超薄氧化矽層成長與熱脫附之研究-掃描探針顯微術的觀察

Abstract

本論文在Si(111)-7×7表面以775oC及850oC成長超薄氧化層(1-2原子層)，並利用熱脫附的方式，研究SiOx/Si(111)介面的結構。實驗方法是以825oC將氧化薄膜逐次熱脫附後，在室溫下以掃描穿隧顯微術(STM)或超高真空原子力顯微術(UHV-AFM)觀察樣品上的變化。實驗結果顯示，以775oC氧化樣品，隨曝氧量的增加，覆蓋率為1.2 ML至1.5 ML，熱脫附過程中所形成的空缺為隨機均勻出現，空缺的深度皆為單層原子高度(0.314nm)，且空缺會有聚合現象產生，STM下的影像氧化層厚度約為0.12 nm；以850oC氧化樣品，隨曝氧量的不同，覆蓋率為2.0 ML至2.2 ML，熱脫附形成的空缺為隨機但不均勻出現，出現的空缺為多層原子高度，STM下的影像氧化層厚度約為0.05 nm，UHV-AFM下的影像氧化層厚度則高達1.4 nm。由實驗中發現，曝氧量的改變與氧化薄膜的成長關係較不密切，而樣品氧化溫度則為成長氧化薄膜的主要因素。

We grew ultrathin oxide layers (about 1-2 atomic layers) on the Si(111)-7×7 surface, and studied the SiOx/Si(111) interfaces structure by means of thermal decomposition. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were used to investigate the surface morphology after ultrathin oxide layers had been partially desorbed on the SiOx/Si(111) surface upon annealing at 825oC. In the case oxide growth at 775oC, our results showed that voids of the grown 1.2 ML to 1.5 ML SiOx layers appears randomly and uniformly. The height of the voids is single atomic-deep (0.31 nm) and the apparent oxide thickness is only about 0.12 nm as observed by STM. For the ~2.0 ML SiOx/Si(111) surface prepared at 850oC, voids on the ultrathin oxide film appears randomly but not uniformly during the thermal desorption process. The height of the voids is multi-step height, and the apparent oxide thickness is approximately 0.05 nm as observed by STM and 1.4 nm by non-contact AFM. Our experiments also showed that the oxidation temperature is the major factor effecting the SiOx thickness at similar oxygen dosage.