Space-charge limitations to throughput in projection electron-beam lithography (SCALPEL)

Abstract

Coulomb interactions in high-throughput charged particle lithography systems lead to an uncorrectable image blur, and can also results in image placement errors. Throughput is ultimately limited by the increasing loss of process latitude with increasing beam current, or by the loss of critical dimension or overlay control due to placement errors. We previously developed an analytical model of the stochastic space-charge induced beam blur for our SCALPEL (SCattering with Angular Limitation Projection Electron Lithography) system, and used it to optimize the design of our experimental tool; principally by constraining the column 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 measurements. We have also begun to quantify pattern distortions due to the global space-charge effects. Preliminary measurements show dose latitudes of ∼ 15%, consistent with a total blur of ∼ 150 nm, and a space-charge component no larger than 30 nm. No evidence for current dependent intrafield distortions has been observed.