| With the rapid development of Micro-Machine System(MEMS) and Micro-Optical-Machine System(MOEMS) technology which require continuous relief micro structure, research in new kinds of micros manufacturing method with high efficiency, low cost and capability of fabricating continuous relief micro structure is one of the orientations of micro manufacturing development.Exist relief micro structure fabrication method include lithography overlay, direct-writing, mask moving lithography, photoresist heat forming, gray-tone mask lithography et al. Any one of them has its advantage and disadvantage, for example lithography overlay needs complex fabrication process and is hard to fabricate continuous profile, direct writing can achieve high resolution but lack of efficiency, and the gray-tone mask is to costly. Digital gray-tone lithography technique is a new kind of maskless lithography technique with which combines the conventional lithography and DLP technique and provides with high efficiency, low cost, simple product process. It can fabricate microstructure with continuous relief surface through one time gray-tone exposing and has a very good application prospect in the fabrication of MEMS and micro optic elements.The projection objective for digital gray-tone lithography is one of the key elements which ensure the quality of image transforming. In the requirement of micro-electronics fabrication, existing projection objectives for lithography usually have a large field of view and are designed for transmission mask with comparatively short front work length, so they can not be transplant to the digital gray-tone lithography system directly. The Digital Micromirror Device is a reflectional device which can conveniently be used as the pattern generator, the large caliber and short front work length make it hard to arrange light path. Further more, for the reasons of cost controlling, the requirement of tolerance in fabrication and assemblage of projection objective for digital gray-tone lithography is much less than conventional lithography objectives. So it's necessary to design a new objective which fit the DMD, can remove the pixel, and low cost.In this paper, we research on factors that affect the image of digital gray-tone expose, choose the reasonable optical structure and parameter for the objective. Based on the high order optical aberration theory analyze the matters causing the optical aberration, educe the aberration tolerance, and research on the optical aberration correction and balance. With the help of optical design software, I design an objective with less optical elements and low requirement for tolerance of optical fabrication and assemblage. This objective meets the requirements of digital gray-tone lithography in the high quality imaging, low cost, and high efficient fabrication. We also carry out digital gray-tone lithography experiments by building up a simple image system to analyze the factors affect imaging quality and test the feasibility of the objective design. The experiment results show that the design ideas of the objective can availably remove the DMD image pixel, and give attention to both the requirement of resolution and efficiency. It provides technical assurance for the building of digital gray-tone lithography system, and is significant for promoting the digital gray-tone lithography practical use. |
