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Structural analysis of chemical vapor deposited β-SiC coatings from CH3SiCl3–H2 gas precursor
ARTICLE IN PRESS
Journal of Crystal Growth 270 (2004) 124–127
Structural analysis of chemical vapor deposited b-SiC coatings from CH3SiCl3–H2 gas precursor RongJun Liu*, ChangRui Zhang, XinGui Zhou, YingBin Cao College of Aerospace and Materials Engineering, Key Laboratory of Advanced Fibers and Composites, National University of Defense Technology, Chang Sha 410073, People’s Republic of China Received 11 March 2004; accepted 2 June 2004 Available online 6 July 2004 Communicated by R.S. Feigelson
Abstract Coatings of b-SiC were prepared from the methyltrichlorosilane by low- pressure chemical vapor deposition (CVD) onto the graphite substrates. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) methods. The surface morphology of CVD SiC shows pyramid structure and (1 1 1) plane is the preferred orientation in the XRD pattern. HRTEM results show that SiC crystal grows according to the preferred orientation of the substrate at the beginning of the deposition, and then the crystal adjusts the growth to (1 1 1) plane. r 2004 Elsevier B.V. All rights reserved. Keywords: A1. Characterization; A1. Crystal structures; A1. Crystal morphology; A3. Chemical vapor deposition processes; A3. Metalorganic chemical vapor deposition; B1. Carbides
1. Introduction Silicon carbide (SiC) is a refractory compound with much promise for certain structural, optical and electronic applications [1–3]. Chemical vapor deposition (CVD) is one of the more widely used processes to grow SiC. CVD SiC has many outstanding properties such as high density, good thermal conductivity, extreme hardness, as well as excellent resistance to chemical attack and thermal *Corresponding author. Tel.: +867314576397; +867314573165. E-mail address: [email protected] (R. Liu).
fax:
shock; these make it very appropriate for a hightemperature structural material. Moreover, its wide energy band gap and high-saturated drift velocity should make it very useful in high temperature semiconductor applications. SiC coatings (films) have been widely grown by many investigators using CVD method in the past years [4–6]; almost all of the studies were concerned with the growth processes or characterization of SiC coatings [7–9]. In this paper, b-SiC was deposited on graphite substrate by methyltrichlorosilane (MTS)-H2 gas system; the goal of this study was to explain the crystal growth mechanism by investigating the structures of the as-deposited coatings.
0022-0248/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2004.06.005
ARTICLE IN PRESS R. Liu et al. / Journal of Crystal Growth 270 (2004) 124–127
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2. Experimental procedure The deposition experiments were performed in a hot-wall vertical reactor. Hydrogen was used as carrier gas, which delivered the MTS source precursor through the bubbler to the reactor; argon was used as diluent and protective gas; isotropy graphite was chosen as a deposition substrate, the crystal structure of graphite is hexagonal and has a (0 0 2) preferred orientation. The flow rate of hydrogen and argon were fixed at 200 and 100 sccm (cm3/min), respectively. All deposition were performed at 1373 K under a total pressure of 5.0 kPa, the detailed experiment process can be found in Ref. [10]. In our experiments, the above process parameter was an optimum from many different conditions to deposit uniform b-SiC. The crystalline phase deposited and its preferred orientation were characterized by X-ray diffracto( (Cu Ka metry (XRD) at a wavelength of 1.5418 A radiation). The microstructures of the CVD SiC coatings were observed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM).
Fig. 1. SEM micrograph of CVD SiC coatings.
Fig. 2. XRD pattern of CVD SiC coatings.
