Determination of the depth resolution in Auger depth profiling measurements

The depth resolution Δz of the Auger depth profiling method was studied in multilayer thin films comprising alternate layers of nickel and molybdenum or of cobalt and molybdenum. The composition-depth profiles of several interfaces located at different depths within the same film were compared. Thus changes which depended on the sputtering depth z could be distinguished from effects which were independent of z. According to a statistical theory the profiles of the interfaces can be described by a gaussian error function. An empirical formula $\text{Δz = αz}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ β}$ was determined from the width of the profiles. The first term agrees with the statistical theory and the constant term is explained by the roughness of the interface. The order of magnitude of β (≈ 3 nm) suggests that the depth resolution in the films is not limited by the escape depth of the Auger electrons (? 1.5 nm). The relative depth resolution $\text{Δz}\text{z}$ improves with increasing sputtering depth.