In situ investigation of the growth of rf glow-discharge deposited amorphous germanium and silicon films

An in situ investigation of the growth of rf glow-discharge amorphous germanium (a-Ge:H) and silicon (a-Si:H) films using fast real-time spectroscopic phase-modulated elipsometry is presented. The influence of the conditions of preparation is studied in both cases. The same behavior is obtained in a-Ge:H and a-Si:H films deposited in similar conditions. In particular, the initial stage of the growth can be described by a nucleation process in both cases, whatever the conditions of preparation. The incomplete coalescence of the nuclei leads to the formation of a surface roughness on a ∼40-Å scale which is observed during film growth. In comparing real-time ellipsometry measurements performed at different wavelengths, a correlation between the internuclei distance and the thickness of the surface roughness is observed. An enhancement of the surface mobility of the reactive species due to an increase of substrate temperature and/or ion-bombardment energy results in an increase in the density of the nucleation centers. The influence of ion bombardment and gas pressure is discussed by comparing the growth of a-Si:H film deposited in a rf discharge to the results of previous studies using a low-pressure multipole plasma.