Control of carrier head sweep and platform shape

Abstract

A controller of the chemical mechanical polishing system is configured to cause the carrier head to sweep over the polishing pad according to the sweep profile. The controller is also configured to select values of the plurality of control parameters so as to minimize a difference between the target removal profile and the expected removal profile. The plurality of control parameters includes a plurality of dwell time parameters. A relationship between a plurality of control parameters and a removal rate is stored in a data structure representing a first matrix comprising a plurality of rows comprising a row for each dwell time parameter and a column for each position on the substrate represented in an expected removal profile and as part of selecting the value, the controller is configured to calculate an expected removal profile by multiplying the first matrix by a second matrix representing a control parameter value.

Description

Technical Field

[0001] The present disclosure relates to chemical mechanical polishing and, more particularly, to controlling the platform shape in chemical mechanical polishing in combination with carrier head sweeping. Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductor, or insulating layers on a silicon wafer. 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. For example, a conductive filler layer may be deposited on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, portions of the metallization layer remaining between the raised patterns of the insulating layer form vias, plugs, and wiring that provide conductive paths between thin film circuits on the substrate. For other applications (such as oxide polishing), the filler layer is planarized, for example, by polishing for a predetermined time period to leave a portion of the filler layer on the non-planar surface. Additionally, photolithography typically requires planarization of the substrate surface.

[0003] One problem in CMP is the variation in the material removal rate of the substrate and the subsequent thickness profile. Variations in slurry distribution, polishing pad condition, the relative speed between the polishing pad and the substrate, and the non-uniform loading of the carrier head's pressurized chamber on the substrate can result in variations in the material removal rate. These variations, along with variations in the initial thickness of the substrate layer, result in variations in the final substrate layer thickness, particularly near the edges of the substrate. Summary of the Invention

[0004] In one aspect, a chemical mechanical polishing apparatus has a platform for supporting a polishing pad. The platform has a central portion with an upper surface and an annular flexure surrounding or surrounded by the central portion and having a top surface, the annular flexure having a first edge adjacent and coplanar with the upper surface and a second edge remote from the central portion. An actuator is arranged to bend the annular flexure to modify a vertical position of the second edge of the annular flexure relative to the central portion. A carrier head holds a surface of a substrate against the polishing pad. A motor generates relative motion between the platform and the carrier head to polish a coating on the substrate. A controller is configured to select values of a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters including a first parameter representing a degree of deflection of the flexure. A relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix, the first matrix including a plurality of rows including a row for the degree of deflection of the flexure and columns for each position on the substrate represented in the expected removal profile, and wherein as part of the selected values, the controller is configured to calculate the expected removal profile by multiplying the first matrix by a second matrix representing values of the control parameters.

[0005] In another aspect, a chemical mechanical polishing apparatus has a platform for supporting a polishing pad, a carrier head for holding a surface of a substrate against the polishing pad, a motor for controlling a lateral position of the carrier head on the polishing pad, and a controller. The controller is configured to cause the motor to sweep the carrier head on the polishing pad according to a sweep profile. The controller is also configured to select values of a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters including a plurality of dwell time parameters, wherein each respective dwell time parameter of the plurality of dwell time parameters represents an amount of time the carrier head spends on a different respective area of the polishing pad. A relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix, the first matrix including a plurality of rows including a row for each dwell time parameter and columns for each position on the substrate represented in the expected removal profile, and as part of the selected values, the controller is configured to calculate the expected removal profile by multiplying the first matrix by a second matrix representing values of the control parameters.

[0006] Specific implementations can achieve the objectives described in this specification to realize one or more of the following technical advantages.

[0007] Radial-specific thickness profile correction can be performed, and non-uniformity within the wafer and wafer-to-wafer non-uniformity can be reduced. Material removal can compensate for thickness profile non-uniformity in the edge region induced after the primary polishing step, or correct the incoming substrate film thickness profile before undergoing preliminary polishing. The amount of flexure of the annular flexure member (e.g., displacement from a planar configuration) causes a modification of the pressure applied to the substrate surface rather than through the backside of the substrate, thereby increasing the polishing position specificity during position-specific polishing.

[0008] The substrate dwell time as a function of the radial position can be an additional adjustable parameter, which permits greater flexibility in choosing the values of other parameters (e.g., carrier head pressure and platform offset displacement). The "Preston matrix" used to calculate the carrier head pressure can be modified to include the relationship between the amount of flexure (e.g., displacement from a planar configuration) and the polishing profile. Similarly, the Preston matrix can include the relationship between the dwell time at different radial positions and the polishing profile. This permits the execution of an optimization algorithm to select the amount of flexure and / or the dwell time in order to provide a desired polishing profile.

[0009] Details of one or more embodiments are set forth in the accompanying drawings and the following description. Other aspects, features, and advantages will be apparent from the description and drawings and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic cross-sectional view illustrating an example of a polishing apparatus having an optical monitoring system and two annular flexure members.

[0011] Figure 2A and Figure 2B A schematic top view illustrating a polishing pad including inner and outer regions with increased polishing rates.

[0012] Figure 3A and Figure 3B A schematic cross-sectional view illustrating an example of a polishing apparatus having a lower platform and an upper platform divided into multiple regions to achieve a target polish.

[0013] Figure 4A A schematic top view illustrating multiple annular regions on a polishing pad for setting the dwell time.

[0014] Figure 4B A schematic graph illustrating a carrier head sweep profile.

[0015] Figure 5 A schematic diagram illustrating an example computing device.

[0016] In the figures, like component symbols indicate like components. DETAILED DESCRIPTION

[0017] In some chemical mechanical polishing operations, a portion of the substrate may be under-polished or over-polished. In particular, at or near the edge of the substrate, the substrate tends to be over-polished or under-polished. One technique for addressing such polishing non-uniformity is to have multiple controllable pressurizable chambers in the carrier head. However, the pressure applied from the back side of the substrate tends to "spread", making it difficult to compensate for radial local polishing non-uniformity. Another technique is to transfer the substrate to a separate "finishing" tool, e.g., to perform edge correction. However, the additional tool takes up valuable space in the clean room and may adversely affect throughput.

