ANGULAR RESOLVED ENERGY ANALYSIS OF 69Ga+ IONS FROM A GALLIUM LIQUID METAL ION SOURCE

An analysis system has been designed and built to characterise liquid metal ion source beams. Both mass and angular resolved energy distribution measurements can be made, from which both FWHM energy spreads and energy deficits can be obtained. This paper briefly describes the system and presents and discusses the first off-axis results taken with a gallium liquid metal ion source. Liquid metal ion (LMI) sources are finding increasing applications in the semiconductor and microanalysis fields. Despite considerable source development much is still to be understood about the ionisation mechanisms and complex internal beam interaction processes occurring. A system for characterising LnI source beams has been developed to study these phenomena. I mE ANALYSIS SYsm The system consists of a 180° electrostatic hemispherical energy analyser and retarding lens coupled with a quadrupole mass filter. Ions are detected using either a Faraday cup or a channeltron electron multiplier. Angular variation is achieved by rotating the ion source about an axis at the needle tip (the ionisation region). The source and analysers are held in a UHV chamber routinely held at .r. 1 x mbar; a schematic diagram is shown in figure 1. The LMI source is supported in a purpose built stage attached to an XIZ translator. This translator enables the source to be positioned on the axis of the retarding lens and is used to rotate both the source and the extraction electrode with respect to the analyser system. The stage holding the source was designed to facilitate alignment of the source needle with the axis of rotation of the translator and to position accurately the extractor electrode with respect to the source. Extractor electrode alignment was important as the emitted beam angle was strongly affected by the axial alignment of the needle tip with the electrode aperture. Alignment of both source needle and extractor electrode could be made to % 20 p. Angular alignment of the needle with the axis of the retarding lens was made t o % 0.3O and the extractor electrode was aligned perpendicular to this axis to < 0.8'. The emitted ion beam axis was aligned with the axis of the retarding lens using the rotational variation provided on the translator. A beam angular misalignment in the plane perpendicular to this rotational plane of % 3 ' was estimated from a set of angular intensity distributions. The entrance aperture of the retarding lens when used for LMI source measurements was 0.1 mm in diameter, allowing a cone of ions with a 0. lo half angle to enter the lens. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987631 C6-190 JOURNAL DE PHYSIQUE The purpose built stage also supported a tungsten wire heater which was electrically isolated from the source needle, and a Chromel-Alumel thermocouple in contact with the source reservoir case. A gallium LMI source on loan from 1.B.T.-Dubilier Ltd. was used for the measurements presented in this paper. The performance of the energy analyser and retarding lens was monitored using two indium oxide thermal ionisation sources, as previously described 111. This enabled the change in transmission of the lens to be estimated, the energy resolution of the analyser to be measured under various operating conditions and the voltage deficit scale to be established. No change in transmission of .the lens was observed when operating under conditions similar to those used for LMI source energy spread measurements. For the following results, the analyser resolution was < 0.4 eV for most energy distributions taken and < 0.9 eV for some selected measurements above 10 VA beam current. LE/E for the analyser was measured to be 0.018. Foradoy Electron multopl~~r High vacuum / L M l S I