四氟甲烷電漿非對稱性表面改質與圖案化之研究

溫俊祥(Chun-Hsiang Wen)

指導教授 ： 薛敬和

國立清華大學/工學院/化學工程學系/博士(2006年)

摘要

在使用射頻電漿對聚酯薄膜進行表面改質的研究當中，我們觀察到使用四氟甲烷氣體時，薄膜兩邊表面改質效果的變化趨勢並不相同，而且表面的親/疏水性質變化會有反轉的現象產生。但是使用氮氣、氧氣或氬氣作為處理氣體時，並未發現類似的現象。因此本論文利用不同的電漿源以進一步研究四氟甲烷氣體的電漿反應與表面性質變化的關係，並因而成功地發展出高分子薄膜的非對稱性表面改質與圖案化技術，利用該技術可以在高分子薄膜表面同步形成親/疏水表面性質，而且其間的水接觸角差異可達100度以上。
在使用射頻CF4電漿對聚酯薄膜的改質研究中，我們觀察到在陰極附近有較高的電漿輝光強度，此現象代表在陰極附近有較高粒子密度的活性物種。以XPS光譜、水接觸角、原子力顯微鏡分析處理後的聚酯薄膜表面，可發現氟原子被接枝在表面，並且在薄膜兩邊表面的F/C比值並不相同；此外，在薄膜兩邊表面的O/C比值也有變化，而且兩邊表面的粗糙度均呈現降低的趨勢。此結果顯示聚酯薄膜兩邊表面的親/疏水變化不一，主要是表面化學組成變化不同所致。文獻顯示CF4電漿中的活性物種，以氟原子自由基為主要的反應物種[57-60]，而且真空紫外光照射，可以促進含氟氣體[45-46]或含氟氣體電漿[64~65]對高分子材料的反應。因此我們推論非對稱性表面改質效果主要是CF4電漿氣氛的非對稱分佈所造成，而且其中的氟原子自由基與輝光中的真空紫外光是影響非對稱性表面改質的主要可能因子。
在微波CF4電漿對聚亞醯胺薄膜的改質研究中，薄膜以順流方式進行處理，也可以得到非對稱性表面改質效果，這顯示所見立的非對稱性表面改質技術並不具材料或設備依存性。分析CF4電漿輝光，可發現氟原子自由基在703.3 nm的放射波峰具有最高的強度，證實氟原子自由基是主要的活性物種。而且該放射波峰在薄膜與微波窗口之間的強度也明顯高於另一邊，顯示薄膜表面與CF4電漿的反應，在面對較高粒子密度的氟原子自由基的一面是以氟化反應為主，因此形成高F/C比值的疏水表面。反之另一面，則是以蝕刻反應為主，而所生成的高分子自由基，除了進行後續的高分子斷鏈或是交聯反應外，高分子自由基會進一步與大氣反應，氧化形成含氧原子的極性官能基。
在圖案化改質研究中，使用微波CF4電漿透過遮罩處理聚亞醯胺薄膜，當縮小遮罩與高分子薄膜表面之間的間隙時，遮蔽區表面性質會由疏水逐漸轉變成親水，而且此一轉變是在間隙接近或小於氟原子在該操作條件下的計算平均自由徑時開始發生。所以可推知在遮蔽區的侷限空間中，氟原子自由基的粒子密度確實低於無遮蔽區，並導致親水化的改質效果，而在無遮蔽區則仍是疏水化的改質效果，其間的水接觸角差異並可達100度以上。在聚亞醯胺薄膜表面所形成的圖案化親/疏水構造，後續再以無電電鍍的處理方法，可以在親水區表面牢靠地附著Sn/Pd觸媒，並使銅離子還原沉積形成銅線路圖案。
在圖案化改質研究中，另外使用MgF2鏡片搭配遮罩以進行CF4電漿改質，如此便可在相同氟原子自由基的粒子密度下，研究真空紫外光對改質反應的影響。結果顯示，在CF4電漿中，輝光中的真空紫外光對聚亞醯胺薄膜表面的CF4電漿反應的影響並不顯著，主要的影響因子為氟原子自由基的粒子密度。

