A study of the effect of ultrasonic agitation during development of poly(methylmethacrylate) for ultrahigh resolution electron-beam lithography

Abstract

Articles you may be interested inOne step electron-beam lithography for multipurpose diffractive optical elements with 200 nm resolution An advanced epoxy novolac resist for fast high-resolution electron-beam lithography J. Vac. Sci. Technol. B 13, 3030 (1995); 10.1116/1.588316 Ultrahigh resolution chirped distributed feedback gratings fabricated by electron-beam lithography using bent waveguides for low-cost photonic components Experiments on poly͑methylmethacrylate͒ electron resist have been performed in order to understand how ultrasonic agitation during development affects sensitivity, contrast, and resolution. A modified JEOL 4000 EX electron microscope with a beam diameter of 1 nm was used for writing the resist patterns. First, the development/exposure characteristics of the ultrasonic development process were measured using large area ͑2ϫ2 m͒ patterns. With a 5 s develop in a mix of 3:7 cellosolve:methanol, it was found that ultrasonic agitation increases the effective sensitivity of the resist by roughly 20% but resist contrast does not change significantly ͑5.7Ϯ0.5͒. It was also found that the sensitivity increases approximately linearly with accelerating voltage from 75 to 400 kV but contrast does not change with voltage significantly. Resolution was explored by writing fine lines at progressively increasing doses in 60 nm of poly͑methylmethacrylate͒ and examining these lines with high resolution scanning electron microscopy. Complete development to the substrate was verified by wet etching a thin chromium layer underneath the resist. The narrowest lines that developed to the substrate had a width of about 10 nm although at this width considerable ''bridging'' of the lines was observed. We were unable with the ultrasonic agitation conditions used in our experiments to reduce the degree of bridging or the minimum linewidth.

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“…It is of paramount importance to carefully control the developing solution temperature, as repeatability is strictly related to how tight the control on the development temperature is. Ultrasound agitation sometimes proves useful during development, 26 but this has to be carefully considered against all the other process parameters. 27 It is important to note that some of the concepts just explained might vary slightly according to the specific brand of tool.…”