Studies on Carrier Trap Levels at Ultrathin SiO_2/Si Interface and Its Relation with Microscopic Structures

(1)在900℃以下，氧化诱发应力使表面粗糙度增大。此外，在Si（100）上形成的氧化物的表面粗糙度与界面结构的周期性变化一致，以0.19 nm的厚度为周期振荡。(2) SiO_2/Si（100）界面粗糙度决定了界面状态。此外，还检测了与SiO_2/Si（111）界面结构相关的界面态。(3)价带键态与o2s核能级之间的能差比体SiO_2的相应能差大约0.2 eV。根据第一线原理分子轨道计算，这种差异可归因于SiO_2/Si界面附近的窄四面体键角约为135度。此外，在中间氧化态的Si原子定义的界面上，两种原子结构之间的价带偏移量相差约0.17 eV。根据第一性原理分子轨道计算，这种差异可以归因于界面上的界面偶极子较小，其特征是含有最多数量的3+氧化态Si原子（Si^<3+>），而界面上的界面偶极子通过退极化效应具有最多数量的1+氧化态Si原子（Si^<1+>）。(4)通过对Si 2p光电子在氧化硅中弹性散射和非弹性散射路径的蒙特卡罗计算，模拟氧化引起的光电子衍射图变化，发现总弹性散射截面为1.54×10^<-20>，总非弹性散射截面为1.26×10^<-20> m^2。(5)在相同的氧化条件下，氧化速率随氧化过程的进行而周期性变化，在特定的界面结构上明显降低。也就是说，氧化速率受SiO_2/Si界面结构的影响。少

(1) Below 900℃ the oxidation-induced-stress causes the increase in surface roughness. Furthermore, the surface roughness of oxide formed on Si (100) oscillates with period in thickness of 0.19 nm in accordance with periodic changes in the interface structures. (2) The interface roughness at SiO_2/Si (100) interface produces the interface states. In addition, the interface states correlated with SiO_2/Si (111) interface structures were detected. (3) The energy difference between the bonding states in the valence-band and the O 2s core-level is larger than the corresponding difference for the bulk SiO_2 by about 0.2 eV.According to a first-principle molecular orbital calculations this difference can be attributed to a narrow intertetrahedral bond angle of about 135 degrees near the SiO_2/Si interfaces. Furthermore, the valence-band offset differs by about 0.17 eV between the two types of atomic structures at the interface defined by the Si atoms in intermediate-oxidation states. Accordin … More g to a first-principle molecular orbital calculations this difference can be attributed to smaller interface dipole at the interface which is characterized as containing a maximum amount of Si atoms in 3+ oxidation states (Si^<3+>) than that at the interface which is characterized as containing a maximum amount of Si atoms in 1+ oxidation states (Si^<1+>) through the depolarization effect. (4) It was found from the Monte Carlo calculation of path of elastically and inelastically scattered Si 2p photoelectrons in silicon oxide for the simulation of oxidation-induced changes in photoelectron diffraction patterns that the total elastic scattering cross-section and the inelastic scattering cross-section are 1.54×10^<-20> and 1.26×10^<-20> m^2, respectively. (5) At the same oxidation condition the oxidation rate changes periodically with the progress of oxidation and decreases significantly at specific interface structures. In other words, the oxidation rate is influenced by the SiO_2/Si interface structures. Less