Evaluation of a Cesium Primary Ion Source on an Ion Microprobe Mass Spectrometer

A commercially available Cs⁺ Ion source has been modified for use as the primary Ion source on an Ion microprobe mass spectrometer. The primary ion current Is stable to ~ 1 % over a 1-h period. Up to 1000 h operation Is achieved on a single charge of cesium. Current densities of 10 mA cm^-2 or better are achieved In microfocused spot sizes ranging from 8 μm to 30 μm. Secondary negative ion yields of electronegative species under Cs⁺ Ion bombardment compare favorably with positive ion yields of electropositive species under O₂⁺ Ion bombardment. Sputtering rates of Si and GaAs are 2 and 5 times faster respectively than O₂⁺ sputtering rates for these substrates. These high sputtering rates facilitate rapid depth profiling analyses. Detection limits have been determined under sample-limited depth profiling conditions for H, C, O, F, and As in Si, and for S in GaAs.