Patent Publication Number: US-10784133-B2

Title: Wafer clamp and a method of clamping a wafer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 15/454,978, filed on Mar. 9, 2017, the entire contents of which are hereby expressly incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a wafer clamp, and more particularly to a wafer clamp adaptable to a robot system for picking and placing a wafer. 
     2. Description of Related Art 
     A robotic hand (or fork) of a robot system is commonly utilized for picking and placing a wafer (or chip) automatically. A vacuum fork is conventionally used to hold a wafer. Owing to misalignment usually occurred in the conventional vacuum fork, the wafer cannot be precisely positioned and picked, therefore falling and breaking. 
     Moreover, the conventional vacuum fork is designed to make physical contact with the top or bottom surface of a wafer to be picked. This type of equipment is not adaptable to a wafer such as an optical component (e.g., an optical lens or glass). 
     An engaged type fork is provided to overcome disadvantages of the vacuum fork. However, conventional engaged type forks are incapable of fast moving or rotating without being flipped over the wafer. 
     For the reasons that conventional robotic forks could not effectively position and pick the wafer, a need has thus arisen to propose a novel wafer clamp to overcome the disadvantages of the conventional robotic forks. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the embodiment of the present invention to provide a wafer clamp adaptable to a robot system and a method of clamping a wafer. The provided wafer clamp is capable of precisely positioning a wafer, and is capable of fast moving and rotating without flipping over the wafer. 
     According to one embodiment, a wafer clamp includes a platform, a stopper, a push rod, at least one actuator, and a sensor. The platform has a top surface. The stopper is disposed at a front end of the platform, and the push rod is disposed at a rear end of the platform. The actuator is pivotally connected to the push rod. The sensor is disposed at the front end of the platform to measure a distance between the sensor and a wafer over the sensor. 
     According another embodiment, a method of clamping a wafer is disclosed. A wafer clamp is moved forward into a slot with the wafer. A sensor detects presence of the wafer over the sensor. The wafer clamp is continuously moved forward until the sensor detects absence of the wafer. The wafer clamp is moved upward and at least one actuator is actuated to move a push rod forward such that the wafer is held tightly between a stopper and the push rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a perspective view of a wafer clamp adaptable to a robot system according to one embodiment of the present invention; 
         FIG. 1B  shows a perspective view of an exemplary pneumatic cylinder according to one embodiment of the present invention; 
         FIG. 1C  shows a perspective view of an exemplary fiber optic sensor according to one embodiment of the present invention; 
         FIG. 2  schematically shows a top view of the wafer clamp of  FIG. 1A ; 
         FIG. 3A  to  FIG. 3D  schematically demonstrate a process flow performed by the wafer clamp of  FIG. 1A  to pick a wafer; and 
         FIG. 4  shows a perspective view of  FIG. 3D . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1A  shows a perspective view of a wafer clamp  100  adaptable to a robot system according to one embodiment of the present invention.  FIG. 2  schematically shows a top view of the wafer clamp  100  of  FIG. 1A . The wafer clamp  100  of the embodiment is capable of temporarily holding a wafer  10  in a fixed position to prevent movement or separation. The wafer clamp  100  is particularly, but not limitedly, adaptable to hold a wafer without making physical contact with the top or bottom surface of the wafer. The term robotic fork is used instead when the wafer clamp  100  is used as a robotic hand for picking and placing a wafer  10 , such as an optical lens or glass, in conjunction with other components of a robot system. 
     In the embodiment, the wafer clamp  100  may include a platform  11  with a substantially flat top surface. The platform  11  is configured to support the wafer  10  by being beneath the wafer and holding it up. 
     The wafer clamp  100  of the embodiment may include a stopper  12  disposed at a front end of the platform  11 . In the embodiment, the stopper  12  is fixed to the platform  11 , and a top surface of the stopper  12  is at a level higher than the top surface of the platform  11 . Accordingly, when the wafer  10  rests on the platform  11 , the top surface of the stopper  12  is preferably at a level equal to or higher than a top surface of the wafer  10 . It is appreciated that, in one embodiment, the stopper  12  may be integrally manufactured with the platform  11 . In another embodiment, the stopper  12  and the platform  11  may be individually manufactured, then being fixed together, for example, by adhesive. 
     The wafer clamp  100  of the embodiment may include a push rod  13  disposed at a rear end of the platform  11 . In the embodiment, the push rod  13  is movable with respect to the rear end of the platform  11 , and a top surface of the push rod  13  is at a level higher than the top surface of the platform  11 . Accordingly, when the wafer  10  rests on the platform  11 , the top surface of the push rod  13  is preferably at a level equal to or higher than a top surface of the wafer  10 . 
     The wafer clamp  100  of the embodiment may also include at least one actuator  14  that is pivotally connected to the push rod  13 . Specifically, the actuator  14  is configured to move the push rod  13  forward (i.e., toward the front end of the platform  11 ), such that the wafer  10  may be held tightly between the stopper  12  and the push rod  13 . In the embodiment shown in  FIG. 1A , two actuators  14  being parallel with each other are pivotally connected to the push rod  13 . In another embodiment, one actuator  14  and at least one auxiliary rod (not shown) being parallel with each other are pivotally connected to the push rod  13 . 
