Effects of Tetramethyl Silane Concentration on Amorphous SiCN Films Deposited by Microwave Sheath-Voltage Combination Plasma at High Substrate Temperatures

Abstract

Amorphous silicon carbon nitride (a-SiCN) films are known for their exceptional mechanical properties. This study explores the impact of tetramethylsilane (TMS) concentration on the deposition of a-SiCN films utilizing a microwave sheath-voltage combination plasma (MVP) source. A mixture of TMS and N₂ gases served as the reaction medium. The substrate temperatures were maintained between 905°C and 981°C. We observed that the deposition rate escalated with an increase in TMS concentration, reaching a peak rate of approximately 270 µm/h at a 20% TMS concentration. Concurrently, as TMS concentration increased, the carbon content rose from 11 at% to 51 at%, while nitrogen and silicon contents decreased to 15 and 18 at%, respectively. Hence, at lower TMS concentrations, the a-SiCN film predominantly comprised Si-N bonds, but at higher TMS concentrations, it transformed into a composite of Si-N, Si-C, C=N, and C=C bonds. The film hardness also augmented with rising TMS concentrations, achieving a maximum of 28 GPa in 20% TMS films. The friction coefficient for the film with 20% TMS concentration was approximately 0.29. In summary, the study successfully deposited a high-hardness a-SiCN film at an accelerated deposition rate using MVP from a high TMS concentration.

1. Introduction

Various ceramic coatings are applied to tools, molds, and friction parts to reduce friction and extend the lifespan of these components. In recent years, diamond-like carbon (DLC) films, which are amorphous carbon films containing a mix of diamond (sp³) and graphite (sp²) structures, have seen a broadening range of applications [1]. However, the environments in which these coatings are used have become increasingly severe, characterized by high temperatures, high pressures, and the need for improved coating functions such as heat resistance, impact resistance, and wear resistance. Among the emerging hard materials are Si-C-N compound films, which exhibit excellent mechanical properties. Achieving either α-SiC²N⁴ or β-SiC²N⁴ structures could potentially result in hardness levels comparable to those of cubic boron nitride (c-BN) [2]. While ultra-hard SiCN crystals have yet to be synthesized, amorphous SiCN films have been reported to possess significant hardness and high thermal resistance [3].

Numerous studies have been conducted on the synthesis of amorphous silicon carbon nitride (a-SiCN) compounds using various chemical vapor deposition (CVD) [4–8] and physical vapor deposition (PVD) [9–15] methods. In plasma CVD, hydrogenated a-SiCN films have been deposited from SiH₄-CH₄-N₂ mixture gases or organosilicon compounds (e.g., tetramethylsilane (TMS) and hexamethyldisilazane)-N₂ mixtures at substrate temperatures below 450°C, achieving hardness values of 3–24 GPa [4–8]. PVD has been used to fabricate hydrogen-free a-SiCN films, with reported hardness values between 6 and 44 GPa [9–15]. Additionally, heat treatment as a post-treatment for SiCN films has been explored. It has been reported that the hardness of a-SiCN films, initially around 20 GPa, can increase to over 30 GPa following heat treatment at approximately 900°C or electron beam irradiation [16, 17]. Therefore, high-hardness SiCN may be achieved through the absence of hydrogen, high ion bombardment, and high-temperature film deposition. The hardness of commonly used ceramic hard films such as TiN and TiCN is around 30 GPa [18], comparable to the hardness of a-SiCN films deposited via PVD. Thus, a-SiCN coatings could potentially serve as alternative coatings to conventional films. Meanwhile, the deposition rate of these SiCN films ranges from 0.1 to 18 µm/h [4, 7, 12, 14]. CVD processes, which are known for their high deposition rates, can achieve SiCN films with a hardness of 19 GPa at a deposition rate of 18 µm/h if appropriate raw materials are selected [7]. DLC films are deposited at several µm/h, potentially realizing higher speed in the case of SiCN deposition. In contrast, PVD processes yield high-hardness SiCN films at slower deposition rates (1.3 µm/h) [12]. These findings suggest that CVD methods may offer high-speed deposition and high-hardness coatings on SiCN films.

