Area-selective atomic layer deposition of platinum using photosensitive polyimide

Area-selective atomic layer deposition (AS-ALD) of platinum (Pt) was studied using photosensitive polyimide as a masking layer. The polyimide films were prepared by spin-coating and patterned using photolithography. AS-ALD of Pt using poly(methyl-methacrylate) (PMMA) masking layers was used as a reference. The results show that polyimide has excellent selectivity towards the Pt deposition, after 1000 ALD cycles less than a monolayer of Pt is deposited on the polyimide surface. The polyimide film could easily be removed after ALD using a hydrogen plasma, due to a combination of weakening of the polyimide resist during Pt ALD and the catalytic activity of Pt traces on the polyimide surface. Compared to PMMA for AS-ALD of Pt, polyimide has better temperature stability. This resulted in an improved uniformity of the Pt deposits and superior definition of the Pt patterns. In addition, due to the absence of reflow contamination using polyimide the nucleation phase during Pt ALD is drastically shortened. Pt patterns down to 3.5 μm were created with polyimide, a factor of ten smaller than what is possible using PMMA, at the typical Pt ALD processing temperature of 300 °C. Initial experiments indicate that after further optimization of the polyimide process Pt features down to 100 nm should be possible, which makes AS-ALD of Pt using photosensitive polyimide a promising candidate for patterning at the nanoscale

Plasma-enhanced atomic layer deposition of tungsten oxide thin films using (tBuN)2(Me2N)2W and O2 plasma

The growth of tungsten oxide (WO3) thin films by atomic layer deposition (ALD) offers numerous merits including atomic-scale thickness control at low deposition temperatures. In this work, we have developed and characterized a new plasma-enhanced ALD process for WO3 thin films using the metalorganic precursor (tBuN)2(Me2N)2W and O2 plasma as co-reactant over a wide temperature range of 100 °C-400 °C. The influence of deposition temperature on the growth behaviour and film properties is investigated in detail. The WO3 ALD process developed in this work yields a relatively high growth per cycle (GPC) which varies from ~0.7 Å at 100 °C to ~0.45 Å at 400 °C, as-determined by in-situ spectroscopic ellipsometry (SE). Rutherford backscattering spectrometry (RBS) measurements revealed a mass density of 5.9 g/cm3 and near stoichiometric film composition (O/W = 2.9). Both RBS and X-ray photoelectron spectroscopy (XPS) measurements confirmed no detectable C as well as N impurity incorporation. Grazing incidence X-ray diffraction (GI-XRD) measurements indicated that the films deposited at 400 °C were polycrystalline in nature

The origin of high activity of amorphous MoS\u3csub\u3e2\u3c/sub\u3e in the hydrogen evolution reaction

\u3cp\u3eInvited for this month′s cover is a collaborative research effort involving experiments by L. Wu, A. Sharma, M. Hendrix, A. A. Bol, E. Hensen, and J. P. Hofmann (Eindhoven University of Technology) as well as A. Longo (European Synchrotron ESRF), and theoretical modelling from N. Dzade and N. De Leeuw (Utrecht and Cardiff Universities). The Communication itself is available at 10.1002/cssc.201901811.\u3c/p\u3

The origin of high activity of amorphous MoS2 in the hydrogen evolution reaction

\u3cp\u3eMolybdenum disulfide (MoS \u3csub\u3e2\u3c/sub\u3e) and related transition metal chalcogenides can replace expensive precious metal catalysts such as Pt for the hydrogen evolution reaction (HER). The relations between the nanoscale properties and HER activity of well-controlled 2H and Li-promoted 1T phases of MoS \u3csub\u3e2\u3c/sub\u3e, as well as an amorphous MoS \u3csub\u3e2\u3c/sub\u3e phase, have been investigated and a detailed comparison is made on Mo−S and Mo−Mo bond analysis under operando HER conditions, which reveals a similar bond structure in 1T and amorphous MoS \u3csub\u3e2\u3c/sub\u3e phases as a key feature in explaining their increased HER activity. Whereas the distinct bond structure in 1T phase MoS \u3csub\u3e2\u3c/sub\u3e is caused by Li \u3csup\u3e+\u3c/sup\u3e intercalation and disappears under harsh HER conditions, amorphous MoS \u3csub\u3e2\u3c/sub\u3e maintains its intrinsic short Mo−Mo bond feature and, with that, its high HER activity. Quantum-chemical calculations indicate similar electronic structures of small MoS \u3csub\u3e2\u3c/sub\u3e clusters serving as models for amorphous MoS \u3csub\u3e2\u3c/sub\u3e and the 1T phase MoS \u3csub\u3e2\u3c/sub\u3e, showing similar Gibbs free energies for hydrogen adsorption (ΔG \u3csub\u3eH*\u3c/sub\u3e) and metallic character. \u3c/p\u3