     In the embodiment, the actuator  14  preferably includes a pneumatic cylinder (also known as an air cylinder), which is a mechanical device that uses the power of compressed gas to produce a force in a reciprocating linear motion. The pneumatic cylinder is preferred because of being quieter, cleaner and requiring less amounts of space.  FIG. 1B  shows a perspective view of an exemplary pneumatic cylinder  14  according to one embodiment of the present invention. A pneumatic cylinder with a model name CJ1 manufactured by Steven Engineering, Inc., California may, but not necessarily, be adopted in the embodiment. Although the pneumatic cylinder is adopted in the embodiment, it is appreciated that other mechanical devices may be used instead. 
     In the embodiment, the pneumatic cylinder  14  may have a spring return feature, indicating that a front end of the pneumatic cylinder  14  will pull back to an original position by an interior spring (not shown) when the pneumatic cylinder  14  is not actuated. Accordingly, the push rod  13  will be pulled backward (i.e., away from the front end of the platform  11 ), thereby releasing the wafer  10 . In another embodiment, the pneumatic cylinder  14  has no spring return feature, and the push rod  13  may be pulled backward by an exterior spring (not shown) that exerts a force on the push rod  13  in a direction away from the front end of the platform  11 . The pneumatic cylinder  14  may be supported by a plate  15 . In one embodiment, the plate  15  with the pneumatic cylinder  14  is manufactured and provided as a module, which may be fixed to other part of the wafer clamp  100 , for example, by screwing via mounting holes  17 . 
     The wafer clamp  100  of the embodiment may further include a sensor  16  disposed at the stopper  12  or the front end of the platform  11 . The sensor  16  is positioned to face upward and is configured to measure a distance between the sensor  16  and an object (the wafer  10  in this case) over the sensor  16 . A control signal transmitted to the sensor  16  and a sense signal received from the sensor  16  may be transferred between the sensor  16  and a controller (not shown), which may also control the actuator  14 . 
     In the embodiment, the sensor  16  preferably includes a fiber optic sensor (e.g., reflective fiber optic sensor), which is a sensor that measures the distance by modifying a fiber so that the quantity to be measured modulates the intensity, phase, polarization, wavelength or transit time of light in the fiber. The fiber optic sensor is preferred because of its small size, immune to electromagnetic interference, resistance to high voltage electricity and temperature.  FIG. 1C  shows a perspective view of an exemplary fiber optic sensor according to one embodiment of the present invention. A fiber optic sensor with a model name FU manufactured by Keyence Corporation, Taiwan may, but not necessarily, be adopted in the embodiment. In one embodiment, the fiber optic sensor is manufactured and provided as a module, which may be fixed to other part of the wafer clamp  100 , for example, by screwing via mounting holes  18 . Although the fiber optic sensor is adopted in the embodiment, it is appreciated that other sensors may be used instead. 
       FIG. 3A  to  FIG. 3D  schematically demonstrate a process flow performed by the wafer clamp  100  of  FIG. 1A  to pick a wafer  10 , for example, from a cassette  31 . At first, in  FIG. 3A , the wafer clamp  100 , acting as a robotic hand of a robot system, moves into a slot of the cassette  31 . At this stage, the actuator  14  is not actuated, and the push rod  13  is thus in a backward position (i.e., original position). The sensor  16  detects the presence of the wafer according to a measured first distance d 1  between the sensor  16  and the wafer  10  over the sensor  16 . In one embodiment, the presence of the wafer  10  is detected while the sensor  16  receives a light signal reflecting back from the wafer  10 . 
     The wafer clamp  100  continues moving forward until the sensor  16  detects the absence of the wafer  10  according to a measured second distance d 2  that is greater than the first distance d 1  as shown in  FIG. 3B . In one embodiment, the absence of the wafer  10  is detected while the sensor  16  receives no light signal reflecting back from the wafer  10 . 
     As shown in  FIG. 3C , upon detecting the absence of the wafer  10 , the wafer clamp  100  moves upward and the actuator  14  is actuated to move the push rod  13  forward (i.e., toward the front end of the platform  11 ), such that the wafer  10  may be held tightly between the stopper  12  and the push rod  13 . Finally, as shown in  FIG. 3D , the wafer clamp  100  lifts the wafer  10  away from the cassette  31 . A perspective view of  FIG. 3D  is shown in  FIG. 4 . 
     According to the embodiments disclosed above, compared with a vacuum fork, the present invention provides a wafer clamp  100  that is capable of precisely positioning a wafer  10  by using a sensor  16 , particularly a fiber optic sensor. The present invention also provides a wafer clamp  100  that is capable of fast moving and rotating without flipping over the wafer  10  by using an actuator  14 , particularly a pneumatic cylinder. 
     Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.