3. Results and discussion Fig. 1 shows the SEM picture of the asdeposited coatings, the crystals are well developed and have a pyramid structures, the pyramid-like grain shape may indicate that SiC coatings have a (1 1 1) preferred orientation. Also, it can be seen from the SEM image that the as-deposited coatings are very dense. Fig. 2 shows the XRD pattern of CVD SiC coatings, it can be noted that the asdeposited coatings are all composed of b-SiC. The preferred orientation of a certain crystal plane (h k l) in polycrystalline SiC coatings can be described by the texture coefficient (TC) using the Harris method [11] TC ¼
ðI=I0 Þ P ; ð1=nÞ n ðI=I0 Þ
Where I is the measured intensity, I0 is the American Society for Testing and Materials (ASTM) standard intensity, and n is the number
of reflection. The texture coefficient of (1 1 1), (2 0 0), (2 2 0) and (3 1 1) is 1.3, 0.5, 1.1 and 1.0 respectively, the (1 1 1) crystal planes have the biggest TC; therefore, the coatings will have a (1 1 1) preferred orientation as shown in the Fig. 1. HRTEM can give a detailed crystal lattice image; therefore, the SiC crystal growth mechanism on the graphite can be investigated by this technique. Fig. 3 is the section HRTEM image of SiC coatings on a graphite substrate, the graphite has an (0 0 2) preferred orientation and the SiC crystal has a (2 0 0) preferred orientation, there exist a interface of about 1 nm thickness between the coatings and substrate. At the interface, the orientation angle between the SiC planes and graphite planes is about 73 , that is to say, the orientation of SiC and graphite almost perpendicular to each other. It can be concluded that the SiC crystal will grow according to the preferred orientation of graphite at the beginning of deposition.
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R. Liu et al. / Journal of Crystal Growth 270 (2004) 124–127
Fig. 3. HRTEM image of SiC coatings on graphite substrate.
Fig. 4 gives the HRTEM picture of the b-SiC coatings, the top of the image is composed of SiC (2 0 0) crystal planes and the bottom is the crystal lattice image of the SiC (1 1 1) plane. There is a disordered block between the SiC (2 0 0) and (1 1 1) crystal lattice image. The disordered block is resulted from the crystal lattice mismatching between SiC (2 0 0) and (1 1 1) plane in the crystal growth. Fig. 5 shows the HRTEM image of SiC (1 1 1) plane, the crystal lattice is perfect. b-SiC is a facecenter-cubic (fcc) structural crystal, and (1 1 1) plane is the densest stack plane for fcc crystals; therefore, after the beginning deposition of SiC (2 0 0), the as-deposited coatings will compose mainly of SiC (1 1 1). In whole, SiC crystal will grow according to the preferred orientation of the substrate at the beginning of the deposition, then the crystal will adjust the growth to (1 1 1) plane; therefore, the asdeposited coatings will show (1 1 1) preferred orientation at last.
4. Conclusion b-SiC coatings were prepared from the methyltrichlorosilane (MTS) by low-pressure chemical vapor deposition (CVD) onto the graphite substrates. The as-deposited coatings of CVD SiC
Fig. 4. HRTEM image of SiC coatings.
Fig. 5. HRTEM image of SiC (1 1 1) plane.
show a pyramid surface morphology, and have a (1 1 1) plane preferred orientation. During the deposition, the SiC crystal film grows according to the preferred orientation of the graphite substrate at the beginning of the deposition, and then adjusts its growth to (1 1 1) plane.
ARTICLE IN PRESS R. Liu et al. / Journal of Crystal Growth 270 (2004) 124–127
Acknowledgements The National Defense Preliminary Research Foundation of China has supported this work. The authors especially thank RenCao Che for his help in TEM tests.
References [1] Xin-Bo He, Xin-Ming Zhang, J. Mater. Sci. Lett. 19 (2000) 417. [2] Hotate, et al., US Pat. 5,448,418, 5 September 1995. [3] T. Kleps, A. Angelescu, Appl. Surf. Sci. 184 (2001) 107.
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[4] Ching Yi Tsai, J. Mater. Res 9 (1994) 104. [5] Han-Su Kim, Doo Jim Choi, J. Am. Ceram. Soc 82 (1999) 331–337. [6] J.H. Oh, D.J. Choi, J. Mater. Sci. Lett 19 (2000) 2043. [7] G.D. Papasouliotis, S. V. Sotirchos. J. Mater. Res 14 (1999) 3397. [8] H. Sone, T. Kaneko, N. Miyakawa, J. Crystal growth 219 (2000) 245. [9] Byung Jin Choi, Dai Ryong Kim, J. Mater. Sci. Lett 10 (1991) 860. [10] Rong-Jun Liu, Chang -Rui Zhang, J. Mater. Sci. Lett. 22 (2003) 841. [11] C. Barret, T.B. Massalski, Structure of Metals, Pergamon, Oxford, 1980, p. 204.
