Systems and methods to significantly reduce the grinding marks in surface grinding of semiconductor wafers

Abstract

The present invention provides systems and methods for varying the speed of a wafer chuck relative to a grinding wheel during the grinding process. The systems and methods involve relative rotation between a wafer and a grinding wheel at a first velocity and subsequently at a second velocity. The variance between the first and second velocities reduces striations on the face of the wafer being ground. In addition, the change in velocity increases the ploughing capability of the grinding element.

What is claimed is:  
     
         1 . A method for fabricating wafers for semiconductor manufacture, the method comprising: 
 providing a wafer, the wafer comprising a wafer face and a wafer back;    coupling the wafer back to a susceptor;    providing a grinding element, the grinding element comprising a grinding face;    providing a relative rotation between the wafer and the grinding face, said relative rotation being about a rotational axis at a first rotational velocity;    applying the grinding face to the wafer face, wherein a portion of the wafer face is removed by grinding action; and    providing said relative rotation about the rotational axis at a second rotational velocity, wherein the first velocity is different than the second velocity, and wherein the variance between the first and second velocities reduces striations on the face of the wafer.    
     
     
         2 . The method of  claim 1 , the method further comprising: 
 providing said relative rotation about the rotational axis at a third rotational velocity, wherein each of the first velocity, the second velocity and the third velocity are different, and wherein the variance between the first, second, and third velocities further reduces striations on the face of the wafer.    
     
     
         3 . The method of  claim 1 , wherein the first velocity is between about 40 and about 250 revolutions per minute, and the second velocity is between about 250 and about 450 revolutions per minute.  
     
     
         4 . The method of  claim 2 , wherein the third velocity is between about 450 and about 700 revolutions per minute.  
     
     
         5 . The method of  claim 1 , wherein the grinding element is a grinding wheel comprising a diamond abrasive material imbedded in the wheel.  
     
     
         6 . The method of  claim 5 , wherein the grinding wheel moves about a fixed axis.  
     
     
         7 . The method of  claim 5  wherein the grinding wheel revolves in an orbital manner.  
     
     
         8 . The method of  claim 2 , wherein the variance regenerates the grinding face to expose abrasive material embedded in the grinding wheel.  
     
     
         9 . The method of  claim 1 , wherein the grinding is performed first at the first velocity and second at the second velocity, wherein the second velocity is greater than the first velocity.  
     
     
         10 . The method of  claim 1 , wherein the grinding is performed first at the first velocity and second at the second velocity, wherein the second velocity is less than the first velocity.  
     
     
         11 . The method as in  claim 1 , wherein said relative rotation is provided by rotating said grinding element.  
     
     
         12 . The method as in  claim 1 , wherein said relative rotation is provided by rotating said grinding element in a first direction and rotating said wafer in a second direction opposite said first direction.  
     
     
         13 . The method as in  claim 1 , wherein said applying said grinding face to said wafer occurs simultaneously with providing said relative rotation at both said first and second velocities, and a transition from said first velocity to said second velocity.  
     
     
         14 . The method of  claim 1 , wherein the striations are ten microns or less.  
     
     
         15 . The method of  claim 1 , the method further comprising: 
 polishing the face of the wafer, wherein the polished face of the wafer is substantially free of striations.    
     
     
         16 . A system for fabricating semiconductor substrates, the system comprising: 
 a grinding wheel;    a wafer mounted on a chuck relative to the grinding wheel;    a microprocessor based controller for controlling a velocity of rotation of the grinding wheel relative to the chuck; and    a database associated with the microprocessor based controller, wherein the database comprises code executable by the microprocessor to cause the grinding wheel to rotate relative to the chuck at a first velocity and subsequently to rotate relative to the chuck at a second velocity, wherein the first velocity is different than the second velocity, and wherein the variance between the first and second velocities reduces striations on the face of the wafer.    
     
     
         17 . The system of  claim 16 , wherein the database further comprises code executable by the microprocessor to cause the wafer to move relative to the grinding wheel, wherein the grinding wheel contacts the wafer.  
     
     
         18 . The system of  claim 16 , wherein the database further comprises code executable by the microprocessor to cause the grinding wheel to rotate relative to the chuck at a third velocity, the second velocity being greater than the first velocity and the third velocity being greater than the second velocity, and wherein the variance between the first, second, and third velocities further reduces striations on the face of the wafer.  
     
     
         19 . The system of  claim 18 , wherein the first velocity is between about 40 and about 250 revolutions per minute, the second velocity is between about 25 and about 450 revolutions per minute, and the third velocity is between about 450 and about 700 revolutions per minute.  
     
     
         20 . The system of  claim 16 , wherein the grinding wheel comprises a diamond abrasive material imbedded in the wheel.  
     
     
         21 . The system of  claim 16 , wherein rotating the grinding wheel relative to the chuck is done at the first velocity and subsequently at the second velocity, the second velocity being greater than the first velocity, wherein the increase in velocity between the first velocity and the second velocity regenerates the face of the grinding wheel.  
     
     
         22 . A method for manufacturing substrates, the method comprising: 
 providing an unpolished substrate, the unpolished substrate comprising a back, a face, and an edge;    placing the unpolished substrate on a rotatable mount, wherein the back is fixed on the rotatable mount;    moving a grinding element relative to the unpolished substrate, wherein the movement is at a first velocity;    applying the grinding element to the face of the unpolished substrate as the grinding element moves relative to the unpolished substrate;    moving the grinding element relative to the unpolished substrate at a second velocity, wherein the second velocity is greater than the first velocity, and wherein the increase in velocity increases the ploughing capability of the grinding element and reduces a presence of striations on the face of the unpolished substrate.    
     
     
         23 . The method of  claim 22 , wherein moving the unpolished substrate relative to the grinding element at a second velocity comprises a gradual change in velocity from the first velocity to the second velocity.