Line-edge roughness due to mask and wafer charging in ion beam proximity lithography can be simply and completely eliminated by neutralizing the ions before they reach the mask. This dramatically increases the usable depth of field and enables high quality imaging below 20 nm. Neutralization is accomplished by charge transfer scattering in a high pressure cell, a process that preserves both the energy and direction of the parent ion with remarkable accuracy. In this article, the authors discuss the design of an energetic atom source and characterize an optimized helium ion injector based on a dc-multicusp ion source. The injector provides a crossover at a fixed position in the charge transfer cell over a design energy range from 30 to 50 keV. For 100 W discharge power, the full width at half maximum diameter and normalized brightness of the crossover are 95 mu m and 100 A/m(2) sr V, respectively. (c) 2007 American Vacuum Society.