Workpiece grinding method

Abstract

A workpiece grinding method includes a first grinding step of grinding a part of a back surface corresponding to a device region of a workpiece using a first grinding wheel to form a first circular recess and an annular projecting part in the back surface, and a second grinding step of grinding at least a bottom surface of the first circular recess using a second grinding wheel including a grindstone having a particle diameter smaller than that of the first grinding wheel. In the first grinding step, the bottom surface of the first circular recess is ground into a concentrical shape differing in thickness in a radial direction from a center to a circumference of the first circular recess. In the second grinding step, the bottom surface of the first circular recess is ground to have a uniform thickness, thereby forming a second circular recess.

What is claimed is: 
     
         1 . A workpiece grinding method for grinding a back surface of a workpiece formed on a front surface thereof with a device region and a peripheral surplus region surrounding the device region, to form a circular recess and an annular projecting part surrounding the circular recess, the workpiece grinding method comprising:
 a holding step of holding the workpiece on a holding surface of a chuck table;   a first grinding step of grinding a part of the back surface corresponding to the device region of the workpiece held by the chuck table, by use of a first grinding wheel to form a first circular recess and an annular projecting part in the back surface of the workpiece; and   a second grinding step of grinding at least a bottom surface of the first circular recess by use of a second grinding wheel including grindstones having a particle diameter smaller than that of the first grinding wheel, after the first grinding step,   wherein, in the first grinding step, the bottom surface of the first circular recess is ground into a shape of being concentrical and differing in thickness in a radial direction from a center to a circumference of the first circular recess, and,   in the second grinding step, the bottom surface of the first circular recess is ground to have a uniform thickness.   
     
     
         2 . The workpiece grinding method according to  claim 1 , wherein, in the first grinding step, the bottom surface of the first circular recess is ground into a shape of being concentrical and differing in thickness in a state in which a grinding surface of the first grinding wheel and the holding surface are positioned in a non-parallel state. 
     
     
         3 . The workpiece grinding method according to  claim 1 ,
 wherein the first grinding step includes
 a wall surface forming step of bringing the grinding surface of the first grinding wheel and the holding surface closer to each other in a state in which the grinding surface of the first grinding wheel and the holding surface are positioned in a parallel state, to form a wall surface of the annular projecting part, and 
 a bottom surface forming step of bringing the grinding surface of the first grinding wheel and the holding surface closer to each other and bringing a rotational axis of the first grinding wheel and a rotational axis of the chuck table closer to each other, to grind the bottom surface of the first circular recess into a shape of being concentrical and differing in thickness in the radial direction, after the wall surface forming step. 
   
     
     
         4 . The workpiece grinding method according to  claim 1 , wherein, in the second grinding step, the bottom surface of the first circular recess is ground by a grinding amount of not less than such a grinding amount that a grinding damage generated in the first grinding step is removable, after the bottom surface of the first circular recess is ground into the shape of being concentrical and differing in thickness in the radial direction in the first grinding step. 
     
     
         5 . The workpiece grinding method according to  claim 4 , wherein, in the first grinding step, the bottom surface of the first circular recess is formed into a shape of differing in thickness by an amount corresponding to such a grinding amount that the grinding damage generated in the first grinding step is removable by grinding in the second grinding step.