關鍵字

電漿 ； 四氟甲烷 ； 表面改質 ； 非對稱性 ； 圖案化 ； 疏水 ； 親水

並列摘要

In the study using radio frequence (RF) plasma to modify the surface properties of polyester film, we observed that the variation trend in treatment effect was different between the two sides when used tetrafluoromethane as plasma gas. And the variation of surface hydrophilic and hydrophobic properties would reverse with treatment conditions. But this was not found when used nitrogen, oxygen, or argon as plasma gas. In this thesis, the further study used different plasma sources to establish the relationship between the CF4 plasma reactions and the varation of surface properties. Thus successfully develops the surface asymmetric modification and patterning technologies, and the hydrophilic and htdrophobic surface properties can be in-situ formed on polymer film surfaces, respectively. Whereas the water contact angle difference between different surfaces can be above 100 degree.
In the study of using RF CF4 plasma to modify polyester films, we had observed the plasma glow had a relatively high intensity nearby the cathode. This represents had a relatively high particle density of active species of CF4 plasma nearby the cathode. The treated PET film surfaces had been characterized with X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy. The analysis results showed that fluorine atoms were being grafted onto the surfaces, and the F/C ratios between the two sides were different. Besides, the O/C ratios also changed and were different between the two side surfaces, and both side surface roughness decreased. In literatures, the major reactive components of CF4 plasma are fluorine atomic radicals[57-60], and the vacuum ultraviolet irradiation may promote the reactions of fluorine-containing gas[45-46] or fluorine-containing gas plasma [64~65] to polymer materials. Therefore we propose that the surface asymmetric modification effect is mainly attributed to the asymmetric distribution of CF4 plasma atmosphere. Moreover, the fluorine atomic radicals and the irradiation of vacuum ultraviolet from plasma glow could be the key factors of the asymmetric surface modification.
In the study of surface modification of polyimide films by microwave CF4 plasma downstream treatment, the results showed that treatment effects were similar to the RF plasma treatment. This reveals that the surface asymmetric modification technique doesn’t have the material and the equipment dependency. In the analyses of microwave CF4 plasma glow, the fluorine peak with the highest intensity shows at 703.3 nm. This reveals that the fluorine atoms are the major reactive species in CF4 plasma. And the relative peak intensities of fluorine atoms between the film and microwave window is higher than another side. This result points out that the CF4 plasma reactions are dominated by the fluorination reactions at polymer surface facing to the high fluorine atomic radical density atmosphere, and thus formed a high F/C ratio hydrophobic surface. In another side, the plasma reactions are dominated by etching reactions, and the resulting product polymer radicals, except the following chain scission or crosslinking reactions, would further react with atmosphere and oxidize to form oxygen-containing polar functional groups.
In the study of surface patterning modification of polyimide films, CF4 microwave plasma treatment was carried on through a shadow mask. The surface property of masking region would gradually transform from hydrophobic to hydrophilic when the gap size is close to or below the calculated mean-free-path of fluorine atom. Therefore we can understand that the available fluorine atoms in the confined space between mask and polyimide film is limited and lower than the non-masking region, and thus resulting the hydrophilic and hydrophobic surfaces at masking and non-masking regions, respectively. Whereas the water contact angle difference between the two regions was above 100 degree. Followed by a typical electro-less plating process, Sn/Pd catalyst can be absorbed onto the hydrophilic region of the texturing polyimide film, and form copper circuits.
In this study, CF4 plasma treatment was carried on through shadow mask and MgF2 lens, thus the effect of vacuum ultraviolet could be studied under the same particle density of fluorine atomic radicals. The results showed that the influence of vacuum ultraviolet irradiation is not remarkable to CF4 plasma reactions at polyimide film surfaces. And the particle density of fluorine atomic radicals in CF4 plasma atmosphere is the key factors for the asymmetric surface modification and patterning technologies.

並列關鍵字

plasma ； tetrafluoromethane ； surface modification ； asymmetric ； patterning ； hydrophobic ； hydrophilic

參考文獻

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