Structure and properties of silicon nitride and [formula omitted] nitride prepared by direct low energy ion beam nitridation

Abstract

Thin films of silicon nitride, germanium nitride and silicon germanium nitride were formed using direct low energy ion beam nitridation. In this process a monoenergetic nitrogen ion beam directly impinges on the material to be nitrided, in the present work Si(100), Ge/Si(100) and Si 0.89Ge 0.11/Si(100). The energies investigated ranged from 100 eV to 1 keV. Germanium and SiGe alloy were grown on Si(100) using molecular beam epitaxy. The kinetic energy of the ion beam introduces activated nitrogen species athermally into the substrate, and allows the formation of nitrides at low temperatures (20–420°C). Properties of the films such as stress, stoichiometry and microstructure are found to depend strongly on ion energy and substrate temperature. Film stress is highly compressive for samples deposited at room temperature, but decreases with temperature and becomes tensile at 420 °C. Film thicknesses, as measured by cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry, were found to be much greater than the projected range of the ions. The creation of an amorphous layer beneath the amorphous nitride films is observed, and is found to be a strong function of ion energy, temperature and nitrogen ion dose.