Effect of deposition conditions and thermal annealing on the charge trapping properties of SiN_x films

The density of charge trapping centers in SiN_x:H films deposited by plasma enhanced chemical vapor deposition is investigated as a function of film stoichiometry and postdeposition annealing treatments. In the as-deposited films, the defect density is observed to increase with an increasing N/Si ratio x in the range of 0.89-1.45, and to correlate with the N-H bond density. Following the annealing in the temperature range of 500-800 °C, the defect density increases for all N/Si ratios, with the largest increase observed in the most Si rich samples. However, the defect density always remains highest in the most N rich films. The better charge storage ability suggests the N rich films are more suitable for the creation of negatively charged nitride films on solar cells.