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Influence of the methyl group on the dielectric constant of boron carbon nitride films containing it
Diamond & Related Materials 19 (2010) 1437–1440
Contents lists available at ScienceDirect
Diamond & Related Materials j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d i a m o n d
Influence of the methyl group on the dielectric constant of boron carbon nitride films containing it Hidemitsu Aoki, Takuro Masuzumi, Makoto Hara, Zhiming Lu, Daisuke Watanebe, Chiharu Kimura ⁎, Takashi Sugino Department of Electrical, Electronic and Information Engineering, Osaka University, 2-l Yamadaoka, Suita, Osaka 565-0871, Japan
a r t i c l e
i n f o
Article history: Received 1 October 2009 Received in revised form 6 June 2010 Accepted 17 June 2010 Available online 22 June 2010 Keywords: Low-k Methyl group ULSI
a b s t r a c t LSI interconnect insulators made using low dielectric constant (low-k) materials are required for high performance devices with a small RC delay. We investigated a boron carbon nitride film containing the methyl group (Me–BCN) using tris-di-methyl-amino-boron (TMAB: B[N(CH3)2]3) gas as a low-k material. In addition, we studied the influence of the methyl group on the dielectric constant (k-value) and the properties of the Me–BCN films. It was found that the k-value of the Me–BCN films decreases with increasing number of C–H bonds due to the methyl group (CH3). The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggested that a lower k-value can be realized by the suppression of water invasion by a hydrophobic surface due to methyl bonds. Thus, the control of the methyl group is important to achieve a low-k material using Me–BCN films. © 2010 Elsevier B.V. All rights reserved.
1. Introduction LSI devices have been miniaturized and processes have become more complex. It is found that hundreds to millions of transistors are assembled on a single chip, resulting in an increase in the signal transmission time, power consumption, and wire cross-talk between multilevel interconnects, which in turn curtail the benefits of interconnection scaling. The integration of a low dielectric constant (low-k) interlayer and Cu interconnection is necessary to achieve high-performance interconnections with a small RC delay for the next-generation system LSI devices [1,2]. Recently, porous low-k films have been integrated to reduce the k-value. However, most porous low-k materials have many serious issues, such as low mechanical stress, water incorporation in the pore, and Cu diffusion into low-k films. The dielectric constant of a porous low-k film increases because of the trapping of water into pores, and the corrosion Cu wiring is induced by water residue in the film. The interconnection reliability overall is degraded by these problems [3]. On the other hand, boron nitride (BN) and boron carbon nitride (BCN) are well known as hard materials; Young's modulus of BCN films is more than 20 GPa [4]. We have investigated device applications of hBN (hexagonal-BN) films deposited by remote PACVD. We have already achieved a low k-value for BCN films [5,6]. In addition, we have reported that unlike the SiOC film, the thermal diffusion of Cu or Ag atoms can be suppressed in the BCN films [7], and increasing the concentration of
⁎ Corresponding author. Tel.: +81 6 6877 5111. E-mail address: [email protected] (C. Kimura). 0925-9635/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2010.06.020
carbon in the BCN films can suppress the incorporation of water into the film [8]. Regarding the relationship between the dielectric constant and the mechanical strength of various low-k films, we have recently devoted efforts to the development of a new low-k material with a SiO based porous structure. We have reported that the methyl BCN films with a low dielectric constant (k) can be achieved by using TMAB gas at radio frequency (RF) plasma power [9]. The film has high resistivity and sufficient Young's modulus for the interlayer of the LSI interconnection. Young's modulus of the Me–BCN films was measured by nanoindentation to be more than 26 GPa [10,11]. The value of Young's modulus is sufficient for the CMP process in which it is required to be more than 10 Gpa. The Me–BCN film is one of the most attractive materials as a low-k material for devices with node of 32 nm devices and beyond. In this study, we investigated the influence of the methyl group on the dielectric constant (k-value) and the properties of Me–BCN films. Especially, we discuss the relation between the methyl group and water incorporation in the Me–BCN films from the viewpoints of O–H bonds, contact angle, and k-value. 2. Experimental procedure Me–BCN films were deposited on a Si substrate by remote plasmaassisted chemical vapor deposition in a quartz reactor (length: 70 cm) by introducing TMAB and N2 gases in the reactor. In order to produce N2 plasma remotely by induction coupling, a coil was installed around the quartz reactor and RF power was supplied to the coil. In order to restrain the stress migration of the interconnection that is caused by high temperatures, the substrate temperature was maintained at 350 °C by an external furnace. The substrates were set on a holder
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Fig. 1. Dependence of the peak intensity of C–H absorption at 2960 cm− 1 (CH3 bonds) on the concentration of carbon in the Me–BCN films.
