電子迴旋共振電漿於本質矽薄膜沉積製程之研究

胡立成(Li-cheng Hu)

指導教授 ： 利定東

國立中央大學/工學院/機械工程學系/博士(2015年)

摘要

本研究整合Langmuir電漿探針、光放射光譜儀(Optical Emission Spectroscopy , OES)以及四極柱質譜儀(Quadrupole mass analyzer, QMS)等設備，並搭配磁化電漿模型修正、光化線強度測定(Optical Actinometry)以及電離能閥值質譜分析 (Threshold ionization mass spectrometry,TIMS)等方法針對電子迴旋(Electron cyclotron resonance,ECR)共振化學氣相沉積矽薄膜製程進行探討。本研究之主要目標係為理解在進行本質型矽薄膜沉積製程時，ECR電漿工作參數、電漿內部性質以及矽薄膜性質三者間之關聯，除分別量測電子溫度、電/離子密度、電漿電位等電漿物理性質以及自由基化學組成的改變外，再根據相對應之製程參數所生成之本質型矽薄膜之光敏感度、微結構因子以及氫含量等矽薄膜特性，建構工作參數、ECR電漿特性以及矽薄膜性質之關聯性與運作機制理論，改善矽薄膜結構性質、光敏感度與沉積均勻性。此外，電漿診斷方法以及不同設備間之相異結果也在本研究中被討論並說明，吾人發現：OES自由基光譜比值，確實可做為電子溫度趨勢的相對指標，然而, 在ECR-CVD電漿製程中，使用Hβ /Hα 較 Si/SiH 更為適當。此外，實時原位探針診斷需考量探針沉積物對量測結果的影響；ECR-CVD製程中，磁場所造成的陰影效應比過去文獻中所估計地更為嚴重。薄膜沉積速度不僅受到電子密度與電漿中矽薄膜前驅物(SiHx)濃度影響，事實上，在如ECR-VD等高表面能的環境下，矽薄膜生長速度受到電漿物理狀態所影響的程度，可能會大於過去研究的估計。在ECR-CVD製程中，微結構因子與TIMS定量計算所得之SiH2 /SiH3 自由基相對濃度趨勢高度吻合, 且R*在大部分的情況下皆與光敏感度呈正相關，故SiH2 /SiH3可作為未來製程中的薄膜品質預測指標，於higher silane不易觀測的時候，取代傳統HSRS (higher silane related reactive species)法。電漿均勻度大致等效於薄膜均勻度，薄膜性質多受電漿巨觀特性影響，無法依照電漿各點狀態作為連結依據。最終，吾人除成功整合電漿診斷工具與方法外，並發現由於檢測設備的功能侷限性，以及電漿的複雜性質，單一診斷工具容易造成誤判，因此整合Langmuir probe, QMS與OES進行電漿診斷確有其必要性。

關鍵字

電漿診斷 ； 本質型非晶矽薄膜 ； 電子迴旋共振電漿 ； 化學氣相沉積

並列摘要

In this study, we present the application of quadrupole mass spectrometry (QMS) with threshold ionization mass spectrometry (TIMS), optical emission spectroscopy (OES) with an actinometry method, and Langmuir probe (LP) as an integrated technique for in situ plasma characterization of the electron cyclotron resonance chemical vapor deposition (ECR-CVD) of hydrogenated amorphous silicon (a-Si:H). The main aim of this study was to determine the relationship among the process parameters, plasma characteristics, and thin film properties, including the microstructure parameter (R*), hydrogen content (CH), and a-Si:H film growth rate. The physical properties of plasma, such as the electron density (Ne), electron energy (Te), and sheath potential (Vs), were studied using an LP and OES. In addition to the general plasma properties, the ion density (Ni) and plasma electronegativity were examined. The results indicate the ECR plasma source has high potential for producing a high-quality a-Si:H film because of the availability of few high silanes (SinH2n+2, n>2); furthermore, the results indicate an obvious difference in the QMS analysis results between plasma and gas. Therefore, the consumption of parent molecules must be considered. The TIMS method was applied to estimate the relative concentration of ground-state silane radicals (SiHx, x < 4) and consumption of SiH4. The results indicate that, in addition to the degree of ionization, the consumption of SiH4 and Vs are key factors affecting the thin film growth rate. When microwave power density increases, the values of Ni, Ne, and Vs increase considerably, but the plasma electronegativity remains unchanged. Furthermore, we compared our results with the TIMS analysis reported by other authors and found that the ratio of SiH2 to SiH3 obtained using QMS and TIMS can be considered an indicator of film quality for R* in the ECR-CVD process.

並列關鍵字

Plasma diagnostics ； Intrinsic Amorphous Silicon Thin-Film. ； Electron cyclotron resonance plasma ； Chemical Vapor Deposition

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