Patent Publication Number: US-9403256-B2

Title: Recording measurements by sensors for a carrier head

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/727,544, filed Nov. 16, 2012. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to sensor measurements during chemical mechanical polishing. 
     BACKGROUND 
     Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. 
     Chemical mechanical polishing (CMP) is one accepted method of planarizing a substrate surface. This planarization method typically requires that the substrate be mounted to a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad. 
     Some carrier heads include a flexible membrane with a mounting surface for the substrate. One or more chambers on the other side of the membrane can be pressurized to press the substrate against the polishing pad. A pneumatic control unit system outside the carrier head can control the pressures applied to the chambers, e.g., through pressure supply lines, in order to control the pressures applied to the substrate. 
     SUMMARY 
     One problem that has been encountered in CMP is that a carrier head includes multiple parts, e.g., membranes, that can fail during operation. Premature failure of the parts can be difficult to analyze due to the multiple interacting factors. However, a dedicated memory can be used to record signals from sensors in or associated with the carrier head, e.g., sensors that measure the pressure in the chambers. The recorded signals can then be used in a variety of techniques, e.g., the carrier head operations can be rerun in order to understand factors contributing to the fault, or the signals can be compared against a standard signature to detect drifting conditions. 
     In one aspect, a pressure control assembly for a carrier head of a polishing apparatus includes a pressure supply line configured to fluidically connect to a chamber of a carrier head, a sensor to responsive to pressure in the chamber and configured to generate a signal representative of the pressure, and a pneumatic control unit configured to receive the signal, to control a pressure applied to the pressure supply line, and to record the signal in a non-transitory storage media of a storage device removably attached to the pneumatic control unit. 
     Implementations may include one or more of the following features. The storage device may include a flash memory. The pneumatic control unit may include a USB port and the pneumatic control unit may be configured to record the signal to the storage device attached to the USB port. The pneumatic control unit may be configured to record the signal acquired during processing of a plurality of substrates. The pneumatic control unit may be configured to cause the storage device to store signals received during processing of a most recent plurality of substrates. The most recent plurality of substrates may include at most 20 substrates. Processing of the plurality of substrates may include one or more of loading or unloading the substrate at a loading station, sensing the presence of the substrate, chucking or dechucking the substrate from the polishing pad, or polishing the substrate. The pneumatic control unit may be configured to sample the signal at a sampling rate to generate a sequence of measured signal values, and may be configured to store the sequence of measured signal values to record the signal. The sampling rate may be at least 10 Hz. A plurality of pressure supply lines may be configured to fluidically connect to chambers of the carrier head. A plurality of sensors may be configured to be responsive to pressures in the chambers and to generate signals representative of the pressures. The pneumatic control unit may be configured to receive the signals and record the signals in the non-transitory storage media of the storage device. 
     In another aspect, a method of operating a polishing system includes holding a substrate in a carrier head in a polishing system, processing the substrate, generating a signal representative of a pressure in a chamber in the carrier head, recording the signal in a non-transitory storage media of a storage device removably attached to a pneumatic control unit for the carrier head, and after recording, detaching the storage device from the pneumatic control unit. 
     Implementations may include one or more of the following features. The carrier head may be detached from the polishing system. The carrier head and the storage device may be sent to a repair facility. A fault may be detected in the carrier head and/or a pressure assembly, and the storage device may be detached in response to detecting the fault. The signal in the storage device may be analyzed. 
     In another aspect, a method of operating a polishing system includes loading a pressure signature into a non-transitory storage media of a storage device, after loading, attaching the storage device to a pneumatic control unit for a carrier head in a polishing system, processing the substrate, generating a signal representative of a pressure in a chamber in the carrier head, and comparing the signal to the pressure signature. 
     Implementations may include one or more of the following features. An alert may be generated if the signal varies by more than a threshold amount from the pressure signature. 
     Advantages of implementations may optionally include one or more of the following. A failure in a carrier head may be easier to analyze, e.g., the cause of the failure may be easier to determine. Potential failure of parts can be detected. Parts can be replaced prior to failure, thus reducing the risk of damage to substrates due to failure in the carrier head and improving yield. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a chemical mechanical polishing system. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example of a polishing apparatus  100 . A description of a CMP apparatus may be found in U.S. Pat. No. 5,738,574, the entire disclosure of which is incorporated herein by reference. 
     The polishing apparatus  100  includes a rotatable disk-shaped platen  120  on which a polishing pad  110  is situated. The polishing pad  110  can be a two-layer polishing pad with an outer polishing layer  112  and a softer backing layer  114 . The platen is operable to rotate about an axis  125 . For example, a motor  122  can turn a drive shaft  124  to rotate the platen  120 . 
