Method for etching a trench having rounded top corners in a silicon substrate

Abstract

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.