[0018] An alternative approach is to have the platform with one or more independently controllable annular flexures that can be deflected, e.g., upward or downward. A portion of the substrate is then moved over the deflected flexure, which results in an increase or decrease in the pressure between the polishing pad and the substrate at that portion and thus achieves the radial target polishing of the edge portion of the substrate.

[0019] Assuming a portion of the platform is deflectable, the effect on polishing will depend on the radial position of the substrate and the degree of deflection. Thus, some technique is needed to select the radial position of the substrate and the degree of deflection. To address this situation, a "Preston matrix" can be used to calculate the expected polishing profile as a function of the values of the control parameters. The dwell time and degree of deflection of the substrate at each of the multiple positions can be considered as control parameters that are part of the Preston matrix. This permits the execution of an optimization algorithm to select the amount of flexure and / or dwell time in order to provide the desired polishing profile.

[0020] Figure 1 A polishing system 20 is shown that can be used to polish a substrate 10. The polishing system 20 includes a rotatable platform 24, and a main polishing pad 30 is located on the rotatable platform 24. The platform can be used to rotate about a rotation axis 25. For example, a motor 21 can rotationally drive a drive shaft 22 to rotate the platform 24 (indicated by arrow B in Figure 2A and Figure 2B ). In some implementations, the platform 24 includes a central portion 26 that is configured to provide an annular upper surface 28 to support the main polishing pad 30.

[0021] The main polishing pad 30 can be fastened to the upper surface 28 of the central portion 26 of the platform 24, e.g., by an adhesive layer. The main polishing pad 30 can be removed and replaced when worn. The main polishing pad 30 can be a two-layer polishing pad having an outer polishing layer 32 (with a polishing surface) and a softer backing layer 34.

[0022] The polishing system 20 may include a polishing liquid delivery arm 82 and / or a pad cleaning system (such as a rinse fluid delivery arm). During polishing, the arm 82 may be used to dispense a polishing liquid 80, such as a slurry having abrasive particles. In some implementations, the polishing system 20 includes a combined slurry / rinse arm. Alternatively, the polishing system may include a port in the platform that may be used to dispense the polishing liquid 80 onto the primary polishing pad 30. The polishing system 20 may also include a conditioner system 40 having a rotatable conditioner head 42 that may include an abrasive lower surface (e.g., on a removable conditioning disk) to condition the polishing surface 36 of the primary polishing pad 30.

[0023] The polishing system 20 includes a carrier head 70 that can be used to hold the substrate 10 against the primary polishing pad 30. The carrier head 70 is suspended from a support structure 72 (e.g., a turntable or track) and is connected to a carrier head rotation motor 76 via a carrier drive shaft 74 so that the carrier head can rotate about an axis 71. In addition, an actuator 78 can cause the carrier head 70 to oscillate laterally on the polishing pad, for example, by moving in radial slots in the turntable when driven by an actuator (e.g., a linear actuator), by rotating the turntable when driven by an actuator (e.g., a motor), or moving back and forth along the track when driven by an actuator. In operation, the platform 24 rotates about its central rotation axis 25, and the carrier head rotates about its central axis 71 and translates laterally across the top surface of the polishing pad.

[0024] The carrier head 70 may include a retaining ring 73 to secure the substrate 10 beneath the flexible membrane 144. The carrier head 70 also includes one or more independently controllable pressurizable chambers (e.g., three chambers 77a to 77c) defined by the membrane that can apply independently controllable pressure to associated areas on the flexible membrane 144 and, in turn, to the substrate 10. Although only the chambers 77a to 77c are shown for ease of illustration, the carrier head 70 may include a retaining ring 73 to secure the substrate 10 beneath the flexible membrane 144. Figure 1 Three chambers are shown in FIG, but there may be one or two chambers, or four or more chambers, for example, five chambers.

[0025] A controller 90 (such as a programmable computer) is connected to the motors 21, 76 to control the rotational rates of the platform 24 and the carrier head 70, and to the actuator 78 to control the radial position of the carrier head on the platform 24. For example, each motor may include an encoder that measures the rotational rate of the associated drive shaft. Feedback control circuitry (which may be in the motor itself, in part of the controller, or in a separate circuit) receives the measured rotational rate from the encoder and adjusts the current supplied to the motor to ensure that the rotational rate of the drive shaft matches the rotational rate received from the controller.

[0026] The controller can also control other components of the polishing system, such as controlling a pressure regulator to control the pressure in chambers 77a to 77c, or controlling a pump to control the flow rate of the polishing liquid.

[0027] The polishing system 20 also includes at least one annular flexure 50 that is fastened to the platen 24 and rotates therewith. A portion of the polishing pad 30 supported on the platen 24 extends over the flexure 50. The flexure 50 can be deformed by at least one or more actuators 52. In particular, the flexure 50 and the actuator 52 can be used to flex the flexure 50 along an arc 15 (see Figure 2A ) that at least covers the entire portion of the substrate on the flexure. In some implementations, the flexure 50 is configured and the actuator is positioned such that the flexure 50 flexes along the entire circumference of the flexure 50. This configuration can be mechanically arranged more simply and reliably compared to the deformation of the angularly limited portion of the flexure 50.

[0028] The polishing system 20 can include an annular flexure 50a that projects outward from the outer edge of the platen 24. Alternatively, if the platen 24 includes an annular support surface 28, the polishing system can include an annular flexure 50b that projects inward from the inner edge of the annular platen 24. Alternatively, there may be two flexures, e.g., flexure 50a and flexure 50b, one for the outer edge and one for the inner edge of the platen 24.

