A STUDY OF THE EFFECT OF ULTRASONIC AGITATION DURING DEVELOPMENT OF POLY(METHYLMETHACRYLATE) FOR ULTRAHIGH-RESOLUTION ELECTRON-BEAM LITHOGRAPHY

Experiments on poly(methylmethacrylate) electron resist have been perf ormed in order to understand how ultrasonic agitation during developme nt affects sensitivity, contrast, and resolution. A modified JEOL 4000 EX electron microscope with a beam diameter of 1 nm was used for writ ing the resist patterns. First, the development/exposure characteristi cs of the ultrasonic development process were measured using large are a (2X2 mu m) patterns. With a 5 s develop in a mix of 3:7 cellosolve:m ethanol, it was found that ultrasonic agitation increases the effectiv e sensitivity of the resist by roughly 20% but resist contrast does no t change significantly (5.7+/-0.5). It was also found that the sensiti vity increases approximately linearly with accelerating voltage from 7 5 to 400 kV but contrast does not change with voltage significantly. R esolution was explored by writing fine lines at progressively increasi ng doses in 60 nm of poly(methylmethacrylate) and examining these line s with high resolution scanning electron microscopy. Complete developm ent to the substrate was verified by wet etching a thin chromium layer underneath the resist. The narrowest lines that developed to the subs trate had a width of about 10 nm although at this width considerable ' 'bridging'' of the lines was observed. We were unable with the ultraso nic agitation conditions used in our experiments to reduce the degree of bridging or the minimum linewidth. (C) 1995 American Vacuum Society .