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

Abstract

Experiments on poly(methylmethacrylate) 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 (2×2 μm) 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 (5.7±0.5). 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 poly(methylmethacrylate) 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.