Patent Publication Number: US-2022216079-A1

Title: Methods and apparatus for wafer detection

Description:
BACKGROUND 
     Field 
     Embodiments of the present disclosure generally relate to substrate processing, and more specifically to methods and apparatus for detecting and/or monitoring, e.g., abnormalities in wafer transfer and handling. 
     Description of the Related Art 
     Wafers can break/bow easily during handling and transfer, particularly when utilizing electrostatic chucks. Electrostatic chucks utilize a platen with integral electrodes which are biased with high voltage to establish an electrostatic holding force between the platen and wafer. The residual charges on the wafer and pedestal dissipate slowly, causing wafer breakage and partial chucking. In addition, wafer breakage occurs when the lift pins are moved before dissipation of the residual charge. As a result, wafer throughput is diminished. Conventional methods of wafer detection within semiconductor fabs typically utilize sensors to monitor the wafer during handling and transfer. However, such sensors are costly, and wafer breakage still presents a challenge even when utilizing the sensors. 
     There is a need for new and improved methods of detecting and/or monitoring, e.g., abnormalities during wafer transfer and handling that overcome one or more deficiencies in the art. 
     SUMMARY 
     Embodiments of the present disclosure relate to methods and apparatus for detecting and/or monitoring, e.g., abnormalities in wafer transfer and handling. 
     In an embodiment, an apparatus for wafer dechucking verification is provided. The apparatus includes a motor coupled to a lift pin, the motor configured to adjust a height of the lift pin above a pedestal, the lift pin for raising or lowering a wafer. The apparatus further includes at least one processor, the at least one processor being configured to control the motor, initiate a wafer transfer operation to transfer the wafer between components of a semiconductor processing system using the motor and the lift pin, measure a parameter during the wafer transfer operation, and change a force applied to the lift pin based on the measured parameter. 
     In another embodiment, a method for wafer dechucking verification is provided. The method includes initiating a wafer transfer operation to transfer a wafer between components of a semiconductor processing system, the semiconductor processing system comprising a motor coupled to a lift pin, the motor configured to adjust a height of the lift pin above a pedestal, the lift pin for raising or lowering the wafer. The method further includes measuring one or more first parameters during the wafer transfer operation, comparing the one or more first parameters to one or more first pre-determined parameter ranges, and changing a force applied to the lift pin based on the one or more first parameters. 
     In another embodiment, a non-transitory computer-readable medium storing instructions that, when executed on a processor, perform operations for wafer dechucking verification is provided. The operations include initiating a wafer transfer operation to transfer a wafer between components of a semiconductor processing system, the semiconductor processing system comprising a motor coupled to a lift pin, the motor configured to adjust a height of the lift pin above a pedestal, the lift pin for raising or lowering the wafer. The operations further include one or more of measuring a first current powering the motor during the wafer transfer operation and determining a difference between the first current and a first pre-determined current range, or measuring a first torque for raising or lowering the wafer during the wafer transfer operation and determining a difference between the first torque and a first pre-determined torque range. The operations further include changing a force applied to the lift pin based on the first current, first torque, or both. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, 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 exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments. 
         FIGS. 1A-1B  shows components of an example apparatus for wafer detection according to at least one embodiment of the present disclosure. 
         FIG. 2A  is an exemplary graph for normal, or benchmark, wafer pick-up data according to at least one embodiment of the present disclosure. 
         FIG. 2B  is an exemplary graph of sample wafer pick-up data according to at least one embodiment of the present disclosure. 
         FIG. 3  shows example operations of a method of wafer detection according to at least one embodiment of the present disclosure. 
         FIG. 4A  is an example chamber that can be utilized with embodiments described herein. 
         FIG. 4B  is an example chamber that can be utilized with embodiments described herein. 
     
    
    
     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 and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments described herein relate to methods and apparatus for detecting and/or monitoring, e.g., abnormalities in wafer transfer and handling. Briefly, the method includes monitoring/measuring a current of a motor in order to determine torque, and the torque determines the lift force used to lift a wafer. This method can be utilized to detect imperfect wafer handoff (or wafer transfer) due to, e.g., residual chucking, extra load applied on the wafer by the lift pin drive, among other abnormalities. Because abnormalities in, e.g., wafer transfer, lift pin position, and/or wafer position are detected, wafer transfer processes and/or other processes can be ceased prior to wafer damage, enabling closed-loop control. 
     Apparatus and methods described herein aid with, e.g., the ascertainment of whether the wafer has fully dechucked from the substrate support. In some embodiments, the apparatus and methods described herein can be used for, e.g., wafer dechucking verification and/or detecting a wafer dechucking status. 
