Monitoring retaining ring wear

Abstract

Disclosed herein is a load cup apparatus for transferring a substrate in a processing system, the load cup including a pedestal assembly having a substrate support, the substrate support may include multiple guide pins and a sensor pin, where the sensor pin is depressible into the substrate support; an actuator configured to move the pedestal assembly into a first position which brings the sensor pin into contact with a first bottom surface of a retaining ring of a carrier head; a sensor configured to generate a signal based on a distance traveled by the sensor pin; and a controller configured to receive the signal from the sensor and to generate a retaining ring thickness value based on the signal.

Description

[0001] Attorney Docket No.44023922WO01;05542-1625WO1 MONITORING RETAINING RING WEAR TECHNICAL FIELD [1] This disclosure relates to monitoring the thickness of a retaining ring. BACKGROUND [2] Chemical mechanical polishing (CMP) is one of many processes used in the fabrication of high-density integrated circuits. Chemical mechanical polishing is generally performed by moving a substrate against a polishing material, e.g., a polishing pad, in the presence of a polishing fluid. In many polishing applications, the polishing fluid contains an abrasive slurry to assist in the planarization of the feature side of the substrate that is pressed against the polishing material during processing. [3] The substrate is generally retained during polishing operations by a polishing head. Conventional polishing heads include a retaining ring bounding a substrate retaining pocket. The retaining ring prevents the substrate from slipping out from under the polishing head during polishing. [4] During polishing, the retaining ring is typically pressed against the polishing pad. A pressurizable chamber in the carrier head can control the vertical position of the retaining ring. The retaining ring is typically formed of a wearable material, and as polishing progresses, the bottom surface of the retaining ring is worn away. Consequently, the thickness of the retaining ring can change over the course of processing multiple substrates. [5] Most CMP systems employ a vertically actuatable transfer mechanism, commonly known as a load cup, to transfer substrates between the polishing head and a blade of a robot. The retaining ring and the load cup can include alignment features so that, as the load cup is raised toward the carrier head, the load cup engages the retaining ring and the substrate is aligned with the pocket in the carrier head. SUMMARY [6] In one aspect, a load cup apparatus for transferring a substrate in a processing system includes a pedestal assembly, an actuator, and a sensor. A pedestal assembly has a substrate support with multiple guide pins and a sensor pin. The sensor pin is depressible into the substrate support. The actuator is configured to move the pedestal assembly into a position Attorney Docket No.44023922WO01;05542-1625WO1 which brings the sensor pin into contact with a first surface of a retaining ring of a carrier head, and the sensor is configured to generate a signal based on a distance traveled by the sensor pin. A controller is configured to receive the signal from the sensor and to generate a retaining ring thickness value based on the signal. [7] In general, an aspect disclosed herein is a load cup apparatus for transferring a substrate in a processing system, the load cup including a pedestal assembly having a substrate support, the substrate support may include multiple guide pins and a sensor pin, where the sensor pin is depressible into the substrate support; an actuator configured to move the pedestal assembly into a first position which brings the sensor pin into contact with a first bottom surface of a retaining ring of a carrier head; a sensor configured to generate a signal based on a distance traveled by the sensor pin; and a controller configured to receive the signal from the sensor and to generate a retaining ring thickness value based on the signal. [8] Examples may include one or more of the following features. The guide pins can be vertically fixed relative to the substrate support. The controller can be configured to cause the actuator to lift the pedestal assembly until stopped at a second position by contact of the guide pins against a second bottom surface of the retaining ring, thereby depressing the sensor pin into the substrate support. The signal generated by the sensor based on the distance traveled by the sensor pin when the sensor pin can be in an extended position and a depressed position. The sensor pin can be in the extended position when the pedestal assembly can be stopped at the first position and the sensor pin can be in the depressed position when the pedestal assembly can be stopped at the second position. The apparatus may include a spring arranged to bias the sensor pin to the extended position from the substrate support. The multiple guide pins can be arranged in an annular configuration at a first distance from the center of the substrate support, and the sensor pin can be arranged at a second distance from the center of the substrate support that can be less than the first distance. The first distance can be equal to half of an outermost diameter of the retaining ring and the second distance can be equal to half a diameter of the substrate. The multiple sensor pins can be arranged at the second distance and at different angular positions. The different angular positions can be at equal angular intervals around the pedestal assembly. The multiple flat pins can be arranged at the second distance and at different angular positions from the multiple sensor pins. The multiple flat pins can be at equal angular intervals around the pedestal assembly. The controller can be configured to compare the retaining ring thickness Attorney Docket No.44023922WO01;05542-1625WO1 signal to a threshold value and to determine whether to generate a notification based on the comparison. The controller can be configured to adjust a pressure of at least one chamber in the carrier head based on the retaining ring thickness value. The at least one chamber may include a chamber that adjusts a vertical position of the retaining ring. The carrier head may include a flexible membrane defining the at least one chamber that applies pressure to a substrate in contact with the flexible membrane. The controller can be configured to store a look-up table relating signal values to corresponding thickness values. The sensor can be a linear encoder. The signal may include a voltage of the sensor. The controller can be configured to receive the retaining ring thickness signal during loading of the substrate into the carrier head. The controller can be configured to receive the retaining ring thickness signal during unloading of the substrate from the carrier head. The pedestal assembly may include a body having a top surface and an inwardly projecting ledge to support the substrate, the ledge having an upper surface below the top surface. The controller can be configured to store an initial position value based on the signal from the sensor when the retaining ring of the carrier head is a fresh retaining ring. The position can be the initial position value. The controller can be configured to generate a notification when the retaining ring thickness value exceeds a maximum threshold value. [9] In general, an aspect disclosed herein is a polishing apparatus including a polishing station; a transfer station including a pedestal assembly and an actuator, the pedestal assembly having a substrate support, the substrate support including multiple guide pins and at least one sensor pin, the actuator configured to move the pedestal assembly into a position which brings the multiple guide pins into contact with a retaining ring of a carrier head; a sensor configured to generate a signal based on a distance traveled by the at least one sensor pin; a carrier head movable between the polishing station and the transfer station, the carrier head including a retaining ring and a plurality of independently pressurizable chambers, where in the position the multiple guide pins contact the retaining ring; and a controller configured to receive the signal from the sensor and adjust a pressure of at least one of the plurality of chambers in the carrier head based on the signal.

