The microstructures on flexible membrane substrate prepared by the traditional methods may introduce large morphology and position errors, making it hard to achieve clear imaging. In this paper, we present a high precision fabrication method composed of two steps: unstressed fixation of the polyimide membrane and high precision fabrication of diffractive microstructures on the flexible membrane substrate. By using precise spin-coating technology, we get 25 μm thick polyimide membranes, whose coefficient of thermal expansion is almost zero. To prepare high precision microstructures, we propose an aerated membrane method, by which the flexible membrane substrate and the photoresist on it can attach tightly to the mask under the air pressure difference between the upper and lower surfaces of the membrane substrate during the contact lithography. The results show that the wave-front error obtained by this method is less than 1/30λ RMS (F# = 25@632.8 nm) at 400 mm aperture, indicating the microstructures have excellent morphologies and high position accuracy.

中文翻译：

---

用于成像的超薄膜菲涅耳衍射透镜的高精度制造方法

传统方法制备的柔性膜基板上的微结构可能会引入较大的形貌和位置误差，难以实现清晰成像。在本文中，我们提出了一种由两个步骤组成的高精度制造方法：聚酰亚胺膜的无应力固定和在柔性膜基板上高精度制造衍射微结构。通过使用精确的旋涂技术，我们得到了 25 μm 厚的聚酰亚胺膜，其热膨胀系数几乎为零。为了制备高精度的微结构，我们提出了一种充气膜法，在接触光刻过程中，柔性膜基板及其上的光刻胶可以在膜基板上下表面之间的气压差下紧密附着在掩模上。