Influence of RF bias on hydrogenated amorphous silicon by high-density plasma chemical vapor deposition

We investigate the microstructure and thermal stability of hydrogenated amorphous silicon (a-Si:H) thin films deposited by high-density plasma chemical vapor deposition (HDP-CVD) with various biases using radio frequency (rf) power. The a-Si:H films were prepared without external heating at a high rf power density of 3.18 W cm2, with the rf power bias varying from 0 to 200 W. Because sputtering also occurs during deposition, hydrogen may be present in a variety of bonding configurations in the a-Si:H films with various biases. Fourier transform infrared spectra show that the HDP-CVD a-Si:H films possess more hydrogen content as well as Si- H2 stretching modes than the conventional plasma-enhanced CVD counterpart. The surface morphology of the films becomes smooth upon ion bombardment under rf bias. In addition, variations of the film stress against temperature correlate to the hydrogen desorption at different stages during thermal annealing. More importantly, the different Si- Hx bonding configurations affect the crystallization behavior upon thermal annealing.