Thermal Nitridation of Si and SiO/sub 2/ for VLSI

Abstract

This paper presents an extensive review of our work on thermal nitridation of Si and SiO/sub 2/. High-quality ultrathin films of silicon nitride and nitrided-oxide (nitroxide) have been thermally grown in ammonia atmosphere in a cold-wall RF-heated reactor and in a lamp-heated system. The growth kinetics and their dependence on processing time and temperature have been studied from very short to long nitridation times. The kinetics of thermal nitridation of SiO/sub 2/ in ammonia ambient have 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. The nitride and nitroxide films were analyzed using Auger electron spectroscopy, grazing angle Rutherford backscattering, and etch rate measurements. MIS devices were fabricated using these films as gate insulators and were electrically characterized using I-V, C-V, time-dependent breakdown, trapping, and dielectric breakdown techniques. Breakdown, conduction, and C -V measurements on metal-insulator semiconductor (MIS) structures fabricated with these films show that very thin thermal silicon nitride and nitroxide films can be used as gate dielectrics for future highly scaled-dowm VLSI devices. The electrical characterization results also indicate extremely low trapping in the nitride films. The reliability of ultrathin nitride was observed to be far superior to SiO/sub 2/ and nitroxide due to its much 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 SiO/sub 2/-Si interfaces.