Critical investigation on hydrogen bonding by Fourier Transform Infrared spectroscopy in hydrogenated amorphous silicon thin films

• Void region starts at CH = 23%, CH = 18% and CH = 14% for RF, PDC and DC films respectively.
• Films with low R* can be deposited by DC sputtering and high R* with PDC and RF.
• Dihydride incorporation is more in RF films followed by pulsed DC and DC films.
• Hydrogen incorporation is more in RF sputtering followed by pulsed DC and DC sputtering.
• Hydrogen radicals are more in RF plasma compared to pulsed DC and DC plasmas.

Fourier Transform Infrared (FTIR) spectroscopic analysis has been carried out on the hydrogenated amorphous silicon (a-Si:H) thin films deposited by DC, pulsed DC (PDC) and RF sputtering process to get insight regarding the total hydrogen concentration (CH) in the films, configuration of hydrogen bonding, density of the films (decided by the vacancy and void incorporation) and the microstructure factor (R*) which varies with the type of sputtering carried out at the same processing conditions. The hydrogen incorporation is found to be more in RF sputter deposited films as compared to PDC and DC sputter deposited films. All the films were broadly divided into two regions namely vacancy dominated and void dominated regions. At low hydrogen dilutions the films are vacancy dominated and at high hydrogen dilutions they are void dominated. This demarcation is at CH = 23 at.% H for RF, CH = 18 at.% H for PDC and CH = 14 at.% H for DC sputter deposited films. The microstructure structure factor R* is found to be as low as 0.029 for DC sputter deposited films at low CH. For a given CH, DC sputter deposited films have low R* as compared to PDC and RF sputter deposited films. Signature of dihydride incorporation is found to be more in DC sputter deposited films at low CH.