Properties of a-Si:H films grown using hot wire-ECR plasma techniques

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We report on the growth and properties of a-Si:H films and nin layers prepared using combination of hot wire and ECR-plasma growth techniques. The films were prepared using both W and Ta hot wire filaments. A distinguishing feature of the reactor was the large spacing, 11 cm, of the filament from the substrate, thereby avoiding over-heating of the substrate. Films were grown at pressures from 2 to 50 mT, and the corresponding optical and electronic properties of the films were measured. The temperature of the substrate was varied between ∼225 and 350 °C. It was found that the growth rates do not follow the maximum at a pressure-distance (pd) product ∼15 mTorr cm postulated by Molenbroek et al.'s model. [J. Appl. Phys. 82, 1909 (1997)]. It was also discovered that the properties of the hot wire films depend upon the pd product, and that the H bonding and electronic properties depend critically upon the growth rate, and on the substrate temperature. The properties of the hot wire films bear a remarkable similarity to the films deposited using expanding thermal plasma (ETP) techniques at similar temperatures. When the films were subjected to low power He plasma, the properties improved dramatically. It was also found that H ions are more efficient at etching a growing film than H radicals alone. The results show that the H bonding and electronic properties of a-Si:H films are determined primarily by the efficiency of H extraction, and that low energy ions have a useful role to play in this process.