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Textured diamond growth by microwave plasma chemical vapor deposition
a ~ surface science ELSEVIER
Applied SurfaceScience92 (1996) 115-118
Textured diamond growth by microwave plasma chemical vapor deposition Y u n g Liou * Institute of Physics, Academia Sinica, Nankang, Taipei, Taiwan, ROC
Received 12 December1994;acceptedfor publication28 May 1995
Abstract
Textured diamond films were deposited on different substrates by microwave plasma chemical vapor deposition. A two-step process, substrate biasing during the nucleation stage and no-biasing during the growth stage, was used in this study. Diamond crystals with the C(001) planes parallel to the substrate surface were grown epitaxially oriented relative to the substrate. On Si(100) substrates, diamond crystals appear to be aligned with C[ll0] directions parallel to Si[ll0]. But diamond crystals are randomly oriented on Si(l 11) substrates. Without the bias pretreatment during the nucleation stage, we were not able to grow a fiat textured diamond surface either. X-ray diffraction, Raman spectroscopy and scanning electron microscopy were used to characterize the diamond films.
1. Introduction
Heteroepitaxial growth of diamond is important for semiconductor device applications. The most important goal in the field of diamond research is to grow large area single-crystal diamond thin films for electronic applications. Selected or textured nucleations have been pursued by Geis [1], Ma et al. [2], Rudder et al. [3], and Kobashi et al. [4]. (100) or (110) oriented diamond films can be easily controlled by the gas composition and the substrate temperature. Local epitaxy of diamond on Si(100) was first reported by Jeng et al. [5] and later a similar result of diamond on (100) /3-SIC was also reported by Stoner [6]. After Yugo et al. [7] reported a high density of diamond nuclei can be generated by negative biasing the substrate, various groups have re* Correspondingauthor. Fax: + 886-2-783-4187.
ported their successful synthesis of highly oriented textured diamond films. In the works presented by Wolter et al. [8] and Stoner et al. [9], it was shown that a three-step, carburization, bias-enhanced nucleation, and textured growth process is necessary to grow epitaxial diamond films on Si(100). In the report by Jiang et al. [10], substrate biasing ( - 100 to - 3 0 0 V) was used to optimize the conditions for nuclei generation, but no detailed information about the process was reported. In this study, it was shown that highly oriented textured diamond films can be grown on Si(100) simply by a two-step process instead of the three-step process reported b y Stoner et al. [9]. No in situ carburization is needed. High nucleation density by negative biasing pretreatment of the substrate is essential for growing highly oriented films. Textured diamond films can be achieved by controlling the carbon concentration and the substrate temperature.
0169-4332/96/$15.00 © 1996ElsevierScienceB.V. All fights reserved SSD1 0169-4332(95)00212-X
116
Y. Liou /Applied Surface Science 92 (1996) 115-118
2. Experimental procedures
Table 1 Two-step process conditions for oriented (100) textured diamond growth
Diamond films were prepared by microwave plasma chemical vapor deposition (MPCVD) using a Tokyo electronics 1.3 kW, 2.45 GHz, vertical type reactor. MKS mass flow and pressure control systems were used to control the flow rate of each gas and the gas pressure in the reactor. Prior to insertion into the reactor the substrates were ultrasonically cleaned in acetone or methanol. None of the conventional methods for nucleation enhancement such as scratching or seeding etc. were used on those biasenhanced substrates. Scratched samples were used only for comparison. The conditions of the two-step process are listed in Table I. The surface morphology of the deposited films was analyzed by scanning electron microscopy (SEM). Micro-Raman ( 5 / z m spot size) spectroscopy was used to characterize the quality of the diamond
Parameters
Bias-pretreatment
Textured growth
Bias voltage Bias current Microwave power Total pressure Substrate temperature C H 4 / H 2 ratio Time
- 150 V 80 mA 650 W 15 Tort 900"C 3% 15 min
500 W 10 Torr 800°C 1% 10-50 h
films. X-ray diffraction (XRD) was used to check the crystal orientation.
3. Results and discussion We have used the two-step process to grow highly oriented diamond films with the diamond (001)
~
\
./ ,
¢,,,.: p'N). . . . .
~
'
,
~
(b)
1i31
'~'\ / ~ z
1800 Fig. 1. SEM micrographs taken at 30° tilt of (a) 4/xm thick, and (b) 12 /~m thick textured (100) diamond films on Si(100) resulting from the bias-enhanced nucleation followed by textured growth.
