THE INFLUENCE OF BACKGRINDING ON THE FRACTURE STRENGTH OF 100 MM DIAMETER (111)P-TYPE SILICON-WAFERS

The influence of grinding geometry and damage depth on the fracture st rength of 100 mm diameter(111) p-type silicon wafers has been studied. The fracture strengths were measured in a biaxial flexure test after the wafers were ground to 0.36 mm from 0.53 mm thick, in a grinding ap paratus that produces a swath of swirls on the silicon wafer surfaces. Analysis of orientations of the swirl geometries and fracture probabi lity was used to deduce the fracture strength relative to the crystall ographic orientation of the wafers. Optical and scanning electron micr oscopy of bevelled, and cleaved and etched samples was used to measure the damage depths from selected locations on the wafers. The depth of damage and fracture strengths were correlated to the geometry of the backgrind swirl pattern and the relative position of the orientation f lat. The damage depth was smaller when the swirl path was parallel or at 45 degrees to the orientation flat as compared to the swirl paths a t 90 degrees and 135 degrees orientations. As a result, the wafers gro und in the former orientations had a higher fracture strength than tho se of the latter orientations (136 and 124 MPa versus 100 and 103 MPa, for the four orientations, respectively).