Influence of rapid thermal annealing processes on the properties of SiNx : H films deposited by the electron cyclotron resonance method

Abstract

We have analyzed the effects of rapid thermal annealing on the composition and on the bonding and optical properties of amorphous hydrogenated silicon nitride (a-Si-x:H) thin films deposited at room temperature by the electron cyclotron resonance plasma method. Films with three different as-grown compositions have been studied, namely x = 0.97, 1.43 and 1.55, Annealing effects were related to film composition. In films with the presence of both Si-H and N-H bonds (as-grown compositions x = 0.97 and 1.43), we found that a reorganization of bonds takes place at temperatures less than or equal to 500 degrees C, where the well-known cross linking reaction Si-Si + N-H --> Si-H + Si-N occurs without detectable release of hydrogen. In the same range of temperatures, an increase of the band gap was observed and attributed to Si-Si bond substitution for Si-H, but no changes in composition were detected. At higher temperatures (T greater than or equal to 600 degrees C), the optical gap decreases and both Si-H and N-H bonds are lost along with a release of hydrogen and nitrogen. For the films with an as-gown composition x = 1.55, we observe that the release of hydrogen only occurs at temperatures above 900 degrees C, but it is not accompanied by any loss of nitrogen. An increase of the optical gap until the release of hydrogen begins and a decrease thereafter is observed.