Notch formation by stress enhanced spontaneous etching of polysilicon

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 l iterature, notching has been attributed to solely charging within the featu re. 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 e ffect of stress on spontaneous etching was demonstrated by applying mechani cal stress to patterned polysilicon samples taken from the same wafer and o bserving the changes in notch formation. (C) 2001 American Vacuum Society.