Projection lithography to print thick resist patterns with triangular and semi-circular cross-section profiles

Patterning technology to print thick resist patterns with triangular and semi-circular cross-section profiles was investigated for applying to fabrication of light-guide plates and lens arrays, surface texturization of solar cells, and others. Positive novolac resist PMER P-LA900PM with an initial thickness of 10 μm was used and the patterns were mainly printed by the exposure light with a wavelength of 405 nm. At this wavelength, the light transmittance through the resist film was 0.5% and 80% before and after the exposure, respectively. Caused by this moderate transmittance characteristics, pattern sidewalls suitably inclined or roundly curved. When 400 μm line-and-space reticle patterns were printed using a projection exposure lens with a reduction ratio of 1/19 and a numerical aperture of 0.125, triangular patterns were obtained under the defocus conditions of around −100 μm. The sidewall angle was widely controlled between 20° and 55° by mainly changing the exposure time. On the other hand, semi-circular profiles were obtained when patterns were printed at the defocus position of +100–200 μm. It was clarified that the circular radius depended only on the defocus position and did not depend on the exposure time. Patterns with circular radiuses of 9–34 μm were successfully obtained.