Theoretical studies on the basic processes of Si thermal oxidation.

在本研究计划中，我们利用第一性原理计算、宏观模拟和二次离子质谱（西姆斯）实验，对SiO_2和Si/SiO_2界面的原子化过程进行了深入的研究。本文用第一性原理计算和联立扩散方程研究了Si/SiO_2界面反应对杂质扩散和Si/SiO_2界面自扩散的影响。因此，我们取得了以下显著成果。(1)研究了硼在SiO_2中的扩散机制。我们发现，B原子在具有点缺陷的SiO_2中形成各种稳定和亚稳定的几何构型，这取决于它的电荷状态和周围环境。当B在SiO_2中存在O间隙时，B原子与O间隙形成一个非常稳定的B-O络合物，其中B原子与O间隙结合。我们还发现，在氧物种存在下，B原子从Si衬底扩散到SiO_2层中。一旦B-O复合体 关于我们 形成时，B原子通过SiO_2网络扩散，保持了这种B-O单元，其活化能出乎意料地小，为2.1-2.3 eV，很好地再现了实验。此外，由于B原子取代了SiO_2中的Si原子，B-O络合物可以看作是B_<Si>-Si-O络合物的络合物。因此，通过SiO的存在，可以期待B的扩散得到促进。由于已有文献报道Si/SiO_2界面附近SiO含量高，因此我们的结果暗示在Si/SiO_2界面附近会促进B的扩散。这些结果与随后的西姆斯实验密切相关，即在Si/SiO_2界面附近观察到高的Si自扩散系数。(2)考虑到Si/SiO_2界面处生成的SiO分子扩散到SiO_2中对Si和SiO_2的同时扩散的影响，建立了Si在热生长SiO_2中的同时扩散模型。在此基础上，我们模拟了共注入Si在SiO_2中的二次西姆斯实验<30><28>，结果表明，在高SiO含量的界面附近有高的扩散系数。实验结果进行了模拟的同时扩散方程，假设的扩散率的SiO，这提高了Si的扩散率。结果表明，SiO_2中的Si原子通过Si/SiO_2界面生成的SiO进行相关扩散。少

In this research project, we have intensively studied the atomistic process in SiO_2 and at Si/SiO_2 interfaces, by using first principles calculations, macroscopic simulations and secondary ion mass spectroscopy (SIMS) experiments. We have investigated the effect of Si/SiO_2 interface reactions to impurity diffusion and Si self-diffusion in and at Si/SiO_2 interfaces by first principles calculations and by simultaneous diffusion equations. As a result, we have obtained the following remarkable results.(1) We investigated the diffusion mechanisms of boron in SiO_2. We find that a B atom forms various stable and meta-stable geometries in SiO_2 with point defects, depending on its charge state and surrounding environments. In the case of B in SiO_2 with an O interstitial, a B atom forms a very stable B-O complex in which the B atom is bound to the O interstitial. We also found that B atoms diffuse from Si substrates into SiO_2 layers under the existence of O species. Once the B-O complex … More is formed, the B atom diffuses via the SiO_2 network keeping this B-O unit with unexpectedly small activation energies of 2.1-2.3 eV that well reproduce experiments. Moreover, B-O complex can be regarded as the complex of B_<Si>-Si-O complex, since it is believed that B atoms substitute Si atoms in SiO_2. Accordingly, B diffusion are expected to be promoted by the existence of SiO. Since it has been reported that SiO content is high near Si/SiO_2 interfaces, our results imply that B diffusion will be promoted near Si/SiO_2 interfaces. These results are intimately related to the following SIMS experiments that high Si self-diffusivity is observed near Si/SiO_2 interfaces.(2) Simultaneous diffusion of Si 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 diffusion. Based on the model, we simulated experimental SIMS profiles of co-implanted ^<30>Si in ^<28>SiO_2, which show high diffusivities near the interface that is supposed to have high SiO content. The experimental results were simulated by simultaneous diffusion equations, assuming that the diffusivity of SiO, which enhances the diffusivities of Si. The present result indicates that Si atoms in SiO_2 diffuse correlatively via SiO generated at Si/SiO_2 interfaces. Less