Effect of Nitrogen on Preparation of Diamond Film by DC-PCVD Method
ã€Abstract】 A diamond thin film was successfully prepared on a Mo substrate by a DC hot cathode plasma chemical vapor deposition method using a mixed gas of methane, hydrogen and nitrogen. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy (Raman) were used to characterize the morphology, orientation and quality of diamond films grown under different nitrogen atmospheres. The results show that the addition of proper amount of nitrogen can not only promote the growth rate of diamond film but also promote the appearance of diamond (100) crystal plane. With the increase of nitrogen content, the diamond grains are gradually refined, and the non-diamond component in the film increases. But the diamond surface becomes smooth and flat. This work contributes to the application of the diamond film coating field. [Key words] chemical vapor deposition; diamond film; nitrogen PACS: 85.15.Gh, 67.30.Hr, 81.05Ug PACC: 8115H, 8110B The effect of nitrogen on the diamond thin films prepared by dc hot-cathode plasma chemical deposition Abstract: Diamond Films have been successfully deposited on Mo substrate by direct current hotcathode plasma chemical vapor deposition method using CH4/H2/N2 gas mixture. The influence of N2 on surface morphology, grain orientation and crystalline quality of diamond films has been characterized by scanning electron microscope ( SEM), x-ray diffraction (XRD), Raman spectroscopy, The results show that appropriate amount of nitrogen can not only improve the diamond growth rate greatly, but also increase gradually the (100) square diamond grain , with the increase of nitrogen, The crystalline size of diamond decreased companied with part of carbon membrane structure emerging in the film and the surface of diamond film becomes smooth and flat. Key words: DC-PCVD; Diamond thin films; Nitrogen PACS: 85.15.Gh, 67.30.Hr, 81.05Ug PACC: 8115H, 8110B 1. Introduction: Diamond has excellent physical and chemical properties, such as High hardness, high wear resistance, highest thermal conductivity, high electron and hole mobility, high chemical inertness, have been widely used in the fields of machinery, optics and electricity. [1-5] Since the successful synthesis of diamond films by low pressure chemical vapor deposition (CVD) in the mid-1970s, the growth of texture and even single crystal diamond films has become the goal pursued by many researchers. [6] Although high-quality diamond films can be prepared, the n-type doping of CVD diamond films is still unresolved, which severely restricts its scale in related industries, especially in electronics and vacuum microelectronics. application, in various diamond films has been studied in the alignment, the (111), (110) textured films as compared to (100) film having a smooth textured surface, fewer defects and lower stress, [ 7] Higher thermal conductivity [8] and larger carrier collection distance [9] , more suitable for applications in thermal, optics, electronics, etc. Therefore, the exploration of the preparation of diamond (100) textured film has important practical significance for the study of the properties and applications of diamond films. Up to now, diamond film preparation methods mainly include: hot wire CVD (HFCVD), direct current hot cathode CVD (DC-PCVD), microwave plasma CVD (MW-PCVD), and the like. These methods of growing diamond films each have their own advantages. The MPCVD method has the advantages of low deposition temperature, concentrated discharge area without diffusion, no gas pollution and electrode pollution, stable operation, easy and precise control, fast deposition speed, and favorable nucleation. It is the main method for growing high quality diamond film. . However, it is expensive and difficult to deposit large-area diamond films, and is less used in industrial production. HFCVD has the advantages of low cost and simple operation, low growth rate, easy carbon deposition on the surface of the hot wire, easy symbiotic graphite during growth, and poor uniformity of large-area growth film. DC hot cathode plasma chemical vapor deposition [10] is a very effective method for preparing synthetic diamond film. It has the advantages of fast growth, large area, good quality, high pressure, stable discharge, simple equipment structure. The conditions are easy to control and so on. Compared with HFCVD and MWPCVD, the DC-PCVD method has the greatest advantages of low cost and high quality diamond film deposition, and it can also deposit diamond film over a large area, especially for industrial applications. Cao et al. introduced nitrogen-doped diamond film by introducing nitrogen into hot filament CVD. [7] Jin et al. reported that nitrogen-doped diamond films were successfully prepared in MPCVD, and the nitrogen doping amount was different. [8] How to mix the proper amount of nitrogen to promote the better growth of diamond film is still under investigation. However, the use of the DC-PCVD method to grow diamond films under a nitrogen atmosphere is still rare. In this paper, DC hot cathode plasma chemical vapor deposition (DC-PCVD) method was used to prepare and study diamond films grown under different nitrogen atmospheres. The results of this work provide new experimental data for studying the growth mechanism of diamond films and help to promote the application of nitrogen-doped diamond films in industry. 