Characterization of plasma-deposited silicon nitride coating used for integrated circuit encapsulation

Abstract

The origin of instability observed in n-channel metal-oxide-semiconductor field effect transistor (MOSFET) devices encapsulated with plasma-deposited silicon nitride films prepared from ammonia-silane (2% in nitrogen) gas mixture was investigated. The physical, chemical and structural properties of these films are compared with those of films prepared by reaction of ammonia and silane without nitrogen. Auger electron spectroscopy and X-ray photoelectron spectroscopy measurements revealed compositional and structural differences in the films prepared from these two processes. Fourier transform IR measurements show that, for the 100% SiH 4 process, 78% of hydrogen is bonded to silicon and 22% to nitrogen, while for the 2% SiH 4 process almost all (94%) of the hydrogen is bonded to nitrogen and only 6% to silicon. It is suggested that these N-H and Si-H bonds are broken during the subsequent plasma etching process, resulting in dangling bonds which are responsible for generating more positive trapped charges in the silicon nitride films, thus affecting the threshold voltage of the n-channel MOSFETs.