Asymmetry correction by variable relative velocity of wafer

Abstract

Certain aspects of the present disclosure provide techniques for a method of removing material on a substrate.An exemplary method includes: rotating the substrate in a first direction about a first axis; pressing the surface of the substrate against a polishing surface of a polishing pad while rotating the substrate; rotating the substrate about the first axis includes rotating the substrate a first angle at a first rotation speed, and then rotating the substrate a second angle at a second rotation speed, the first rotation speed being different from the second rotation speed.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to chemical mechanical polishing (CMP), and more particularly to correcting thickness asymmetries during CMP. [Background technology]

[0002] Integrated circuits are generally formed on a substrate by successive deposition of conductive, semiconductive, or insulating layers on a semiconductor substrate. Various manufacturing processes require planarization of layers on the substrate. For example, one manufacturing step involves depositing a fill layer on a non-planar surface and planarizing the fill layer. In some applications, the fill layer is planarized until the top surface of the patterned layer is exposed. For example, a metal layer may be deposited on a patterned insulating layer to fill trenches and holes in the insulating layer. After planarization, the remaining portions of the metal in the trenches and holes of the patterned layer form vias, plugs, and lines to provide conductive paths between integrated circuits (ICs) on the substrate. As another example, a dielectric layer may be deposited on a patterned conductive layer and then planarized to allow for subsequent photolithography steps.

[0003] Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method generally requires that a substrate is mounted on a carrier head. The exposed surface of the substrate, the surface with the layer deposition, is generally placed against a rotating polishing pad. The carrier head exerts a controllable load on the substrate to press it against the polishing pad. A polishing slurry with abrasive particles is generally applied to the surface of the polishing pad and spreads between the substrate and the polishing pad. The polishing pad and carrier head each rotate at a constant rotational speed, and the abrasive slurry removes material from one or more of the layers. The material is removed flatly, and the material removal process is symmetric about a central axis. A symmetric removal process can be problematic because a substrate with an asymmetrically non-uniform thickness profile remains asymmetric after the CMP process is completed. For example, asymmetric thickness of a substrate can cause circuits formed on a surface of a substrate to have different RC time constants relative to integrated circuits in devices formed on the opposite side of the same surface of the substrate because ICs formed on the thinner edge of the substrate have less metal than ICs formed on the thicker edge of the substrate. The resulting integrated circuits will have varying processing speeds based on the corresponding substrate thickness. Thus, the variation in RC time constants results in devices of varying quality, which is undesirable. Although described as opposite sides or edges, the locations of the thinnest and thickest sides or areas of the substrate can be at other locations on the substrate.

[0004] Therefore, there is a need in the art for a method to correct for substrate asymmetry during CMP. Summary of the Invention

[0005] FIELD OF THE DISCLOSURE Embodiments of the present disclosure generally relate to polishing a substrate by use of a chemical mechanical polishing (CMP) process. In particular, embodiments herein provide a method for correcting asymmetry in a thickness profile of a substrate by use of a CMP process.

[0006] In one embodiment, a method for removing material on a substrate is provided. In general, the method includes rotating the substrate in a first direction about a first axis and pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate. Rotating the substrate about the first axis includes rotating the substrate a first angle at a first rotational speed profile, and then rotating the substrate a second angle at a second rotational speed profile. The first rotational speed profile is different from the second rotational speed profile.

[0007] In another embodiment, a method for removing material on a substrate is provided. In general, the method includes rotating the substrate in a first direction about a first axis, and pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate about the first axis. Rotating the substrate about the first axis includes rotating the substrate 180 degrees or less within 360 degrees of a first rotational speed profile, then rotating the substrate 180 degrees or less within 360 degrees of a second rotational speed profile, the second rotational speed profile being different from the first rotational speed profile, and repeating the first and second rotational speed profiles at least one more time.

[0008] In another embodiment, a non-transitory computer-readable medium includes computer-executable instructions that, when executed by a processing system, cause the processing system to perform a method for removing material on a substrate. In general, the method includes rotating the substrate in a first direction about a first axis and pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate. Rotating the substrate about the first axis includes rotating the substrate a first angle at a first rotational speed profile and then rotating the substrate a second angle at a second rotational speed profile. The first rotational speed profile is different from the second rotational speed profile.

[0009] An embodiment of the present disclosure may further provide a method of removing material on a substrate, comprising orienting the substrate according to a thickness profile, receiving the oriented substrate by a carrier head, and aligning the substrate to a known position in the carrier head, the carrier head being configured to perform a process of pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate about a first axis, and rotating the substrate about the first axis comprises rotating the substrate at a different rotation speed based on the alignment of the substrate. Orienting the substrate according to the thickness profile includes aligning the substrate based on a maximum thickness of the substrate. In one example, the maximum thickness of the substrate is at a first radius of the substrate, and the maximum thickness is rotated at a higher relative speed than other positions on the first radius during the method.

[0010] An embodiment of the present disclosure may further provide a chemical mechanical polishing system comprising a carrier head having a first axis of rotation, a polishing pad disposed on a surface of a platen, the platen having a second axis of rotation, and a non-transitory computer readable medium comprising computer executable instructions that, when executed by the processing system, cause the processing system to perform a method of removing material on a substrate, the method including rotating the carrier head in a first direction about the first axis of rotation, and pressing a surface of the substrate against a polishing surface of the polishing pad while rotating the substrate about the first axis of rotation using the carrier head, the rotating the substrate about the first axis of rotation includes rotating the substrate a first angle at a first rotational speed profile, and then rotating the substrate a second angle at a second rotational speed profile, the first rotational speed profile being different from the second rotational speed profile.

[0011] An embodiment of the present disclosure may further provide a method of removing material on a substrate, the method including rotating the substrate in a first direction about a first axis and pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate about the first axis, wherein rotating the substrate about the first axis includes (a) rotating the substrate 180 degrees or less within a 360 degree rotation in a first rotational speed profile, (b) then rotating the substrate 180 degrees or less within a 360 degree rotation in a second rotational speed profile, the second rotational speed profile being different from the first rotational speed profile, and (c) repeating (a) and (b) at least one more time.

[0012] An embodiment of the present disclosure may further provide a method of removing material on a substrate, the method including rotating the substrate in a first direction about a first axis and pressing a surface of the substrate against a polishing surface of a polishing pad while rotating the substrate. Rotating the substrate about the first axis includes rotating the substrate a first angle at a first rotational speed profile and then rotating the substrate a second angle at a second rotational speed profile, the first rotational speed profile being different from the second rotational speed profile.

[0013] So that the above recited features of the present disclosure may be understood in detail, a more particular description of the present disclosure, briefly summarized above, may be made by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that since the present disclosure may admit of other equally effective embodiments, the accompanying drawings merely illustrate typical embodiments of the present disclosure and therefore should not be considered as limiting its scope. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic plan view of an exemplary chemical mechanical polishing (CMP) system. [Diagram 2] 2 is a schematic cross-sectional view of an exemplary polishing station of the CMP system from FIG. 1 according to embodiments described herein. [Figure 3A] 3 is a schematic plan view of a carrier head positioned over a polishing pad from the polishing station of FIG. 2 according to an embodiment described herein. [Figure 3B] FIG. 3B is a schematic side view of the substrate from FIG. 3A according to embodiments described herein. [Figure 4A] FIG. 2 illustrates several points on a substrate and their relative velocities according to embodiments described herein. [Figure 4B] FIG. 2 illustrates several points on a substrate and their relative velocities according to embodiments described herein. [Figure 4C] FIG. 2 illustrates several points on a substrate and their relative velocities according to embodiments described herein. [Figure 4D] FIG. 4B is a schematic plan view of a polishing pad and substrate that can be used to determine the magnitude of relative velocity at a point on the substrate from FIG. 4A during a portion of a polishing process according to embodiments described herein. [Figure 4E] FIG. 4B is a schematic plan view of a polishing pad and substrate that can be used to determine the magnitude of relative velocity at a point on the substrate from FIG. 4A during a portion of a polishing process according to embodiments described herein. [Figure 5A] 5A-5D at different rotation rates of the carrier head according to embodiments described herein. FIG. [Figure 5B] 5A-5D at different rotational speeds of the carrier head according to embodiments described herein. FIG. [Figure 5C] 5A-5B as the carrier head rotates at variable rotational speeds, according to embodiments described herein. FIG. [Figure 5D]5A-5B as the carrier head rotates at variable rotational speeds, according to embodiments described herein. FIG. [Figure 5E] 5C-5D according to embodiments described herein. FIG. 5C shows different rotational speed profiles and relative velocities for different angular positions of points from FIG. 5D according to embodiments described herein. [Figure 5F] 5C-5D according to embodiments described herein. FIG. 5C shows different rotational speed profiles and relative velocities for different angular positions of points from FIG. 5D according to embodiments described herein. [Figure 6] FIG. 2 illustrates an example functional block diagram of a controller for a carrier head and / or platen or polishing pad according to embodiments described herein. [Figure 7] FIG. 2 illustrates an example of an asymmetric polishing process sequence that may be implemented in a polishing system according to embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] For ease of understanding, wherever possible, the same reference numbers have been used to designate like elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0016] In the following description, details are described by way of example to facilitate understanding of the disclosed subject matter. However, it will be apparent to those skilled in the art that the disclosed embodiments are illustrative and do not cover all possible embodiments. Therefore, it should be understood that reference to the described examples does not limit the scope of the present disclosure. Changes and further modifications to the described devices, instruments, methods, and any further applications of the principles of the present disclosure are fully contemplated, as would normally occur to those skilled in the art to which the present disclosure pertains. In particular, it is fully contemplated that the features, components, and / or steps described with respect to one embodiment may be combined with the features, components, and / or steps described with respect to other embodiments of the present disclosure. The term "about" as used herein may refer to a variation of + / - 10% from the nominal value. It should be understood that such variations may be included in any value provided herein.