[0010] Examples may include one or more of the following features. The at least one chamber may include a chamber that adjusts a vertical position of the retaining ring. The carrier head may include a flexible membrane defining the at least one chamber that applies pressure to a substrate in contact with the flexible membrane. The controller can be configured to store an initial Attorney Docket No.44023922WO01;05542-1625WO1 position value based on the signal from the sensor when the retaining ring of the carrier head is a fresh retaining ring. The position can be the initial position value.

[0011] In general, an aspect disclosed herein is a method of operating a polishing apparatus. The method includes polishing a substrate loaded to a carrier head; and unloading the substrate from the carrier head to a pedestal assembly, the unloading includes: raising the pedestal assembly to a position at which the pedestal assembly is in proximity with a retaining ring of a carrier head, generating a retaining ring thickness signal based on a distance traveled by a sensor pin of the pedestal assembly, and adjusting a pressure of at least one of a plurality of chambers in the carrier head based on the retaining ring thickness signal.

[0012] Examples may include one or more of the following features. Raising the pedestal assembly may include storing, in a controller of the polishing apparatus, a predetermined position for the pedestal assembly, and raising the pedestal to the predetermined position. Storing the predetermined position for the pedestal assembly may include affixing a fresh retaining ring to the carrier head, raising the pedestal assembly while monitoring a signal from a distance sensor of the pedestal assembly, and, when the signal from the distance sensor can be equal to or less than a calibration distance value, storing the predetermined position. The method may include generating a notification when the retaining ring thickness value exceeds a maximum threshold value. Generating the retaining ring thickness signal may include receiving, from a distance sensor, a signal indicative of the distance traveled by the sensor pin, and generating the retaining ring thickness signal from the received signal.

[0013] Advantages of implementations can optionally include, but are not limited to, one or more of the following. The thickness of the retaining ring may be measured reliably before a polishing operation and without loss of throughput. The measured thickness may be used to adjust polishing parameters, particularly a pressure applied by the carrier head, and within wafer non-uniformity (WINU) may be improved. The measured thickness can improve retaining ring utilization, e.g., increasing the total thickness of the retaining ring which is allowed to wear before replacement. Increasing utilization reduces overall polishing process costs and reduces system downtime for maintenance.

[0014] Other aspects, features and advantages will be apparent from the detailed description, including the drawings and the claims. Attorney Docket No.44023922WO01;05542-1625WO1 BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG.1 is a simplified side view, partially in section, of an implementation of a chemical mechanical polishing system.

[0016] FIG.2A is a sectional view of one embodiment of a load cup and a retaining ring.

[0017] FIG.2B is a top view of the load cup of FIG.2A.

[0018] FIG.3A is a sectional view of one embodiment of the load cup and retaining ring being out of contact.

[0019] FIG.3B is a sectional view of the load cup and retaining ring of FIG.3A being brought into contact.

[0020] FIG.3C is a sectional view of the load cup and retaining ring of FIG.3A being fully contacted.

[0021] FIG.3D is a sectional view of the load cup of FIG.3A being fully contacted with a worn retaining ring.

[0022] To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. DETAILED DESCRIPTION

[0023] During polishing, the polishing pad wears away the bottom surface of the retaining ring thus changing the overall thickness of the retaining ring. Through a series of polishing processes, the ongoing change in retaining ring thickness can lead to variation in the pressure applied to the substrate by a pressurized membrane in the carrier head. Without adjusting the carrier head pressure, the polishing rate profile can drift as the retaining ring wears. Since the retaining ring wears over time, different substrates will undergo different removal profiles, leading to wafer-to-wafer non-uniformity (WTWNU). If the wear of the retaining ring is known, carrier head pressures can be adjusted to compensate for drift in the polishing rate profile.

[0024] Hypothetically, a carrier head or retaining ring could be periodically removed from the polishing system to measure the retaining ring wear, but this is time-consuming and reduces throughput. A technique to measure retaining ring wear, while avoiding system downtime, is to vertically actuate a load cup to bring pins associated with distance sensors into contact with the lower surface of the retaining ring. The pins depress while the load cup is further vertically actuated to bring the lower surface into contact with the guide pins. The sensor monitors the Attorney Docket No.44023922WO01;05542-1625WO1 total distance traveled by sensor pins before the retaining ring contacts the guide pins to determine the wear of the retaining ring, e.g., an amount of thickness removed from the retaining ring.