The recently proposed microwave sheath-voltage combination plasma (MVP) generates higher-density plasma along a metal surface [19, 20]. MVP, sustained by microwave propagation as surface waves and plasma-sheath interface near the metal surface, employs a negatively biased metal to expand the sheath layer. This method has been used in plasma sources for plasma CVD [21–23]. In the formation of Si-DLC films using plasma CVD with MVP, a hardness of over 20 GPa and a deposition rate exceeding 100 µm/h have been achieved [21]. Tanaka et al. reported an MVP deposition rate of over 500 µm/h after selecting the source gas [22]. Furthermore, due to the high plasma density, substantial ion bombardment on the substrate during film formation leads to rapid temperature increases [21]. Exploiting the high deposition rate and inherent temperature-rise characteristics of MVP, we can realize high-hardness a-SiCN films deposited at faster rates at high temperatures (∼900°C).

However, the film’s composition and structure are dependent on the gas concentration and plasma generation conditions. Therefore, this study aims to achieve high-speed film deposition of a-SiCN films with a targeted hardness of approximately 30 GPa. We investigated the effects of TMS concentration on the film composition, structure, and mechanical properties of a-SiCN films using an MVP source.

2. Experimental Procedure

The SiCN films were deposited on Si wafers using a MVP apparatus. Figure 1 presents a schematic of the MVP apparatus. The apparatus is connected to a stainless-steel chamber via a rotary pump. Microwave radiation at 2.45 GHz is injected from a coaxial waveguide attached to the lower flange, propagating into the chamber through a quartz window. The substrate is placed on a carbon substrate holder, which is connected to a copper shaft. This shaft allows the substrate to be negatively biased relative to the grounded chamber via a DC power supply. The waveguide portion of the copper shaft is water-cooled during experiments. Further details about the microwave introduce port are discussed in our previous study [23]. The substrate temperature was measured using a radiation thermometer (JAPANSENSOR Corp./FLHX-TNE0160). Table 1 lists the deposition conditions. Prior to deposition, the Si substrates were cleaned using ultrasonic cleaning in an acetone bath. The initial substrate temperature was maintained below 140°C at the start of coating. Sputter cleaning of the substrates was performed using Ar-H₂ plasma at a DC voltage of 500 V for 10 min before coating. A mixture of TMS and N₂ gases served as the reaction gas, with TMS concentrations varying from 2 to 20%. The TMS concentration was capped at 20% because higher TMS concentrations (i.e., 30%) caused abnormal precipitation. The pressure, voltage, deposition time, and microwave power were consistently set to 100 Pa, −200 V, 60 seconds, and 300 W, respectively.

Fig. 1

Schematic of the MVP apparatus.

Table 1 Deposition conditions.

The deposited films were imaged using scanning electron microscopy (SEM; JEOL/JSM-7001F), and film thickness was determined from SEM cross-sectional images. Raman spectroscopy (JASCO Corp./NRS-5100) was conducted at an excitation wavelength of 532 nm. The structure of the deposits was characterized using X-ray diffraction (XRD; Rigaku Corp./Smartlab), employing the 2θ method with an incident angle of 0.8°. The chemical bonds in the deposits were analyzed via X-ray photoelectron spectroscopy (XPS; PHI 5000 VersaProbe/ULVAC-PHI) using monochromated Al Kα radiation at a photoelectron energy of 1486.6 eV. The hardness of the films was estimated using a nanoindentation tester (ELIONIX Inc./ENT-1100a), with tests conducted using a Berkovich indenter made of single-crystalline diamond. The maximum load was set at 5 mN for 5 s, with equal loading and unloading times of 10 s each. In the friction test, a steel ball (SUJ2, JIS) with an 8 mm diameter was rubbed against a coated steel disk at a normal load of 0.3 N and a sliding speed of 0.05 m/s. Experiments were conducted at a relative humidity of 50% under dry conditions in ambient air.

