Ultra-deep anisotropic etching of (110)silicon

The anisotropic etching behavior of (110) silicon wafers in KOH and TMAH was studied with emphasis on ultra-deep microchannels. Effects which degrade the etching behavior when etching to a depth of the order of a millimeter were encountered and investigated. In particular, oxygen precipitates and their growth during high temperature processing apparently strongly affect the etching of the (111) and (110) planes and reduce the achievable anisotropy ratio. A new 1300 °C high temperature step significantly reduces these negative effects by dissolving oxygen precipitates back into the crystal. Additionally, the influence of pattern alignment, solution concentration and the solution dissolved silicon content as well as the influence of varying masking layers on the achievable anisotropy ratio were investigated and optimized.