Theoretical studies on the basic processes of Si thermal oxidation.

在本研究项目中，我们通过第一性原理计算、宏观模拟和二次离子质谱（SIMS）实验，深入研究了SiO_2和Si/SiO_2界面的原子过程。通过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Si/SiO_2界面内和界面处杂质扩散和Si自扩散的影响。结果，我们获得了以下显著的结果。(1)研究了硼在SiO_2中的扩散机理。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形状，这取决于它的电荷状态和周围环境。在含有O间隙的SiO_2中，B原子与O间隙结合，形成非常稳定的B-O配合物。我们还发现，在O的存在下，B原子从Si衬底扩散到SiO_2层中。一旦B- o络合物形成，B原子通过SiO_2网络扩散，使这个B- o单元具有意想不到的2.1-2.3 eV的小活化能，很好地再现了实验。此外，B- o配合物可以看作是B_<Si>-Si-O配合物，因为在SiO_2中B原子取代了Si原子。因此，SiO的存在有望促进B的扩散。由于已有报道表明Si/SiO_2界面附近SiO含量较高，我们的结果表明Si/SiO_2界面附近会促进B扩散。这些结果与随后在Si/SiO_2界面附近观察到高Si自扩散率的SIMS实验密切相关。(2)考虑了SiO分子在Si/SiO_2界面生成并扩散到SiO_2中促进Si在热生长SiO_2中的同时扩散的影响，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^<30>Si在^<28>SiO_2中共注入的实验SIMS剖面，在界面附近显示出高SiO含量的高扩散系数。同时利用扩散方程对实验结果进行了模拟，假设SiO的扩散系数增大，使得Si的扩散系数增大。结果表明SiO_2中的Si原子通过在Si/SiO_2界面上生成的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