     Example Apparatus 
       FIG. 1A  is a side view of an apparatus utilized for wafer detection and for detecting the above mentioned abnormalities. The apparatus includes a lead screw shaft  105  coupled to a motor  115  via shaft coupling  111 . The lead screw shaft  105  can be a lead screw shaft and a nut  104 . Additionally, or alternatively, the lead screw shaft  105  and nut  104  can be a ball screw shaft and ball nut. Bearing  114  supports the lead screw shaft  105 . A lifting shaft  109 , which extends into a chamber during operation, is coupled to the nut  104  by a carrier block  113 . The lifting shaft  109  extends through a chamber mount  102  and attached to a hoop mount  101  positioned in a chamber. A linear motion rail  103  serves as a guide surface for the nut  104 . As shown in  FIG. 1B , a hoop ring  152  is coupled to the hoop mount  101 , and lift pins  151  for raising and lowering a substrate are coupled to the hoop ring  152 . The drive assembly  153 , which includes the lead screw shaft  105  and nut  104 , bearing  114 , and other components, is coupled to the hoop ring  152  and the lift pins  151 . The motor  115  is connected to a power source (not shown) through a power cable  107 . The motor  115  is also connected to other components of the system such as the programmable logic controller (PLC)  125 , discussed below, by a communication cable  108 . 
     In operation, the current driving the motor  115  can also be monitored and measured, and this current is related to the torque used to lift or lower the load by equation (1): 
         I   a   =T/K   T   (1)
 
     where I a  is the armature current of the motor  115  (units of amperes (amp)), and K T  is the motor torque constant (units of N·m/amp). An armature is a component of an electric machine which carries alternating current. As the load on the motor  115  increases, the motor  115  draws more current from a motor driver  120 . The motor driver  120  is coupled to the motor  115  to enable control of the motor  115 . The motor driver  120  is also coupled to the PLC  125 . The PLC  125  controls various components of the motor driver  120 . 
     The motor driver  120  (e.g., a drive motor control unit) detects the increased/decreased torque and/or the increased/decreased current when there is, e.g., partial chucking and/or the wafer is, e.g., lifted, handed-off, et cetera. The motor driver  120  includes a CPU that controls/monitors the motor  115 . The changes in torque (and/or current) are communicated from the motor driver  120  to the PLC  125 . Detection and response time using, e.g., ether-CAT and ether-net drivers can be in microseconds. Such response time is improved over traditional sensors. 
     As stated above, the PLC  125  controls the motor driver  120 , and the motor driver  120  controls the power to drive the motor(s)  115  during, e.g., lifting, moving, and/or transferring of the wafer. The PLC  125  is a “master” driver (e.g., the “controller device”), while other drivers, e.g., the motor driver  120 , are “slave” driver(s) (e.g., the “controlled device(s)”). The PLC  125  includes a controller  126 . The controller  126  includes a central processing unit (CPU)  127 , a memory  128 , and support circuits  129  for the CPU  127 . The controller  126  may be any suitable type of general-purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory  128 , or other computer-readable medium, for the CPU  127  may be one or more of any readily available memory forms, such as random access memory (RAM), read only memory (ROM), a floppy disk, a hard disk, or any other form of digital storage, local or remote. The support circuits  129  may be coupled to the CPU  127  in an effort to support the processor in a conventional manner. These circuits may include cache, power supplies, clock circuits, input/output (I/O) circuitry and subsystems, and the like. In some embodiments, the techniques disclosed herein for a deposition process as well as a cleaning regime may be stored in the memory as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU. 
     In some embodiments, a software algorithm with a pre-defined range for a current value (and/or torque value) at a defined position with wafer resting on the pedestal can trigger shut-off of the motor through the (PLC)-to-motor driver circuitry. According to at least one embodiment, one or more operations of the apparatus and methods described herein can be included as instructions in a computer-readable medium for execution by the controller unit (e.g., controller  126 ) or any other processing system. 
     As stated above, the motor driver  120 , which is controlled by the PLC  125 , is utilized to detect the current. This current, a sample current (I S ) can then be converted into torque using equation (1). The torque (sample torque, T S ) is then compared to benchmark operation data for torque (normal torque, T N ). The normal torque, T N , is the amount of torque for normal operation with a suitable sample size of normal wafer exchange. The T N  can be in the form of a range of values. Additionally, or alternatively, the sample current (I S ) can be compared to a benchmark current (e.g., a normal current, I N ). The I N  can be in the form of a range of values. 
