated propagated signal, e.g., a computer-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to an appropriate receiving device for execution by the data processing apparatus. The computer storage medium can be a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory device, or a combination of one or more of these.

[0075] The term "data processing apparatus" refers to data processing hardware and encompasses all kinds of apparatus, devices, and machines for processing data, including, for example, a programmable digital processor, a digital computer, or multiple digital processors or computers. An apparatus may be or may further include special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). An apparatus may optionally include, in addition to hardware, code that creates an environment for the execution of computer programs, such as code consisting of processor firmware, a protocol stack, a database management system, an operating system, or any combination of one or more of these.

[0076] 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 type of programming language, including compiled, interpreted, declarative, or procedural languages, and may be deployed as a stand-alone program or in any form including modules, components, subroutines, or other units suitable for use in a computing environment. A computer program may correspond to a file in a file system, but need not. A program may be stored in part of a file that holds 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., files that store one or more modules, subprograms, or code portions. A computer program may be deployed to run on one computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a data communication network.

[0077] The processes and logic flows described herein can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data to generate output. The processes and logic flows can also be performed by special purpose logic circuits, such as FPGAs (field programmable gate arrays) or ASICs (application specific integrated circuits), and the devices can also be implemented as special purpose logic circuits. When one or more computer systems are "configured" to perform a particular operation or function, it means that the system has installed thereon software, firmware, hardware, or a combination thereof that, during operation, causes the system to perform the operation or function. When one or more computer programs are configured to perform a particular operation or function, it means that one or more programs contain instructions that, when executed by a data processing device, cause the device to perform the operation or function.

[0078] A computer suitable for executing a computer program may be based on, for example, a general-purpose or special-purpose microprocessor, or both, or any other type of central processing unit. In general, the central processing unit will receive instructions and data from a read-only memory, or a random access memory, or both. The essential elements of a computer are a central processing unit for implementing or executing instructions, and one or more memory devices for storing instructions and data. In general, a computer will also include one or more mass storage devices, such as magnetic disks, magneto-optical disks, or optical disks, for storing data, or be operatively coupled to receive data, or transmit data, or both. However, a computer need not have the above devices. Furthermore, a computer can be embedded in another device, such as a mobile phone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a global positioning system (GPS) receiver, or a portable storage device, such as a universal serial bus (USB) flash drive, to name just a few.

[0079] Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including, by way of 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 may be supplemented by, or incorporated in, special purpose logic circuitry.

[0080] The control of the various systems and processes described herein, or portions thereof, may be implemented in a computer program product that is stored on one or more non-transitory computer-readable storage media and includes instructions executable on one or more processing devices. The systems described herein, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing devices and memory that store executable instructions to perform the operations described herein.

[0081] Although the present specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or what may be claimed, but rather as descriptions of features that may be specific to certain embodiments of a particular invention. Certain features described in the present specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in a particular combination and may even initially be claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and the claimed combination may also be subject to subcombinations or various subcombinations.

[0082] Similarly, although steps are depicted in the figures in a particular order, this should not be understood as requiring such steps to be performed in the particular order shown, or in sequential order, or that all of the illustrated steps be performed, to achieve desired results. In certain situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system modules and components in the above embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products.

[0083] Specific embodiments of the present subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims may be performed in a different order and still achieve desirable results. By way of example, the processes illustrated in the accompanying figures do not necessarily require the particular order illustrated, or order to occur, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.

[0084] Other embodiments are within the scope of the following claims.

Claims

1. 1. A carrier head for holding a substrate in a polishing system, comprising: a housing including a carrier plate; a first flexible membrane secured to the housing, the first flexible membrane having an upper surface and a lower surface providing a substrate mounting surface; a plurality of independently operable piezoelectric actuators secured to the carrier plate and positioned above the first flexible membrane to provide an independently adjustable compressive pressure to the upper surface of the first flexible membrane, the plurality of independently operable piezoelectric actuators being disposed at different angular positions about a central axis of the carrier head; a second flexible membrane secured to the housing to form a pressurizable chamber; and an outer surface of the second flexible membrane is positioned to contact the top surface of the first flexible membrane and to apply pressure at a central portion of the substrate mounting surface, and the plurality of independently operable piezoelectric actuators are disposed about a periphery of the second flexible membrane to apply pressure at edge portions of the substrate mounting surface surrounding the central portion. A carrier head, wherein pressure from the pressurizable chamber is applied to a center of the substrate through a central membrane portion of the second flexible membrane, the central membrane portion being located only radially inward of the plurality of independently operable piezoelectric actuators.

2. The carrier head of claim 1 , wherein the plurality of piezoelectric actuators are arranged in a plurality of arcuate zones.