[0025] The system can use the wear of the retaining ring to change one or more polishing parameters to correct the polishing profile for the substrate. In one example, the system uses the wear when determining the pressure for one or more membrane chambers in the carrier head. As the wear increases, the membrane pressures can be reduced to maintain or achieve a consistent polishing profile. The wear can also be used when determining a pressure for a membrane chamber which determines a vertical position of the retaining ring with respect to the carrier head.

[0026] FIG.1 depicts a partially sectional view of a simplified chemical mechanical polishing system 100 that includes a polishing station 102, a carrier head 104 and a load cup 110. Although the load cup 110 is shown in one implementation of a polishing system 100, the load cup 110 may be utilized in other processing systems that use a substrate-retaining head to retain a substrate in a face down orientation during processing.

[0027] In one implementation, the polishing station 102 includes a rotatable platen 106 having a polishing material 116 disposed thereon. The polishing material 116 may be a conventional polyurethane polishing pad, a fixed abrasive material, or another pad suitable for chemical mechanical polishing.

[0028] The polishing station 102 additionally includes a fluid source 108 adapted to provide a polishing fluid to the working surface of the polishing material 116 during processing. In the embodiment depicted in FIG.1, an arm 112 having at least one nozzle 114 is positioned to flow polishing fluid onto the polishing material 116 during processing.

[0029] The carrier head 104 is generally supported above the polishing station 102 by a transfer mechanism 118 coupled to a base 126. The transfer mechanism 118 is generally adapted to position the carrier head 104 selectively between a processing position over the polishing material 116 and a transfer position over the load cup 110. In the implementation depicted in FIG.1, the transfer mechanism 118 includes a stanchion 120 having a cantilevered arm 122 that may be rotated to laterally position the carrier head 104. The carrier head 104 can be coupled to the arm 122 by a drive mechanism 124. The drive mechanism 124 can be adapted to impart rotation to the carrier head 104. The elevation of the carrier head 104 relative to the base 126 Attorney Docket No.44023922WO01;05542-1625WO1 can be controlled by the drive mechanism 124 or by a pressurizable chamber inside the carrier head 104.

[0030] Generally, the carrier head 104 comprises a housing 140 and a retaining ring 150 secured near an edge of the housing 140, e.g., to a rim 142, to further retain the substrate within a pocket 146 in the carrier head 104 during polishing. The carrier head 104 can optionally include a membrane 151 defining a pressurizable chamber 151a between the retaining ring 150 and the housing 140. The chamber 151a can be arranged between the retaining ring 150 and the housing 140 such that adjusting a pressure in the chamber 151a changes a position, e.g., a vertical position, of the retaining ring 150 with respect to the housing 140. The chamber 151a is coupled to a pressure source 154 (only one is shown in FIG.1 for simplicity) such that the chamber 151a can be independently controllably inflated or deflated.

[0031] In some implementations, the carrier head 104 includes a flexible membrane 148, behind which are a plurality of independently pressurizable chambers, which can apply different pressures to different radial zones of the substrate. For example, the carrier head can include a first chamber 152a to apply pressure to a central portion of the substrate and a second chamber 152b to apply pressure to an edge portion of the substrate. The chambers 152a, 152b are coupled to the pressure source 154 such that the chambers 152a, 152b can be independently controllably inflated or deflated. In order to perform a polishing operation, one or more the chambers 152a, 152b can be inflated, thus pressing the substrate against the polishing pad 115.

[0032] The load cup 110 generally includes a pedestal assembly 128 and a cup 130. The pedestal assembly 128 is supported by a shaft 136. The cup 130 is supported by a shaft 138. The shafts 136, 138 extend through a hole 134 in the base 126 and are respectively coupled to actuators 133, 132 that respectively control the elevation of the pedestal assembly 128 and the cup 130 relative to the base 126. The pedestal assembly 128 provides a structure that mates with the carrier head 104 to ensure alignment therebetween during a substrate transfer operation. The pedestal assembly 128 is generally extended, e.g., vertically actuated, to transfer the substrate to the carrier head 104, e.g., a loading position. The pedestal assembly 128 retracts from the extended position to receive the substrate during the process of de-chucking, e.g., unloading, as further described below.

[0033] A controller 160, e.g., a programmed computer including non-transitory storage medium and a microprocessor, is coupled to the actuators 132, 133 to control the actuators 132, Attorney Docket No.44023922WO01;05542-1625WO1 133 in accord with a processing procedure, and to receive signals at least from the actuator 133 indicating the vertical extension and / or position information of the pedestal assembly 128. The controller 160 can also be coupled to the drive mechanism 124, or to the pressure source 154 to control the pressures in the chambers 151a, 152a, and / or 152b in the carrier head 104.

[0034] In order to perform a transfer operation, the flexible membrane 148 can be brought in contact with the substrate, and one or more of the chambers 152a, 152b can be depressurized (reduced to below atmospheric pressure), thus creating a vacuum between the substrate and the flexible membrane 148 and thereby securing the substrate on the carrier head 104. The controller 160 operates the transfer mechanism 118 to move the carrier head 104 with the secured substrate over the load cup 110. The pedestal assembly is vertically actuated by the actuator 132 to bring the pedestal assembly into contact with the retaining ring 150 and the substrate.