2. Experiment: In this experiment, a nitrogen-doped plasma chemical vapor deposition method was used to prepare a nitrogen-doped diamond film. In order to promote the nucleation density and nucleation rate of the diamond film, the substrate needs to be processed before deposition, and the substrate used in the experiment. It is a molybdenum circle. The surface of the substrate is uniformly ground with a diamond slurry of w40 for 10-15 minutes, and then ground with a diamond slurry of w10 for 10-15 minutes, treated with ethanol for 2 minutes, and then treated with a deionized water mixed solution for 1 minute. Then, dry it with nitrogen, and finally place the treated substrate on the anode copper seat in the reaction chamber, wipe the cathode clean and screw it on the cathode copper seat, and evacuate the vacuum to adjust the distance between the poles to about 15 mm. Water, N2 was mixed in CH4 and H2, and the glow was ignited when the pressure was raised to 2-5 Torr. The deposition time was 8 h. The specific experimental parameters are given in Table 1. Table 1 Deposition parameters for nitrogen doped diamond thin films Experimental equipment and characterization techniques: This experiment uses JEOL JXA-8200 scanning electron microscopy (SEM) to observe the morphology of the sample; RM-1000 On the inVia micro Raman spectrometer, the phase composition of the sample was analyzed. The Ar+ laser wavelength was 514.5 nm, and the crystal structure was analyzed using a D/max-rA type X-ray diffractometer. [11] 3. Results and discussion: Figure 1 is a scanning electron micrograph of all samples. It can be seen that the diamond film (sample a) without nitrogen is dense, the crystal grains are dense, the crystal edges are obvious, the crystal quality is good, and the main light is revealed. The crystal plane is (111); (b)-(f) is the morphology of the film with a nitrogen flow rate of 0.6-4.0 sccm. When the flow rate of N 2 is 0.6 sccm, the compactness of the crystal can be seen from (b). And the integrity is reduced, a large number of grain boundaries appear, and it can be seen from the exposed part of the grain boundary that the (100) surface begins to appear, accompanied by the exposure of other small-sized crystal faces, which indicates that the addition of nitrogen can promote the (100) surface exposure. A non-diamond phase is also introduced in the grain boundary, thereby reducing the quality of the diamond film. When the flow rate of N 2 is 1.2 sccm, it can be seen from (c) that the crystal grains become more sparse, the grain boundaries become larger, and a distinct (100) crystal plane appears. When the flow rate of N 2 is 2.4 sccm, it can be seen from (d) that the crystal form is further deteriorated, and the crystal faces are disorderly arranged. Although the crystal faces are mainly (100), they are accompanied by fine diamond particles. When the nitrogen flow rate is 3.2 sccm, it can be seen from (e) that the morphology of the diamond film is similar to (d), but the fine diamond particles are further increased and the size is decreased. When the nitrogen flow rate is 4.0 sccm, it can be seen from (f) that the fine particles are maximized, that is, the diamond and the non-diamond phase coexist in a large amount, but the exposed crystal face can be seen as (100). In contrast, the diamond film prepared by the hot wire CVD method under a nitrogen atmosphere has a long flow of nitrogen gas and a serious pollution, and can also obtain a (100) crystal plane, [21] while MWPCVD takes a short time, but Its cost is high and it is inconvenient for industrial mass production. Figure 2 is a picture of the Raman spectroscopy test of the sample, (a) is a test result without adding nitrogen, and a strong peak at 1332 cm-1 , that is, a diamond characteristic peak, which has a center at 1580 cm-1 , can be seen. The weaker peak is the G peak. The reason for this peak is that hydrogen does not completely etch the non-diamond structure during the growth process. Figures (b)-(f) show the nitrogen flow rate from 0.6-4.0 sccm. Man test map. With the increase of nitrogen flow rate, the characteristic peak of 1332 cm-1 diamond gradually weakens, the graphite peak of 1580 cm-1 gradually increases, and the non-diamond phase gradually increases. From the peak shape, when the nitrogen flow rate is less than 2.4sccm, with the nitrogen flow rate Increasing the Raman peak of the sample is more obvious. When the nitrogen flow rate is greater than 2.4 sccm, the Raman peak changes slowly, and the diamond peak decreases. The graphite peak increases, which is consistent with the results of the SEM image, that is, the quality of the film is reduced. Figure 3 is the XRD pattern test result of the sample, (a) is the test result without nitrogen, and the standard diamond powder diffraction peak value comparison shows the (111) diffraction peak, which is consistent with the SEM image. The strong equilateral triangle crystal face, with the increase of nitrogen flow rate (bf), the (111) diffraction peak gradually weakens, the (100) crystal plane begins to appear and gradually strengthens, and the (111) and (110) crystal planes gradually weaken, that is, The square crystal plane of the SEM image began to appear and gradually increased, and finally the (100) crystal plane was dominant. 