     In some embodiments, force on the lift pins can be changed in accordance with a sensor signal from e.g., a motor drive unit, pressure sensors embedded between the wafer and the electrostatic chuck, and/or the chucking current drawn by the electrostatic chuck. Each of the motor drive unit, pressure sensor(s), and chucking current can include a processor which can relay information to the PLC  125  in order to, e.g., control the motor. 
       FIG. 2A  is an exemplary graph for normal, or benchmark, wafer pick-up data, where torque (T N ) is plotted as a function of wafer lift pin position.  FIG. 2B  is an exemplary graph of sample wafer pick-up data, where torque (T S ) is plotted as a function of lift pin position. 
     By comparing the slope of the sample wafer pick-up data versus the slope of the benchmark wafer pick-up data, the status of the wafer transfer can be determined.  FIGS. 2A and 2B  could be plotted as current versus position by using the equation (1). For simplicity, only the plots of torque versus lift pin position are shown. 
     The slope of the line  201  ( FIG. 2A ) shows a progressive increase in torque, where a “normal” torque (or current) slope is observed over a selected scan zone. In this case, a linear progressive increase in torque (or current) indicates, e.g., normal operation. The sample wafer pick-up data ( FIG. 2B ) of line  203  illustrates, e.g., abnormal wafer pick-up, abnormal wafer transfer, wafer breakage, and/or abrupt release of the wafer. Specifically, the spike in torque (or current)—shown as line  204 —indicates, e.g., increased force, while the decline in slope of torque (or current)—shown as line  206 —indicates, e.g., wafer breakage, abrupt release of wafer from the pedestal, and/or abnormal wafer transfer. Additionally, or alternatively, the sample current can be compared to the current of the benchmark operation data. As such, the plots can be current versus lift pin position. 
     Referring back to equation (1), output torque is directly proportional to armature current. Accordingly, the rate of armature current, I a , with respect to position (x) or time (t) is also directly proportional to the rate of torque (T) with respect to position (x) or time (t), as given by equations (2) and (3), respectively: 
         dI   a   /dx=dT/dx   (2)
 
         dI   a   /dt=dT/dt   (3)
 
     Here, detection of an additional load due to abnormal wafer pick-up is found when the slope for the rate of armature current spike is above a threshold slope (e.g., normal operation). Wafer breakage and/or abnormal wafer release from the pedestal is found when the slope begins to reach a negative slope. 
     Example Transfer and Detection Sequence 
     Embodiments described herein are useful for monitoring and detecting wafer handoff. Wafer handoff, can occur between various hardware components of semiconductor processing systems. For example, wafer handoff can occur between the lift pins and a robot (e.g., a blade of the robot), between the pedestal and the lift pins, and between the lift pins and an indexer (e.g., a blade of the indexer). An illustrative, but non-limiting, wafer transfer sequence for indexer-based architectures is as follows: 
     (1) First, the wafer, held by a robot blade, enters the chamber through a slot in the chamber. (2) The lift pins  151  are raised via the motor and drive assembly  153 , lifting shaft  174 , and hoop ring  152  and pick up the wafer from the robot blade, and (3) the robot blade retracts. (4) The lift pins are retracted to place the wafer onto a pedestal. (5) The lift pins are retracted back below the pedestal, and (6) the pedestal is raised for substrate processing. (7) Once substrate processing is complete, the pedestal is retracted to a wafer release position. (8) The lift pins are then raised to the wafer release position to pick up the wafer from the pedestal. (9) The lift pins are then raised to handoff the wafer to the indexer blade, and (10) the indexer blade receives the wafer and the lift pins are retracted. 
     (11) The indexer blade rotates, and (12) the lift pins are raised to pick up a new wafer from the indexer blade. (13) The indexer blade then rotates and moves out of the way of lift pins. (14) The lift pins are retracted to place the wafer on the pedestal. (15) Operations (6)-(14) are then repeated until the process is completed. (16) After completion of the process, operation (14) is avoided in the loop, and the lift pins from operations (12), (13) are raised to handoff the wafer to the robot blade. 
     In this example, the indexer and robot blade move in the horizontal directions, though other directions are contemplated. In addition, a simplified sequence can include operations (1)-(8) and (16). At, e.g., operations (2), (4), (8), (10), (12), (14), (15), and (16), the current and/or torque can be monitored and measured to determine whether wafer handoff is abnormal. One or more operations in the wafer transfer sequence can be performed by one or more processors, such as the PLC. 
