Characterization of Atmospheric Impurities in Tungsten Silicide Films by Secondary Ion Mass Spectrometry (SIMS)

Abstract

AbstractConcentrations of atmospheric impurities in tungsten silicide films and impurity areal densities silicide / polysilicon interface can usually only be measured using Secondary Ion Mass Spectrometry (SIMS). Normally these measurements are made using a Cs+ primary beam with negative secondary ions being monitored. This mode is used to achieve the best possible detection limits. However the Relative Sensitivity Factors (RSFs) used to quantify the impurities, as well as the reference matrix signal, change dramatically in going from one matrix to the other. These changes affect the quantification of the impurities at the interface. An alternate mode of analysis would be to use the Cs+ primary beam and monitor MCs+ ions, where M is the impurity, because these ions typically have less matrix dependent RSFs. We measure carbon and oxygen in a tungsten silicide film on polysilicon using both modes of analysis. Preliminary data indicates that we have determined the absolute accuracy of interface areal density to within a factor of 2.2 for oxygen and to within a factor of 1.5 for carbon.