Development of CO2 gas-assisted micro embossing process

傳統微熱壓製程需先將塑膠基板加熱到玻璃轉移溫度（Tg）之上，再以表面有微結構的母模加壓，接著降至室溫脫模取出成品；如此升降溫不僅耗時，且塑膠基板會因熱脹冷縮，尺寸精度受影響，並有殘留內應力。而加壓方面，藉壓板機構加壓，壓力分佈不均，複製面積及精度都受限，也無法以脆性材料（如矽晶圓、石英玻璃）作模具。 為了解決上述傳統微熱壓製程的缺陷，本研究提出以高壓CO2氣體來塑化塑膠基板，降低成型溫度，並利用氣體等向、等壓之施壓特性來進行壓印，可將大面積母模上的微結構在低於Tg的成型溫度，完整轉印至塑膠基材上。 實驗結果顯示，CO2氣體輔助微熱壓製程可在低於塑膠玻璃轉移溫度（Tg），完整複製出微結構。且壓印塑膠成品殘留應力極低。對於轉印次微米深度之微結構，在常溫下（23℃），即可達完整轉印；轉印較深之微結構，可藉著提升製程溫度與滲入壓力，成功轉印微結構。 本研究進一步將所開發的壓印製程，應用於增亮膜、導光板、光碟片、微透鏡、Fresnel lens、微流道等微結構元件複製，成功的將模具之微結構均勻轉印至PMMA塑膠基材上，並將轉寫效果與傳統微熱壓製程作比較，突顯本製程的優勢所在。In conventional hot embossing, the polymer substrate is first heated to a temperature higher than its glass transition temperature(Tg); the substrate and the stamp are then brought into contact and are compressed directly by the hot plates. The accuracy and area of replication are limited due to the inherent non-uniform pressure distribution of the hot-plate compression. Besides, materials such as Si-wafers and glass are too brittle to be used as the embossing molds in the conventional hot embossing operation. This paper reports the development of a CO2–assisted embossing process. Since CO2 is a good solvent for polymers such as PMMA, it can serve as the plasticizing agent to soften the substrate; the embossing temperature can be operated below Tg, even at room temperature. Furthermore, CO2 is used as the pressing medium. The distribution of gas pressure is uniform, the process is advantageous to large-area imprinting. The Si and glass-based materials can be used as embossing mold. The results show that patterns can be transferred onto the surface of polymer substracts with low pressure at a temperature below Tg. The low-temperature and low-pressure imprinting can reduce residual stress and shrinkage of the embossed substrates. The sub-micron patterns can even be transferred onto the surface of polymer substracts at room temperature﹗ For replicating microstructure with deeper patterns, higher temperature and absorption pressure are needed. In this study, the CO2-assisted embossing method has been successfully employed to fabricate optical components including brightness enhancement film, light guiding plate, VCD micro-patterns, micro lens arrays, and Fresnel lens. CO2-assisted micro-embossing has been proven to be an effective and efficient process for replicating microstructured-parts with low residual stress at low-temperature and with low-pressure.第一章 導論1 1.1 前言1 1.2 傳統微熱壓成型1 1.3 傳統微熱壓的問題2 1.4 流體微熱壓成型3 1.5 CO2氣體（溶劑）用於低溫塑化塑膠材料4 1.6 研究動機及目的5 1.7 研究重要性與具體研究方向5 1.8 論文架構6 第二章 文獻回顧22 2.1 塑膠微熱壓成型文獻22 2.2 奈米壓印技術文獻24 2.3 CO2氣體輔助微熱壓成型文獻26 2.4 流體微熱壓製程 29 2.5 綜合歸納29 第三章 實驗設置與實驗方法36 3.1 實驗設備36 3.2 實驗方法44 3.3 本章結論46 第四章 製程參數之實驗結果與討論62 4.1 探討CO2氣體輔助微熱壓製程於常溫下之成型能力62 4.2 製程參數對微結構成型性探討66 4.3 CO2氣體輔助微熱壓製程應用於軟模壓印實驗69 4.4 CO2氣體輔助微熱壓製程缺陷及解決之道70 4.5 本章結論74 第五章 CO2氣體輔助微熱壓製作增亮膜元件98 5.1 增亮膜元件的應用與製作方法98 5.2 CO2輔助微熱壓製程製作增亮膜元件99 5.3 製程操作窗繪製 102 5.4 製程應用於其它微結構元件複製103 5.5 本章結論104 第六章 結論與未來研究方向123 6.1 結論123 6.2 未來研究方向124 參考文獻126 附錄A 表面輪廓儀量測圖133 附錄B 個人著作15