Secondary ion yield matrix effects in SIMS depth profiles of Si/Ge multilayers

Thin multilayer samples of Si/Ge, with individual layer thicknesses of 4–33 nm, have been analyzed by secondary ion mass spectrometry (SIMS) using Ar⁺, O₂⁺ and Cs⁺ primary ion beams. Bombardment with both Ar⁺ and O₂⁺ produced positive secondary ion depth profiles in which pronounced distortions were observed. Similar effects were found in negative secondary ion depth profiles with Cs⁺ bombardment. In each case, the SIMS depth profiles were characterized by abrupt interfacial secondary ion signal variations and a shift in the secondary ion signal maxima indicating that the layers were superposed, a condition that was not consistent with sample preparation, as verified by Auger electron spectroscopy. Auger electron spectroscopy depth profiling was also used to quantify the level of oxygen in the films. From these data it was concluded that the distortions in the positive secondary ion depth profiles under Ar⁺ bombardment were the result of secondary ion yield variations induced by enhanced incorporation of ambient oxygen, during sample preparation, into the stronger oxide‐forming silicon layers. Under O₂⁺ and Cs⁺ bombardment, the profile distortions were introduced by differential incorporation of the implanted primary species into the lower‐sputter‐yield silicon layers.