[0035] FIG.2A depicts a sectional view of one implementation of the pedestal assembly 128 and the retaining ring 150 of the carrier head 104 (the remainder of the carrier head 104 is not illustrated for simplicity). The pedestal assembly 128 includes at least an upper pedestal 202 which provides a substrate support. In some implementations, the upper pedestal 202 is coupled to a lower pedestal and is generally configured to move both angularly and laterally with respect to the lower pedestal. This permits the upper pedestal 202 to shift so as to permit alignment of the substrate 10 with the pocket 146 inside the retaining ring 150.

[0036] The upper pedestal 202 also includes a ledge 206, e.g., an annular ledge, surrounding a recessed area 208. The ledge 206 supports an edge of a substrate 10 in an exclusion zone of the substrate 10. The exclusion zone of the substrate 10 is an outer perimeter of the feature side of the substrate, e.g., an outer 2 millimeters, that has no features formed on it.

[0037] The pedestal assembly can also include other features, such as gripper assemblies to mechanically retain the substrate within the load cup, rinsing nozzles to spray a cleaning fluid on the substrate and / or retaining ring, and / or a sensor adapted to detect the presence of the substrate in the load cup 110.

[0038] An outer diameter surface of the retaining ring 150 can include an alignment feature to mate with a corresponding feature on the pedestal assembly 128. This permits the retaining ring 150 and the pedestal assembly 128 to align so that the substrate 10 is aligned with the pocket 146 inside the retaining ring 150. The alignment feature can include a slanted portion 230 of the Attorney Docket No.44023922WO01;05542-1625WO1 outer diameter that is sloped inwardly from the top toward the bottom of the retaining ring 150. The retaining ring 150 can also include a flange 198 portion that has a generally horizontal lower surface 232 located radially outward of the slanted portion 230.

[0039] A raised guide pin 212 protrudes along the outer edge of the upper pedestal 202. The guide pin 212 includes a sloped inner wall 214 configured to mate with the slanted portion 230 of the outer diameter surface of the retaining ring 150. The sloped inner wall 214 and the slanted portion 230 can have the same angle of inclination, e.g., 45°. The guide pin 212 can also include a horizontal top surface 216. The guide pin 212 are affixed to the upper pedestal 202 to provide a static reference for alignment of the retaining ring to the upper pedestal 202, e.g., the guide pins 212 are fixed vertically and radially with respect to the upper pedestal 202.

[0040] In some implementations, the retaining ring 150 includes a lower portion 224 and an upper portion 226. The upper portion 226 is formed of a material, e.g., a metal, that is harder than the lower portion 224. The lower portion 224 of the retaining ring 150 has a bottom surface 220 that will be brought into contact with the polishing pad 115. As noted, the lower portion 224 is typically formed of a wearable material, e.g., a plastic. As polishing progresses and the bottom surface 220 is contacted with the pad 115, the retaining ring 150 is worn away from the bottom surface 220. Thus, the total height of the retaining ring 150 will vary from substrate to substrate. The total height can be measured between the bottom surface 220 and the top surface 222, or between the bottom surface 220 and the lower surface 232.

[0041] The upper pedestal 202 includes flat pins 236 arranged in an annular region around the top surface 204. The flat pins 236 includes a flat upper surface which provides a contact point, e.g., a stop, for the bottom surface 220 of the retaining ring 150. The flat pins 236 are spring loaded but will recess into the pedestal assembly 128 as the bottom surface 220 of the retaining ring 150 is brought into proximity with the pedestal assembly 128. The flat pins 236 thus protrude from the pedestal assembly 128 when the bottom surface 220 is brought out of proximity to the pedestal assembly 128. The flat pin 236 can prevent contact between the bottom surface 220 and the pedestal assembly 128 which can reduce or prevent damage to the pedestal assembly 128 or carrier head 104.

[0042] The flat pins 236 are designed to constrain the wafer in a “load” position. The flat pins 236 form a cylindrical space but prevent the substrate 10 from shifting laterally during a wafer load operation. This allows the substrate 10 to be transferred in / out vertically from the carrier Attorney Docket No.44023922WO01;05542-1625WO1 head 104, e.g., the flat pins 236 are arranged around a perimeter of the substrate 10 position to act as guide pins for the substrate 10. During the wafer load operation, the actuator 133 lifts the pedestal 128 upward (e.g., away from the cup 130, or toward the carrier head 104). The actuator 133 lifts the pedestal 128 upward to a ‘load’ position a first distance, below the bottom surface 220 of the retaining ring 150 (e.g., a ‘substrate load’ position).

[0043] The sensor pins 238 are designed to constrain the wafer during an “unload” operation. For a wafer “unload” operation, the actuator 133 lifts the pedestal 128 to an ‘unload’ position a second distance below the surface 220 (e.g., a ‘substrate unload’ position) that is larger than the first distance. The first distance can be less than 3 mm, e.g., about 1 mm, below the bottom surface 220, whereas the second distance can be 5 -15 mm, e.g., about 11 mm, below the bottom surface 220. The sensor pins 238 form a cylindrical space but prevent the substrate 10 from shifting laterally during the substrate unload operation. In some examples, the sensor pins 238 have a tapered profile at an end which contacts the retaining ring 150.

[0044] The upper pedestal 202 includes a series of sensor pins 238 in the annular region around the top surface 204. Each of the sensor pins 238 is spring-loaded to travel vertically in a direction normal to the top surface 204. Said another way, the sensor pin 238 recedes into the upper pedestal 202 when a downward, e.g., toward the top surface 204, force is applied to the sensor pin 238. In this manner, the guide pins 212 guide the retaining ring 150 downward as the bottom surface 220 approaches the flat pins 236.