1600 1400 WAVENUMBER ( cm-~ )
Fig. 2. Raman spectra of a textured (100) diamond film, (a) at the grain boundaries, and (b) at the center of the largest grain in the film.
Y. Liou / Applied Surface Science 92 (1996) 115-118
planes parallel to the substrate surface on Si(100) substrates, as shown in Fig. 1. Most of the squared diamond grains are oriented at the same direction, diamond[001] IIsilicon[001] and diamond[110] IIsilicon[ll0]. The substrate orientation is indicated in Fig. lb. As the thickness of the film increased, we have seen a rough film (4/xm thick) with separated small grains (grain size smaller than 5 /xm), as shown in Fig. la, transformed to a smooth film (12 /xm thick) with highly oriented large flat crystals with grain size as big as 10/~m, as shown in Fig. lb. Some of the oriented grains have merged with the neighboring crystals and formed larger crystals without notable grain boundaries. The secondary nucleation may responsible for these mergences at the grain boundaries of most small grains. The film quality is characterized by Raman spectroscopy. The Raman spectrum at the grain boundary of the highly oriented diamond crystal shows a shoulder around 1500 cm -I after the diamond 1331 cm -1 peak, as shown in Figs. 2a, indicating that some amorphous carbon was incorporated with the diamond in the film. At the center area of the diamond crystal, only
117
the diamond 1331 cm -t peak is seen in the Raman spectrum, as shown in Fig. 2b, indicating that there is only good quality diamond in the film. Without the bias-pretreatment of the substrate, we observed less dense (100) diamond grains randomly oriented grown on the scratched pretreated silicon samples at the same growth condition, as shown in Fig. 3a. For diamond deposited on Si(111) with the same two-step process. Fig. 3b shows that the densely growing diamond crystals are randomly oriented and the surface of the film is much rougher than the diamond deposited on Si(100). The orientation of the (100) diamond film was also characterized by standard powder X-ray diffraction. In the XRD spectrum, we have also found a stronger diamond (400) peak appearing instead of the usually only diamond(111) peak appearing on most polycrystalline diamond films.
4.
Summary
This study has shown that oriented diamond grains have been nucleated on Si(100) better than on Si(111) by bias-enhanced nucleation. Textured diamond films were deposited by a two-step process with bias-pretreatment of the substrate followed by a textured growth process. The crystal orientation in the textured diamond films was aligned with the orientation of the silicon substrate. These highly oriented textured diamond films are composed of good quality diamond crystals and amorphous carbon at the grain boundaries.
Acknowledgements This work was supported by the National Science Council of the Republic of China under Contract No. NSC 84-2216-E-001-002. The assistance of Dr. C.C. Chiu and W.T. Yang for SEM, Raman and XRD works are acknowledged.
References Fig. 3. SEM micrographs of (100) diamond on (a) a scratched pretreated Si(ll I) sample, and (b) a bias-enhanced pretreated Si(l 11) sample.
[1] M. Geis, Appl. Phys. Lett. 55 (1989) 550. [2] J. Ma, H. Kawarada, T. Yonehara, J. Suzuki, J. Wei, Y. Yokata and A. Hiraka, Appl. Phys. Lett. 55 (1989) 1071.
118
Y. Liou / Applied Surface Science 92 (1996) 115-118
[3] R. Rudder, J. Posthill, G. Hudson, M. Mantini and R. Markunas, SPIE 969 (1988) 72. [4] K. Kobashi, K. Nishimura, K. Miyata, K. Kumagai and A. Nakane, J. Mater. Res. 5 (1990) 2469. [5] D.G. Jeng and H.S. Tuan, AppL Phys. Left. 56 (1990) 1968. [6] B.R. Stoner and J.T. Glass, Appl. Phys. l..¢tt. 60 (1992) 698. [7] S. Yugo, T. Kanai, T. Kimura and T. Muto, Appl. Phys. Left. 58 (1992) 1036.
[8] S.D. Wolter, B.R. Stoner, J.T. Glass, PJ. Ellis, D.S. Buhaenko, C.E. Jenkins and P. Southworth, Appl. Phys. Lett. 62 (1993) 1215. [9] B.R. Stoner, S. Sahaida, J.P. Bade, P. Southworth and P.J. Ellis, J. Mater. Res. 8 (1993) 1334. [10] X. Jiang and C.-P. Klages, R. Zachai, M. Hartweg and H.-J. Fusser, Appl. Phys. Left. 62 (1993) 3438.