[0029] The polishing pad 30 extends onto the flexure 50a and / or the flexure 50b. In the case where the polishing system includes an inwardly projecting annular flexure 50b, the polishing pad 30 can be annular and have pores 38 aligned with the grooves 27 in the platen to permit vertical movement of the flexure 50b. In the case where the polishing system includes only an outwardly projecting annular flexure 50a, the polishing pad 30 can be circular (not annular in this context).

[0030] When the annular flexure 50 flexes upward, the radially restricted portion of the polishing pad 30 is pushed upward. If a portion of the substrate 10 is present on the flexure, the pressure against that portion will increase. Conversely, when the annular flexure 50 flexes downward, the radially restricted portion of the polishing pad 30 is pushed downward. If a portion of the substrate 10 is present on the flexure, the pressure against that portion will decrease. As used herein, the terms "upward" and "downward" are with reference to Figure 1 the orientation. Upward represents the direction from the platen 24 to the polishing pad 30 to the substrate 10, while downward represents the opposite direction; in operation, the polishing surface can be vertically oriented or some other orientation relative to gravity.

[0031] The annular flexure member 50 extends from the outer edge of the platform 24 a distance within the range of from 5% to 20% (e.g., from 5% to 15%, from 5% to 10%, from 10% to 15%, or from 15% to 20%) of the outer diameter of the polishing pad 30. The outer edge of the polishing pad 30 may be aligned with the outer edge of the outer flexure member 50a, or set back from or extend beyond that outer edge by up to about 1 inch. For the annular polishing pad 30, the inner edge of the polishing pad 30 may be aligned with the inner edge of the inner flexure member 50b, or set back from or extend beyond that inner edge by up to about 1 inch.

[0032] As Figure 1 shown in the example of, the polishing system 20 includes an annular flexure member 50 that projects radially outward from the central portion 26 of the platform 24. If not deflected or deformed, the top surface of the annular flexure member 50 is generally coplanar with the upper surface 28 of the platform 24. The inner edge of the annular flexure member 50 is fastened to the platform 24 and can rotate together with the platform 24. Thus, when the drive shaft 22 rotates the platform 24, the annular flexure member 50 rotates together with the platform 24 (and thus the annular flexure member 50 does not require a separate motor for rotation).

[0033] The annular flexure member 50 is connected to at least one actuator 52 that is arranged to be supported by the central portion 26 of the platform 24. In some implementations (such as Figure 1 the example of), the actuator 52 is arranged to provide a generally lateral force on the flange 54. The flange 54 projects downward from the outer edge of the annular flexure member 50. In these implementations, the actuator 52 provides an inward force (e.g., toward the axis of rotation 25) or an outward force (e.g., away from the axis of rotation 25). The system 20 includes a sufficient number of actuators 52 to control the outer edge of the annular flexure member 50 around the circumference of the platform 24. The system 20 may include two or more, four or more, or eight or more actuators 52. In the case of multiple actuators, the actuators may be spaced at uniform angular intervals about the axis of rotation 25 of the platform 24.

[0034] When the actuator 52 provides an inward force, the outer edge of the upper surface of the annular flexure member 50 deflects downward. Conversely, when the actuator 52 provides an outward force, the outer edge of the upper surface of the annular flexure member 50 deflects upward. The controller 90 controls the actuator 52 to adjust the force on the flange 54 to control the outer edge of the upper surface of the annular flexure member 50 to deflect upward or downward.

[0035] The system can be configured such that the annular flexure 50 flexes along the entire circumference of the flexure 50. In some implementations, there is a single actuator, and the flexure 50 is rigid enough in the angular direction such that pressure from the actuator causes the flexure 50 to flex along the entire circumference in a limited region. In some implementations, there are multiple actuators, and the actuators are electrically coupled to a single control signal such that all the actuators are driven together. In some implementations, each of the actuators 52 is individually controlled by the controller 90, but the controller 90 controls all the actuators 52 to cause the annular flexure 50 to flex along the entire circumference.

[0036] In many polishing processes, due to reduced pressure control in the outermost radial regions of the three chambers 77a to 77c, the outer edges of the substrate 10 are under-polished, resulting in an increased layer thickness at the edges of the substrate 10. As such, the annular flexure 50 bends upward and is biased against the bottom surface of the substrate 10 to increase the pressure between the substrate 10 and the polishing pad 30.

[0037] The controller 90 operates the actuator 52 to change the position of the outer edge of the annular flexure 50 upward or downward by a distance. In some implementations, the distance ranges from 1 micron to 300 microns (e.g., 1 micron to 250 microns, 10 microns to 250 microns, 50 microns to 250 microns, 10 microns to 50 microns, or 1 micron to 50 microns).

[0038] In some implementations, the annular platform 24 includes a groove 27 at the center of the platform 24 that extends partially through the thickness of the platform 24 and is aligned with the axis of rotation 25. For example, the groove 27 can be circular, and the center of the groove 27 can be coaxial with the axis of rotation 25. In some implementations, the groove 27 extends through the entire thickness of the platform 24.

[0039] The groove houses a central annular flexure 51 including a flange 54 and one or more actuators 52 to apply a force to the flange 54. The inner edge of the central annular flexure 51 (e.g., closest to the axis of rotation 25) flexes upward or downward based on the force applied to the flange 54 by the actuator 52, while the outer edge of the central annular flexure 51 remains substantially coplanar with the upper surface 28.

[0040] The central annular flexure 51 extends from the inner edge of the platform 24 a distance within the range of 5% to 25% (e.g., 5% to 15%, 5% to 10%, 10% to 25%, or 15% to 25%) of the innermost and outermost diameters of the polishing pad 30.

[0041] The arrangement of actuator 52, outer annular flexure 50a, and central annular flexure 50b defines a region of pad 30, where the pressure between pad 30 and substrate 10 is at least partially controlled by the amount of flexure provided by actuator 52. Refer to Figure 2A and Figure 2B , which show top views of polishing pad 30 and substrate 10 and outline specific polishing regions. Figure 2A depicts an implementation where device 100 includes only outer annular flexure 50a, while Figure 2B depicts an implementation where device 100 includes outer annular flexure 50a and central annular flexure 50b. Although fixed ring 73 surrounds substrate 10 in device 100 during the polishing operation, this component has been visually removed in Figure 2A and Figure 2B for simplicity.

