<title>Liquid Metal Ion Sources For Lithography Some Recent Advances</title>

Abstract

Liquid metal ion sources for lithographySome recent advancesP. D. Prewett (Dubilier Scientific Limited, England)D. J. McMillan, D. K. Jefferies (UKAEA Culham Laboratory)and G. L. R. Mair (Aston University)AbstractThe high brightness liquid metal ion source (LMIS) is being used for ion beamlithography.Recent technological advances include a source for reactive metals and a source of7Li+ for light ion beam lithography seems possible. Alloy sources for microfabricationby direct doping are being studied by several groups and a gold -silicon alloy source hasalso been used for lithography.Fundamental understanding of the LMIS is still advancing and the emission process isnow generally held to be field evaporation. Recent energy spread measurements haverevealed two modes of behaviour which may be linked to hydrodynamic effects.IntroductionThe liquid metal ion source (LMIS) was originally developed for its potential as an ionbeam thruster for spacecraft propulsionl. While interest in this application continuesusing liquid caesium as the propellant2,3 much more attention is being paid to the roleof the LMIS in microcircuit fabrication. Several groups are now actively engaged in ionbeam lithography using finely focussed beams from LMISs4,5 and considerable attention isbeing paid to the alternative or complementary approach of direct implantation doping ofsemiconductors without masks using focussed beams of dopant ions.The advantages of using ion beams rather than electrons for lithography to submicrontolerances are now well- known6'7 while direct writing of dopant implants could have aneven more profound impact upon the manufacture of VLSI circuits. For both approaches,the chief advantage of the LMIS is its exceptionally high brightness8 (up to 106 A cm-2