Abstract
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask.
Highlights
In a diffraction phenomenon where a light ray can bend around the edges of its target and reach to its backside, a bokeh of the size near a wavelength is often observed
The performance of an X-ray grayscale mask that consisted of Si absorbers processed by tapered-trench-etching, and of a SU-8 membrane was evaluated using a beamline BL-4 of TERAS synchrotron radiation (SR)
Three kinds of characteristic are required of a membrane material for X-ray lithography
Summary
In a diffraction phenomenon where a light ray can bend around the edges of its target and reach to its backside, a bokeh of the size near a wavelength is often observed. We fabricated a three-dimensional Si absorber employing a tapered-trench-etching technique using a mixed gas of SF6, C4F8, and O2; and we had developed a stencil X-ray mask [21] and a SU-8 membrane X-ray mask [22] By combining these X-ray masks with a LIGA process, a micro-needle array was formed [23]. This paper reports on the evaluation results of SU-8 as regard to three characteristics namely transmittance, dimensional stability, and durability that are required of a membrane of any X-ray mask. This information, that shows excellent characteristics of SU-8 in the X-ray energy region, is expected to be quite valuable to the researchers in this field
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