Potassium Hydroxide, or KOH, etches the silicon crystals anisotropically. In an anisotropic etch, the etch rate is different for all Si crystal planes. The etch rate for the Si(100) plane is about 1.4 um/min depending on the temperature and the KOH solution concentration, while on the Si(111) the etch rate is about 0.25 - 0.5 um/min. The etch rate with various temperatures can be found in the standard operating procedure found below. It is important to notice that taking advantage ofthe difference in etch rate among the Si faces one could choose between the different plane profiles.
Very good reference KOH Etch
Standard Operating Procedure
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Returning to the Cleanroom
Wafers which have been polished using CMP, developed in metal-ion bearing developer (e.g. AZ 400K) or etched in KOH; they must be given an additional piranha clean and SC2 in Acid Bench 92, and an RCA clean in RCA Bench 81 before returning to the cleanroom.