Low-temperature plasma-enhanced atomic layer deposition of 2-D MoS\u3csub\u3e2\u3c/sub\u3e:Large area, thickness control and tuneable morphology

\u3cp\u3eLow-temperature controllable synthesis of monolayer-to-multilayer thick MoS\u3csub\u3e2\u3c/sub\u3e with tuneable morphology is demonstrated by using plasma enhanced atomic layer deposition (PEALD). The characteristic self-limiting ALD growth with a growth-per-cycle of 0.1 nm per cycle and digital thickness control down to a monolayer are observed with excellent wafer scale uniformity. The as-deposited films are found to be polycrystalline in nature showing the signature Raman and photoluminescence signals for the mono-to-few layered regime. Furthermore, a transformation in film morphology from in-plane to out-of-plane orientation of the 2-dimensional layers as a function of growth temperature is observed. An extensive study based on high-resolution transmission electron microscopy is presented to unravel the nucleation mechanism of MoS\u3csub\u3e2\u3c/sub\u3e on SiO\u3csub\u3e2\u3c/sub\u3e/Si substrates at 450 °C. In addition, a model elucidating the film morphology transformation (at 450 °C) is hypothesized. Finally, the out-of-plane oriented films are demonstrated to outperform the in-plane oriented films in the hydrogen evolution reaction for water splitting applications.\u3c/p\u3

Tuning material properties of oxides and nitrides by substrate biasing during plasma-enhanced atomic layer deposition on planar and 3D substrate topographies

\u3cp\u3eOxide and nitride thin-films of Ti, Hf, and Si serve numerous applications owing to the diverse range of their material properties. It is therefore imperative to have proper control over these properties during materials processing. Ion-surface interactions during plasma processing techniques can influence the properties of a growing film. In this work, we investigated the effects of controlling ion characteristics (energy, dose) on the properties of the aforementioned materials during plasma-enhanced atomic layer deposition (PEALD) on planar and 3D substrate topographies. We used a 200 mm remote PEALD system equipped with substrate biasing to control the energy and dose of ions by varying the magnitude and duration of the applied bias, respectively, during plasma exposure. Implementing substrate biasing in these forms enhanced PEALD process capability by providing two additional parameters for tuning a wide range of material properties. Below the regimes of ion-induced degradation, enhancing ion energies with substrate biasing during PEALD increased the refractive index and mass density of TiO\u3csub\u3ex\u3c/sub\u3e and HfO\u3csub\u3ex\u3c/sub\u3e and enabled control over their crystalline properties. PEALD of these oxides with substrate biasing at 150 °C led to the formation of crystalline material at the low temperature, which would otherwise yield amorphous films for deposition without biasing. Enhanced ion energies drastically reduced the resistivity of conductive TiN\u3csub\u3ex\u3c/sub\u3e and HfN\u3csub\u3ex\u3c/sub\u3e films. Furthermore, biasing during PEALD enabled the residual stress of these materials to be altered from tensile to compressive. The properties of SiO\u3csub\u3ex\u3c/sub\u3e were slightly improved whereas those of SiN\u3csub\u3ex\u3c/sub\u3e were degraded as a function of substrate biasing. PEALD on 3D trench nanostructures with biasing induced differing film properties at different regions of the 3D substrate. On the basis of the results presented herein, prospects afforded by the implementation of this technique during PEALD, such as enabling new routes for topographically selective deposition on 3D substrates, are discussed.\u3c/p\u3