Journal of Crystal Growth 270 (2004) 124–127
Structural analysis of chemical vapor deposited b-SiC coatings from CH3SiCl3–H2 gas precursor RongJun Liu*, ChangRui Zhang, XinGui Zhou, YingBin Cao College of Aerospace and Materials Engineering, Key Laboratory of Advanced Fibers and Composites, National University of Defense Technology, Chang Sha 410073, People’s Republic of China Received 11 March 2004; accepted 2 June 2004 Available online 6 July 2004 Communicated by R.S. Feigelson
Abstract Coatings of b-SiC were prepared from the methyltrichlorosilane by low- pressure chemical vapor deposition (CVD) onto the graphite substrates. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) methods. The surface morphology of CVD SiC shows pyramid structure and (1 1 1) plane is the preferred orientation in the XRD pattern. HRTEM results show that SiC crystal grows according to the preferred orientation of the substrate at the beginning of the deposition, and then the crystal adjusts the growth to (1 1 1) plane. r 2004 Elsevier B.V. All rights reserved. Keywords: A1. Characterization; A1. Crystal structures; A1. Crystal morphology; A3. Chemical vapor deposition processes; A3. Metalorganic chemical vapor deposition; B1. Carbides
1. Introduction Silicon carbide (SiC) is a refractory compound with much promise for certain structural, optical and electronic applications [1–3]. Chemical vapor deposition (CVD) is one of the more widely used processes to grow SiC. CVD SiC has many outstanding properties such as high density, good thermal conductivity, extreme hardness, as well as excellent resistance to chemical attack and thermal *Corresponding author. Tel.: +867314576397; +867314573165. E-mail address: [email protected] (R. Liu).
fax:
shock; these make it very appropriate for a hightemperature structural material. Moreover, its wide energy band gap and high-saturated drift velocity should make it very useful in high temperature semiconductor applications. SiC coatings (films) have been widely grown by many investigators using CVD method in the past years [4–6]; almost all of the studies were concerned with the growth processes or characterization of SiC coatings [7–9]. In this paper, b-SiC was deposited on graphite substrate by methyltrichlorosilane (MTS)-H2 gas system; the goal of this study was to explain the crystal growth mechanism by investigating the structures of the as-deposited coatings.
0022-0248/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2004.06.005
ARTICLE IN PRESS R. Liu et al. / Journal of Crystal Growth 270 (2004) 124–127
125
2. Experimental procedure The deposition experiments were performed in a hot-wall vertical reactor. Hydrogen was used as carrier gas, which delivered the MTS source precursor through the bubbler to the reactor; argon was used as diluent and protective gas; isotropy graphite was chosen as a deposition substrate, the crystal structure of graphite is hexagonal and has a (0 0 2) preferred orientation. The flow rate of hydrogen and argon were fixed at 200 and 100 sccm (cm3/min), respectively. All deposition were performed at 1373 K under a total pressure of 5.0 kPa, the detailed experiment process can be found in Ref. [10]. In our experiments, the above process parameter was an optimum from many different conditions to deposit uniform b-SiC. The crystalline phase deposited and its preferred orientation were characterized by X-ray diffracto( (Cu Ka metry (XRD) at a wavelength of 1.5418 A radiation). The microstructures of the CVD SiC coatings were observed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM).
Fig. 1. SEM micrograph of CVD SiC coatings.
Fig. 2. XRD pattern of CVD SiC coatings.
