24 February 2009 Subwavelength photoresist patterning using liquid-immersion interference exposure with a deep-UV hologram mask
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Abstract
Interference exposure using a deep-UV laser in combination with dry etching is instrumental in manufacturing subwavelength patterns used at visible wavelengths. For well resolved patterns, interference fringes must be held still during exposure to achieve a high fringe contrast. Two-beam interference exposure requires a lot of space and equipment to build stable optics and produce patterns on an industrial scale. On the other hand, hologram mask exposure is theoretically far more robust in unfavorable surrounding conditions since a resist layer is placed directly beneath the mask. To produce good-quality resist patterns by using hologram masks, two issues need to be addressed. First, light reflections occurring at interfaces between the mask, the air gap and the resist need to be reduced to secure a high uniformity of exposure intensity. Second, only two diffraction beams should be generated to make an interference field with a high fringe visibility. What mask configurations should be chosen depends on what patterns are to be made. The best answer to produce sub-100-nm patterns is using a hologram mask in Bragg geometry and filling the air gap with a high-index liquid.
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Daisuke Sawaki, Daisuke Sawaki, Jun Amako, Jun Amako, } "Subwavelength photoresist patterning using liquid-immersion interference exposure with a deep-UV hologram mask", Proc. SPIE 7202, Laser-based Micro- and Nanopackaging and Assembly III, 72020L (24 February 2009); doi: 10.1117/12.808809; https://doi.org/10.1117/12.808809
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