Nanosphere Lithography for Nitride Semiconductors

Abstract

Nanolithography has been widely studied in recent years, considering its wide-ranging applications in electronics and photonics. In the ideal case, lithography using shortwavelength electromagnetic wave through a pre-defined mask is probably the most desirable solution. However, as technology progresses further, traditional photolithography is becoming exceedingly complex and incurring higher cost associated with light source as the wavelength of light goes shorter. Therefore, other nanolithography methods become strong competitors excelling with lower equipment cost and simpler fabrication procedures. In particular, nanosphere lithography as a self-assembly bottom-up approach for producing periodic array of spherical particles is simple and inexpensive as compared to other lithographic methods. Originally developed by Deckman et al. for defining a large area lithographic mask (Deckman & Dunsmuir, 1982), nanosphere lithography was further optimized by Hultenn et al. for applications involving surface-enhanced Raman spectroscopy (Haynes & Van Duyne, 2003; Hulteen & Vanduyne, 1995). Nanospheres that are used in lithography are commercially available in solution form, and through a simple coating procedure with optimized conditions, ordered hexagonal array of nanospheres can be naturally assembled as the nano-particles achieve equilibrium in an initially disordered system, i.e., a solution of nanospheres. Although only hexagonal array can be formed by this lithographic technique, the hexagonal pattern is useful for a range of applications, for instance, in nanophotonics where ordered hexagonal patterns can be used for the fabrication of photonic crystal (Han et al., 2005; Su et al., 2008) and also in plasmonics (Jensen et al., 2000; Malinsky et al., 2001; Stewart et al., 2006). With rivals like nanoimprint lithography (Byeon et al., 2007; Kim et al., 2007) and electron beam (e-beam) lithography (Berrier et al., 2004; David et al., 2006; Noda et al., 2007), the low cost and high through-put (albeit being less precise) nature of nanosphere lithography is especially suited for photonic applications. Gallium nitride (GaN) semiconductors and devices thus serve well as a platform for nanosphere lithography. In recent years, GaN has emerged as the most successful semiconductor material in optoelectronics, delivering a range of commercialized products which has since revolutionized our lives, including violet laser diodes for ultra-high capacity optical storage and white light LEDs for solid-state lighting (Humphreys, 2008; Schubert & Kim, 2005). While GaN technology is becoming mature, there is still plenty of Source: Lithography, Book edited by: Michael Wang, ISBN 978-953-307-064-3, pp. 656, February 2010, INTECH, Croatia, downloaded from SCIYO.COM