分子束磊晶成長鉍薄膜的分析與製程

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、輕摻雜矽基板以及二氧化矽/矽(SiO2/Si)三種基板上，同時成長出鉍(Bi)奈米線，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。透過改變成長時基板溫度、鉍靶材溫度、成長時間以得到接近單晶的鉍(Bi)薄膜。 我們初步掌握到成長成單晶鉍(Bi)薄膜的條件。當基板溫度為 100℃、靶材溫度為 600℃、成長時間為 20 分鐘時，鉍薄膜在高解析X射線繞射儀(HRXRD)出現的鉍(Bi) (0003) 面訊號有著最小的半高寬(FWHM)。我們也進行原子力顯微鏡(AFM)量測表面粗糙度，在此成長條件下同時有著最平整的表面，粗糙度(RMS)為 1.531 nm。 另外，我們也將成長於二氧化矽/矽(SiO2/Si)基板上的鉍(Bi)奈米線挑起，利用穿透式電子顯微鏡(TEM)分析晶格、成長方向，其中藉由選區電子繞射圖(SAED pattern)觀察發現鉍(Bi)奈米線有著一致的成長方向為[11-20]。 我們為了觀察鉍薄膜從半金屬特性到半導體特性的轉變，發展一套可控制的乾式蝕刻技術。我們使用反應式離子蝕刻機(RIE)，使用的氣體為三氟甲烷(CHF3)，並且得到一個可控制的蝕刻速率，蝕刻速率為 0.425 nm/s 成功製作出小於 10 nm 的鉍(Bi)薄膜，且藉由原子力顯微鏡(AFM)量測可驗證此乾式蝕刻技術不破壞鉍薄膜的表面結構。 此外本論文藉由黃光微影技術、電子束蒸鍍技術、以及上述的反應式離子蝕刻(RIE)技術在鉍薄膜上製作出電性量測結構，並藉由傳輸線模型(Transmission line model, TLM)、霍爾量測(Hall bar measurement)量測分析得到鉍薄膜的基本電特性，我們也利用I-V量測分析鉍/矽基板的接面性質，最後並藉由反應式離子蝕刻(RIE)將鉍薄膜減薄，觀察其電阻率隨厚度的變化。

In this dissertation, Molecular beam epitaxy (MBE) system was used to grow Bi films on heavily doped, lightly doped Si substrates and SiO2/Si substrates , and Bi nanowires were grown at the same time. We used high resolution X-ray diffraction (HRXRD), X-ray reflectivity (XRR), transmission electron microscope (TEM), scanning electron microscope (SEM), and atomic force microscopic (AFM) to measure and analyze the Bi film and nanowires. By changing the substrate temperature of growth time, effusion cell temperature, a Bi thin film close to a single crystal was obtained. When the substrate temperature was 100°C, the effusion cell temperature is 600°C, and the growth time was 20 minutes, we believed that this was a great condition for growing a single-crystal Bi thin film. Under this growth condition, the HRXRD measurement shows only the Bi (0003) peak and have the smallest FWHM. We also perform AFM to measure the surface roughness. This growth condition had the flattest surface with a roughness (RMS) of 1.531 nm. In addition, we also picked up Bi nanowires that grown on a SiO2/Si substrate and analyzed the lattice and growth direction using a transmission electron microscope (TEM). The observation of the SAED pattern revealed that the Bi nanowires had a consistent growth direction [11-20]. We developed a controlled dry etching technique in order to observe the transition of the Bi film from a semimetal property to a semiconductor property. We used the RIE machine and the gas used was CHF3. The etching rate was 0.425 nm/s. We successfully produced the Bi film that less than 10 nm, and by AFM measurements, can verify that this dry etching technique didn’t not damage the surface structure of the Bi film. In this paper, an electrical measurement structure was fabricated on a Bi film by photolithography technique, electron beam evaporation technique, and reactive ion etching (RIE) technique described above. The basic electrical properties of the Bi film was measured by the transmission line model (TLM) and Hall bar measurement. We also used the IV measurement to analyze the junction properties of the Bi/Si substrate. The Bi film was thinned by reactive ion etching (RIE) to observe the change in its resistivity.