[0017] Aspects of the present disclosure provide an apparatus, method, processing system, and computer-readable medium for correcting thickness profile asymmetry through the use of a chemical mechanical polishing (CMP) process.

[0018] In a particular polishing system, a platen and a carrier head are used, and a polishing pad is placed on and attached to the platen. A substrate to be polished is placed between the carrier head and the polishing pad. The carrier head and / or the platen and polishing pad rotate so that a slurry containing abrasive particles is applied to the surface of the polishing pad. A membrane in the carrier head is used to apply pressure to the substrate during polishing to adjust the material removal rate and control the planarization and uniformity results achieved on the substrate. However, prior to being polished, the substrate may have an initial asymmetric, non-uniform thickness profile, which results from the use of a conventional CMP process in that the asymmetric thickness profile does not change during and after polishing due to the symmetric material removal rate provided in the conventional CMP process. As will be further described below, to counteract the initial asymmetric thickness profile, an asymmetric removal profile is provided by the use of one or more of the embodiments described herein. When the asymmetric removal profile is known, it can be combined with the initial asymmetric thickness profile of the substrate, resulting in the polished substrate having a highly symmetric final thickness profile.

[0019] The initial thickness profile of the substrate can be determined using different measurement or metrology tools and methods. The measurements can be done manually, such as with a granite table and measuring height gauges, or automatically, such as with an automated system. The measurements can be done using contact methods, such as using gauges, or non-contact methods, such as using lasers or optical instruments. In some embodiments, a metrology station can be used to measure the thickness profile. The thickness profile can be referenced to features or markings on the substrate through a reference mapping. For example, the substrate can include a V-shaped notch (e.g., notch 313 in FIG. 3A) in its perimeter or edge, and the orientation of the thickness profile is described or logged with respect to the notch. As described further below, the reference mapping is used when developing an asymmetric removal profile.

[0020] In one or more of the embodiments of the present disclosure provided herein, an asymmetric removal profile can be achieved by varying the rotation speed of the carrier head and / or polishing pad during processing. When the polishing pad and carrier head rotate at a constant rotation speed, the relative velocity of a point on the radius of the substrate will be, on average, the same as any other point on the radius. For example, the average relative velocity of a point on the periphery of the substrate is the same as every other point on the periphery. When varying one of many polishing processes, the use of a constant average relative velocity tends to promote the production of a symmetric removal profile. As will be further described below, by varying the rotation speed of the carrier head and / or polishing pad and platen during processing, the relative velocities of different points on the radius of the substrate can be adjusted so that the relative velocities are different from each other, such that an asymmetric removal profile can be produced.

[0021] The asymmetric removal profile is used to correct one or more material thickness asymmetries of the substrate. In an attempt to form a desired asymmetric removal profile, in some embodiments, the rotation speed of the polishing pad can be held at a constant value, while the rotation speed of the carrier head can be varied with the angular rotation position of the carrier head. It is believed that varying the rotation speed at different rotation angles can result in a desired asymmetric removal profile. When properly aligned, the asymmetric removal profile and the asymmetric thickness profile of the substrate can at least partially cancel each other out, thus reducing or eliminating the asymmetry of the final substrate thickness profile.

[0022] The present application often refers to rotation, rotational rate, rotational speed, speed, and / or velocity with respect to the movement of carrier head 210 ( FIG. 2 ). However, it should be understood that such descriptions apply equally to substrate 115, as substrate 115 is in contact with carrier head 210 and rotates therewith, unless otherwise noted. The present application refers to rotational speed, rotational rate, speed, and velocity. However, these terms are not limiting and may be used interchangeably unless otherwise noted. For example, velocity may mean velocity with speed and direction, or the magnitude of velocity (e.g., speed).

[0023] Exemplary System for Asymmetry Correction FIG. 1 is a plan view of one embodiment of a chemical mechanical polishing ("CMP") system 100. The CMP system 100 includes a factory interface module 102, a cleaning apparatus 104, and a polishing module 106. A wet robot 108 is provided for transferring substrates 115 between the factory interface module 102 and the polishing module 106. The wet robot 108 may also be configured to transfer substrates 115 between the polishing module 106 and the cleaning apparatus 104. The factory interface module 102 includes a dry robot 110 configured to transfer substrates 115 between one or more cassettes 114, one or more metrology stations 117, and one or more transfer platforms 116. In one embodiment shown in FIG. 1, four substrate storage cassettes 114 are shown. The dry robot 110 in the factory interface module 102 has a sufficient range of motion to facilitate transfer between the four cassettes 114 and the one or more transfer platforms 116. Optionally, the drying robot 110 may be mounted on rails or tracks 112 for positioning the robot 110 laterally within the factory interface module 102. The drying robot 110 is further configured to receive substrates 115 from the cleaning device 104 and return clean, polished substrates to the substrate storage cassette 114.

[0024] Still referring to FIG. 1 , the polishing module 106 includes multiple polishing stations 124 on which the substrate 115 is polished while held in a carrier head 210. The polishing stations 124 are sized to interface with one or more carrier heads 210 so that polishing of the substrate 115 can occur in a single polishing station 124. The carrier head 210 is coupled to a carriage (not shown) that is mounted on an overhead track 128, shown in phantom in FIG. 1 . The overhead track 128 allows the carriage to be selectively positioned about the polishing module 106, which facilitates selectively positioning the carrier head 210 over the polishing stations 124 and the load cup 122. In the embodiment shown in FIG. 1 , the overhead track 128 has a circular configuration, which allows the carriage holding the carrier head 210 to be selectively and independently rotated on and / or off the load cup 122 and the polishing stations 124.

[0025] 1, there are three polishing stations 124 located in the polishing module 106. At least one load cup 122 is located at a corner of the polishing module 106 between the polishing stations 124 closest to the wet robot 108. The load cup 122 facilitates transfer between the wet robot 108 and the carrier head 210.

[0026] Each polishing station 124 includes a polishing pad 204 having a polishing surface (e.g., polishing surface 204A in FIG. 2) capable of polishing the substrate 115. Each polishing station 124 includes one or more carrier heads 210, a conditioning assembly 132, and a polishing fluid supply module 135. In one embodiment, the conditioning assembly 132 may include a pad conditioning assembly 140 that prepares the polishing surface of the polishing pad 204 by removing polishing debris and opening pores in the polishing pad 204 by use of a pad conditioning disk 133. In another embodiment, the polishing fluid supply module 135 may include a fluid supply arm 134 for supplying a slurry. In one embodiment, each polishing station 124 includes a pad conditioning assembly 132. In one embodiment, the fluid supply arm 134 is configured to supply a fluid stream (e.g., fluid 222 in FIG. 2) to the polishing station 124. The polishing pad 204 is supported on a platen (e.g., platen 202 in FIG. 2) that rotates the polishing surface during processing. The CMP system 100 is coupled to a power supply 180 .

[0027] In some embodiments, a substrate 115, such as a silicon wafer with one or more layers deposited thereon, is loaded into the CMP system 100 via a cassette 114. The substrate 115 typically has a notch, flat, or other type of fiducial mark that can be used to indicate the rotational orientation of the substrate's major surface relative to a central axis. The factory interface module 102 begins processing by extracting the substrate 115 from the cassette 114 while the controller 190 coordinates the operation of the CMP system 100. The factory interface module 102 transfers the substrate 115 to a metrology station 117, which measures the thickness profile of the substrate 115 and determines the orientation of the thickness profile relative to the notch of the substrate 115. The metrology station 117 may use optical, eddy current, resistivity, or other useful processes as described with respect to FIG. 2. The controller 190 receives the thickness profile measurements and orientation from the metrology station 117 and uses the notch to track the orientation of the thickness profile as the substrate 115 is processed. The factory interface module 102 transfers the substrate 115 to a transfer platform 116 , and the wet robot 108 transfers the substrate through subsequent processing components, including the CMP system 100 .

[0028] The load cup 122 serves multiple functions, including receiving the substrate 115 from the wet robot 108, rinsing the substrate 115, and loading the substrate 115 onto a carrier head (e.g., carrier head 210 in FIG. 2). Each polishing station includes a polishing pad 204 affixed to a rotatable platen 202. Different polishing pads 204 may be used in different polishing stations 124 to control material removal of the substrate 115. Aspects of the CMP system operation are further illustrated in FIG.

[0029] In some embodiments, the factory interface module 102 may also include a pre-aligner 118 for positioning the substrate 115 in a known and desired rotational orientation. Pre-aligning the substrate to a desired rotational orientation allows the substrate to be positioned and oriented such that when the substrate is transferred by one or more robots in the system to a position where the carrier head 210 can receive the substrate, the substrate is oriented in a known and desired orientation relative to the carrier head 210 and the rotatable platen 202. The pre-aligner 118 includes a notch detection system, such as an optical interrupter sensor (not shown), for sensing when a substrate notch is at a particular angular position. For example, after a polishing operation, the substrate 115, which may be at an uncertain angular position, has a known orientation when scanned by the metrology station 117, thus enabling accurate determination of the xy (or r-θ) location of measurements on the substrate 115.

