Influence of pre and post process conditions on the composition of thin Si₃N₄ thin Alms (3 nm) studied by XPS and TOFSIMS

Abstract

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.