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Anisotropic etching of monocrystalline silicon plays an important role in Microsystems technology in the recent years. TMAH, as one of the anisotropic etchants, is used to fabricate pores with square cross-section. Careful choice of concentration, isopropyl alcohol additives and temperature of alkaline solution allows for certain crystallographic directions to be preferentially etched. In this way, pores with square, eight-sided (octagonal) or rotated square shapes can be attained and convert to each other. We show the etch selectivity on (100) and (110) planes in TMAH solution with low concentration. The etch rates on (100) and (110) planes at different temperature and concentration has been measured. The results indicated that the perfect orthogonal array of pores with sharp edges and corners can be obtained at more than 40℃ in 1wt% TMAH solution. There is good etch selectivity on (110) surface and the etch rate on (110) surface is slower than (100) surface under the condition.

The application fields of high aspect ratio Si microchannel arrays have increased considerably, for example, Si microchannel plates, MEMS devices and so on. By the method of photo-electrochemical etching (PEC), Si microchannel arrays are prepared using n-Si wafer covered by anti-corrosion layers and initiation array pits. The dark current intensity curve of an n-type silicon wafer was presented in aqueous HF. The relationship among temperature, etching voltage and carrier transportation was presented. The influences of temperature and etching voltage on the surface morphology of silicon microchannel arrays were researched. The perfect Si microchannel arrays structure with the pore depth of 297 μm, the pore size of 3 μm and the aspect ratio of 99 was obtained by the method of reducing etching voltage gradually.

The influence of several surfactants in electrolyte during silicon electrochemical etching was reported in this paper. The morphologies of macroporous silicon arrays in n-type silicon are strongly influenced by the chemical nature of these additives. Conventional solvents (HF-Ethanol) with cationic (hexadecyl trimethyl ammonium chloride), non-ionic (Triton-X100) and anionic (sodium alpha-olefin sulfonate) surfactants were experimented respectively. Prominent differences in microchannel morphologies and apertures were observed depending on the nature of the additive. The different behaviors of the additives during the electrochemical etching process were linked to the physical properties of the additives. We found the electric double layer model of the reaction interface partially to explain these results. However, not only the morphology of the microchannel but also the degree of electrochemical reaction is affected by surfactant. The anionic surfactant is more suitable for the preparation of silicon microchannel plate with high aspect ratio and pore size uniform. The depth of microchannels etched by photoelectrochemical etching silicon with anionic surfactant is 264 μm, and the pore size is 2 μm.