WO2012018425A2

WO2012018425A2 - Real-time monitoring of retaining ring thickness and lifetime

Info

Publication number: WO2012018425A2
Application number: PCT/US2011/036731
Authority: WO
Inventors: Peter Mcreynolds; Eric S. Rondum; Garlen C. Leung; Adam H. Zhong; Gregory E. Menk; Gopalakrishna B. Prabhu; Thomas H. Osterheld
Original assignee: Applied Materials, Inc.
Priority date: 2010-07-26
Filing date: 2011-05-17
Publication date: 2012-02-09
Also published as: WO2012018425A3; CN102725830A; KR20130088738A; JP2013532588A; CN102725830B; TWI530359B; US20120021671A1; TW201204509A; KR101754855B1

Abstract

A method and apparatus for monitoring the condition of a surface of a retaining ring disposed on a carrier head in a polishing module is described. In one embodiment, an apparatus is provided. The apparatus includes a carrier head movable in a travel path between at least one polishing station for polishing a substrate as the substrate is retained in the carrier head, and a transfer station for transferring the substrate to and from the carrier head, the carrier head having a retaining ring, and a sensor disposed in the travel path of the carrier head, the sensor operable to provide a metric indicative of a condition of the retaining ring.

Description

REAL-TIME MONITORING OF RETAINING RING THICKNESS AND LIFETIME

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] Embodiments of the invention relate to polishing systems for polishing a substrate, such as a semiconductor substrate. More particularly, to a method and apparatus for monitoring components of a polishing system.

Description of the Related Art

[0002] Chemical mechanical polishing (CMP) is one process commonly used in the manufacture of high-density integrated circuits to planarize or polish a layer of material deposited on a substrate. The substrate may be provided to a polishing station on a polishing system and retained in a carrier head that controllably urges the substrate against a moving polishing pad. CMP is effectively employed by providing contact between a feature side of the substrate and moving the substrate relative to the polishing pad while in the presence of a polishing fluid. Material is removed from the feature side of the substrate that is in contact with the polishing surface through a combination of chemical and mechanical activity.

[0003] The carrier head typically includes a retaining ring that circumscribes the substrate and may facilitate holding of the substrate in the carrier head. One or more surfaces of the retaining ring are typically in contact with the polishing pad during polishing. While the retaining ring is adapted to endure polishing of multiple substrates, the surfaces that are in contact with the polishing pad experience wear and periodic replacement of the retaining ring is necessary. Thus, inspection of the retaining ring is necessary to monitor wear and determine replacement intervals.

[0004] The conventional inspection methods are time-consuming, require personnel to physically handle components in the station and requires shutdown of the polishing system. Additionally, the conventional methods may require partial disassembly of the polishing station and removal of the carrier head from the station, which may expose other components within the system to contamination. [0005] Therefore, there is a need for a method and apparatus that facilitates monitoring of the retaining ring without the need to physically handle the retaining ring or shut down the polishing system.

SUMMARY OF THE INVENTION

[0006] The invention generally provides a method and apparatus that facilitates monitoring of a retaining ring within a polishing system to determine condition of the retaining ring and/or assess lifetime of the retaining ring. In one embodiment, an apparatus is provided. The apparatus includes a carrier head movable in a travel path between at least one polishing station for polishing a substrate as the substrate is retained in the carrier head, and a transfer station for transferring the substrate to and from the carrier head, the carrier head having a retaining ring, and a sensor disposed in the travel path of the carrier head, the sensor operable to provide a metric indicative of a condition of the retaining ring.

[0007] In another embodiment, a transfer station disposed in a polishing module for transferring substrates between a substrate transfer device and at least one carrier head is provided. The transfer station includes a load cup assembly having a body that is sized to receive a substrate and at least a portion of a retaining ring that is coupled to the at least one carrier head, and a sensor disposed on the body, the sensor operable to provide a metric indicative of a condition of the retaining ring, wherein the substrate includes a first radius and the sensor is positioned on the body at a second radius that is greater than the first radius.

[0008] In another embodiment, a method for monitoring at least one surface of a retaining ring coupled to a carrier head is provided. The method includes moving the carrier head adjacent a sensor device disposed in a polishing module, transmitting energy from the sensor device toward the retaining ring, receiving energy reflected from the retaining ring, and determining a condition of the retaining ring based on the received energy. [0009] In another embodiment, a method for monitoring at least one surface of a retaining ring coupled to a carrier head is provided. The method includes moving the carrier head adjacent a load cup assembly disposed in a polishing module, the sensor device being disposed in a body of the load cup assembly, transmitting energy from the sensor device toward a surface of the retaining ring as the retaining ring is in the line-of-sight of the sensor device, receiving energy reflected from the surface, and determining a thickness of the retaining ring based on the received energy.

