||The Lloyd’s mirror interference system is the most common for fabrication technology of the periodic structure in recent years, Comparison of two beam and Lloyd’s mirror (single beam) exposure systems, advantage of single beam is optical path set up simply, stability highly, period adjusted conveniently, and position of the placement for sample is stable, so the systems can reduce operative cost. However, the rotation angle must be adjusted to above 30 degrees for fabrication sub-wavelength structure by Lloyd’’s mirror interference system, the larger angle will cause cosine loss of the surface energy, so the uniformity of interference fringes are relatively poor.|
In the study, establishing a novel prism immersion interference lithography technology by Lloyd’’s mirror interference lithography system combined with higher than the air dielectric environment. The mathematical simulation was used by the LightTools software which can calculate light track and interference angle in the prism. The He-Cd laser (λ=442nm) can produce a homogeneous parallel beam after through optical system, then the light wave front is divided by the prism, and proceed the two light beam is overlapped to form interference fringes in space areas. Final, the periodic structure can be obtained through change rotation angle by interference exposure.
The shake of air can be reduce through prism instead of Lloyd’’s mirror, and the two light intensity can reach consistent due to internal total reflection in prism, so that the fringe contrast is increased. The period can be made smaller due to increased environmental refractive index. The water is immersed between the prism and the sample, so that vibration of prism is synchronized with the sample to maintain a higher visibility of interference fringes. The reflectivity is decreased due to refractive index of water in middle value, and immersion of water can raise numerical aperture to increases resolution degree, and to improve the uneven stripes that is caused by multiple reflections within the photoresist. The deficiencies of the original system is improved and compensated through the system of interference by prism. In the experiments, the grating structure has been produced in area of 1.5cm×1.5cm, period is 300nm to 500nm. The optical system by prism for the production of sub wavelength periodic structures can be achieved a target of convenient, fast, stable and uniform.
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