Dopant Diffusion in Silicon Substrate during Oxynitride Process
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Dopant Diffusion in Silicon Substrate during Oxynitride Process Nobutoshi Aoki, Toshitake Yaegashi, Yuji Takeuchi, Makoto Fujiwara, Naoki Kusunoki, Tsutomu Sato, Ichiro Mizushima, Yoshitaka Tsunashima, Hiroaki Hazama, Seiichi Aritome, and Riichiro Shirota, Microelectronics Engineering Laboratory, TOSHIBA Corporation, 8, Shinsugita-cho, Isogo-ku, Yokohama, 235-8522, Japan Takashi Shimizu Manufacturing Engineering Center, TOSHIBA Corporation, 8, Shinsugita-cho, Isogo-ku, Yokohama, 235-8522, Japan
ABSTRACT We found an anomalous behavior of dopant diffusion in Si substrate during the oxynitride process. SIMS measurements showed a notably enhanced diffusion during the NO and N2O oxynitride process. The considerably enhanced diffusion was also observed in re-oxidation of oxynitride film grown by the NO annealing or NH3 nitridation of a SiO2 film. In order to simulate the enhanced diffusion, an enhancement coefficient was introduced, showing that the simulation results are in reasonable agreement with the experimental ones. We applied the diffusion model to the simulations of MOSFETs fabricated under various conditions of the oxynitride process. The device characteristics of MOSFETs were successfully reproduced by adopting a suitable dependence of nitrogen concentration CN on the surface recombination rate of interstitial Si at the oxynitride/Si substrate interface. INTRODUCTION Oxynitride (SiON) film has become indispensable for MOSFET gate insulator because it blocks dopant penetration from gate to Si substrate. From the viewpoint of device characteristics, the thermal process of gate insulator formation is a critical issue, since peculiar diffusion phenomena, such as the oxidation enhanced (retarded) diffusion OED (ORD) effect, largely modify the distribution of impurities in Si substrate. It is, therefore, an important task to clarify the behavior of impurity diffusion during the SiON process. Recent studies have shown that an abnormally enhanced diffusion of B and P in Si substrate was observed during a re-oxidation process of NH3 nitrided SiO2 film [1]. In this paper, we investigate dopant diffusion during the oxynitride process including NO and N2O oxynitridation, showing that the considerably enhanced diffusion is a common feature in the oxynitride process and re-oxidation of SiON films. We propose a simple model to describe the enhanced diffusion. Moreover, we apply the model to the simulation of MOSFETs with oxynitride gate dielectrics.
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Figure 1. SIMS depth profile and simulation result of B diffusion in Si substrate. (a)NO at 950C (thickness 2.5nm), (b)N2O at 900C (thickness 3.4nm) oxynitridation.
DIFUSSION IN OXYNITRIDE PROCESS For the sake of later discussion, we briefly refer to the diffusion mode
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