Radiofrequency power effects on the optical and structural properties of hydrogenated silicon films prepared by radiofrequency magnetron sputtering

The optical and structural properties of hydrogenated silicon films, deposited by radiofrequency (rf) magnetron sputtering at low temperature (Ts = 100 °C), were carefully investigated by means of optical transmission measurements (OT), Fourier transform infrared (IR) spectroscopy and spectroscopic ellipsometry (SE) technique. By varying the rf-power from 100 W to 350 W, and keeping all other parameters of the plasma constant, the growth rate increases up to 1.02 nm/s. A remarkable change in the hydrogen-bonding configurations for both wagging and stretching vibration modes was observed. The observed changes demonstrate definite structural transformation of the films from a completely amorphous phase to another one with crystalline Si when the rf-power is increased from 180 W to 200 W. The difference between the two phases is well revealed by the OT and the IR absorption results, and strongly confirmed by the SE ones. The effect of hydrogen on the band gap and on the microstructure of the films is discussed.