Fig. 3. Dependence of the peak intensity of O–H bonds on that of C–H absorption (CH3 bonds) in the Me–BCN films.
inside the reactor tube for deposition. Fig. 1 shows the chemical structure of the TMAB (B[N(CH3)2]3) gas, which was used in this experiment. The flow rates of the TMAB and N2 gases were 0.5 and 5 sccm, respectively. The RF plasma power (power of RF electromagnetic waves) was controlled in the range of 10 W–90 W, and the growth pressure was 2.0 Torr. X-ray photoelectron spectroscopy (XPS) measurements were performed mainly to examine the concentrations of the constituent atoms of the film. We analyzed the bonding in the films by Fourier transform infrared absorption (FT-IR). The sample's capacitances were measured by a capacitance–voltage (C–V) measurement using an MIS (Cu/Me–BCN film/Si) structure. The dielectric constant of the films was calculated from the capacitance in the accumulation region at a frequency of 1 MHz and thickness of the films.
investigate methyl bonds in Me–BCN films, we took particular note of the FT-IR absorption bands at 2960 cm− 1 due to the asymmetric stretching mode of C–H of the methyl group. The C–H absorption band at 2960 cm− 1 (C–H) was clearly seen for the BCN films deposited by TMAB. The intensity of the C–H absorption increases with decreasing RF plasma power, indicating that the methyl bonds can easily remain in the BCN films at low RF plasma power. Because the interatomic binding energy of the C–H bond is larger than those of the B–N and C– N bonds, it is easy to maintain the C–H bonds in the film at a low RF plasma power. The concentrations of B, N, C, and O were estimated using XPS signal intensities from B1s, N1s, C1s, and O1s core levels. The concentrations of B, C, N, and O atoms were estimated to be 32.3– 37.8%, 17.1–27.8%, 30.5–33.2%, and 9.4–14.3%, respectively. The concentrations of B and N increase with RF plasma power. The concentration of C increases when the power decreases below 50 W. The concentration of C clearly depends on the intensity of the C–H absorption peak as shown in Fig. 1. The FT-IR results indicate that the intensity of the O–H bond around 3410 cm− 1 decreased with RF plasma power. Fig. 3 shows the dependence of the peak intensity of O–H absorption on the intensity of C–H absorption peak. The O–H absorption can be suppressed by increasing the amount of C–H absorption. In addition, to study the incorporation of water in the Me–BCN films, we investigated the contact angle of de-ionized water dropped on the Me–BCN films. Fig. 4 shows the relationship between the peak intensity of the C–H absorption and the contact angle on the Me–BCN films. This result indicates that the hydrophobicity of the Me–BCN films increases with the amount of C–H bonds in the films. Here, when the contact angle of the water that is dropped on the Me–BCN surface is more than 50°, the surface has hydrophobicity. It was found that the surface of the Me–BCN films is covered with methyl bonds with high hydrophobicity. The k-values of the films are estimated from C–V measurement using the MIS structure and thickness of the films. We have already reported that the minimum k-value is as low as 1.8 at an RF plasma power of 10 W, and the kvalue of Me–BCN films deposited with a low RF plasma power is lower than that with high RF plasma power [10]. Fig. 5 shows the dependence of k-value on the peak intensity of C–H absorption. It is found that the k-value tends to decrease with an increase in the peak intensity of C–H bonds due to the methyl group. The invasion of water
3. Result and discussion Fig. 2 shows the FT-IR absorption spectra of the Me–BCN films for RF plasma power. We observed a large, broad absorption band due to a stretching mode of the h-BN bond at 1380 cm− 1, indicating that the Me–BCN films are mainly formed by h-BN bonds. In this study, we particularly discuss methyl bonds formed by the TMAB gas. To
Fig. 2. FT-IR spectra of the Me–BCN films (RF power: 10 W, 50 W and 70 W).
