Crystal Growth and Evaluation of Silicon for VLSI and ULSI

167From Silicon Ingots to Silicon Wafers

5.6 Edge Profiling of Slices

After mechanical lapping, the wafers are separated and are taken for edge contouring,

where the edge of the silicon wafer is changed from a sharp to a round shape. This is usu-

ally done in cassette-fed, high-speed equipment, and each wafer is handled separately, as

shown in Figure 5.11. The advantages are that the sharp-edged silicon wafer does not dam-

age the polishing pads and aids in controlling the buildup of photoresist at the wafer edge

while applying the photoresist coating for the photolithography step. Figure 5.12 shows

one type of commercial equipment used for th ...