Dimensional constraints on high aspect ratio silicon microstructures fabricated by HF photoelectrochemical etching

The fabrication of macropores in crystalline silicon by photoelectrochemical etching in a hydrofluoric acid electrolyte is investigated. It is shown that the dimensional constraints on the pore diameters, which, in previous literature, are considered to depend on substrate doping, can be significantly relaxed. We show that it is possible to fabricate arrays of square section macropores with sides ranging from 2 to 15 mum using the same n-doped (2.4- 4 Omega cm) silicon substrate. Moreover, we demonstrate that macropore arrays with pitch variation up to 100% (8 and 16 mum) can be simultaneously grown on the same silicon sample. The same process is used to fabricate arrays of silicon walls with different spacing and pitch as well. A simple model, based on the coalescence in a single pore of multiple stable pores, is proposed to explain the experimental data. (C) 2002 The Electrochemical Society.