The influence of alcohol concentration on etch rate and surface morphology of (100) and (110) Si planes was investigated in this paper. The etching processes were carried out in KOH solutions with different concentrations of isopropanol and butanols. The etch rate minima versus alcohol concentration were observed for all the alcohols used in the experiments. Furthermore, close to the concentrations of etch rate minima, the smooth (110) planes were obtained. However, the (100) surfaces were covered with hillocks at these concentrations. Based on the surface tension measurements and literature reports, the explanation of appearance of the etch rate minimum was suggested. In the proposed model, the adsorption maximum corresponds to the complete formation of an alcohol monolayer on Si surface and, consequently, to the etch rate minimum. At higher concentrations of alcohol, the monolayer disappears and the etch rate increases.
Anisotropic etching of Si (100) and (110) planes in alkaline solutions containing the nonionic surfactant is studied in this paper. Triton X-100 surfactant, normally used for the modification of TMAH (tetramethylammonium hydroxide) etchant, is added to KOH (potassium hydroxide) solution. As a result, the (100) and (110) etch rates are significantly reduced and the etch rate ratio R(100)/R(110) >1 is obtained. The influence of KOH concentration (at 10 and 100 ppm (v/v) of the surfactant) on the etching process is also investigated. Low roughness of (110) surface is achieved in the 2 M KOH solution containing Triton. The smooth {110} sidewall planes inclined at 45°toward the (100) substrate are fabricated by etching in the KOH + Triton solution. The 45°{110} sidewalls are potentially attractive as MEMS micromirrors for optical beam reflection at an angle of 90°. The low etch rate of (100) plane is kind of a disadvantage of the fabrication method, but it can be fairly overcome by elevating the process temperature and stirring the etching solution.[
2012-0371]Index Terms-Anisotropic etching, potassium hydroxide (KOH), silicon, surfactant, Triton X-100.
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