Effect of crystallographic directions on porous silicon formation on patterned substrates

Growth kinetics of porous silicon, formed by electrochemical anodisation of (100) and (111) n+ and p+ substrates, was measured. We show that the growth rate along 〈100〉 is always higher than along 〈111〉. The 〈111〉/〈100〉 growth rate ratio induces the etching profiles and the final shapes of the porous silicon regions obtained on patterned Si substrates. The profile is sharper in the case of the n+ than that of the p+ (100) substrates. For n+ (111) Si substrates, the etching profile is different and depends on the alignment of the mask patterns according to the axis of symmetry of the silicon crystal.