Effects of rapid thermal anneal on refractive index and hydrogen content of plasma-enhanced chemical vapor deposited silicon nitride films

The objective of this paper is to understand and quantify the effects of rapid thermal anneal (RTA) on refractive index, thickness, and hydrogen content of plasma-enhanced, chemical vapor-deposited (PECVD) silicon nitride films. It is shown that RTA is more effective than identical furnace anneal. A threshold in as-deposited refractive index value is found, above which the index of a silicon nitride film increases, while the thickness and bonded hydrogen content decreases as result of the RTA. In addition, the magnitude of increase in the index is proportional to the as-deposited index value. The threshold index value increases with the increase in silicon nitride deposition temperature. A direct correlation is found between the annealing-induced increase in refractive index and the corresponding decrease in total bonded hydrogen concentration in the PECVD silicon nitride films. Finally, it is shown that the release of bonded hydrogen from the film can passivate defects in the underlying silicon substrate and increase the performance of silicon devices such as solar cells. (C) 1996 American Institute of Physics.