[0010] In another embodiment, a method for monitoring at least one surface of a retaining ring coupled to a carrier head is provided. The method includes moving the carrier head adjacent a load cup assembly disposed in a polishing module, the sensor device being disposed in a body of the load cup assembly, rinsing the retaining ring, transmitting energy from the sensor device toward a surface of the retaining ring as the retaining ring is in the line-of-sight of the sensor device, receiving energy reflected from the surface, and determining a thickness of the retaining ring based on the received energy.

[0011] In another embodiment, an apparatus is provided. The apparatus includes a carrier head movable in a travel path between at least one polishing station for polishing a substrate as the substrate is retained in the carrier head and a transfer station for transferring the substrate to and from the carrier head, the carrier head having a retaining ring, and a sensor disposed in the travel path of the carrier head, the sensor operable to provide a metric indicative of a condition of the retaining ring.

[0012] In another embodiment, a transfer station disposed in a polishing module for transferring substrates between a substrate transfer device and at least one carrier head is provided. The transfer station includes a load cup assembly having a body that is sized to receive a substrate and at least a portion of a retaining ring that is coupled to the at least one carrier head, and a sensor disposed on the body, the sensor operable to provide a metric indicative of a condition of the retaining ring, wherein the substrate includes a first radius and the sensor is positioned on the body at a second radius that is greater than the first radius.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0014] Figure 1 is a plan view of one embodiment of a polishing system.

[0015] Figure 2 is a partial cross-sectional view of one embodiment of a transfer station that may be utilized in the polishing system of Figure 1.

[0016] Figure 3 is a schematic cross-sectional view of another embodiment of a transfer station that may be utilized with the polishing system of Figure 1.

[0017] Figure 4 is a schematic cross-sectional view of another embodiment of a transfer station that may be utilized with the polishing system of Figure 1.

[0018] Figure 5A is a partial plan view of one embodiment of a retaining ring.

[0019] Figure 5B is a schematic cross-sectional view of another embodiment of a transfer station that may be utilized with the polishing system of Figure 1.

[0020] Figure 6 is a schematic cross-sectional view of another embodiment of a transfer station that may be utilized with the polishing system of Figure 1.

[0021] Figure 7 is a flow chart showing one embodiment of a method.

[0022] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

[0023] The invention generally provides a method and apparatus that facilitates monitoring of a retaining ring within a polishing system to determine wear of the retaining ring and/or assess lifetime of the retaining ring. An on-tool monitoring device is described that provides monitoring of the retaining ring without the need to physically handle the retaining ring or shut down the polishing system. Additionally, data from the monitoring device may be provided to a controller and utilized for tuning subsequent polishing processes.

[0024] Figure 1 is a plan view of a polishing system 100 having a polishing module 105 and a substrate transfer device that is suitable for electrochemical mechanical polishing and/or chemical mechanical polishing. The polishing module 105 includes a first polishing station 11 OA, a second polishing station 110B, and a third polishing station 110C disposed in an environmentally controlled enclosure 115. The substrate transfer device, such as a carousel 125, moves substrates between the polishing stations 11 OA, 110B and 110C. Any of the polishing stations 1 OA, 110B, 110C may perform a planarizing or polishing process to remove material from a feature side of a substrate to form a planar surface on the feature side. The module 105 may be part of a larger polishing system, such as, for example REFLEXION®, REFLEXION® LK, REFLEXION® LK ECMP™, MIRRA MESA®, and REFLEXION GT™ polishing systems available from Applied Materials, Inc., located in Santa Clara, California, although other polishing systems may be utilized. Other polishing modules, including those that use other types of polishing pads, belts, indexable web-type pads, or a combination thereof, and those that move a substrate relative to a polishing surface in a rotational, linear or other planar motion may also be adapted to benefit from embodiments described herein.

[0025] In one embodiment, each of the polishing stations 110A-110C of the polishing module 105 are adapted to perform a conventional chemical mechanical polishing (CMP) process. Alternatively, the first polishing station 11 OA may be configured to perform an electrochemical mechanical planarization (ECMP) process, while the second polishing station 1 1 OB and the third polishing station 110C may perform a CMP process. In one embodiment of a process, a substrate having feature definitions formed therein and covered with a barrier layer and a conductive material disposed over the barrier layer may have the conductive material removed in two steps in the first and second polishing stations 11 OA, 11 OB, by a CMP process, with the barrier layer processed in the third station 110C by a third CMP process to form a planarized surface on the substrate.

