微波電漿化學氣相沈積法合成鑽石於多晶矽基材之研究

Abstract

本實驗以微波電漿化學氣相沈積法合成鑽石於多晶矽基材上，探討多晶矽基材方位對鑽石沈積的影響。藉先進的分析技術: XRD、SEM、AFM、EDS、FIB、TEM、EBSD與Raman spectroscopy 分析試片的方位與沈積鑽石形貌、密度、組成、粗糙度與界面層的探討。負偏壓時相同甲烷濃度下鑽石密度由高至低在不同方位基材上依序是: Si(100)>Si(110)>Si(111)，且負偏壓時甲烷濃度的變化對鑽石形貌的影響不大，影響較大的是成核密度。以AFM檢測鑽石連續膜在不同矽方位上的粗糙度，發現鑽石膜在不同方位基材上粗糙度由高至低依序是: Si(111)>Si(110)>Si(100)。以拉曼光譜儀檢測不同方位上的鑽石膜品質，發現在靠近Si(100)上沈積之鑽石膜品質最差，而品質最佳的則是沈積在靠近Si(111)方位的基材上。以TEM觀察界面層，發現高甲烷濃度(2.4% CH4 ; 負偏壓 35 分鐘 )下，連續膜內鑽石與不同方位基材的界面存在碳化矽層。低甲烷濃度(2% CH4 ; 負偏壓 30 分鐘 )下，界面並無中間層存在。以單一個試片配合最先進分析設備，同時獲得客觀且完整的資訊，這是本實驗最大的目的。

In this work, diamond was deposited on mirror-polished poly-silicon substrates by microwave plasma chemical vapor deposition using gas mixtures of methane and hydrogen. The poly-silicon substrate consists of micrometer-sized grains of characteristic morphologies in petal-like shape which contains various orientations. Using scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD), diamond deposition on individual Si grains with different orientations can be identified. Also, x-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, focused ion beam method (FIB), and transmission electron microscopy (TEM) with selected area diffraction were used to characterize correlation of deposited diamond crystallites with orientations of silicon grains.

From examinations of SEM with EBSD, it is found that the diamond nucleation density is strongly influenced by the Si orientations. The diamond nucleation density is highest ( ~ 108 cm-2) when the Si grains are oriented close to <100>, which is about one order of magnitude higher than on those close to <110> and <111>. In bias stage, two different methane concentrations were used. The result shows the nucleation densities are affected by the Si orientations in the same tendency mentioned above, suggesting that the orientation effect of Si grains is not closely related with methane. Using FIB, the diamond crystallites on the Si grains which had been identified by EBSD could be precisely cut for TEM observations. It shows that SiC exists between diamond and silicon at high methane concentration(2.4% CH4 in bias process), while low methane concentration (2% CH4 in biasing process) would not result in formation of SiC at the interface between diamond and silicon. Planar defects such as twin and stacking faults which intersect with the surfaces of differently oriented silicon grains have a negligible effect on diamond nucleation. Hydrogen plasma in the initial stage of deposition process resulted in significant etching on the surface of Si (001) oriented grains. Such a rough surface might enhance diamond nucleation.