Applied SurfaceScience92 (1996) 115-118
Textured diamond growth by microwave plasma chemical vapor deposition Y u n g Liou * Institute of Physics, Academia Sinica, Nankang, Taipei, Taiwan, ROC
Received 12 December1994;acceptedfor publication28 May 1995
Abstract
Textured diamond films were deposited on different substrates by microwave plasma chemical vapor deposition. A two-step process, substrate biasing during the nucleation stage and no-biasing during the growth stage, was used in this study. Diamond crystals with the C(001) planes parallel to the substrate surface were grown epitaxially oriented relative to the substrate. On Si(100) substrates, diamond crystals appear to be aligned with C[ll0] directions parallel to Si[ll0]. But diamond crystals are randomly oriented on Si(l 11) substrates. Without the bias pretreatment during the nucleation stage, we were not able to grow a fiat textured diamond surface either. X-ray diffraction, Raman spectroscopy and scanning electron microscopy were used to characterize the diamond films.
1. Introduction
Heteroepitaxial growth of diamond is important for semiconductor device applications. The most important goal in the field of diamond research is to grow large area single-crystal diamond thin films for electronic applications. Selected or textured nucleations have been pursued by Geis [1], Ma et al. [2], Rudder et al. [3], and Kobashi et al. [4]. (100) or (110) oriented diamond films can be easily controlled by the gas composition and the substrate temperature. Local epitaxy of diamond on Si(100) was first reported by Jeng et al. [5] and later a similar result of diamond on (100) /3-SIC was also reported by Stoner [6]. After Yugo et al. [7] reported a high density of diamond nuclei can be generated by negative biasing the substrate, various groups have re* Correspondingauthor. Fax: + 886-2-783-4187.
ported their successful synthesis of highly oriented textured diamond films. In the works presented by Wolter et al. [8] and Stoner et al. [9], it was shown that a three-step, carburization, bias-enhanced nucleation, and textured growth process is necessary to grow epitaxial diamond films on Si(100). In the report by Jiang et al. [10], substrate biasing ( - 100 to - 3 0 0 V) was used to optimize the conditions for nuclei generation, but no detailed information about the process was reported. In this study, it was shown that highly oriented textured diamond films can be grown on Si(100) simply by a two-step process instead of the three-step process reported b y Stoner et al. [9]. No in situ carburization is needed. High nucleation density by negative biasing pretreatment of the substrate is essential for growing highly oriented films. Textured diamond films can be achieved by controlling the carbon concentration and the substrate temperature.
0169-4332/96/$15.00 © 1996ElsevierScienceB.V. All fights reserved SSD1 0169-4332(95)00212-X
116
Y. Liou /Applied Surface Science 92 (1996) 115-118
2. Experimental procedures
Table 1 Two-step process conditions for oriented (100) textured diamond growth
Diamond films were prepared by microwave plasma chemical vapor deposition (MPCVD) using a Tokyo electronics 1.3 kW, 2.45 GHz, vertical type reactor. MKS mass flow and pressure control systems were used to control the flow rate of each gas and the gas pressure in the reactor. Prior to insertion into the reactor the substrates were ultrasonically cleaned in acetone or methanol. None of the conventional methods for nucleation enhancement such as scratching or seeding etc. were used on those biasenhanced substrates. Scratched samples were used only for comparison. The conditions of the two-step process are listed in Table I. The surface morphology of the deposited films was analyzed by scanning electron microscopy (SEM). Micro-Raman ( 5 / z m spot size) spectroscopy was used to characterize the quality of the diamond
Parameters
Bias-pretreatment
Textured growth
Bias voltage Bias current Microwave power Total pressure Substrate temperature C H 4 / H 2 ratio Time
- 150 V 80 mA 650 W 15 Tort 900"C 3% 15 min
500 W 10 Torr 800°C 1% 10-50 h
films. X-ray diffraction (XRD) was used to check the crystal orientation.
3. Results and discussion We have used the two-step process to grow highly oriented diamond films with the diamond (001)
~
\
./ ,
¢,,,.: p'N). . . . .
~
'
,
~
(b)
1i31
'~'\ / ~ z
1800 Fig. 1. SEM micrographs taken at 30° tilt of (a) 4/xm thick, and (b) 12 /~m thick textured (100) diamond films on Si(100) resulting from the bias-enhanced nucleation followed by textured growth.
