User-defined Microlens Array Fabricated By DMD Based Multistep Lithography With Dose Modulation

Microlens arrays(MLA)have been widely used in light collection and imaging applications,such as charge-coupled devices(CCD),fiber coupling,beam shaping,and optical neural networks in the past few decades.However,production methods of micro-optical components have limited their development to a certain extent.The currently widely used methods mainly include laser direct writing technology and DMD maskless lithography technology.The resolution of the single-point laser direct writing technology is determined by its spot size,so its resolution is limited to about 1 ?m.And its single-point scanning mode limits the processing efficiency generally.The maskless lithography technology based on Digital Micromirror Device(DMD)has attracted wide attention due to its high efficiency,masklessness,and low cost among many manufacturing methods.But this method also has its own shortcomings.First,since the working mode of DMD maskless lithography is to perform maskless lithography by controlling the inversion of DMD micromirrors,the resolution is one pixel,and the period for making a microlens array can only be a single pixel.Integer multiples,it is not possible to achieve any shape and period of the microlens array.Secondly,when making a microlens array,the percentage of the lens area to the total area is also limited by the DMD resolution,and a high lens area ratio not only capturing most of the incident light to increase the signal-to-noise ratio(SNR)can also effectively avoid stray light effects,thereby avoiding unnecessary diffraction effects.Therefore,it has become an urgent need to improve the resolution of a DMD maskless lithography system.The traditional way to improve the resolution must be replaced with a high-power lens,which will lead to a reduction in lithographic efficiency.Changing the high-power lens will also cause the writing depth of focus to become smaller,which will lead to an increase in the rate of writing off glue and affect the quality of writing.Therefore,this article has carried out corresponding research around the use of DMD maskless lithography for user-defined microlens array fabrication,and proposed corresponding solutions to the problems described above:(1)This paper proposes a method that combines DMD maskless lithography technology with high-resolution stepping motion of a piezoelectric platform(PZS),builds a DMD multi-step lithography system,and flexibly controls the DMD digital mask.Combining the version with exposure dose modulation,without changing the high magnification lens,it breaks the limit of DMD resolution,reduces edge jaggedness,and performs smooth writing of micro structures.After simulation and experimental verification,using this technology can complete the sub-pixel microstructure writing.(2)Aiming at the limitation of resolution when fabricating microlens arrays by DMD maskless lithography and the problem of being unable to achieve any period and shape,this paper proposes that the proposed multi-step lithography technology of DMD can be used in combination with thermal reflow,Make user-defined microlens array with high fill factor.The simulation results show that the technology can achieve the above functions well,and the microlens array of any shape and period can be efficiently produced by actual writing inthe laboratory.The fabricated microlens array has a smooth surface and a good structure under the observation of a bright field microscope and a scanning electron microscope(SEM);and the imaging quality is tested with good test results.