軟模氣體熱壓應用於大面積微奈米壓印製程研究

Abstract

摘 要

本論文致力於大面積熱壓式微奈米壓印製程探討。當前的熱壓式壓印製程，有效壓印面積無法有效提升，主要原因在於施壓機構使用壓板，壓板施壓容易導致壓印力分佈不均；壓印模具若是屬於矽基底或玻璃基底模，容易發生破裂。而且當使用在奈米壓印時，由於阻劑塗佈層極薄（約數百奈米），有效的壓印面積往往受限於模具與基板之平坦度或壓印盤面之平坦度，這些常造成模具與基板間的接觸不完整。

本研究使用PDMS軟模並使用氣體施壓進行微奈米壓印。本研究第一部份比較PDMS軟模與矽模、鎳模在氣體壓印均勻度、有效壓印面積及模具表面抗沾黏能力。結果發現，利用PDMS精確翻鑄微奈米結構，再搭配氣體進行熱壓印成型，PDMS軟模可與基材表面完整接觸，因此有效壓印面積大幅提昇，且達到均勻的壓印效果，成型結構的精度品質也能各處維持一致；而且PDMS軟模表面自由能低，壓印時不易與阻劑沾黏，是製程上一大優勢，且PDMS軟模製作容易、翻鑄時間短，可有效降低成本。

本研究進一步有系統探討PDSM軟模氣體熱壓印製程，包括：解決軟模壓印變形問題、探討製程參數對轉寫效果之影響、評估PDMS模具壽命。結果發現：在軟模四周使用高度小於軟模且緊密配合的支承載具（Holder），可避免壓印變形。製程參數中，熱壓壓力影響不大，但會使殘留層厚度不同；熱壓溫度取決於阻劑PMMA之分子量大小，一般需高於Tg溫度40∼60℃；再者熱壓時間影響不大，30秒∼5分鐘皆可成型。以反覆施壓及升降溫來評估壽命，發現在20週期內未見缺陷；但以實際壓印測試，結果顯示模具壽命與結構的特徵尺寸、深寬比及週期值有關。

最後並實際進行6吋及12吋大面積壓印實驗，並嘗試壓印曲面。實驗結果顯示，以PDMS軟模搭配氣體加壓方式（軟模與軟壓），確實在大面積壓印有極佳的表現，並且可以在曲面上成旦F到均勻的壓印。本研究可壓印出最小特徵尺寸約為300nm。

Abstract

This thesis is devoted to the development a system and process for large area micro-nano imprinting. Conventional molds for impriting are of Si-based, glass-base or electroplated metal-based. Poor contact is a common problem when such molds are used for replication, especially when the area is large. When the substrate and the mold are brought into contact and are compressed using conventional hot press, the accuracy and area of replication were limited due to the contact condition and the inherent non-uniform pressure distribution. Si-wafers are easily broken if imprinting area is very large. Besides, when the resist coated thickness is thin, the effective imprinting area is further limited.

In this study, the soft mold made of PDMS is used; Gas is used employed as pressuring media. Compared to Si-base and Ni-base molds using conventional hot-plate compressing, the contact condition between the PDMS mold and the substrate is much better, as demontrated in the image using a pressure film. Conformal contact and uniform imprinting pressure throughout the whole area can be achieved. This technique has great potential for effectively replicating micro-nano structures directly from large wafers. Furthermore, PDMS mold had low surface energy can anti-adhere to resist.

For developing the PDMS molds for gas-assited imprinting process, three studies have been carried out: (i) preventing distortion of the PDMS mold, (ii) understanding the replication capacity under different processing parameters, and (iii) evaluating the mold life. Results showed that using a holder to support PDMS mold can overcome distortion. The rigid outer holder should match the outward lateral geometry of the PDMS mold with a height equal to or less than that of the PDMS mold. Imprinting using a gas pressure between 10 to 100 kgf/cm2 and with imprinting time between 30 seconds to 5 minutes yields good replication; but different gas pressure will determine the final thickness of the residual layer of photo-resist. Imprinting temperature is found to depend upon the molecular weight of resist, usually they are 40~60℃above the Tg's of the resist. Mold life depends on the micro-features; it is shorter than molds made of other material.

The capacity of gas-assisted imprinting using PDMS molds for large-area micro-feature replications has been demonstrated in this study. Succesful replication of micro-features onto the photo-resists on flat 6-inch and 12-inch Si substrates and 2-inch curved surface have been achieved. The minimum critical dimension is about 300nm.