E-Beam nanolithography integrated with nanoassembly: Precision chemical engineering

Abstract

The minimum feature size of electronic devices used in microprocessors has shrunk to the nanoscale (^lt;100 nm) in 2004 (http://www.intel.com/research/ silicon/nanotechnology.htm). These electronic devices still work on multielectron processes. However, interest in single electron (quantum) devices has been of academic interest for a number of years (Daniel 2004), and is increasingly becoming of interest to industry as conventional microelectronic devices shrink toward the quantum regime. In addition, apart from the drive to create smaller structures on native SiO2 for use in nanoelectronics, a significant challenge in current nanoscience and nanotechnology is to spatially self-organise selfassembled nanoscale components (such as metal nanoparticles, carbon nanotubes, proteins, cells, organic molecules, polymers, etc.) onto surfaces to fabricate functional nanostructured systems for electronic, optoelectronic, biological, or sensing applications (Mendes et al. 2003; Ball 2000; Dagani 2000). Precise control over the relative position and orientation of the nanocomponents is frequently required in such systems to obtain useful properties. Moreover, the integration and the stability of interfaces to these nanostructures from the micronlength and macroscopic scales are key to the success of future applications. Nanostructuring surfaces by top-down nanolithography techniques, and subsequently building into the third dimension utilising bottom-up selforganisation of self-assembled nanoentities, is an attractive approach for creating such a bridge between macroscopic systems and the nanoscale dimensions that many modern technologies demand (Dagani 2000; Whitesides 2002). The integration of both top-down and bottom-up approaches has been termed precision chemical engineering (Mendes 2004), and is based on the concept that surfaces are written with precision engineering (i.e. in a spatially controlled fashion to direct the surface chemistry), coupled with the engineering that is involved in fabricating three-dimensional architectures from the surface using molecular and condensed phase entities. Besides requiring lithographic techniques with nanometre resolution, ultra-high resolution patterning also needs materials that allow a controlled modification of their physical and/or chemical properties. However, it is becoming increasingly clear that the photolithographic process for creating structures on the native oxide of silicon is rapidly reaching a physical limit in terms of the lateral resolution that is achievable. This limitation is a result of (i) the diffraction limit, (ii) limitations of the optics, and (iii) the materials used to transfer patterns to the surface (Silverman 1997). Thus, several methodologies have been developed in recent years that may be the successor to conventional photolithography. In this review we will discuss electron beam (e-beam) lithography (Roberts 1987), and in particular the development of the organic based resist materials that have been used, starting with polymeric materials, through molecular materials and finally self-assembled monolayers (SAMs). © Springer-Verlag Berlin Heidelberg 2006.