[0030] In some embodiments, the substrate 115 is moved by the drying robot 110 to a metrology station 117 where properties of the substrate 115 are measured, such as thickness uniformity and / or thickness of the substrate as a function of angular orientation relative to a reference mark, such as a notch. For example, the factory drying robot 110 "picks up" the substrate, e.g., by vacuum suction, and transports the unpolished substrate to the metrology station 117. The metrology station 117 may perform multiple thickness or flatness measurements across the substrate 115. The controller 190 may determine that the thickness and / or flatness of the substrate 115 is asymmetric, e.g., thicker on one side than the other. For example, the controller 190 determines a thickness profile of the substrate, e.g., a three-dimensional (3D) map of the substrate thickness. Metrology stations 117 suitable for measuring thickness are available from Nanometrics and Nova Measuring Instruments.

[0031] The dry robot 110 then transfers each substrate 115 to the transfer platform 116, and the wet robot 108 then transports the substrate to a different polishing station 124 in the CMP system 100. Finally, the substrate 115 is loaded into the load cup 122, so that the carrier head 210 can transport the substrate 115 to each of one or more polishing stations 124 to hold the substrate 115 and undergo a CMP process according to selected polishing parameters. During CMP, the controller 190 controls aspects of the polishing stations 124. In some embodiments, the controller 190 is one or more programmable digital computers that execute digital control software. The controller 190 can include a processor 192, e.g., a programmable computer such as a personal computer, that is located near the polishing apparatus. The controller can include a memory 194 and support circuits 196. The controller 190 can coordinate, for example, the rotation of the polishing pad and the carrier head such that the asymmetric removal profile is aligned with the asymmetric thickness profile of the substrate 115. Aligning these profiles ensures that the thickest portions of substrate 115 have the most material removed, reducing asymmetry of substrate 115 during polishing. Controller 190 is further described in FIG.

[0032] After polishing, the wet robot 108 transports the substrate 115 from the load cup 122 to a cleaning chamber in the cleaner 104 where slurry and other contaminants that accumulated on the substrate surface during polishing are removed. In the embodiment shown in Figure 1, the cleaner 104 includes two pre-clean modules 144, two megasonic cleaner modules 146, two brush box modules 148, a spray jet module 150, and two dryers 152.

[0033] The drying robot 110 then removes the substrate 115 from the cleaning apparatus 104 and transfers it to the metrology station 117 to be measured again. In some embodiments, the post-polishing layer thickness measurements can be used to adjust the polishing process parameters for subsequent substrates. Finally, the drying robot 110 returns the substrate 115 to one of the cassettes 114.

[0034] In some embodiments, the metrology station 117 is part of the factory interface module 102. In some embodiments, the metrology station 117 is housed in a separate module (not shown) that is connected to the factory interface module 102.

[0035] 2 shows a schematic cross-sectional view of the polishing station 124 of the CMP system 100 from FIG. 1, comprising a polishing assembly 200 having a polishing pad 204 formed according to an embodiment described herein. In particular, FIG. 2 shows how a carrier head 210 is positioned relative to the polishing pad 204. A coordinate system 201, having x, y, and z axes, shows the orientation of the different components of the polishing assembly 200 in this and subsequent figures. The coordinate system 201 shows the positive directions of the x, y, and z axes, and the positive direction for rotation about the z axis, which is in a counterclockwise direction. The opposite direction (not shown) is the negative direction.

[0036] In some embodiments, the polishing pad 204 is affixed to the platen 202 using an adhesive, such as a pressure sensitive adhesive (PSA) layer (not shown), disposed between the polishing pad 204 and the platen 202. Facing the platen 202 and polishing pad 204 mounted thereon, a carrier head 210 includes a flexible diaphragm 212 configured to apply differential pressures to a surface of the substrate 115 disposed between the carrier head 210 and the polishing pad 204. The carrier head 210 includes a carrier ring 218 surrounding the substrate 115, which holds the substrate in place. The carrier head 210 rotates about a carrier head axis 216 while the flexible diaphragm 212 presses the surface of the substrate 115 to be polished against the polishing surface 204A of the polishing pad 204. During polishing, a down force on the carrier ring 218 presses the carrier ring 218 against the polishing pad 204, improving polishing process uniformity and preventing the substrate 115 from slipping out from under the carrier head 210. In some embodiments, the carrier head 210 includes a shaft 211 having an axis that is collinear with the carrier head axis 216. In some embodiments, the platen 202 and carrier head 210 each have a rotational sensor (not shown), such as an encoder, to measure their angular position and / or rotational speed as they rotate. In further embodiments, the platen 202 and carrier head 210 each have a mechanism or motor (not shown) that drives their rotation. The encoder and motor may be incorporated into a controller as an input and output, respectively, as further described in FIG. 6. In further embodiments, the controller may use the encoder and internal timing elements to calculate the rotational speed of the carrier head 210 and / or the platen 202 and polishing pad 204.

[0037] In some embodiments, the polishing pad 204 rotates about a platen axis 205. In some embodiments, the polishing pad 204 has a polishing pad axis 206 that is collinear with the platen axis 205. In some embodiments, the polishing pad 204 rotates in the same rotational direction as the carrier head 210. For example, the polishing pad 204 and the carrier head 210 both rotate in a counterclockwise direction as illustrated in FIG. 3. As illustrated in FIG. 2, the polishing pad 204 has a surface area that is larger than the surface area of ​​the substrate 115 to be polished. However, in further embodiments, the polishing pad 204 has a surface area that is smaller than the surface area of ​​the substrate 115 to be polished.

[0038] This application often refers to the platen 202 and platen axis 205, including the rotational speeds of the platen 202 and platen axis 205. However, it should be understood that such descriptions apply equally to the polishing pad 204 and polishing pad axis 206, unless otherwise noted, since in some embodiments the polishing pad 204 and platen 202 rotate as one and the polishing pad axis 206 and platen axis 205 are collinear.

[0039] In some embodiments, an endpoint detection (EPD) system 224 directs light toward the substrate 115 during processing through the platen opening 226 and also through an optically transparent window feature 227 of the polishing pad 204 disposed over the platen opening 226 to detect properties of the substrate during polishing. The EPD system 224 allows thickness measurements of the substrate 115 to be made while the polishing assembly 200 is in use. In a further embodiment, an eddy current probe is used to measure the thickness of a conductive layer formed on the surface of the substrate 115.

[0040] In particular, the application may refer to the rotation, rotational velocity, speed, and / or velocity of carrier head 210. It should be understood that such descriptions also apply to substrate 115, unless otherwise noted, as substrate 115 generally rotates with carrier head 210.

[0041] During polishing, a fluid 222 is introduced to the polishing pad 204 through a fluid delivery arm 134 portion of the polishing fluid delivery module 135 that is positioned above the polishing pad 204. In some embodiments, the fluid 222 is a polishing fluid, a polishing slurry, a cleaning fluid, or a combination thereof. In some embodiments, the polishing fluid may include an aqueous chemistry that includes abrasive particles. The fluid 222 may also include a chemically active component, such as a pH adjuster and / or an oxidizer, to enable CMP of the material surface of the substrate 115 in conjunction with the polishing pad 204. In some embodiments, the fluid 222 removes material from the substrate as the carrier head 210 presses the substrate against the polishing pad 204.

[0042] 3A shows a schematic top view of the carrier head 210 positioned over the polishing pad 204 from the polishing assembly 200 of FIG. 2 according to an embodiment described herein. In particular, FIG. 3A shows an example of how the carrier head 210 and polishing pad 204 rotate relative to one another. The substrate 115 and carrier ring 218 are shown as phantom lines since they are hidden beneath the carrier head 210 in this view.

[0043] In some embodiments, the substrate 115 has an asymmetric thickness profile 328 as previously described with respect to FIG. 1. In one configuration, as shown in FIG. 3B, the substrate 115 includes a base substrate 301 (e.g., a monocrystalline or polycrystalline silicon substrate) having a deposition layer 303 formed thereon. In this example, due to the performance of a previous semiconductor device processing step, the deposition layer 303 (e.g., a metal layer or a dielectric layer) includes a varying film thickness, which resulted in the asymmetric thickness profile 328. The asymmetric thickness profile 328 has a thicker portion 330 and a thinner portion 332. The portions 330 and 332 are separated by a dividing line 334, which is shown as an imaginary line in FIG. 3A for illustrative purposes and is not physically present on the substrate 115. The asymmetric thickness profile 328 is further described in FIG. 3B.

[0044] The substrate 115 has a notch 313, such as the V-shaped notch previously described in FIG. 1. The notch 313 generally indicates the orientation of a crystal plane formed in the substrate 115 and may be used to further orient the substrate 115 during processing. For example, the asymmetric thickness profile 328 is written, logged, or stored in memory with reference to the notch 313, so that the positions and orientations of the thicker portion 330 and the thinner portion 332 are known during processing of the substrate 115. A controller (e.g., controller 190 in FIG. 1) may be used to track the orientation of the asymmetric thickness profile 328 as the substrate 115 is processed as previously described in FIG. 1.

[0045] As shown in FIG. 3A , the polishing pad 204 and the carrier head 210 both rotate in a counterclockwise direction. In some embodiments, the polishing pad 204 and the carrier head 210 both rotate in a clockwise direction. In other embodiments, the polishing pad 204 and the carrier head 210 rotate in opposite directions. For example, the polishing pad 204 rotates in a clockwise direction and the carrier head 210 rotates in a counterclockwise direction. The polishing pad 204 rotates with the platen 202 and the substrate 115 rotates with the carrier head 210. Although described with respect to FIG. 3A , the rotational directions of the polishing pad 204 and the carrier head 210 may be applied to any figure and / or embodiment disclosed herein.