3. Results and discussion Fig. 1 shows the SEM picture of the asdeposited coatings, the crystals are well developed and have a pyramid structures, the pyramid-like grain shape may indicate that SiC coatings have a (1 1 1) preferred orientation. Also, it can be seen from the SEM image that the as-deposited coatings are very dense. Fig. 2 shows the XRD pattern of CVD SiC coatings, it can be noted that the asdeposited coatings are all composed of b-SiC. The preferred orientation of a certain crystal plane (h k l) in polycrystalline SiC coatings can be described by the texture coefficient (TC) using the Harris method [11] TC ¼
ðI=I0 Þ P ; ð1=nÞ n ðI=I0 Þ
Where I is the measured intensity, I0 is the American Society for Testing and Materials (ASTM) standard intensity, and n is the number
of reflection. The texture coefficient of (1 1 1), (2 0 0), (2 2 0) and (3 1 1) is 1.3, 0.5, 1.1 and 1.0 respectively, the (1 1 1) crystal planes have the biggest TC; therefore, the coatings will have a (1 1 1) preferred orientation as shown in the Fig. 1. HRTEM can give a detailed crystal lattice image; therefore, the SiC crystal growth mechanism on the graphite can be investigated by this technique. Fig. 3 is the section HRTEM image of SiC coatings on a graphite substrate, the graphite has an (0 0 2) preferred orientation and the SiC crystal has a (2 0 0) preferred orientation, there exist a interface of about 1 nm thickness between the coatings and substrate. At the interface, the orientation angle between the SiC planes and graphite planes is about 73 , that is to say, the orientation of SiC and graphite almost perpendicular to each other. It can be concluded that the SiC crystal will grow according to the preferred orientation of graphite at the beginning of deposition.
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Fig. 3. HRTEM image of SiC coatings on graphite substrate.
Fig. 4 gives the HRTEM picture of the b-SiC coatings, the top of the image is composed of SiC (2 0 0) crystal planes and the bottom is the crystal lattice image of the SiC (1 1 1) plane. There is a disordered block between the SiC (2 0 0) and (1 1 1) crystal lattice image. The disordered block is resulted from the crystal lattice mismatching between SiC (2 0 0) and (1 1 1) plane in the crystal growth. Fig. 5 shows the HRTEM image of SiC (1 1 1) plane, the crystal lattice is perfect. b-SiC is a facecenter-cubic (fcc) structural crystal, and (1 1 1) plane is the densest stack plane for fcc crystals; therefore, after the beginning deposition of SiC (2 0 0), the as-deposited coatings will compose mainly of SiC (1 1 1). In whole, SiC crystal will grow according to the preferred orientation of the substrate at the beginning of the deposition, then the crystal will adjust the growth to (1 1 1) plane; therefore, the asdeposited coatings will show (1 1 1) preferred orientation at last.
4. Conclusion b-SiC coatings were prepared from the methyltrichlorosilane (MTS) by low-pressure chemical vapor deposition (CVD) onto the graphite substrates. The as-deposited coatings of CVD SiC
Fig. 4. HRTEM image of SiC coatings.
Fig. 5. HRTEM image of SiC (1 1 1) plane.
show a pyramid surface morphology, and have a (1 1 1) plane preferred orientation. During the deposition, the SiC crystal film grows according to the preferred orientation of the graphite substrate at the beginning of the deposition, and then adjusts its growth to (1 1 1) plane.
ARTICLE IN PRESS R. Liu et al. / Journal of Crystal Growth 270 (2004) 124–127
Acknowledgements The National Defense Preliminary Research Foundation of China has supported this work. The authors especially thank RenCao Che for his help in TEM tests.
References [1] Xin-Bo He, Xin-Ming Zhang, J. Mater. Sci. Lett. 19 (2000) 417. [2] Hotate, et al., US Pat. 5,448,418, 5 September 1995. [3] T. Kleps, A. Angelescu, Appl. Surf. Sci. 184 (2001) 107.
127
[4] Ching Yi Tsai, J. Mater. Res 9 (1994) 104. [5] Han-Su Kim, Doo Jim Choi, J. Am. Ceram. Soc 82 (1999) 331–337. [6] J.H. Oh, D.J. Choi, J. Mater. Sci. Lett 19 (2000) 2043. [7] G.D. Papasouliotis, S. V. Sotirchos. J. Mater. Res 14 (1999) 3397. [8] H. Sone, T. Kaneko, N. Miyakawa, J. Crystal growth 219 (2000) 245. [9] Byung Jin Choi, Dai Ryong Kim, J. Mater. Sci. Lett 10 (1991) 860. [10] Rong-Jun Liu, Chang -Rui Zhang, J. Mater. Sci. Lett. 22 (2003) 841. [11] C. Barret, T.B. Massalski, Structure of Metals, Pergamon, Oxford, 1980, p. 204.