Effect of aging on stress in silicon nitride films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition technique

Tensile and compressive silicon nitride films have been deposited at low temperatures from mixtures of Ar, N2 and SiH4 as precursors using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) technique. It has been found that the stability of the mechanical stress during aging of the films depends significantly on the deposition parameters. In most cases, as-deposited compressive films become more compressive while as-deposited tensile films become less tensile or even compressive during aging. The stress change was not found to be related with die atmospheric water or oxygen, since no oxygen was observed in the spectra of non-Rutherford Backscattering Spectroscopy within its detection limit (1 at. per cent). Using a careful combination of the deposition parameters we have succeeded in depositing an almost stress-free (5 MPa) film showing a negligible change in stress during aging of the film. The deposition rate of the stress-free film was 18 nm/min. The density determined by the RBS combined with ellipsometric technique was 2.08 g/cm3.