[0045] At least one of the sensor pins 238 interacts with a distance sensor 240. As the sensor pin 238 associated with the distance sensor 240 travels vertically, the distance sensor 240 generates a signal indicative of the distance traveled by the associated sensor pin 238. The controller 160 can receive the signal and determines an amount of travel through which the associated sensor pin 238 travels based on the signal. The distance sensor 240 can be connected to the controller 160 through a wired, or a wireless connection.

[0046] A spring 242 biases the sensor pin 238 upward with respect to the upper pedestal 202. The spring 242 biases the sensor pin 238 upward when a downward force is applied to the sensor pin 238. In some examples, relative motion between the upper pedestal 202 and the retaining ring 150 causes the bottom surface 220 to contact the sensor pin 238. The relative motion causes the bottom surface 220 to depress the sensor pin 238. When the relative motion ceases, the sensor pin 238 is at a depressed position. The depression position varies depending on the Attorney Docket No.44023922WO01;05542-1625WO1 relative position of the upper pedestal 202 and the carrier head 104, and the total wear of the retaining ring 150. As the retaining ring 150 wears, the thickness of the lower portion 224 is decreased. Thus, given a constant relative position between the carrier head 104 and the upper pedestal 202, the depressed position of the sensor pin 238 will be higher with respect to the upper pedestal 202 for a worn retaining ring 150 than a fresh retaining ring. flat pins 236 and sensor pins 238

[0047] In some examples, the controller 160 causes the actuator 133 to move the pedestal assembly 128 away from the retaining ring 150. The spring 242 biases the sensor pin 238 upwards until the maximum vertical travel of the sensor pin 238 is reached at an extended position.

[0048] The distance sensor 240 has a resolution that is sufficient to determine the wear of the retaining ring 150 with high accuracy and precision (e.g., sub-micron resolution). An example of the distance sensor 240 is a linear encoder having a resolution that is 0.5 μm or less. A distance sensor 240 having such a resolution increases the accuracy by which the system 100 determines the thickness of the retaining ring 150 and thus increases the total lifespan of a retaining ring 150 by accurately determining the end-of-life thickness.

[0049] As the actuator 133 causes the pedestal assembly 128 to lift upward (arrow A), the sloped inner wall 214 engages the sloped portion 230, causing the upper pedestal 202 and / or the retaining ring 150 to shift laterally to align the substrate 10 with the pocket 146 inside the retaining ring 150. The actuator 133 can send a signal indicative of the distance that the pedestal assembly 128 moves upward to the controller 160.

[0050] As the actuator 133 continues to lift the pedestal assembly 128 upward, the top surface 216 of the guide pin 212 contacts the lower surface 232 of the flange 198 of the retaining ring 150. Thus, the flange 198 acts as a hard stop on the motion of the pedestal assembly 128. The actuator 133 lifts the pedestal 128 upward. A side surface 215 (e.g., the vertical surface) of the guide pin 212 contacts the side surface 231 of the flange 198. The guide pins 212 contact the pedestal assembly 128 to control a lateral position of the retaining ring 150 so that the pedestal 128, the carrier head 104, and the retaining ring 150 align along a central axis for substrate 10 transfer. The actuator 133 controls the vertical position of the pedestal assembly 128 compared to the retaining ring 150. The vertical position is calibrated for each load and unload position. The controller 160 stores the vertical position for each load and unload position. Alternatively, if Attorney Docket No.44023922WO01;05542-1625WO1 the retaining ring is sufficiently thin, then as the actuator 133 continues to lift the pedestal assembly 128 upward, a top surface of the flat pins 236 contacts the bottom surface 220 of the retaining ring 150 as the top surface 204 of the pedestal assembly 128 approaches the bottom surface 220.

[0051] A top view of an example arrangement of the sensor pins 238, flat pins 236, and guide pins 212 is shown in FIG.2B. The annular ring of guide pins 212, including guide pins 212a-d, is shown at a greater radial distance, r2, than the radial distance, r1, of the ring of flat pins 236 (e.g., flat pins 236a-d) and the ring of sensor pins 238 (e.g., sensor pins 238a-234d). In the example shown, each of the four guide pins 212, the sensor pins 238, and the flat pins 236 are arranged at unique angular positions and are equally spaced around the respective ring, though this is non- limiting. The radial distances r1 and r2 are measured from the center of the pedestal assembly 128 to an innermost surface of the respective pins. For example, r1 is measured to a side surface 237 of the sensor pins 238, a side surface 235 of the flat pins 236, or both. r2is measured to the side surface 215 of the guide pins 212.

[0052] In some examples, the pedestal assembly 128 includes an equal number of guide pins sensor pins 238, flat pins 236, and guide pins 212. In some examples, the pedestal assembly 128 includes five or more (e.g., six) sensor pins 238, flat pins 236, and guide pins 212. In some examples, radial distance r1 is equal to half the diameter of a substrate 10. The radial distance, r1, being half the radius of the substrate 10 facilitates centering the substrate 10 with the retaining ring 150 and pedestal assembly 128 during a load or unload operation. In some examples, radial distance, r2, is equal to half the outermost diameter of the retaining ring 150, e.g., the radius of the retaining ring 150 at the side surface 231. The radial distance, r2, being half the outermost diameter of the retaining ring 150 facilitates centering the retaining ring 150 with the pedestal assembly 128 during a load or unload operation.

