Physical properties of thermally evaporated silicon films nitrided at different rf plasma-processing time

Nitrided surfaces and composition gradients in thin films exhibit interesting mechanical, electrical, and optical properties. Therefore, amorphous hydrogen-free silicon (a-Si) thin films were deposited by electron beam evaporation and subsequently nitrided by an inductively coupled rf plasma. The effects of successive plasma-processing cyclic time on structural and optical properties as well as electrical resistivity were examined by different characterization techniques. It was found that the rf plasma treatment has a massive effect on the physical properties of the Si films. The Si thin films were transformed gradually into nitrides compound and the amount of nitrogen in the film increased with increasing the rf plasma-processing time. The Si nitrided films showed structural, optical, and electrical properties dependent on the plasma-nitriding time. Increasing the rf plasma-processing time reduced the thickness, increased transmittance, increased resistivity, and decreased the reflectance of the nitrided Si films. The electrical resistivity increased to about nine orders of magnitude when the film was nitrided at a plasma-processing time of 25 min. The optical band gap increased from 2.42 to 3.52 eV with increasing the plasma-processing time from 10 to 35 min. The decrease in the refractive index with the increase in the plasma-processing time is attributed to the possible change in the bucking density as well as to the increase in the band gap.