| Summary: | 博士 === 國立交通大學 === 電子工程系所 === 95 === In this dissertation, we report that reoxidation behavior of high-nitrogen ultrathin oxynitride in rapid thermal process (RTP). Simultaneously, we develop a novel process to grow robust ultrathin oxynitride with high nitrogen content close to its surface.
Reoxidation experiments on high-nitrogen ultrathin oxynitride, which is formed by thermally nitridizing a chemical silicon oxide with pure ammonia, are conducted using an alternation of nitrous oxide and oxygen gas in rapid thermal oxidation (RTO). The new finding herein is the zig-zag characteristic of the oxidation rate by O2 and N2O. It is clear that the N2O oxidation rate is almost independent of the concentration of nitrogen in oxynitride through out the rapid thermal oxidation process, but the O2 oxidation rate is decreased as nitrogen content increased. Furthermore, non-uniform thickness of oxynitride was also observed after N2O gas treatment. Particularly, the thickness is thinner in the center part of the wafer instead of at the edge of the wafer. It should be noted that O2 gas does not produce the same results. Any conventional oxidation model based on simple bulk diffusion and/or surface reaction mechanisms simply would not do it. The non-uniformity of N2O gas reoxidation can be explained by combining a mechanism with radial thermally induced stress, exothermic N2O oxidation and depletion of atomic oxygen.
Finally, we have proposed an approach for growing robust ultrathin oxynitride, including NH3 nitridation of chemical oxide and reoxidation with O2. In this method, we obtain oxynitride with high nitrogen concentration (≈13 at.%) on the top and low interface state density (Dit=2×1010 cm-2 eV-1). The films demonstrate excellent properties in terms of low leakage current, high endurance in stressing and superior boron diffusion blocking behavior. This process does not involve any additional capital equipment. In addition, it obtains high-quality oxynitride film with low thermal budget. Most importantly, this process is simple and fully compatible with current process technology. It would be important and interesting to the process engineers who engaged in the field of gate dielectrics.
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