以電漿表面改質技術於可撓式塑膠基板上製備多功能性薄膜之研究

A study of Multifunctional Thin Films Prepared on Flexible Plastic Substrates using Plasma Surface Modification Technique

吳政洋(Cheng-Yang Wu)

指導教授 ： 劉代山

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/博士(2012年)

摘要

本論文內容主要分為四個部份，第一部份為於可撓式基板上進行表面改質層沉積，第二部份為增強硬化膜沉積於可撓式塑膠基板上的附著度，第三部份為改善可撓式塑膠基板的水氣阻障性能，第四部份為有機/無機多層阻障結構於可撓式基板上之應力控制。
在本論文第一部份，利用電漿增強化學氣相沉積法，使用四甲基矽烷與氧氣混合氣體為源材料，在可撓式塑膠基板上進行表面特性改質，沉積出具有含矽薄膜材料。研究結果顯示，表面濕潤性與薄膜內之碳-氫及氫氧相關的化學鍵結有著密切的關聯。當外加一氧氣反應物於電漿內進行輝光放電時，所沉積的薄膜內具有無機的矽-氧-矽結構的存在，能明顯地增加塑膠基板的硬度。而隨著機械硬度的改變，也亦將影響無機氧化矽薄膜的表面均勻性，在沉積期間當氧氣離子轟擊增大時，則會使得薄膜的表面均勻性降低。除此之外，當增加混合氣體內之氧氣反應物時，所沉積的薄膜內之氧對矽原子比成比例的上升，反之則造成光學折射率的降低。另外，藉由四甲基矽烷與氧氣混合氣體為源材料所沉積的硬化膜能有效地減低塑膠基板對於水氣的滲透特性，且於適當的氧氣離子轟擊下所沉積出具有高堆積密度的薄膜可以達到較低的水氣滲透率。
在本論文第二部份，利用電漿增強化學氣相沉積法，使用相同的有機矽基前驅物為源材料，製作出一介面緩衝層以改善硬化膜與可撓式塑膠基板間的附著度特性。研究結果顯示，藉由刮痕測試標準進行方格測試來評估薄膜的附著度情形中可以發現，當沉積一介面緩衝層時，硬化膜在聚碳酸脂及聚甲基丙烯酸甲酯基板上之附著度等級為5B（未剝落），具有良好的附著度特性。且從利用刮痕測試來量測薄膜之附著力中也可發現，隨著薄膜附著度的改善，能使得薄膜之臨界負載提升，同時具有優異的附著度特性之硬化膜結構也亦可減低薄膜內之殘留應力。而造成附著度改善的機制是歸因於緩衝層內具有碳-氫及矽-碳化學鍵結，碳-氫鍵結為疏水基團，在沉積時可以減少污穢的吸附，且矽-碳鍵結屬於交聯性的結構，可以補償存在於氧化矽硬化膜內較大的張應力。此外，由於此一介面緩衝層在硬化膜與基板界面間的接觸面呈現緊密的接觸，使得薄膜具有優異的附著度特性。
在本論文第三部份，利用電漿增強化學氣相沉積法，分別使用四甲基矽烷單體及四甲基矽烷與氧氣混合氣體為源材料，在聚對苯二甲酸乙二醇酯基板上連續沉積有機矽基/氧化矽多層阻障結構。研究結果顯示，首先藉由優化於聚對苯二甲酸乙二醇酯基板上所沉積的氧化矽薄膜厚度，可以獲得良好的水氣阻障特性，同時也能擁有最佳的表面均勻性及矽-氧-矽結構的等級。當於氧化矽薄膜與聚對苯二甲酸乙二醇酯基板間沉積一適當厚度之有機矽基薄膜時，能進一步地改善其水氣滲透率。而造成有機矽基/氧化矽阻障結構之水氣滲透特性改善的機制是歸因於有機矽基薄膜能夠釋放存在於阻障結構內之殘留應力，同時亦造成氧化矽薄膜的緻密性及結構品質獲得改善。因此，利用電漿增強化學氣相沉積法並使用相同的單體前驅物，在聚對苯二甲酸乙二醇酯基板上沉積六對有機矽基/氧化矽多層阻障結構時，其水氣滲透率低於1 × 10-2 g/m2/day，可達到商用水氣滲透率機台的量測極限。
在本論文第四部份，利用調變有機矽基薄膜厚度來控制藉由電漿增強化學氣相沉積法所製作之有機矽基/氧化矽多層阻障結構的殘留應力。研究結果顯示，結構品質、附著度性能及水氣滲透特性與阻障結構之殘留應力有著密切的關聯。藉由仔細地控制有機矽基薄膜厚度，有利於減低阻障結構內表面缺陷的形成。而當利用電漿增強化學氣相沉積法，在聚對苯二甲酸乙二醇酯基板上連續沉積三對有機矽基/氧化矽多層阻障結構時，其水氣滲透率可低於1 × 10-2 g/m2/day。