3. A drive shaft; 1. A carrier head for holding a substrate in a polishing system, comprising: a housing fixed to and movable by the drive shaft, the housing including a carrier plate; a plurality of independently operable piezoelectric actuators secured to the carrier plate for independently adjusting pressure on a substrate held by the carrier head; and A circuit fixed to the housing A carrier head including: A motor for rotating the drive shaft; Slip ring and A controller; voltage supply lines and data lines connecting the controller to the circuit through the slip ring; A polishing assembly, wherein the circuitry is configured to receive a voltage on a voltage supply line, receive data including one or more control values ​​on a data line, and control pressure on the substrate by controlling a voltage applied to the multiple independently operable piezoelectric actuators based on the control value from the data.

4. 1. A carrier head for holding a substrate in a polishing system, comprising: Housing and a second flexible membrane secured to the housing and defining one or more pressurizable chambers for applying pressure to a center portion of a substrate through a central membrane portion of the second flexible membrane; a plurality of independently operable piezoelectric actuators supported by the housing, the plurality of independently operable piezoelectric actuators positioned radially outward of the central membrane portion and at different angular positions for independently adjusting pressure on a plurality of angular zones within an annular outer region of the substrate surrounding the central portion of the substrate; the central membrane portion provides a mounting surface for the central portion of the substrate; the central membrane portion through which pressure from the one or more pressurizable chambers is applied is located only radially inward of the plurality of independently operable piezoelectric actuators; Career head.

5. The carrier head of claim 4 , wherein the plurality of independently operable piezoelectric actuators comprises at least one piezoelectric actuator every 30° about a central axis of the carrier head.

6. 5. The carrier head of claim 4, wherein an annular outer portion of the second flexible membrane extends beneath the multiple independently operable piezoelectric actuators such that the multiple independently operable piezoelectric actuators provide independently adjustable compressive pressures on an upper surface of the annular outer portion of the second flexible membrane, the annular outer portion of the second flexible membrane providing a mounting surface for an outer portion of the substrate.

7. 5. The carrier head of claim 4, comprising a first flexible membrane supported by the housing and extending beneath the plurality of independently operable piezoelectric actuators such that the plurality of independently operable piezoelectric actuators provide independently adjustable compressive pressures on an upper surface of the first flexible membrane.

8. 8. The carrier head of claim 7, wherein the first flexible membrane extends below the second flexible membrane such that the second flexible membrane controls a compressive pressure on the top surface of the first flexible membrane, and the first flexible membrane provides a mounting surface for the center and the annular outer region of the substrate.

9. The carrier head of claim 7 , wherein the central membrane portion provides a mounting surface for the central portion of the substrate.

10. 1. A carrier head for holding a substrate in a polishing system, comprising: Housing and a second flexible membrane secured to the housing to form one or more pressurizable chambers, the second flexible membrane having a lower surface providing a substrate mounting surface at a central portion of the substrate; a plurality of independently operable piezoelectric actuators supported by the housing, the plurality of independently operable piezoelectric actuators positioned radially outward of the second flexible membrane and at different angular positions about a central axis of the carrier head; an edge control ring that is stiffer than the second flexible membrane, the edge control ring being coupled to the plurality of independently operable piezoelectric actuators such that the plurality of independently operable piezoelectric actuators control an overall tilt of the edge control ring relative to the housing by controlling an extension of the plurality of independently operable piezoelectric actuators, the edge control ring being positioned such that the edge control ring applies pressure to an annular region on the substrate surrounding the central portion of the substrate. Career head.

11. 11. The carrier head of claim 10, comprising a first flexible membrane, the first flexible membrane supported by the housing and extending below the edge control ring such that the edge control ring provides an adjustable compressive pressure on an upper surface of the first flexible membrane.

12. 12. The carrier head of claim 11, wherein the first flexible membrane extends below the second flexible membrane such that the second flexible membrane controls a compressive pressure on the top surface of the first flexible membrane, and the first flexible membrane provides a mounting surface for the central portion and annular outer region of the substrate.

13. The carrier head of claim 10 , wherein a central membrane portion provides a mounting surface for a central portion of the substrate.

14. a platen for supporting the polishing pad; A drive shaft; 1. A carrier head for holding a substrate in a polishing system, comprising: a housing fixed to the drive shaft 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 backside of a substrate held by the carrier head, the plurality of independently operable piezoelectric actuators being disposed at different angular positions about a central axis of the carrier head and being independently controllable; A carrier head, a control system configured to control voltages applied to the plurality of independently operable piezoelectric actuators to thereby control the pressure on the edge portion, and to vary a location at which maximum pressure is applied to the edge portion of the back surface of the substrate over time in conjunction with precession of the substrate within the carrier head. Polishing system.

15. 15. The polishing system of claim 14, wherein the plurality of independently operable piezoelectric actuators comprises at least one piezoelectric actuator every 30 degrees about a central axis of the carrier head.

16. 15. The polishing system of claim 14, wherein the carrier head includes an edge control ring having greater rigidity than the first flexible membrane, the edge control ring being coupled to the plurality of independently operable piezoelectric actuators such that the plurality of independently operable piezoelectric actuators control the tilt of the edge control ring relative to the housing, and the edge control ring is positioned to apply pressure to the edge portion of the substrate.

Images