Total reflection X-ray fluorescence analysis of light elements with synchrotron radiation and special X-ray tubes

Abstract

Total reflection X-ray fluorescence analysis (TXRF) of light elements, such as C, O and Al (atomic numbers 5–13) generally has poor sensitivity and detection limits due to poor excitation and low fluorescent yields. Special excitation sources are necessary to compensate for these physical limitations. Synchrotron radiation is the ideal source for TXRF due to its high intensity and wide spectral range extending into the low energy region required for light elements. For more routine use, special X-ray tubes can be constructed. Experiments have been performed at the Stanford Synchrotron Radiation Laboratory (SSRL) using beamline III-4, which is specially designed for the use of low energy photons. Light elements on Si wafers have been analyzed, leading to detection limits below 100 fg for Na, Mg and Al, which corresponds to about 109 atoms. A new vacuum chamber is introduced meeting the requirements of wafer handling without the risk of contamination and offering the possibility of scanning a certain area of the wafer. Boron was detected on a wafer with 1014 atomscm−2 implanted in the surface layer. A special windowless X-ray tube with Mo, Al and Si as anode materials was also tested. With the optimization of anode geometry, beam path and excitation conditions, a detection limit of 5 pg (corresponds to 1011 atoms) for Al was achieved. © 1997 Elsevier Science B.V.