Clarification of nitridation effect on oxide formation methods

The electrical characteristics of gate dielectrics have been intensively studied. We examined four types of gate dielectrics: thermal oxide films formed in a pyrogenic steam ambient, those in a dry oxygen ambient: chemical vapor deposition (CVD) oxide films, and the thermal/CVD stacked oxide films. The effects of nitridation on oxide properties have been also systematically investigated using the nitrogen implantation technique. It is found that hot-carrier degradation can be improved by nitridation irrespective of the oxidation methods. This improvement is attributed to the suppression of interface state generation and the reduction in the number of electron traps in the oxide films. Our extensive investigation concludes that the nitridation of gate oxide films by nitrogen implantation is very promising for the improvement in reliability in spite of the difference in oxide formation methods.