Abstract
The influence of the flooding gas during ToF-SIMS depth profiling was studied to reduce the matrix effect and improve the quality of the depth profiles. The profiles were measured on three multilayered samples prepared by PVD. They were composed of metal, metal oxide, and alloy layers. Dual-beam depth profiling was performed with 1 keV Cs+ and 1 keV O2+ sputter beams and analyzed with a Bi+ primary beam. The novelty of this work was the application of H2, C2H2, CO, and O2 atmospheres during SIMS depth profiling. Negative cluster secondary ions, formed from sputtered metals/metal oxides and the flooding gases, were analyzed. A systematic comparison and evaluation of the ToF-SIMS depth profiles were performed regarding the matrix effect, ionization probability, chemical sensitivity, sputtering rate, and depth resolution. We found that depth profiling in the C2H2, CO, and O2 atmospheres has some advantages over UHV depth profiling, but it still lacks some of the information needed for an unambiguous determination of multilayered structures. The ToF-SIMS depth profiles were significantly improved during H2 flooding in terms of matrix-effect reduction. The structures of all the samples were clearly resolved while measuring the intensity of the MnHm–, MnOm–, MnOmH–, and Mn– cluster secondary ions. A further decrease in the matrix effect was obtained by normalization of the measured signals. The use of H2 is proposed for the depth profiling of metal/metal oxide multilayers and alloys.
Highlights
Thin layers are often depth profiled when we want to analyze the chemical composition and thickness of a single layer or a multilayer structure
The results of our experiments show that the introduction of H2 gas during the SIMS depth profiling improves the chemical sensitivity of the SIMS method, provides a clear distinction between the metallic and metaloxide layers, allowing the easier identification of elements and their oxides in thin films, and improves the depth resolution
Our study shows that introducing different gases into the analysis chamber during SIMS depth profiling can lead to very different depth profiles with respect to the type of gas used
Summary
Thin layers are often depth profiled when we want to analyze the chemical composition and thickness of a single layer or a multilayer structure. Corrosion properties,[1−4] diffusion mechanisms,[5] native or artificially prepared oxide layers,[6,7] layers that compose integrated circuits,[8−11] and the composition of nanoparticles, nanolayers, and nanocomposite coatings,[12,13] paints,[14] adhesives,[15] catalysts,[16,17] thin polymer films,[18] biological compounds[19,20] and even cells and tissues[21,22] can be studied Such analyses can be performed using a variety of surface-sensitive analytical techniques such as SIMS (secondary ion mass spectrometry), XPS (X-ray photoelectron spectroscopy) or AES (Auger electron spectroscopy) in combination with ion sputtering for material removal.[23−25] Laser ablation or plasma etching is an option,[10] but these approaches are less commonly applied. Cross sections prepared in this way can be analyzed using, for example, a scanning electron microscope (SEM)[29] or SIMS imaging.[28]
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