High mass resolution surface imaging with a time-of-flight secondary ion mass spectroscopy scanning microprobe

Abstract

This article describes first applications of a time-of-flight secondary ion mass spectroscopy (TOF-SIMS) scanning microprobe, based on a high mass resolution TOF-SIMS instrument, combined with two pulsed primary ion sources: (a) 10 keV Ga liquid metal ion source (LMIS), probe size: 0.5–1 μm; (b) 10 keV electron impact (EI) ion source (Ar+,Xe+,O+2), probe size 4–10 μm. The detection limits for elemental and molecular surface species as a function of probe size are discussed. At a lateral resolution of 1 μm secondary ion images with about 1000 counts/pixel can be acquired in about 30 min. The high useful yields achieved by TOF-SIMS allows the analysis of submonolayers of inorganic as well as organic materials at high lateral resolution. Currently up to 24 secondary ion images for different masses and a complete mass spectrum can be acquired simultaneously. The performance of the instrument is demonstrated by multielemental and molecular imaging of inorganic and organic patterns on Si wafers. Secondary ion images of a polymer with an average molecular weight of 1400 amu prepared on a silver substrate are presented. As an example for the analysis of insulating materials secondary ion images of an electrically isolated surface mounted device solder pad on an electronic board are shown.