Effect of Substrate temperature on the microstructure variation in sputter-deposited hydrogenated amorphous silicon thinfilms

Vacancy, void incorporation and Si-H_x configuration in hydrogenated amorphous silicon (a-Si:H) thin films was studied. Films were grown by Direct Current (DC), pulsed DC and Radio Frequency (RF) magnetron sputtering. Fourier Transform Infrared (FTIR) spectroscopic analysis has been carried out on the films and found that, the a-Si:H films grown by DC magnetron sputtering are of good quality compared to pulsed DC and RF deposited films. The effect of Substrate temperature (T_S) on the total hydrogen concentration (C_H), configuration of hydrogen bonding, density (decided by the vacancy and void incorporation) and the microstructure factor (R*) was studied. T_S is found to be an active parameter in affecting the above said properties of the films. The films contain both vacancies and voids. At low hydrogen dilutions the films are vacancy dominated and at high hydrogen dilutions they are void dominated. It is found that T_S favors monohydride (Si-H) bonding at the cost of dihydride (Si-H₂) bonding. This dividing line is at C_H=14 at.%H for DC sputter deposited films. The microstructure structure factor R* is found to be zero for as deposited DC films at T_S=773K. The threshold C_H for void dominated region is found to be C_H=23 at.%H for RF, C_H=18 at.%H for PDC and C_H~14 at.%H for DC sputter deposited films.