[0026] In one embodiment, the system 100 includes a module base 118 that supports the polishing stations 11 OA, 11 OB and 1 0C, a transfer station 120, and the carousel 125. Each of the polishing stations 1 OA, 11 OB, and 110C include a polishing fluid delivery arm 128 adapted to deliver a polishing fluid to a polishing surface 175 during a polishing process. A plurality of conditioning devices 130 are shown coupled to the module base 118 and are movable in the direction A in order to selectively place the conditioning device 130 over each of the polishing stations 11 OA, 11 OB, and 110C. The transfer station 120 generally facilitates transfer of a substrate 135 to and from the system 100 via a wet robot 140. The wet robot 140 typically transfers substrates 135 between the transfer station 120 and a factory interface (not shown) that may include a cleaning module, a metrology device and one or more substrate storage cassettes. The transfer station 120 comprises a first buffer station 145, a second buffer station 150, a transfer robot 155, and a load cup assembly 160. The transfer robot 155 transfers substrates between the first buffer station 145, the second buffer station 150 and the load cup assembly 160. The load cup assembly 160 includes a monitoring device 162 that is coupled to a controller.

[0027] The carousel 125 includes a plurality of arms 170, and each arm 170 supports a carrier head 165A-165D. Carrier heads 165C and 165D as well as a portion of the two arms 70 are shown in phantom so that the transfer station 120 and the polishing surface 175 of the polishing station 110C may be seen. The polishing surface 175 comprises the upper surface of a pad assembly disposed on a rotatable platen (not shown in this view). Each of the carrier heads 165A-165D includes an actuator 168. The carousel 125 moves the carrier heads 165A-165D between the transfer station 120 and polishing stations 11 OA, 11 OB and 110C and the actuator 168 is adapted to move the carrier heads 165A-165D relative to the carousel 125. The carousel 125 is indexable such that the carrier heads 165A- 165D may be moved between polishing stations 11 OA, 11 OB, 110C and the transfer station 120 in a sequence defined by the user. Each of the carrier heads 165A- 165D retain one substrate 135 during a polishing process on the polishing stations 1 0A-110C. Other polishing modules, such as the REFLEXION GT™ polishing system, which includes more than one carrier head per polishing station, may also be adapted to benefit from embodiments described herein. Each of the carrier heads 165A-165D are movable in a longitudinal axis of each arm 170. A polished substrate 135 may be transferred from each carrier head 165A-165D at the transfer station 20A. Additionally, an unpolished substrate 135 may be transferred to each carrier head 165A-165D at the transfer station 120. As shown in reference to carrier head 165D, the carrier head 165D is movable along a longitudinal axis of the arm 170 in a travel path 164 indicated by dashed lines to allow the carrier head 165D to access the load cup assembly 160 and facilitate transfer of substrates.

[0028] In one embodiment, the carousel 125 is sequentially advanced in a counterclockwise direction (direction B) to move the carrier heads 165A-165D above the polishing stations 110A-110C and the transfer station 120. During processing, three of the four carrier heads 165A-165D, having substrates retained therein, are disposed above the polishing stations 11 OA, 10B, 1 10C to perform a polishing process thereon. The substrates 135 are sequentially processed by moving the substrate between stations while being retained in the same carrier head 165A-165D. In one example, three carrier heads 165A-165C contain substrates and urge the substrates 135 toward the polishing surface 175 of the polishing stations 11 OA, 110B, and 1 0C. During polishing, the carrier heads 165A-165C containing substrates are rotated in a counterclockwise direction (direction C) while the polishing surfaces 175 are rotated in a counterclockwise direction (direction D).

[0029] As the three carrier heads, which are shown as carrier heads 165A-165C in this example, are utilized at the stations 110A-110C, the carrier head 165D is adjacent the transfer station 120 where a substrate transfer process occurs. The carrier head 165D may be idle for a time period as the three carrier heads 165A- 165C perform a polishing process. During this time period, the carrier head 165D is readied for use in the polishing station 11 OA in a following cycle at the transfer station 120. The carrier head 165D may be advanced along the travel path 164 to be proximate the transfer station 120. While the carrier head 165D is at the transfer station 120, the carrier head 165D may unload a polished substrate 135, be washed, and receive a new, un-polished substrate 135 for a polishing process on the polishing station 110A. In one embodiment, the carrier head 165D is inspected using the monitoring device 162 disposed in the transfer station 120.

[0030] The polishing surface 175 is roughened to facilitate mechanical removal of material from substrates 135. The polishing surface 175 of the polishing pad may be a polymer material which may be solely dielectric to facilitate removal of materials from substrates 135 during a polishing process. Alternatively, the polishing surface 175 of the polishing pad may be at least partially conductive to facilitate electrochemical dissolution of material from substrates in an electrochemical mechanical polishing (ECMP) process. Suitable polymeric materials that may be used include polyurethane, polycarbonate, fluoropolymers, PTFE, PTFA, polyphenylene sulfide (PPS), or combinations thereof, and other polishing materials used in polishing substrate surfaces. In one embodiment, polishing surface 175 of the polishing pad includes a polymeric material, such as open-pored or closed-pored polyurethane material typically used in the fabrication of polishing pads for service in the polishing of semiconductor substrates. In another embodiment, the polishing surface 175 of the polishing pad may contain fixed abrasives. A polishing fluid is typically delivered to the polishing surface 175 of the polishing pad during polishing. The polishing fluid may be a slurry or an electrolytic fluid depending on the polishing process and type of polishing pad used.