[0046] 3A, the polishing pad axis 206 and the carrier head axis 216 are substantially parallel and not collinear. In other embodiments, the carrier head 210 is at a different position relative to the polishing pad axis 206.

[0047] In other embodiments, during polishing, the carrier head 210 sweeps back and forth along the x-axis of the coordinate system 201 from the inner diameter of the polishing pad 204 to the outer diameter of the polishing pad 204, in part to improve polishing uniformity and reduce uneven wear of the substrate 115. In some embodiments, the carrier head 210 sweeps up and down the y-axis of the coordinate system 201 during polishing. In some embodiments, the carrier head 210 sweeps about the polishing pad axis 206 during polishing. In other embodiments, the polishing pad 204 sweeps during polishing, but the carrier head 210 does not. In other embodiments, the polishing pad 204 and the carrier head 210 sweep during polishing. In general, the sweep of the carrier head 210 across the platen also affects the relative velocity calculation at any instant in time and therefore may be compensated for in one or more of the methods disclosed herein.

[0048] 3B shows a schematic side view of the substrate 115 according to an embodiment described herein. In particular, FIG. 3B shows an asymmetric thickness profile 328 of the substrate 115.

[0049] In this embodiment, the dividing line 334 is shown such that the surface area of ​​the thinner portion 332 is equal to the surface area of ​​the thicker portion 330. In some embodiments, the surface area of ​​the thinner portion 332 is not equal to the surface area of ​​the thicker portion 330. Although in this embodiment, and the embodiment shown in Figure 3A, the dividing line 334 is shown as a straight line, in some embodiments, the dividing line 334 is a different type of line, such as an arc, a spline, or a freeform line.

[0050] In these embodiments, the asymmetric thickness profile 328 of the substrate 115 has a minimum thickness 333 and a maximum thickness 331. For ease of explanation, it is assumed that the thickness of the substrate 115 increases linearly between the minimum thickness 333 and the maximum thickness 331. However, the assumption that the thickness varies linearly is not limiting with respect to the scope of the disclosure provided herein.

[0051] 3A and 3B, minimum thickness 333 and maximum thickness 331 are located on the periphery of substrate 115. In some embodiments, peak thicknesses 331 and 333 are not located on the periphery, but instead are located at other locations within thinner portion 332 and / or thicker portion 330, respectively.

[0052] 4A-4C show plots of several points on the substrate 115 and their relative velocities, according to embodiments described herein. In particular, FIGS. 4A-4C show how the relative velocities of points on the substrate 115 vary with angular position and / or distance (e.g., radius) from the carrier head axis 216. The relative velocities of the points vary with the radial and angular positions of the points based on the radial and angular velocity components of the substrate 115 and the polishing pad 204. Thus, the varying relative velocities can result in different wear rates (e.g., polishing rates) for different portions or points of the substrate 115.

[0053] 4A shows the locations of several points on substrate 115. The points are shown in pairs that are on opposite sides of substrate 115 (e.g., 180 degrees apart) and at the same distance from carrier head axis 216. For example, a first point 440 and a second point 442 are on opposite ends of substrate 115 and on the same diameter (e.g., radial distance from carrier head axis 216). The following points are also pairs: 435a and 435b, 436a and 436b, 437a and 437b, 438a and 438b, and 439a and 439b, with each pair on the same diameter. As shown, points 436a, 436b, 438a, 438b, 440, and 442 are located a first radial distance from carrier head axis 216, and points 435a, 435b, 437a, 437b, 439a, and 439b are located a second radial distance from carrier head axis 216. The first radial distance is greater than the second radial distance.

[0054] 4A shows several angular position markers 426 (e.g., angular position marker 426a at 0 degrees, angular position marker 426b at 90 degrees, angular position marker 426c at 180 degrees, and angular position marker 426d at a 270 degree angular position) that represent the angular position of a point. The substrate 115 rotates as part of a system with a carrier head (not shown) and polishing pad 204 similar to that previously described in FIG. 2. As shown in FIG. 4A, the carrier head axis 216 is a distance 426d (e.g., R d ) offset, so that at any instant in time, the rotation of polishing pad 204 results in a relative velocity between each of the points on the surface of substrate 115 and their corresponding points on polishing pad 204. Portions of polishing pad 204 and platen 202 are shown in phantom to indicate that only portions of polishing pad 204 and platen 202 are shown.

[0055] In FIG. 4A, the relative velocity of the first point 440 consists of the velocity of the point on the polishing pad 204 that is at the location of the first point 440 and the velocity of the point on the carrier head (e.g., carrier head 210 in FIG. 3A) that is at the location of the first point 440. Thus, the rotational speed of the polishing pad 204 and the rotational speed of the carrier head each contribute to the relative velocity of the first point 440, and varying either one will result in the different relative velocities described with respect to FIG. 4D. In the example described in FIGS. 4A-4C, the rotational speed of the polishing pad is 81 revolutions per minute (RPM) and the rotational speed of the carrier head is 66 RPM. In further embodiments, different rotational speeds are used for the polishing pad and the carrier head.

[0056] Referring to Figure 4B, curve 428 represents the relative velocity at all points on substrate 115 at a first radial distance as a function of angular position. The relative velocities of points 436a, 436b, 438a, 438b, 440, and 442 are shown on curve 428 according to their angular positions. For example, second point 442 is at 0 degrees and point 438b is at 35 degrees. Figure 4B thus shows an example of relative velocity at a constant rotational speed for a first radial distance.

[0057] In particular, the relative velocity along curve 428 changes as substrate 115 rotates about carrier head axis 216. For example, the relative velocity increases as angular position changes from second point 442 to point 438b. In this embodiment, the relative velocity continues to increase until it reaches a maximum relative velocity at 90 degree angular position marker 426b, which coincides with a radial position extending from polishing pad axis 206, through carrier head axis 216, and through point 436b. The relative velocity then decreases as angular position increases until it reaches a minimum at point 436a, and then increases until angular position once again reaches point 442. In this example, the rotational speed of carrier head 210 and substrate 115 is significantly different from the rotational speed of polishing pad 204 (e.g., carrier head / substrate rotational speed is 90% or less of polishing pad rotational speed). Thus, as will be explained further below, in this example, the velocity vectors at point 493 on substrate 115 and at point 436 on polishing pad 204 are aligned in the same direction due to the counterclockwise rotation of both substrate 115 and polishing pad 204, but the polishing rate is greater on substrate 115 at point 436b than at point 436a, and their velocity vectors are in the opposite direction at point 436a, primarily due to the increased velocity difference at point 436b versus point 436a due to the difference in radii extending from polishing pad axis 206. This effect is explained further in Figures 4D-4E and 5A.

[0058] 4B, the relative velocity at a first point 440 is the same as a second point 442. Although the relative velocity varies with angular position, when using a constant rotational velocity, the difference will average out to be the same for a given radius when a full rotational angular sweep (e.g., >360 degrees) is repeated at least once, and more generally multiple times. Thus, in this embodiment, all points on a given radius of the substrate 115 (e.g., points 436a, 436b, 438a, 438b, 440, and 442) will wear at the same rate.

[0059] 4C shows the relative velocities of points 435a, 435b, 437a, 437b, 439a, and 439b according to their angular positions. The angular positions of points 435a, 435b, 437a, 437b, 439a, and 439b are the same as the angular positions of points 436a, 436b, 438a, 438b, 440, and 442 (in FIG. 4B), respectively. For example, the first point 440 and point 439a are both located at 180 degrees from the position marker 426a (e.g., at 0 degrees).

[0060] Curve 429 represents the relative velocity at all points on substrate 115 at the second radial distance, including points 435a, 435b, 437a, 437b, 439a, and 439b, as a function of angular position. As shown, the relative velocities of points 435a, 435b, 437a, 437b, 439a, and 439b vary with angular position in a manner similar to that described in FIG. 4B. Thus, the relative velocity of curve 429 increases and decreases with angular position in the same manner as curve 428 shown in FIG. 4B, but curve 429 has a smaller difference between its maximum and minimum relative velocities (e.g., at points 435b and 435a, respectively) than curve 428 (e.g., the maximum relative velocity at point 436b and the minimum relative velocity at point 436a). The difference is smaller because the second radial distance is smaller than the first radial distance. However, the relative velocities of curves 428 and 429 will average out to be the same over the course of one complete rotation (e.g., from 0 to 360 degrees) when a constant rotational speed is used for polishing pad 204 and carrier head, as shown by the dashed lines in Figures 4B and 4C. Thus, the average relative velocity is the same for all points on substrate 115.

[0061] Varying the rotational speed of the polishing pad 204 and / or the carrier head can also change the relative speed and therefore the polishing process material removal rate, also referred to herein as the polishing rate, of the substrate 115. In particular, varying the rotational speed of the carrier head along with the angular position of a given point on the substrate 115 can result in different relative speeds (and therefore polishing process material removal rates) for different portions or points of the substrate 115. This concept can be used to produce asymmetric removal profiles as illustrated in Figures 5B-5D.

[0062] Relative Velocity Analysis 4D is a schematic plan view of polishing pad 204 and substrate 115 that is used herein to describe a process for determining the magnitude of the relative velocity of a point (e.g., point 438a) that coincides with a point on substrate 115 during a portion of a polishing process according to embodiments described herein. In some embodiments, carrier head 210 and / or polishing pad 204 typically sweep during polishing, but this motion is ignored in this description for simplicity of explanation. Coordinate system 401 is similar to coordinate system 201. In some embodiments, coordinate system 401 has an origin at polishing pad axis 206. In other embodiments, the origin is at carrier head axis 216.

