> I am doing anisotropic etching of (110) Si Wafers. > I use KOH solution with IPA. > The problem is that at the bottom of (110) surface form line like hills. > the short axis of this lines points to [100] direction. > the concentration and dimentions of this fetures become smaller by adding > IPA but don't disapear. > I think it has something to do with, may be local, etch rate changes of > {110}/{100} planes but I dont know how to suppress it. > Any suggestion will be welcome. Fairly recently a japanese group published a paper called "Groove depth uniformization in (110) Si anisotropic etching by ultrasonic wave...". I think it was a Hilton Head Conference. Authors are K. Ohwada, Y. Negoro,. They used an ultrasonic cleaner capabel of of "Dynashock" waves. We could not find such a device in the US. We bougt a pulsed wave cleaner. It does not to work as nicely as theirs. Using 55 wt.% KOH gave me almost as good smoothness as on a (100) wafer. Thry that, but your oxide mask has to be thicker. For these high concentrations (>35 wt.% or so), planes start to form were the (110) bottom intersects with the (111) vertical side walls. D. Kendall et al "Orientations of the third kind: The coming age of (110) Silocon" claims these are (113) type planes. We could only find it is close to that plane and that it etches slower that the bottom (110) plane. (That reduces your aspect ratio if you try to etch narrow slots). In yet another article "Vertical etching of silicon at very high aspect ratios" he mentions certain additives that make the bottom essentially flat, as a reference. Good luck Alexander Hoelke University of Cincinnati MEMS group