Tan Jun Ying, Goh Gyuhyeong, Kim Jungkwun
Department of Electrical and Computer Engineering, Kansas State University, Manhattan, KS 66506, USA.
Department of Statistics, Kansas State University, Manhattan, KS 66506, USA.
Micromachines (Basel). 2020 Mar 7;11(3):277. doi: 10.3390/mi11030277.
This paper presents a microlens fabrication process using the timed-development-and-thermal-reflow process, which can fabricate various types of aperture geometry with a parabolic profile on a single substrate in the same batch of the process. By controlling the development time of the uncrosslinked negative photoresist, a state of partial development of the photoresist is achieved, called the timed development process. The thermal reflow process is followed after the timed development, which allows the photoresist to regain its liquid state to form a smooth meniscus trench surrounded by a crosslinked photoresist sidewall. Microlens with larger aperture size forms deeper trench with constant development time. With constant aperture size, longer developing time shows deeper meniscus trench. The depth of the meniscus trench is modeled in the relationship of the development time and aperture size. Other characteristics for the microlens including the radius of curvature, focal length, and the parabolic surface profile are modeled in the relationship of the microlens thickness and diameter. Microlens with circular, square, and hexagonal bases have been successfully fabricated and demonstrated where each geometry of the lens-bases shows different fill factors of the lens arrays. To test the fabricated lenses, a miniaturized projection lithography scheme was proposed. A centimeter-scale photomask pattern was photo-reduced using the fabricated microlens array with a ratio of 133, where the smallest linewidth was measured as 2.6 µm.
本文介绍了一种采用定时显影和热回流工艺的微透镜制造工艺，该工艺能够在同一批工艺中的单个基板上制造出具有抛物线轮廓的各种孔径几何形状。通过控制未交联负性光刻胶的显影时间，实现光刻胶的部分显影状态，即定时显影工艺。定时显影之后进行热回流工艺，这使得光刻胶恢复液态，形成由交联光刻胶侧壁包围的光滑弯月形沟槽。在显影时间恒定的情况下，孔径尺寸较大的微透镜形成的沟槽更深。在孔径尺寸恒定的情况下，显影时间越长，弯月形沟槽越深。弯月形沟槽的深度在显影时间与孔径尺寸的关系中进行建模。微透镜的其他特性，包括曲率半径、焦距和抛物面轮廓，在微透镜厚度与直径的关系中进行建模。已经成功制造并展示了具有圆形、方形和六边形基底的微透镜，其中透镜基底的每种几何形状显示出不同的透镜阵列填充因子。为了测试制造的透镜，提出了一种小型化投影光刻方案。使用制造的微透镜阵列以133的比例对厘米级光掩模图案进行光刻缩小，其中测量的最小线宽为2.6 µm。
