Insights on the deposition mechanism of sputtered amorphous carbon films (original) (raw)
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Stress-induced formation of high-density amorphous carbon thin films
Journal of applied …, 1997
Amorphous carbon films with high sp 3 content were deposited by magnetron sputtering and intense argon ion plating. Above a compressive stress of 13 GPa a strong increase of the density of the carbon films is observed. We explain the increase of density by a stress-induced phase transition of sp 2 configured carbon to sp 3 configured carbon. Preferential sputtering of the sp 2 component in the carbon films plays a minor role compared to the sp 2 ⇒sp 3 transition at high compressive stress formed during the deposition process. Transmission electron microscopy shows evidence of graphitic regions in the magnetron sputtered/Ar plated amorphous carbon thin films. Differences in the microstructure of the tetrahedral amorphous carbon ͑ta-C͒ films deposited by filtered arc and mass selected ion beam; and those films deposited using magnetron sputtering combined with intense ion plating can be used to explain the different electronic and optical properties of both kinds of ta-C films. © 1997 American Institute of Physics. ͓S0021-8979͑97͒09422-X͔
Thin Solid Films
Structure evolution of amorphous carbon (a-C) films deposited by dc magnetron sputtering of graphite in argon was investigated as a function of substrate temperature Ts (20–800°C) and dc substrate bias voltage Ub (floating — −175 V). Film structure was studied by transmission electron microscopy, selected area electron diffraction, reflective high energy electron diffraction and Raman spectroscopy. Film resistivity in two directions — parallel and perpendicular to the substrate — was also measured. The results obtained allow for the assumption that the film structure is based on coexistence of D- and G-phases formed of sp2 bonded carbon atoms. G-phase consists of small graphite-like ordered areas embedded in continuous uniform amorphous D-phase. The evolution of a-C film structure in 20−450°C interval occurs by temperature induced graphite-like ordering of small areas within D-phase (G-phase nucleation). In the 500–800°C range the change of C-film growth mechanism takes place. Inste...
Diamond and Related Materials, 2000
This work investigates the evolution of the structural, mechanical and tribological properties of amorphous carbon films (a-C) undergoing thermal annealing. Two different types of a-C film were studied: hard, stressed and dense films, henceforth called 'diamond-like', and soft, more relaxed and less dense films, called 'polymer-like'. The two sets of films were deposited by dc magnetron sputtering at 0.36 and 1.4 Pa argon plasma pressures, respectively, and both were annealed in vacuum for 1 h at temperatures between 300 and 700°C. Raman results provided indications of a remarkable increase of the sp2 hybridized domains, that occurs mainly at temperatures higher than 400°C for the diamond-like films and in a continuous way for the polymer-like films. The friction coefficient of both types of film approaches the same value with increasing temperature, whereas the surface roughness is nearly constant. For diamond-like films, the hardness and compressive internal stress are nearly constant up to 500°C, and then undergo a fast decrease. In contrast, the hardness of the polymer-like film continuously decreases with temperature, whereas the compressive stress remains constant.
Thin Solid Films, 2005
Amorphous carbon (a-C) films have been produced by unbalanced magnetron sputtering (UBMS) on silicon (Si), aluminium (Al), and chromium (Cr) substrates as a function of substrate bias voltage. The chemical bonding configurations were investigated by Raman and nearedge X-ray absorption fine structure (NEXAFS) spectroscopies. It was found that the structural changes induced by bias voltage are substrate-dependent, revealing the key role of the substrate type on film microstructures. The Raman G peak position and I D /I G ratio were strongly dependent on substrate material and negative bias voltage. Negative bias voltage had a small effect on the structure of carbon films on metal substrates (Al and Cr). However, the films on silicon showed significant change in the structure with bias voltage. The intensity and area of k* peak at the C K (carbon) edge increased with the increase of substrate bias voltage. The NEXAFS analysis was in agreement with Raman observations, which clearly indicated an increase of sp 2 content with increasing bias voltage. The films deposited in the low-bias voltage regime (50-100 V) showed reduced sp 2 configurations. The possible changes of structure with substrate bias are thoroughly discussed. D
Diamond and Related Materials, 2007
The relationship between metal-induced (W, Mo, Nb and Ti) structures and the surface properties of Me-DLC thin films is discussed. Nanocomposite films were deposited on c-Si wafers by pulsed-DC reactive magnetron sputtering controlling the gas ratio CH 4 /Ar. The sputtering process of metals such as Ti, Nb and Mo (unlike the tungsten) in the presence of methane shows a low reactivity at low methane concentration. The deposition rate and the spatial distribution of sputtered material depend of Z-ratio of each metal. The surface contamination of metal targets by carbon, owing to methane dilution, limits the incorporation of metals into DLC films according to an exponential decay. Results of electron probe microanalysis and X-ray photoelectron spectroscopy indicate a C rich Me/C composition ratio for low relative methane flows. According to the depth profile by secondary ion mass spectrometry, the films are systematically homogeneous in depth, whereas at high carbon contents they exhibit a metal-rich interfacial layer on the substrate. Moreover, high resolution transmission electron microscopy has evidenced important structural modifications with respect to DLC standard films, with marked differences for each Me/C combination, providing nanodendritic, nanocrystallized or multilayered structures. These particular nanostructures favour the stress decrease and induce significant changes in the tribological characteristics of the films. This study shows the possibilities of controlling the amorphous carbon films structure and surface properties by introducing metal in the DLC matrix.