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Fig. 1 SEM image of diamond film under nitrogen atmosphere Fig 1 SEM micrograph of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm (f) 4.0sccm .jpg)
Raman shift (cm-1) Figure 2 Raman spectroscopy of diamond film under nitrogen atmosphere Fig 2 Raman spectroscopy of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm (f) 4.0sccm 
2θ/(deg) Figure 3 XRD pattern of diamond film under nitrogen atmosphere Fig 3 XRD patterns of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm ( f) 4.0sccm experimental results show that the (100) crystal plane of diamond is obtained under nitrogen atmosphere, and as the nitrogen concentration increases, the square crystal plane of (100) also increases gradually, but too high concentration of nitrogen will cause The quality of the diamond film deteriorates. Because atomic hydrogen can saturate the diamond surface carbon suspension bond to form SP3 hybrid bond, thus avoiding the generation of SP2 bond, because the binding energy of CH bond is larger than that of CC bond, the addition of nitrogen introduces CN group, and the concentration of N2 is higher. When low, the CN group can extract atomic hydrogen adsorbed on the diamond growth surface like atomic hydrogen to form a growth site and form a very stable HCN molecule in the gas phase. Since the bond energy of the HC bond in HC≡N is higher than the bond energy of the HH bond in hydrogen, the CN group produces a higher growth rate than the atomic hydrogen, so the CN group can increase the diamond film to some extent. The growth rate; at high concentrations, a large number of CN groups generate excessive surface dangling bonds, especially adjacent dangling bonds. In the absence of sufficient methyl groups to be adsorbed, the bonds on the diamond surface collapse and reconstitute. The graphite bond causes a decrease in the growth rate of the film, and [12-20] at the same time, the quality of the large grain film cannot be deteriorated. Experiments have shown that nitrogen-containing groups such as CN and NH can promote the growth of diamond, especially the (100) crystal plane. Compared with (111) and (110) textured films, (100) texture has a smooth surface, less defects and lower stress, higher thermal conductivity and larger carrier collection distance, [21] -23] It is more suitable for applications in thermal, optical and microelectronics. In addition, the (100) crystal plane has a lower friction coefficient and a stronger micro-strength of the wear edge than the (111) and (110) crystal planes. [24] is more conducive to improving the front and back flank of the tool, that is, the preparation of the (100) textured diamond film is of great significance for the research and development of high-quality diamond film coated cemented carbide tools and improving the performance of the product. 4. Conclusion: The diamond film was successfully prepared under nitrogen atmosphere by DC hot cathode plasma chemical vapor deposition under nitrogen atmosphere. The experimental results show that the addition of nitrogen promotes the appearance of the diamond (100) crystal plane and reduces the roughness of the diamond film surface, making the surface of the diamond film more flat. With the increase of nitrogen flow rate, the diamond grains are gradually refined. The non-diamond phase content gradually increases; the appearance and increase of the non-diamond phase does not change the diamond (100) orientation. This work has helped to develop high-quality diamond film on carbide tools and high-performance diamond films for applications in optics and microelectronics. References: [1] Berman R, 1979 Thermal properties of diamond, in the properties of diamond (JEField, New York, Academic Press) p34 [2] Pickrell DJ, Kline KA and Taylor RE 1994 Appl. Phys. Lett. 64 2353 [3] Balducci A, D'Amico A, 2005 Di Natale C Sensors and Actuators B. 34 111 [4] Malshe AP, Naseem HA, Brown WD, et al. 1995 Recent Advances in Diamond Based Multichip Modules (MCMs) [J] ].3nd Inter.Conf.on the Appl.of Diamond Films and Related Materials, 611-618 [5] Yin Z, Akkerman Z, Yang BX, et al. 1997 Diamond Related. Mater. 