基于大气等离子体刻蚀的聚酰亚胺薄膜超精密加工机理及工艺研究

The thin film optical device made of polyimide (PI) possesses the advantages of light weight, easy folding and low cost etc, which shows great application potential in the next generation of large aperture optical system. However, the forming process mechanism of the PI film makes it difficult to obtain thin film PI optical device with nanoscale surface precision and roughness directly. What’s more, the conventional ultra-precision machining technology (such as such as grinding, magneto rheological, ion beam polishing etc.) is not suitable for the postprocessing of PI film. Therefore, the ultra-precision machining method based on atmospheric pressure plasma etching is proposed to process PI film. By first researching the surface kinetic in the processing with reactive ion etching theory, then analyzing the reaction mechanism between active particles and PI materials with chemical simulation, and at last studying the forming mechanism of surface sediment with chemical simulation, the theoretical model of atmospheric pressure plasma ultra-precision processing for PI film can be established finally. On this basis, the ultra-precision processing experiment and techniques for fabricating PI film with nanoscale surface precision and roughness can be developed. The proposed method can improve the fabrication ability of PI thin film optical device significantly, and plays an important role in promoting the development of ultra-large aperture space optical technology in the future.

聚酰亚胺（PI）薄膜光学器件具有重量轻、易折叠、成本低等优点，在下一代大口径（>10m）或轻量化空间光学系统有巨大的应用潜力。然而，PI材料成型工艺机理决定其难以直接获得纳米级面形精度和粗糙度的PI薄膜光学器件，常规超精密加工技术（如研磨、磁流变、离子束抛光等）又不适于PI薄膜再加工。本项目提出基于大气等离子体刻蚀的聚酰亚胺薄膜超精密加工方法。通过反应离子刻蚀理论研究大气等离子体加工的表面动力学过程，从化学模型上分析多种活性粒子与PI材料分子的反应机制，并利用化学仿真对大气等离子体加工过程中沉积物的生成机理进行分析，掌握抑制沉积物生成的工艺优化方法并最终建立PI薄膜大气等离子体超精密加工的理论模型。在此基础上开展PI薄膜大气等离子超精密加工实验，研究获得纳米级面形精度和粗糙度的PI薄膜的工艺方法。该方法能极大提高PI薄膜光学器件制备能力，对未来超大口径空间光学技术发展将起到重要推动作用。

针对聚酰亚胺薄膜在柔性薄膜光学器件中的应用需求，探索了基于大气等离子体刻蚀的聚酰亚胺（polyimide, PI）材料表面微纳尺度的精密加工方法。进行了高分子材料化学、微纳加工工艺等多学科交叉研究，阐明了相关的工艺方法特性和数学模型，验证了大气等离子体刻蚀工艺方法在聚酰亚胺薄膜表面进行精细加工的方案可行性。具体包括：①研究了聚酰亚胺材料与常见等离子体相互作用的化学原理，阐明了大气等离子体作用下聚酰亚胺薄膜表面沉积物的化学成分和形成机理；②研究了消除薄膜表面沉积物和提升光学粗糙度的优化方法，提出了基于反应离子束等比刻蚀工艺的聚酰亚胺薄膜表面抛光工艺；实验表明，经过表面抛光工艺处理后的聚酰亚胺薄膜表面粗糙度提升至（PV：66nm，RMS：10nm）。③建立了大气等离子体刻蚀加工过程的数理模型，并实验验证了该工艺方法用于精密薄膜光学器件性能优化的可行性，口径50mm的聚酰亚胺薄膜的透射波前RMS从约λ/2提升至优于λ/8。从技术上证明了基于大气等离子体刻蚀工艺方法有可能成为未来制备大尺寸、高精度的薄膜光学器件的可行路线。本项目的研究为后续相关的专用工艺设备的研制奠定了基础，并可指导薄膜光学器件的制备工艺流程优化。