AVS 70 Session AS-MoA: Chemical Processes at Surfaces

Silicon dioxide (SiO₂) crystals serve as a relevant material in sputtering processes for their well-defined properties and broad applications in material science. The material offers a stable, reproducible target, aiding in the accurate calibration of sputtering equipment and standardizing experimental conditions. This stability is crucial for developing thin films, coatings, and semiconductor devices, where precise material control is essential [1].

The objective of this study is to explore the atomic layer structure and the composition of SiO₂ surfaces at different thicknesses from both experimental and numerical point of views. We first measure depth profiles of different thicknesses of SiO₂ using Low Energy Ion Spectroscopy (LEIS) at various energies. LEIS is a highly surface sensitive technique which probes only the top atomic layer of a material surface [2]. Our findings indicate that combining sputtering with LEIS is an effective technique for probing the in-depth structure of SiO₂ crystals grown on Si substrates. Distinct profile variations were observed for different surface oxidation processes, including O₂ plasma, thermal oxide, and native oxide, particularly for oxide thicknesses varying between 1.2 to 2 nm. In contrast, for thicker oxides between 30 and 60 nm, the profiles converged, showing minimal dependence on the oxidation method employed.

To provide additional physical insights into the obtained depth profiles by LEIS measurements, we subsequently perform sputtering simulations using SDTrimSP [3]. Sputtering simulations calculate the interaction between incident ions and surface atoms and describe sputtering, as well as surface degradation and ion implantation in the target material. For Ar⁺, simulations demonstrate preferential sputtering of oxygen compared to silicon and suggest a layer intermixing in SiO₂ of 1.2 nm for 0.5 keV incident ion energy and 3.2 nm for 2 keV incident ion energy. Our simulations further show that simulated sputtering depth profiles correlate well with the depth profiles obtained by the LEIS measurements. Ultimately, the well-established stoichiometry of SiO₂ will be used as a reference for oxygen content by integrating experimental measurements with simulation results. This method will enable quantification with LEIS for any material surface that contains oxygen

[1]Kelly, J. J. (2003) "SiO2: A Versatile Reference Material for Sputtering and Thin Film Research." Journal of Vacuum Science & Technology A, vol. 21, no. 4.

[2]Brongersma, H. H., Draxler, M. (2007). Surface composition analysis by low-energy ion scattering. Surface Science Reports, 62(3), 63-109.

[3]Mutzke, A. et al. (2019) “SDTrimSP Version 6.00”