Composition and electron stress effects in silicon nitride thin films made by thermal growth and chemical etching of LPCVD MNOS structures as studied by x-ray photoelectron spectroscopy (XPS)

Abstract

XPS has been used in conjunction with stopped-flow chemical etching and angular resolution to obtain depth profies and interface structures of native oxide LPCVD MNOS structures and thermally-grown silicon nitride films. Depth profiling of LPCVD samples required stopped-flow etching with HF/H3PO4/ethanol (15:10:60). A uniform composition of nearly stoichiometric Si3N4 was found throughout the bulk; SiO2 was found intact at the interface along with a sharp Si3N4/SiO2 interface width of 8–10 Å. Another LPCVD sample was etched to ∠30 Å and subjected to a low-energy electron flux in an XPS investigation of degradation mechanisms of MNOS devices; cleavage of Si–H bonds was observed. Angle-resolved XPS on thin, thermally grown films showed a compositional gradient ranging from a high concentration of oxide at the surface to nearly pure Si3N4 at the interface. The results are related to interface state formation and mechanisms of MNOS memory degradation and film growth.