Plasma deposition of semiconductor multilayer structures
The early stages of thin film growth from the rf glow discharge of silane-based gas mixtures have been systematically studied by structural characterizations of the silicon based multilayers. The x-ray diffraction, its rocking curve and x-ray interference of hydrogenated amorphous silicon(a-Si:H, 10 % 200 A thick)/stoichiometric silicon nitride (a-SigNq:H, 25 % 250 A) multiple layers have been carefully measured. The results indicated that the amorphous silicon/silicon nitride interface is atomically abrupt and the thicknesses of the respective layers are atomically flat regardless of substrate materials. This demonstrates that the precursors impinging onto a substrate from the gas phase homogeneously cover the growing surface and layer by layer growth proceeds on atomic scale. In the plasma deposition of the covalently bonded semiconductors and insulators studied in the present experiments, the island formation on a substrate at the beginning of thin film growth is very unlikely. The extremely flat features of the ultra thin multilayer structures are also confirmed by observing the quantum size effects in the amorphous silicon/silicon nitride system.