Effect of noble metal catalyst species on the morphology of macroporous silicon formed by metal-assisted chemical etching

Macroporous silicon with ordered pore intervals was fabricated by the site-selective chemical etching of a Si substrate using patterned noble-metal thin films as a catalyst. The morphology of the etched silicon surface and the etching rate was affected by the shape of deposits and metal catalyst species such as Pt-Pd, Au, and Pt. The etching rate increased in the following order: Au < Pt ≤ Pt-Pd. The pores of macroporous silicon prepared by using Pt-Pd catalyst were conical in shape because of the chemical dissolution of the surface of the macropores. On the other hand, by using Au catalyst, relatively straight pores with uniform diameter were formed in the direction of pore depth. The morphology of macroporous silicon was assumed to be affected by the difference in the shape of metal catalysts and the diffusion behaviour of injected positive holes at the silicon/metal interface.