Study of H− beams for ion-projection lithography

Abstract

The desired properties of ion sources used in ion-projection lithography are high brightness and low energy spread. Due to a very stringent demand in many other applications, the state of the art of negative hydrogen ion (H−) beams has advanced significantly in recent years. H− ion beams with the transverse ion temperature of about 0.3 eV have been obtained from surface plasma sources in pulsed mode operation [V. G. Dudnikov and G. E. Derevyankin, AIP Conf. Proc. 287, 239 (1994)]; a design for a cw source to achieve a comparable, or even lower energy spread and high brightness has been reported [S. K. Guharay, M. Reiser, and V. G. Dudnikov, Rev. Sci. Instrum. 65, 1745 (1994)]. The energy spread of H+ ion beams now in use is in the range of about 6–10 eV. This renders the H− ion beams an attractive alternative to the H+ ion beams for ion-projection lithography. No data of H− ion exposure of resists are available, and we have carried out experiments illuminating PMMA resists with various doses of H− ions and H+ ions at 24 keV. Within experimental accuracy the exposure characteristics (e.g., sensitivity and contrast) are identical for both H− and H+ ions.