1600 1400 WAVENUMBER ( cm-~ )
Fig. 2. Raman spectra of a textured (100) diamond film, (a) at the grain boundaries, and (b) at the center of the largest grain in the film.
Y. Liou / Applied Surface Science 92 (1996) 115-118
planes parallel to the substrate surface on Si(100) substrates, as shown in Fig. 1. Most of the squared diamond grains are oriented at the same direction, diamond[001] IIsilicon[001] and diamond[110] IIsilicon[ll0]. The substrate orientation is indicated in Fig. lb. As the thickness of the film increased, we have seen a rough film (4/xm thick) with separated small grains (grain size smaller than 5 /xm), as shown in Fig. la, transformed to a smooth film (12 /xm thick) with highly oriented large flat crystals with grain size as big as 10/~m, as shown in Fig. lb. Some of the oriented grains have merged with the neighboring crystals and formed larger crystals without notable grain boundaries. The secondary nucleation may responsible for these mergences at the grain boundaries of most small grains. The film quality is characterized by Raman spectroscopy. The Raman spectrum at the grain boundary of the highly oriented diamond crystal shows a shoulder around 1500 cm -I after the diamond 1331 cm -1 peak, as shown in Figs. 2a, indicating that some amorphous carbon was incorporated with the diamond in the film. At the center area of the diamond crystal, only
117
the diamond 1331 cm -t peak is seen in the Raman spectrum, as shown in Fig. 2b, indicating that there is only good quality diamond in the film. Without the bias-pretreatment of the substrate, we observed less dense (100) diamond grains randomly oriented grown on the scratched pretreated silicon samples at the same growth condition, as shown in Fig. 3a. For diamond deposited on Si(111) with the same two-step process. Fig. 3b shows that the densely growing diamond crystals are randomly oriented and the surface of the film is much rougher than the diamond deposited on Si(100). The orientation of the (100) diamond film was also characterized by standard powder X-ray diffraction. In the XRD spectrum, we have also found a stronger diamond (400) peak appearing instead of the usually only diamond(111) peak appearing on most polycrystalline diamond films.
4.
Summary
This study has shown that oriented diamond grains have been nucleated on Si(100) better than on Si(111) by bias-enhanced nucleation. Textured diamond films were deposited by a two-step process with bias-pretreatment of the substrate followed by a textured growth process. The crystal orientation in the textured diamond films was aligned with the orientation of the silicon substrate. These highly oriented textured diamond films are composed of good quality diamond crystals and amorphous carbon at the grain boundaries.
Acknowledgements This work was supported by the National Science Council of the Republic of China under Contract No. NSC 84-2216-E-001-002. The assistance of Dr. C.C. Chiu and W.T. Yang for SEM, Raman and XRD works are acknowledged.
References Fig. 3. SEM micrographs of (100) diamond on (a) a scratched pretreated Si(ll I) sample, and (b) a bias-enhanced pretreated Si(l 11) sample.
[1] M. Geis, Appl. Phys. Lett. 55 (1989) 550. [2] J. Ma, H. Kawarada, T. Yonehara, J. Suzuki, J. Wei, Y. Yokata and A. Hiraka, Appl. Phys. Lett. 55 (1989) 1071.
118
Y. Liou / Applied Surface Science 92 (1996) 115-118
[3] R. Rudder, J. Posthill, G. Hudson, M. Mantini and R. Markunas, SPIE 969 (1988) 72. [4] K. Kobashi, K. Nishimura, K. Miyata, K. Kumagai and A. Nakane, J. Mater. Res. 5 (1990) 2469. [5] D.G. Jeng and H.S. Tuan, AppL Phys. Left. 56 (1990) 1968. [6] B.R. Stoner and J.T. Glass, Appl. Phys. l..¢tt. 60 (1992) 698. [7] S. Yugo, T. Kanai, T. Kimura and T. Muto, Appl. Phys. Left. 58 (1992) 1036.
[8] S.D. Wolter, B.R. Stoner, J.T. Glass, PJ. Ellis, D.S. Buhaenko, C.E. Jenkins and P. Southworth, Appl. Phys. Lett. 62 (1993) 1215. [9] B.R. Stoner, S. Sahaida, J.P. Bade, P. Southworth and P.J. Ellis, J. Mater. Res. 8 (1993) 1334. [10] X. Jiang and C.-P. Klages, R. Zachai, M. Hartweg and H.-J. Fusser, Appl. Phys. Left. 62 (1993) 3438.