FURNACE FORMATION OF SILICON OXYNITRIDE THIN DIELECTRICS IN NITROUS-OXIDE (N2O) - THE ROLE OF NITRIC-OXIDE (NO)

We have studied the growth kinetics of the N2O furnace oxynitridation process demonstrating the importance of input flow rate, and therefore gas residence time, in determining the final film thickness and the nitrogen concentration. This dependence on residence time can explain the variation in the tendency to thickness saturation observed in the film growth data reported by several groups. Using published gas phase kinetic data, we have shown that, for a 950 degrees C oxynitridation process, N2O decomposes into N-2, O-2, and NO before reaching the wafer load. Again using published information, we have derived a simple equation which describes the subsequent reaction between NO and O-2 to produce NO2 as the gas flows down the tube. This reaction results in loss of NO by an amount which depends on the gas residence time and therefore on the input gas flow rate and the dimensions of the system. Since it can be argued that NO2 does not contribute to nitridation, this system-dependent loss of NO can explain the variation in the reported film growth data. Combining our experimental data and model, we find that the peak nitrogen concentration in the film depends linearly on the NO gas phase concentration. Further, the oxynitride grows more slowly as the NO concentration increases supporting the idea that oxidation sites are blocked by nitrogen as oxynitridation time increases.