Characterizing damage on Si wafer surfaces cut by slurry and diamond wire sawing

We have measured and compared surface roughness and the degree of damage for wafers cut by three different sawing techniques - slurry, Ni-based diamond wire, and resin-based diamond wire sawing. The local damage was determined by angle polishing followed by defect etching, TEM, SEM/EBSD imaging and Raman imaging. It showed that each of the cutting processes produces a thin layer of amorphous Si at the surface and dislocation loops that can go about 1 μm deep below the surface. A new approach was used to quantify the average damage over a large area. We determined the effective surface recombination (SRV) as a function of depth. Because the effective SRV is a function of the carrier loss close to the surface, it is well-suited to define damage distribution at and below the surface. Wafers with surface damage were step etched in (HF:HNO 3 :CH 3 COOH::1:1:5), and the effective lifetime was measured with a Sinton system after each etching step, with iodine-ethanol passivation. The SRV plots as a function of depth, representing depth distribution of the damage, were compared for large groups of wafers cut by each technique. Our results show that for optimized cutting, all three cutting methods produce damage depth of about 5μm (each surface). However, the degree of damage is higher for slurry cut wafers.