SPACE-CHARGE LIMITATIONS TO THROUGHPUT IN PROJECTION ELECTRON-BEAM LITHOGRAPHY (SCALPEL)

Coulomb interactions in high-throughput charged particle lithography s ystems lead to an uncorrectable image blur, and can also results in im age placement errors. Throughput is ultimately limited by the increasi ng loss of process latitude with increasing beam current, or by the lo ss of critical dimension or overlay control due to placement errors. W e previously developed an analytical model of the stochastic space-cha rge induced beam blur for our SCALPEL (SCattering with Angular Limitat ion Projection Electron Lithography) system, and used it to optimize t he design of our experimental tool; principally by constraining the co lumn length and optimizing the numerical aperture to achieve the best balance between electron-optical aberrations and the stochastic blur. We have attempted to validate this model with experimental measurement s. We have, also begun to quantify pattern distortions due to the glob al space-charge effects. Preliminary measurements show dose latitudes of similar to 15%, consistent with a total blur of similar to 150 nm, and a space-charge component no larger than 30 nm. No evidence for cur rent dependent intrafield distortions has been observed.