Edge trimming method and edge trimming apparatus

Abstract

An edge trimming method for removing a chamfered portion on an outer periphery of a grinding-object wafer in a bonded wafer is provided. The method includes a holding process to hold the bonded wafer on a chuck table, a finishing-grindstone mark forming process to form a finishing-grindstone mark in the grinding-object wafer with the finishing grindstone, a finishing-grindstone mark height measuring process to measure a height of a bottom of the finishing-grindstone mark with a height measurer, a finishing-grindstone height calculating process to calculate a height of the finishing grindstone based on the measured height of the bottom, a rough-grinding process to lower the rough grindstone and rotate the bonded wafer to roughly grind the grinding-object wafer with the rough grindstone, and a finish-grinding process to lower the finishing grindstone to the calculated height and rotate the bonded wafer to finely grind the grinding-object wafer with the finishing grindstone.

What is claimed is: 
     
         1 . An edge trimming method for removing a chamfered portion on an outer periphery of a grinding-object wafer in a bonded wafer, the bonded wafer including the grinding-object wafer with the chamfered portion and a base wafer bonded together, by grinding with a rough grindstone and thereafter grinding with a finishing grindstone, the method comprising:
 a holding process including operating a chuck table to hold the bonded wafer by the base wafer;   a finishing-grindstone mark forming process including lowering the finishing grindstone from a position above an outer peripheral portion of the grinding-object wafer in the bonded wafer to a predetermined height and forming a finishing-grindstone mark in the grinding-object wafer with the finishing grindstone;   a finishing-grindstone mark height measuring process including measuring a height of a bottom surface of the finishing-grindstone mark formed in the finishing-grindstone mark forming process with a height measurer;   a finishing-grindstone height calculating process including calculating a height of the finishing grindstone to be located when grinding the grinding-object wafer based on the height of the bottom surface of the finishing-grindstone mark measured in the finishing-grindstone mark height measuring process;   a rough-grinding process including lowering the rough grindstone from a position above the outer peripheral portion of the grinding-object wafer in the bonded wafer and rotating the bonded wafer to roughly grind the grinding-object wafer with the rough grindstone; and   a finish-grinding process including lowering the finishing grindstone from a position above a ground surface of the grinding-object wafer having been ground with the rough grindstone to the height calculated in the finishing-grindstone height calculating process and rotating the bonded wafer to finely grind the grinding-object wafer with the finishing grindstone.   
     
     
         2 . The edge trimming method according to  claim 1 , further comprising:
 a finish-ground surface height measuring process including measuring a height of the ground surface having been ground with the finishing grindstone in the finish-grinding process with the height measurer;   a calculating process including calculating a difference between the height of the ground surface and a height of an upper surface of the base wafer; and   a correcting process including correcting the height of the finishing grindstone calculated in the finishing-grindstone height calculating process by shifting the height in a lowering direction by the difference calculated in the calculating process.   
     
     
         3 . The edge griming method according to  claim 1 , further comprising:
 a rough-grindstone mark forming process including lowering the rough grindstone from a position above the outer peripheral portion of the grinding-object wafer in the bonded wafer to a predetermined height and forming a rough-grindstone mark in the grinding-object wafer with the rough grindstone;   a rough-grindstone mark height measuring process including measuring a height of a bottom surface of the rough-grindstone mark formed in the rough-grindstone mark forming process with the height measurer; and   a rough-grindstone height calculating process including calculating a height of the rough grindstone to be located when grinding the grinding-object wafer based on the height of the bottom surface of the rough-grindstone mark measured in the rough-grindstone mark height measuring process,   wherein, in the rough-grinding process, the rough grindstone is lowered to the height calculated in the rough-grindstone height calculating process.   
     
     
         4 . An edge trimming apparatus, comprising:
 a chuck table including a holding surface configured to hold a bonded wafer, the bonded wafer including a grinding-object wafer with a chamfered portion on an outer periphery thereof and a base wafer bonded together;   a rotating device configured to rotate the chuck table about an axis at a center of the holding surface;   a rough-grinding device configured to roughly grind an outer peripheral portion of the grinding-object wafer in the bonded wafer held by the chuck table in a ring shape with a rough grindstone;   a finish-grinding device configured to finely grind the outer peripheral portion of the grinding-object wafer with a finishing grindstone, of which grain diameter is smaller than a grain diameter of the rough grindstone;   a height measurer configured to measure a height of a surface of the grinding-object wafer having been ground with the finishing grindstone; and   a controller configured to:
 control the finishing grindstone to form a process mark on the outer peripheral portion of the grinding-object wafer; 
 measure a height of the process mark with the height measurer and calculate a height of the finishing grindstone to be located when grinding the grinding-object wafer; 
 control the rough grindstone to contact and roughly grind the outer peripheral portion of the grinding-object wafer, and 
 control the finishing grindstone to be located at the calculated height and to finely grind a ground surface of the grinding-object wafer having been ground roughly with the rough grindstone.