Effect of etching solution concentration on preparation of Si holes by metal-assisted chemical etching

The effect of the etching solution concentration on the etching profile of vertical microscale holes formed on a Si(100) substrate by metal-assisted chemical etching (MacEtch) was investigated. MacEtch was performed at different solution concentration ratios (characterized by their molar ratio rho=[HF]HF]+[H2O2 <i ), and the Au catalyst split above a certain concentration ratio. The Au-Si interface in the samples after MacEtch was observed using transmission electron microscopy, which revealed that there was a porous SiO (x) interlayer between the Au and Si, and that the SiO (x) layer became thinner as the concentration ratio increased. The interlayer almost disappeared under solution conditions when the catalyst was split. We propose two hypotheses for the mechanism of catalytic fracture during MacEtch: chemical fracture due to Si atoms diffusing into the grain boundaries of polycrystalline Au by Au-Si interdiffusion, and mechanical fracture due to stress on the catalyst caused by heterogeneous etching.