In situ Ellipsometric Studies of the growth of a-Si:H films Prepared by the Hot wire Deposition

Abstract

AbstractIn situ ellipsometric studies have been performed during the nucleation and growth of hydrogenated amorphous silicon (a-Si:H) films prepared by the hot wire chemical vapour deposition (HWCVD) method in order to understand the growth mechanism of these films. For a comparison with films deposited by plasma enhanced chemical vapour deposition (PECVD), the hot wire deposition was carried out under similar conditions and reactor geometry as for the PECVD process. It is observed from the kinetic ellipsometry measurements that low filament temperature (TFil) and low gas pressure favour the growth of more dense films, but at lower deposition rates. Moreover, for a given set of conditions an increase in substrate temperature (Ts) leads to a higher final value of the film density with a different growth behaviour in the initial stage. Thus, the filament temperature in the hot wire method seems to have a similar effect on the film density as the rf power has in the PECVD process, which has been observed earlier. Film density and surface roughness obtained from spectroscopic ellipsometry using a tetrahedron model which takes into account the effect of hydrogen on the dielectric function, is used to get information about the film microstructure. A correlation between this microstructure, the growth behaviour and the electronic properties as the defect density or the ambipolar diffusion length in the films is also reported.