Study of Copper Surface Oxidation by Grazing Angle X-Ray Excitation

HÉCTOR JORGE SÁNCHEZ; CARLOS PÉREZ

SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2010 vol. 65 p. 466 - 470

0584-8547

This work reports measurements of copper surface oxidation by XRF analysis under grazing angle excitation.The mathematical model for analyzing data is based on the usual equation for XRF intensity, corrected by thestratified model for the layer excitation. The final expressions are fitted to the data by using the Simplexalgorithm.Three samples of silicon wafers with surface layers of copper were made by using the controlled-evaporationtechnique under vacuum. The final layer thicknesses were 190 Å, 400 Å, and 800 Å. For each sample, severalmeasurements were carried out by performing an angular scan in the region of the critical angle for totalreflection. Different measurements were taken immediately after evaporation, after 30 min, after 1 h, after4 h, and after 30 min in oven at 65°.The results show small variations among the different spectra measured for each sample. The mostsignificant variations are observed for the first measurement (after evaporation) and the last one (after theheating in oven). The mathematical model works correctly for a two-layer scheme but shows inconsistenciesfor more complex schemes. This indicates that the stratified model is not appropriate for continuous mediadue to the nature of the theoretical assumptions in which the stratified model is based. Our results show alsothat the surface oxidation process takes place in the first moments of exposition to air and does not progressafterwards except if the sample is heated.