RF power density dependent phase formation in hydrogenated silicon films

Hydrogenated amorphous and micro/nanocrystalline silicon films have been deposited using RF (13.56 MHz) PECVD technique in the RF power density range of 177 to 885 mW/cm2 exploiting SiH4 + H2 + Ar gaseous mixture. Predominant crystalline phase was observed in the films, as revealed from Raman spectroscopic study, deposited at power densities of 531 and 708 mW/cm2 and amorphous phase at 177, 354 and 885 mW/cm2. Amorphous to microcrystalline phase transition occurred near RF power density of 531 mW/cm2. The high crystalline phase (~ 80%) was found in the film deposited at 708 mW/cm2. Lower values of bond angle distortion of 6.7 and 5° were found for the films deposited at 531 and 708 mW/cm2 as compared to bond angle distortion of 8.4, 9.3 and 9.1° for the films deposited at 177, 354 and 885 mW/cm2, respectively. Plasma parameters extracted from V/I probe and properties of the films revealed contribution of ions to be beneficial for the enhancement of deposition rate of the films. The increased ion energy (sheath field) and ion flux together with SiHx (x = 1,2,3) radicals on growing film surface might help in the enhancement of crystallinity at 708 mW/cm2.