A great amount of research has been devoted to the fabrication of micrometer or nano-size patterns and structures. Ultra-precision patterning technologies have been extended to numerous applications such as mechanical components, sensors as well as optical and electronic devices. There is also a hard-X-ray-based lithography technology that utilizes synchrotron-radiated ultra-short-wavelength X-rays. Such a process is useful for manufacturing high-aspect-ratio microstructures, given the good collimation property and high intensity of synchrotron-based X-rays.
X-ray-based lithography has a drawback with respect to the fabrication of multi-layered structures: specifically, the difficulty of the alignment process, due to the opaque property of the X-ray mask. It is for this reason that hard-X-ray lithography has been applied mainly to mono-layered microstructures. Another drawback of hard-X-ray lithography is the difficulty of the demolding process when precise structures fabricated by X-ray lithography and the subsequent electroforming process are utilized as mold inserts for the purposes of mass production. There are also other drawbacks to this X-ray process as an ultra-precision patterning technique for realization of sub-micron or nano-scale structures due to the difficulty of fabricating a precise X-ray mask. In the present dissertation, novel technologies for fabricating micro- and nano-scale structures by overcoming afore-mentioned difficulties were proposed and developed.
In term of novel microstructures, two types of novel technology developed for fabrication of multi-layered microstructures are proposed. One, vertically modularized micro-mold systems, and the other, hybrid machining based on the combination of the conventional micro-milling process and hard-X-ray lithography. The proposed technologies could overcome the pattern-accuracy limitation of conventional machining as well as the pattern-flexibility drawback of the X-ray process. Their respective utilities were demonstrated through fabrication of various multi-layered structures of tens of microns lateral size and millimeter-range height. In addition, in order to overcome the difficulty encountered in the demolding process when X-ray-based microstructures are utilized as mold inserts for mass production, proposed sacrificial polymer-based mold inserts were tested. These mold inserts proved controllable in their mechanical hardness and chemical solubility by introduction of unique second X-ray irradiation. With such sacrificial inserts, powder-injection molding could be used to achieve ceramic-based microstructures with an aspect ratio of 5 and a lateral size of about 40~50 μm, which are difficult to realize by other machining or lithography technologies.
In order to fabricate sub-micron- or nano-size patterns, two types of technique were developed. The first is based on precise stage movement and utilization of a micron-scale X-ray mask. Ultra-long channels or structures of about 500 nm scale were realized without the aid of advanced lithography for fabrication of X-ray masks such as electron-beam writing or ion-beam lithography. The second technique proceeds via the fabrication of a nano-X-ray mask using typical UV lithography and metal deposition to sidewalls. Then, a novel multi-scale fabrication technique utilizing multiple X-ray irradiations or multiple X-ray masks was developed for fabrication of various micro- and nanostructures. This technique is a cost-effective means of achieving ultra-precision structures that are difficult to realize using typical UV lithography. Also, high-aspect-ratio or oblique-shape sub-micron or nanostructures were demonstrated. According to the easy realization of nano-channels by the proposed techniques, a feasibility study on the application of nanofluidics also was carried out.
It should be noted that all of the proposed techniques offer, additionally to their micro- and nano-structural fabrication performances, simplicity and ease of use, which attributes provide further evidence of their great utility as precision manufacturing technologies