Research On Optimization Of Patterning Quality For DMD Maskless Lithography

The maskless lithography technology based on digital micromirror device(Digital Micromirror Device,DMD)has become one of the commonly used lithography methods in the preparation of micro-nano devices by virtue of its digital mask and grayscale modulation function.However,similar to other lithography methods,the final patterning quality,including exposure uniformity,sidewall structure of photoresist,limit resolution,pattern fidelity,etc.,is closely related to both lithography system and process.At present,from principle to implementation,DMD maskless lithography system still has a large space for optimization in the above patterning quality.Therefore,it is of great significance to optimize research on the above issues for improving the reliability and wide applicability of DMD maskless lithography system.The in-depth study on the prominent problems of patterning quality in the DMD maskless lithography system was carried out,and some targeted solutions were given in this thesis.The main contents include:(1)In order to improve the edge contrast and linewidth consistency of the exposure pattern in the exposure area.Firstly,for the problem of aberration caused by the defocusing exposure,a method of correcting the focus position of the focused beam was proposed.In addition,in terms of exposure uniformity optimization,a homogenization method was proposed based on the grayscale modulation function of DMD.The quantitative results of the nine point sampling method showed that the exposure uniformity of the system increased from 66% to 96% by using the homogenization method.(2)In order to improve the yield rate of the film lift-off process,the sidewall structure of the exposure pattern is optimized.From the perspective of lithography process,three optimization methods are provided,and exposure experiments and result analysis are carried out for the influence of relevant process parameters on their sidewall structures.(3)In order to improve the pattern resolution and fidelity of DMD maskless lithography system,a lithography imaging model was established based on Fraunhofer diffraction theory.For one thing,a method for improving the channel resolution of the DMD maskless lithography system based on the sub-pixel size shift was proposed.Then,exposure experiment were carried out under the guidance of the lithography imaging model,which reveals that the channel resolution of the lithography system has been improved from 2.3 μm to the sub-micron level(810 nm).For another,in order to reduce the distortion of exposure pattern,by the use of the lithography imaging model and genetic algorithm,an optical proximity correction method based on pixel-level grayscale modulation was proposed for digital mask optimization of DMD maskless lithography system.Firstly,the simulation results showed that the algorithm has robust convergence and the correct direction of mask optimization.Secondly,the exposure experiment results displayed that the exposure pattern optimized by the OPC method has higher fidelity,and the quantitative results also revealed that the matching rate between the exposure pattern and the mask pattern can be improved by about 20% after optimization.Finally,the optimization experiments for the complex masks proved that this method is universal for mask optimization.