Abstract
An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO2 on a SiO2 surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.
Highlights
Atomic layer deposition (ALD)1 is a variant of the chemical vapor deposition (CVD) technique for depositing thin films
An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes
A new sample environment dedicated for studying ALD using ambient pressure x-ray photoelectron spectroscopy is described
Summary
Atomic layer deposition (ALD) is a variant of the chemical vapor deposition (CVD) technique for depositing thin films. Some previous studies involving operando XPS focused on investigating the surface chemistry of thermal ALD of TiO2 and HfO2 with water as the oxygen precursor and Ti and Hf alkylamido complexes as the metal precursors In the literature, these ALD processes have been so far proposed to follow a unimolecular two-step ligand-exchange mechanism releasing alkylamine.. As the new studies have provided information during the ALD process, the ligand-exchange mechanism was revised.52 Another important result was for the ALD of HfO2 on InAs: it has been found that the substrate plays an active role as a source of oxygen during the very first metal half-cycle.. We report on the development of an APXPS sample environment for true in situ and operando XPS studies on atomic layer film deposition. The beamline provides a wide energy range of 30–1500 eV, allowing for XPS measurements at most core levels with surface-sensitive energies while providing a unique access to valence band measurements at a high photon flux
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