ABSTRACT
In this chapter, we describe colloidal self-assembly pathways towards fabricating ultrahigh-density ordered nanostructures over large areas. Colloidal self-assembly directed by templates has been shown to enable the formation of controlled nanosphere arrays with periods well below 100 nm. We developed our nanopattern transfer techniques using reactive ion etching and mask layers for fabrication of nanopatterns from dense colloidal arrays and for increasing the pattern height. Their combination with nanoimprint lithography may provide a new technology for high-resolution, high-throughput, and low-cost nanopattern formation. 1.1 IntroductionPhotolithography is the most reliable and economical lithography technology for industrial micro-and nanofabrication [1]. This is
especially true for the semiconductor and magnetic recording industries where the current characteristic feature sizes reach down to sub-100 nm. In these technologies, the fabrication of even smaller nanostructures is often desirable to further improve device properties. Miniaturization technology is also desired in other fields in order to realize new functional devices. In state-of-the-art photolithography systems, excimer laser sources and complex immersion lens systems are used to enhance resist-pattern resolution; they enable pattern sizes smaller than UV laser wavelengths. To fabricate far smaller nanostructures, however, greater progress is required in photolithography technology [2,3]. Extreme UV (EUV) light sources of far shorter wavelengths, their specific optical systems, photoresist materials, and pattern transfer techniques have all been extensively studied for higher resolution photolithography. Nevertheless, their industrial application remains challenging [4]. There are other lithography technologies such as electron beam (EB) lithography, focused ion beam lithography, and scanning probe lithography, which can be used, to some extent, to fabricate smaller nanopatterns than conventional photolithography. Their throughput is, however, very low at the highest resolution due to their serial writing characteristic, while the equipment is rather expensive for large scale use. Direct use of these technologies for manufacturing would critically deteriorate throughput performance and result in a tremendous increase in product costs. Instead of photoexposure and the development of photoresists, nanoimprint lithography uses moulding with a stamp and etching to create resist patterns [5-7]. This technique is promising since nanoimprint lithography enables ultrahigh-resolution large-area patterning in a single, fast step in thermally or UV-curable resist. There are, nonetheless, still some technological challenges in nanoimprint lithography technology, particularly in nanoimprint mould fabrication for ultrahigh-density nanopatterning. For the mechanical moulding of resist, nanostructures with the same dimensions are the prerequisite for a mould. It means that the original nanostructures of a mould must be fabricated by other high-resolution lithography techniques. Moreover, mould nanopatterns must be of sufficiently large aspect ratio and sharpness to maintain the fidelity of nanopatterns imprinted into the resist during the subsequent etching of residual resist in the compressed areas.
