Influence of precursor gases on the structure of plasma deposited amorphous hydrogenated carbon–nitrogen films

Abstract

The atomic structure of amorphous hydrogenated carbon-nitrogen films was studied by electron energy loss spectroscopy ͑EELS͒. The films were deposited onto Si͑100͒ substrates by rf plasma decomposition of CH 4 -NH 3 and CH 4 -N 2 mixtures, with substrates placed on the powered electrode of a diode glow-discharge system. The sp 2 fraction of C and N atoms as a function of the nitrogen content in the films was obtained by EELS analysis. An increase of the carbon sp 2 fraction with increasing fraction of NH 3 and N 2 feed gases was observed. The variation in the atomic structure of the a-C͑N͒:H thin films is correlated to the internal compressive stress. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01319-8͔In the last few years there has been an increasing interest in the study of nitrogen incorporation into hard amorphous hydrogenated carbon ͑a-C:H͒ films. Research into the search for the proposed ␤-C 3 N 4 phase, which is predicted to be harder than diamond was initiated by Liu and Cohen. 1 As a result of nitrogen incorporation into carbon films it was found that both optical and electrical properties, 2-4 as well as their mechanical properties 5-7 can be modified. Particularly with respect to the mechanical properties, it was found that nitrogen incorporation results in a substantial reduction of the compressive internal stress of the films. The improvement in adhesion that resulted from the stress reduction has made it possible to use amorphous hydrogenated carbonnitrogen ͓a-C͑N͒:H͔ films as antireflective coatings in Ge based IR sensors. 7 One of the key factors in determining the structure and properties of hard amorphous carbon films is the hybridization state of the atoms that form the amorphous network. 8 Previous results on a-C͑N͒:H films 9 allude to an increase in the graphitic clustering (sp 2 bonding͒ upon nitrogen incorporation, which may be correlated to the observed internal stress reduction. 5 A similar reduction in stress is observed for highly tetrahedral C:N films 10,11 in which nitrogen incorporation above 1 at. % resulted in both stress reduction and increase in the sp 2 carbon fraction.All of the above-cited deposition studies on a-C͑N͒:H films are based on addition of N 2 to the deposition atmosphere, in the deposition of the a-C films. To date, few researchers have studied the use of ammonia as the source gas for nitrogen. 12,13 Contrary to the above research, Seth et al. 12 reported an increase in the sp 3 carbon atoms fraction upon nitrogen incorporation in a-C͑N͒:H films deposited by PECVD in C 4 H 6 -NH 3 atmospheres. In order to clarify the role of the nitrogen precursor gas on the structure and properties of a-C͑N͒:H films, we report a study on the influence of the precursor gases NH 3 and N 2 in the determination of they hybridization state of carbon and nitrogen atoms in a-C͑N͒:H films, as a function of the nitrogen content. The compressive internal stress was also measured and correlated with the other results.The a-C͑N͒:H films were produced by plasma decomposition of CH 4...

IR characterization of a-C:H:N films sputtered in Ar/CH4/N2 plasma

“…One of the key factors in determining the structure and properties of hard amorphous carbon films is the hybridization state of the atoms that form the amorphous network [3]. Various kinds of preparation methods have been applied to fabricate carbon nitride films, but samples with sufficient amount of crystallized C 3 N 4 phase or with mechanical properties comparable to the predicted values have not been reported.…”

“…The incorporation of nitrogen could also affect the amount of bonded hydrogen in the films [6]. Franceschini et al [3] reported that nitrogen incorporation strongly affects the hybridization state of carbon atoms by increasing the sp 2 fraction for both nitrogen precursor gas N 2 and NH 3 . At the same time the nitrogen can be used to dope the material; however, the doping process remained inefficient because the diversity of bonding configuration allowed nitrogen to be incorporated in different environments [7].…”

Effect of nitrogen in the properties of diamond-like carbon (DLC) coating on Ti6Al4V substrate

“…Thus, the use of techniques as oxide layer removal and the use of film interlayer previously to the DLC film deposition can improve this adhesion feature. Another used technique consists of the doping of the film with different elements, such as boron, fluorine and nitrogen, which has been widely used to relieve the internal stress of the film [14][15][16].The effects of the nitrogen incorporating in DLC film is the reduction of the internal stress due to the decrease in the formation of carbon atoms with sp 3 hybridization. As a consequence, the film hardness is reduced and the DLC film adhesion on the substrate is facilitated, arousing interest in synthesis and application of these films [15][16][17][18][19][20][21]67].The production of DLC and N-DLC films by plasma enhanced chemical vapor deposition (PECVD) technique comes as a potential alternative of a surface treatment since it presents a relatively low cost, clean technology and formation of the homogeneous and uniform film [9,22].…”

“…Another used technique consists of the doping of the film with different elements, such as boron, fluorine and nitrogen, which has been widely used to relieve the internal stress of the film [14][15][16].The effects of the nitrogen incorporating in DLC film is the reduction of the internal stress due to the decrease in the formation of carbon atoms with sp 3 hybridization. As a consequence, the film hardness is reduced and the DLC film adhesion on the substrate is facilitated, arousing interest in synthesis and application of these films [15][16][17][18][19][20][21]67].The production of DLC and N-DLC films by plasma enhanced chemical vapor deposition (PECVD) technique comes as a potential alternative of a surface treatment since it presents a relatively low cost, clean technology and formation of the homogeneous and uniform film [9,22]. This technique is being the focus of research for DLC film formation in Ti 6 Al 4 V alloy for space application [23], for application of DLC film in 316L stainless steel to act as anti-bactericidal agent in biomedical device [24], used to produce DLC film on inner surface of a long stainless steel tube [25], used to show the beneficial effects on the increased electrochemical activity of the DLC film doped with nitrogen [16,26] and to investigate the lubricating effect of the DLC film doped with nitrogen deposited on 3024 stainless steel to improve the tribocorrosion properties of the studied material [27].Since nitrogen is a low cost and environmentally friendly gas, it could be used to modify the undesirable properties of the DLC film, maintaining the high hardness and low coefficient of friction characteristic of the a-C:H films.…”

The Alignment Effect of Nematic Liquid Crystal on NDLC Thin Films Surface

“…Thus nitrogen incorporation at concentrations high results in the increase of the fraction of carbon atoms with sp 2 hybridization. In other words, nitrogen incorporation strongly affects the hybridization state of carbon atoms by increasing the sp 2 fraction [13][14][15][16]. Preparation of the NDLC thin films can be carried out at low substrate temperature and with high deposition rates using PECVD [17].…”