| 摘要: | 本篇論文是以電子迴旋共振化學氣相沉積法(Electron Cyclotron Resonance Chemical Vapor Deposition, ECR-CVD)於矽基板Si(100)上沉積高結晶率之鍺薄膜並探討薄膜特性。由於鍺材料相較於矽材料具有較高的載子遷移率和較小的能隙，因此常被利用在作用於紅外光波段的光通訊元件。又因鍺的晶格常數和高效率III-V族太陽能電池主要材料 – 砷化鎵較為匹配，因此鍺晶片常被使用為III-V族太陽能電池的基板。然而，鍺晶片的成本大約是矽晶片的四倍，為降低成本，於矽晶片上成長磊晶的鍺薄膜以取代原鍺晶片的基板之技術越來越受矚目。但因矽鍺異質磊晶會有晶格不匹配和熱膨脹係數差易所造成的缺陷，傳統製程多為600℃以上的高溫。而本論文是利用ECR-CVD，在180℃的低溫下，於矽晶片上成長高結晶鍺薄膜，並成功成長40 nm的磊晶鍺薄膜。
本文探討工作壓力、ECR共振區位置、微波功率、氫氣稀釋比、後退火溫度、後退火時間及厚度等參數對薄膜結構的影響，並利用電漿放射光譜儀以探測製程時的電漿光譜，利用橢圓儀、拉曼光譜儀、X光繞射儀及原子力顯微鏡等方法量測薄膜的厚度、結晶率、晶相及表面形貌等結構特性。實驗結果發現在微波功率700 W、主磁場電流55 A、工作壓力30 mTorr及氫稀釋比100的製程參數下，可以成功成長厚度40 nm的高結晶鍺薄膜，其Ge (400) 晶相X光繞射搖擺曲線之半高寬為4119 arcsec；當厚度增加至90 nm的薄膜，則為多晶結構，但仍擁有平整的表面(表面粗糙度為1.44 nm)。
In this research, we use the electron cyclotron resonance chemical vapor deposition (ECR-CVD) to deposit high-crystallinity germanium thin films on single crystal silicon substrate, and investigate the structural properties of the films. Because of the higher carrier mobility and the lower energy bandgap compared with Si, Ge is widely used for near infrared optical communication devices. Moreover, for the lattice constant of Ge matches that of GaAs, a common material for high efficiency III-V solar cell, crystal Ge is also used as the substrate of this kind of solar cell. However, the cost of crystal Ge is about 4 times higher than that of crystal Si, so in order to lower the cost, many researches have been doing efforts to grow high quality epitaxial Ge films on Si substrates to replace the crystal Ge substrates. Traditional methods to grow Ge on Si heteroepitaxy are usually at high substrate temperature (> 600℃), here, we present a new way to grow the Ge epilayers under low substrate temperature (180℃).
In this work, we use optical emission spectroscopy (OES) to monitor the plasma distribution when processing. The structural properties are measured and analyzed by spectroscopy ellipsometry (SE), Raman Spectrometer, and X-ray diffractometer (XRD), and atomic force microscopy (AFM). Without annealing, we can obtain a high-crystallinity structure in a 40-nm film with the full width at half maximum of Ge (400) XRD rocking curve of 4119 arcsec, and an 1.44-nm root mean square surface roughness in a 90-nm film. |