[0042] Refer to Figure 1 and Figure 2A , which show top views of pad 30 supported by platform 24 and substrate 10, where system 20 includes only outer annular flexure 50a. The central portion 26 of platform 24 supports the central region 31 of pad 30. Annular flexure 50a is arranged around platform 24 in a circle and supports outer region 33. The outer edge of outer region 33 flexes up or down while the inner edge of outer region 33 remains substantially coplanar with central region 31.

[0043] Substrate 10 is moved by carrier head 70 such that portion 12 of substrate 10 is above outer region 33. Depending on whether flexure 50a is biased up or down, outer region 33 will experience an increased or decreased pressure against portion 12 of substrate 10. Due to the rotation of carrier head 70 and substrate 10 (shown by arrow A), the annular portion 12a of substrate 10 will experience an increased or decreased polishing rate (compared to a flexure that remains in a planar state).

[0044] Refer to Figure 1 and Figure 2B , which show top views of pad 30 supported by platform 24 and substrate 10, where system 20 includes annular flexure 50 and central annular flexure 50b. Central annular flexure 50b defines inner region 35 of polishing pad 30, while outer annular flexure 50a defines outer region 33. Polishing pad 30, supported by central portion 26 that remains substantially planar during polishing, is defined as central region 31. In this way, outer region 33 and inner region 35 define two regions where the pressure between substrate 10 and polishing pad 30 can be modified.

[0045] When the substrate 10 is moved by a carrier head 70 (not shown) across the internal region 35, a portion 13 of the substrate 10 overlaps the internal region 35. As the internal region 35 flexes up or down through the central annular flexure 51, the portion 13 is subjected to increased or decreased pressure. Again, due to the rotation of the carrier head 70 and the substrate 10 (shown by arrow A), the annular portion 13a of the substrate 10 experiences an increased or decreased polishing rate. In Figure 2A and Figure 2B embodiments, assuming insufficient edge polishing of the substrate, the polishing rate of portions 12 and 13 of the substrate 10 that overlap the internal region 35 and the external region 33 can be increased to compensate and thus improve within-wafer and wafer-to-wafer uniformity.

[0046] In some implementations, the polishing apparatus includes an in-situ monitoring system 160, e.g., an optical monitoring system, such as a spectral monitoring system that can be used to measure the spectrum of reflected light from a substrate undergoing polishing. The monitoring system 160 can include a sensor supported on a platform, e.g., one end of an optical fiber coupled to a light source 162 and a photodetector 164. Due to the rotation of the platform, as the sensor travels under the carrier head 70 and the substrate 10, the monitoring system 160 receives measurements at a sampling frequency such that measurements are made at arcuate positions across the substrate 10. Through the measurements, the in-situ monitoring system 160 generates a signal that depends on the thickness of the material layer being polished, e.g., a thickness profile. Additionally or alternatively, the in-situ monitoring system 160 generates a signal that depends on the polishing rate of the material layer being polished, e.g., a polishing rate profile.

[0047] A controller 90 receives the signal, converts the signal into a process profile (e.g., a thickness profile or a polishing rate profile), and compares the process profile with a target profile. For example, the target profile can be a predetermined target thickness profile of the radially-dependent thickness of the layer at the end of polishing, or a target polishing rate profile that stores the radially-dependent target polishing rate during polishing. The process profile can be based on measurements for the radial width of the substrate 10 or a portion of the radial width of the substrate 10. In some implementations, the controller 90 calculates the process profile for that portion of the substrate 10 corresponding to the outermost annular region of the substrate 10, such as the outermost 5%, outermost 10%, or outermost 20% of the substrate.

[0048] The controller 90 compares the process profile with the target profile. If the difference between the process profile and the target profile exceeds a threshold amount, the controller 90 determines to change the polishing parameters. If the difference occurs in a substrate region controllable by the flexure, e.g., in the outermost annular region adjacent to the edge of the substrate 10, the flexure can be used to compensate for the deviation of the process profile from the target profile.

[0049] If the polishing rate of this area of the substrate is higher than the target polishing rate, the controller 90 can determine to position this area above the flexure and deflect the flexure downward. The downward deflection will reduce the polishing rate in that area to achieve the target polishing rate profile. If the polishing rate in that area of the substrate is lower than the target polishing rate for that area, the controller 90 can determine to position this area above the flexure and deflect the flexure upward to increase the polishing rate in that area.

[0050] The carrier head 70 moves the substrate 10 over the central area 31, and the optical monitoring system 160 receives a signal indicating the updated thickness of the overlying material layer (e.g., the updated thickness profile), and calculates a new uniformity value for the updated thickness profile.

[0051] The controller 90 compares the updated uniformity value with the uniformity threshold. If the uniformity value is lower than the uniformity threshold, the controller 90 determines to interrupt increasing the polish of the area of the substrate 10 corresponding to the area exceeding the uniformity threshold.

[0052] Figure 1 Only one technique for adjusting the height of the platform edge is illustrated, and other techniques are possible. The flexure can be a part removable from the platform or an integral part of the platform. The flexure can have a generally uniform depth (as Figure 1 shown), or be tapered, e.g., the edges of the flexure are thinner than the portion adjacent to the central area of the platform. The actuator 52 can be a pneumatic linear actuator or a rotary actuator that drives an adjustment screw. The actuator 52 can push or pull laterally on the downward extension of the flange, or can provide a vertical force directly on the flange.