[0053] The sensor pin 238 is elevated such that a top-most surface 239 of the sensor pin 238 is above the top-most surface of the flat pin 236 (e.g., closer to the bottom surface 220) and below the top surface 216 of the guide pins 212 (e.g., farther from the bottom surface 220).

[0054] In general, the radial distance of the guide pins 212 is sufficient such that an innermost edge of the guide pins 212, e.g., an edge closest to the center of the upper pedestal 202, is farther from the center of the upper pedestal 202 than an outermost edge of the sensor pins 238 or the flat pins 236. Such arrangement permits the top surface of the sensor pins 238 to contact the Attorney Docket No.44023922WO01;05542-1625WO1 bottom surface 220 of the retaining ring 150 before the top surface 216 of the four guide pins 212 contacts the lower surface 232 of the retaining ring 150.

[0055] The radial distance, r2, of the ring of guide pins 212 aligns the top surface 216 of the guide pins 212 with the horizontal lower surface 232 of the outer retaining ring 150. The ring of flat pins 236 and sensor pins 238 are arranged at radial distance r1 to align the respective top surfaces of the flat pins 236 and sensor pins 238 with the bottom surface 220 of the retaining ring 150. The ring of flat pins 236 and sensor pins 238 are located radially inward from the guide pins 212, e.g., r1 < r2. While the ring of flat pins 236 is shown at the same radial distance, r1, as the sensor pins 238, this is one example and in some other examples, the flat pin 236 are at a different radial distance than the sensor pins 238.

[0056] Each ring includes four of the sensor pins 238, flat pins 236, and the guide pins 212, though this is exemplary. Each ring can have more (e.g., five, six, seven, or eight) or fewer (e.g., three, or two) pins. Other examples include different numbers of each type of pin, e.g., four guide pins 212, three flat pins 236, and six sensor pins 238.

[0057] As noted above, during the loading procedure, the actuator 133 lifts the pedestal assembly 128 upward until the top surface 204 of the pedestal assembly 128 is near the bottom surface 220 of the retaining ring 150. As the pedestal assembly 128 is raised, a top-most surface 239 of the sensor pin 238 contacts the bottom surface 220. As the pedestal assembly 128 continues upward, the sensor pin 238 is depressed into the pedestal assembly 128. This process is shown in FIGS.3A-3C. As the sensor pin 238 is depressed, the distance sensor 240 generates a signal indicating the distance by which the sensor pin 238 is depressed as the pedestal assembly 128 continues upward.

[0058] As the ring 150 and the pedestal assembly 128 are brought into proximity, the bottom surface 220 of the retaining ring 150 contacts the top surfaces 239 of the sensor pins 238 shown in FIG.3B. The pedestal assembly 128 and ring 150 are then brought closer until the lower surface 220 is in proximity with the top surface 204 as shown in FIG.3C, e.g., into contact with the flat pins 236. The controller 160 stores the relative position of the carrier head 104 and the pedestal assembly 128 as a preset relative position based on a signal received from the sensor 240. The controller 160 stores the preset relative position value (e.g., an “initial” position value) so that the controller 160 can cause pedestal assembly 128 to be raised until it reaches the preset Attorney Docket No.44023922WO01;05542-1625WO1 relative position. In this way, the distance between the retaining ring 150 and the assembly 128 is consistent between measurements.

[0059] In one example in which a fresh, e.g., unworn, retaining ring 150 is installed to the carrier head 104, the controller 160 stores a thickness of the fresh retaining ring 150, e.g., a user inputs a thickness value for fresh retaining ring 150 into the controller 160. The controller 160 causes the actuator 133 to lift the pedestal assembly 128 upward until the top surface 204 of the pedestal assembly 128 is the first distance, e.g., 1 mm, from the bottom surface 220 of the retaining ring 150 based on the stored thickness value of the retaining ring 150. This can provide the initial relative position for a fresh retaining ring against which subsequent measurements are determined.

[0060] As the distance between the retaining ring 150 and the pedestal assembly 128 changes, the distance sensor 240 registers the depression of the sensor pin 238 and communicates the signal to the controller 160.

[0061] If the retaining ring is relatively thicker, then the distance the sensor pin 238 is depressed is greater than if the retaining ring is relatively thinner, e.g., worn. On the other hand, as the retaining ring wears and becomes thinner, the distance the sensor pin 238 is depressed decreases. Consequently, the signal from the distance sensor 240 measured or generated when the pedestal assembly 128 is in proximity with the bottom surface 220 of the retaining ring 150 can correlate to the thickness of the retaining ring 150. In this manner, the usable lifetime of the retaining ring 150 can be accurately determined and monitored.

[0062] FIG.3D illustrates an exemplary retaining ring 150a which has been worn and the lower portion 224 of the retaining ring 150a is thinner than the example shown in FIG.3C. Thus, the surface 220 depresses the sensor pins 238 by a smaller distance than when the retaining ring 150a is brought into proximity with the pedestal assembly 128 and the distance sensor 240 generates a signal indicative of the smaller distance. In some implementations, a separate sensor, e.g., a linear encoder or an optical distance sensor, detects the distance traveled by the pedestal or the position of the pedestal assembly 128 when in proximity to the bottom surface 220 of the retaining ring 150.

