Ultra-deep anisotropic etching of (110) silicon

The anisotropic etching behavior of (110) silicon wafers in KOH and TMAH wa s studied with emphasis on ultra-deep microchannels. Effects which degrade the etching behavior when etching to a depth of the order of a millimeter w ere encountered and investigated. In particular, oxygen precipitates and th eir growth during high temperature processing apparently strongly affect th e etching of the (111) and (110) planes and reduce the achievable anisotrop y ratio. A new 1300 degrees C high temperature step significantly reduces t hese negative effects by dissolving oxygen precipitates back into the cryst al. Additionally, the influence of pattern alignment, solution concentratio n and the solution dissolved silicon content as well as the influence of va rying masking layers on the achievable anisotropy ratio were investigated a nd optimized.