以負型光阻SU-8開發雙面多重部份曝光製程技術

Abstract

近年來使用高分子材料與基本微影技術製作三維立體微結構的應用越來越多元化，其中以封閉微結構為熱門項目之一，此外也有研究指出負型光阻SU-8為高分子材料中被運用最廣泛的材料。因此本研究的目標是以負型光阻SU-8來開發雙面多重部份曝光製程技術，並以此技術製作具有多變化性截面的封閉微結構，而本製程方法只需要標準的黃光微影設備，單次地塗佈光阻和無須額外的接和過程。 在實驗參數上，正向部分曝光與背向部分曝光其曝光劑量與顯影厚度關係已完成建立，而在實驗中發現玻璃基板上的鉻金屬層會影響到正向部分曝光的顯影厚度，因此，我們提出一模擬模型來估算受到反射效應影響的部分曝光顯影厚度，並且利用兩種不同的負光阻微結構來討論曝光劑量與塗佈厚度對於顯影厚度的關係，其也可用來驗證模型的準確性，而不管是曝光劑量或塗佈厚度對於顯影厚度的關係，其實驗與模擬結果的誤差最大值為3.1 %，這證實我們的模組有很高的準確性。除此之外，我們也發現利用模具方式塗佈較高的光阻厚度，不僅可以降低反射效應於顯影厚度上的影響，且可以減輕因正向與背向部分曝光重疊的部分而產生的鍵結效應，而最終，具有非對稱截面的封閉微結構成功地被製作出，其驗證了我們完成以負型光阻SU-8進行雙面多重部份曝光製程技術的開發，使其成為經濟實惠的製程平台，將可用來構建三維微結構並應用於微機電系統中。

Here a double-side multiple partial exposure (DoMPE) method is proposed to fabricate an embedded SU-8 microstructure with more flexible inside cross section. The proposed method uses standard lithography equipment and needs only single-layer coating of negative photoresist SU-8 on glass substrate without bonding process. Process parameters, including development thickness at different front and back-side partial exposure doses, are experimentally characterized. Reflection effect due to Cr layer on glass substrate is shown to have influence on the development depth of SU-8 in front partial exposure. Here, we propose a simulation model to predict SU-8 thickness after development under partial exposure with reflection effects. Two kinds of SU-8 micro structures with different exposure dosages and coated thickness are fabricated on glass substrates to demonstrate the capability of the proposed model. For different exposure dosages or coated SU-8 thickness, the maximum difference between simulated and experimental results is shown to be less than 3.1%, which verifies the accuracy of the proposed model. Furthermore, it is found that coating thicker SU-8 not only can reduce reflection effect, but also can attenuate cross-link effect due to exposure dose accumulation on SU-8 from both front and back sides. Finally, an embedded SU-8 microstructure is demonstrated to verify that the proposed DoMPE method needs only single-layer SU-8 coating to fabricate not just embedded microstructures, but also embedded microstructure with asymmetric inside cross section.