Fundamentals of Electron Beam Exposure and Development
Electron Beam Lithography (EBL) is a fundamental technique of nanofabrication, allowing not only the direct writing of structures down to sub-10 nm dimensions, but also enabling high volume nanoscale patterning technologies such as (DUV and EUV) optical l
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Fundamentals of Electron Beam Exposure and Development Mohammad Ali Mohammad, Mustafa Muhammad, Steven K. Dew, and Maria Stepanova
Abstract
Electron Beam Lithography (EBL) is a fundamental technique of nanofabrication, allowing not only the direct writing of structures down to sub-10 nm dimensions, but also enabling high volume nanoscale patterning technologies such as (DUV and EUV) optical lithography and nanoimprint lithography through the formation of masks and templates. This chapter summarizes the key principles of EBL and explores some of the complex interactions between relevant parameters and their effects on the quality of the resulting lithographic structures. The use of low energy exposure and cold development is discussed, along with their impacts on processing windows. Applications of EBL are explored for the fabrication of very small isolated bridge structures and for high density master masks for nanoimprint lithography. Strategies for using both positive and negative tone resists are explored.
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Introduction
With its ability to form arbitrary two-dimensional patterns down to the nanometer scale, electron beam lithography (EBL) is one of the most important techniques in nanofabrication. In short, it involves the exposure by a highly focused electron
M.A. Mohammad (*) • M. Muhammad • S.K. Dew Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada e-mail: [email protected] M. Stepanova National Institute for Nanotechnology, National Research Council, and Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada M. Stepanova and S. Dew (eds.), Nanofabrication, DOI 10.1007/978-3-7091-0424-8_2, # Springer-Verlag/Wien 2012
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Fig. 2.1 Outline of EBL process steps to form a nanoscale pattern in a positive-tone resist layer
Fig. 2.2 Electron beam exposures systems: (a) schematic diagram, (b) Raith 150TWO commercial EBL system (used with permission [7])
beam to dramatically modify the solubility of a resist material during a subsequent development step, see Fig. 2.1. EBL was originally developed using scanning electron microscopes to which a pattern generator and beam blanker was added to control which areas of the viewing field are exposed [1–3] (see Fig. 2.2a for a schematic description of an EBL system). Modern EBL tools are fully dedicated patterning systems (Fig. 2.2b) that employ high brightness electron sources for faster throughput and high resolution mechanical stages to be able to expose step-by-step large substrates under the relatively narrow field of focus of the electron beam. These direct write systems have the advantage of extremely high resolution and the ability to create arbitrary patterns without a mask. Their disadvantage is the long times taken to write large, complex patterns. Efforts to overcome this challenge include projection EBL [4, 5] and the use of massively parallel beams [6]. Due to the developmental stage of these latter techniques, however, this chapter
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