F. L. Freire

AMORPHOUS NITROGENATED CARBON FILMS : STRUCTURAL MODIFICATIONS INDUCED BY THERMAL ANNEALING

Hard amorphous nitrogenated carbon films [a‐C:H(N)] deposited by self‐bias glow discharge were annealed in vacuum in the temperature range of 300–800 °C. The annealing time was 30 min. The structural and compositional modifications induced by thermal annealing were followed by several analytical techniques: secondary ion mass spectrometry (SIMS), Raman spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection (ERDA), and nuclear reaction analysis. The internal stress of the films was also measured. Nuclear analyses indicate that both nitrogen and hydrogen losses occur for annealing temperatures higher than 300 °C. ERDA and SIMS results suggest that hydrogen and nitrogen out‐diffusion occurs by molecular transport through an interconnect network of voids. In the same temperature range, Raman scattering reveals an increase of the number and/or the size of the graphite domains. Internal stress is compressive for the as‐deposited films and changes to tensile for samples annealed at 800 °C...

Atomic force microscopy of amorphous hydrogenated carbon–nitrogen films deposited by radio‐frequency‐plasma decomposition of methane–ammonia gas mixtures

Atomic force microscopy was used for the surface characterization of hard amorphous hydrogenated carbon–nitrogen films deposited by plasma enhanced chemical vapor deposition. The films were deposited onto silicon substrates by rf‐plasma decomposition of methane–ammonia mixtures. The film roughness and the friction coefficient between the silicon nitride tip and the film surface were determined. The results indicate that the surface roughness increases with the amount of nitrogen incorporated in the film. The friction coefficients, measured in air, are almost constant for nitrogen incorporation up to 11 at. %.

Growth kinetics and relationship between structure and mechanical properties of a-C(N):H films deposited in acetylene–nitrogen atmospheres

Amorphous hydrogenated carbon–nitrogen films, a-C(N):H, were deposited by plasma enhanced chemical vapor deposition using acetylene–nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the film microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at. %. As for films obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene–nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp3 fraction was inferred for nitrogen contents higher than 10 at. %, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at. %.

Effects of thermal annealing on the microstructure and mechanical properties of carbon–nitrogen films deposited by radio frequency-magnetron sputtering

Amorphous carbon–nitrogen films deposited by radio frequency-magnetron sputtering were annealed in vacuum for 30 min at temperatures between 300 and 700 °C, without any kind of sequential annealing. The annealing-induced modifications on the chemical composition of the films were followed by ion beam analysis (IBA). Raman scattering and infrared absorption spectroscopies were used to determine the microstructure modifications, while atomic force microscopy (AFM) was used to investigate the surface morphology. The internal stress of the films was obtained by measuring the bending of the substrate and the nanoindentation technique was used to measure the film hardness. Besides the nitrogen loss, determined by IBA analyses, Raman results suggested an increase in the size or in the number of the graphitic domains with the annealing temperature. AFM shows a decrease of the surface roughness as a function of the annealing temperature. The density, the hardness, and the internal stress of the films present a sim...

Hydrogenated Carbon-Nitrogen Films Obtained by Pecvd using Acetylene and Nitrogen as Precursor Gases

Amorphous hydrogenated carbon-nitrogen films were deposited by plasma enhanced chemical vapor deposition (PECVD) using acetylene-nitrogen mixtures. The atomic composition and density of the films were determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERDA). Raman and Infrared spectroscopies monitored their structure. The addition of nitrogen gas to the deposition atmosphere resulted in a decrease in the film deposition rate. The increase of the nitrogen content is accompanied by the reduction of the carbon content. The IR absorption spectra show an increase intensity of the C=N Raman band and the N-H and CsN stretching bands. On the other hand, the IR results show a decrease in the intensity of the C-H stretching band. Raman results suggest an increase with the nitrogen content of the fraction of carbon atoms in a sp 2 state of hybridization with the nitrogen content. The internal compressive stress has been measured by the determination of the bending of the substrate; a reduction of up to 50 % has been observed depending on the nitrogen content.

Amorphous carbon films deposited by direct current-magnetron sputtering: Void distribution investigated by gas effusion and small angle x-ray scattering experiments