H. Aoki et al. / Diamond & Related Materials 19 (2010) 1437–1440
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Fig. 4. Dependence of the contact angles on the peak intensity of C–H absorption (CH3 bonds).
with a high k-value (k-value: 78) induces an increase in the k-value of Me–BCN films. Thus, suppressing the water invasion by a hydrophobic surface is very important for maintaining a lower k-value. In a previous report, it was suggested that increasing the C–H bond with low polarizability can realize a lower k value. In addition, there is a possibility of existing nanospaces in the film by CH3 bonds in the BCN films [9,10]. From this experiment, it is found that the formation of O–H bonds on the dangling bonds of B, C, or N atoms is suppressed by the termination of the methyl bonds. Therefore, we suggest that the methyl group is useful for suppressing the invasion of water, which causes the k-value to increase, into pores in the Me–BCN films. Fig. 6 shows (a) the TMAB gas structure and (b) a speculated structure of the Me–BCN films. TMAB has the following interatomic binding energies: B–N, 389 kJ/mol; C–N, 292 kJ/mol; and C–H, 416 kJ/ mol. The C–H bond has the largest binding energy in these bonds. Thus, it is easy for the C–H bonds to remain in the film (as CH3) at a low RF power. The structure of the Me–BCN films is speculated, as
Fig. 6. (a) TMAB gas structure and (b) a speculated structure of the Me–BCN films.
shown in Fig. 6 (b). This creates the possibility for an existing nanospace in the film formed by CH3 bonds. In addition, the invasion of water in the pores can be suppressed by hydrogen termination by carbons (i.e., methyl bonds). Hence, there is a possibility that the dielectric constant of the film can be decreased while keeping the strength of BCN structure high. 4. Conclusion We have investigated the influence of the methyl group contained in a Me–BCN films on the properties and k-value of the Me–BCN films. We found that the k-value of the Me–BCN films decreases with an increase in the number of C–H bonds due to the methyl group. The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggest that the suppression of water invasion by a hydrophobic surface due to methyl bonds can realize a lower k-value. Therefore, it is important to control the number of methyl bonds to achieve low-k materials using Me–BCN films. Acknowledgements This study has been supported by JSPS Program “Grants-in-Aid for Scientific Research”. References
Fig. 5. Dependence of the k-value of the Me–BCN films on the peak intensity of C–H absorption (CH3 bonds) in the Me–BCN films.
[1] A. Grill, V. Patel, Appl. Phys. Lett. 79 (2001) 803. [2] L.L. Chapelon, J. Vitiello, D. Neira, J. Torres, J.C. Royer, D. Barbier, F. Naudin, G. Tas, P. Mukundhan, J. Clerico, Microelectron. Eng. 83 (2006) 2346. [3] L. Yunlong, I. Ciofi, L. Carbonell, K. Maex, Z. Tokei, Proc. 45th Reliability physics symposium, IEEE international, 2007, p. 405, Vol., Issue , 15–19. [4] C. Morant, D. Cáceres, J.M. Sanz, E. Elizalde, Diamond Relat. Mater. 16 (2007) 1441.
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[5] T. Sugiyama, T. Tai, T. Sugino, Appl. Phys. Lett. 80 (2002) 4214. [6] S. Umeda, T. Yuki, T. Sugiyama, T. Sugino, Diamond Relat. Mater. 13 (2004) 1135. [7] M.K. Mazumder, R. Moriyama, D. Watanabe, C. Kimura, H. Aoki, T. Sugino, Jpn. J. Appl. Phys. 46 (2007) 2006. [8] H. Aoki, D. Watanabe, R. Moriyama, M.K. Mazumder, N. Komatsu, C. Kimura, T. Sugino, Diamond Relat. Mater. 17 (2007) 628.
[9] H. Aoki, T. Masuzumi, M. Hara, D. Watanabe, C. Kimura, T. Sugino, Thin Solid Films 518 (2010) 2102. [10] S. Tokuyama, M. Hara, M.K. Mazumder, D. Watanabe, C. Kimura, H. Aoki, T. Sugino, Jpn. J. Appl. Phys. 47 (2008) 2492. [11] H. Aoki, S. Tokuyama, T. Masuzumi, M. Hara, M.K. Mazumder, D. Watanabe, C. Kimura, T. Sugino, Diamond Relat. Mater. 18 (2009) 1048.
