Edge gripping prealigner

Abstract

A method for holding and orienting a wafer having an alignment feature, the method includes gripping a wafer with an end effector attached to an end of a robot arm, the end effector including a gripping mechanism which includes a first contacting member, a second contacting member, and a drive element, and wherein gripping includes increasing and decreasing the space between the first and second contacting members, the method also including rotating the wafer about an axis that is perpendicular to the plane of the wafer and sensing the alignment feature on the wafer as the gripping mechanism rotates the wafer.

1 . A method for holding and orienting a wafer having an alignment feature, said method comprising: 
 gripping a wafer with an end effector attached to an end of a robot arm, said end effector including a gripping mechanism which comprises a first contacting member, a second contacting member, and a drive element, and wherein gripping comprises increasing and decreasing the space between the first and second contacting members;    rotating the wafer about an axis that is perpendicular to the plane of the wafer; and    sensing the alignment feature on the wafer as the gripping mechanism rotates the wafer.    
     
     
         2 . The method of  claim 1 , further comprises: 
 controlling the gripping mechanism with a controller, wherein controlling comprises: 
 sending a control signal to the gripping mechanism to increase and decrease the space between the first and second contacting members.  
   
     
     
         3 . The method of  claim 1 , wherein the first and second contacting members are arranged to grip opposing edges of the wafer.  
     
     
         4 . The method of  claim 1  wherein the first contacting member comprises a first roller element.  
     
     
         5 . The method of  claim 4  wherein the second contacting member comprises second and third roller elements separated in space from each other.  
     
     
         6 . The method of  claim 5  wherein the gripping mechanism comprises a mechanical actuator coupled to the first roller element, wherein gripping further comprises: 
 moving the first roller element using the mechanical actuator towards and away from the second and third roller elements.  
 
     
     
         7 . The method of  claim 4  wherein the first roller element has a cylindrically-shaped outer surface with a circumferential groove formed therein.  
     
     
         8 . The method of  claim 5  wherein the first, second and third roller elements are arrayed in a common plane and have parallel axes of rotation.  
     
     
         9 . The method of  claim 4  wherein the gripping mechanism further comprises a drive motor, wherein rotating the wafer further comprises: 
 rotating the first roller element using the drive motor.  
 
     
     
         10 . The method of  claim 2  wherein sensing further comprises: 
 sensing using a light emitter and a light detector.  
 
     
     
         11 . The method of  claim 10  wherein the light emitter and the light detector are positioned to lie on opposite sides of the wafer when the wafer is being gripped by the gripping mechanism.  
     
     
         12 . The method of  claim 11  wherein the sensing further comprises: 
 detecting a feature on the perimeter of the wafer using the light emitter and light detector as the wafer is rotated.  
 
     
     
         13 . A method for holding and orienting a wafer having an alignment feature, said method comprising: 
 gripping the wafer using an end effector attached to the working end of a robot arm, said end effector including a gripping mechanism which comprises three contacting members separated in space from each other, and wherein gripping comprises contacting the edges of the wafer using the three contacting members;    rotating the wafer using the gripping mechanism relative to the end effector and about an axis that is perpendicular to the plane of the wafer;    sensing using a sensing element the alignment feature on the wafer as the gripping mechanism rotates the wafer past the sensing element; and    moving the wafer laterally relative to the axis using the robot arm.    
     
     
         14 . The method of  claim 13  wherein one of the contacting members is a drive member coupled to a drive motor and wherein rotating further comprises: 
 rotating the drive member using the drive motor.  
 
     
     
         15 . The method of  claim 14  wherein the gripping mechanism further comprises a mechanical actuator coupled to the drive member, wherein gripping further comprises: 
 moving the drive member using the mechanical actuator towards and away from the other two contacting members.