Very high sensitivity ZEP resist using MEK:MIBK developer

Low throughput is the major drawback for electron beam lithography. Chemically amplified resists that have high sensitivity are often used to keep the exposure time within practical limit. In this Letter the authors show that the popular non-chemically amplified electron beam resist ZEP-520A can achieve 2.6 C/cm² sensitivity when using methyl ethyl ketone:methyl isobutyl ketone developer and 5 keV exposure, though at the cost of reduced contrast compared to standard developers xylene, n-amyl acetate or hexyl acetate. The achievable resolution was found to depend strongly on the resist´s adhesion to the substrate or under-layer and thus obtained 40´nm half-pitch resolution using ZEP resist spun on a layer of anti-reflection coating that was treated by oxygen plasma.