Study On The Key Technique For Fabricating Curved 3D Micro-structure Using Digital Mask Lithography

Curved three-dimensional(3D)micro-structure has compact structure,special dispersion and flexible freedom of design.Therefore,it has been used as the important foundation element in modern industrial and national defense area.At present,the fabrication techniques for curved 3D micro-structure have disadvantages such as high cost,long cycle and low efficiency,which may be the restrictive factors of the industrial application of curved 3D micro-structure.In this dissertation,based on the digital mask lithography,we focus on the key fabrication technique that curved 3D micro-structure is fabricated on planar substrate using planar digital mask.The mapping relation of the fabrication depth,exposure dose and digital mask are deeply studied.The digital mask lithography for curved 3D micro-structure,using two-dimensional(2D)square column arrays to approximately express the profile of curved 3D micro-structure,is proposed.Compared with the existing fabrication techniques,the digital mask lithography for curved 3D micro-structure is a fast area-write technique,which has the advantages including the lower cost,shorter cycle and higher efficiency.It can be widely applied in the field of micro/nano fabrication.The main contents and contributions of this dissertation are as follows:1.A novel method for fabricating curved 3D micro-structure using digital mask lithography is proposed.The digital discrete modulation of exposure dose by spatial light modulator(SLM)is fully utilized,and then the modulated 2D discrete square column arrays of exposure dose are exposed on the planar substrate by projection lithography.In order to overcome the difficulty that the profile of curved 3D micro-structure cannot be exactly expressed in a single coordinate system,the proper mask optimal design algorithms for curved 3D micro-structure are proposed,including the iterative optimization and point by point optimization.2.A novel method of multi-gray digital mask lithography is proposed to break through the curvature restriction which exists in the single gray digital mask lithography for curved 3D micro-structure.The maximum gray number for the use of modulating exposure dose is increased by the multi-exposure of multiple digital masks.Three geometry separation methods for the curved 3D micro-structure are studied,and the mask design algorithms corresponding to geometry separation methods are proposed.3.The curved splicing digital mask lithography for the fabrication of large-area curved 3D micro-structure is proposed to break through the restriction of fabrication area.Multiple digital masks are horizontally spliced,and the gray of the mask connection area should be properly designed to make the curvature variation in the connection area in accord with the overall curvature of curved 3D micro-structure.The corresponding mask design algorithm for curved splicing is proposed.4.Several digital mask lithography methods for curved 3D micro-structure are developed aiming at the limitation of horizontal and transverse resolution.The curved moving digital mask lithography method is developed,which combines static with dynamic exposure,and the application scope of digital mask lithography may be expanded.Two design algorithms for curved moving digital mask are proposed corresponding to two kinds of motions.The curved division digital mask lithography method is developed.A curved 3D micro-structure with periodic structure can be divided into multiple low-frequency structures by sampling periodic structure.Thus the influence of low-pass property of reduction lens can be effectively reduced by the decrease of mask spatial frequency.Two design algorithms for curved division digital mask are proposed corresponding to two kinds of division,including the line and the circle division.