[0063] An equation for calculating the magnitude of the relative velocity of point 438a is derived in several steps. "Analysis of Slurry Flow in Chemical-Mechanical Polishing" by Krzysztof D. Kopanski, Thesis (SM)-Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005, which is incorporated herein by reference in its entirety, describes some methods related to calculating relative velocity as described herein. Furthermore, "Mechanics, Mechanisms, and Modeling of the Chemical Mechanical Polishing Process" by Jiun-Yu Lai, Thesis (Ph.D.)-Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001, which is incorporated herein by reference in its entirety, describes further methods related to calculating relative velocity as described herein. Using similar notation as described in these references, the relative velocity vector of a point on substrate 115 is calculated as follows, where the variables used may differ from the references: TIFF0007635435000001.tif10170, where V rel is the relative velocity of a point (e.g., point 438a) on the substrate 115, and ω p is the angular velocity 441p of the polishing pad 204, and ω s is the angular velocity 443s of the substrate 115, and r s is the radius 443r between the carrier head axis 216 and that point, and R d is the distance 441d between the polishing pad axis 206 and the carrier head axis 216, and φ is R d4. The angle 443a between the x-axis 401x of the coordinate system 401 and the radius 443r, which is collinear with the x-axis 401x of the coordinate system 401. As explained in "Analysis of Slurry Flow in Chemical-Mechanical Polishing," the typical oscillating sweeping movement of the carrier head 210 relative to the polishing pad 204 can be ignored since that movement does not contribute significantly to the relative velocity.

[0064] The magnitude of the relative velocity is calculated as follows: TIFF0007635435000002.tif13170, where |V rel | is the magnitude of the relative velocity. Thus, a larger difference between the angular velocity 441p of the polishing pad 204 and the angular velocity 443s of the substrate 115 will result in a larger difference between the maximum and minimum relative velocities. Similarly, a point that is rotated at a larger radius (e.g., radial distance) between the carrier head axis 216 and the point will experience a larger maximum and minimum relative velocity than a point that is rotated at a smaller radius. However, as illustrated in Figures 4B and 4C, over the course of one complete rotation, the angular velocity 441p of the polishing pad 204 on the substrate 115 may be larger than the angular velocity 443s of the substrate 115 at a given radius (e.g., r s ) will be the same when polishing pad 204 and carrier head 210 rotate at a constant angular velocity.

[0065] Although not used in the previous equation for the relative velocity vector, the polishing pad 204 is rotated along a radius 441r between the polishing pad axis 206 and the point (e.g., r p), and angle 441a (e.g., θ) between x-axis 401x and radius 441r. Angles 441a and 443a are oriented as shown by angular position markers 446 (e.g., angular position marker 446a at 0 degrees, angular position marker 446b at 90 degrees, angular position marker 446c at 180 degrees, and angular position marker 446d at 270 degree angular position). Notably, angular position markers 446 are oriented differently than 426 in FIG. 4A, which is described later in FIG. 4D.

[0066] The angular velocities 441p and 443s are calculated according to the following formulas: ω=RPM / (60sec / min)*2πrad / rev where ω is angular velocity. In one example, the carrier head 210, and thus the substrate 115, rotates at a constant rate of 66 RPM. Thus, the angular velocity 443s of the substrate 115 is 6.91 rad / sec. In one example, the polishing pad 204 rotates at a constant rate of 81 RPM, and thus, the angular velocity 441p is 8.48 rad / sec.

[0067] In one example, substrate 115 is a 300 mm wafer, so radius 443r is 0.15 m since point 438a is at the outer periphery or edge of substrate 115. Point 438a is at angle 443r of 125 degrees (2.18 rad). Distance 441d between polishing pad axis 206 and carrier head axis 216 is 0.19 m. Thus, the magnitude of the relative velocity at point 438a is 1.49 m / s.

[0068] As previously explained, the angular position markers 446 are shown in a different orientation than the angular position markers 426 in FIG. 4A such that they are shifted by 90 degrees compared to FIG. 4A. For example, the 90 degree angular position marker 426b in FIG. 4A is in the same orientation as the 0 degree angular position marker 446a in FIG. 4D. Therefore, when calculating the relative velocity for points at different angular positions, this 90 degree shift should be taken into account. In this example, the radius 443r is oriented such that the radius 443r, and thus the point 438b, is at an angular position of 125 degrees. However, as shown in FIGS. 4A and 4B, the point 438b is at an angular position of 215 degrees (90 degrees more than 125 degrees). Therefore, when calculating the magnitude of the relative velocity of the point, 90 degrees must be added to the angle to convert to the angular position marker 426.

[0069] In other embodiments, polishing pad 204 and / or carrier head 210 may rotate at different constant speeds or at variable rotational speeds, as described in Figures 5A-5F. In such embodiments, the equations described in this section may be used to calculate the relative velocities for the period during which the angular velocity is constant.

[0070] 4E is a schematic plan view of the polishing pad 204 and the substrate 115 that is used herein to describe a process for determining the magnitude of the relative velocity of a different point (e.g., a first point 440) that coincides with a point on the substrate 115 during a portion of the polishing process according to embodiments described herein. The magnitude of the relative velocity is calculated in a manner substantially similar to that described in FIG. 4D.

[0071] In FIG. 4E, a first radius 453r (e.g., r1 s ) is between the carrier head axis 216 and the first point 440, and a first angle 443a (e.g., φ1) is between the x-axis 401x of the coordinate system 401 and the first radius 453r. p) is between the polishing pad axis 206 and the first point 440, and a second angle 451a (eg, θ2) is between the x-axis 401x and the second radius 451r.

[0072] In one example, the substrate 115 is a 300 mm wafer, and therefore the first radius 453r is 0.15 m since the point 438a is at the outer periphery or edge of the substrate 115. The angular velocity 443s of the substrate 115 is 6.91 rad / sec, and the angular velocity 441p of the polishing pad 204 is 8.48 rad / sec. The first point 440 is at a first angle 453a of 90 degrees (1.57 rad). The distance 441d between the polishing pad axis 206 and the carrier head axis 216 is 0.19 m. Thus, the magnitude of the relative velocity at the point 440 is 1.62 m / s. When considering the angle shift described in FIG. 4D, the first point 440 is at 180 degrees as shown in FIG. 4A and FIG. 4B.

[0073] Asymmetric Removal Process Example 5A and 5B show the relative velocities of a first point 540 and a second point 542 on a substrate 115 at different rotational speeds of a carrier head 210, according to embodiments described herein. In particular, the substrate 115 may rotate about the carrier head axis 216, and what were formally known simply as first point 440 and second point 442 are now referred to as first point 540 and second point 542. For example, points 540 and 542 rotate with the substrate 115 to different angular positions from their initial starting points, which coincide with points 440 and 442 in FIG. 4A. The relative velocities vary with the angular positions of points 540 and 542, similar to those previously described in FIGS. 4A-4E.

[0074] Figure 5A shows angular positions for points 540 and 542 on substrate 115. In particular, Figure 5A is substantially similar to Figure 4A and shows substrate 115 in carrier head 210 with angular position marker 426.

[0075] Figure 5B shows a graph of the relative velocities of points 540 and 542 at different, constant rotational speeds of carrier head 210, relative to a constant polishing pad (e.g., polishing pad 204 in Figure 3A) rotational speed. In particular, Figure 5B shows the relative velocities of points 540 and 542 at different angular positions for different rotational speeds of carrier head 210, relative to a constant polishing pad rotational speed.

[0076] In this embodiment, both the polishing pad 204 and the carrier head 210 rotate in a counterclockwise direction. In one example polishing process, the rotational speed of the polishing pad 204 is constant at 81 RPM. Lines 564a and 564b show the relative speed at a carrier head 210 rotational speed of 66 RPM (e.g., the carrier head / substrate rotational speed is approximately 80% of the polishing pad rotational speed) as a function of the angular position of points 540 and 542 of the substrate 115 from the 0 degree position. Similarly, lines 565a and 565b show the relative speed for 73.5 RPM (e.g., the carrier head / substrate rotational speed is approximately 90% of the polishing pad rotational speed). Lines 567a and 567b show the relative speed for 88.5 RPM (e.g., the carrier head / substrate rotational speed is approximately 110% of the polishing pad rotational speed). 568a and 568b show relative speeds for 96 RPM (eg, the carrier head / substrate rotation speed is approximately up to 120% of the polishing pad rotation speed).

[0077] In one embodiment of this configuration, where the rotational speed of polishing pad 204 and the rotational speed of carrier head 210 are both 81 RPM, as is the case for lines 566a and 566b, the relative speed of each of points 540 and 542 is constant, equal, and does not vary with the position of carrier head 210. In particular, the relative speed increases and decreases as carrier head 210 rotates and when the rotational speed of carrier head 210 differs from the rotational speed of polishing pad 204. As shown, the relative speed converges at 0 degrees, 180 degrees, and 360 degrees.

[0078] Although this application refers to 360 degrees and 0 degrees, these terms are not limiting and may be used interchangeably unless otherwise noted. For example, 360 degrees is the same physical angular position as 0 degrees and may be referred to or shown in figures as 0 degrees.

