Preferential Sputtering

Stoichiometric Shift

Alteration of the surface composition during sputter cleaning or depth profiling can lead to incorrect chemical analysis results. For example, during the profiling of a nickel phosphorus alloy, preferential sputtering of phosphorus or nickel can distort the measured elemental ratio at the surface. This effect makes the exposed layer appear artificially rich in the slower-sputtering element, which leads to errors in interpreting the composition of the finish.

Measurement Modification

Correcting for this analytical bias requires using relative sensitivity factors that have been calibrated against reference standards of known composition. Additionally, analysts can reduce preferential sputtering by lowering the energy of the incident ion beam or utilizing alternative sputtering gases. By optimizing these instrument settings, it is possible to reconstruct the true chemical gradient of the surface finish and ensure the reliability of the test data.

This is particularly important when evaluating the ultra-thin palladium and gold coatings of advanced board finishes, where even minor sputtering anomalies can obscure the true thickness of the layers.