     The polishing apparatus  100  can include a port  130  to dispense polishing liquid  132 , such as abrasive slurry, onto the polishing pad  110 . The polishing apparatus can also include a polishing pad conditioner to abrade the polishing pad  110  to maintain the polishing pad  110  in a consistent abrasive state. 
     The polishing apparatus  100  includes at least one carrier head  140 . The carrier head  140  is operable to hold a substrate  10  against the polishing pad  110 . In addition, the carrier head  140  can load or unload the substrate at a loading station, sense the presence of the substrate, and chuck or dechuck the substrate from the polishing pad. Each carrier head  140  can have independent control of the polishing parameters, for example pressure, associated with each respective substrate. 
     The carrier head  140  can include a retaining ring  142  to retain the substrate  10  below a flexible membrane  144 . The carrier head  140  also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers  146   a - 146   c , which can apply independently controllable pressures to associated zones on the flexible membrane  144  and thus on the substrate  10 . Although only three chambers are illustrated in  FIG. 1  for ease of illustration, there could be one or two chambers, or four or more chambers, e.g., five chambers. In addition, although the retaining ring  142  is illustrated as fixed to the carrier head  140 , there can be a chamber that controls the downward pressure of the retaining ring on the polishing pad  110 . 
     The carrier head can also include a base  148  to which the retaining ring  142  is connected. The base  148  can be directly secured to a drive shaft  152 . Alternatively, the base  148  can be connected to a housing which is secured to the drive shaft  152 , and a chamber between the base  148  and the housing can control the vertical position of the base  148 . Other features of the carrier head may be found in U.S. Pat. No. 7,699,688, the entire disclosure of which is incorporated herein by reference. 
     The carrier head  140  is suspended from a support structure  150 , e.g., a carousel, and is connected by the drive shaft  152  to a carrier head rotation motor  154  so that the carrier head can rotate about an axis  155 . Optionally each carrier head  140  can oscillate laterally, e.g., on sliders on the carousel  150 , or by rotational oscillation of the carousel itself. In typical operation, the platen is rotated about its central axis  125 , and each carrier head is rotated about its central axis  155  and translated laterally across the top surface of the polishing pad. 
     Each chamber  146   a - 146   c  is fluidically connected by an associated pressure supply line  160   a - 160   c  to a pneumatic control system  170 , e.g., a system of pressure sensors and valves that can regulate pressure in the pressure supply line  160   a - 160   c  and thus the pressure in the associated chamber  146   a - 146   c . The pneumatic control system  170  is coupled to a fluid supply line  172 , e.g., a source of pressurized air, nitrogen or other gas. The pneumatic control system  170  is also coupled to a vacuum line  174 . The pneumatic control system  170  can selectively couple the respective pressure supply lines  160   a - 160   c  to the fluid supply line  172  or the vacuum line  174 . The collection of the pressure supply lines  160   a - 160   c  and pressure control system  170  can be considered an “upper pressure assembly” (UPA). 
     Each pressure supply line  160   a - 160   c  can include a passage  162  that extends through the base  148 , a passage  164  in the drive shaft  152 , a rotary coupler  166 , and tubing  168 , e.g., a pipe or hose. A first end of the passage  162  in the base  148  opens to an associated chamber  146   a - 146   c . A second end of the passage  162  in the base  148  can be connected to the first end of the passage  164  in the drive shaft  152 . A second end of the passage  164  in the drive shaft  152  can be connected to a first end of the tubing  168  by the rotary coupler  166 . A second end of the tubing  168  is connected to the pneumatic control system  170 . However, many other arrangements are possible for the pressure supply lines  160   a - 160   c . For example, if the drive shaft  152  does not rotate, then the rotary coupler  166  could be omitted or the tubing  166  could be connected directly to the carrier head  140  (bypassing the drive shaft  152 ). 
     While only one carrier head  140  is shown, more carrier heads can be provided to hold additional substrates so that the surface area of polishing pad  110  may be used efficiently. Thus, the number of carrier head assemblies adapted to hold substrates for a simultaneous polishing process can be based, at least in part, on the surface area of the polishing pad  110 . 
     A controller  190 , such as a programmable computer with a microprocessor  192 , memory  194  and I/O system  196 , is connected to the motors  122 ,  154  to control the rotation rate of the platen  120  and carrier head  140 . For example, each motor can include an encoder that measures the rotation rate of the associated drive shaft. A feedback control circuit, which could be in the motor itself, part of the controller, or a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft matches at a rotation rate received from the controller. 
     The polishing apparatus can optionally include an in-situ monitoring system with a sensor  180  to monitor the substrate during polishing. The in-situ monitoring system can be, for example, an optical monitoring system, an eddy current monitoring system, or a motor current monitoring system, which can be used to determine a polishing endpoint. 
