Silicon anisotropic etching of TMAH solution

Detailed characteristics of tetramathyl ammonium hydroxide (TMAH, (CH₃)₄ NOH) as a silicon anisotropic etching solution with various concentrations from 5 to 40 wt% and temperatures between 60 to 90°C have been studied. The etching of (100) crystal decreases with increasing concentration and decreasing temperature. The etched (100) planes are covered by a pyramidal hillock below 15 wt% and very smooth surfaces are obtained above 22 wt % solution. The etch rate of silicon dioxide is almost four orders of magnitude lower than that for (100) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Finally this paper presents different characteristics of etching in three etchants; EPD, KOH and TMAH solution and a way to control the geometrical structure of the accelerometer proof mass by a method of convex corner compensation which can be categorized to square corner compensation, 45 degree rectangle corner compensation and triangle corner compensation methods