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 n itrogen concentration. This dependence on residence time can explain t he variation in the tendency to thickness saturation observed in the f ilm growth data reported by several groups. Using published gas phase kinetic data, we have shown that, for a 950 degrees C oxynitridation p rocess, N2O decomposes into N-2, O-2, and NO before reaching the wafer load. Again using published information, we have derived a simple equ ation which describes the subsequent reaction between NO and O-2 to pr oduce NO2 as the gas flows down the tube. This reaction results in los s of NO by an amount which depends on the gas residence time and there fore on the input gas flow rate and the dimensions of the system. Sinc e it can be argued that NO2 does not contribute to nitridation, this s ystem-dependent loss of NO can explain the variation in the reported f ilm growth data. Combining our experimental data and model, we find th at 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.