[0053] In some implementations, the platform includes an upper platform 412 supported on a lower platform 410. The upper platform 412 is composed of multiple parts that are actuated independently to achieve the desired configuration of the polishing pad 30. Figure 3A and Figure 3B shows an example configuration of a rotatable platform 24, where the upper platform 312 is divided into several parts by a flexure 314, e.g., points that are more flexible than the surrounding material. The flexure 314 can be implemented by an annular area of reduced thickness in the upper platform 312 material, or be constructed separately from a material that is more flexible than the rest of the upper platform 312 (e.g., the outer area 316 or the inner part 318). The area of reduced thickness can be formed by a groove formed into the lower surface of the platform 24; when not actively biased, the top surface of the platform can be generally planar.

[0054] The lower platform 310 includes a recess 328 in which one or more actuators are disposed. The actuators provide a vertical force to the inner portion 318. In these implementations, the vertical position of the inner portion 318 is controlled to adjust the polishing rate in the outer region 316. In Figure 4A the example, the recess 328 houses two actuators 330 and 332 supported by a support member 327. The actuators 330 and 332 provide a vertical force (e.g., parallel to the central axis 125) to the inner portion 318, causing the inner portion 418 to shift upward or downward with respect to the edge of the outer region 316 to effect differential polishing of the area of the substrate 10 in contact with the outer region 316.

[0055] In some implementations, the upper platform 312 is divided into more than two regions having differential polishing rates. In Figure 4B the exemplary implementation, three actuators 330, 332, and 334 are supported by the support member 327 in the recess 328. The actuators 330, 332, and 334 control the positions of the inner portion 318 and the central portion 320. In this implementation, the vertical positions of the inner portion 318 and the central portion 320 are independently controlled such that one or more portions have a positional difference, thereby creating a pressure bias against the substrate 10.

[0056] Referring to Figure 1 , the polishing rate (i.e., the rate at which material is removed from the substrate 10) can vary according to a number of polishing system control parameters, e.g., the degree of deflection of the flexure 50, and the dwell time of the carrier head 70 and the substrate 10 at each of a plurality of radial distances from the axis of rotation 25 of the platform 24, and the pressures in the chambers 77a to 77c, the pressure on the retaining ring 73, the rotational rate of the carrier head 70, the rotational rate of the platform 24, etc. Thus, a combination of these parameters can determine the surface profile of the substrate 10 after polishing.

[0057] Generally speaking, the polishing system 20 is controlled to attempt to make the polished substrate have a target surface profile, e.g., a target thickness across the substrate surface. The target surface profile can be uniform (e.g., planar) or non-uniform across the substrate surface. For example, assuming the polishing is symmetric in angle, the target surface profile can be set as a function of the distance from the center of the substrate 10, but this is not necessary. The target surface profile can be set manually by the manufacturer of the polishing system, manually by the operator of the polishing system (e.g., an employee of a semiconductor wafer fab), or can be automatically generated by computer software based on measurements performed by other tools in the semiconductor wafer fab, (e.g.) to compensate for non-uniform deposition or removal by other tools.

[0058] The controller 90 may be configured to store a target removal profile. The controller 90 uses the target removal profile to set values of the polishing control parameters of the polishing system 20, such as the pressure in the chambers 77a to 146c of the carrier head 140, the degree of deflection of the flexure 50, and the dwell time of the carrier head 70 and the substrate 10 at each of a plurality of radial distances from the axis of rotation 25 of the platen 24. The target removal profile represents the desired amount of material to be removed from the front surface of the substrate. In some implementations, the target removal profile may be determined by, for example, the controller 90 or another computer system that forwards the target removal profile to the controller 90 based on the initial surface profile of the substrate 10 (e.g., measured at a metrology station before polishing or measured by an in-situ monitoring system). For example, the target removal profile may be calculated as

[0059] TRP = ISP - TSP (1)

[0060] where TRP is the target removal profile, ISP is the initial surface profile, and TSP is the target surface profile. Alternatively, if the initial surface profile is unknown, the initial surface profile may be set to a default value. Also, in some situations, the operator of the polishing system may desire to remove a targeted amount of material from the substrate rather than achieve a target profile. Additionally, in some situations, the operator of the polishing system may simply set the target removal profile, e.g., based on first principles or prior experience. In this latter case, the user may generate the target removal profile by, for example, user input to the controller 90 or to another computer system that forwards the target removal profile to the controller 90.

[0061] The controller 90 may generate and store an expected removal profile (i.e., the expected amount of material to be removed from the front surface of the substrate 10) for a given set of values of the polishing control parameters.

[0062] Generally speaking, it is advantageous to select values of the polishing control parameters, such as the pressure in the chambers 77a to 77c of the carrier head 70, the degree of deflection of the flexure 50, and the dwell time of the carrier head 70 at each of a plurality of radial distances from the axis of rotation 25 of the platen 24, such that the expected removal profile is very close to (including an exact match with) the target removal profile. For example, if the expected removal profile is very close to the target removal profile, the actual removal profile (i.e., the amount actually removed from the substrate during polishing) should also be very close to the target removal profile.

[0063] It should be noted that the removal profiles described herein may be expressed as the amount of material removed from the substrate surface or equivalently as the material removal rate (e.g., by dividing the removal profile by the actual or expected time taken for polishing). Additionally, it should also be understood that the data used for calculations may be stored in a variety of different units, provided that the data is converted to consistent units for calculation.

[0064] As a simplified model, the expected removal rate at any given location can linearly depend on each polishing control parameter. That is, assuming only one polishing control parameter changes while the other polishing control parameters remain constant, the removal rate at each radial location on the substrate can be a linear function of the changing polishing control parameter.

[0065] The relationship between the polishing control parameters and the removal profile can be determined based on measured data. For example, the removal profile can be measured for test substrates, where each test substrate is polished using a different set of calibrated values of the polishing control parameters. In particular, one substrate can be polished at a set of baseline calibrated values of the polishing control parameters, and the baseline removal profile can be measured from that one substrate. Then, for each control parameter to be set by the process, additional substrates are polished, where that control parameter is set to a modified calibrated value different from the baseline calibrated value (but the other control parameters are set to their baseline calibrated values), and the adjusted removal profile is measured from that additional substrate.

