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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.
‘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.
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.
Atmospheric-pressure plasma-enhanced spatial ALD of Al2O3 and SiO2 was investigated by using dedicated micro-diagnostics by means of gas-phase Infrared Spectroscopy on the plasma exhaust gas and in situ Optical Emission Spectroscopy.
For Al2O3 films grown at 80-200 oC from trimethylaluminum, Al(CH3)3, and Ar-O2 plasma we found that the CH3-ligands are removed during the plasma half-cycle through two reaction pathways: i)-combustion by the O2-plasma yielding CO2 and H2O, and ii)-thermal ALD reactions of H2O with the CH3-ligands yielding CH4.
Similarly, for SiO2 grown at 100-250 oC using bisdiethylaminosilane (BDEAS) and O2-plasma we propose a reaction mechanism where BDEAS adsorbs on –OH surface sites by exchanging part of its amine-ligands yielding diethylamine (DEA) desorption. The remaining amine-ligands are removed through combustion-like reactions in the O2-plasma yielding the desorption of H2O, CO2, CO and byproducts such as N2O, NO2, and CH-containing species. These volatile byproducts, theoretically predicted, can react further by gas-phase reactions in the plasma as indicated by the presence of OH*, CN* and NH*excited fragments.
This work expands the knowledge on atmospheric-pressure PE-s-ALD of Al2O3 and SiO2 and opens up ways to better process control in spatial ALD.