6 153 [6] H.Chat .ei, Bougdira J, Remy M, et al. 1997 Diamond Relat. Mater. 6 107 [7] Huang TC, Lim G, Parmigiani F et al. 1983 J Vac Sci Tech. 6 2161 [8] Chang Gu, Zengsu J Xianyi Lu et al. 1998 Thin Solid Films. 311: 124 [9] Wang WL, Liao KJ, Kong CY et al. 2001 Functional Metals and Devices. 7 318 [10] Zhao Kaihua, Zhong Xihua 1984 Optics. (Peking University Press Page 12 [11] Cao GZ, Schermer JJ, Van Enckevart WJP et al. 1996 Appl. Phys. 79 1357 [12] S. J in, T. D. Moust akan 1994 Appl. Phys. Lett. 65 403. [13] Jin Zengsun, Lu Xianyi, Jiang Zhigang, etc. Process for preparing diamond film by hot cathode glow plasma chemical vapor deposition Chinese invention patent CN94116283.4 [14] Sun B, Zhang X, Lin Z 1993 Phys. Rev. B. 47 9824 [15] Hong SP, Yoshikawa H, Wazumi K, et al. 2002 Diamond Related. Mater 11 877 [16] Han WQ, Han GR, Fan SS, et al. 1997 Chin. Phys. Lett. 14 682 [17] Suo DC, Liu YC, Liu Y, et al .2004 Chin. Phys. Lett. 21 400 [18] L.Chow, D.Zhou, Hussain A, et al.2000 Thin Solid Films 36 193 [19] Yan Xuegui, Chen Zezhen, Wang Guanzhong, Liao Yuan 2004 Inorganic Materials Journal 19 404 [20] Tang CJ, Neves AJ, Pereira S 2008 Diamond&Related Materials 17 72 [21] Huang TC, Lim G, Parmigiani F et al. 1983 J Vac Sci Tech. A 6 2161 [22] Chang Gu, Zengsu J, Xianyi Lu et al. 1998 Thin Solid Films.311 124 [23] Wang Wan-lu, Liao Ke-jun, Kong Chun-yang et al. 2001 Functional Metals and Devices 18 307 [24] Zhou Ming, Yuan Zhejun 1999 Journal of Harbin Institute of Technology 31(4)
Fig. 1 SEM image of diamond film under nitrogen atmosphere Fig 1 SEM micrograph of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm (f) 4.0sccm Raman shift (cm-1) Figure 2 Raman spectroscopy of diamond film under nitrogen atmosphere Fig 2 Raman spectroscopy of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm (f) 4.0sccm 2θ/(deg) Figure 3 XRD pattern of diamond film under nitrogen atmosphere Fig 3 XRD patterns of nitrogen doped diamond thin films (a) 0sccm (b) 0.6sccm (c) 1.2sccm (d) 2.4sccm (e) 3.2sccm ( f) 4.0sccm experimental results show that the (100) crystal plane of diamond is obtained under nitrogen atmosphere, and as the nitrogen concentration increases, the square crystal plane of (100) also increases gradually, but too high concentration of nitrogen will cause The quality of the diamond film deteriorates. Because atomic hydrogen can saturate the diamond surface carbon suspension bond to form SP3 hybrid bond, thus avoiding the generation of SP2 bond, because the binding energy of CH bond is larger than that of CC bond, the addition of nitrogen introduces CN group, and the concentration of N2 is higher. When low, the CN group can extract atomic hydrogen adsorbed on the diamond growth surface like atomic hydrogen to form a growth site and form a very stable HCN molecule in the gas phase. Since the bond energy of the HC bond in HC≡N is higher than the bond energy of the HH bond in hydrogen, the CN group produces a higher growth rate than the atomic hydrogen, so the CN group can increase the diamond film to some extent. The growth rate; at high concentrations, a large number of CN groups generate excessive surface dangling bonds, especially adjacent dangling bonds. In the absence of sufficient methyl groups to be adsorbed, the bonds on the diamond surface collapse and reconstitute. The graphite bond causes a decrease in the growth rate of the film, and [12-20] at the same time, the quality of