[0031] Figure 2 is a partial cross-sectional view of one embodiment of the transfer station 120 of Figure 1. As described above, the transfer station 120 includes the load cup assembly 160 adjacent the first buffer station 145. The first buffer station 145 may be an input or output buffer station that is configured to support a substrate 135. The transfer robot 155 transfers substrates 135 between the first buffer station 145 and the load cup assembly 160 facilitating transfer of substrates to the carrier head 165D.

[0032] In one embodiment, the first buffer station 145 supports a polished substrate 135 to allow the wet robot 140 (Figure 1) to transfer the substrate 135 to a factory interface for subsequent polishing and/or storage. In another embodiment, the first buffer station 145 supports an un-polished substrate 35 to allow the carrier head 165D to receive the substrate 135 for polishing on the polishing station 1 OA. In one embodiment, the transfer robot 155 is configured to transfer substrates 135 between the first buffer station 145 and the load cup assembly 160 to allow the carrier head 165D to receive a substrate 135 as shown in phantom in Figure 2.

[0033] The carrier head 165D is coupled to a shaft 200, which is coupled to a motor 215 configured to move the carrier head 165D laterally in a linear motion (X and/or Y direction) relative to the arm 170. The carrier head 165D also includes an actuator or motor 210 to lift or lower the carrier head 165D in the Z direction relative to arm 170. The carrier head 165D is also coupled to a rotary actuator or motor

220 that is adapted to rotate the carrier head 165D about a rotational axis relative to the arm 170. The motors 210, 215 and 220 disposed on the carrier head 165D are also configured to provide movement of the carrier head 165D relative to the polishing surface 175 (Figure 1) of a polishing pad. In one embodiment, the motors

210, 215 and 220 are configured to rotate the carrier head 165D relative to a rotating polishing surface 175 as well as provide a down-force to urge the substrate

135 retained therein against the polishing surface 175 of a polishing pad during processing. The carrier head 165D construction and operation depicted in Figure 2 is representative of the carrier heads 165A-165C of Figure 1 and carrier heads 165A-165C will not be described further for brevity.

[0034] The carrier head 165D includes a body 225 circumscribed by a retaining ring 230. The carrier head 165D also contains one or more bladders 235A, 235B that are adjacent a flexible membrane 240. The flexible membrane 240 contacts a backside of the substrate 135 when the substrate 135 is retained in the carrier head 165D. The bladders 235A and 235B are coupled to a first variable pressure source 245A that selectively delivers a fluid to the bladders 235A and 235B to apply force to the flexible membrane 240. In one embodiment, the bladder 235A applies force to an outer zone of the flexible membrane 240 while the bladder 235B applies force to a central zone of the flexible membrane 240. Forces applied to the flexible membrane 240 from the bladders 235A and 235B are transmitted to portions of the substrate 135 and may be used to urge portions of the substrate 135 toward the polishing surface of a polishing pad (not shown). The first variable pressure source 245A is configured to deliver fluids to each of the bladders 235A and 235B independently in order to control forces to discrete regions of the substrate 135 through the flexible membrane 240. Additionally, vacuum ports (not shown) may be provided in the carrier head 135 to apply suction to the backside of the substrate 135 facilitating retention of the substrate 135 in the carrier head 165D. Examples of a carrier head 165D that may be utilized include the TITAN HEAD™, the TITAN CONTOUR™ and the TITAN PROFILER™ carrier heads, which are available from Applied Materials, Inc. of Santa Clara, California.

[0035] In one embodiment, the retaining ring 230 is coupled to the body 225 by an actuator 232. The actuator 232 is controlled by a second variable pressure source 245B. The second variable pressure source 245B provides or removes fluid from the actuator 232 which causes the retaining ring 230 to move relative to the body 225 of the carrier head 165D in at least the Z direction. The second variable pressure source 245B is adapted to provide the Z directional movement of the retaining ring 230 independent of movement provided by the motor 210. The second variable pressure source 245B may provide movement of the retaining ring 230 by applying negative pressure or positive pressure to the actuator 232 and/or the retaining ring 230. In one aspect, pressure is applied to the retaining ring 230 to urge the retaining ring 230 toward the polishing surface 175 (Figure 1) of a polishing pad (not shown) during a polishing process. Each of the first variable pressure source 245A and the second variable pressure source 245B may be coupled with the controller to facilitate execution of a polish recipe that automatically controls pressures to zones of the substrate 135 during a polishing process.

[0036] The retaining ring 230 contacts the polishing surface 175 during the polishing process. The retaining ring 230 may also facilitate transportation of the polishing fluid on the polishing surface 175 and create heat due to friction from contact with the polishing surface 175. The fluid transportation and generated heat may be utilized to advantage during a polishing process. The contact with the polishing surface 175 causes the retaining ring 230 to wear. The wear of surfaces of the retaining ring 230 affect the polishing process and the retaining ring 230 will eventually require replacement. Thus, thickness of the retaining ring 230 must be periodically assessed to determine wear and replacement intervals.

