Dual mechanical behaviour of hydrogen in stressed silicon nitride thin films

International Journal of Hydrogen Energy, 2013

The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film.

Journal of Alloys and Compounds, 2012

Amorphous silicon nitride films, 500 and 700 nm thick, were deposited on Eurofer substrates by applying reactive radio-frequency magnetron sputtering from pure Si targets in an argon/nitrogen atmosphere. The hydrogen permeation through such double-layered, 40 mm diameter membranes at 400°C and 1 bar upstream pressure involved the use of a conventional technique with enhanced sensitivity. The extremely high barrier efficiency for these films with respect to hydrogen, expressed as a permeationreduction factor in excess of 2000, was only achieved with films containing 6-7 at.% of hydrogen. The achieved permeation-reduction factor at 400°C corresponds to the permeability of silicon nitride, which is as low as P = 1 Â 10 À17 mol H 2 /m s Pa 0.5 . The hydrogen concentration was determined with an Elastic Recoil Detection Analysis, which indicated that this high concentration represents only the strongly bound hydrogen that is not mobile at this low temperature, but impedes the mobility of the diffusive hydrogen. A silicon nitride film with a low hydrogen content is a far less efficient barrier, which supports the role of the strongly bound hydrogen.

Journal of applied …, 1996

Hydrogen incorporation in silicon layers prepared by plasma-enhanced chemical-vapor deposition using silane dilution by hydrogen has been studied by infrared spectroscopy ͑IR͒ and elastic recoil detection analysis ͑ERDA͒. The large range of silane dilution investigated can be divided into an amorphous and a microcrystalline zone. These two zones are separated by a narrow transition zone at a dilution level of 7.5%; here, the structure of the material cannot be clearly identified. The films in/near the amorphous/microcrystalline transition zone show a considerably enhanced hydrogen incorporation. Moreover, comparison of IR and ERDA and film stress measurements suggests that these layers contain a substantial amount of molecular hydrogen probably trapped in microvoids. In this particular case the determination of the total H content by IR spectroscopy leads to substantial errors. At silane concentrations below 6%, the hydrogen content decreases sharply and the material becomes progressively microcrystalline. The features observed in the IR-absorption modes can be clearly assigned to mono-and/or dihydride bonds on ͑100͒ and ͑111͒ surfaces in silicon crystallites. The measurements presented here constitute a further indication for the validity of the proportionality constant of Shanks et al. ͓Phys. Status Solidi B 110, 43 ͑1980͔͒, generally used to estimate the hydrogen content in ''conventional'' amorphous silicon films from IR spectroscopy; additionally, they indicate that this proportionality constant is also valid for the microcrystalline samples.

ISRN Nanomaterials, 2012

The mechanical properties of hydrogenated silicon thin films deposited using high-frequency PECVD process were studied, which certainly have importance for optoelectronic devices particularly for getting stability and long operating lifetime in harsh conditions. Nanoindentation technique was used to measure the load versus displacement curves, hardness (H), elastic modulus (E), plastic resistance parameter (H/E), elastic recovery (ER), and plastic deformation energy (U r ), while laser scanning stress measurement setup was used to measure the intrinsic stress of these films. The concentration of bonded hydrogen in these films was found in the range of 3.6 to 6.5 at. % which was estimated using integrated intensity of IR absorption peak near 640 cm −1 . Dependence of mechanical properties of these films on hydrogen content and bonding environment has been investigated. The film containing minimum hydrogen content (3.6%) shows the maximum elastic recovery (52.76%) and minimum plastic deformation energy (3.95 × 10 −10 J). Surface roughness measured by AFM was found to decrease with the increase in hydrogen content in the film. The dependency of stress on the plasma frequency and applied power has also been discussed.

Solar Energy Materials and Solar Cells, 2002

This paper presents results of the investigation of hydrogen influence on the stability of low pressure chemical vapour deposition a-Si films. We measured boron-or phosphorus-doped films post-hydrogenated by ion implantation with different hydrogen doses. The dark conductivity after fast quenching and slow cooling and the isothermal relaxation were measured at different annealing temperatures. It was found that higher hydrogen concentration causes greater metastable changes but shorter relaxation time of defects. r

ChemPhysChem, 2019

Metal-hydrogen (M-H) systems offer grand opportunities for studies on fundamental aspects of thermodynamics and kinetics. When the system size is reduced to the nano-scale, microstructural defects as well as mechanical stress affect the systems' properties. This is contemplated for the model system of epitaxial niobium-hydrogen (Nb-H) thin films. Hydrogen absorption in metals commonly leads to lattice expansion which is hindered when the metal adheres to a flat rigid substrate. Consequently, high mechanical stresses of about-10 GPa for 1 H/Nb are predicted, in theory. However, metals cannot yield such high stresses and respond with plastic deformation, commonly limiting measured stresses to-2 to-3 GPa for 100 nm Nb-H films. It will be shown that the coherency state changes with film thickness reduction, shifting the onset of plastic deformation to larger hydrogen concentrations. Below critical film thicknesses, plastic deformation is fully absent. The system then behaves purely elastic and ultra-high stress of about-10 (±2) GPa can be obtained. Arising stresses control the phase stability of M-H systems, and the coherency state strongly affects the nucleation and growth dynamics of the phase transition. In case of Nb-H thin films of less than 8 nm thickness the

Structural and transport properties near the amorphous to microcrystalline transition region of Si:H samples deposited from a silane-hydrogen mixture have been studied. The gas pressure during the plasma enhanced chemical vapor deposition process has been varied from 1.0 to 0.1 Torr. The defect density in the subband gap region measured by modulated photocurrent and constant photocurrent methods vary asymmetrically above and below midgap with changes in pressure. The transport properties of the electrons and holes studied by measurement of mobility lifetime product (ls) and diffusion length (L D ), respectively, change in the opposite direction with pressure. The sample deposited at 0.2 Torr exhibits high L D but low ls product. Moreover, an increase of the band gap was observed with decreasing pressure. These unusual behaviors have been explained on the basis of quantum confinement effect. The changes in plasma chemistry observed by optical emission spectroscopy present an interesting perspective in understanding the evolution of the structural and electronic properties with the changes in pressure.

