Plasma-enhanced chemical vapour deposition of microcrystalline silicon: on the 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 measurements and transmission electron microscopy observations on the deposited samples are compared and discussed. Continuous deposition is observed to result in a growth which is initially amorphous and then evolves to microcrystalline. At this stage, the grains are observed to propagate towards the interface with the substrate. In order to obtain very thin layers, a deposition+hydrogen etching+deposition sequence was also used. This technique produces 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. Electrical measurements are correlated with the sample structure. The dark conductivity confirms the microcrystalline nature of samples, but is also shown to depend on the distribution of the microcrystalline phase.