Jan-Eric Sundgren

Nitrogen bonding structure in carbon nitride thin films studied by soft x-ray spectroscopy

Soft x-ray absorption (SXAS) and emission (SXES) spectroscopies were applied to study the nitrogen bonding structure in magnetron sputtered CNx thin films. By comparing with calculated spectra of N in different model systems, N in three main bonding environments can be identified: (i) C≡N bonds, with a sharp SXAS peak at 399.5 eV, (ii) pyridine-like N (i.e., N bonded to two C atoms), with an x-ray absorption resonance at ∼398.5 eV, and (iii) N substituted in graphite, possibly with one sp3 carbon as a neighbor (SXAS energy ∼401 eV). These bondings are present in all CNx films analyzed; however, as shown earlier, the relative intensities between the peaks may vary with the growth conditions. Differences in the coordination of the nearest or second nearest C neighbors only cause slight changes in the peak positions and spectrum shape.

Effect of chemical sputtering on the growth and structural evolution of magnetron sputtered CNx thin films

Abstract The growth and microstructure evolution of carbon nitride CN x (0≤ x ≤0.35) films, deposited by reactive d.c. magnetron sputtering in Ar/N 2 discharges has been studied. The substrate temperature T S varied between 100 and 550°C, and the N 2 fraction in the discharge gas varied from 0 to 100%. It is found that the deposition rate and film morphology show strong dependence on T S and nitrogen fraction. For growth temperature of 100°C, the films are amorphous, and essentially unaffected by the nitrogen fraction. For T S >200°C, however, the nitrogen fraction has more significant effect on the growth and structural evolution of the films. The pure carbon films appear porous and have a high surface roughness. For increasing nitrogen fraction the films become denser and the roughness decreases by one order of magnitude. It is suggested that a chemical sputtering process, during which desorption of volatile N 2 and CN-species, predominantly C 2 N 2 , is important not only for the deposition rate and the nitrogen incorporation, but also for the resulting film structure. The chemical sputtering process becomes more pronounced at elevated temperatures with higher nitrogen fractions.

Effects of substrate temperature and substrate material on the structure of reactively sputtered TiN films

Abstract Stoichiometric TiN films were reactively magnetron sputtered in an Ar - N 2 atmosphere. The films were deposited at various substrate temperatures in the range 200–650°C onto two types of substrate material, high speed steel and stainless steel. The microstructure of the films obtained was investigated by the use of a transmission electron microscope and the morphology was studied in a scanning electron microscope. Measurements of the hardness were also performed. The analysis of the microstructure shows that the growth of the film is markedly influenced by the substrate material. In particular, the high speed steel substrates were found to have a considerable influence on the microstructure. The vanadium carbide particles in these steels, which have a good lattice match to TiN, stimulate a localized epitaxial growth to occur on these carbide particles. This results in a microstructure consisting of large grains surrounded by small grains. The shape of the large grains is influenced by the temperature. In the development of these large grains cracks and/or voids occur in and around the grains at substrate temperatures above 400°C and the hardness drops by about 20%. No large grains were found on films deposited onto stainless steel and their hardness increases slightly with temperature. High hardness for films deposited onto the high speed steel substrate at temperatures above 400°C can also be obtained if a substrate bias is used. Ion bombardment during film growth suppresses the formation of the large grains with voided or cracked boundaries because of a continuous renucleation process. The formation of the different microstructures is discussed in terms of surface energy minimization and thermally activated processes as surface and grain boundary migration.

Influence of plasma parameters on the growth and properties of magnetron sputtered CNx thin films

Carbon nitride CNx thin films were grown by unbalanced dc magnetron sputtering from a graphite target in a pure N2 discharge, and with the substrate temperature Ts kept between 100 and 550 °C. A solenoid coil positioned in the vicinity of the substrate was used to support the magnetic field of the magnetron, so that the plasma could be increased near the substrate. By varying the coil current and gas pressure, the energy distribution and fluxes of N2+ ions and C neutrals could be varied independently of each other over a wide range. An array of Langmuir probes in the substrate position was used to monitor the radial ion flux distribution over the 75-mm-diam substrate, while the flux and energy distribution of neutrals was estimated through Monte Carlo simulations. The structure, surface roughness, and mechanical response of the films are found to be strongly dependent on the substrate temperature, and the fluxes and energies of the deposited particles. By controlling the process parameters, the film struc...