Contents lists available at ScienceDirect
Diamond & Related Materials j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d i a m o n d
Influence of the methyl group on the dielectric constant of boron carbon nitride films containing it Hidemitsu Aoki, Takuro Masuzumi, Makoto Hara, Zhiming Lu, Daisuke Watanebe, Chiharu Kimura ⁎, Takashi Sugino Department of Electrical, Electronic and Information Engineering, Osaka University, 2-l Yamadaoka, Suita, Osaka 565-0871, Japan
a r t i c l e
i n f o
Article history: Received 1 October 2009 Received in revised form 6 June 2010 Accepted 17 June 2010 Available online 22 June 2010 Keywords: Low-k Methyl group ULSI
a b s t r a c t LSI interconnect insulators made using low dielectric constant (low-k) materials are required for high performance devices with a small RC delay. We investigated a boron carbon nitride film containing the methyl group (Me–BCN) using tris-di-methyl-amino-boron (TMAB: B[N(CH3)2]3) gas as a low-k material. In addition, we studied the influence of the methyl group on the dielectric constant (k-value) and the properties of the Me–BCN films. It was found that the k-value of the Me–BCN films decreases with increasing number of C–H bonds due to the methyl group (CH3). The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggested that a lower k-value can be realized by the suppression of water invasion by a hydrophobic surface due to methyl bonds. Thus, the control of the methyl group is important to achieve a low-k material using Me–BCN films. © 2010 Elsevier B.V. All rights reserved.
1. Introduction LSI devices have been miniaturized and processes have become more complex. It is found that hundreds to millions of transistors are assembled on a single chip, resulting in an increase in the signal transmission time, power consumption, and wire cross-talk between multilevel interconnects, which in turn curtail the benefits of interconnection scaling. The integration of a low dielectric constant (low-k) interlayer and Cu interconnection is necessary to achieve high-performance interconnections with a small RC delay for the next-generation system LSI devices [1,2]. Recently, porous low-k films have been integrated to reduce the k-value. However, most porous low-k materials have many serious issues, such as low mechanical stress, water incorporation in the pore, and Cu diffusion into low-k films. The dielectric constant of a porous low-k film increases because of the trapping of water into pores, and the corrosion Cu wiring is induced by water residue in the film. The interconnection reliability overall is degraded by these problems [3]. On the other hand, boron nitride (BN) and boron carbon nitride (BCN) are well known as hard materials; Young's modulus of BCN films is more than 20 GPa [4]. We have investigated device applications of hBN (hexagonal-BN) films deposited by remote PACVD. We have already achieved a low k-value for BCN films [5,6]. In addition, we have reported that unlike the SiOC film, the thermal diffusion of Cu or Ag atoms can be suppressed in the BCN films [7], and increasing the concentration of
⁎ Corresponding author. Tel.: +81 6 6877 5111. E-mail address: [email protected] (C. Kimura). 0925-9635/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2010.06.020
carbon in the BCN films can suppress the incorporation of water into the film [8]. Regarding the relationship between the dielectric constant and the mechanical strength of various low-k films, we have recently devoted efforts to the development of a new low-k material with a SiO based porous structure. We have reported that the methyl BCN films with a low dielectric constant (k) can be achieved by using TMAB gas at radio frequency (RF) plasma power [9]. The film has high resistivity and sufficient Young's modulus for the interlayer of the LSI interconnection. Young's modulus of the Me–BCN films was measured by nanoindentation to be more than 26 GPa [10,11]. The value of Young's modulus is sufficient for the CMP process in which it is required to be more than 10 Gpa. The Me–BCN film is one of the most attractive materials as a low-k material for devices with node of 32 nm devices and beyond. In this study, we investigated the influence of the methyl group on the dielectric constant (k-value) and the properties of Me–BCN films. Especially, we discuss the relation between the methyl group and water incorporation in the Me–BCN films from the viewpoints of O–H bonds, contact angle, and k-value. 2. Experimental procedure Me–BCN films were deposited on a Si substrate by remote plasmaassisted chemical vapor deposition in a quartz reactor (length: 70 cm) by introducing TMAB and N2 gases in the reactor. In order to produce N2 plasma remotely by induction coupling, a coil was installed around the quartz reactor and RF power was supplied to the coil. In order to restrain the stress migration of the interconnection that is caused by high temperatures, the substrate temperature was maintained at 350 °C by an external furnace. The substrates were set on a holder
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Fig. 1. Dependence of the peak intensity of C–H absorption at 2960 cm− 1 (CH3 bonds) on the concentration of carbon in the Me–BCN films.
