Thin microcrystalline silicon by a microwave remote plasma deposition scheme for heterojunction solar cells and thin film transistors

A microwave remote plasma system, operating in an electron cyclotron resonance (ECR) condition, has been designed to deposit microcrystalline silicon (μ c-Si). The plasma properties have been studied by Langmuir probe measurements in the deposition region. Microcrystalline silicon films of thickness < 0.3 μm have been grown by the decomposition of 2% SiH₄/Ar diluted in H₂. The films were analyzed for dark and photoconductivity, crystallinity and total H₂ content. Raman spectroscopy indicates >50% crystallinity for films deposited between 300-400°C at pressures of 10 m Torr with an input power in the range of 200-600 W for a H₂/SiH₄ ratio of 60. An increase in deposition temperature from 300 to 400°C resulted in an increase in conductivity along with a decrease in the activation energy. H₂ evolution studies indicate that the purely μ c-Si films show a total 2.5% H₂ content compared with the 16.5% seen for the totally amorphous films. Better structural and electrical properties have more recently been obtained using 2% SiH₄/He mixtures.