[0066] In some implementations, the various profiles generated from experimental measurements (e.g., the baseline removal profile and the adjusted removal profile) include measured removal values at multiple locations under each chamber. Similarly, the calculated expected removal includes calculated values of the expected removal at multiple locations under each chamber. In some implementations, the profiles (e.g., the baseline removal profile, the adjusted removal profile, and the expected removal profile) include values at twenty to three hundred locations on the substrate. For example, the profile can include values at locations with a regular spacing of 1 mm on the substrate.

[0067] In some implementations, the expected removal profile can be calculated as

[0068] ERP = BRP + [K][P′]*BRP (2)

[0069] where ERP is the expected removal profile, BRP is the baseline removal profile, [K] is a constant matrix (referred to as the "Preston matrix") whose number of rows is equal to the total number N of polishing control parameters, and the number of columns is equal to the total number M of radial locations on the substrate surface where the profile is measured, and [P'] is a vector of adjusted polishing control parameter values. Here, the "*" operation indicates multiplication of the corresponding terms in the vector, rather than the dot product or cross product. That is, the i-th component of ERP is equal to the i-th component of BRP plus the i-th component of the row vector obtained by multiplying [K][P'] by the i-th component of BRP by the i-th component of VAP. The total number of locations M can be greater than the number of chambers in the carrier head and can be greater than the total number N of polishing control parameters.

[0070] The total number of locations M can be greater than the number of chambers in the carrier head and can be greater than the total number N of polishing control parameters.

[0071] By polishing a test wafer with a set of preset polishing control parameter values P0 1 、P0 2 、...P0 N and comparing the surface profile measured (e.g., at a metrology station) after polishing with the initial surface profile to determine the baseline removal profile. For example, the baseline removal profile can be calculated as

[0072] BRP = ISP - BSP (4)

[0073] where BRP is the baseline removal profile, ISP is the initial surface profile, and BSP is the baseline surface profile achieved by polishing the test substrate with the preset polishing control parameter values P0 1 、P0 2 、...P0 N .

[0074] The constants of the matrix [K] can be determined from the baseline removal profile and the modified removal profile. As described above, the modified removal profile can be generated by polishing additional substrates while modifying that parameter (one substrate at a time) for each parameter. For example, the modified removal profile can be calculated for each modified parameter according to the equation

[0075] ARP i = ISP - SAP i (4)

[0076] where ARP i is the adjusted removal profile due to adjusting the i-th polishing parameter, ISP is the initial surface profile, and ASP i is the adjusted surface profile measured due to adjusting the i-th parameter.

[0077] In particular, the constant value of the matrix [K] can be calculated as

[0078]

[0079] where K x,i is the value of the matrix [K] corresponding to the substrate profile position x of the i-th parameter, ARP x,i is the amount of material removed at the radial position x for the i-th adjusted parameter, BRP x is the amount of material removed at the radial position x according to the previously calculated baseline removal profile, PA i is the value of the i-th parameter used to generate the i-th adjusted removal profile, and P0 i is the value of the i-th parameter of the baseline removal profile.

[0080] Thus, the matrix [K] can be expressed as

[0081]

[0082] Where M is the total number of radial substrate positions x at which profile measurements are taken, and N is the total number of parameters.

[0083] Vectors [P'], P 1 ', P 2 '... P N The variable expressions of'are defined as

[0084]

[0085] Where P i ' is the value of the vector [P'] corresponding to the i-th parameter, P0 i is the i-th parameter value of the baseline-removed profile, and P i is the variable proposed parameter value.

[0086] Thus, the expected profile removal can be expressed as

[0087]

[0088] Where ERP is the expected profile removal, BRP is the baseline-removed profile, and the values of the matrix [K] and the vector [P'] are calculated as described above with reference to equations (5) and (7).

[0089] The polishing control parameters can include parameters representing the pressure in each of the chambers 77a to 77c in the carrier head 70. Thus, at least two of the polishing control parameters are the carrier head chamber pressures. The value of the chamber pressure can be in psi, but other units (e.g., pascals) are possible.

[0090] The polishing control parameters can include parameters representing the rotational rate of the platen 24 and / or parameters representing the rotational rate of the carrier head 70. The value of the rotational rate can be in rpm, but other units (e.g., the drive current of the corresponding motor) are possible.

[0091] The polishing control parameters can include parameters representing the degree of deflection of the flexure 50. If the system 20 includes an external flexure 50a and an internal flexure 50b, there will be two parameters, one for each of the internal and external flexures. The values of the degree of deflection and the rotational rate can be in units of distance, such as microns or mils (thousandths of an inch), but other units (e.g., the current or voltage of an electromechanical actuator, or the pressure of a pneumatic actuator) are possible.

[0092] To set the sweep profile of the carrier head 70, the polishing control parameters can include multiple parameters representing the dwell time. In particular, each corresponding parameter among the multiple parameters can represent the dwell time of the carrier head at different corresponding radial annular regions on the platen.

[0093] For example, referring to Figure 4A , platform 24 can be divided into a plurality of concentric annular regions 200, for example, regions 200a to 200e. Optionally, there may be a circular central region, for example, region 202f. Although FIG. 4 shows seven regions, this is not necessary; there can be two to twenty regions. For at least one of the regions, the substrate will overlap with the flange 54, for example, the substrate will overlap with the outer region 33. Each region can be represented by a radial distance (e.g., the average of the inner diameter and the outer diameter of the region) or a series of radial distances (e.g., the inner diameter and the outer diameter of the region).

[0094] During operation, the carrier head 70 (for example) laterally sweeps across the outer diameter of the platform 24 over the platform 24 and the polishing pad (indicated by arrow C). For each region, there may be a corresponding dwell time control parameter that represents the dwell time of the carrier head 70 within or at that region. The substrate can span multiple regions, in which case each corresponding dwell time control parameter can represent the dwell time of the center point of the carrier head (at axis 71) within or at that corresponding region. The value of the dwell time parameter can be in units of a fraction of the total time (i.e., the sum of all dwell times equals 1), but other units (e.g., expected time, e.g., seconds) are possible.