3. Results and Discussions

During all deposition conditions, the substrate temperature rapidly increased at the start of coating, reaching between 905°C and 981°C. Figure 2 presents surface and cross-sectional SEM images of films fabricated with various TMS concentrations. Surface SEM images revealed crater formation at 2% TMS concentration. At 5% TMS, a mixed surface of crater and grain was observed. The grain size at 10% and 20% TMS was between 0.3 and 0.5 µm. Film thicknesses at TMS concentrations of 2, 5, 10, and 20% were 0.4, 0.7, 2.8, and 4.4 µm, respectively. The absence of voids and structure in these films indicates their dense nature.

Fig. 2

Surface and cross-sectional SEM images of films fabricated using various TMS concentrations.

Figure 3 illustrates the deposition rate calculated from film thicknesses in Fig. 2. The deposition rate increased with higher TMS concentrations, particularly between 5% and 10%. The maximum deposition rate reached approximately 270 µm/h at 20% TMS.

Fig. 3

Deposition rate calculated from film thickness.

Figure 4 details the composition of films fabricated with varying TMS concentrations, consisting primarily of Si, C, and N. As TMS concentration increased, the predominant element in the films shifted from N to C. When the C content increased from 11 at% to 51 at%, the N and Si contents decreased by 30 at% and 10 at%, respectively. O observed in all samples was attributed to a natural oxide film formed on the surface by exposing the substrate to the atmosphere post-deposition. The increase in oxygen content in the 10% and 20% TMS samples is attributed to changes in the film’s primary elements. In typical films fabricated by hydrogen-containing deposition processes, many dangling bonds are terminated by hydrogen. The number of Si and C dangling bonds is likely increased at high deposition temperatures due to the reduced nitrogen, increasing the amount of adsorbed oxygen.

Fig. 4

Composition of films fabricated using various TMS concentrations.

Figure 5 displays the XRD patterns of films fabricated with different TMS concentrations. At 5% TMS, peaks at 52° and 55° were observed, attributed to natural oxide Si and the Si substrate. In the XRD patterns, none of the films showed peaks indicative of SiCN, SiC, Si₃N₄, or carbon materials, suggesting that the film structure was amorphous.

Fig. 5

XRD patterns of films fabricated using various TMS concentrations.

Figure 6 shows the Raman spectra of films fabricated with various TMS concentrations. No peak was observed at 2% TMS, indicating the absence of a carbon-related structure such as SiC, diamond, graphite, or diamond-like carbon, as these materials typically exhibit peaks in the wavenumber range of 1000 to 2000 cm⁻¹ in the Raman spectrum. In contrast, films with 5%, 10%, and 20% TMS produced spectra characteristic of amorphous carbon, with peaks centered around the G (1580 cm⁻¹) and D (1350 cm⁻¹) bands [24, 25]. Therefore, the spectra of the 5%, 10%, and 20% TMS films can be deconvoluted into two peaks corresponding to the D- and G-bands, which are typically used in DLC analyses. Waveform deconvolution reveals the carbon structures within the films.

Fig. 6

Raman spectra of films fabricated using various TMS concentrations.

