3, Lund University, Lund, , Sweden
2, Sorbonne Universités - UPMC Univ Paris 06, Paris, , France
Atomic layer deposition (ALD) and chemical vapour deposition (CVD) are very important methods that enable a highly controlled growth of thin films . The surface chemistry of the underlying processes remains, however, little understood. While idealised reaction mechanisms have been developed, they represent postulates rather than models based on the factual identification of surface species and kinetics . New in situ and operando methods offer the prospect of gaining a much more thorough understanding of the involved molecular and atomic surface processes and (dynamic) structures, which, in turn, means that a much better knowledge basis can be achieved for the future improvement of materials and growth recipes (see, e.g. [3,4]). One such operando method, which can be applied to the investigation of ALD and CVD, is synchrotron-based ambient pressure x-ray photoelectron spectroscopy (APXPS). While conventional x-ray photoelectron spectroscopy (XPS) is limited to vacuum pressures of 10-5 mbar and below, APXPS can be carried out at realistic pressure. Today, most APXPS machines can operate at pressures up to the 10 mbar regime, which is an ideal match to the pressure regime used in standard ALD reactors.
Here, I will report on our recent efforts to apply synchrotron-based APXPS to the ALD/CVD of oxides (TiO2, SiO2, and HfO2) on semiconductor (InAs and Si) and oxide surfaces (TiO2, RuO2) [3-5]. I will show that APXPS allows the identification of the surface species occurring during thin film growth and the real-time monitoring of their evolution, presently with a time resolution of around 1 s. I will also report on our efforts to further improve instrumentation with the goal of achieving a much closer match of the APXPS sample environment with the geometries used in conventional ALD reactors. The development will also open for the use of a wider range of precursors and growth protocols. Further, we work on making the millisecond timescale attainable in the APXPS study of ALD.
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