[0037] In one embodiment, the surfaces of the retaining ring 230 are monitored by the monitoring device 162 disposed in the load cup assembly 160. Surfaces of the retaining ring 230 may be sensed as the carrier head 165D is adjacent the load cup assembly 160 and data representative of wear of the retaining ring 230 may be sent to a controller. The controller may be in communication with a monitor to display the data for a user. The data from the monitoring device 162 is used to predict and/or ascertain a condition of the retaining ring 230 that is utilized to determine lifetime and replacement of the retaining ring 230. In one embodiment, the data is indicative of the thickness of the retaining ring 230. Alternatively or additionally, the controller may be a system controller that may analyze the data and implement corrective measures in a process recipe to compensate for wear of the retaining ring 230 in the polishing process. Thus, data from the monitoring device 162 is used to determine lifetime and replacement of the retaining ring 230 and may be additionally utilized as a control knob to tune the polishing process. Moreover, in systems having multiple carrier heads with retaining rings, the data from the monitoring device 162 may be utilized to adjust the process recipe of individual retaining rings independently from other retaining rings on other carrier heads in the system. For example, as individual retaining rings may wear at different rates, a process recipe for one retaining ring on one carrier head may be adjusted while other process recipes on other retaining rings on remaining carrier heads may remain the same.

[0038] Figure 3 is a schematic cross-sectional view of another embodiment of a transfer station 120 that may be utilized with the polishing system 100 of Figure 1. The transfer station 120 includes a load cup assembly 160 and a carrier head 165D is disposed adjacent the load cup assembly 160. In this embodiment, the load cup assembly 160 is configured as a wash station 300 adapted to clean the carrier head 165D when the carrier head 165D is not utilized for polishing on the polishing stations 110A-1 10C of Figure 1.

[0039] In one embodiment, the load cup assembly 160 includes a body 305 having a reference cone or ring 307 that is coupled to a base 309. The ring 307 and the base 309 are movable relative to a module base 118 by a first actuator 31 OA. The first actuator 31 OA may be utilized to move the body 305 in at least a linear direction (Z direction) relative to the module base 118. The load cup assembly 160 also includes a pedestal 320 adapted to support a substrate 135 (shown in phantom). The pedestal 320 is coupled to a second actuator 310B adapted to raise and lower a support surface 321 of the pedestal 320. The second actuator 310B facilitates transfer of the substrate 135 to or from the carrier head 165D by moving the support surface 321 in the Z direction relative to the body 305.

[0040] The body 305 also includes a plurality of nozzles 315 utilized to wash the carrier head 165D when a substrate is not present on the pedestal 320. The nozzles 315 are in fluid communication with a pressurized fluid supply 330. The pressurized fluid supply 330 contains a fluid, such as deionized water, that is applied through nozzles 315 to clean the carrier head 165D. In one embodiment, the support surface 321 of the pedestal 320 is configured as a ring having multiple open areas to allow cleaning fluid from the nozzles 315 to impinge the carrier head 165D. The cleaning fluid washes polishing liquid and other debris from the polishing process that may be retained on the carrier head 165D. The wash station 300 also contains an opening 325 formed in the base 309 that is adapted as a drain to selectively remove fluid and polishing debris dislodged from the carrier head 165D.

[0041] In this embodiment, the wash station 300 includes a monitoring device 162 comprising a sensor 335 coupled to a controller. The sensor 335 is adapted to measure a thickness T of the retaining ring 230. In one embodiment, the sensor 335 is an ultrasonic sensor. The sensor 335 may be coupled to or embedded within the body 305 to transmit and receive sound waves. The sound waves are transmitted to the controller to provide a metric indicative of the thickness T of the retaining ring 230. In one embodiment, the retaining ring 230 comprises two annular portions, such as an upper portion 355A and a lower portion 355B. In one embodiment, the upper portion 355A and lower portion 355B may contain a material which is chemically inert in a CMP process, such as metal material, a ceramic material, or a plastic material. In one embodiment, the lower portion 355B contains a plastic, e.g., polyphenylene sulfide (PPS), polyetheretherketone (PEEK), a carbon containing PEEK material, a TEFLON^® containing PEEK material, or a composite material. The upper portion 355A may contain a material that is more rigid or dense than the lower portion 355B. In one embodiment, the upper portion 355A contains stainless steel, aluminum, molybdenum or ceramic materials.

[0042] In one example of operation, the sensor 335 is mounted on an active surface 340 of a land area 345 of the body 305. The land area 345 may be defined as a region of a bottom surface of the ring 307 where the lower portion 355B of the retaining ring 230 contacts a surface of the ring 307. The active surface 340 may be flush with the surface of the ring 307 at the land area 345 where the retaining ring 230 is positioned. In one embodiment, sound waves are transmitted to or through the lower portion 355B of the retaining ring 230 and are reflected from the upper portion 355A. The reflected signals are transmitted to the controller and utilized to determine thickness T of the lower portion 355B of the retaining ring 230. The change in thickness T over time is indicative of the wear of the retaining ring 230.

