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The capability to detect and quantify sulfur at the part-per-billion (ppb) concentration level in ultrapure hydrochloric acid rinse solutions used in GaAs wafer fabrication is described. Nonvolatile residues formed from the deposition of nanoliter aliquots of solution onto high purity silicon wafers are analyzed using a high performance CAMECA IMS 4f ion microanalyzer. The dynamic SIMS analysis of microdroplet residues is referred to as Microvolume-SIMS (MV-SIMS). The Microvolume-SIMS analyses of two acid solutions are presented. The concentration of total sulfur detected in these solutions was 98 and 650 ppb; both values are below the SEMI specification standard of less than 1300 ppb total sulfur concentration. Despite this, the acid solution containing 650 ppb of total sulfur was responsible for causing an isolation failure halting wafer production. This finding corroborated electrical failure analyses using these same acids.

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An experimental protocol using secondary ion mass spectrometry to measure Al in vapor phase decomposition (VPD) solutions has been developed to achieve a detection limit of 108 atoms/cm2. The analytical technique is called VPD/SIMS. The procedure utilizes sample preparation techniques developed for microvolume SIMS. Preliminary SIMS analysis of simulated VPD solutions consisting of dilute HF indicate that a theoretical detection limit of 5.7×105 Al atoms/cm2 is possible from a 6″ wafer.

Concentrations 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.