Study On Digital Mask Fabrication Technique For Micro-optical Elements

Micro-Optical Elements (MOEs) have advantages of small volume, light weight and low cost.Moreover, some new function such as miniaturization, array, integration, imaging and wavefronttransform can be realized by using MOEs. However, it’s difficult for the common optical elements torealize these new functions. In china, the problem of fabrication level lagging behind design theory isparticularly outstanding, which is the background of our research work in this dissertation. In order toimprove the digital lithography resolution and expand the application of digital lithography techniques,we make a comprehensive and systemic study on series of digital mask fabrication technique such asdigital dividing mask，digital grey-gradual-change mask，digital moving mask and digital rotatingmask. The main contents and contributions of this dissertation are as follows:1. Due to the effect of DMD discrete pixel, the relief profile is discontinuous by using digitalgrey mask technique. How to precisely replace the continuous profile with multiple steps becomes akey problem, so digital grey-gradual-change mask technique is proposed. The DMD pixel error hasbeen analyzed. And the design principle for digital grey-gradual-change mask has been built. Thetheoretical equation for calculating grey-gradual-change mask according to exposure has beenestablished. Digital grey-gradual-change mask technique provides a new idea for the precise controlof relief profile.2. By using traditional moving mask technique for reference, the digital moving mask techniquehas been systematically developed for the fabrication of MOE with continuous relief profile. In orderto satisfy the demand of fabricating different MOEs, one-direction moving mask or multi-directionmoving mask method has been presented. And the design method of one-direction or multi-directionmask function has been detailedly explained. In addition, in order to overcome the shortcoming of theone-direction or multi-direction moving method limited by moving direction, another moving methodbased on micro-slice projection has been proposed. The above moving methods are great extension ofthe traditional moving technique.3. By using traditional rotating mask technique for reference, the digital rotating mask techniquehas been systematically developed for MOE fabrication. Aiming at various MOEs, two designmethods for digital rotating mask have been proposed. One method is suitable for MOE withrotating-symmetric-phase distribution, and another method based on micro-slice projection can beused to fabricate MOE with non-strict-rotating-symmetric-phase distribution. Digital rotating mask technique greatly expands the application area of traditional rotating technique and provides a newidea for the fabrication of MOE with complex relief.4. Aiming at the fuzzy edge of lithography pattern induced by the low-pass property of projectionlens, a series of digital division mask methods have been presented, including periodic amplificationdivision, bit coding division and the two combine. Periodic amplification division method is suitablefor MOE with discrete periodic structures. Bit coding division method is suitable for MOE withcontinuous relief. Method combining periodic amplification with bit coding division can be used tofabricate MOE with special structure. We have calculated the diffraction orders and energy involvedin imaging, respectively for the division masks and the original mask, which proves that thelithography resolution can be advanced by adopting the digital dividing mask technique. Thefeasibility of improving lithography resolution with the above division mask methods has beenverified by experimental fabrication as well.