Mobile and stable hydrogen species in the interface layer between poly silicon and gate oxynitride

The diffusion behavior of hydrogen contained in the surface layer of oxynitrides serving as models for poly-Si/oxynitride interfaces in MOS transistors was studied with H depth profiling by nuclear reaction analysis. The poly-Si/oxynitride interface is found to contain mobile and stable H species. The mobile H species tends to desorb in vacuum at room temperature. A TDDB improvement caused by resting in air for more than 24 h prior to the post nitridation annealing is attributed to the reduction of mobile H species. Eliminating the mobile H from the gate interface is thus suggested to improve the reliability of oxynitride dielectrics.