Figure 7 displays the results for (a) I_D/I_G ratio, (b) G peak position, and (c) full width at half maximum (FWHM) of the G peak in the Raman spectra of films deposited with 5%, 10%, and 20% TMS. The I_D/I_G ratio varied from 1.3 to 1.5, increasing with the TMS concentration. Conversely, the G peak position decreased from 1590 cm⁻¹ to 1545 cm⁻¹ as the concentration increased. The FWHM of the G peak, ranging between 133 and 139 cm⁻¹, showed no clear correlation with TMS concentration, reaching a maximum of 139 cm⁻¹ at 20% TMS. The I_D/I_G ratio and G peak position are inversely correlated with the sp³/sp² ratio of the carbon structure; a smaller value indicates a higher sp₃ ratio [25]. The FWHM of the G peak is associated with film density, with larger values indicating higher film density [25]. For Si-doped hydrogenated amorphous carbon films, the Raman parameters of I_D/I_G ratio, G peak position, and FWHM decrease with increasing Si content [26]. Conversely, the G peak position of nitrogen-doped DLC shifts to higher wavenumbers as the amount of N increases [25]. These parameters are likely influenced by the complex interplay of film composition and carbon structure.

Fig. 7

Analysis of Raman spectroscopy parameters for films deposited with different TMS concentrations. (a) Variation in the I_D/I_G ratio, (b) changes in the G peak position, (c) full width at half maximum (FWHM) of the G peak, for films deposited using 5%, 10%, and 20% TMS concentrations.

From these observations, the sample with 5% TMS, which had a higher content of N and Si compared to 20% TMS, exhibited a low I_D/I_G ratio and a high G peak position. In contrast, the 20% TMS sample, with lower N and Si content, showed a lower G peak position and a wider FWHM of the G peak. These results suggest that the film at 20% TMS has a higher sp³ ratio and greater film density.

Figure 8 presents the XPS spectra [(a) Si 2p, (b) C 1s, and (c) N 1s] of deposits fabricated with various TMS concentrations, with spectral assignments based on literature data [27–29]. Table 2 shows the deconvoluted peak areas of the C1s, N1s, and Si2p spectra of the films. The Si 2p spectra [Fig. 8(a)] revealed peaks for Si–C (100.8 eV), Si–N (101.9 eV), and Si–O (102.9 eV). In the C 1s spectra [Fig. 8(b)], peaks were observed for Si–C (283.7 eV), C=C (284.5 eV), N–C=N (286.1 eV), C–N (287.4 eV), and C=O (288.8 eV). The N 1s spectra [Fig. 8(c)] showed peaks for Si–N (397.4 eV), C=N (398.3 eV), C–N (400.1 eV), and N–O (403 eV). The predominant peak in the Si 2p spectra of all films was the Si-N bond, which was also the main peak in the N 1s spectra. With increasing TMS concentration, the Si–C bond appeared in the Si 2p and C 1s spectra of films with 20% TMS. Simultaneously, the C–N=C bond was detected in both the C 1s and N 1s spectra. Therefore, films with lower TMS concentrations were primarily composed of the Si–N bond, while those with higher TMS concentrations became a mixture of Si–N, Si–C, C=N, and C=C bonds. In addition, the areas under the C=O and SiO₂ bonds were increased in the 10% and 20% TMS films.

Fig. 8

XPS [(a) Si 2p, (b) C 1s, and (c) N 1s] spectra of the deposits fabricated by various TMS concentrations.

Table 2 Deconvoluted peak areas of the C1s, N1s, and Si2p spectra of the films.

These results suggest that films produced using the microwave sheath-voltage combination plasma (MVP) from a TMS-N₂ mixture gas are amorphous silicon carbon nitride. Furthermore, an increase in TMS concentration led to the inclusion of amorphous carbon structures in the films.

Table 3 presents the hardness (H), elastic modulus (E), H/E ratio, and H³/E² ratio of the films. There was a notable increase in hardness with rising TMS concentrations. The hardness values of the films at 10 and 20% TMS concentrations exceeded 20 GPa, with the TMS 20% films achieving a hardness of 28 GPa. A similar upward trend was observed for the elastic modulus. Additionally, the elastic strain to failure (H/E) [18, 30] and the plastic deformation resistance factor (H³/E²) [18, 31] H/E is commonly used to qualitatively assess materials for their resistance to failure. The H³/E² ratio, indicative of a film’s resistance to cracking, increased with higher TMS concentrations, reaching peaks of 0.11 and 0.37 at 20% TMS, respectively. A previous study reported that the H/E ratios for DLC [32], TiN [18], and TiAlN [18] range from 0.07 to 0.11, 0.06, and 0.07, respectively, while their H³/E² values are between 0.15 and 0.45, 0.14, and 0.18. Therefore, the film deposited with 20% TMS is anticipated to exhibit high wear resistance and durability. In summary, increasing TMS concentration not only enhances the deposition rate of the amorphous SiCN film but also improves its mechanical properties.

