Notch formation by stress enhanced spontaneous etching of polysilicon

Abstract

Notch formation during overetching of polysilicon is shown to be caused by stress enhanced spontaneous etching in part, and is not solely a result of feature charging. Notch formation in plasma etching is the lateral etching at the polysilicon–oxide interface that occurs during overetching. In the literature, notching has been attributed to solely charging within the feature. In this work, it is shown that the fields necessary for ion bombardment deflection alone to form a notch are too large to be sustained by an oxide surface. Stress at the polysilicon–oxide interface can induce spontaneous etching of the polysilicon, contributing to the formation of a notch. The effect of stress on spontaneous etching was demonstrated by applying mechanical stress to patterned polysilicon samples taken from the same wafer and observing the changes in notch formation.