Processing Grinding-Damaged Silicon Wafers by High-Frequency Nano-Second Laser Irradiation

Ultraprecision diamond-ground silicon wafers were irradiated by a high-frequency nanosecond pulsed Nd:YAG laser equipped on a four-axis numerically controlled stage. The resulting specimens were characterized using a white-light interferometer, a micro-Raman spectroscope and a transmission electron microscope. The results indicate that around the laser beam center where the laser energy density is sufficiently high, the grinding-induced amorphous silicon was completely transformed into the single-crystal structure. The optimum conditions for one- and two-dimensional overlapping irradiation were experimentally obtained for processing large-diameter silicon wafers. It was found that the energy density level required for completely removing the dislocations is higher than that for recrystallizing the amorphous silicon. After laser irradiation, the surface unevenness has been remarkably flattened.