Evolution of nc-Si Network and the Control of Its Growth by He/H2 Plasma Assistance in SiH4 at PECVD

Abstract

The evolution of nc-Si network and the control of its growth within quantum dot structures have been systematically studied by He/H2 plasma assistance in SiH4. Using the beneficial aspects of He* and He+ in the purely helium-diluted silane plasma and optimizing the process parameters, nanocrystalline silicon films are produced at high growth rates. The nc-Si:H network of increasing electrical conductivity and improved crystallinity are obtained with simultaneously increasing deposition rates, which deserve extensive technological impact. Starting with a mixed phase heterogeneous matrix in the neighborhood of amorphous-to-crystalline transition zone, the effect of H2 in the reconstruction of the network, triggering nanocrystallization, was studied using (SiH4+He+H2)-plasma. A radical change in the materials properties has been accomplished by the inclusion of a small amount of H2 as the component diluent. Sharp rise in the overall crystallinity, well aligned crystallographic lattice distribution, gross removal of porosity and sharp elevation of electrical conductivity by several orders of magnitude are the consequences which are accompanied by a relatively insignificant lowering in the growth rate because of required H2-dilution in trivial amounts. Partial hydrogenation to the mostly He diluted SiH4 plasma has been identified as the favored route for attaining spontaneous nanocrystallization in the Si-network and its confinement of structures within quantum dot dimensions.