Ghosh Siddharth, Ananthasuresh G K
Department of Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, Karnataka, India.
Third Institute of Physics, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz-1, Göttingen 37077, Germany.
Sci Rep. 2016 Jan 4;6:18428. doi: 10.1038/srep18428.
We report microstructures of SU-8 photo-sensitive polymer with high-aspect-ratio, which is defined as the ratio of height to in-plane feature size. The highest aspect ratio achieved in this work exceeds 250. A multi-layer and single-photon lithography approach is used in this work to expose SU-8 photoresist of thickness up to 100 μm. Here, multi-layer and time-lapsed writing is the key concept that enables nanometer localised controlled photo-induced polymerisation. We use a converging monochromatic laser beam of 405 nm wavelength with a controllable aperture. The reflection of the converging optics from the silicon substrate underneath is responsible for a trapezoidal edge profile of SU-8 microstructure. The reflection induced interfered point-spread-function and multi-layer-single-photon exposure helps to achieve sub-wavelength feature sizes. We obtained a 75 nm tip diameter on a pyramid shaped microstructure. The converging beam profile determines the number of multiple optical focal planes along the depth of field. These focal planes are scanned and exposed non-concurrently with varying energy dosage. It is notable that an un-automated height axis control is sufficient for this method. All of these contribute to realising super-high-aspect-ratio and 3D micro-/nanostructures using SU-8. Finally, we also address the critical problems of photoresist-based micro-/nanofabrication and their solutions.
我们报道了具有高纵横比的SU-8光敏聚合物的微观结构，高纵横比定义为高度与平面内特征尺寸之比。在这项工作中实现的最高纵横比超过了250。本工作采用多层单光子光刻方法来曝光厚度达100μm的SU-8光刻胶。在这里，多层和延时写入是实现纳米级局部可控光诱导聚合的关键概念。我们使用波长为405nm、孔径可控的会聚单色激光束。会聚光学器件从下方硅衬底的反射导致了SU-8微观结构的梯形边缘轮廓。反射诱导干涉点扩展函数和多层单光子曝光有助于实现亚波长特征尺寸。我们在金字塔形微观结构上获得了75nm的尖端直径。会聚光束轮廓决定了沿景深的多个光学焦平面的数量。这些焦平面以不同的能量剂量进行非同时扫描和曝光。值得注意的是，对于这种方法，非自动化的高度轴控制就足够了。所有这些都有助于使用SU-8实现超高纵横比和三维微/纳米结构。最后，我们还讨论了基于光刻胶的微/纳米制造的关键问题及其解决方案。