Table 3 Hardness (H), elastic modulus (E), H/E, and H³/E² ratios of films.

Figure 9 illustrates the relationship between various parameters and hardness. The peaks corresponding to the D- and G-bands were absent in the spectrum of the 2% TMS film (Fig. 6); therefore, the deconvolution results could not be obtained. Therefore, the results of this film are excluded from Fig. 9(a), (b), and (c). It was observed that the hardness correlates with the G peak position, which is indicative of the sp³ carbon ratio. Moreover, the hardness is significantly influenced by the film’s composition, particularly the increase in carbon content. Despite the presence of amorphous carbon structures in the Raman spectrum, the films were formed at high temperatures ranging from 905°C to 981°C, where graphitization typically occurs, leading to reduced hardness. Therefore, the increase in hardness observed in this study cannot be solely attributed to the formation of a diamond-like carbon structure within the film. It is hypothesized that the hardening is a result of hydrogen elimination and an increase in harder chemically bonded components. SiC, SiN, and SiCN films produced by CVD at temperatures below 500°C, which contain hydrogen, exhibit hardness values between 3 and 24 GPa [4–8]. This suggests that the high hardness of SiCN films, which either lack hydrogen or are formed at high temperatures, may be attributed to their hydrogen-free nature, as supported by the fact that hydrogen-free amorphous SiCN films produced by PVD demonstrate a high hardness of 30 GPa [14]. Additionally, crystalline SiC, SiN, or SiCN films obtained by CVD at approximately 1000°C also exhibit high hardness [33]. The desorption of hydrogen may also accelerate the release of carbon, particularly at low TMS concentrations, due to the formation of CH. Figure 10 shows the relationship between TMS concentration and the C/Si ratio. The C/Si ratio in TMS is 4.0, yet the carbon content in all films is lower than that of TMS. An increase in TMS concentration seems to facilitate the formation of H₂ from CH on the substrate surface, thereby reducing the etching of carbon. Additionally, at low TMS concentrations, excessive ion bombardment by species such as N₂⁺ and CH⁺ occurs due to the slow deposition rate, potentially introducing defects into the film. Therefore, the rapid increase in the deposition rate at higher TMS concentrations, which leads to denser films, may be due to a balance between the ions incident on the substrate and the deposited species.

Fig. 9

Relationship between hardness and various parameters such as (a) I_D/I_G ratio, (b) G position, (c) FWHMG, (d) carbon concentration, (e) nitrogen concentration, and (f) silicon concentration.

Fig. 10

Relationship of TMS concentration and C/Si ratio.

Figure 11 presents results corresponding to sliding cycles ranging from 0 to 6000. The average friction coefficients for TMS concentrations of 2%, 20%, and the Si substrate were 0.81, 0.29, and 0.69, respectively. However, the friction coefficient of the 2% TMS sample exceeded that of Si after 2000 cycles, suggesting that part of the film remained. The structure of the 2% TMS film is SiN-rather than carbon-based (as in the 20% TM film); therefore, the observed differences in friction coefficient can be feasibly attributed to variations in the contact conditions or shear forces between the films and the balls. A detailed analysis of the friction and wear characteristics, including measurements of surface roughness and wear volume, is required.

Fig. 11

Results corresponding to the sliding cycle from 0 to 6000.