[0063] Moreover, the measurement of the retaining ring thickness can be performed during the regular substrate loading or unloading procedure, without removing the retaining ring 150 or affecting substrate throughput. Attorney Docket No.44023922WO01;05542-1625WO1

[0064] In some implementations, the retaining ring thickness can be measured empirically for multiple signal values, or the retaining ring thickness can be measured to generate a sequence of signal values. A look-up-table can be generated to convert each value of the sequence of signal values into a thickness value, e.g., a thickness measurement. In some implementations, the “raw” signal from the distance sensor 240, e.g., a voltage value, can be used as a thickness signal.

[0065] In some implementations, the controller 160 is configured to determine the amount of wear of, i.e., the thickness removed from, the retaining ring 150. For example, the controller can store, e.g., in non-transitory memory, the thickness signal value generated for a “fresh” retaining ring 150. Thereafter, as the retaining ring 150 is worn, later thickness signals value can be subtracted from the stored thickness signal value to generate a difference value. This difference value represents the thickness removed from the retaining ring 150. In some examples, the thickness value for a “fresh” retaining ring is a predetermined value stored in the controller 160. In some examples, the thickness value for a “fresh” retaining ring is determined by moving the pedestal assembly 128 into the loading position and recording the thickness value generated by the distance sensor 240 of the “fresh” retaining ring 150.

[0066] The “raw” signal, the thickness measurement, and the amount of wear are all considered a retaining ring thickness signal.

[0067] In some implementations, the controller 160 can compare the thickness signal to a threshold value which can be stored in the controller 160. In the case of the raw signal or thickness measurement, if the thickness signal falls below the threshold value (or exceeds the threshold value in the case of the difference signal), then the controller 160 can generate a notification, e.g., a visual or audible notification to the operator, that the retaining ring thickness value exceeds the threshold value. In one example, the notification is indicative of the retaining ring 150 needing to be replaced. This permits the retaining ring 150 to be replaced when the retaining ring 150 has been worn to a predetermined thickness, rather than after a predetermined number of polishing operations, which can permit the retaining ring 150 to be used until closer to its maximum lifetime.

[0068] In some implementations, the controller 160 uses the thickness signal to determine an adjustment to one or more pressures applied by the carrier head 104. For example, the vertical position of the retaining ring 150 can be adjusted with respect to the carrier head 104, e.g., by Attorney Docket No.44023922WO01;05542-1625WO1 setting an appropriate pressure from the pressure source 154, so that the polishing pad is compressed by a more uniform amount from substrate-to-substrate as the retaining ring 150 wears. The pressure adjustment can modulate the vertical distance between a lower surface of the membrane and the bottom surface 220 of the retaining ring 150. The vertical distance can be at a predetermined distance to provide consistent pressure applied to the substrate 10 based on the wear of the retaining ring 150.

[0069] Alternatively or in addition, the pressure in one or more of the chambers 152a, 152b can be adjusted to compensate for changes in polishing rate at the edge of the substrate induced by the change in thickness of the retaining ring 150. In some implementations, the controller 160 stores a table that relates different thickness signal values to different correction factors. The correction factor can be additive or multiplicative. By applying the correction factor to the pressures applied by the carrier head 104, within-wafer non-uniformity (WIWNU) and wafer-to- wafer non-uniformity (WTWNU) can be reduced over the lifetime of the retaining ring.

[0070] In some examples, the controller 160 is configured to determine a radial thickness profile of the retaining ring 150. In such examples, the pedestal assembly 128 includes multiple distance sensors 240. The multiple distances sensors 240 are arranged at different radial positions around the pedestal assembly 128, e.g., associated with at least some, e.g., all, of the sensor pins 238. Each of the distance sensors 240 generate a signal based on the thickness of the retaining ring at a different radial location based on the position of the associated sensor pin 238 around the pedestal assembly 128. The controller 160 receives the signals from each of the distance sensors 240. The controller 160 determines a radial thickness profile of the retaining ring 150 using the multiple received signals.

[0071] The present invention has been described in terms of a number of embodiments. The invention, however, is not limited to the embodiments depicted and described. Rather, the scope of the invention is defined by the appended claims.

Claims

Attorney Docket No.44023922WO01;05542-1625WO1 What is claimed is:

1. A load cup apparatus for transferring a substrate in a processing system, comprising: a pedestal assembly having a substrate support, the substrate support comprising multiple guide pins and a sensor pin, wherein the sensor pin is depressible into the substrate support; an actuator configured to move the pedestal assembly into a first position which brings the sensor pin into contact with a first bottom surface of a retaining ring of a carrier head; a sensor configured to generate a signal based on a distance traveled by the sensor pin; and a controller configured to receive the signal from the sensor and to generate a retaining ring thickness value based on the signal.

2. The apparatus of claim 1, wherein the guide pins are vertically fixed relative to the substrate support.

3. The apparatus of claim 2, wherein the controller is configured to cause the actuator to lift the pedestal assembly until stopped at a second position by contact of the guide pins against a second bottom surface of the retaining ring, thereby depressing the sensor pin into the substrate support.

4. The apparatus of claim 3, wherein the signal generated by the sensor based on the distance traveled by the sensor pin when the sensor pin is in an extended position and a depressed position.

5. The apparatus of claim 4, wherein the sensor pin is in the extended position when the pedestal assembly is stopped at the first position and the sensor pin is in the depressed position when the pedestal assembly is stopped at the second position.

