Ultrathin thermal silicon nitride and nitroxide gate insulators for VLSI

High quality ultrathin films of silicon nitride and nitroxide have been thermally grown in an RF-heated reactor and in a lamp-heated system. MIS devices were fabricated using these films as gate insulators and were characterized using I-V, C-V, time dependent breakdown, trapping and dielectric breakdown techniques. The structure and interface morphology of nitride films were studied using high resolution cross-sectional transmission electron microscopy. The results indicate extremely low trapping in the nitride films. The reliability of nitride was observed to be superior to SiO2and nitroxide due to less trapping. Studies show that the interface transition from nitride to silicon is almost abrupt and the morphology and roughness of the interface are comparable to the SiO2/Si interfaces. The kinetics of nitridation of SiO2has also been studied. In nitroxide, nitrogen rich layers are formed at the surface and interface at a very early stage of the nitridation. Then the nitridation reaction mainly goes on in the bulk region with the surface and near interface nitrogen content remaining fairly constant. Our results also indicate the formation of an oxygen rich layer at the interface underneath the nitrogen rich layer whose thickness increases slowly with nitridation time.