ToF-SIMS Depth Profiling of Metal, Metal Oxide, and Alloy Multilayers in Atmospheres of H₂, C₂H₂, CO, and O₂

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 O 2 + sputter beams and analyzed with a Bi + primary beam. The novelty of this work was the application of H 2 , C 2 H 2 , CO, and O 2 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 C 2 H 2 , CO, and O 2 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 H 2 flooding in terms of matrix-effect reduction. The structures of all the samples were clearly resolved while measuring the intensity of the M n H m – , M n O m – , M n O m H – , and M n – cluster secondary ions. A further decrease in the matrix effect was obtained by normalization of the measured signals. The use of H 2 is proposed for the depth profiling of metal/metal oxide multilayers and alloys.

AFM Study of Roughness Development during ToF-SIMS Depth Profiling of Multilayers with a Cs+ Ion Beam in a H2 Atmosphere

“…White dots represent interfaces and layers where the analyses of the surface roughnesses were made. Adapted with permission from ref . Copyright 2022 creative commons.…”

“…The intensities of some signals were multiplied by a specific factor as a way of reducing the intensity scale interval and making the profile clearly readable. Adapted with permission from ref . Copyright 2022 creative commons.…”

“…Finally, we compared the surface roughening caused by Cs + ion beams with different energies, i.e., 1 and 2 keV. We must also emphasize that we tested only the Cs + ion beam since our previous study 12 showed that H 2 flooding works optimally when combined with Cs + sputtering. Since the main objective of this study is to show the effects of the H 2 atmosphere on surface roughening during depth profiling, we did not include other types of sputtering ions.…”

“…Ion sputtering is the main process taking place during an analysis based on secondary ion mass spectrometry (SIMS) . It is also an essential process for depth profiling, combined with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). − All three methods employ ion guns for sputtering, although the sputtering process itself is also present in the case of glow-discharge optical emission spectroscopy (GDOES) or glow-discharge mass spectrometry (GDMS). ,− The main difference is the characteristic of the GDOES or GDMS processes, as ions are intrinsic to the plasma that flows toward the cathode, causing its surface to be sputtered away. , These methods are used in many areas of research, for example, during the analysis of oxide layers, while studying corrosion properties, polymer films, mono- and multilayers, biomaterials, microelectronics, , power-storage materials, solar cells, , and catalysts . However, regardless of the exact process used for the ion sputtering, the ion beam generated by the ion gun or the plasma flow, some damage caused by the ion bombardment is always present. − The accumulation of damage is observed as surface roughening, which is most commonly determined with atomic force microscopy (AFM). , This technique is especially suitable for the characterization of nanostructures formed on the surface since it is optimized to achieve molecular and atomic resolutions. − However, AFM can also be used to study many other topographical characteristics of the sample, its conductivity at the nano level, and different forces using its spectroscopy mode. − …”

“…As we have shown in our recent work, the time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling of metals, metal oxides, and alloys is improved in terms of sensitivity and a reduction of the matrix effect if a H 2 atmosphere is applied instead of ultrahigh vacuum (UHV) . Since H 2 flooding is a novelty in the field of atmosphere manipulation and has, at least to some degree, similar effects to O 2 flooding, we made AFM measurements of the sputtered craters and checked whether less surface roughening can be observed in the case of our experiments as well.…”