關鍵字

電漿表面改質 ； 電漿增強化學氣相沉積 ； 四甲基矽烷 ； 濕潤性 ； 硬化膜 ； 水氣滲透率 ； 附著度 ； 可撓式塑膠基板 ； 介面緩衝層 ； 有機矽基/氧化矽多層阻障結構 ； 殘留應力

並列摘要

This thesis mainly consists of four parts: (1) Surface modification layer deposition on flexible substrates; (2) Adhesion enhancement of hard coatings deposited on flexible plastic substrates; (3) Improvement in water vapor barrier performance of flexible plastic substrates; (4) Stress-controlled organic/inorganic multilayered barrier structure on flexible substrates.
In the 1st part of this thesis, silicon-containing thin films were synthesized from a tetramethylsilane (TMS)–oxygen gas mixture by plasma-enhanced chemical vapor deposition (PECVD) to modify the surface properties of a flexible plastic substrate. The surface wettability was strongly correlated with the presence of hydrocarbon- and hydroxyl-related bonds in the films. The presence of inorganic Si-O-Si networks in the deposited film, originating from an additional oxygen reactant in the glow discharge, significantly increased plastic substrate hardness. Surface uniformity of the inorganic silicon oxide (SiOx) film varied with mechanical hardness. All such properties were degraded by increased oxygen ion bombardment during the deposition. Additionally, the atomic ratios of O to Si in the deposited films increased at a rate proportional to the oxygen reactant in the gas mixture and brought about a reduction in the optical refractive index. The hard coatings prepared using the TMS–oxygen gas mixture effectively reduced the permeability of the plastic substrate to water vapor. A low water vapor transmission rate (WVTR) was achieved using the film with a high packing density under adequate oxygen ion bombardment.
In the 2nd part of this thesis, an interfacial buffer layer has been developed to improve the SiOx hard coating adhered to a flexible plastic substrate through a consecutive PECVD process, using the same organosilicon precursor. The adhesion of the hard coating structure, correlated with the buffer layer thickness, was rated by the standard tape-peeling test. An excellent adhesion (rank 5B) was available for the hard coating structure with an interfacial buffer layer deposited on polycarbonate and polymethylmethacrylate substrates. The degree of adhesion strength for the hard coating structures was measured by the standard scratch test. The increase in the critical loads determined from the scratch test was well correlated with the tape-peeling test results. The hard coating structure showed excellent adhesion and also corresponded to a minimum residual stress. The mechanisms responsible for the adhesion enhancement were linked to the specific chemical bonds of the hydrocarbon C-H bond, and cross-linking Si-C bond appeared in the interfacial buffer layer. The C-H bond was recognized as a hydrophobic group that was favourable for minimizing the adsorption of ambient contaminants potentially arising during deposition, while the cross-linking Si-C bond functioned to compensate the large tensile stress residing in the SiOx hard coating. As a consequence, a close contact and progressive morphology resulting in excellent adhesion were observed at the interface of the hard coating structure with an interfacial buffer layer.
In the 3rd part of this thesis, an organosilicon/SiOx multilayered barrier structure was consecutively deposited onto the polyethylene terephthalate (PET) substrate by PECVD using TMS monomer and TMS-oxygen gas mixture, respectively. The thickness of the SiOx film directly deposited onto the PET substrate was firstly designed to perform the best barrier property to water vapor permeation, which also possessed the optimal surface uniformity and Si-O-Si structural order. By insetting an adequate thickness of the organosilicon layer plasma-polymerized from TMS monomer between the SiOx film and PET substrate, the WVTR was further improved. The mechanism responsible for the enhancement of the organosilicon/SiOx barrier structure to water vapor permeation was ascribe to be the inset organosilicon layer was able to release the internal stress resided in the barrier structure, resulting in the improvement on the densification and structural quality of the SiOx barrier film, as observed from the surface morphology observation and determined by the chemical bond configurations. Accordingly, low water vapor permeation below the MOCON detection limit (< 1 × 10-2 g/m2/day) was achievable from the PET substrate coated with the 6-pairs of the organosilicon/SiOx multilayered barrier structure by PECVD using the same monomer precursor.
In the 4th part of this thesis, the residual stress of the PECVD-deposited organosilicon/SiOx multilayered barrier structure was controlled by altering the thickness of the organosilicon layer. It was found that the structural quality, adhesion behavior, and vapor permeation were deeply correlated to the residual stress of the barrier structure. By carefully controlling the thickness of the organosilicon layer, which was beneficial to minimize the formation of the surface defects in the barrier structure, a WVTR value below 1 × 10-2 g/m2/day was achieved from a 3-pairs of organosilicon/SiOx multilayered barrier structure consecutively deposited onto the PET substrate by using PECVD.

並列關鍵字

Plasma surface modification ； plasma-enhanced chemical vapor deposition ； tetramethysilane ； wettability ； hard coating ； water vapor transmission rate ； adhesion ； flexible plastic substrate ； interfacial buffer layer ； organosilicon/silicon oxide multilayered barrier structure ； residual stress

參考文獻

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