Interpretation of stress variation in silicon nitride films deposited by electron cyclotron resonance plasma

Abstract

We report here on internal stress variations in SiNx films deposited on silicon by plasma enhanced chemical vapor deposition-electron cyclotron resonance (PECVD-ECR) plasma. The effects of deposition parameters, film thickness and surface morphology have been considered. SiNx films can exhibit a compressive or a tensile internal stress, ranging from −1970 to +465MPa, depending on deposition parameters. Among published results, usual reported residual stress for PECVD films is compressive. Versatility of our experimental ECR equipment allows one to deposit films exhibiting a weak stress in the range of a few tens MPa. On the basis of atomic force microscopy observations, a correlation between the intensity of the stress and the granular morphology of the films has been observed. The rms value for SiNx film surfaces is never higher than 1.5nm, with a grain height ranging from 1.2 to 5nm and a grain width varying from 20 to 60nm. Both the grain size and the residual stress vary with the thickness of the films. This work highlights the influence of the initial surface properties on the deposition mechanism. An exhaustive review of the stress generation model is given and a tentative interpretation for the origin of stress, either compressive or tensile, is proposed.