Quantitative trace metal analysis of silicon surfaces by ToF-SIMS

Abstract

Volumetric relative sensitivity factors (RSFs) are determined for 52Cr, 56Fe and 58Ni in an O2+-formed silicon oxide using a 12 keV Ga+ primary ion beam, and the influence of matrix oxygen content on these RSF values is evaluated. A multivariate expression for Si2+-referenced RSF values as a function of oxygen content is developed. This expression indicates that 12 keV Ga+ ion beam RSF values for 52Cr, 56Fe and 58Ni in O2+-formed oxide at 1.0 nm depth are in excellent agreement with well-established 8 keV O2+ RSF values in a silicon matrix. Because calculated RSF values for O2+-formed oxide at 1.0 nm depth and native silicon oxide are almost equivalent, time-of-flight (ToF) SIMS metal RSF values and detection limits in native oxide for a Ga+ liquid metal ion source are predicted, using the well-established 8 keV O2+ RSF values for metals in a silicon matrix. Time-of-flight SIMS silicon surface detection limits of 5×106 to 5×108 atoms cm−2 @ 0.5 nm are predicted for most metals of interest to the semiconductor community. © 1998 John Wiley & Sons, Ltd.