[0095] Once the dwell time parameter value is calculated (the calculation of the parameter value is discussed below), the dwell time parameter value can be converted into a sweep profile. Generally speaking, in the sweep profile, the dwell time for each region will be allocated according to the dwell time parameter value.

[0096] In some implementations, the carrier head sweeps at a constant speed within each region but can be different for each region. For example, referring to Figure 4B , one possible technique is to set the sweep rate of the carrier head for that region according to the reciprocal of the fraction indicated by the dwell time parameter for each region 200a to 200f (i.e., the slope of line 202). For example, given an oscillation period T, the dwell time for a half-sweep (inward or outward) of a given region i can be calculated as T*DT i / 2, where DT i is the fractional dwell time value for the ith region. For example, during an inward sweep, the amount of time T 1 consumed by the center of the substrate 10 in the outermost region 200a will be T*DT 1 / 2. Then, the speed at which the carrier head sweeps across a specific region i can be (R 1i / R 2i ) / (T i ), where R 1i and R 2i are the inner diameter and the outer diameter of the ith region. Thus, in time T1 During this period, the speed of the carrier head and the slope of line 202 will be 2*(R 11 / R 21 ) / (T*DT 1 ).

[0097] In some implementations, appropriate parameter combinations can be determined by solving for the parameters that minimize the difference between the expected removal profile and the target removal profile. That is, minimizing the value of ERP - TRP. In many cases, one or more sets of distinct parameters can be determined mathematically that provide an expected removal profile equivalent to the target removal profile, such that ERP - TRP = 0. In other cases, by using the following equation, the difference between the expected removal profile and the target removal profile can be minimized to an acceptable non - zero value

[0098]

[0099] where Δ is the difference, ERP x is the variable value of the expected removal profile at the radial position x on the substrate, and TRP x is the constant value of the target removal profile at this radial position x. The value of P i can be calculated to find an expected removal profile that is very close to the target removal profile.

[0100] In some examples, an iterative process (e.g., Newton optimization method) can be used in conjunction with equation (9) to determine the appropriate combination of parameter values to find the minimum difference between the estimated pressure profile and the target pressure profile, e.g., finding the minimum value of Δ. For example, commercially available solver functions (e.g., Microsoft Excel solver function, MATLAB solver function, and / or Wolfram Mathematica solver function, etc.) can be used to determine the appropriate combination of parameter values. In some cases, there may be several appropriate combinations of parameter values.

[0101] Once a set of appropriate parameter values has been determined, as described above, the controller 190 can be configured to store the parameter values and accordingly execute the polishing technique to provide one or more substrates with the target surface profile.

[0102] In most cases, when all other parameter values are held constant, the polishing rate at a particular location on the substrate 10 can vary linearly with the pressure applied to the substrate on the polishing pad (at that location of the substrate).

[0103] In some examples, an iterative process (e.g., Newton optimization method) can be used in combination with either equation (16) or (17) to determine an appropriate combination of chamber pressures to find the minimum difference between the estimated pressure profile and the target pressure profile, e.g., to find the minimum value of Δ. For example, a commercially available solver function can be used to determine the appropriate combination of chamber pressures. In some cases, there may be several appropriate combinations of chamber pressures.

[0104] Once an acceptable expected pressure profile is determined, interpolation and / or extrapolation techniques (other known mathematical approximation techniques can also be used) can be applied to the measured baseline pressure distribution to determine the corresponding chamber pressure for each chamber. When using the pressure distribution from a single baseline pressure, it may be necessary to assume a zero-scale pressure distribution (i.e., when the chamber is not pressurized, little or no polishing pressure is applied).

[0105] Figure 5 FIG. is a block diagram of an exemplary computer system 500. For example, the controller 190 can be an example of the above-described system 500, which can be a computer system used by any of the users accessing the resources of the system 500. The system 500 includes a processor 510, a memory 520, a storage device 530, and one or more input / output interface devices 540. Each of the components 510, 520, 530, and 540 can be interconnected, for example, using a system bus 550.

[0106] The processor 510 is capable of processing instructions for execution within the system 500. As used herein, the term "execution" represents the technique by which program code causes the processor to execute one or more processor instructions. In some implementations, the processor 50 is a single-threaded processor. In some implementations, the processor 50 is a multi-threaded processor. The processor 510 is capable of processing instructions stored in the memory 520 or stored on the storage device 530. The processor 510 can perform operations such as controlling the polishing operations as described herein.

[0107] The memory 520 stores information within the system 500. In some implementations, the memory 520 is a computer-readable medium. In some implementations, the memory 520 is a volatile memory unit. In some implementations, the memory 520 is a non-volatile memory unit.

[0108] The storage device 530 can provide large-capacity storage for the system 500. In some implementations, the storage device 530 is a non-transitory computer-readable medium. In various different implementations, the storage device 530 may include, for example, a hard disk drive device, an optical disc device, a solid-state drive, or a flash drive. In some implementations, the storage device 530 can be a cloud storage device, for example, a logical storage device including one or more physical storage devices distributed over a network and accessed using the network.

[0109] The input / output interface device 540 provides input / output operations for the system 500. In some implementations, the input / output interface device 540 may include one or more of a network interface device (e.g., an Ethernet network interface) and / or a wireless interface device. The network interface device allows the system 500 to communicate, for example, to transmit and receive data via a network. In some implementations, mobile computing devices, mobile communication devices, and other devices can be used.

[0110] The software can be implemented by instructions that, when executed, cause one or more processing devices to perform the above-described processes and functions. These instructions may include, for example, interpretive instructions (such as, script instructions), or executable code, or other instructions stored in a computer-readable medium.

[0111] Although example processing systems have been described Figure 5 implementations of the subject matter of the present invention and the functional operations described above can be implemented in other types of digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or a combination of one or more of them. Implementations of the subject matter described in this specification (e.g., storage, maintenance, and display of articles) can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible program carrier, such as a computer-readable medium, for execution by a processing system or to control the operation of a processing system. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of them.

