Changes of hydrogen evolution thermodynamics induced by He and H-2 dilution in PECVD a-Si : H films: influence on thermal crystallization

Intrinsic and n-type amorphous silicon films were deposited by plasma-enhan ced chemical vapour deposition on Qz (fused silica). crystalline silicon an d aluminium substrates. Different substrate temperatures (200 degrees C and 300 degrees C) and 50% diluted SiH4 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 usi ng differential scanning calorimetry to obtain the entropy change and the a ctivation energy of hydrogen evolution process. Crystallization of a-Si:H w as obtained by an isothermal annealing performed at a pressure of 30 mTorr, at 650 degrees C, using different annealing times (30-480 s). Different en tropy variations an observed in the a-Si:H films. The hydrogen evolution af fects the crystallization kinetics, in fact, crystallization was delayed in the samples with a greater disorder after hydrogen evolution. (C) 2000 Els evier Science B.V. All rights reserved.