Crystal orientation dependence of macropore formation in n-Si with backside-illumination in HF-electrolyte

The formation of macropores on anodically biased n-type silicon with backsi de-illumination was investigated as a function of crystal orientation and b ias voltage. Specimens were cut from bulk crystals with various orientation s from {100} to {111}, polished and subjected to anodic etching in HF. The resulting pores were investigated on cleaved samples by SEM. All pores were found to grow in either a < 100 > direction or a < 113 > direction, depend ing on the misorientation angle. This finding applies also to the branching of a single pore. The results can be understood if the valence for the dis solution reaction is approximately 2.6 in < 100 > and approximately 4 in th e < 113 > direction, and if all other directions are not allowed for the gr owth of pores in Si.