Fabrication and characterization of atomic-step-free silicon/oxide interface by controlling step arrangement

我们研究了Si表面的台阶动力学、扫描隧道显微镜(STM)表征Si/SiO_2界面粗糙度的方法以及氧化过程中Si/SiO_2界面的粗化，以实现原子平坦和无台阶的Si/SiO_2界面。首先，利用高温扫描隧道显微镜，研究了邻近Si(113)表面刻面转变过程中的台阶动力学。我们阐明了台阶运动的驱动力，台阶运动在介观尺度上引起了相当大的形态变化。基于连续介质台阶模型，我们可以解释刻面转变中观察到的台阶网络的粗化现象。我们对台阶网络进行了数值模拟，表明连续介质台阶模型可以定量地再现复杂台阶构型的演化。其次，利用超高真空扫描隧道显微镜建立了亚纳米尺度的Si/SiO_2界面粗糙度表征方法。我们用原子分辨率实现了对界面形貌的STM观察，通过在高温下照射从STM针尖提取的场发射电子束来去除SiO_2覆盖层。利用这种方法，我们评估了湿化学法形成的化学氧化物和半导体工业过程中的热氧化物的界面粗糙度。结果表明，湿化学过程使热氧化物的界面粗化，界面粗糙度由氧化前的工艺决定。通过本研究得到的总体结果表明，控制Si衬底上的原子步骤以形成原子平坦的衬底对于制备原子平坦的Si/SiO_2界面是至关重要的。

We investigated the step dynamics on Si surfaces, the characterization method of Si/SiO_2 interface roughness by scanning tunneling microscopy (STM), and roughening of Si/SiO_2 interface during oxidations, in order to realize atomically flat and step free Si/SiO_2 interfaces. First, using high temperature STM, we studied the step dynamics during faceting transformation on vicinal Si(113) surfaces. We clarified the driving forces for step motion which causes considerable morphological changes in mesoscopic scale. We could interpret the observed coarsening of a step network in faceting transformation based on the continuum step model. We performed numerical simulations of a step network, demonstrating that the continuum step model can reproduce quantitatively the evolution of complicated step configurations. Second, we developed the characterization method of Si/SiO_2 interface roughness in sub-nanometer scale, using ultrahigh vacuum STM. We achieved STM observation of the interface morphology with atomic resolution, removing the SiO_2 overlayer by irradiating a field emission electron beam extracted from a STM tip at elevated temperatures. Using this method, we evaluated the interface roughness for chemical oxides formed by a wet chemical process and thermal oxides from semiconductor industrial processes. We showed that the wet chemical process roughen the interface morphology and the interface roughness of the thermal oxides is determined by the processes prior to the oxidation. Overall results obtained through this research indicate that control of the atomic steps on Si substrates to form atomically flat substrates is crucial, for fabrication of atomically flat Si/SiO_2 interfaces.