Structure and optical properties of carbon nitride films deposited by magnetron sputtering (original) (raw)
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Thin carbon nitride (CN x ) films were synthesized on silicon substrates by reactive RF magnetron sputtering of a graphite target in mixed N 2 /Ar discharges and the N 2 gas fraction in the discharge gas, F N , varied from 0.5 to 1.0. The atomic bonding configuration and chemical composition in the CN x films were examined using X-ray photoelectron spectroscopy (XPS) and the degree of structural disorder was studied using Raman spectroscopy. An increase in the nitrogen content in the film from 19 to 26 at% was observed at F N = 0.8 and found to influence the film properties; normality tests suggested that the data obtained at F N = 0.8 are not experimental errors. The interpretation of XPS spectra might not be always straightforward and hence the detailed and quantitative comparison of the XPS data with the information acquired by Raman spectroscopy enabled us to interpret the decomposed peaks in the N 1s and C 1s XPS spectra. Two N 1s XPS peaks at 398.3 and 399.8 eV (peaks N 1 and N 2 , respectively) were assigned to a sum of pyridine-like nitrogen and CN bond, and to a sum of pyrrole-like nitrogen and threefold nitrogen, respectively. Further, the peaks N 1 and N 2 were found to correlate with C 1s XPS peaks at 288.2 and 286.3 eV, respectively; the peak at 288.2 eV might include a contribution of sp 3 carbon.
Carbon nitride thin films prepared by reactive r.f. Magnetron sputtering
Carbon, 1998
Nitrogenated amorphous carbon thin films (CN,) were prepared by reactive r.f. magnetron sputtering from a graphite target in a nitrogen containing plasma (up to 4.4 at%) on Si substrates. All main controllable deposition conditions (such as base and deposition pressure, power at target, target-substrate distance, substrate bias voltage) were kept constant throughout the series of experiments and the only variable parameter was the nitrogen flux (O-2 seem). In situ spectroscopic ellipsometry (SE) in the energy region 1.5-5.5 eV in combination with Bruggeman's effective medium theory analysis was used per iterative deposition layer to monitor the film thickness and diamond character. The C:N chemical bonding characteristics of the films were also examined with the new Fourier transform IR ellipsometry technique. It was found that the films have a mixed character composed of constituents (phases) of sps and sp' type bonding. The film composition in terms of sp", sp' and void concentration as a function of film thickness and nitrogen concentration in the plasma was determined. The plasma nitrogen concentration seems to directly affect the film deposition rate and diamond character of the films by favoring sp3 bond formation.
Vibrational and optical properties of carbon nitride films prepared by reactive magnetron sputtering
Journal of Physics-condensed Matter, 1999
Carbon nitride films were prepared by reactive magnetron sputtering of a graphite target in a nitrogen atmosphere at different pressures and temperatures. The films were characterized by infrared, Raman and ultraviolet-visible spectroscopies, as well as by ellipsometry. We obtained hydrogen-free dark films when a negative bias was applied to the substrates; the samples prepared at room temperature without bias were soft and hydrogen could be detected in their infrared spectra. The most prominent features, between 1000 and 1700 cm-1, in both the Raman and infrared spectra were modelled using two Gaussian curves. As the nitrogen content was varied, the ratio between their areas followed opposite trends in the Raman and the infrared spectra. The presence of hydrogen caused the main feature to absorb more strongly at lower frequencies but did not alter the trend. The presence of six and five membered heteroaromatic rings is suggested to explain the increase of the infrared vibrations associated with double conjugated double bonds. The index of refraction can be correlated with features in the infrared spectra, suggesting that its value increases as the number of carbon and nitrogen double bonds increases. Ion bombardment reduces nitrogen incorporation; it is responsible for the densification of the films and the introduction of several defects that make films prepared under bias more absorbing in the low energy region.
Characterisation of carbon nitride thin films prepared by reactive magnetron sputtering
Carbon, 1998
Carbon nitride (CN,) thin films have been obtained by reactive magnetron sputtering in a pure N, discharge. The films have been characterised by Fourier transform infrared spectroscopy (IR), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. A maximum value of N/C =0.5 has been achieved. Evidence is presented of the formation of a polymer-like CN, amorphous phase which contains C=N, C=N and C-N bonds. A new peak at 286.5 eV energy loss in the C K-edge EELS spectra has been assigned to C=N bonds with carbon in the sp' hybridisation state. Infrared spectroscopy indicates that cyanogen-like groups are present in the films and can be partially removed by thermal annealing. The contribution of C-N and C=N bonds has also been determined by infrared and XPS spectroscopy.