Fig. 3. Dependence of the peak intensity of O–H bonds on that of C–H absorption (CH3 bonds) in the Me–BCN films.
inside the reactor tube for deposition. Fig. 1 shows the chemical structure of the TMAB (B[N(CH3)2]3) gas, which was used in this experiment. The flow rates of the TMAB and N2 gases were 0.5 and 5 sccm, respectively. The RF plasma power (power of RF electromagnetic waves) was controlled in the range of 10 W–90 W, and the growth pressure was 2.0 Torr. X-ray photoelectron spectroscopy (XPS) measurements were performed mainly to examine the concentrations of the constituent atoms of the film. We analyzed the bonding in the films by Fourier transform infrared absorption (FT-IR). The sample's capacitances were measured by a capacitance–voltage (C–V) measurement using an MIS (Cu/Me–BCN film/Si) structure. The dielectric constant of the films was calculated from the capacitance in the accumulation region at a frequency of 1 MHz and thickness of the films.
investigate methyl bonds in Me–BCN films, we took particular note of the FT-IR absorption bands at 2960 cm− 1 due to the asymmetric stretching mode of C–H of the methyl group. The C–H absorption band at 2960 cm− 1 (C–H) was clearly seen for the BCN films deposited by TMAB. The intensity of the C–H absorption increases with decreasing RF plasma power, indicating that the methyl bonds can easily remain in the BCN films at low RF plasma power. Because the interatomic binding energy of the C–H bond is larger than those of the B–N and C– N bonds, it is easy to maintain the C–H bonds in the film at a low RF plasma power. The concentrations of B, N, C, and O were estimated using XPS signal intensities from B1s, N1s, C1s, and O1s core levels. The concentrations of B, C, N, and O atoms were estimated to be 32.3– 37.8%, 17.1–27.8%, 30.5–33.2%, and 9.4–14.3%, respectively. The concentrations of B and N increase with RF plasma power. The concentration of C increases when the power decreases below 50 W. The concentration of C clearly depends on the intensity of the C–H absorption peak as shown in Fig. 1. The FT-IR results indicate that the intensity of the O–H bond around 3410 cm− 1 decreased with RF plasma power. Fig. 3 shows the dependence of the peak intensity of O–H absorption on the intensity of C–H absorption peak. The O–H absorption can be suppressed by increasing the amount of C–H absorption. In addition, to study the incorporation of water in the Me–BCN films, we investigated the contact angle of de-ionized water dropped on the Me–BCN films. Fig. 4 shows the relationship between the peak intensity of the C–H absorption and the contact angle on the Me–BCN films. This result indicates that the hydrophobicity of the Me–BCN films increases with the amount of C–H bonds in the films. Here, when the contact angle of the water that is dropped on the Me–BCN surface is more than 50°, the surface has hydrophobicity. It was found that the surface of the Me–BCN films is covered with methyl bonds with high hydrophobicity. The k-values of the films are estimated from C–V measurement using the MIS structure and thickness of the films. We have already reported that the minimum k-value is as low as 1.8 at an RF plasma power of 10 W, and the kvalue of Me–BCN films deposited with a low RF plasma power is lower than that with high RF plasma power [10]. Fig. 5 shows the dependence of k-value on the peak intensity of C–H absorption. It is found that the k-value tends to decrease with an increase in the peak intensity of C–H bonds due to the methyl group. The invasion of water
3. Result and discussion Fig. 2 shows the FT-IR absorption spectra of the Me–BCN films for RF plasma power. We observed a large, broad absorption band due to a stretching mode of the h-BN bond at 1380 cm− 1, indicating that the Me–BCN films are mainly formed by h-BN bonds. In this study, we particularly discuss methyl bonds formed by the TMAB gas. To
Fig. 2. FT-IR spectra of the Me–BCN films (RF power: 10 W, 50 W and 70 W).