[0079] The increasing and decreasing maximum and minimum relative velocities may be beneficially used to control the relative velocity for points such as first point 540, which is at the maximum thickness of substrate 115, to adjust the polishing rate at those points. For example, if the rotational speed of first point 540 is 66 RPM within the angular region of 0 degrees to 180 degrees, the relative velocity is shown as line 564a, with a maximum relative velocity (i.e., maximum polishing rate) at 90 degrees. If the rotational speed switches to 96 RPM when first point 540 is within the angular region of 180 degrees to 360 degrees, the relative velocity follows line 568b, with a second maximum relative velocity at 270 degrees. The relative velocity of second point 542, which is at the opposite edge of substrate 115, would then follow lines 564b and 568a, which have minimum relative velocities at 90 degrees and 270 degrees. The average relative velocity of lines 564a and 568b is higher than the average relative velocity of lines 564b and 568b, and thus the polishing rate experienced by the first point 540 is different from the polishing rate experienced by the second point 542. Thus, as explained, varying the rotational speed of the carrier head 210 along with the angular position of the first point 540 ensures that the first point 540 experiences a higher average relative velocity during this portion of the polishing process than the second point 542. This is used to result in a polishing rate experienced by the second point 542, which corresponds to a minimum thickness, in this example, versus a higher polishing rate for the first point 540, which corresponds to a maximum thickness of the substrate, during the polishing process, thus resulting in an asymmetric removal profile.

[0080] 5C and 5D show the relative velocities of points 540 and 542 as carrier head 210 rotates at variable rotational speeds, according to embodiments described herein. In particular, Figures 5C and 5D show a first rotational speed 570 and a second rotational speed 572. As described in Figure 5B, the relative velocity varies with the rotational speed and angular position of carrier head 210.

[0081] 5C shows a first zone 571 and a second zone 573 separated by a dividing line 579. The dividing line 579 is shown in phantom for purposes of illustration and does not physically exist on the substrate 115. The dividing line connects the 0 degree and 180 degree angular positions and is fixed in space. The zones 571 and 573 are used to explain how the rotational speed of the carrier head 210 (e.g., first rotational speed 570 and second rotational speed 572) varies with the angular position of the first point 540.

[0082] As carrier head 210 rotates, the first point 540 is in one of the zones and the second point 542 is in the other zone, unless both point 540 and point 542 are between zone 571 and zone 573 on dividing line 579. For example, when first point 540 is in second zone 573, second point 542 is in first zone 571. As previously described in FIG. 5B, the average relative velocity of points 540 and 542 can be controlled by varying the rotational speed of carrier head 210 as a function of angular position. As mentioned above, in this example, it is assumed that the platen and polishing pad are rotating at a constant speed, and therefore the average relative velocity of points 540 and 542 is directly affected by adjusting the rotational speed of carrier head 210. In one example, while the first point 540 is in the second zone 573, the carrier head 210 rotates at a second rotational speed 572, and while the first point 540 is in the first zone 571, the carrier head 210 rotates at a first rotational speed 570. This ensures that the average relative speed of the first point 540 is higher than the average relative speed of the second point 542 when appropriate rotational speeds 570 and 572 are used. The higher average relative speed of the first point 540 results in a higher polishing rate for the first point 540, which results in an asymmetric removal profile in which more material is removed at the first point 540 than at the second point 542. The asymmetric removal profile is beneficial when the first point 540 is at or near a maximum thickness of the substrate 115 and the second point 542 is at or near a minimum thickness.

[0083] In this manner, the asymmetric removal profile can be used to correct layer thickness asymmetry in the substrate 115. As previously described in FIG. 1, the measurements and orientation of the thickness profile formed on the substrate are detected and recorded prior to polishing. The asymmetric removal profile can be modeled prior to polishing using the concepts described in the previous figures. For example, the material removal rate can be calculated or correlated using the rotational speed of the polishing pad and carrier head 210. In this embodiment, the material removal rate varies between zones 571 and 573 because different rotational speeds 570 and 572 are used for each of zones 571 and 573. Other factors, such as the downforce applied to the substrate 115 during polishing, the fluid used for polishing, and the flow rate of that fluid, can also be considered in adjusting the asymmetric removal profile model. The model further uses the determined positions and orientations of the maximum and minimum thicknesses of the substrate 115 to define the alignment of the asymmetric removal profile with the asymmetric thickness profile of the substrate 115 such that the asymmetry of the substrate is reduced or eliminated after polishing.

[0084] 5D shows a plot of the relative velocities of points 540 and 542 at rotational speeds 570 and 572 of carrier head 210 during polishing. In particular, FIG. 5D shows the effect of varying the rotational speed of carrier head 210 based on whether first point 540 is in zone 571 or zone 573.

[0085] In this embodiment, the first rotational speed 570 is 66 RPM and the second rotational speed 572 is 96 RPM. As the first point 540 travels through the second zone 573, the relative speed of the first point 540 is shown by line 574a and the relative speed of the second point 542 is shown by line 576a. As the first point 540 travels through the first zone 571, the relative speed of the first point 540 is line 574b and the relative speed of the second point 542 is line 576b.

[0086] Varying the rotational speed of carrier head 210 results in the relative velocity of first point 540 (e.g., line 574) being generally higher than the corresponding second relative velocity of second point 542 (e.g., line 576). In this example, first point 540 travels at a maximum relative velocity of about 1.85 m / sec at 90 degrees and 270 degrees, respectively. While the first point is at its maximum relative velocity, second point 542 is at a minimum relative velocity of about 1.38 m / sec at 270 degrees and 90 degrees. The higher relative velocity of first point 540 (e.g., lines 574a and 574b) beneficially results in an asymmetric removal profile, as previously described in Figures 5B and 5C.

[0087] As described in Figures 4A-4E, points along the same radius (e.g., radius 443r in Figure 4D) will have maximum and minimum relative velocities at the same angular positions (e.g., points 436b and 435b in Figures 4B and 4C, respectively). Thus, if the substrate 115 is oriented such that its maximum thickness coincides with the radius of the first point 440 described in Figures 5A-5D, the point at the maximum thickness will travel at the highest average relative velocity and wear at a faster rate than other angular positions of the substrate 115. This is true even if the maximum thickness is at a shorter radius than the minimum thickness and thus the relative velocity of the point at the maximum thickness has a smaller magnitude than the relative velocity of the point at the minimum thickness. Thus, orienting the substrate 115 such that the point at the maximum thickness induces rotational velocities 570 and 572 as described in Figure 5D ensures that the point at the maximum thickness experiences the highest wear rate. In some embodiments, this means placing or aligning the point at maximum thickness (eg, first point 540) at the angular position marker 426a (eg, 0 degrees) at the beginning of the polishing process.

[0088] 5E shows a chart of two rotational speed functions, such as a square wave 580 and a sine wave 578, that vary rotational speeds 570 and 572 as a function of the angular position of a first point 540 during a full rotational cycle of carrier head 210. As shown, first point 540 begins the cycle at 0 degrees, which is a different starting angular position than in FIG.

[0089] In some embodiments, such as in Figures 5B and 5D, a square wave 580 function is used to achieve the rotational speeds 570 and 572. In this embodiment, when using the square wave 580 function, the second rotational speed 572 is set to 96 RPM while the first point 540 is in the second zone 573, and the first rotational speed 570 is set to 66 RPM while the first point 540 is in the first zone 571. The first rotational speed 570 and the second rotational speed 572 are achieved through a first rotational speed profile and a second rotational speed profile, respectively, because the carrier head 210 must ramp up and down when transitioning between the rotational speeds 570 and 572. For example, the carrier head 210 cannot instantly switch between 96 RPM and 66 RPM. Thus, the rotational speeds 570 and 572 each include multiple rotational speeds. Thus, the substrate 115 may be rotated about an angle about the carrier head axis 216 in a first rotational speed profile, and then rotated about another angle in a second rotational speed profile such that the first rotational speed profile differs from the second rotational speed profile. Alternatively, the substrate 115 may be rotated 180 degrees or less within a 360 degree rotation in a first rotational speed profile, and then rotated 180 degrees or less within a 360 degree rotation in the second rotational speed profile such that the second rotational speed profile differs from the first rotational speed profile. This process may be repeated at least once.

[0090] This cycle continues as the carrier head 210 continues to rotate during processing. However, the sudden and repeated changes in rotational speeds 570 and 572 may be hard on the mechanisms, motors, or actuators that drive the rotation of the carrier head 210, and a smoother transition between zones 571 and 573 may be desired. Thus, in some embodiments, a sine wave 578 is used to achieve the rotational speeds 570 and 572 through the first and second rotational speed profiles. In one example, when using a sine wave 578 function, the second rotational speed profile starts at 81 RPM at 180 degrees while the first point 540 is in the second zone 573, gradually increases to a second rotational speed 572 (e.g., 96 RPM) at 270 degrees, and then gradually decreases back to 81 RPM at 360 degrees. Upon entering the first zone 571 at 0 degrees, the rotational speed transitions to the first rotational speed profile at 81 RPM, gradually decreases to the first rotational speed (e.g., 66 RPM) at 90 degrees, and then gradually increases back to 81 RPM at 180 degrees. The cycle repeats when the first point 540 re-enters the second zone 573. The gradual increase and decrease of the sine wave 578 provides a more gradual, smoother transition between zones 571 and 573 than the square wave 580 for the mechanisms, motors, or actuators that drive the rotation of the carrier head 210, thus improving the life of the mechanical components in the system.

