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.