Thin layer etching of silicon nitride: A comprehensive study of selective removal using NH3/NF3 remote plasma

Abstract

Silicon nitride spacer etching realization is considered today as one of the most challenging processes for the fully depleted silicon on insulator devices realization. For this step, the atomic etch precision to stop on silicon or silicon germanium with a perfect anisotropy (no foot formation) is required. In a recent study, the authors demonstrated the benefit of an alternative etch chemistry based on silicon nitride film modification by H2 or He plasma followed by a removal step of this modified layer using hydrofluoric acid based wet cleaning. In this paper, the authors investigate the silicon nitride modified layer removal by mixing fluorine based gas (NF3) with hydrogen based gas (NH3) performed in a remote plasma followed by an annealing step. The interaction mechanisms between modified silicon nitride and the NF3-NH3 plasma have been understood, thanks to x-ray photoelectron spectroscopy and infrared spectroscopy analyses. Finally, the efficiency of the best NF3-NH3 plasma process to remove the modified silicon nitride layer has been evaluated on pattern structures.