[0091] FIG 5F shows a chart of the relative velocities of points 540 and 542 using the rotational speed function described in FIG 5E according to embodiments described herein. In particular, FIG 5F shows the effect of using a square wave 580 and a sine wave 578 to control the rotational speeds 570 and 572 of carrier head 210 based on whether first point 540 is in zone 571 or zone 573. In this example, first rotational speed 570 is 66 RPM and second rotational speed 572 is 96 RPM. Thus, the relative speed of first point 540 as it travels through second zone 573 is shown by line 574a when using square wave 580 and by line 575a when using sine wave 578. The corresponding relative velocity for second point 542 is shown by line 576a when using square wave 580 and by line 577a when using sine wave 578. Similarly, the relative velocity of first point 540 as it progresses through first zone 571 is shown by line 574b when using square wave 580 and by line 575b when using sine wave 578. The corresponding relative velocity for second point 542 is shown by line 576b when using square wave 580 and by line 577b when using sine wave 578.

[0092] As shown, the relative velocities 574 and 576 (e.g., lines 574 and 576) for square wave 580 have, on average, a greater magnitude than the relative velocities 575 and 577 (e.g., lines 575 and 577), respectively, of sine wave 578. In one example, the average of the relative velocities 574 and 576 for square wave 580 is about 20% greater than the average of the relative velocities 575 and 577 for sine wave 578. However, as previously described, sine wave 578 beneficially provides a smoother transition between rotational velocity 570 and rotational velocity 572. Thus, in some embodiments, sine wave 578 is used to avoid excessive wear on the carrier head rotation actuator.

[0093] In further embodiments, other rotational speed profiles, or wave patterns, such as triangular or sawtooth rotational motion profiles, are used in place of the square wave 580 or sine wave 578. Although the examples provided herein disclose only a few different rotational speeds of the polishing pad 204 and / or carrier head 210, these examples are not limiting with respect to the disclosure described herein, as other rotational speeds can be used for the polishing pad 204 and / or carrier head 210. Moreover, the rotating polishing pad configurations described herein are also not limiting with respect to the scope of the disclosure provided herein, as configurations utilizing linear motion of the polishing pad (e.g., belt-style processes) can alternatively be used to achieve a desired relative velocity over the surface of the substrate.

[0094] In further embodiments, the zones 571 and 573 may be defined to include other angular positions than 0 degrees and 180 degrees. In further embodiments, the zones may not cover equal angular rotation positions. For example, the substrate rotates about a first angle other than 180 degrees at a first rotation speed, and then rotates about a second angle other than 180 degrees at a second rotation speed. For example, the first angle may be 30 degrees (such as between a 30 degree rotation position and a 60 degree rotation position) and the second angle may be 300 degrees (such as between a 60 degree rotation position, through a 360 degree rotation position, and a 30 degree rotation position). In further embodiments, more than two zones (e.g., zones 571 and 573) may be used to vary the rotation speed.

[0095] In a further embodiment, the rotational speed of the polishing pad 204 is varied and the rotational speed of the carrier head 210 is held at a constant rotational speed. This process can achieve a similar effect to varying the rotational speed of the carrier head 210 and holding the rotational speed of the polishing pad constant. For example, the average relative speed of the first point 540 can be made higher than the average relative speed of the second point 542, beneficially producing an asymmetric removal profile.

[0096] In further embodiments using the concepts described herein, the rotational speeds of the polishing pad and carrier head 210 are varied to beneficially produce an asymmetric removal profile. In some embodiments, the rotational speed of the polishing pad 204 and the rotational speed of the carrier head 210 are both adjusted to improve the speed at which the asymmetric removal process is performed and / or to achieve better control of the removal rate during different stages of the polishing process. In one example, it may be desirable to include a high removal rate at the beginning of the polishing process and then gradually slow that removal rate as the asymmetry is reduced by adjusting the relative speeds (e.g., varying the rotational speeds of both) during one or more different stages of the process.

[0097] 6 illustrates a functional block diagram of an example of a controller 190 for a carrier head (e.g., carrier head 210 in FIG. 2) and / or a platen or polishing pad (e.g., platen 202 or polishing pad 204 in FIG. 2). The controller 190 includes a processor 192 in data communication with a memory 194, an input device 630, and an output device 640. Although not illustrated, other embodiments of the controller 190 have similar components as those illustrated for the controller 190. In some embodiments, the processor 192 is further in data communication with an optional network interface card 650. Although described separately, it should be appreciated that the functional blocks described with respect to the controller 190 need not be separate structural elements. For example, the processor 192 and the memory 620 may be embodied in a single chip. The processor 192 may be a general purpose processor, a digital signal processor ("DSP"), an application specific integrated circuit ("ASIC"), a field programmable gate array ("FPGA") or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any suitable combination thereof designed to perform the functions described herein. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0098] The processor 192 may be coupled to read or write information from or to the memory 620 via one or more buses. The processor may additionally or alternatively include memory, such as processor registers. The memory 620 may include a processor cache, including a multi-level hierarchical cache, where different levels have different capacities and access speeds. The memory 620 may also include random access memory (RAM), other volatile storage devices, or non-volatile storage devices. The storage may include hard drives, flash memory, and the like. In various instances, the memory is referred to as a computer-readable storage medium. A computer-readable storage medium is a non-transitory device capable of storing information, and is distinguishable from a computer-readable transmission medium, such as an electronic transitory signal capable of conveying information from one location to another. The computer-readable medium described herein may generally refer to a computer-readable storage medium or a computer-readable transmission medium.

[0099] The processor 192 may also be coupled to input devices 630 and output devices 640 for receiving input from and providing output to a user of the controller 190, respectively. Suitable input devices include, but are not limited to, a keyboard, buttons, keys, switches, pointing devices, mice, joysticks, remote controls, infrared detectors, barcode readers, scanners, video cameras (possibly coupled with video processing software, e.g., to detect hand or facial gestures), motion detectors, or microphones (possibly coupled with audio processing software, e.g., to detect voice commands). The input devices 630 include encoders or other sensors for measuring rotation of the carrier head 210 or platen 202 as described in FIG. 2. Suitable output devices include, but are not limited to, visual output devices, including displays and printers, audio output devices, including speakers, headphones, earphones, and alarms, additive manufacturing machines, and haptic output devices. As illustrated in FIG. 2, the output device 640 includes various electrical components configured to drive and control the mechanisms or motors used to drive rotation of the carrier head 210 or platen 202 .

[0100] In some embodiments, the processor 192 includes a timing element 615, such as a crystal or a resistor-capacitor combination, used as part of an internal oscillator. The timing element may be used by the processor 192 to keep time, for example, in conjunction with an encoder to calculate rotational speed.

[0101] In further embodiments, the input devices 630, the output devices 640, the network interface card 650, and / or other components are considered support circuitry (eg, the support circuitry in FIG. 1).

[0102] Process sequence example FIG. 7 illustrates an example of an asymmetric polishing process sequence 700 that may be performed in a polishing system, such as the CMP system 100 shown in FIG. 1. The process sequence described with respect to FIG. 7 focuses primarily on the processes used to perform the asymmetric polishing process, but this abbreviated list of processes is not limiting with respect to the scope of the disclosure described herein, as other polishing process operations may be inserted before, during, or after the operations described with respect to the asymmetric polishing process sequence 700 without departing from the basic scope of the disclosure provided herein. In one example, as briefly described above, one or more cleaning processes may be performed on the substrate in the cleaning apparatus 104 in the CMP system 100 after the asymmetric polishing process sequence 700 is performed on the substrate. In another example, one or more additional polishing processes (i.e., asymmetric polishing processes or conventional symmetric polishing processes) may also be performed on the substrate on the same or different polishing pad 204 in the CMP system 100 using the same carrier head 210, either before or after performing the asymmetric polishing process sequence 700.

[0103] In operation 702, the substrate 115 is removed from the cassette 114 by the drying robot 110 and placed in the pre-aligner 118. The pre-aligner 118 is then used to determine an orientation of the substrate 115 by detecting one or more features formed on the surface of the substrate 115, such as the notch 313. The pre-aligner 118 then positions the substrate 115 in a desired angular orientation such that the drying robot 110 can then receive the oriented and pre-aligned substrate 115.

[0104] In operation 704, the oriented and pre-aligned substrate 115 is then removed from the pre-aligner 118 by the drying robot 110 and placed in the metrology station 117. As described above, the metrology station 117 is then used to measure the thickness profile of the substrate 115 and determine the orientation of the thickness profile relative to one or more features formed on the surface of the substrate 115, such as the notch 313. During operation 704, the controller 190 receives the thickness profile measurements and orientation from the metrology station 117. The controller 190 can then use the measurements and substrate orientation information to coordinate the asymmetric polishing process(es) performed in a subsequent operation, for example, as described in FIG. 5D.

[0105] In some embodiments, operations 702 and 704 are performed in the same chamber, and therefore a separate pre-aligner 118 may not be required since the metrology station 117 includes one or more substrate orientation detection elements.

[0106] In operation 706, the oriented, pre-aligned, and thickness profiled substrate 115 is then transferred by the dry robot 110 to the transfer platform 116, and the wet robot 108 then transfers the substrate 115 to the load cup 122. Based on the known orientation, alignment, and thickness profile of the substrate 115, the substrate 115 is then placed in the load cup 122 at a desired position and orientation such that the carrier head 210 can pick up the substrate 115 at a known angular orientation. In some embodiments, the pre-alignment step(s) performed during operation 702 are configured to align and position the substrate 115 such that a subsequent transfer step performed by the dry robot 110 and wet robot 108 will result in the angular alignment of the substrate 115 ending up in the desired orientation in the load cup 122. The ability of the carrier head 210 to receive a substrate 115 having a known thickness profile in a known and desired orientation allows the subsequent asymmetric polishing process in operation 710 to be performed on desired areas of the substrate 115 in one or more of the polishing stations 124.