H. Aoki et al. / Diamond & Related Materials 19 (2010) 1437–1440
1439
Fig. 4. Dependence of the contact angles on the peak intensity of C–H absorption (CH3 bonds).
with a high k-value (k-value: 78) induces an increase in the k-value of Me–BCN films. Thus, suppressing the water invasion by a hydrophobic surface is very important for maintaining a lower k-value. In a previous report, it was suggested that increasing the C–H bond with low polarizability can realize a lower k value. In addition, there is a possibility of existing nanospaces in the film by CH3 bonds in the BCN films [9,10]. From this experiment, it is found that the formation of O–H bonds on the dangling bonds of B, C, or N atoms is suppressed by the termination of the methyl bonds. Therefore, we suggest that the methyl group is useful for suppressing the invasion of water, which causes the k-value to increase, into pores in the Me–BCN films. Fig. 6 shows (a) the TMAB gas structure and (b) a speculated structure of the Me–BCN films. TMAB has the following interatomic binding energies: B–N, 389 kJ/mol; C–N, 292 kJ/mol; and C–H, 416 kJ/ mol. The C–H bond has the largest binding energy in these bonds. Thus, it is easy for the C–H bonds to remain in the film (as CH3) at a low RF power. The structure of the Me–BCN films is speculated, as
Fig. 6. (a) TMAB gas structure and (b) a speculated structure of the Me–BCN films.
shown in Fig. 6 (b). This creates the possibility for an existing nanospace in the film formed by CH3 bonds. In addition, the invasion of water in the pores can be suppressed by hydrogen termination by carbons (i.e., methyl bonds). Hence, there is a possibility that the dielectric constant of the film can be decreased while keeping the strength of BCN structure high. 4. Conclusion We have investigated the influence of the methyl group contained in a Me–BCN films on the properties and k-value of the Me–BCN films. We found that the k-value of the Me–BCN films decreases with an increase in the number of C–H bonds due to the methyl group. The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggest that the suppression of water invasion by a hydrophobic surface due to methyl bonds can realize a lower k-value. Therefore, it is important to control the number of methyl bonds to achieve low-k materials using Me–BCN films. Acknowledgements This study has been supported by JSPS Program “Grants-in-Aid for Scientific Research”. References
Fig. 5. Dependence of the k-value of the Me–BCN films on the peak intensity of C–H absorption (CH3 bonds) in the Me–BCN films.
[1] A. Grill, V. Patel, Appl. Phys. Lett. 79 (2001) 803. [2] L.L. Chapelon, J. Vitiello, D. Neira, J. Torres, J.C. Royer, D. Barbier, F. Naudin, G. Tas, P. Mukundhan, J. Clerico, Microelectron. Eng. 83 (2006) 2346. [3] L. Yunlong, I. Ciofi, L. Carbonell, K. Maex, Z. Tokei, Proc. 45th Reliability physics symposium, IEEE international, 2007, p. 405, Vol., Issue , 15–19. [4] C. Morant, D. Cáceres, J.M. Sanz, E. Elizalde, Diamond Relat. Mater. 16 (2007) 1441.
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H. Aoki et al. / Diamond & Related Materials 19 (2010) 1437–1440
[5] T. Sugiyama, T. Tai, T. Sugino, Appl. Phys. Lett. 80 (2002) 4214. [6] S. Umeda, T. Yuki, T. Sugiyama, T. Sugino, Diamond Relat. Mater. 13 (2004) 1135. [7] M.K. Mazumder, R. Moriyama, D. Watanabe, C. Kimura, H. Aoki, T. Sugino, Jpn. J. Appl. Phys. 46 (2007) 2006. [8] H. Aoki, D. Watanabe, R. Moriyama, M.K. Mazumder, N. Komatsu, C. Kimura, T. Sugino, Diamond Relat. Mater. 17 (2007) 628.
[9] H. Aoki, T. Masuzumi, M. Hara, D. Watanabe, C. Kimura, T. Sugino, Thin Solid Films 518 (2010) 2102. [10] S. Tokuyama, M. Hara, M.K. Mazumder, D. Watanabe, C. Kimura, H. Aoki, T. Sugino, Jpn. J. Appl. Phys. 47 (2008) 2492. [11] H. Aoki, S. Tokuyama, T. Masuzumi, M. Hara, M.K. Mazumder, D. Watanabe, C. Kimura, T. Sugino, Diamond Relat. Mater. 18 (2009) 1048.