鉍薄膜在多種減薄方法下的性質改變——形貌，晶格以及電學特性

Abstract

本論文利用分子束磊晶技術(MBE System)將鉍(Bi)薄膜成長於重摻雜、輕摻雜矽基板、二氧化矽/矽(SiO2/Si)基板以及使用原子層沉積的氧化鋁四種基板上，利用四種不同方法減薄鉍薄膜的厚度，並用高解析X射線繞射儀(HRXRD)、X射反射儀(XRR)、穿透式電子顯微鏡(TEM)、掃描式電子顯微鏡(SEM)、原子力顯微鏡(AFM)進行量測與分析。 我們發現以125倍水稀釋過後的稀硫酸可以較慢蝕刻鉍薄膜，初步研究了該溶液蝕刻鉍薄膜的機理，即會在晶界處較快蝕刻，因此較長蝕刻時間會帶來島狀形貌，使得遵循滲透理論(percolation theory)。 另外，我們首次應用紫外光臭氧氧化于減薄鉍薄膜厚度，我們找到了較適合的氧化溫度。氧化時間為一小時，高於120°c時，鉍就完全被氧化。我們發現在該條件下的氧化產物是氧化鉍以及氧化亞鉍。氧化過程中的鉍薄膜片電阻值呈現三個階段最終在固定溫度下達到飽和。同時，鉍的縱向側向氧化各向異性也與其結構特性相符。 接著我們研究了長在氧化層上鉍的性質，並利用等離子蝕刻(RIE)減薄其厚度，發現隨之出現的電場調控效應(Electric field effect)。該電晶體展現出電子導電的性質，初步計算出其遷移率最高可達486cm^2/(Vs)。 最後我們利用機械剝離法成功在300nm二氧化矽基板上撕出小於100nm的鉍薄膜通過TEM以及電子背向散射(EBSD)技術我們分析出垂直於基板的方向為(003)或(012)，我們還做出了在該基板上不同厚度鉍薄膜對應顏色的理論值。

In this thesis, the bismuth (Bi) film is grown on heavily doped, lightly doped ‎Silicon dioxide substrate, Silicon dioxide/ Silicon (SiO2/Si) substrate and ALD-grown aluminum oxide substrate by molecular beam epitaxy (MBE System). The thickness of the bismuth film is reduced by four different methods, and high-resolution X-ray diffraction (HRXRD), X-ray reflectometer (XRR), transmission electron microscope (TEM), scanning electron microscope (SEM), atomic force microscopy (AFM) is applied for measurement and material analysis during those reduction. Also, the electrical properties were checked. We found that sulfuric acid diluted with 125 times water can etch the bismuth film slowly. The mechanism of etching the bismuth film is preliminarily studied, that is, it will be etched faster at the grain boundary, so the longer etching time will bring island shape. And the conductivity followed the percolation theory. In addition, for the first time we applied UV-Ozone oxidation to reduce the thickness of the bismuth film and we found a suitable oxidation temperature. When the oxidation time is one hour, above 120°C, the bismuth is completely oxidized. We have found that the oxidation products under this condition are bismuth oxide and bismuth suboxide. The sheet resistance of the bismuth film during the oxidation process appears in three stages and eventually reaches saturation at a fixed temperature. At the same time, the longitudinal lateral oxidation anisotropy of bismuth is also consistent with its structural characteristics. Next, we studied the properties of bismuth thin film grown on the oxide layer and thinned its thickness by plasma etching (RIE) to investigate the electric field effect of it. The transistor exhibits the property of electronic conduction (N-channel FET), and a highest mobility of 486 cm^2/(Vs). Finally, we successfully used the mechanical exfoliation method to obtain a bismuth film of less than 100 nm on a 300 nm SiO2 substrate by Nitto tape. Using TEM and electron backscatter (EBSD) technics, we analyzed the direction perpendicular to the substrate follows (003) or (012). We also made theoretical values for the corresponding colors of the different thickness of the film on the substrate.