[0043] Figure 4 is a schematic cross-sectional view of another embodiment of a transfer station 120 that may be utilized with the polishing system 100 of Figure 1. In this embodiment, the load cup assembly 160 is configured as a wash station 400 that may be substantially similar to the embodiment shown in Figure 3. Elements of the transfer station 120 that are similar to the transfer station 120 of Figure 3 will not be repeated for brevity.

[0044] In this embodiment, the monitoring device 162 comprises a sensor 335 which is an eddy current sensor adapted to measure a thickness T of the lower portion 355B. In this embodiment, a contact surface 405 of the lower portion 355B is in contact with the active surface 340 of the ring 307. In other embodiments, the sensor 335 may be utilized as the retaining ring 230 is spaced away from the ring 307. In one aspect, the sensor 335 adapted as an eddy current sensor may be utilized to measure the displacement between the active surface 340 and the contact surface 405 of the upper portion 355A of the retaining ring 230. The displacement corresponds to a change in thickness of at least the lower portion 355B of the retaining ring 230. The displacement may be determined when the lower portion 355B of the retaining ring 230 is in contact with the active surface 340 or when the lower portion 355B is held a constant distance from the active surface 340.

[0045] Figure 5A is a partial plan view of one embodiment of a retaining ring 230 having one or more grooves 500. Each of the one or more grooves 500 are formed in the retaining ring 230 at a desired depth between a contact surface 405 of the retaining ring 230 and a bottom 505 of the groove 500. Each of the grooves 500 disposed on the retaining ring 230 may be utilized to facilitate polishing by enhancing transportation of polishing fluid during a polishing process. [0046] Figure 5B is a schematic cross-sectional view of another embodiment of a transfer station 120 that may be utilized with the polishing system 100 of Figure 1 and the retaining ring 230 shown in Figure 5A. The retaining ring 230 comprises a one or more grooves 500 having a depth D' defined by a contact surface 405 and a bottom 505. The change in the depth D' of the groove 500 corresponds to the change in thickness of the retaining ring 230. In one embodiment, the sensor 335 may be coupled to or embedded within the ring 307. The sensor 335 may be an optical sensor, an eddy current sensor, an ultrasonic sensor, or other suitable sensing device. In one embodiment, the sensor 335 is an ultrasonic sensor configured to transmit and receive sound waves illustrated as signals 510 that impinge the contact surface 405. The sound waves are transmitted to the controller to provide a metric indicative of the depth D' of the groove 500, and, accordingly the thickness of the retaining ring 230, whether the retaining ring 230 is sensed dry or wet. Thus, the depth of the groove 500 measured between the contact surface 405 and the bottom 505 to determine wear without physical contact between the retaining ring 230 and other portions of the load cup assembly 160. The carrier head 165D may be rotated at a predetermined rotational velocity to provide sensing at multiple locations of the retaining ring 230. Thus, multiple grooves 500 may be monitored. Alternatively, the carrier head 165D may be motionless to allow sensing of a single groove 500. In another embodiment, a controlled air column or liquid column may be utilized to surround the signals 510 and control the interface between the retaining ring 230 and the sensor 335. For example, a bubbler (not shown) may be utilized to form a cylindrical air column that surrounds the path of the signals 510.

[0047] In one embodiment, the position of the monitoring device 162 is outside of the area of the substrate 135 to prevent any inadvertent sensing of the substrate 135 or portions of the carrier head 165D that are not of interest. For example, the substrate 135 includes a first radius Ri in the case of a circular substrate. In one embodiment, the first radius Ri includes a radius of about 100 mm for a 200 mm diameter substrate. In another embodiment, the first radius Ri includes a radius of about 150 mm for a 300 mm diameter substrate. In one embodiment, the monitoring device 162 is positioned at a second radius R₂ that is greater than or outside of the first radius Ri. The second radius R₂ may be greater than about 100 mm, such as about 105 mm to about 120 mm from a centerline C for a 200 mm substrate. In another example, the second radius R₂ may be greater than about 150 mm, such as about 155 mm to about 170 mm from the centerline C for a 300 mm substrate. The centerline C may be a geometric center of the load cup assembly 160 and/or a center of the carrier head 165D. Thus, the positioning of the monitoring device 162 prevents any inadvertent sensing of the substrate 135 or portions of the carrier head 165D that are not of interest.

[0048] Figure 6 is a schematic cross-sectional view of another embodiment of a transfer station 120 that may be utilized with the polishing system 100 of Figure 1. In this embodiment, the load cup assembly 160 is similar to the embodiment shown in Figures 3, 4 and 5. Elements of the transfer station 120 that are similar to the transfer station 120 of Figures 3-5 will not be repeated for brevity. In one embodiment, the retaining ring 230 comprises a one or more grooves 500 similar to the embodiment of the retaining ring 230 of Figure 5.

