Changes of hydrogen evolution thermodynamics induced by He and H2 dilution in PECVD a-Si:H films: influence on thermal crystallization

Abstract Intrinsic and n-type amorphous silicon films were deposited by plasma-enhanced chemical vapour deposition on Qz (fused silica), crystalline silicon and aluminium substrates. Different substrate temperatures (200°C and 300°C) and 50% diluted SiH 4 in He or H 2 process gas were used to change hydrogen content and microstructure of deposited amorphous material. The hydrogen evolution thermodynamics of a-Si:H films was investigated using differential scanning calorimetry to obtain the entropy change and the activation energy of hydrogen evolution process. Crystallization of a-Si:H was obtained by an isothermal annealing performed at a pressure of 30 mTorr, at 650°C, using different annealing times (30–480 s). Different entropy variations are observed in the a-Si:H films. The hydrogen evolution affects the crystallization kinetics; in fact, crystallization was delayed in the samples with a greater disorder after hydrogen evolution.