Abstract
A new solution system consisting of 
, 
, and 
was found useful for etching 
wafers. This solution system can be divided into four regions a–d, according to etching characteristics. The boundaries between the regions are given by a mole ratio 
of 
to 
of about 2.3 and a mole fraction 
of 
of about 0.9 at room temperature. Rate‐limiting processes are: a, adsorption of 
(
, 
); b, diffusion of 
(
, 
); c, dissolution of oxidized products (
, 
); and d, adsorption of 
(
,
). Solutions in region a have a reproducible etching rate of 0.01–0.1 μm/min, which is useful for MESFET processing. Crystallographic etching is also available with solutions in region c.