Advanced Materials Research, 2014

Stress development upon hydrogenation of about 100 nm thick palladium layers on thermally oxidized silicon wafers with and without an intermediate Ti layer is studied. Stress developed is investigated by in-situ XRD in H2/N2 (hydrogenation) and N2 (dehydrogenation) gas at RT. The method adopted to measure residual stress involved specimen omega- (ω) and psi- (ψ) tilting, on two different diffractometer geometries (focusing and parallel). For the stress analysis, the presence of intrinsic elastic anisotropy of the film is considered. Upon hydrogenation α-Pd transformation to β-PdHoccurs and because of the constrained in-plane expansion a large compressive stress develops. Scanning electron microscopy shows that films with a Ti intermediate layer adhere better to the substrate upon hydrogen cycling, whereas, pure Pd film start cracking and buckling.

2012

Structural, optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) films, deposited from silane (SiH4) and helium (He) gas mixture without hydrogen by hot wire chemical vapor deposition (HW-CVD) method were investigated as a function of helium dilution of silane (RHe). We observed that the deposition rate is much higher (4-33 Å/s) compared to conventional plasma enhanced chemical vapour deposited (PE-CVD) nc-Si:H films. Raman spectroscopy revealed that the crystalline volume fraction decreases with increasing He dilution of silane whereas the crystallite size remains almost constant (~ 2 nm) for the entire range of He dilution of silane studied. Furthermore, an increase in the structural disorder in the nc-Si:H films has been observed with increasing He dilution of silane. The hydrogen content was ~ 9 at. % in the film deposited at 60 % RHe and decreases rapidly as RHe increases further. The photoresponse decreases by order of 1 with increasing helium dilution of silane from 60 to 97 %. It has been concluded that adding helium gas to the silane induces the structural disorders in the hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared by HW-CVD method. .

Thin Solid Films, 2004

The bonding structure and hydrogen content of amorphous hydrogenated silicon nitride (a-SiN x :H) thin films have been investigated by infrared spectroscopy and ion beam techniques. Electron cyclotron resonance plasma enhanced chemical vapor deposition was used to produce these films under different values of gas flow ratio, deposition temperature, and microwave power.

Physical Review B, 2012

Hydrogenated amorphous silicon (a-Si: H) refers to a broad class of atomic configurations, sharing a lack of long-range order, but varying significantly in material properties, including optical constants, porosity, hydrogen content, and intrinsic stress. It has long been known ...

Journal of Non-Crystalline Solids, 2002

Silicon films were deposited at high rate by reactive magnetron sputtering in a plasma mixture of H 2 and Ar. The hydrogen pressure ratio r H ¼ P H2 =P tot was varied in percentage from 0% to 100%. For r H below 5%, a transition from amorphous to crystalline Si takes place as evidenced by X-ray diffraction (XRD) and Raman spectroscopy measurements. In parallel, the apparent density, as deduced from X-ray reflectivity measurements, shows a stepped decrease. This phase transition arises because of the critical role of H radicals during the deposition process. For higher values of r H , the crystalline degree improves, whereas the apparent density deteriorates for r H P 80%. The surface roughness, determined by atomic force microscopy, correlates inversely with the apparent density. This behaviour suggests that the deposition rate is high and would then exceed the 'speed' of network relaxation. Such a rough surface would be the counterpart of the high deposition rate, even though the compactness and high crystallinity of the film bulk would result from some 'chemical annealing' and effects of diffusing H species.

Journal of Applied Physics, 2014

A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps Author(s) Legesse, Merid; Nolan, Michael; Fagas, Gíorgos Publication date 2014-05-28 Original citation Legesse, M., Nolan, M. and Fagas, G. (2014) 'A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps',

Journal of Low Temperature Physics, 1994

We have investigated the adsorption of 4He onto a quench-condensed H2 film by means of surface state electrons. Oscillations in the surface state electron conductivity clearly reveal the layerwise character of the adsorption. At temperatures below 2K we have observed an anomaly in the conductivity around the completion of the first monolayer. This new feature is interpreted as an indication of a liquid-to-solid phase transition in the first layer.

Diamond and Related Materials, 2002

Proper hydrogen addition in sputtered carbon nitrides is shown to remarkably reduce the film internal constraints. Significant differences in the hydrogen bonding are evidenced by infrared (IR) spectroscopy. Thus, the small variation (from 14 to 20%) of the total film H-content is accompanied by relevant changes in the microstructures of a-CN:H films. The results of the IR characterisation and Raman analysis of the 1000-1700 cm (Dand G-modes) region are comparatively discussed in the y1 light of the currently-utilised model, as well as of the recently-emerging interpretations contemplating vibrations of odd-fold rings. ᮊ