[0107] In operation 708, the carrier head 210 then picks up the oriented and aligned substrate 115 from its known position in the load cup 122 and transfers the substrate 115 to the surface 204A of the polishing pad 204 in the polishing station 124 so that a subsequent asymmetric polishing process in operation 710 can be performed. Prior to or during operation 708, one or more carrier head 210 orientation sensing elements are used to ensure that the angular orientation of the carrier head 210 relative to the load cup 122 and the position of one or more features formed on the surface of the substrate 115, such as the notch 313, are known and correctly oriented. In some embodiments, the carrier head 210 includes an encoder, position flag, or other orientation sensing element(s) coupled to an actuator (not shown) that cooperate to allow the carrier head 210 to be oriented in a known and desired angular orientation when the carrier head 210 picks up the aligned and oriented substrate 115 from the load cup 122.

[0108] In process 710, the controller 190 then coordinates the relative motion of the carrier head 210 and the polishing pad 204 and / or the platen 202 to perform the process steps used to perform the asymmetric polishing process described with respect to one or more of the asymmetric removal processes described above. In one example, as described with respect to FIG. 5D, the polishing pad 204 may rotate at a constant rotational speed while the rotational speed of the carrier head 210 is varied with the angular position of the carrier head 210. The controller 190 coordinates the rotational speed with the thickness profile of the oriented and aligned substrate 115, such that the orientation of the thickness profile is known with respect to the angular position of the carrier head 210. Coordination of the rotational speed as a function of the angle of the carrier head 210 results in portions of the substrate 115, such as the thicker portions 330, being polished at a different polishing rate than the thinner portions 332. As explained above, providing a higher relative velocity to the thicker portion 330 with respect to the thinner portion 332 results in an asymmetric removal profile that beneficially removes more material from the thicker portion 330 than the thinner portion 332 during polishing. As previously explained, the carrier head 210 and polishing pad 204 or platen 202 may each rotate at different constant and / or varying rotational speeds to achieve a desired asymmetric polishing profile. In some embodiments, the controller 190 uses an orientation sensing element(s) to determine the angular positions of the carrier head 210 and polishing pad 204 or platen 202 and their respective actuators and adjusts the rotational speeds to result in asymmetric removal of material from the substrate.

[0109] After performing operation 710, it may be desirable to perform a symmetric polishing process as described in FIGS. 4A-4E in operation 712. The symmetric polishing process may begin when the difference between the high and low points (e.g., 440 and 442 in FIG. 4A, respectively) of the substrate 115 reaches a minimum value, which may be predetermined, for example, as a set value or as a percentage of thickness. At that minimum value, the substrate is considered to have a uniform thickness profile. During operation 712, the controller 190 rotates the carrier head 210 and the polishing pad 204 and / or platen 202 at a constant rotational speed to provide a symmetric material removal profile. In other embodiments, operation 712 is performed before operation 710.

[0110] After performing operations 710 and / or 712, it may be desirable to measure a post asymmetric polishing process thickness profile on the substrate 115 to determine if an alternative asymmetric polishing process needs to then be performed on the substrate in operation 714. During operation 714, multiple intermediate processes may be performed, such as the carrier head depositing the polished substrate 115 into the load cup 122, the wet robot 108 transferring the substrate 115 to the cleaning apparatus 104, the substrate 115 being cleaned in the cleaning apparatus 104, and the dry robot 110 then receiving the cleaned substrate 115 from the cleaning apparatus 104 and transferring the substrate 115 to the metrology station 117 so that the current thickness profile may be measured. Operations 706-714 may then be completed at least one additional time, if desired, by use of commands from the controller 190. In other embodiments, operation 714 is performed between operations 710 and 712 to check or verify if the difference between the high point and the low point is at or below a minimum value. Processes 710 and 714 may be repeated at least once until a minimum is achieved. Process 714 may then be performed again after process 712 is completed to verify that the results of process 712 are satisfactory.

[0111] The preceding description is provided to enable those skilled in the art to practice the various embodiments described herein. The examples described herein do not limit the scope, applicability, or embodiments described in the claims. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. For example, changes may be made in the function and arrangement of the elements described without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components, as appropriate. For example, the methods described may be performed in different orders than those described, and various steps may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented and a method may be practiced using any number of aspects described herein. Furthermore, the scope of the disclosure is intended to cover such apparatus or methods practiced using other structures, functions, or structures and functions in addition to or other than the various aspects of the disclosure described herein. It should be understood that the aspects of the disclosure disclosed herein may be embodied by one or more elements of a claim.

[0112] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects.

[0113] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. As an example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same element (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other permutation of a, b, and c).

[0114] The term "determining" as used herein encompasses a wide variety of actions. For example, "determining" may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, database, or another data structure), ascertaining, and the like. Also, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, "determining" may include resolving, selecting, choosing, establishing, and the like.

[0115] The methods disclosed herein include one or more steps or actions for achieving the method. Method steps and / or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions may be modified without departing from the scope of the claims. Furthermore, various operations of the methods described above may be performed by any suitable means capable of performing the corresponding functions. Those means may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs), or processors. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.

[0116] The following claims are not limited to the embodiments set forth herein, but are to be accorded the full scope consistent with the language of the claims. Within the claims, reference to an element in the singular does not mean "only one" unless expressly stated as such, but rather means "one or more." The term "some" refers to one or more, unless expressly stated otherwise. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase "means for" or, in the case of a method claim, unless the element is recited using the phrase "step for." All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or that later become known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is made public, regardless of whether such disclosure is expressly recited in the claims.

Claims

1. 1. A method for removing material on a substrate, comprising: rotating a carrier head in contact with a substrate in a first direction about a carrier head axis at a variable rotational speed that varies as a function of an angular position of a reference point on the carrier head during each complete rotational cycle of the carrier head; pressing a surface of the substrate against a polishing surface of a polishing pad supported on a platen while rotating the carrier head; A method comprising:

2. The method of claim 1, further comprising rotating the platen in a second direction about a platen axis.

3. The method of claim 2 , wherein the carrier head axis and the platen axis are substantially parallel and non-collinear.

4. The method of claim 1, wherein the variable rotational speeds include a plurality of first rotational speeds for the angular positions between a first angular position and a second angular position, and a plurality of second rotational speeds for the angular positions between the second angular position and a third angular position.

5. The method of claim 4, wherein the variable rotational speed comprises at least a portion of a step function or a sine function.

6. The method of claim 5 , wherein an average rotational speed of the first rotational speed is greater than an average rotational speed of the second rotational speed.

7. The method of claim 2 , wherein the first direction and the second direction are both rotated in a clockwise direction or both rotated in a counterclockwise direction.

8. The method of claim 2 , wherein rotating the platen about the platen axis comprises rotating the platen at a constant rotational speed.

9. The method of claim 2 , wherein rotating the platen about the platen axis comprises rotating the platen at a variable rotational speed.

10. The method of claim 4, wherein the difference between the third angular position and the first angular position is less than or equal to approximately 360 degrees.

11. The method of claim 1, further comprising measuring a thickness profile of the substrate prior to rotating the carrier head in the first direction about the carrier head axis.

12. orienting and aligning the substrate in accordance with the thickness profile prior to rotating the carrier head about the carrier head axis in the first direction; receiving the oriented and aligned substrate by the carrier head; Further comprising: The method of claim 11 , wherein the carrier head is configured to press the surface of the substrate against the polishing surface of the polishing pad while rotating the carrier head.

13. The method of claim 1 , wherein the variable rotation speed is such that the material is asymmetrically removed from the surface of the substrate.

14. 5. The method of claim 4, wherein rotating the carrier head about the carrier head axis further comprises rotating the carrier head at a constant rotational speed for the angular position between the third angular position and a fourth angular position, the fourth angular position being greater than 360 degrees.

15. 1. A method for removing material on a substrate, comprising: rotating a carrier head in contact with the substrate in a first direction about a carrier head axis; pressing a surface of the substrate against a polishing surface of a polishing pad supported on a platen while rotating the carrier head about the carrier head axis; Rotating the carrier head about the carrier head axis comprises: (a) rotating the carrier head less than 180 degrees within a 360 degree rotation at a plurality of first rotational speeds; (b) then rotating the carrier head 180 degrees or less within the 360 ​​degree rotation at a plurality of second rotational speeds different from the plurality of first rotational speeds; (c) repeating (a) and (b) at least one more time; Including, method.

16. The method of claim 15, further comprising rotating the platen in a second direction about a platen axis.

17. 17. The method of claim 16, wherein the first direction and the second direction are both in a clockwise direction or both in a counterclockwise direction.

18. The method of claim 15 , further comprising varying the plurality of first rotational speeds and the plurality of second rotational speeds according to a step function or a sinusoidal function.

19. a carrier head having a first axis of rotation; a polishing pad disposed on a surface of a platen, the platen having a second axis of rotation; A non-transitory computer-readable medium having computer-executable instructions; 16. A chemical mechanical polishing system comprising: a processing system including: a processing unit configured to: rotating the carrier head in contact with the substrate in a first direction about the first axis of rotation at a variable rotational speed that varies as a function of an angular position of a reference point on the carrier head during each complete rotational cycle of the carrier head; and pressing a surface of the substrate against a polishing surface of the polishing pad using the carrier head while rotating the carrier head about the first axis of rotation. Chemical Mechanical Polishing System.

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