6. The apparatus of claim 4, comprising a spring arranged to bias the sensor pin to the extended position from the substrate support.Attorney Docket No.44023922WO01;05542-1625WO1 7. The apparatus of claim 1, wherein the multiple guide pins are arranged in an annular configuration at a first distance from the center of the substrate support, and the sensor pin is arranged at a second distance from the center of the substrate support that is less than the first distance.

8. The apparatus of claim 7, wherein the first distance is equal to half of an outermost diameter of the retaining ring and the second distance is equal to half a diameter of the substrate.

9. The apparatus of claim 7, comprising multiple sensor pins, wherein the multiple sensor pins are arranged at the second distance and at different angular positions.

10. The apparatus of claim 9, wherein the different angular positions are at equal angular intervals around the pedestal assembly.

11. The apparatus of claim 9, comprising multiple flat pins, wherein the multiple flat pins are arranged at the second distance and at different angular positions from the multiple sensor pins, and wherein the flat pins are depressible into the substrate support.

12. The apparatus of claim 11, wherein the multiple flat pins are at equal angular intervals around the pedestal assembly.

13. The apparatus of claim 1, wherein the controller is configured to compare the retaining ring thickness signal to a threshold value and to determine whether to generate a notification based on the comparison.

14. The apparatus of claim 1, wherein the controller is configured to adjust a pressure of at least one chamber in the carrier head based on the retaining ring thickness value.Attorney Docket No.44023922WO01;05542-1625WO1 15. The apparatus of claim 14, wherein the at least one chamber comprises a chamber that adjusts a vertical position of the retaining ring.

16. The apparatus of claim 14, wherein the carrier head comprises a flexible membrane defining the at least one chamber that applies pressure to a substrate in contact with the flexible membrane.

17. The apparatus of claim 1, wherein the controller is configured to store a look-up table relating signal values to corresponding thickness values.

18. The apparatus of claim 1, wherein the sensor is a linear encoder.

19. The apparatus of claim 18, wherein the signal comprises a voltage of the sensor.

20. The apparatus of claim 1, wherein the controller is configured to receive the retaining ring thickness signal during loading of the substrate into the carrier head.

21. The apparatus of claim 1, wherein the controller is configured to receive the retaining ring thickness signal during unloading of the substrate from the carrier head.

22. The apparatus of claim 1, wherein the pedestal assembly comprises a body having a top surface and an inwardly projecting ledge to support the substrate, the ledge having an upper surface below the top surface.

23. The apparatus of claim 1, wherein the controller is configured to store an initial position value based on the signal from the sensor when the retaining ring of the carrier head is a fresh retaining ring.

24. The apparatus of claim 23, wherein the position is the initial position value.Attorney Docket No.44023922WO01;05542-1625WO1 25. The apparatus of claim 1, wherein the controller is configured to generate a notification when the retaining ring thickness value exceeds a maximum threshold value.

26. A polishing apparatus, comprising: a polishing station; a transfer station including a pedestal assembly and an actuator, the pedestal assembly having a substrate support, the substrate support comprising multiple guide pins and at least one sensor pin, the actuator configured to move the pedestal assembly into a position which brings the multiple guide pins into contact with a retaining ring of a carrier head, a sensor configured to generate a signal based on a distance traveled by the at least one sensor pin; a carrier head movable between the polishing station and the transfer station, the carrier head including a retaining ring and a plurality of independently pressurizable chambers, wherein in the position the multiple guide pins contact the retaining ring; and a controller configured to receive the signal from the sensor and adjust a pressure of at least one of the plurality of chambers in the carrier head based on the signal.

27. The apparatus of claim 26, wherein the at least one chamber comprises a chamber that adjusts a vertical position of the retaining ring.

28. The apparatus of claim 26, wherein the carrier head comprises a flexible membrane defining the at least one chamber that applies pressure to a substrate in contact with the flexible membrane.

29. The apparatus of claim 26, wherein the controller is configured to store an initial position value based on the signal from the sensor when the retaining ring of the carrier head is a fresh retaining ring.

30. The apparatus of claim 29, wherein the position is the initial position value.

31. A method of operating a polishing apparatus, comprising:Attorney Docket No.44023922WO01;05542-1625WO1 polishing a substrate loaded to a carrier head; and unloading the substrate from the carrier head to a pedestal assembly, the unloading comprising: raising the pedestal assembly to a position at which the pedestal assembly is in proximity with a retaining ring of a carrier head, generating a retaining ring thickness signal based on a distance traveled by a sensor pin of the pedestal assembly, and adjusting a pressure of at least one of a plurality of chambers in the carrier head based on the retaining ring thickness signal.

32. The method of claim 31, wherein raising the pedestal assembly comprises storing, in a controller of the polishing apparatus, a predetermined position for the pedestal assembly, and raising the pedestal to the predetermined position.

33. The method of claim 32, wherein storing the predetermined position for the pedestal assembly comprises affixing a fresh retaining ring to the carrier head, raising the pedestal assembly while monitoring a signal from a distance sensor of the pedestal assembly, and, when the signal from the distance sensor is equal to or less than a calibration distance value, storing the predetermined position.

34. The method of claim 31, comprising generating a notification when the retaining ring thickness value exceeds a maximum threshold value.

35. The method of claim 31, wherein generating the retaining ring thickness signal comprises receiving, from a distance sensor, a signal indicative of the distance traveled by the sensor pin, and generating the retaining ring thickness signal from the received signal.

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