Applying an interferometric exposure model to analyze the influences of process parameters on the linewidth
Department of Mechanical Engineering, National Central University, Jhongli, Taiwan. Applied Optics
(Impact Factor: 1.78).
12/2006; 45(32):8278-87. DOI: 10.1364/AO.45.008278
We utilize a modified interferometric exposure model, enhanced with the Beer-Lambert law, to study how some process parameters influence the structural dimensions within the whole exposure area. An experimental apparatus is built to verify the accuracy of this model. The simulation results indicate that when the incident angle is larger than 15 degrees, the effect of the beam deformation cannot be neglected. One cannot readily obtain periodic structures with the same dimensions during static exposure because of the Gaussian distribution of the light intensity. The theoretical results match the experimental ones quite well. The variation of Dill's parameter A has a greater influence on the transmittance and the linewidth when A is decreasing. If a poor contrast fringe is exposed in the photoresist, it will not only cause a greater nonuniformity of the structural dimensions but also a decreased aspect ratio in the structure after the development process.
Available from: J.-C. Chen
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ABSTRACT: In present study, we applied the interferometric lithography with an exposure mathematical model, and set up an experimental system to verify the validity of this model. A simple and convenient interferometric lithography system for patterning large-area with nano-scaled dimensions gratings was built. Due to the position for patterning large-area grating, a two-axis servo-motion system will be added to the original interferometric lithography system. Based on the characters of the interference, we modified an exposure model to predict the exposure condition, and then calculate the step for the next movement. From the simulation results, the best moving distance can be suggested. The different situations at the overlapping region and the interference are also simulated. The gratings at the overlapping region will be shown as three types due to different moving conditions. The experiment results can clearly be illustrated from the simulations. Finally, the results show that our interferometric lithography system and exposure model can be potentially used for fabricating uniform periodic structures.
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ABSTRACT: An interferometric lithographic technique and double exposure method are applied to theoretically and experimentally investigate several kinds of 2D periodic structures. The shape, lattice symmetries, and lattice constants of the 2D structures, for different substrate rotational angles, are obtained from the simulated predictions. The shape of the 2D structures can be varied by controlling the rotational angle of the substrate and the development process, and they are validated experimentally. The variation of the lattice symmetry of the 2D structure with the substrate rotational angle is discussed in detail in relation to the axial angle and lattice constant. It is found that square, circular, rectangular, and elliptical scatterers which are arranged in parallelogram, triangular, and square lattices (with different lattice constants) can be obtained. The photonic bandgaps for each condition are also investigated. When the substrate rotational angles are the same, the normalized frequency (omega a/2 pi c) of photonic bandgap structures with an equal filling factor are very similar regardless of the interference angle. The results are helpful in designing the forbidden frequency when the lattice constant and the scatterer shape can be controlled by the interferometric lithographic technique.
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