Hydrogen-related mechanical stress in amorphous silicon and plasma-deposited silicon nitride

Hydrogen concentrations in amorphous silicon (a-Si) prepared by electron beam evaporation or plasma deposition as well as in plasma-deposited silicon nitride were measured as a function of annealing conditions using the photon-proton scattering method. Comparison with IR evaluations of SiH bonds shows the existence of “quasi-free” (IR inactive) hydrogen in a-Si. The amount of this component can be altered by annealing. The dependence of the mechanical stress on the annealing conditions was determined interferometrically, and the intrinsic contribution was separated in the case of plasma-deposited silicon nitride. As the hydrogen content decreases monotonically with increasing annealing temperature, the initial compressive stress of plasma-deposited a-Si or silicon nitride films changes to a tensile stress. For these films a linear correlation between the amount of mechanical stress and the number of SiH or NH bonds is shown. Evaporated a-Si films show a totally different stress behaviour from that of plasma-deposited a-Si. No correlation of stress with the hydrogen concentration was found for the evaporated a-Si films.