應用實驗設計法與電漿診斷技術探討電漿沉積氟碳膜製程之研究

The Investigation of Process-structure-property Relationship of Plasma Deposited Fluorocarbon Films Using Design of Experiment and Plasma Diagnostics

劉志宏(Chi-Hung Liu)

指導教授 ： 魏大欽

中原大學/工學院/化學工程研究所/博士(2006年)

https://doi.org/10.6840/cycu200500785

摘要

氟化非晶碳膜（氟碳膜）因具極佳之物理及化學特性而廣受產學界之重視。本論文乃以電漿輔助化學氣相沉積法來製備氟碳膜，研究中藉由實驗設計法、電漿診斷技術及膜材特性分析來獲得電漿製程參數、膜材特性及電漿性質三者間相互關係，其重要研究結果如下：
應用實驗設計法探討CH2F2/CF4電漿製程參數對其製備氟碳膜性質影響發現，CF4流量及沉積溫度為影響成膜速率及膜材折射率最顯著之因子。高沉積速率可於適當CF4流量、低溫及高功率中獲得；高CF4流量、低溫及適當電漿功率條件可製備具低折射率的氟碳膜。高膜材F/C比具低折射率特性，但其熱穩定性表現較差；然而，熱穩定性可由沉積溫度提高及熱處理步驟進行改善。氟碳膜之F/C比可間接由FTIR及膜厚關係進行預測。此外，藉由參數改變及其對應膜材特性之分析數據，吾人建立電漿氟碳膜之可能成膜機制。
藉由電漿性質量測與膜材特性分析結果的交叉比較，發現隨電漿功率上升其電漿密度隨之增加亦進而提升沉積速率；隨著CF4含量（CH2F2/CF4 Plasma）提升因H原子來源相對降低，而造成沉積速率因而下降，但其薄膜氟碳比則隨CF4增加呈現上升趨勢。於氟碳電漿其它電漿性質分析中發現，低電漿功率與高操作壓力製程下具有較高的陰電性，且CH2F2亦屬高陰電性之氣體。
以C7系列氟碳單體（C7F8、C7F14及C7F16）進行電漿沉積氟碳膜之研究發現，於不同成膜先驅物鍍膜製程中其成膜速率皆隨沉積溫度提高而降低，且具芳香環或環狀結構之單體有較高沉積速率；於薄膜折射率探討中，其值隨基板溫度提高而上升。具芳香環結構之氟碳膜有較佳熱穩定性呈現，而以單體C7F8並於沉積溫度條件400℃下可獲得熱穩定性高達450℃之電漿氟碳膜；此外，由膜材性質量測發現，熱穩定性的提升可經由高沉積溫度及降低F/C比方式達到，亦可由成膜先驅物鍵結型態的選定來獲得改善。
以L-shape反應器（單體為C7F8）製備含芳香環結構之電漿聚合氟碳膜之研究顯示，單體由後輝光區導入之downstream製程的成膜速率較單體由電漿區上游導入之upstream製程為快；然而，於upstream製程中可獲得低折射率與高氟碳比之氟碳膜。於FTIR及XPS數據中，downstream製程條件下之膜材仍可保有原單體官能基（即aromatic ring structure）；此外，在光學性質測試發現，downstream製程下獲得的氟碳膜具有發藍光特性，且製程中產生的氟碳球具有超疏水性質（接觸角達153o）。

