High-brightness negative ion beams from a plasma source and merits for new applications in materials science and microelectronics

Abstract

Summary form only given, as follows. High-brightness ion beams, with low energy spread, are attractive for many applications in microelectronics and materials science. Critical needs exist to develop an integrated technology using intense ion beams from a source and a matched ion-optical column. With this goal, we have developed a compact plasma source with a lens system. Either positive or negative ion species can be extracted from this source; we focus on negative ions. When negative ions strike a surface, especially an electrically isolated surface, the charging voltage of the surface is limited to few volts. This property can be very effective in applications where (a) damages due to voltage breakdown are issues of concern, and (b) focused ion beams are used to modify or examine a small region, especially on electrically floating or insulator structures. H/sup -/ beams from our plasma source have brightness within an order of magnitude of the value for beams from liquid metal ion sources. Our plasma source can yield beams with angular beam intensity of >40 mAsr/sup -1/ and energy spread of /spl sim/2.5 eV for H/sup -/ beams. Using a simple Einzel lens with magnification of about 0.1 we obtained a focused beam current density of about 40 mAcm-. Adding another stage of lens with additional magnification of about 0.1 we expect a focused current density of >1 Acm/sup -2/ and a focused spot size of < about 200 nm. A comparative study of beams from different sources reveals the merit of our plasma source for focused ion beam applications. In its pulsed mode of operation, with pulse length of 1 ms and repetition rate of 6 Hz, the present source ran reliably over more than 500 hours. We plan to operate this source in cw mode and examine characteristics of focused beam spots for different ion species.