An electron beam lithography system: setup and characterization

An electron beam lithography system was realized by externally controlling a Hitachi S-4 100 field emission scanning electron microscope with a computer. Associated facilities were established for applying resist layers to substrates and for developing and etching exposed patterns. Procedures for the system’s use were developed and optimized as it is anticipated that many researchers will use the system in the future. The system’s performance was characterized with importance being placed on those issues that impacted on the goal of achieving sub 50 nm resolution with high pattern uniformity. The results were found to depend on many parameters including the resist thickness, resist composition, development time, and the specific pattern that was written. Resolutions of—50 nm with feature spacings of -200 rim were achieved in polymethylmethacrylate (PMMA) resist layers —200 imi thick. Indications are that moving to thinner resist layers, shorter development times, and higher contrast developers will enable better resolution to be achieved in the future. Nonuniformities on the order of -10 nm over —5 p.m scales have been achieved on both line and dot array patterns. These patterns were emphasized because of their applications in distributed feedback semiconductor lasers, and in the construction of artificial atom arrays. Systematic and random noise limitations were encountered that require further investigation to improve the uniformity beyond this level. Several patterning and processing concerns were also investigated to provide data important for the design of devices that incorporate nanometre scale structures. The most important issues are a limitation on the overall pattern size due to a fluctuating beam current, and a rotation effect that changes the orientation of the patterns on the substrate as the beam energy and working distance are varied.Science, Faculty ofPhysics and Astronomy, Department ofGraduat