Amorphous carbon films were deposited by direct current-magnetron sputtering onto p-doped (100) silicon crystals and onto ultrapure aluminum foils at different argon pressures, ranging from 0.17 to 1.4 Pa. The film density was determined by the combination of the areal density, obtained from ion beam analysis, and the film thickness measured by a stylus profilometer. Film density decreased when the argon pressure used during deposition was increased. Gas effusion measurements indicated that the films deposited at low pressures are more compact than the films deposited at higher pressures. In the case of the latter, C2Hn effusion at temperatures as low as 250 °C indicated that they have an open structure that allows the evolution of large molecules. Small angle x-ray scattering results revealed an increase of the void density with increasing plasma pressure. Guinier plots show that these voids have a broad distribution of sizes, ranged from 7 to 26 A, which is nearly independent of the plasma pressure. A direct correlation between film density and the open volume fraction in the films was found. These different film microstructures could be explained by the existence of different bombardment regimes during film growth: films deposited at lower plasma pressures are hard and dense, while soft films grown at higher pressures have an open microstructure.Amorphous carbon films were deposited by direct current-magnetron sputtering onto p-doped (100) silicon crystals and onto ultrapure aluminum foils at different argon pressures, ranging from 0.17 to 1.4 Pa. The film density was determined by the combination of the areal density, obtained from ion beam analysis, and the film thickness measured by a stylus profilometer. Film density decreased when the argon pressure used during deposition was increased. Gas effusion measurements indicated that the films deposited at low pressures are more compact than the films deposited at higher pressures. In the case of the latter, C2Hn effusion at temperatures as low as 250 °C indicated that they have an open structure that allows the evolution of large molecules. Small angle x-ray scattering results revealed an increase of the void density with increasing plasma pressure. Guinier plots show that these voids have a broad distribution of sizes, ranged from 7 to 26 A, which is nearly independent of the plasma pressure. A d...

Structural Disorder in Hard Amorphous Carbon Films Implanted with Nitrogen Ions

Hard amorphous hydrogenated carbon films deposited by self-bias glow discharge were implanted at room temperature with 70 keV-nitrogen ions at fluences between 2.0 and 9.0 {times} 10{sup 16} N/cm{sup 2}. The implanted samples were analyzed by Raman spectroscopy, SIMS and positron annihilation spectroscopy (Doppler broadening technique with the determination of the parameter S). For samples implanted with 2.0 {times} 10{sup 16} N/cm{sup 2} the S parameter follows the vacancies depth profile predicted by Monte Carlo simulation. For higher fluences the authors observed a reduction in the measured value of S. This result is discussed in terms of both hydrogen loss and structural modifications (increase of disorder at local scale and of the number of graphitic domains) induced in the carbon film by ion implantation.

Fluorine Incorporation Into Hard Amorphous Hydrogenated Carbon Films Deposited by PECVD

The incorporation of fluorine into amorphous hydrogenated carbon films deposited by the plasma enhanced chemical vapor deposition technique (PECVD) was investigated. Different mixtures of CH 4 and CF 4 were employed as the plasma atmosphere, with the partial pressure of CF 4 ranging from 0 to 100 %. For all depositions, the self-bias was kept at –350 V. In the case of atmospheres richer than ∼80 % of CF 4 , no film deposition but substrate erosion was observed. The composition of the films was determined by Ion Beam Analysis (IBA), revealing that fluorine is incorporated into the amorphous network by replacing hydrogen. Infrared (IR) transmission measurements confirmed these results. It was also found that the incorporation of fluorine has the effect of reducing both the internal stress and hardness due to atomic density reduction.

Voids Investigation of Amorphous Carbon Films Deposited by DC-Magnetron Sputtering: A Small Angle x-ray Scattering and Gas Thermal Effusion Study

Amorphous carbon films were deposited onto (100) Si crystals and onto ultra-pure Al foils by dc-magnetron sputtering with different Ar plasma pressures, from 0.17 to 1.4 Pa. We investigate the voids structure and the voids density in these films by means of small angle x-ray scattering (SAXS) and mass spectrometry of effused gases. The analysis of the effusion spectra provided clear evidence that films deposited at lower pressures are compact, while the films deposited at higher pressure present a more open structural arrangement, confirming density results obtained by using ion beam techniques. SAXS results reveal that the fraction of open volumes increases with the plasma pressure: a direct correlation between film density and open volume fraction is found. These different film microstructures could be explained by the existence of different bombarding regimes during film growth

On the Effects of the Thermal Treatment on the Structural, Mechanical and Tribological Properties of Amorphous Carbon-Nitrogen Films Deposited by Magnetron Sputtering

Amorphous carbon-nitrogen films, a-CN x , deposited by rf-magnetron sputtering in N2 atmosphere were annealed in vacuum at temperatures between 300 and 700 °C. The annealing time was 30 minutes. The modifications on the film microstructure were monitored by infrared spectroscopy (IR), while the composition and the atomic density were determined by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). The internal stress was determined by measuring the film-induced bending of the substrate and the hardness was measured by nanoindentation. Atomic force microscopy (AFM) provided the friction coefficient and the surface roughness. The ratio between nitrogen and carbon atomic concentration decreases for temperatures higher than 500 °C, whereas the film density increases with the annealing temperature: 40 % in the temperature range here studied. The behavior of the D and G Raman bands, IR active due to the nitrogen incorporation in the carbon network, suggests a progressive increase of the size of the graphite-like domains. The hardness of the as-deposited a-CN x film is around 2 GPa. However, both hardness and internal stress increase by a factor of three in samples annealed at 700 °C, while the surface roughness and the friction coefficient decrease by a factor of about two.