SELECTIVE ETCHES FOR REDUCING CONE FORMATION IN SHALLOW TRENCH ISOLATIONS

摘要

To fabricate shallow trench isolation structures that reduce or minimize a number of trench cones during the formation of shallow trenches, separate etch steps etch shallow trenches with small feature dimensions and shallow trenches with large feature dimensions. For example, the a first shallow trench is etched in a first region of a substrate with a first etching parameter (316), and a second shallow trench is etched in a second region of a substrate with a second etching parameter different from the first etching parameter (326). The etching parameter may include an etching selectivity ratio of silicon to an etch retardant that contributes to cone formations. Because of the separate etch steps (316, 326), the sidewall slopes between the first and second shallow trenches may be within a few degrees of deviation.