Undercutting Phenomena in Al Plasma Etching

Abstract

Undercutting phenomena in Al plasma etching were investigated. Photoresist, SiO₂ and Si₃N₄ were used for etching masks. PSG, Si(100), Si₃N₄ and Al₂O₃ were used for underlying layers. In various combinations of etching masks and underlying layers, only photoresist mask exhibits no undercutting. However, even in this case, undercutting occurs according to over-etching time and pattern density. An hypothesis that a film observed on an Al pattern sidewall acts as a protection against undercutting was proposed. Undercutting phenomena were easily explained by this hypothesis.