Comparison of the mechanisms of hydrogenation by rf plasma and SiNx

Abstract

In low temperature poly-silicon (LTPS) TFT's, the electrical characteristics are controlled by the inter-and intra-grain defects in the poly-silicon films. Hydrogen passivation is an effective way to reduce the density of these defects and can improve TFT's characteristics. In this study we investigated the characteristics of TFT's as a function of the hydrogenation time for two different hydrogenation techniques: H,/Ar plasma and PECVD silicon nitride film deposition. It was found that the characteristics of TFTs could be greatly improved after a very short period of time by both hydrogenation processes. In the H,/Ar RF plasma hydrogenation process, the characteristic parameters would be apparently improved within 30 min., and with only limited improvement after that. In the nitride hydrogenation process, the electrical characteristics of TFTs would be optimized within 5 min. of annealing, but started to degrade with longer annealing time. From these result, we concluded that the hydrogenation mechanism of these two techniques are very much different from each other.