OPTICAL DIELECTRIC FUNCTION AND INFRARED-ABSORPTION OF HYDROGENATED AMORPHOUS-SILICON NITRIDE FILMS - EXPERIMENTAL RESULTS AND EFFECTIVE-MEDIUM-APPROXIMATION ANALYSIS

The optical dielectric function (1.56.5 eV), ir absorption (4004000 cm-1), and film density have been measured for a series of hydrogenated amorphous silicon nitride (a-SixNyHz) films deposited at 400°C via rf plasma-enhanced chemical vapor deposition for varying [NH3]/[SiH4] ratios R. From a detailed analysis of the ir and density results, the concentrations of Si-N, N-H, Si-H, and Si-Si bonds and of Si, N, and H atoms have been obtained for the films studied. An effective-medium-approximation analysis of the measured based on the Si-centered tetrahedron model presented in the preceding paper has provided a more sensitive means of determining the concentration of Si-Si bonds in the films and has demonstrated that careful measurements of 1 and 2 can serve as a useful probe of the bonding in these alloys. Approximately 9×1020 Si-Si bonds/cm3 have been found in N-rich films which are close in composition to silicon diimide, Si(NH)2, and these Si-Si bonds have been found to have a significant influence on both the optical energy gap Eopt and the refractive index n of the films. New results obtained from the ir absorption measurements include the identification of (1) a shoulder near 1030 cm-1 on the main 880-cm-1 Si-N(s) band and (2) a weak absorption feature near 640 cm-1 which is not hydrogen related. It has been found that the N-rich diimidelike films prepared here have very low porosities and are thermally stable up to 700°C, properties which will be important for their future applications. © 1990 The American Physical Society.