High-energy Electron Beam Lithography for Nanoscale Fabrication

Recently, there has been much research in the field of nanostructure technology. The objective of this article is to explore the basic physics, technology, and applications of ultrasmall structures and devices with dimensions in the sub-100-nm range. Nanostructure devices are now being fabricated in many laboratories to explore various effects, such as those created by downscaling existing devices, quantum effects in mesoscopic devices, tunneling effects in single electron transistors, and so on. In addition, new phenomena are being explored in an attempt to build switching devices with dimensions down to the molecular level. Today, the minimum size of semiconductor production devices is down to 45 nm or less. Miniaturization and performance improvements are allowing the electronics industry to shrink the future size of semiconductor devices. For the last three decades, technological advances in optical lithography have led the semiconductor industry. In the present day mass-production line, deep ultraviolet (DUV 193 nm) optics is used for critical dimensions approaching 90 nm. A further decrease in immersion lithography has pushed the production line into the 32-nm era. However, as wavelengths decrease, optical lithography begins to suffer from difficulties associated with shallow focus length and materials (including lenses, masks and resists) to do with dispersion relationships. Therefore, non-optical lithographic techniques such as electron-beam direct write (L. Pain et al., 2006), electron-beam projection (J. Yamamoto et al., 2000), ion-beam projection (Y. Lee et al., 1998), and soft X-ray extreme ultraviolet (EUV 13 nm) (S. Hector, 1998; C. W. Gwyn et al., 1998) are being increasingly focused in order to replace or “mix & match” with optical lithography. Electron beam direct write is the only technology that does not require masking. Electron beam lithography (EBL) is one of the versatile lithographic tools widely used for nanostructure fabrication. In EBL, the critical dimension of the exposure patterns is limited by electron scattering in both electron-beam resists and substrates. The demand for fine patterns calls for EBL systems with high acceleration voltages. These have the advantage of having smaller forward scattering angles in the resist and a wide secondary-electron spread in the Source: Lithography, Book edited by: Michael Wang, ISBN 978-953-307-064-3, pp. 656, February 2010, INTECH, Croatia, downloaded from SCIYO.COM