Liquid Metal Ion Sources for Scanning SIMS

Liquid metal ion sources (LMIS) were introduced in the field of microanalysis by SIMONS et al. [1] who demonstrated that the high ion currents which can be extracted from a single liquid metal tip can be usefully applied for high sensitivity compositional analysis of liquefied metal alloys. KROHN and RINGO [2] were the first to suggest the use of a finely focused liquid metal ion beam as the primary beam in a scanning ion microprobe. Somewhat later, true submicron scanning ion beam columns of high current density (1 A/cm2 50nm diameter) were developed for applications in ion lithography, microfabrication and maskless ion implantation [3], [4], The first demonstration of the feasibility of a submicron primary ion beam in SIMS was given by PREWETT et al. [5], Obviously, submicron lateral resolution was the main driving force behind the introduction of the LMIS in SIMS. There are. however, a number of reasons why the LMIS could be a useful alternative to the routinely used gaseous primary ion beams. In addition, some unexpected properties of LMIS beams have emerged which, if judiciously exploited, could also be useful in microanalysis (see Table 1).