Investigation of Na impurities on Si wafer surfaces using TXRF

Synchrotron Radiation from the Stanford Synchrotron Radiation Laboratory (SSRL) has been used as an excitation source for Total Reflection X-ray Fluorescence Analysis (TXRF) of Na impurities on Si wafer surfaces. A wafer intentionally contaminated by a droplet containing 1.4×1014 atoms/cm2 of sodium and a wafer uniformly contaminated with 4.4×1012 atoms/cm2 of Na were investigated. The minimum detection limit for this element has been found to be 1.1×1011 atoms/cm2 for the blanket sample and 3×1011 atoms/cm2 for the droplet sample. Theoretical considerations show that the detection limit for Na can be further improved by at least a factor of 2 by exploiting the tunability of synchrotron radiation to even lower excitation energies.