Ultra-trace analysis of metallic contaminations on silicon wafer surfaces by vapour phase decomposition/total reflection X-ray fluorescence (VPD/TXRF)

Abstract

Total reflection X-ray fluorescence (TXRF) analysis in combination with vapour phase decomposition (VPD) of the surface oxide is presented as a sensitive tool for monitoring metal trace contamination on silicon wafers. Sensitivities of the order of 10 9 atoms per cm 2 are obtained, e.g. for Zn, Fe or Ni, which are effectively collected by the VPD preparation using HF vapour for decomposition and a DI water droplet for sampling. Quantitation is easily achieved for these elements by comparison with standard solutions taking into account the geometrical enhancement factor given by the ratio of the wafer surface area to the analysed area as defined by the TXRF detector aperture. Copper still presents a problem owing to electrochemical plating in the VPD process leading to poor collection efficiency