QUANTIFICATION OF METAL TRACE CONTAMINANTS ON SI WAFER SURFACES BY LASER-SNMS AND TOF-SIMS USING SPUTTER-DEPOSITED SUBMONOLAYER STANDARDS

We have shown that quantitative determination of metal trace impuritie s in the range between 10(9) cm(-2) and 10(12) cm(-2) on top of the na tive oxide of a Si wafer by laser postionization of sputtered neutrals in combination with time-of-flight mass spectrometry (Laser-SNMS) and time-of-flight secondary ion mass spectrometry (TOF-SLMS) is possible . Trace metal standards with concentrations in the range between 10(9) cm(-2) and 10(12) cm(-2) were used for calibration. These standards w ere prepared by sputter deposition and were independently controlled b y Total Reflection X-Ray Fluorescence Analysis. Relative sensitivity f actors for 12 metals on Si for Laser-SNMS were determined. Additionall y, we compared postionization with different wavelengths (193 nm and 2 48 nm). With Laser-SNMS it was then possible to determine the influenc e of UV/ozone treatment on the measured surface concentration of metal species. The UV/ozone treatment is necessary to achieve high and repr oducible useful yields for the metal species in TOF-SIMS. With this kn owledge, we were able to determine relative sensitivity factors for th e metals on UV/ozone-treated Si wafer surfaces measured by TOF-SIMS. D etection limits down to 10(8) cm(-2) and 10(12) cm(-2) for sample surf ace areas of 100 mu m in diameter and 1 mu m in diameter, respectively , were found for both Laser-SNMS and TOF-SIMS. (C) 1996 American Vacuu m Society.