Abstract
Investigation was focused on the formation of {311} planes by wet anisotropic etching of (100) silicon and, in particular, on the characterization by means of surface roughness, etch rates and related convex and concave corner dynamic behaviour during maskless etching. KOH and TMAH water solutions were tested for their influence on previously mentioned parameters as well as the effect of isopropyl alcohol (IPA). It was found that convex corner undercutting is significantly reduced if {311} bounding planes are utilized instead of {111} bounding planes. For shallow structures a self-compensation can be obtained with KOH and when certain conditions are met, also with TMAH. The rounding of the concave corner that arises through prolonged etching is reported, which is particularly emphasized in KOH and less in TMAH etchant. Addition of IPA in maskless mode is experimentally investigated, showing minor influence on etching conditions and on reducing the undercut of convex corners. Etch rates and dimensional control of some microstructures are discussed and presented comparatively for different etching systems in a temperature range of 50-100 °C. By evaluation of surface quality with a surface profiler and SEM, it was found that the smoothest surface was achieved by etching in TMAH. The role of solution temperature in surface roughness was found to be of minor importance, as well as the stirring of the solution. It was determined that the IPA additive increases roughness when used with KOH, while with TMAH, the influence on roughness of the {311} planes is insignificant.
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