Influence of inert gases on the reactive high power pulsed magnetron sputtering process of carbon-nitride thin films

The influence of inert gases (Ne, Ar, Kr) on the sputter process of carbon and carbon-nitride (CNx) thin films was studied using reactive high power pulsed magnetron sputtering (HiPIMS). Thin solid films were synthesized in an industrial deposition chamber from a graphite target. The peak target current during HiPIMS processing was found to decrease with increasing inert gas mass. Time averaged and time resolved ion mass spectroscopy showed that the addition of nitrogen, as reactive gas, resulted in less energetic ion species for processes employing Ne, whereas the opposite was noticed when Ar or Kr were employed as inert gas. Processes in nonreactive ambient showed generally lower total ion fluxes for the three different inert gases. As soon as N2 was introduced into the process, the deposition rates for Ne and Ar-containing processes increased significantly. The reactive Kr-process, in contrast, showed slightly lower deposition rates than the nonreactive. The resulting thin films were characterized regarding their bonding and microstructure by x-ray photoelectron spectroscopy and transmission electron microscopy. Reactively deposited CNx thin films in Ar and Kr ambient exhibited an ordering toward a fullerene-like structure, whereas carbon and CNx films deposited in Ne atmosphere were found to be amorphous. This is attributed to an elevated amount of highly energetic particles observed during ion mass spectrometry and indicated by high peak target currents in Ne-containing processes. These results are discussed with respect to the current understanding of the structural evolution of a-C and CNx thin films. VC 2013 American Vacuum Society. [http://dx.doi.org/10.1116/1.4769725

Electronic excitation of transition metal nitrides by light ions with keV energies

We investigated the specific electronic energy deposition by protons and He ions with keV energies in different transition metal nitrides of technological interest. Data were obtained from two different time-of-flight ion scattering setups and show excellent agreement. For protons interacting with light nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom were found, which coincide with literature data of N2 gas for primary energies <= 25 keV. In case of the chemically rather similar nitrides with metal constituents from the 5th and 6th period, i.e. ZrN and HfN, the electronic stopping cross sections were measured to exceed what has been observed for molecular N2 gas. For He ions, electronic energy loss in all nitrides was found to be significantly higher compared to the equivalent data of N2 gas. Additionally, deviations from velocity proportionality of the observed specific electronic energy loss are observed. A comparison with predictions from density functional theory for protons and He ions yields a high apparent efficiency of electronic excitations of the target for the latter projectile. These findings are considered to indicate the contributions of additional mechanisms besides electron hole pair excitations, such as electron capture and loss processes of the projectile or promotion of target electrons in atomic collisions

CrNx Films Prepared by DC Magnetron Sputtering and High-Power Pulsed Magnetron Sputtering: A Comparative Study

Abstract-CrN x (0 ≤ x ≤ 0.91) films synthesized using highpower pulsed magnetron sputtering, also known as high-power impulse magnetron sputtering (HiPIMS), have been compared with those made by conventional direct-current (dc) magnetron sputtering (DCMS) operated at the same average power. The HiPIMS deposition rate relative to the DCMS rate was found to decrease linearly with increasing emission strength from the Cr ions relative to Cr neutrals, in agreement with the predictions of the target-pathway model. The low deposition rate in HiPIMS is thus a direct consequence of the high ionization level (∼56%) of the target material and effective capturing of Cr ions by the cathode potential. Although the HiPIMS deposition rate did not exceed 40% of the DCMS rate, the drop in the relative deposition rate upon increasing the N 2 -to-Ar flow ratio, f N 2 /Ar , was found to be similar for both sputtering techniques. Films prepared by HiPIMS contained similar amounts of atomic nitrogen as the dc-sputtered samples grown at the same f N 2 /Ar , indicating that the nitride formation at the substrate takes place mostly during the time period of the high-power pulses, and the N 2 uptake between the pulses is negligible. The microstructure evolution in the two types of CrN x films, however, differed clearly from each other. A combination of a high substrate bias and a high flux of doubly charged Cr ions present during the HiPIMS discharge led to a disruption of the grain growth and renucleation, which resulted in column-free films with nanosized grains not observed in the conventional DCMS-based process. The comparison of nanoindentation hardness as a function of f N 2 /Ar revealed superior properties of HiPIMS-sputtered films in the entire range of gas compositions. Index Terms-CrN, high-power impulse magnetron sputtering (HiPIMS), high-power pulsed magnetron sputtering, magnetron sputtering

Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy

The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk {\alpha}-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk {\alpha}-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible -111, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material. For the bulk {\alpha}-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to {\alpha}-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 {\AA}, c=3.520 {\AA}) in comparison to the bulk target material (a=3.175 {\AA}, c=3.540 {\AA}) while in hexagonal closest-packed metal ({\alpha}-phase, a=3.254 {\AA}, c=5.147 {\AA}).Comment: 15 pages, 5 Figures, 4 table

Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere

W-B-C films were deposited on Si(100) substrates held at elevated temperature by reactive sputtering from a W target in Kr/trimethylboron (TMB) plasmas. Quantitative analysis by X-ray photoelectron spectroscopy (XPS) shows that the films are W-rich between ~ 73 and ~ 93 at.% W. The highest metal content is detected in the film deposited with 1 sccm TMB. The C and B concentrations increase with increasing TMB flow to a maximum of ~18 and ~7 at.%, respectively, while the O content remains nearly constant at 2-3 at.%. Chemical bonding structure analysis performed after samples sputter-cleaning reveals C-W and B-W bonding and no detectable W-O bonds. During film growth with 5 sccm TMB and 500 oC or with 10 sccm TMB and 300-600 oC thin film X-ray diffraction shows the formation of cubic 100-oriented WC1-x with a possible solid solution of B. Lower flows and lower growth temperatures favor growth of W and W2C, respectively. Depositions at 700 and 800 oC result in the formation of WSi2 due to a reaction with the substrate. At 900 oC, XPS analysis shows ~96 at.% Si in the film due to Si interdiffusion. Scanning electron microscopy images reveal a fine-grained microstructure for the deposited WC1-x films. Nanoindentation gives hardness values in the range from ~23 to ~31 GPa and reduced elastic moduli between ~220 and 280 GPa in the films deposited at temperatures lower than 600 oC. At higher growth temperatures the hardness decreases by a factor of 3 to 4 following the formation of WSi2 at 700-800 oC and Si-rich surface at 900 oC.Comment: 14 pages, 8 figure

Job Creation and the Role of Dependencies

We contribute to the large literature on the relation between firm size and job creation by examining the effects of dependences between enterprises. Using Finnish monthly data encompassing the population of Finnish private businesses, we calculate gross job creation and destruction, together with net job creation, for different size classes and industries. Importantly, we divide firms into a dependent (i.e. owned, at least partially, by a large company) and independent category. The analysis is based on both a dataset including entry and exit and a sample considering only continuous companies, to control for the effects of firm's age. Due to the quality of the data, we are able to isolate the 'organic' growth of firms, disregarding the effects of mergers and split-offs together with other legal restructurings. We find that independent companies have shown considerably higher net job creation, even after taking age into account. However, dependent firms do not show particularly different behavior with respect to the sensitivity to aggregate conditions, compared to their independent counterparts