Structural and electrical properties of thin microcrystalline silicon films deposited by an electron cyclotron resonance plasma discharge of 2% SiH₄/Ar further diluted in H₂

Microcrystalline silicon (μc-Si) was deposited in a simple, low cost microwave electron cyclotron resonance plasma system by H₂ dilution of 2% SiH₄/Ar. The film growth and properties have been examined with substrate temperatures between 300 and 450°C for pressures of 1-40 mTorr. Raman spectroscopy has been used extensively to study the microstructure of the film, and to determine the crystallized fraction and grain sizes in the film, for growth variations caused by H₂ dilution, growth pressure, and temperature. H₂ dilution of the plasma is found to increase the grain size and the crystallized fraction of the deposited films. Crystallization could also be initiated in the films deposited using only the Ar diluted SiH₄ by increasing the power coupled to the discharge. Increasing the H₂ dilution results in compact films with a low hydrogen content, while a decrease is seen to create more voids in the film. The μc-Si films (∼70% crystallized fraction), prepared at 400°C, with grain sizes between 200 and 300 Å, exhibit a low dark conductivity of 3 × 10^-6 S/cm with conduction activation energies between 0.3 and 0.43 eV. The structural properties of the film, evaluated by Raman spectroscopy and evolved gas analysis, are correlated with the dark/ photoconductivity observed in the film. The experimental data suggest etching by atomic hydrogen to be the primary mechanism responsible for the crystallization of the films.