Nanoscale resist morphologies of dense gratings using electron-beam lithography

Abstract

Negative electron-beam resist hard mask ion beam etching process for the fabrication of nanoscale magnetic tunnel junctions J. Vac. Sci. Technol. B 30, 06FA01 (2012); 10.1116/1.4767123 Long nanoscale gaps on III-V substrates by electron beam lithography J. Vac. Sci. Technol. B 30, 06F305 (2012); 10.1116/1.4766881 Nanomachining and clamping point optimization of silicon carbon nitride resonators using low voltage electron beam lithography and cold development J. Vac. Sci. Technol. B 28, C6P36 (2010); 10.1116/1.3517683Accurate control of remaining resist depth for nanoscale three-dimensional structures in electron-beam grayscale lithography J.The authors report a systematic investigation, both by experiment and by numerical modeling, of resolution limits for dense nanoscale gratings fabricated in polymethylmethacrylate through low-energy electron-beam lithography ͑EBL͒ using 10 keV electrons. In particular, they have studied the resist morphologies that develop in various exposure regimes for gratings with periods from 20 to 100 nm and categorized the potential sources of resist damage in such gratings. Through comparison of their experimental and numerical results, they have elucidated the major mechanisms that limit the EBL process resolution at the stages of exposure and resist development. The authors have also suggested semiempirical criteria to predict the risk of resist damage when fabricating dense nanostructures.

The Interdependence of Exposure and Development Conditions when Optimizing Low-Energy EBL for Nano-Scale Resolution

“…The explanation is that in periodic gratings, the exposure dose per line at which the depth clearance is achieved can be viewed as independent of the interline distance. This leads to the corresponding dose per unit area decreasing roughly in proportion to the inverse of the period (Mohammad et al, 2007).…”

“…The underlying mechanism would comprise relocation of individual molecules of PMMA driven by thermodynamic forces associated with the surface tension between the insoluble PMMA fraction and the developer. In our works we denote this mechanism as micellization, to emphasize the expected involvement of solventophobic interactions resulting in phase separation (Mohammad et al, 2007). To summarize, we observe four factors that may damage the resist morphology.…”

“…in a 1:3 MIBK:IPA solution at room temperature. The lateral size of all images is 1 μm×1 μm (Mohammad et al, 2007).…”

“…The experimental methodology that we have employed has been described in detail elsewhere (Mohammad et al, 2007). In brief, cleaned silicon substrates were spin coated with 950k mol.…”

“…Clearly, this systematic understanding should rely on a solid knowledge of the physico-chemical molecular-level processes behind the resist exposure to electrons as well as the subsequent post-exposure development stages. Over the last several years we have been investigating thoroughly, both experimentally and by numeric modeling, the impact of the major EBL process factors on the quality of dense nanoscale patterns in the popular positive-tone resist, PMMA (Aktary et al, 2006;Mohammad et al, 2007;Mohammad et al, 2009. In this chapter, we outline the methodologies that we have developed for fabrication and visualization of nanopatterns in PMMA, as well as our model for the exposure, fragmentation, and dissolution of positive resists.…”