Plasma-enhanced chemical vapour deposition of microcrystalline silicon: onthe dynamics of the amorphous-microcrystalline interface by optical methods

Very-high-frequency plasma-enhanced chemical vapour deposition was used to produce p-type microcrystalline samples. Spectroscopic ellipsometry measure ments and transmission electron microscopy observations on the deposited sa mples are compared and discussed. Continuous deposition is observed to resu lt in a growth which is initially amorphous and then evolves to microcrysta lline. At this stage, the grains are observed to propagate towards the inte rface with the substrate. In order to obtain very thin layers, a deposition +hydrogen etching+deposition sequence was also used. This technique produce s an increase in the microcrystalline fraction by a factor of more than ten with respect to continuous deposition: a crystalline fraction as large as 48% at the film-substrate interface for a 20 nm film is detected. Electrica l measurements are correlated with the sample structure. The dark conductiv ity confirms the microcrystalline nature of samples, but is also shown to d epend on the distribution of the microcrystalline phase.