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

(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. According 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^) than that at the interface which is characterized as containing a maximum amount of Si atoms in 1+ oxidation states (Si^) 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^ and 1.26×10^ 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.