A focused gas-ion beam system for submicron application

Our gas field ion source, equipped with a supertip, has been complemented with an ion-optical column in order to produce a finely focused beam. The rather simple optical system consists of two einzel lenses of the Riddle type, an x-y steerer pair and a 12-pole deflector after Bonshtedt. Our calculations indicate that a limiting current of about 10 nA can be delivered into a 100 nm image spot, corresponding to a current density of 100 A/cm2, when previously measured ion source currents at a transmission of 75% are assumed. The presently obtained values are still considerably lower due to several technical limitations which are being overcome by a few slight modifications of the mechanical construction. The smallest image spot observed so far has been limited to 0.25 μm due to mechanical vibrations. First applications of submicron beams will be reported and further plans on both material analysis and modification discussed. (orig.)