Polydimethylsiloxane (PDMS) is a material used for bio-chips and micro total analysis systems / lab-on-chips. For further development, it is inevitable to develop a technique to fabricate precise structures on micrometer scale at high aspect ratio. In the previous works, we reported a technique for high-quality micromachining of PDMS sheets, by means of ablating the PDMS sheets using EUV radiations around 10 nm from laser-produced plasma. In the present work, we have investigated fabricated structures based on wave optics, for fabricating designed strutures at submicrometer precision at high aspect ratio up to 10. We experimentally found that a deep hole with a diamter of 100 nm
is formed at the center of flat ablated region after EUV irradiation of a PDMS sheet through a circular aperture with a diamter of two micrometers in a contact mask. In the case of EUV irradiation through square apertures, the deep hole was not found on a PDMS sheet, while narrow dip is formed at the edge of the ablated region. We numerically calculated propagations of EUV plane wave light in PDMS sheets. After traveling one micrometer from a circular aperture, an intense peak appears at the center of the beam, which is caused by diffraction. For the square apertures, the enhancement does not occur, while intense profile near the edge is formed due to the Fresnel diffraction. Interestingly, at 100 micormeters from the aperture, the Frenel peaks are superposed at the center, resulting in a narrow and intense beam.
Tetsuya Makimura, Hikari Urai, Eriko Kira, and Hiroyuki Niino, "Microfabrication of PDMS structures based on wave optics using EUV radiations from laser-produced plasma (Conference Presentation)," Proc. SPIE 10519, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXIII, 105190X (Presented at SPIE LASE: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289413.5751428918001.
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