Improving contact lithography resolution using index matching fluids

In the process scenario of combining contact lithography and laser interference lithography, the gap between the mask and the substrate may cause a series of problems, such as reducing the contrast of the pattern, misalignment of the two interference beams, and unexpected macroscopic patterns. This article introduces a method of adding refractive index matching liquid to suppress interference caused by gaps. Matching liquids can buffer the refractive index changes at the interface of the medium. As a result, the reflectivity of the medium interface decreases, thereby suppressing harmful macroscopic patterns. In addition, matching liquids can reduce the refractive angle of interference beams, thereby reducing their misalignment and increasing the area ratio of effective patterns. This article identified suitable matching liquid materials and conducted numerical simulations and analysis to demonstrate the effect of adding matching liquid on improving pattern contrast. For the production of gratings ranging from 550nm to 1500nm, the stripe contrast is below 0.05. In summary, the most suitable refractive index matching liquid has been explored and tested under the given refractive index of the mask and substrate. Experiments have shown that adding matching liquids can provide significant advantages.