       FIG. 3  shows example operations of a method  300  of wafer detection according to at least one embodiment of the present disclosure. Method  300  can be utilized to detect, e.g., imperfect wafer handoff (wafer transfer) due to, e.g., residual chucking, extra load applied on the wafer by the lift pin drive, among other abnormalities. Because abnormalities in, e.g., wafer transfer, lift pin position, and/or wafer position are detected, transfer processes and/or other processes can be ceased prior to wafer damage, enabling closed-loop control. 
     Method  300  begins with the PLC, e.g., PLC  125 , initiating a wafer handoff/transfer operation (and/or lift pin operation) at operation  310 . The wafer transfer operation can include causing wafer transfer between components (e.g., lift pins, pedestal, an indexer (or blade thereof), a robot (or blade thereof), or a combination thereof) of a semiconductor processing system. The components can be controlled by the PLC. The wafer transfer sequence can include wafer lift-pin movement (which may also be initiated by the PLC). Here, the wafer lift pins are raised (or lowered)—by, e.g., the movement of the shaft, hoop ring, and motor drive assembly—to a position to lift the wafer from a robot blade, to lift the wafer off a pedestal, or lift the wafer from a robot or indexer blade. For example, the lift pin(s) can be moved to the wafer transfer plane. The wafer transfer plane is the plane at a fixed height where wafer handoff occurs between a robot blade and the lift pins. As another example, the lift pins can be retracted (or raised) to position the wafer onto the pedestal. As another example, the lift pins can be raised (or retracted) to a position where the indexer can grab the wafer. Other examples are described above in the example wafer transfer sequence. In these and other examples, the load can be detected to determine whether additional load (e.g., from incomplete dechucking from the pedestal) is encountered. 
     At operation  320 , a parameter ((e.g., a current driving the motor (e.g., motor  115 ), a torque applied to the motor drive assembly, or a combination thereof) is measured and/or monitored. In some embodiments, one or more processors can be configured to measure the parameter, convert the parameter to a signal, transmit a signal, and/or receive a signal from a sensor that is measuring the parameter. In some examples, the sensor can include a processor to transmit the signal to the PLC. Operation  320  can include various sub-operations. These sub-operations can include the PLC triggering a drive current measurement (read) operation based on the scan zone of the lift pin position. The scan zone is, e.g., a lift pin position window in which current (and/or torque) is monitored. Measuring and/or monitoring the current and/or torque in operation  320  can further include plotting a graph of current versus lift pin position, torque versus lift pin position, or both. 
     Another sub-operation of operation  320  can include determining a derivative of current versus lift pin position (dI a /dx) for each lift pin position window. Here, dI a /dx can be plotted for each of the lift pin position windows. For example, dI a  per 10 μm of wafer movement (raising and lowering) is determined and can then be plotted. Additionally, or alternatively, another sub-operation of operation  320  can include determining a derivative of torque versus lift pin position (dT/dx) for each lift pin position window. Here, dT/dx can be plotted for each of the lift pin position windows. For example, dT per 10 μm of wafer movement (raising and lowering) is determined and can then be plotted. The plot(s) can be represented by the example shown in  FIG. 2B . For any wafer handoff where lift pins are involved, embodiments described herein enable monitoring and measuring of current/torque versus lift position to determine whether wafer handoff is abnormal. Examples of wafer handoff include, but are not limited to, handoff between the pedestal and lift pins, handoff between lift pins and an indexer, and handoff between lift pin and robot blade. 
     At operation  330 , the sample data (e.g., the data from operation  320 ) is compared with a pre-defined data range (e.g., range of current and/or range of torque) based on normal operation data. The normal operation data can be reference data collected for normal (or proper) wafer transfer, such as that shown in  FIG. 2A . The normal operation data can be a data set stored in the PLC. In some embodiments, and for determining whether the wafer-lifting operation is normal, the reference data is set to current and/or torque depending on, e.g., the nature of plot. Thus, the comparison performed in operation  330  indicates, e.g., wafer break and/or slide off. 
     If the sample data is determined to be within the pre-defined range (indicating normal operation) the wafer transfer sequence/lift-pin operation can continue. If the sample data is determined to be outside the pre-defined range (indicating, e.g., wafer breakage or abrupt wafer release), the PLC triggers shut-off of the motor (e.g., motor  115  and/or other components) at operation  340 . Here, a shut-off command (e.g., software to control all slave hardware together at the same time) can be sent from PLC  125  to the motor driver (e.g., motor driver  120 ) to shut off the motor  115 . Because the motor controls the lift pin position, shut-off of the motor stops movement of the lift pin. At operation  350 , the lift pin(s) can then be retracted by the PLC  125  commanding motor driver  120  to cause the motor  115  to retract the lift pin(s). Retraction of the lift pin(s) serves to, e.g., avoid breaking the wafer. For example, if the lift pin is not stopped or retracted, then the motor applies additional load on the wafer. The additional force can break the wafer in partially chucked conditions. 
