Plasma Etching of Copper Thin Film over a Dielectric Step and Electromigration Failure Mechanism

Abstract

ABSTRACTProcess and electromigration issues of the copper line over a dielectric step etched with a new plasma-based process have been studied. The N2 and CF4 additive gas effects on the line profile, undercut, and “neck” formation at the cusp area were investigated with respect to changes of the plasma phase chemistry and ion bombardment energy. The sidewall passivation layer hindered the excessive attack of the cusp region. The undercut of the photoresist pattern caused the residue formation. The lifetime of the etched copper was related to the line shape and the film topography, which directly affected the local current density and stress. With the proper control the plasma phase chemistry and ion bombardment energy, the Cu film over a topographic surface can be etched into fine lines with a long electromigration lifetime.