Improved Hot Carrier Reliability in Strained-Channel NMOSFETS with TEOS Buffer Layer

Both the presence of the SiN capping layer and the deposition process itself exert significant impacts on the device operation and the associated reliability characteristics. The accompanying bandgap narrowing, increased carrier mobility and hydrogen diffusion from the SiN capping process tend to worsen the hot-electron reliability. This work shows that, owing to the use of hydrogen-containing precursors, abundant hydrogen species is presumably incorporated in the oxide and may contribute to the hot-electron degradation, even if the SiN layer is removed later and the channel strain is relieved. Furthermore, by blocking the diffusion of hydrogen species, the devices with 20nm-thick TEOS buffer layer can effectively improve the hot-electron reliability without compromising the performance enhancement by the strain induced by the SiN capping. Optimization of both the thickness of buffer layer and SiN deposition process are thus essential to the implementation of the uniaxial strain in NMOS devices.