幾何與製程參數對於熱壓印製程製作微透鏡陣列的影響

Geometry and Process Effects on the Fabrication of Microlens Array by Thermal Imprinting Process

陳廉凱

指導教授 ： 宋震國

國立清華大學/工學院/動力機械工程學系/博士(2013年)

https://doi.org/10.6843/NTHU.2013.00328

摘要

在完全發展流理論為基礎之下，本論文利用模擬與實驗的方式來研究熱壓印製程配合微洞狀模具製造非球面玻璃微透鏡陣列。在模擬方面，為了分析微透鏡陣列的成型，本研究建構了一個物理模型，並利用有限元素分析軟體ANSYS與軟體內提供的141流體元素來模擬玻璃微透鏡的壓印過程與玻璃流的充填。在模擬的時候，模具被視為一個剛體，而玻璃材料加熱超過其玻璃轉換溫度時可視為一牛頓黏滯流體。為了了解製程參數與幾何參數對於微透鏡陣列壓印的影響，不同的壓印溫度630K與635K、不同孔徑的微洞狀模具50μm與100μm與不同穴寬節距比的模具0.5與0.25分別被模擬。最後由模擬的結果可知，壓印的溫度、微洞狀模具的孔徑與模具的週期都是影響玻璃微透鏡陣列壓印的重要參數。
在實驗方面，光學玻璃K-PG375(日本住田公司生產)被採用當做壓印的基板，並分別採用微電鑄技術與微鑽孔技術來製造實驗所需的微洞狀模具。之後利用實驗室自行開發的熱壓印設備進行直徑50μm與100μm微透鏡陣列的壓印實驗，而壓印完的試片透過3D雷射共軛焦顯微鏡、白光干涉儀與掃描式電子顯微鏡做透鏡表面形貌的量測。由實驗的結果說明了，使用同一副微洞狀模具配合不同的壓印參數是可以製作出不同焦距的微透鏡陣列，另外當微透鏡陣列的幾何尺寸愈小時也會增加壓印的難度，而這些實驗的結果與模擬做比較後，可看到兩者具有相近的趨勢。另外本研究也比較了不同製造技術所做出微洞狀模具的壓印結果(微電鑄技術與微鑽孔技術)，很明顯可以知道微鑽孔技術目前是不適合用來製作微洞狀模具，除非洞口邊緣嚴重的毛邊問題能夠被解決。最後，透過實驗的結果來分析壓印後微透鏡陣列的均勻性，小面積的壓印是可以得到絕佳的均勻性，因為壓力的分佈在微結構區域中央與邊緣部分的差異會比較小。
最後，為了提升本論文的品質以及將本研究的內容做一延伸，一些未來工作也在本文的最後一章節被提出來。本研究結合了有限元素法的分析與壓印實驗的探討，相信可以幫助我們深入的去了解製程參數的評估、玻璃微結構的成型能力、玻璃流的填充過程以及壓印後微透鏡陣列的均勻性。

關鍵字

玻璃 ； 微透鏡陣列 ； 熱壓印製程 ； 有限元素法

並列摘要

This thesis presents a simulation and experimental investigation focusing on the fabrication of aspheric glass microlens array using thermal imprinting process with micro-hole molds, and establishes a theoretical model based on the theory of fully developed flow. In the simulation, a physical model for analyzing the formation of microlens array was constructed. The commercial finite element software ANSYS with four-node 141 fluid elements was adopted to model the imprinting process of glass microlenses and represent the glass flow. The mold was viewed as a rigid body and the glass material was regarded as Newtonian viscous flow when heated over the glass transition temperature. In order to realize the process-parameter and geometry-parameter effects on the imprinting of microlens array, six types of cases were simulated, including different imprinting temperatures of 630 and 635 K, hole-diameters of 50 and 100 μm, and duty ratios of 0.5 and 0.25. The simulation results indicated that imprinting temperature, micro-hole diameter, and duty ratio were important parameters to influence the imprinting of microlens array.
In the experiment, K-PG375 was used as a glass substrate and micro-hole molds were fabricated by electroforming technology and precision micro-drilling. Some experiments were implemented by a self-developed thermal imprinting equipment, including the formation of microlenses with diameters of 50 and 100 μm. The imprinting results were analyzed by 3D confocal laser microscope, white light interferometer, and scanning electron microscope (SEM). The experimental results indicated that various focal lengths of microlens were obtained by using the identical micro-hole mold with specified imprinting conditions and the fabrication of small-size microlens array became difficult as the hole diameter gradually decreased, which showed good agreement with the simulation results. Additionally, comparing the imprinting quality by micro-hole molds fabricated using various technologies, such as electroforming technology and precision micro-drilling process, we can clear know that the micro-drilling process is unsuitable to fabricate micro-hole mold for the imprinting of microlens array unless the serious burr problem around the micro-hole can be resolved. In the analysis of uniformity, small-area imprinting can obtain excellent uniformity because the pressure distribution between the middle and border of micro-pattern area has a slight difference.
Ultimately, some future works were pointed out in order to enhance the quality of this thesis and extend this study. Combining the FEM analysis and imprinting experiments, this study can assist us in profoundly apprehending numerous issues, such as the estimation of process parameters, the formability of microstructures for glass material, the filling condition of glass flow, and the uniformity after imprinting.

並列關鍵字

Glass ； Microlens array ； Thermal imprinting ； Finite element method

參考文獻

[2] Lloyd R. Harriott, “Limits of Lithography,” Proceedings of the IEEE, Vol. 89 (2001), No. 3, pp. 366-374.

[4] Y. Hirai, K. Kanakugi, T. Yamaguchi, K. Yao, S. Kitagawa, and Y. Tanaka, “Fine pattern fabrication on glass surface by imprint lithography,” Microelectronic Engineering, Vol. 67-68 (2003), pp. 237-244.

[5] Y. Saotome, K. Imai, and N. Sawanobori, “Microformability of optical glasses for

precision molding,” J. of Materials Processing Technology, Vol. 140 (2003), pp. 379-384.

[6] T. Yamaguchi, K. Yao, T. Kanakugi, S. Kitagawa, and Y. Hirai, “Fabrication of Micro Optical Elements on Glass Surface by Imprint Lithography,” Proceeding of SPIE, Vol. 5183 (2003), pp. 163-171.