We report a multiple patterning approach utilizing digital-micromirror-device (DMD)-based grayscale lithography, providing a solution to improve fabrication accuracy for entire target three-dimensional structure. Because DMD-based lithography system consists a projection lens system, better resolution can be obtained around focal position comparing to the outer region of depth of focus. Thus, for thick-film resist micro structuring, exposing with multiple focal positions with separate grayscale masks leads to improvement of fabrication accuracy. In order to find the best combination of the multiple focal positions and their grayscale masks, the computational optimization is combined to the multiple patterning approach. Through a several experiments, effectiveness of the proposed approach was successfully demonstrated.

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Digital Micromirror Device (DMD)-based grayscale lithography is a promising tool for three dimensional (3D) microstructuring of thick-film photoresist since it is a maskless process, provides possibility for the free-form of 3D microstructures, and therefore rapid and cost-effective microfabrication. However, process parameter determination lacks efficient optimization tool, and thus conventional look-up table (indicating the relationship between development depth and exposure dose value under a fixed development time) approach with manual try-and-error adjustment is still gold standard. In this paper, we firstly present a complete “input target-output parameters” single exposure optimization method for 3D microstructuring utilizing DMD-based grayscale lithography. This numerical optimization based on lithography simulation and sensitivity analysis can automatically optimize a combination of three process parameters for target microstructure; exposure dose pattern, a focal position, and development time. Through a series of experiments using a 20 μm thick positive photoresist, validity of the proposed optimization approach has been successfully verified. Secondly, with the purpose of further advancing accuracy and improve the uniformity of precision for the target area, a multiple exposure optimization method is proposed. The simulated results proved that the multiple exposure optimization method is a promising strategy to further improve precision for thicker photoresist structure.@en

A novel process optimization tool for grayscale lithography is developed and demonstrated to fabricate three-dimensional (3D) microstructures using thick-film photoresists. For the first time, the two process parameters in grayscale lithography: exposure dose profile and development time are determined automatically for a user-specified target 3D profile. This provides an inexpensive and effective alternative to conventional trialand-error based process design. The optimized parameters were verified by fabricating various 3D microstructures and the experiments revealed good quantitative agreement with the target profile . KEYWORDS Grayscale Photolithography, 3D Microstructuring, Design Optimization, Automatic Process Design@en

With the ongoing development of thick photoresists, promising possibilities have emerged to use these transparent and flexible layers for micro-structures and micropatterns directly and not exclusively as a sacrificial layer in the processing. These 3D polymer microstructures have many potential applications in the field of MEMS: including micro-sensors and actuators, micro-optics and micro-fluidics. Using modern 3D exposure techniques, it is possible to vary the dissolution rate of thick photo resists locally and create complex relief-type three-dimensional structures in just one exposure and development cycle. Unfortunately, realizing the proper exposure conditions needed for a specific 3D micro pattern is complicated, because of the non-linear and smoothing nature of the physical processes. Nowadays, the most widely used approach is based on trial-and-error designed exposure conditions. In this research a systematic approach is developed, based on computational process simulation, associated adjoint sensitivity analysis and optimization techniques.@en

In the present paper the automated optimization of the exposure dose for UV moving-mask lithography is presented. Moving-mask lithography is a promising new technique for micro patterning thick positive photo resists. The design task is to design the mask and the mask motion such that the requested micro pattern is achieved as good as possible. As an intermediate step towards a computational engineering tool for moving mask lithography, the present paper puts focus on the automated optimization of the required light dose distribution. The method relies on a recent model which links the spatial distribution of the dissolution rate to the light dose distribution at the top surface of the photo resist. This model is combined with a search-free and, thus, cost efficient quality measure. For the latter, adjoint sensitivities can be calculated using a backward integration scheme. The fact that adjoint sensitivities can be retrieved easily, implies that the light dose can be obtained with an high spatial resolution. The proposed method will be demonstrated on the basis of a number of test problems.@en