Sputter depth profiling by secondary ion mass spectrometry coupled with sample current measurements

Ion-induced secondary electron emission determined via sample current measurements (SCM) was employed as a useful adjunct to conventional secondary ion mass spectrometry (SIMS). This paper reports on the results of 3-6 keV O2+ SIMS-SCM sputter depth profiling through CrN/AlN multilayer coatings on nickel alloy, titanium dioxide films deposited on stainless steel, and corrosion layers formed onto surface of magnesium alloy after long-term interaction with an ionic liquid. For Au/AlNO/Ta films on silicon, in addition to SIMS-SCM profiles, the signal of mass-energy separated backscattered Ne+ ions was monitored as a function of the depth sputtered as well. The results presented here indicate that secondary electron yields are less affected by “matrix effect” than secondary ion yields, and at the same time, more sensitive to work function variations and surface charging effects. SCM depth profiling, with suppression of “the crater effect” by electronic gating of the registration system is capable of monitoring interfaces in the multilayer structure, particularly, metal-dielectric boundaries. In contrast to SIMS, SCM data are not influenced by the angle and energy windows of an analyser. However, the sample current measurements provide lower dynamic range of the signal registration than SIMS, and SCM is applicable only to the structures with different secondary electron emission properties and/or different conductivity of the layers. To increase the efficiency, SCM should be accompanied by SIMS measurements or predetermined by proper calibration using other elemental-sensitive techniques.