4. Conclusion

In this study, amorphous silicon carbon nitride films were successfully deposited using MVP from TMS and N₂ gas mixtures. Key findings include an increase in the deposition rate, carbon content, and hardness with rising TMS concentrations. Notably, the deposition rate reached 270 µm/h at a TMS concentration of 20%. An increase in TMS concentration also resulted in an elevated C/Si ratio and a significant decrease in nitrogen content. Furthermore, SiCN films with 20% TMS concentration exhibited the highest hardness, measuring 28 GPa. These high-hardness SiCN films demonstrated a friction coefficient of approximately 0.29.

Acknowledgments

This work was partially supported by the KAKENHI grant from the Japan Society for the Promotion of Science (JSPS) (21K14440), Japan, and the Iketani Science and Technology Foundation.

REFERENCES

• 1)   J.  Robertson: Diamond-like amorphous carbon, Mater. Sci. Eng. 37 (2002) 129–281. doi:10.1016/S0927-796X(02)00005-0
• 2)   H.J.  Du,  D.C.  Li,  J.L.  He,  D.L.  Yu,  B.  Xu,  Z.Y.  Liu,  H.-T.  Wang and  Y.J.  Tian: Hardness of α- and β-Si3 − nCnN4 (n = 0, 1, 2, 3) crystals, Diam. Relat. Mater. 18 (2009) 72–75. doi:10.1016/j.diamond.2008.09.025
• 3)   C.  Jongwannasiri,  X.  Li and  S.  Watanabe: Improvement of thermal stability and tribological performance of diamond-like carbon composite thin films, Mater. Sci. Appl. 4 (2013) 630–636. doi:10.4236/msa.2013.410077
• 4)   B.  Plujat,  H.  Glénat,  A.  Bousquet,  L.  Frézet,  J.  Hamon,  A.  Goullet,  É.  Tomasella,  E.  Hernandez,  S.  Quoizola and  L.  Thomas: SiCN:H thin films deposited by MW-PECVD with liquid organosilicon precursor: gas ratio influence versus properties of the deposits, Plasma Process. Polym. 17 (2020) 1900138. doi:10.1002/ppap.201900138
• 5)   R.G.S.  Batocki,  R.P.  Mota,  R.Y.  Honda and  D.C.R.  Santos: Effect of argon ion bombardment on amorphous silicon carbonitride films, J. Phys. Conf. Ser. 480 (2014) 012021. doi:10.1088/1742-6596/480/1/012021
• 6)   D.H.  Zhang,  Y.  Gao,  J.  Wei and  Z.Q.  Mo: Influence of silane partial pressure on the properties of amorphous SiCN films prepared by ECR-CVD, Thin Solid Films 377–378 (2000) 607–610. doi:10.1016/S0040-6090(00)01277-3
• 7)   D.  Probst,  H.  Hoche,  Y.  Zhou,  R.  Hauser,  T.  Stelzner,  H.  Scheerer,  E.  Broszeit,  C.  Berger,  R.  Riedel,  H.  Stafast and  E.  Koke: Development of PE-CVD Si/C/N:H films for tribological and corrosive complex-load conditions, Surf. Coat. Technol. 200 (2005) 355–359. doi:10.1016/j.surfcoat.2005.02.111
• 8)   A.O.  Kozak,  V.I.  Ivashchenko,  O.K.  Porada,  L.A.  Ivashchenko,  T.V.  Tomila,  V.S.  Manjara and  G.V.  Klishevych: Structural, optoelectronic and mechanical properties of PECVD Si-C-N films: An effect of substrate bias, Mater. Sci. Semicond. Process. 88 (2018) 65–72. doi:10.1016/j.mssp.2018.07.023
