Digital Lithography Method For The Fabrication Of Micro Structures Based On Spatial Energy Integral Coded Modulation

The Digital Micro-Mirror Device(DMD) based digital lithography applies a DMD chip as dynamic mask generator,which effectively avoids the fabrication cost the process defects introduced by the usage of physical mask.Moreover,by combining the “step exposure” or the “scanning exposure” method,the fabrication efficiency and throughput can be further improved.Hence,the DMD based digital lithography has been widely applied in the fabrication of two-dimensional and three-dimensional micro structures for its huge advantages and great application prospect.The current research,however,is mainly centered on the improvement of system structure or the optimization of processing principle,and is lack of exploration and application of the special characteristic that digital lithography possesses.In this condition,this paper particularly researched the DMD based three-dimensional spatial light field modulation capabilities,and explored the specific applications of such capabilities,thereby improving the low-cost and high-efficiency performances of DMD based lithography.First of all,the physical model of DMD based lithography was analyzed.In the beginning of this paper,the DMD based digital lithography experiment setup and its subsystem were introduced in detail,and the core modules were disassembled and further analyzed,including the design and selection of UV illumination system,the optical focus measurement system and the optical projection system.Combined with the practical process environment of the laboratory and the research requirements of this project,a digital lithography experiment setup with a minimum resolution of about 1.3?m and an exposure field of about 1.4mm×1.05 mm was finally established.On that basis,the following studies were carried out:(1)Based on the equivalent three-dimensional optical field multi-step control method depend upon the layer-slicing manner,this paper combined the characteristics of DMD to dynamically generate the mask patterns,and contrastively analyzed the equivalent three-dimensional optical field single-step control method depend upon the pulse-width-modulation theory.Furthermore,the equivalent three-dimensional optic control model of DMD based pixelated light field was established.(2)Through theoretical derivation and actual exposure experiment,this paper specifically analyzed the spatial interaction relationship between the photosensitive polymer and equivalent three-dimensional optical field.Moreover,a pixel grayscale coding based technology for the optimization of exposure-field uniformity was proposed,which can effectively improve the capability of DMD based digital lithography without extra physical cost.(3)The non-linear effects caused by the pulse trigger edges in DMD based three-dimensional light field modulation was corrected and compensated.Thus,the pixelated optical intensity can be controlled with great precision.On this basis,a planar compound eye was fabricated in a rapid and low-cost way via this technology.Subsequent profile surface and optical performance experiment further approved the effectiveness of this method for the fabrication of three-dimensional microstructures with complex surface.(4)Based on the theory of partial coherent imaging,the optical proximity effect in the digital lithography was emulated and analyzed.Combined with the two-dimensional interaction model between the photosensitive polymer and equivalent three-dimensional optical field,this paper proposed a pixel coding based optical proximity correction method.By coding the grayscale of each pixel on the digital mask,the exposure energy and the exposure area on the photoresist can be precisely controlled.Thus,the disagreement between the ideal mask image and actual exposure pattern is corrected in a pixel-by-pixel way.This subject detailedly researched the current defects in the DMD based digital lithography,and proposed corresponding solutions based on the technology of equivalent three-dimensional optical field modulation.The effectiveness of such solutions was approved via theoretical analysis,numerical simulation and experimental verification.This subject further expands the process advantages of digital lithography such as low-cost,high-efficiency,and high-flexibility,and provides both theoretical foundation and technical support for the development of digital lithography.