關鍵字

實驗設計法 ； 氟碳比 ； 氟碳膜 ； 超疏水膜 ； 電漿鍍膜 ； 陰電性 ； 電漿診斷 ； 發光性膜材

並列摘要

Fluorinated amorphous carbon (a-C:F) films have attracted much attention in the last several decades due to their chemical stability, low surface energy, low refractive index, good electrical and thermal insulation. Plasma polymerization is one of the most popular techniques for obtaining a-C:F film with several favorable advantages such as a dry process and controlled thickness. The properties of plasma deposited a-C:F film are strongly affected by its chemical structure, which in turn, is strongly dependent on the plasma characteristics. However, few literatures reported the plasma characteristics and process-structure-property relationships of a-C:F film at the same time. In this study, the plasma diagnostics and experimental design methodology were used to characterize the plasma and elucidate the process-structure-property relationships of a-C:F film deposited in 13.56 MHz RF plasma reactor. The dissertator can be divided into four subjects and the results are summarized below.
Firstly, the experimental design methodology was used to investigate the influence of process parameters on the characteristics of fluorocarbon films deposited in CH2F2/CF4 plasma. It was found that the CF4 flow rate and substrate temperature were the most significant factors that affect the deposition rate and refractive index of the deposited film. A higher deposition rate was obtained in films deposited under moderate CF4 feed; lower substrate temperature and higher RF power conditions. The lower refractive index was obtained under higher CF4 feed; lower substrate temperature and moderate RF power conditions. It was also found that the fluorocarbon film with a higher F/C ratio was less cross-linked with a lower refractive index and less thermal stability. Potential reactions were proposed to explain the effect of process parameters on the film characteristics.
Secondly, the plasma diagnostics tools (including OES, Langmuir probe and QMS) were used to investigate the influences of operating parameters on the inductive-coupled CH2F2/CF4 plasma. It was found that CH2F2/CF4 plasma is highly electro-negative. The electron density increases with the increase of RF power, resulting in the enhancement of deposition rate. The dominant ion is CHF2+ for pure CH2F2 plasmas at low RF powers. As the input power is increased, abundant high-carbon ions are produced, C3H3F2+, C3H2F3+ and C3HF4+ ions being the dominant ones. Since the F/C atomic ratio is lower in C3 ions than in CHF2+, the F/C ratio of a-C:F film decreases as the power is increased. When 15% CF4 is added to CH2F2 plasmas, the dominant ionic species shifts to CF3+, and the most abundant C3 ions changes from C3H3F2+ to C3HF4+, which correlates to the experimental results that higher F/C ratio was found in films deposited in CH2F2 plasma with CF4 addition. Although the plasma density is not changed with increasing the CF4 flow rate, the dominant charged species become all perfluorocarbon ions when the feed contains 40% CF4, with the order of CF3+>C3F5+>C4F7+, which results in the decrease of deposition rate.
Thirdly, the aromatic C7F8, cyclic C7F14 and linear C7F16 monomers with Ar or H2 additive gas were used to deposit a-C:F film in a 13.56 MHz RF parallel plate plasma reactor. It was found that the deposition rate decreased with substrate temperature. The monomer contains unsaturated bonds had the highest deposition rate, especially the a-C:F film with F/C ratio higher than 0.8 could be obtained by C7F8/Ar plasma at 400℃ with a deposition rate of 35 nm/min. As the flow rate of hydrogen additive increased, the deposition rate increased at first, reached a maximum and then decreased in C7Fx/H2 process. But too much H2 addition dilutes the concentration of C7Fx monomers. The F/C ratio and refractive index were only slightly influenced by substrate temperature in C7Fx/Ar plasma polymer; however, they were significantly affected by substrate temperature in C7Fx/H2 plasma-deposited film. According to the FTIR and XPS spectra, the film possessed the aromatic-ring structure or the lower F/C ratio had the higher thermal stability. In addition, the TGA data indicated the thermal stability up to a temperature of 450℃ from the film deposited by C7F8 plasma at 400℃.
Finally, the aromatic C7F8 monomer was used to deposit a-C:F film in an RF plasma reactor. While keeping the argon gas inlet position fixed, the inlet position effect of the C7F8 monomer on the deposited a-C:F film characteristics was investigated. It was found that, when C7F8 entered upstream of the plasma, the deposited film possessed no aromatic structure and the deposition rate was low. The F/C ratio of the film was higher than 1.4, and the surface was smooth. For film deposited as the C7F8 entered in the afterglow (the so-called ‘downstream’ process), the deposition rate was quite high and copious amount of the aromatic structure were preserved. The F/C ratio of the film was lower than 1.0, and the surface was rough.

並列關鍵字

super-hydrophobic ； fluorocarbon film ； F/C ratio ； plasma deposition ； design of experimental ； emitting material ； plasma diagnostic ； electronegativity

參考文獻

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