Patent ID: 7811464

Claim:
A preferential etching method wherein a preferential etchant, which contains at least a hydrofluoric acid having a concentration of 49 to 50 weight %, a nitric acid having a concentration of 60 to 62 weight %, an acetic acid having a concentration of 99 to 100 weight %, and water, where a volume ratio of hydrofluoric acid, nitric acid and acetic acid in the etchant composition falls within the range of 0.02-0.1:0.5-0.6:0.2-0.25, is used to etch a silicon single crystal substrate whose electrical resistivity is less than 10 mΩ·cm at a rate higher than 0.1 μm/min, thereby eliciting bulk micro defects on a surface of the silicon single crystal substrate.