Negative chemically amplified resist characterization for direct write and SCALPEL nanolithography

Despite the common link of using high energy electrons as exposure probes in direct write and SCALPEL lithography, the imaging systems in both are different. The question arises then if an optimal process for direct write lithography will provide optimal results in SCALPEL. Characterization of a series of negative tone chemically amplified resists for use in direct write (at 50 kV) and projection electron beam (at 100 kV) nanolithography is reported. The current work has explored modifying the postapplied bake and postexposure bake temperatures and times to find an optimum process for direct write nanolithography and then verify it is applicable to SCALPEL. Results, using NEB-22A (Sumitomo Chemical Co.), show that this is possible. We have demonstrated that in direct write, the NEB-22A resist has excellent resolution (36 nm in 125-nm-thick resist, 75 nm in 500-nm-thick resist) and process latitude (>20%), with a sensitivity of about 14 mu C/cm(2) at 50 kV exposure. The etch resistance is 3 nm/s and is being used for gate level e-beam lithography of single level field-effect transistors. The optimal bake conditions are found to be longer than usual postapplied and postexposure bake times. We have also demonstrated that the optimal bake conditions can be transferred to a SCALPEL exposure with similar process latitude and resolution. (C) 1998 American Vacuum Society. [S0734-211X(98)12406-X].