Low temperature magnetron sputter deposition of polycrystalline silicon thin films using high flux ion bombardment

Abstract

We demonstrate that the microstructure of polycrystalline silicon thin films depends strongly on the flux of low energy ions that bombard the growth surface during magnetron sputter deposition. The deposition system is equipped with external electromagnetic coils which, through the unbalanced magnetron effect, provide direct control of the ion flux independent of the ion energy. We report the influence of low energy (<27eV) Ar+ on the low temperature (<450°C) growth of polycrystalline silicon thin films onto amorphous substrates. We use spectroscopic ellipsometry, Raman scattering, x-ray diffraction, and cross sectional transmission electron microscopy to analyze the film microstructure. We demonstrate that increasing the flux ratio of Ar+ ions to silicon neutrals (J+∕J0) during growth by an order of magnitude (from 3 to 30) enables the direct nucleation of polycrystalline Si on glass and SiO2 coated Si at temperatures below 400°C. We discuss possible mechanisms for this enhancement of crystalline microstructure, including the roles of enhanced adatom mobility and the formation of shallow, mobile defects.