Remediation for TXRF saturation effects on microdroplet residues from preconcentration methods on semiconductor wafers

Abstract

In metallic contamination analysis of semiconductor wafers, preconcentration methods such as vapor phase decomposition–droplet collection (VPD-DC) or droplet sandwich etch (DSE) are combined with sensitive analytical techniques, often total-reflection X-ray fluorescence spectrometry (TXRF). Previously we have reported about the occurrence of TXRF saturation effects in the analysis of microdroplet residues from these methods and identified the origin as a mass-absorption effect of primary X-rays. In this study, different approaches to deal with TXRF saturation effects in semiconductor applications are evaluated. Corrective approaches are tested for the application of VPD-DC-TXRF on Si wafers. The application of correction factors resulted in an overestimation of the effect of 20%. Internal standardization approaches did not perform well because of the separation of the internal standard element apart from the analytes during the drying step. We suggest another internal approach using the intensity of scattered primary X-rays as an indicator for accuracy.The parameters in a Ge matrix removal method have been investigated. The application of the method on samples from the DSE method on spin coated Ge wafers resulted in efficiencies at 100% compared to only 40% without matrix removal. Finally, the use of nanoliter deposition or ink-jet spray methods is proposed to extend the dynamic range of TXRF on microdroplet residues. This suggestion is motivated with calculations based on a mass-absorption model and with experimental results from the study of linearity of TXRF on Ni spin coated Si wafers and the related morphology of the surface species.