Simulation of correlated diffusion of Si and B in thermally grown SiO2

Abstract

Simultaneous diffusion of Si and B in thermally grown SiO 2 is modeled taking into account the effect of SiO molecules generated at the Si/ SiO 2 interface and diffusing into SiO 2 to enhance both Si and B diffusion. Based on the model, we simulated experimental profiles of coimplanted 30 Si and B in 28 SiO 2 , which showed increasing diffusivities with decreasing distance from the interface. The simulation results show that the SiO diffusion is so slow that the SiO concentration at the near-surface region critically depends on the distance from the interface. In addition, the simulation explains that the diffusivities of both Si and B increase with longer annealing times because more SiO molecules arrive from the interface. Furthermore, we examined the effect of high-concentration B on the diffusivities of Si and B in SiO 2 , both of which increase with higher B concentration. The experimental results were simulated assuming that the diffusivity of SiO, which enhances the diffusivities of Si and B, increases with higher B concentration. The present results indicate that Si and B diffusion in SiO 2 are correlated via SiO molecules; namely, the enhancement of SiO diffusion at high B concentrations also causes enhanced diffusion of both Si and B.

Effect of Nitrogen on Diffusion in Silicon Oxynitride

“…Recently, we have shown that SiO molecules, which are important diffusing species in SiO 2 , enhance both Si self-diffusion and B diffusion in SiO 2 . 7,8) This leads us to assume that the incorporation of N reduces the SiO diffusivity in SiO 2 because the existence of N retards B diffusion, which is enhanced by SiO. This assumption is also consistent with the increase of SiO 2 viscosity with N incorporation because diffusion of SiO is closely related to the viscosity of SiO 2 and viscosity is inversely proportional to diffusivity.…”

“…The assumption that the SiO diffusivity exponentially decreases with increasing N concentration was introduced in analogy with B diffusivity in SiO 2 , which exponentially increases with B concentration. 7,8) During oxynitridation, the SiO diffusion is strongly retarded by the N at the interface. This retardation increases the SiO concentration in SiO 2 near the interface as oxynitridation proceeds, which decreases the oxynitridation rate with time.…”

Self-diffusion and impurity diffusion in silicon dioxide

“…Figure 3 shows the experimental B profiles in lowdose samples with various thicknesses after annealing at 1250°C for 6 h. In the same way as Si self-diffusion, the B diffusion shows a clear dependence on the thickness of the 28 SiO 2 layer; the shorter the distance from the Si-SiO 2 interface, the higher the B diffusivity in SiO 2 . [15,16] This tendency was also observed for the high-dose samples and other temperatures used in this study. The distance dependence of B diffusivity indicates that the SiO molecules, which are generated at the Si-SiO 2 interface and diffusing into SiO 2 , enhance not only Si self-diffusion but also B diffusion.…”

“…The profile of 30 Si in the high-dose samples shows larger diffusion than that without B. [15,16] On the other hand, the 30 Si profile of the low-dose samples (not shown in Fig. 4) showed no significant difference from that without B.…”

Microscopic Mechanism of Silicon Thermal Oxdation Process

“…We have studied the transport of Si during the thermal oxidation experimentally as well as theoretically. Experiments based on isotope technology have revealed that some Si-related species diffuse from the interface and enhance the diffusion in the oxide (28,29,31,32,36,47,48). These experimental results indicate that the transport of Si is a very important consideration in the thermal oxidation process, while the microscopic picture for the Si-related species is not well clarified yet.…”