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My research activities focus on investigating and developing new functional ultrathin-film materials and plasma-enhanced processes by Atomic Layer Processing, i.e. Deposition (ALD), and Etching (ALE) and cleaning. In addition, in situ microdiagnostics is being developed for application in spatial ALD. The research is on both conventional (=vacuum-based) and on spatial ALD contributes in particular to the TNO roadmaps on “High Tech Materials” (Nanotechnology) and “High Tech Systems & Materials” (Fab-of-the-Future).
The spatial variant of ALD is attractive to industry because of its potential in the manufacture of atomic-scale and conformal thin films with superior quality, that can be scaled up to large-area, high throughput in the application fields of photovoltaics, displays, etc., including roll-to-roll or sheet-to-sheet systems. Applications can also be in semicon (e.g. Selective-Area ALD) and ALE-based cleaning (e.g. tin cleaning of EUV optics). The main objectives in the daily research are Selective-Area ALD of oxides (e.g. of SiO2 on dielectrics vs. metals), and ALE for cleaning.
Area-Selective Atomic Layer Deposition1
‘ABC’-type area-selective ALD of SiO2 was developed by pulsing acetylacetone inhibitor (A), bis(diethylamino)silane-precursor (B), and O2-plasma (C). IR-spectroscopy and DFT calculations showed selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2. The area-selectivity stems from the chemoselective adsorption of the inhibitor.
Atomic Layer Etching2
Radical-plasma driven ALE was developed for ZnO utilizing alternating acetylacetone (Hacac) and O2-plasma. In-situ ellipsometry and IR-spectroscopy confirmed self-limiting half-reactions and ~1.3 Å/cycle etching at 100-250 °C. TEM-microscopy on 3D ZnO-covered nanowires before and after etching proved isotropic and damage-free ALE.
Microdiagnostics of (atmospheric) plasmas3
We employed gas-phase IR-spectroscopy and optical emission spectroscopy (OES) to study the underlying chemistry of atmospheric spatial-ALD Al2O3-films grown from Al(CH3)3 and Ar-O2-plasma. We identified CO, CO2, H2O, and CH4 as main by-products from combustion-like reactions of the methylated surface with O-plasma radicals and O3 and from a concurrent thermal ALD component involving produced and/or residual H2O-molecules. CH2O and CH3OH were identified as by-products unique to spatial ALD and originating from the surface or formed in the plasma.