以雙面部分曝光製作封閉型SU-8具高低差微流道

Abstract

本論文提出一個使用SU-8負型光阻，製作封閉型微流道的新式製程。以往封閉式微流道的製作方法多需用到晶片接合製程或多次光阻塗佈。本新式製程特點是僅需單層光阻塗佈，結合雙面部分曝光，無需晶片接合，即可做出封閉型微流道，並且內部截面可具有高低差。 使用負型光阻時，不同正向曝光劑量配合顯影製程，可製作出不同深度的光阻結構已是熟知技術，在此是進一步結合背向曝光，在玻璃基板上鍍鉻圖案作為背向曝光的光罩，可使顯影後底部光阻高度不同，所以結合正向與背向部份曝光後，即可製作出上下皆有高低差的封閉型光阻微結構。在光阻製程部份，實驗結果顯示，先軟烤再洗邊可以大幅提升塗佈厚度的均勻度，並且在塗佈厚度為100μm時，增加軟烤95℃時間至30分鐘，可使光阻不會沾黏在光罩上。另外，也探討了曝光微影時的晶片底部反射效應，以注入模具法代替標準旋轉塗佈法可製作出塗佈厚度大於 200μm的光阻結構，並發現正向部分曝光劑量78 mJ/cm2時，塗佈厚度達 380μm以上，可以大幅消減反射效應，使顯影後的光阻，在鍍鉻區與透明區具有相同顯影深度。在結合正向與背向部份曝光製程部份，實驗結果發現，SU-8厚度不足時，正向部分曝光及背向部分曝光在未鍍鉻透明區域會有明顯疊加作用，易造成曝光過量，在提高塗佈厚度至380μm以上時，本研究找出可行的正向及背向曝光劑量參數組合，成功製作出內部截面具有上下高低差的微流道結構。

Here a novel process is proposed to fabricate sealed micro channels by using negative photoresist SU-8. In previous studies, fabricating sealed micro channels needs either wafer bonding or multiple photoresist coating. The proposed method needs only SU-8 single-layer coating and double-side partial exposure, without wafer bonding, to fabricate not just sealed micro channels, but also sealed micro channels with non-uniform inside cross section. It is a common technique to fabricate negative photoresist structures having different thickness from the top by various front-side exposure dosages. Here, by further combining back-side exposure, plating Cr pattern on glass substrate to act as the mask for back-side exposure, negative photoresist structures with different thickness, either from the top or the bottom, can be fabricated. From experimental results, it is found that thickness uniformity can be greatly improved when soft bake is conducted before edge bead removal. Also, soft bake at 95℃ for 30 minutes can avoid stickiness between the mask and photoresist. Furthermore, reflection effect during exposure is found to be a critical factor on developed photoresist thickness. Using injection mold instead of conventional spin coating method, thickness of SU-8 2075 can be coated above 200 μm easily. It is shown that for front-side exposure dosage of 78 mJ/cm2, the reflection effect can be effectively reduced while coated SU-8 thickness is above 380μm. In combining front-side and back-side exposure, it is also found that, without coating sufficient SU-8 thickness, cross-link effect from double-side exposure will happen to result in over exposure. Finally, while coating SU-8 above 380μm, a feasible recipe is established to successfully fabricate sealed micro channels with variable inside cross section.