CALIBRATION PROCEDURE FOR QUANTITATIVE SURFACE-ANALYSIS BY TOTAL-REFLECTION X-RAY-FLUORESCENCE

Total reflection x-ray fluorescence analysis (TXRF) is a new technique able either to achieve elemental analysis of microquantities deposite d on a very flat reflecting surface or to detect very low levels of su rface contamination on reflecting substrates like silicon wafers. In t his paper we report a calibration procedure to achieve an impurity qua ntification in the range of one hundredth of an atomic monolayer and b elow. To reach this goal, it is necessary to distinguish between two t ypes of surface deposits: submonolayer surface atoms and particulate m atter deposited onto the reflector surface. We show how these two situ ations can be differentiated, both theoretically and experimentally. F or surface contamination, calibration curves were obtained from nickel submonolayer standards prepared by a method of quantitative contamina tion. These standards were certified by Rutherford backscattering anal ysis (RBS). Results show that linear regression is suitable for calibr ation. For elements other than nickel it is shown that the correlation between TXRF and RBS is good, except for concentrations of <5 x 10(11 ) atoms cm-2. This is mainly owing to the difficulty of obtaining cert ified low contamination levels with RBS. Quantification limits for TXR F analysis are found to be extremely low in comparison to most surface analysis techniques, and TXRF is able to detect metallic impurities l ike Fe, Ni, Cr, Zn and Cu at approximately 2 x 10(10) atoms cm-2 in a short time (1000 s) without any sample preparation.