With the downscaling of the electronic devices and the increase in the frequency of the electronic circuits, a large search for new gate dielectric is ongoing. The exact composition and element distribution in the dielectric film have a large impact on the electrical characteristics of these films. We studied here the formation of ultrathin Si3N4 films (3 nm) under different conditions and concentrated on their composition analysis. The Si substrates were cleaned using RCA and/or HF dip. The Si3N4 films were subsequently fabricated either by RTCVD (SiH4/NH3) either by remote plasma (SiH4/N2) with or without a pre-anneal to form a 0.5 nm SiO2 layer. Post annealing was made using NO, N2O or NH3 at various temperatures and for various times. The quantification of the composition was realized using XPS and elemental distribution was analyzed using TOFSIMS with Ar+ sputtering and positive ion detection mode.
The results show that the fabrication method of the nitride film has only a very limited influence on the O/N content of the films. However, both the preparations of the substrate (HF last or RCA last) and the post-annealing influence strongly the film composition. The presence of an interfacial oxide increases significantly the oxygen content of the film. Post-annealing with N2O also increases the oxygen content of the film while the NH3 post-annealing leads to a significant decrease. The results are compared with electrical characterization of the same films.