• 9)   S.K.  Mishra,  H.  Gaur,  P.K.P.  Rupa and  L.C.  Pathak: Deposition of nanostructured Si–C–N superhard coatings by rf magnetron sputtering, J. Vac. Sci. Technol. B 24 (2006) 1311–1317. doi:10.1116/1.2200377
• 10)   A.S.  Bhattacharyya,  S.K.  Mishra and  S.  Mukherjee: Correlation of structure and hardness of rf magnetron sputtered silicon carbonitride films, J. Vac. Sci. Technol. A 28 (2010) 505–509. doi:10.1116/1.3420430
• 11)   P.  Gao,  J.  Xu,  Y.  Piao,  W.  Ding,  D.  Wang,  X.  Deng and  C.  Dong: Deposition of silicon carbon nitride thin films by microwave ECR plasma enhanced unbalance magnetron sputtering, Surf. Coat. Technol. 201 (2007) 5298–5301. doi:10.1016/j.surfcoat.2006.07.197
• 12)   S.K.  Mishra,  D.  Verma,  S.  Bysakh and  L.C.  Pathak: Hard and soft multilayered SiCN nanocoatings with high hardness and toughness, J. Nanomater. 2013 (2013) 949416. doi:10.1155/2013/949416
• 13)   S.  Ma,  B.  Xu,  G.  Wu,  Y.  Wang,  F.  Ma,  D.  Ma,  K.  Xu and  T.  Bell: Microstructure and mechanical properties of SiCN hard films deposited by an arc enhanced magnetic sputtering hybrid system, Surf. Coat. Technol. 202 (2008) 5379–5382. doi:10.1016/j.surfcoat.2008.06.057
• 14)   F.  Zhou,  B.  Yue,  X.  Wang,  X.  Wu and  L.  Zhuge: Surface roughness, mechanical properties and bonding structure of silicon carbon nitride films grown by dual ion beam sputtering, J. Alloy. Compd. 492 (2010) 269–276. doi:10.1016/j.jallcom.2009.11.063
• 15)   Z.  Shi,  Y.  Wang,  C.  Du,  N.  Huang,  L.  Wang and  C.  Ning: The structure, surface topography and mechanical properties of Si–C–N films fabricated by RF and DC magnetron sputtering, Appl. Surf. Sci. 258 (2011) 1328–1336. doi:10.1016/j.apsusc.2011.09.036
• 16)   R.  Ctvrtlik,  V.  Kulikovsky and  J.  Tomastik: Effect of nitrogen content on the mechanical properties of amorphous SiCN films, Key Eng. Mater. 662 (2015) 95–98. doi:10.4028/www.scientific.net/KEM.662.95
• 17)   W.L.  Li,  Z.G.  Zhang,  J.L.  Yang and  W.D.  Fei: Effect of electron beam irradiation on structure and properties of SiCN thin films prepared by plasma assisted radio frequency magnetron sputtering, Vacuum 86 (2011) 457–460. doi:10.1016/j.vacuum.2011.09.013
• 18)   M.  Bartosik,  C.  Rumeau,  R.  Hahn,  Z.L.  Zhang and  P.H.  Mayrhofer: Fracture toughness and structural evolution in the TiAlN system upon annealing, Sci. Rep. 7 (2017) 16476. doi:10.1038/s41598-017-16751-1
• 19)   H.  Kousaka,  N.  Umehara,  K.  Ono and  J.  Xu: Microwave-Excited High-Density Plasma Column Sustained along Metal Rod at Negative Voltage, Jpn. J. Appl. Phys. 44 (2005) L1154–L1157. doi:10.1143/JJAP.44.L1154
• 20)   J.  Xu,  H.  Kousaka,  N.  Umehara and  D.  Diao: Plasma properties of a new surface-wave-sustained plasma source under the conditions of depositing DLC films, Surf. Coat. Technol. 201 (2006) 408–412. doi:10.1016/j.surfcoat.2005.11.133
• 21)   H.  Kousaka,  Y.  Takaoka and  N.  Umehara: Ultra-high-speed coating of Si-containing a-C:H film at over 100 µm/h, Procedia Eng. 68 (2013) 544–549. doi:10.1016/j.proeng.2013.12.219
