氮氣在偏壓條件下對鑽石成核的影響

Abstract

本研究採用微波電漿化學氣相沈積法 （MPCVD），並輔以負偏壓（ Negative Bias） 於試片前處理，探討在加負偏壓下使用甲烷-氮氣混合 氣體在鑽石成核階段的影響。以及 在負偏壓下各種參數對於鑽石成核密 度的影響。希望對於負偏壓成核的機制有更進一步 的瞭解，並探討使 用甲烷-氮氣混合氣體成核的試片在鑽石成長階段的一些特性分析。 實驗結果顯示使用負偏壓成核技術對於不同的氣體源（甲烷-氮氣、甲烷- 氫氣）都 可以形成鑽石核，顯示只要使用碳氫化合物氣體源，於電漿 中加以負偏壓都可以將碳的 SP2鍵結轉化成鑽石的SP3鍵結。在改變負 偏壓的電壓值時，我們發現鑽石成核密度隨著 負偏壓升高而升高，但 是到了偏壓值為400V時，因為偏壓過高而導致電漿球局部放電而 導至 鑽石無法成核。造成鑽石成核密度隨著偏壓升高而升高的原因可能是電漿 中沒有足 夠的蝕刻物（氫原子）去除碳的SP2鍵結使鑽石能夠優先成核 。在負偏壓處理時間方面， 實驗結果顯示當處理時間為15分鐘時，試片 擁有最高的成核密度。而在改變甲烷濃度參 數時，成核密度似乎也是 呈現一個正比關係，但在高濃度時，試片表面會形成一層灰色 的非晶 形碳膜，並且非常容易去除，當去除這層碳膜後，成核密度在甲烷濃度 為21.6﹪ 時有最大值。X-光光電子儀(XPS, ESCA)顯示了在成核階段會 形成Si- C鍵結而有助於鑽 石的成核。 在成長階段我們分為兩個情況；高偏壓和低濃度甲烷與低偏壓和高濃度甲 烷。實驗結果 顯示在高偏壓時，無法形成具有良好結晶面的鑽石薄膜 ，鑽石品質較差，使用X光繞射 儀分析可得知在成核階段由於高偏壓 而造成了Si3N4的形成而影響了鑽石的品質，而在低 偏壓下，鑽石的品 質有明顯的提昇而X光繞射儀則偵測不到Si3N4 最後我們探討經偏壓成核後，在鑽石成長階段使用甲烷-氫氣系與甲烷-二 氧化碳系 反應氣體源時對其合成的鑽石膜品值的影響。實驗結果顯示 使用甲烷-二氧化碳氣體源的 鑽石品質高於甲烷-氫氣，其原因很可能是 二氧化碳分解反應後的氧原子及成核階段氮氣 原子之殘留所致。 The effect of diamond nuclei using CH4/N2 gas source in bias enhanced nucleation (BEN) was examined by microwave plasma chemical vapor deposition. Various parameters of bias condition will be discussed with diamond nucleation density. Attempts were made to understand more about the mechanism of negative bias enhanced nucleation, and to investigate the characteristics of diamond films using CH4/N2 gas mixture nucleation. The results indicated that diamond nuclei formed in different gas sources, such as CH4-H2, CH4/N2. It means that if the gas source contained hydrocarbon, adding negative bias in plasma can transform the carbon sp2 bonding to diamond sp3 bonding. Diamond nucleation density increases with an increasing bias voltage until 400 V. When the bias voltage increased to 400 V, plasma ball would locally arc to the substrate surface so that the diamond nuclei can't form. The reason of increasing nucleation density might be not enough etchant (H2 atom) to remove carbon sp2 bonding so it has enough diamond precursor. It has a maximum of nucleation density with bias treatment time at 15 min. When we change the methane concentration, nucleation density seems to have a direct relationship with methane concentration, but a high concentration caused to form an amorphous carbon thin film on the substrate and easy to remove. When we removed this thin film, we found the nucleation density decreases lightly and has a maximum at 21.6％. X-ray photoelectron spectroscopy (XPS, ESCA) shows a Si-C bonding to increase the diamond nucleation. Two conditions will be discussed in diamond growth step, high bias voltage and low methane concentration , low bias voltage and high methane concentration.The results indicated that it didn't formed a well-defined facets diamond films with high bias voltage, and a worse quality of diamond film, and X-ray diffraction pattern shows the formation of Si3N4 due to high bias voltage to effect the quality of diamond films. In low bias voltage, the quality of diamond films has a evident improvement, and no Si3N4 existed by X-ray diffraction. Finally we investigated the effect between using CH4-H2 and CH4- CO2 gas sources mixtures to deposited diamond films in growth step pretreated with BEN. The results indicated diamond quality using CH4-CO2 gas mixture is higher than CH4- H2. It might be caused by the oxygen atom decomposed from CO2 and nitrogen residue in BEN step.