The present disclosure includes a method of
plasma etching a trench having rounded top corners in a
silicon substrate. One embodiment includes the following general steps: a) providing a
semiconductor structure comprising a hard masking layer, overlying a
silicon substrate; b)
plasma etching through said hard masking layer and any additional underlying
layers overlying said
silicon substrate using at least one
plasma feed gas which does not provide
polymer deposition on surfaces of said
semiconductor structure during
etching; where said
plasma etching exposes a face of said silicon substrate; and c)
plasma etching at least a first portion of a trench into said silicon substrate using reactive species generated from a feed gas comprising a source of
fluorine, a source of carbon, a source of
hydrogen, and a source of
high energy species which provide physical bombardment of said silicon substrate. Top corner
rounding is effected by deposition of a
thin layer of
polymer on a top corner of the trench during etching of the first portion of the trench, resulting in the formation of a rounded "shoulder" at the top corner of the trench. Typically a layer of
silicon oxide overlies at least a portion of the silicon
substrate surface. The method described provides excellent
critical dimension control over the active area of a
transistor produced using the method and reduces the need to remove
polymer from substrate and reactor surfaces after etching of the silicon trench.