• 22)   I.  Tanaka,  T.  Ikeda,  T.  Nakano,  H.  Kousaka and  T.  Furuki: Effect of humidity on the friction properties of a-C:H and a-C:H:Si films deposited by PECVD employing microwave sheath-voltage combination plasma, Jpn. J. Appl. Phys. 58 (2019) SAAC06. doi:10.7567/1347-4065/aaeb3c
• 23)   I.  Tanaka,  H.  Okubo and  Y.  Harada: Diamond synthesis on Si by plasma chemical vapor deposition using microwave sheath-voltage combination plasma, Surf. Coat. Technol. 423 (2021) 127592. doi:10.1016/j.surfcoat.2021.127592
• 24)   A.C.  Ferrari: Raman spectroscopy of graphene and graphite: Disorder, electron–phonon coupling, doping and nonadiabatic effects, Solid State Commun. 143 (2007) 47–57. doi:10.1016/j.ssc.2007.03.052
• 25)   A.C.  Ferrari and  J.  Robertson: Raman spectroscopy of amorphous, nanostructured, diamond–like carbon, and nanodiamond, Philos. Trans. R. Soc. A 362 (2004) 2477–2512. doi:10.1098/rsta.2004.1452
• 26)   S.E.  Ong,  S.  Zhang,  H.  Du and  D.  Sun: Relationship between bonding structure and mechanical properties of amorphous carbon containing silicon, Diam. Relat. Mater. 16 (2007) 1628–1635. doi:10.1016/j.diamond.2007.02.009
• 27)   V.I.  Ivashchenko,  O.K.  Porada,  L.A.  Ivashchenko,  I.I.  Timofeeva,  O.K.  Sinel’Nichenko,  O.O.  Butenko,  M.V.  Ushakov and  L.A.  Ushakova: Characteristics of thin plasmachemical silicon carbon nitride films deposited using hexamethyldisilane, Powder Metall. Met. Ceram. 48 (2009) 66–72. doi:10.1007/s11106-009-9096-9
• 28)   B.  Mitu,  G.  Dinescu,  E.  Budianu,  A.  Ferrari,  M.  Balucani,  G.  Lamedica,  A.  Dauscher and  M.  Dinescu: Formation of intermediate SiCN interlayer during deposition of CNx on a-Si:H or a-SiC:H thin films, Appl. Surf. Sci. 184 (2001) 96–100. doi:10.1016/S0169-4332(01)00666-3
• 29)   C.W.  Chen,  C.C.  Huang,  Y.Y.  Lin,  L.C.  Chen and  K.H.  Chen: The affinity of Si–N and Si–C bonding in amorphous silicon carbon nitride (a-SiCN) thin film, Diam. Relat. Mater. 14 (2005) 1126–1130. doi:10.1016/j.diamond.2004.10.045
• 30)   A.  Leyland and  A.  Matthews: On the significance of the H/E ratio in wear control: a nanocomposite coating approach to optimised tribological behavior, Wear 246 (2000) 1–11. doi:10.1016/S0043-1648(00)00488-9
• 31)   J.  Musil and  M.  Jirout: Toughness of hard nanostructured ceramic thin films, Surf. Coat. Technol. 201 (2007) 5148–5152. doi:10.1016/j.surfcoat.2006.07.020
• 32)   O.S.  Panwar,  R.K.  Tripathi and  S.  Chockalingam: Improved nanomechanical properties of hydrogenated tetrahedral amorphous carbon films measured with ultra low indentation load, Mater. Express 5 (2015) 410–418. doi:10.1166/mex.2015.1256
• 33)   L.C.  Chen,  K.H.  Chen,  S.L.  Wei,  P.D.  Kichambare,  J.J.  Wu,  T.R.  Lu and  C.T.  Kuo: Crystalline SiCN: a hard material rivals to cubic BN, Thin Solid Films 355–356 (1999) 112–116. doi:10.1016/S0040-6090(99)00490-3