[0049] In this embodiment, the monitoring device 162 comprises a sensor 335 that is an ultrasonic sensor although an optical sensor, an eddy current sensor, or other suitable sensing device may be utilized. In one embodiment, the sensor 335 may be utilized when the retaining ring 230 is in the line-of-sight or field of view of the sensor 335. In other embodiments, the sensor 335 may be utilized when the retaining ring 230 is at least partially disposed in the load cup assembly 160. In one aspect, the sensor 335 includes a tubular conduit 600 disposed adjacent the sensor 335. The tubular conduit 600 is coupled to a fluid supply 605 that delivers a fluid, such as deionized water, to surround the signal path of the sensor 335. The fluid is utilized to eliminate uncontrolled air that may affect the signals from the sensor 335. In one embodiment, the contact surface 405 of the retaining ring 230 is in direct contact with the active surface 340 of the ring 307. In another embodiment, the tubular conduit 600 is coupled to an actuator 610 that allows the tubular conduit 600 to extend and retract relative to an active surface 340 of the ring 307. The tubular conduit 600 may be actuated toward the contact surface 405 as shown in phantom to a position adjacent the contact surface 405 of the retaining ring 230 when the carrier head 165D is not in contact with the ring 307. The tubular conduit 600 may contain at least a portion of the sensor 335 which moves with the tubular conduit 600 toward the contact surface 405 of the retaining ring 230. The actuator 610 may also retract the tubular conduit 600 when the sensor 335 is not needed.

[0050] Figure 7 is a flow chart showing one embodiment of a method 700. At 705, a carrier head 165D having a retaining ring 230 is moved adjacent a monitoring device 162. In one embodiment, the monitoring device 162 is disposed on a load cup assembly 160 within a polishing module 105. In other embodiments, the monitoring device 162 may be adjacent the transfer station 120 or in a travel path of the carrier head 165D adjacent the transfer station 120 or other position on the polishing module 105. The monitoring device 162 includes a sensor 335 and energy is transmitted from the sensor 335 as shown at 710. The energy may be ultrasonic waves, optical waves or magnetic fields or magnetic signals. At 715, energy reflected from the retaining ring 230 is received by the sensor 335. The reflected energy may be from an internal or external surface or surfaces of the retaining ring 230. At 720, a condition of the retaining ring is determined based on the received energy. The reflected signals may be provided to a controller to obtain a metric indicative of the condition of the retaining ring 230, for example, a thickness of the retaining ring 230 or portion thereof, or a depth of a groove 500 of the retaining ring 230 that may be associated with a thickness of the retaining ring 230. The data may be utilized to determine replacement intervals for the retaining ring 230 and/or tuning of variables in subsequent polishing processes.

[0051] Embodiments described herein provide a method and apparatus for monitoring the condition of a surface of a retaining ring 230 disposed on a carrier head in a polishing station, such as carrier heads 165A-165D as described herein. A monitoring device 162 is described that may be mounted on-tool and, in one embodiment, senses the retaining ring 230 condition between polishing cycles. The sensing of the retaining ring 230 may be set by a user at pre-defined intervals as part of routine monitoring or at chosen intervals based on user preferences. Data from the monitoring device 162 is provided to a controller that may be used to monitor wear of the retaining ring 230, determine lifetime of the retaining ring 230 and/or determine replacement intervals for the retaining ring 230. In one aspect, data from the monitoring device 162 could be used to predict the lifetime of the retaining ring 230 and facilitate replacement of the retaining ring 230 at the end of the useful lifetime. In another aspect, data from the monitoring device 162 could be used to predict the lifetime and facilitate a convenient replacement interval even if the retaining ring 230 is not completely worn out.

[0052] Embodiments of the monitoring device 162 as described herein minimize or eliminate physical handling and/or mechanical contact with the carrier heads 165A-165D and retaining ring 230. For example, mechanical measuring devices such as calipers require contact with the retaining ring 230. The contact with the mechanical measuring devices may damage the retaining ring 230 during measurement which, in turn, may damage the polishing surface 175 during processing. The measurements may be taken within the tool and there is no need for shutting down the polishing system. Additionally, there is no need to completely dry the retaining ring 230 for measurements. The monitoring device 162 is mounted on-tool such that the environment contained in the environmentally controlled enclosure 115 (Figure 1). Thus, the monitoring device 162 as described herein provides monitoring of the retaining ring 230 with less potentially damaging handling or contact with the carrier heads 165A-165D and/or breaching of the environment of the polishing module 105. The method and apparatus also eliminates or minimizes visual inspections, which are time consuming and may be inaccurate. Additionally, throughput may be maximized as the polishing system will not require shut downs for measurement and/or observation of the retaining ring 230.

