Kinefuchi Ikuya, Yamaguchi Hiroki, Sakiyama Yukinori, Takagi Shu, Matsumoto Yoichiro
Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
J Chem Phys. 2008 Apr 28;128(16):164712. doi: 10.1063/1.2905209.
Thermal decomposition of ultrathin oxide layers on silicon surface was investigated with temperature programed desorption. Oxide layers were formed on Si(100) at 400 degrees C by exposure to O(2) molecular beam. Desorption spectrum for oxygen coverages between 1.7 and 2.6 ML exhibits a single dominant peak with an additional broad peak at lower temperatures. The former peak corresponds to stable binding states of O atoms at dimer bridge sites and dimer backbond sites. The high peak intensity indicates that most O atoms are at stable states. The latter peak corresponds to an unstable binding state, where O atoms are presumably trapped at dangling bonds. The SiO desorption rate from the stable binding states is well described by Avrami kinetics, suggesting that the decomposition process is spatially inhomogeneous with void formation and growth. The rate-determining step is the reaction at void perimeter even if the overlap between voids becomes quite large. The Avrami exponents determined from our experiment indicate that the increase in the initial coverage makes the oxide layer more stable and suppresses the rate of void formation at the potential nucleation sites.
采用程序升温脱附法研究了硅表面超薄氧化层的热分解。通过暴露于O₂分子束在400℃下在Si(100)上形成氧化层。氧覆盖量在1.7至2.6 ML之间的脱附谱显示出一个单一的主峰，在较低温度下还有一个额外的宽峰。前一个峰对应于O原子在二聚体桥位和二聚体反键位的稳定结合态。高的峰强度表明大多数O原子处于稳定状态。后一个峰对应于不稳定的结合态，其中O原子可能被困在悬空键处。来自稳定结合态的SiO脱附速率可以用阿弗拉米动力学很好地描述，这表明分解过程在空间上是不均匀的，有空洞的形成和生长。即使空洞之间的重叠变得相当大，速率决定步骤仍是空洞周边的反应。从我们的实验中确定的阿弗拉米指数表明，初始覆盖率的增加使氧化层更稳定，并抑制了潜在成核位点处空洞形成的速率。