     The controller  190  can be configured to store or determine a desired pressure for the chambers  146   a - 146   c  in the carrier head  140 . The controller  190  and pneumatic control system  170  can communicate. For example, the controller  190  can be configured to send commands to the pneumatic control system  170  in response to which the pneumatic control system applies the desired pressure to the pressure supply lines  160   a - 160   c . The controller  190  can include a computer program product implemented in non-transient computer readable media to perform these and other operations. 
     The pneumatic control system  170  includes a sensor  176  for each pressure supply line  160   a - 160   c . The sensor  176  is configured to detect the pressure in the pressure supply line  160   a - 160   c , and thus the pressure applied to the chamber  142   a - 142   c . The measured pressure can be used in a feedback loop in the pneumatic control system  170  so the actual pressure in the pressure supply lines  160   a - 160   c  more closely matches the desired pressure received from the controller  190 . Although illustrated as located in the pneumatic control system  170 , the sensor  176  could be at another position along the pressure supply line  160   a - 160   c  or even within the carrier head  140 . 
     Despite the use of a feedback loop, the actual pressure in a pressure supply line  160   a - 160   c  might not match the desired pressure, e.g., if a part is failing and there is a leak or similar problem. 
     A memory device  200  can be removably connected to the pneumatic control system  170 . The memory device  200  can be a flash memory card, although another memory device such as miniaturized hard drive is possible. The memory device  200  can be manually removably connected to a data port of a pneumatic control system  170 . For example, the data port can be a universal serial bus (USB) port, e.g., a USB receptacle, and the memory device  200  can be a USB mass storage device, e.g., a USB flash memory drive. 
     The pneumatic control system  170  is configured to record the output from the sensors  176  on the memory device  200 . The pneumatic control system  170  can be configured to sample the sensors  176  at a relatively high sampling rate, e.g., 10 Hz or more, e.g., 100 Hz, and store the sampled output of the sensors  176  on the memory device  200 . Due to the limited memory of the memory device  200 , only the sensor signals acquired during processing of a number of the most recent substrates can be recorded. For example, the memory device  200  can record the sensor readings for the most recent five to twenty substrates. 
     The pneumatic control system  170  can include its own processor, memory and I/O system programmed to perform the sampling and recording, as well as to perform the feedback control of the pressure. 
     The memory device  200  can be removed either during regular maintenance of the carrier head  140  and/or upper pressure assembly, or following a fault in the carrier head and/or upper pressure assembly. 
     In the case of a fault, the sensor readings obtained during processing of the substrate can be analyzed to better understand the factors causing the fault. For example, depressurization of a particular chamber can indicate the location where a membrane failed. 
     Some semiconductor device manufacturers have repair or maintenance of the carrier head and/or upper pressure assembly performed by another party, e.g., by the manufacturer of the equipment. Having the memory device  200  be manually detachable permits the acquired sensor data to be easily transferred to the party performing the repair or maintenance. For example, in case of a fault, both the carrier head  140  and the memory device  200  can be removed and sent together to the repair facility. 
     In the case of regular maintenance, the sensor readings can be compared against a “gold signatures” for the sensors. The gold signatures can be obtained by measuring and recording the sensor readings during processing of a substrate that does not undergo a fault. Deviations from the gold signatures can indicate a part that is likely to fail and may need early replacement. This enables the operator to create prediction algorithms to avoid catastrophic failures, schedule protective maintenance, and minimize tool down time. 
     In some implementations, the gold signatures can be stored on the memory device  200 , and the pneumatic control system  170  can be configured to compare the sensor readings to the gold signatures. Again, deviations from the gold signatures can indicate that a part is likely to fail and that the carrier head and/or upper pressure assembly should undergo maintenance. The pneumatic control system  170  and/or the controller  190  can be configured to generate an alert, e.g., an audible or visual signal, or an electronic message that is sent to the controller  190 , if the sensor signals deviate by more than a threshold amount from the gold signatures. 
     In some implementations, an RFID device  210  can be embedded into the carrier head  140 . The RFID device  210  head can include a non-volatile memory. The system  100  can include an RFID scanner  220 . The RFID scanner  220  can be used to track when a carrier head is removed or attached to the polishing system  100 . Data that can be stored in the memory of the device  210  and tracked include an identification code for the carrier head  140 , the date(s) the carrier head  140  is installed and/or removed from the system  100 , and the number of substrates polished with the carrier head  140 . In addition, the RFID scanner can be used to move data stored in the non-volatile memory into a separate storage system, e.g., the controller  190 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, although the carrier head has been described as part of a chemical mechanical polishing apparatus, it may be adaptable to other types of processing systems, e.g., wafer transfer robots or electroplating systems. In the CMP system, the platen need not be rotatable or could be omitted entirely, and the pad could be circular or linear and could be suspended between rollers rather than attached to a platen. 
     Accordingly, other embodiments are within the scope of the following claims.