Hydrogen uptake in alumina thin films synthesized from an aluminum plasma stream in an oxygen ambient

We describe the hydrogen uptake during the synthesis of alumina films from H2O present in the high vacuum gas background. The hydrogen concentration in the films was determined by the 1H(15N,αγ)12C nuclear resonance reaction. Furthermore, we show the presence of hydrogen ions in the plasma stream by time-of-flight mass spectrometry. The hydrogen content increased in both the film and the plasma stream, as the oxygen partial pressure was increased. On the basis of these measurements and thermodynamic considerations, we suggest that an aluminum oxide hydroxide compound is formed, both on the cathode surface as well as in the film. The large scatter in the data reported in the literature for refractive index and chemical stability of alumina thin films can be explained on the basis of the suggested aluminum oxide hydroxide formation.

Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges

Hydrogenated carbon nitride films were deposited by reactive dc magnetron sputtering in mixed Ar/N2/H2 discharges at temperatures of 100 and 350 °C. The total pressure was kept constant at 0.33 Pa and the gas mixtures were varied in order to study the effect of the hydrogen on the resulting film structure and properties. Chemical sputtering effects taking place during deposition were found to be an important factor for the growth and structural evolution. When H2 is mixed into the discharge gas, the growth rate decreases considerably and the films become denser due to desorption of volatile species, like hydrocarbons, NH3 and HCN. For a H2 fraction above 15%, no net film growth takes place. The hydrogen concentration incorporated into the films was highest (up to ∼33 at. %) for low growth temperatures and low nitrogen concentrations. Furthermore, the results indicate that substantial amount of hydrogen are bonded to nitrogen. The incorporation of hydrogen in the structure interrupts the relatively long ba...

Thermal stability of carbon nitride thin films

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N-2 discharge, was studied for postdeposition annealing temperatures T-A up to 1000 degre ...

Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering

Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O2 gas mixtures at substrate temperatures ranging from 650 to 850 °C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1Ti0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of ∼300 nm, the typical dielectric constants as measured at ∼77 K...

Anisotropies in magnetron sputtered carbon nitride thin films

Carbon nitride CNx (0⩽x⩽0.35) thin films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges have been studied with respect to microstructure using electron microscopy, and elastic modulus using nanoindentation and surface acoustic wave analyses. For growth temperature of 100 °C, the films were amorphous, and with an isotropic Young’s modulus of ∼170–200 GPa essentially unaffected by the nitrogen fraction. The films grown at elevated temperatures (350–550 °C) show anisotropic mechanical properties due to a textured microstructure with standing basal planes, as observed from measuring the Young’s modulus in different directions. The modulus measured in the plane of the film was ∼60–80 GPa, while in the vertical direction the modulus increased considerably from ∼25 to ∼200 GPa as the nitrogen content was increased above ∼15 at. %.

Time-resolved measurements of the formation of single-domain epitaxial Ni films on MgO( 111) substrates using in-situ RHEED analysis

Abstract The mechanisms behind the formation of smooth 〈111〉 oriented single domain epitaxial Ni films grown on MgO(111) substrates by ultra-high vacuum dc magnetron sputtering were studied using time-resolved in-situ reflection high energy electron diffraction (RHEED) measurements. The results show that whether a single- or a two-domain 〈111〉 oriented film forms is decided already during the deposition of the first two or three monolayers of Ni, and that the Ni appears to nucleate as strained islands during this initial growth. This implies that an interaction between the atoms in the second Ni layer and the second and third atomic layers of the substrate must exist, making the Ni atoms always choose the same stacking sequence at a growth temperature of 300°C. Prior to growth, the MgO(111) surface is smooth, non-faceted and without reconstructions.