Characterization of the density, structure and chemical states of carbon nitride films
Applied Surface Science, 2001
Carbon nitride ®lms prepared by rf magnetron sputtering were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and grazing-incidence X-ray re¯ectivity. In these ®lms, nitrogen atoms were found to be bound with sp 3 , sp 2 and sp hybridized carbon and about 30% of the C±N solid may have C 3 N 4 structure. The nitrogen to carbon ratios (N/C) of the ®lm, sp 3 and sp 2 C±N phases were $0.17, 1.05 and 0.26, respectively. The density of the ®lms was about 1.9 g cm À3 . The N/C and density of the ®lms only slightly decreased and increased, respectively, with increasing the substrate temperature. The analysis of the annealed samples indicated that these ®lms had a good thermal stability. #
Solid State Communications, 2008
Amorphous carbon nitride films (CN x ) were grown by reactive radio-frequency (RF) magnetron sputtering of a high-purity graphite target in argon/nitrogen (Ar/N 2 ) gas mixture. The total discharge pressure was 1 Pa and the total nitrogen partial pressure (NPP) in plasma was between 0 and 0.10%. The properties of films were determined using X-ray photoelectron spectroscopy (XPS), infrared absorption, and transmission spectroscopy. The electrical resistivity of films was studied as a function of temperature between 110 and 573 K. The optical gap varies from 0.30 to 0.7 eV in the range of the studied N content in good agreement with the resistivity measurements. The two types of conduction mechanisms can be interpreted basis on the band structure model of the π electrons in a disordered carbon with the presence of localized states.
Diamond and Related Materials, 2001
. Amorphous carbon nitride thin-films a-CN have been prepared in a hybrid plasma-based deposition process that allows independent control of nitrogen ion bombardment, by combining r.f.-magnetron sputtering of a graphite target with simultaneous nitrogen-ion-beam assistance from a capacitively coupled r.f. ion source. The films were deposited on unheated silicon substrates at 0.3 Pa of total pressure, using Ar and N gas flows of 3 and 1 sccm, respectively. The increase in nitrogen ion energy from 140 2 Ž . to 800 eV, leads to a reduction of both the deposition rate from 4.4 to 1.6 nmrmin and the nitrogen to carbon ratio in the films Ž . from 0.26 to 0.17 , which suggested chemical sputtering of deposited material by the impingement of energetic nitrogen atoms. In addition, changes in the film structure and nitrogen-bonding configuration were also induced with the increasing in ion energy, as revealed by X-ray photoelectron spectroscopy and Raman analysis. Preliminary nanoindentation and pin-on-disk tests Ž . Ž . indicated the films are relatively hard 19 GPa and with low friction coefficients between 0.1 and 0.2 measured in air ambient. ᮊ
Chemical bonding, structure, and hardness of carbon nitride thin films
Carbon nitride films are deposited on Si 001 substrates by reactive d.c. magnetron sputtering graphite in a pure N discharge. 2 Ž . The chemical bonding and structure of carbon nitride films were probed using Fourier transformation infrared FTIR and near Ž . edge X-ray absorption fine structure NEXAFS , and the hardness was evaluated using nanoindentation experiments. The Ž . structure and hardness for the films are dependent on the substrate temperature T . FTIR and NEXAFS spectra show that N s atoms are bound to sp 1 , sp 2 and sp 3 hybridized C atoms, and the intensity of U resonance for C1s NEXAFS spectra is the lowest for the film grown at T s 350ЊC, having a turbostratic-like structure, high hardness and stress. The correlation between the s structure and hardness of carbon nitride films is discussed. ᮊ
Effect of target self-bias on carbon nitride thin films deposited by RF magnetron sputtering
Solid State Communications, 2001
Analysis of carbon nitride ®lms (CN x) deposited by RF magnetron sputtering on crystalline silicon, under different target selfbias, is reported. The properties of ®lms were determined in their as-deposited state using X-ray photoelectron spectroscopy (XPS), IR absorption, transmission spectroscopy and residual stress measurements. The presence of various types of C±N bonds, as well as of hydrogen and oxygen, is revealed. A good correlation is observed between the variation of N/C ratio, the optical gap E 04 and the internal stress as a function of the target bias. The optical gap E 04 decrease is discussed in terms of N/C ratio evolution, the sp 2 bond content and the local distortions of the sp 2 bonds.