[0053] Additionally, the retaining ring 230 wear data may be used as a control variable during a polishing process. For example, if the retaining ring 230 contains grooves 500, and the grooves 500 show a predetermined amount of wear, one or more polishing parameters may be adjusted to compensate for any retaining ring 230 thickness effects in polishing uniformity. In one example, polishing parameters such as rotational velocity and down-force of the carrier head 165A-165D may be adjusted to account for wear of the retaining ring 230 and mimic the polishing effects of a less-worn retaining ring 230. In one aspect, the rotational velocity of the carrier head 165A-165D may be accelerated to facilitate transportation of the polishing fluid and create heat on the polishing surface 175 that is substantially equivalent to the effect of a less-worn retaining ring 230.

[0054] In another example, the retaining ring 230 wear data may be utilized to minimize within wafer non-uniformity during the lifetime of the retaining ring 230. Wear data of the retaining ring 230 may be utilized with an automated process control system that is coupled to the bladders 235A and 235B in multi-zone carrier heads, such as the carrier head 165D shown in Figure 2. Additionally, the automated process control system may be in communication with the actuator 232 on the carrier head 165D shown in Figure 2. In one aspect, the pressure applied to outer zones (bladder 235A) and/or the retaining ring 230 by the actuator 232 may be modified in response to changes in the thickness of the retaining ring 230. Changes to the pressure applied to the substrate by the bladders 235A and 235B and/or pressures applied to the retaining ring 230 may be made in real-time based on the thickness data of the retaining ring 230. Thus, removal rate, removal profile and/or topography of the substrates being polished may be controlled by manipulating the polishing parameters based on the wear of the retaining ring 230. Additionally, as the polishing parameters may be tuned for each carrier head 165A- 165D, carrier head to carrier head variation may be minimized.

[0055] Embodiments described herein provide methods and apparatus that facilitate monitoring of a retaining ring within a polishing system to determine condition of the retaining ring and/or assess lifetime of the retaining ring. In one embodiment, an apparatus is provided. The apparatus includes a carrier head movable in a travel path between at least one polishing station for polishing a substrate as the substrate is retained in the carrier head and a transfer station for transferring the substrate to and from the carrier head, the carrier head having a retaining ring, and a sensor disposed in the travel path of the carrier head, the sensor operable to provide a metric indicative of a condition of the retaining ring.

[0056] In another embodiment, a transfer station disposed in a polishing module for transferring substrates between a substrate transfer device and at least one carrier head is provided. The transfer station includes a load cup assembly having a body that is sized to receive a substrate and at least a portion of a retaining ring that is coupled to the at least one carrier head, and a sensor disposed on the body, the sensor operable to provide a metric indicative of a condition of the retaining ring, wherein the substrate includes a first radius and the sensor is positioned on the body at a second radius that is greater than the first radius.

[0057] While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.

Claims

What is claimed is:

1. An apparatus, comprising:

a carrier head movable in a travel path between at least one polishing station for polishing a substrate as the substrate is retained in the carrier head; and

a transfer station for transferring the substrate to and from the carrier head, the carrier head having a retaining ring, and a sensor disposed in the travel path of the carrier head, the sensor operable to provide a metric indicative of a condition of the retaining ring.

2. The apparatus of claim 1 , wherein the sensor is an ultrasonic sensor.

3. The apparatus of claim 1 , wherein the sensor is an eddy current sensor.

4. The apparatus of claim 1 , wherein the sensor is an optical sensor.

5. The apparatus of claim 4, wherein the sensor comprises a plurality of waveguides disposed in a body of the transfer station and positioned to direct light towards the retaining ring when the retaining ring is aligned with the body of the transfer station.

6. The apparatus of claim 4, wherein the sensor comprises a transmitter and receiver.

7. The apparatus of claim 1 , wherein the transfer station comprises one or more nozzles in fluid communication with a water source.

8. The apparatus of claim 2, wherein the transfer station comprises a body that is shaped to contain a fluid.

9. The apparatus of claim 7, wherein the substrate includes a first radius and the sensor is positioned at a second radius that is greater than the first radius.

10. A method for monitoring at least one surface of a retaining ring coupled to a carrier head, the method comprising:

moving the carrier head adjacent a sensor device disposed in a polishing module;

transmitting energy from the sensor device toward the retaining ring;

receiving energy reflected from the retaining ring; and

determining a condition of the retaining ring based on the received energy.

1 1. The method of claim 10, wherein the transmitted and received energy is a sound wave.

12. The method of claim 10, wherein the transmitted and received energy is an optical signal.

13. The method of claim 10, wherein the transmitted and received energy is a magnetic field.

14. The method of claim 10, wherein the energy is transmitted and received through a liquid.

15. The method of claim 10, further comprising:

moving the carrier head adjacent a load cup assembly disposed in the polishing module, the sensor device being disposed in a body of the load cup assembly.