     At operation  360 , the wafer transfer and/or lift-pin operation can be resumed. Here, one or more of operations  310 - 350  can be repeated, such as operations  310 - 330 . If data indicating that, e.g., wafer breakage or abrupt wafer release (as determined at operation  330 ), is observed again, the processing chamber can be opened for inspection. For example, the chamber can be opened to inspect whether the wafer, in fact, broke or slipped off. If data indicates no abnormality (or no abnormality outside of a certain deviation), the wafer transfer sequence/lift-pin operation continues. 
     Example Chamber 
       FIGS. 4A and 4B  show an illustrative, but non-limiting, example chamber  400  that can be used with embodiments described herein. As shown in  FIGS. 4A and 4B , a pedestal  405 , as well as other chamber component(s), is in different positions for wafer transfer. Other chambers (having different or additional components) are contemplated. For example, although bellow(s) are utilized in the example chamber described herein, it is contemplated that the chamber can be free of bellow(s). 
     The pedestal  405  is positioned above bellow(s)  401  (e.g., a vacuum separation bellow). The pedestal  405  has a plurality of openings  409  through which one or more lift pin(s)  403  can move up and down for wafer movement/transfer. Bolts/screws  411  couple a flange  407  to pedestal  405 . One or more surfaces of flange  407  contact one or more surfaces of bellow(s)  401 . The bellow(s)  401  expands and contracts via movement of, e.g., pedestal  405 . 
     The motor driver  120 , which is controlled by the PLC  125 , is utilized to detect the current. The PLC  125  includes the controller  126 . The controller  126  includes the central processing unit (CPU)  127 , the memory  128 , and support circuits  129  for the CPU  127 . Motor driver  120 , PLC  125 , controller  126 , CPU  127 , memory  128 , and support circuits  129  are discussed above. 
     During processing, and as shown in  FIG. 4A , the bellow(s)  401  are in an expanded state and the lift pin(s)  403  are retracted below a top surface of pedestal  405 .  FIG. 4B  shows the position for wafer transfer between lift pin(s)  403  and a robot blade (not shown). During wafer/shutter transfer, and as shown in  FIG. 4B , a portion of the lift pin(s)  403  are located above pedestal  405 . The bellow(s)  401  will be compressed as the motor (not shown), which is controlled by motor driver  120 , drives the lift pin(s)  403 —via all the components that raise the lift pin(s)—upward to pick up a wafer (not shown). The bellow(s)  401 , having a spring rate (k), are compressed linearly based on the position of the lift pin(s)  403 . Operation increases the load on the motor (e.g., motor  115 ) linearly as a function of k×y, where k is the spring rate and y is the compression of bellow(s)  401 . 
     In the case of electrostatic chucks, residual charge left in the wafer, the pedestal, e.g., pedestal  405 , and/or other chamber components (e.g., lift pin(s)  403 ) can cause residual chucking forces to exist. As discussed above, these residual chucking forces can lead to wafer damage/breakage. Typically, the residual charges dissipate after about 2-3 seconds, though charge dissipation varies based on conditions such as temperature and pressure. In typical operations, the lift pin(s) (e.g., lift pin(s)  403 ) are moved once the charge has dissipated. Detected spikes in torque (or current) of the motor, e.g., motor  115 , can be correlated to residual chucking forces that can cause wafer breakage, enabling detection by the motor driver  120  and/or the PLC  125 . Accordingly, embodiments described herein allow for early detection of wafer transfer issues and/or wafer abnormalities. 
     Any of the operations described above, such as one or more operations of method  300  may be included as instructions in a computer-readable medium for execution by a control unit (e.g., controller  126 ) or any other processing system. The computer-readable medium may comprise any suitable memory for storing instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, an electrically erasable programmable ROM (EEPROM), a compact disc ROM (CD-ROM), a floppy disk, and the like. 
     Embodiments described herein provide for methods and apparatus for detecting and/or monitoring, e.g., abnormalities in wafer transfer handling. Embodiments described herein enable early detection of wafer breakage and prevention (or mitigation) of wafer breakage or other abnormalities during, e.g., wafer transfer. As a result, higher wafer throughput and decreased fab downtime can be realized. Moreover, lower production costs are achieved by using an apparatus and method that is free of conventional sensors and a lower incidence of wafer breakage. 
     In the foregoing, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the foregoing aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.