Comprehensive study on the properties of multilayered amorphous carbon films
Amorphous carbon (a-C ) multilayered films consisting of sequential layers rich in sp2 (A) and sp3 (B) content have been developed by magnetron sputtering. We study here the effect of thickness d of the A layer in developing stable thick films with controllable stress and elastic properties. In situ spectroscopic ellipsometry is used to calculate the thickness and the composition of the individual layers. The latter were compared with those obtained by depth profiling X-ray photoelectron spectroscopy, which also provides the different chemical bonding of the multilayers in depth. The stress and hardness of the deposited a-C films were found to be related to the thickness of the A j layers and the relative ratio d A j /d B of thicknesses. The possible mechanisms for the stress control, stability and enhancement of elastic properties of multilayered a-C films are discussed.
Optimization of nitrogenated amorphous carbon films deposited by dual ion beam sputtering
Materials Science and Engineering: B, 1999
Optimization of deposition conditions for nitrogenated amorphous carbon (a-C:N) films prepared by a dual ion beam sputtering (DIBS) technique is reported. A ripple structure was observed on the surface of a-C:N films, which was believed to be corresponding to the off-normal incidence bombardment by N ions during deposition. Infrared spectra indicated that the nitrogen atoms incorporated were bonded as C-N, C N and C N in the carbon network. The relative intensity of D and G bands obtained by fitting the Raman spectra showed that the sp 3 content in the a-C:N films increased as the Ar ion energy was increased and the sp 3 content was the highest with 100 eV N ion bombardment. The maximum micro-hardness achieved was about 25 GPa for the 200 nm thick a-C:N films deposited under the optimized conditions. The compressive stress ranged from 1 to 3 GPa. The optical band gap determined by spectral ellipsometry ranged from 0.6 to 1.0 eV. The refractive index and extinction coefficient at 633 nm wavelength were about 2.14 and 0.22 for the films deposited under the optimized conditions, respectively. Hardness, stress and optical band gap measurements showed a similar trend with the relative intensity of I D /I G .
Properties of amorphous carbon films deposited by ion beam methods
Thin Solid Films, 1987
Amorphous carbon films were prepared by the ion beam sputtering of graphite, by the ion beam sputtering of graphite with simultaneous ion bombardment of the growing film, and by primary ion beam deposition using a beam from a methaneargon plasma. The films are semiconducting in nature, having band gaps of the order of 1 eV. A nuclear reaction involving an energetic (2 MeV) beam of 1 ~ B ÷ was used to obtain hydrogen profiles of the films. It was found that the electrical, optical and mechanical properties of the films could be correlated with the hydrogen content. The observed properties are explained qualitatively in terms of amorphous semiconductor theory.
Stability, enhancement of elastic properties and structure of multilayered amorphous carbon films
Applied Surface Science, 1999
Ž . The growth of sputtered amorphous carbon a-C films in layer structure with alternating negativerpositive substrate bias voltage V , was applied to control their intrinsic stress level and stability. The main benefit of the process was the b development of thick, stable, hard and rich in sp 3 sites films proving their usefulness for many practical applications. In order to investigate the structure and the mechanisms of film stability we performed in-situ Spectroscopic Ellipsometry, Ž . Stress, Nanoindentation, Raman and Transmission Electron Microscopy TEM measurements. The latter provides details about the layered structure of the films. A stress relief was found to occur in films depending on the sequence of layers and their modulation period. Despite the film stability an improvement in film hardness and elastic modulus was also achieved, whereas nanocrystalline carbon phases were detected and identified by Raman spectra. q 1999 Elsevier Science B.V. All rights reserved.