Effect of hydrogen dilution on the growth of hydrogenated amorphous silicon studied by in-situ phase-modulated ellipsometry

Abstract

We have conducted a study of the growth of hydrogenated amorphous silicon (a-Si:H) thin films, deposited in SiH4H2 r.f. discharges, through spectroscopic and real-time phase-modulated ellipsometry. The study focused on the microstructure of the a-Si:H-crystalline Si interface and the a-Si:H bulk layer. Real-time data were analysed using a theoretical growth model, previously proposed, which assumes cylindrical nucleation, coalesence and long-term growth phases. For high silane fractions (above 60%) the results are compatible with the existence of an abrupt interface, whereas for low silane fractions (20%) the real-time ellipsometric data can be modelled assuming the existence of an interface, 1.2 nm thick, composed of SiO2 (95%) and a-Si:H (5%). The ellipsometric results indicate an optimal degree of silane fraction for which the bulk void fraction is minimized. The results are discussed in terms of growth kinetics. © 1993.