[0112] A computer program (also referred to as a program, software, software application, script, executable logic, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and can be deployed 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. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile or volatile memory, media, and memory devices.

[0113] Throughout this specification, when referring to measurable values such as amounts, durations, and the like, the recitation of the value should be considered to disclose the exact value, disclose approximations of the value, and disclose about the value, e.g., within ±10% of the value. For example, the reference to 100 microns here can be considered to be a reference to either the exact 100 microns, an approximation of 100 microns, and within ±10% of 100 microns.

[0114] Although this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular examples. Certain features described in the context of separate implementations in this specification may also be combined. Conversely, the various features described in the context of a single implementation may also be implemented separately or in any suitable sub-combination in multiple embodiments.

Claims

1. A chemical mechanical polishing apparatus, the chemical mechanical polishing apparatus comprises: a platform for supporting a polishing pad, the platform having a central portion with an upper surface and an annular flexure surrounding or surrounded by the central portion and having a top surface, the annular flexure having a first edge adjacent to and coplanar with the upper surface and a second edge remote from the central portion; an actuator arranged to bend the annular flexure to modify a vertical position of the second edge of the annular flexure relative to the central portion; a carrier head for holding a surface of a substrate against the polishing pad; a motor for generating relative movement between the platform and the carrier head to polish an overlying layer on the substrate; and a controller configured to select values of a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters including a first parameter representing a degree of deflection of the flexure, wherein a relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix, the first matrix including a plurality of rows, the plurality of rows including a row for the degree of deflection of the flexure and columns for each position on the substrate represented in the expected removal profile, and wherein as part of selecting the values, the controller is configured to calculate the expected removal profile by multiplying the first matrix by a second matrix representing values of the control parameters.

2. The polishing apparatus according to claim 1, wherein the carrier head includes a plurality of independently pressurizable chambers, and the plurality of polishing control parameters include a plurality of chamber pressure parameters, wherein each respective chamber pressure parameter is associated with a respective one of the plurality of pressurizable chambers.

3. The polishing apparatus according to claim 2, wherein the plurality of rows of the first matrix include a row for each chamber pressure parameter.

4. The polishing apparatus according to claim 2, wherein the values of the chamber pressure parameters are in units of pressure.

5. The polishing apparatus according to claim 1, wherein the platform includes the annular flexure surrounding the central portion, and the first matrix includes a row for the degree of deflection of the flexure surrounding the central portion.

6. The polishing apparatus according to claim 1, wherein the platform includes the annular flexure surrounded by the central portion, and the first matrix includes a row for the degree of deflection of the flexure surrounded by the central portion.

7. The polishing apparatus according to claim 1, wherein the platform includes a first annular flexure surrounding the central portion and a second annular flexure surrounded by the central portion, and the first matrix includes a first row for the degree of deflection of the first flexure and a second row for the degree of deflection of the second flexure.

8. The polishing apparatus according to claim 1, wherein the degree of deflection of the flexure is in units of distance.

9. The polishing apparatus according to claim 1, wherein the controller is configured to apply a minimization algorithm to reduce the difference between an expected thickness profile and a target thickness profile, and wherein applying the minimization algorithm includes iteratively calculating the expected removal profile using different values of the degree of deflection of the flexure member.

10. A chemical mechanical polishing apparatus, the chemical mechanical polishing apparatus comprising: a platform for supporting a polishing pad; a carrier head for holding a surface of a substrate against the polishing pad; a motor for controlling a lateral position of the carrier head on the polishing pad; a controller configured to cause the motor to sweep the carrier head on the polishing pad according to a sweep profile, wherein the controller is configured to select values of a plurality of control parameters to minimize the difference between a target removal profile and an expected removal profile, the plurality of control parameters including a plurality of dwell time parameters, wherein each respective dwell time parameter of the plurality of dwell time parameters represents an amount of time spent by the carrier head on a different respective area of the polishing pad, wherein a relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix, the first matrix including a plurality of rows, the plurality of rows including a row for each dwell time parameter and columns for each position on the substrate represented in the expected removal profile, and wherein as part of selecting the values, the controller is configured to calculate the expected removal profile by multiplying the first matrix by a second matrix representing values of the control parameters.

11. The polishing apparatus according to claim 10, wherein the carrier head includes a plurality of independently pressurizable chambers, and the plurality of polishing control parameters includes a plurality of chamber pressure parameters, wherein each respective chamber pressure parameter is associated with a respective one of the plurality of pressurizable chambers.

12. The polishing apparatus according to claim 11, wherein the plurality of rows of the first matrix includes a row for each chamber pressure parameter.

13. The polishing apparatus according to claim 11, wherein the values of the chamber pressure parameters are in units of pressure.

14. The polishing apparatus according to claim 11, wherein the controller is configured to apply a minimization algorithm to reduce the difference between an expected thickness profile and a target thickness profile, and wherein applying the minimization algorithm includes iteratively calculating the expected removal profile using different values for each dwell time parameter.

15. The polishing apparatus according to claim 11, wherein the controller is configured to calculate a sweep profile from values of the plurality of dwell time parameters.

16. The polishing apparatus according to claim 15, wherein the controller is configured to set the sweep profile to have a respective speed for each respective annular area on the platform.

17. The polishing apparatus according to claim 16, wherein the controller is configured to set the respective speed to a constant value within the respective area for each respective annular area of the plurality of annular areas.

18. The polishing apparatus according to claim 17, wherein the value of the dwell time parameter is in units of a fraction of the total time.

19. The polishing apparatus according to claim 17, wherein the controller is configured to calculate a sweep speed to be inversely proportional to the value of the dwell time parameter of the region for each respective one of the plurality of annular regions.

20. The polishing apparatus according to claim 10, wherein the fractional dwell time value is for the i-th region.

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