the large grain film cannot be deteriorated. Experiments have shown that nitrogen-containing groups such as CN and NH can promote the growth of diamond, especially the (100) crystal plane. Compared with (111) and (110) textured films, (100) texture has a smooth surface, less defects and lower stress, higher thermal conductivity and larger carrier collection distance, [21] -23] It is more suitable for applications in thermal, optical and microelectronics. In addition, the (100) crystal plane has a lower friction coefficient and a stronger micro-strength of the wear edge than the (111) and (110) crystal planes. [24] is more conducive to improving the front and back flank of the tool, that is, the preparation of the (100) textured diamond film is of great significance for the research and development of high-quality diamond film coated cemented carbide tools and improving the performance of the product. 4. Conclusion: The diamond film was successfully prepared under nitrogen atmosphere by DC hot cathode plasma chemical vapor deposition under nitrogen atmosphere. The experimental results show that the addition of nitrogen promotes the appearance of the diamond (100) crystal plane and reduces the roughness of the diamond film surface, making the surface of the diamond film more flat. With the increase of nitrogen flow rate, the diamond grains are gradually refined. The non-diamond phase content gradually increases; the appearance and increase of the non-diamond phase does not change the diamond (100) orientation. This work has helped to develop high-quality diamond film on carbide tools and high-performance diamond films for applications in optics and microelectronics. References: [1] Berman R, 1979 Thermal properties of diamond, in the properties of diamond (JEField, New York, Academic Press) p34 [2] Pickrell DJ, Kline KA and Taylor RE 1994 Appl. Phys. Lett. 64 2353 [3] Balducci A, D'Amico A, 2005 Di Natale C Sensors and Actuators B. 34 111 [4] Malshe AP, Naseem HA, Brown WD, et al. 1995 Recent Advances in Diamond Based Multichip Modules (MCMs) [J] ].3nd Inter.Conf.on the Appl.of Diamond Films and Related Materials, 611-618 [5] Yin Z, Akkerman Z, Yang BX, et al. 1997 Diamond Related. Mater. 6 153 [6] H.Chat .ei, Bougdira J, Remy M, et al. 1997 Diamond Relat. Mater. 6 107 [7] Huang TC, Lim G, Parmigiani F et al. 1983 J Vac Sci Tech. 6 2161 [8] Chang Gu, Zengsu J Xianyi Lu et al. 1998 Thin Solid Films. 311: 124 [9] Wang WL, Liao KJ, Kong CY et al. 2001 Functional Metals and Devices. 7 318 [10] Zhao Kaihua, Zhong Xihua 1984 Optics. (Peking University Press Page 12 [11] Cao GZ, Schermer JJ, Van Enckevart WJP et al. 1996 Appl. Phys. 79 1357 [12] S. J in, T. D. Moust akan 1994 Appl. Phys. Lett. 65 403. [13] Jin Zengsun, Lu Xianyi, Jiang Zhigang, etc. Process for preparing diamond film by hot cathode glow plasma chemical vapor deposition Chinese invention patent CN94116283.4 [14] Sun B, Zhang X, Lin Z 1993 Phys. Rev. B. 47 9824 [15] Hong SP, Yoshikawa H, Wazumi K, et al. 2002 Diamond Related. Mater 11 877 [16] Han WQ, Han GR, Fan SS, et al. 1997 Chin. Phys. Lett. 14 682 [17] Suo DC, Liu YC, Liu Y, et al .2004 Chin. Phys. Lett. 21 400 [18] L.Chow, D.Zhou, Hussain A, et al.2000 Thin Solid Films 36 193 [19] Yan Xuegui, Chen Zezhen, Wang Guanzhong, Liao Yuan 2004 Inorganic Materials Journal 19 404 [20] Tang CJ, Neves AJ, Pereira S 2008 Diamond&Related Materials 17 72 [21] Huang TC, Lim G, Parmigiani F et al. 1983 J Vac Sci Tech. A 6 2161 [22] Chang Gu, Zengsu J, Xianyi Lu et al. 1998 Thin Solid Films.311 124 [23] Wang Wan-lu, Liao Ke-jun, Kong Chun-yang et al. 2001 Functional Metals and Devices 18 307 [24] Zhou Ming, Yuan Zhejun 1999 Journal of Harbin Institute of Technology 31(4)Glass Pot,Glass Teapot,Small Glass
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