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H2 carrier gas dependence of Young's modulus and hardness of chemical vapor deposited polycrystalline 3C-SiC thin films
ARTICLE IN PRESS Microelectronics Journal 39 (2008) 1413– 1415
Contents lists available at ScienceDirect
Microelectronics Journal journal homepage: www.elsevier.com/locate/mejo
H2 carrier gas dependence of Young’s modulus and hardness of chemical vapor deposited polycrystalline 3C-SiC thin films Gwiy-Sang Chung , Ki-Bong Han School of Electrical Engineering, University of Ulsan, San 29, Mugerdong, Namgu, Ulsan 680-749, Republic of Korea
a r t i c l e in fo
abstract
Article history: Received 20 March 2008 Accepted 14 June 2008 Available online 5 August 2008
This paper presents the mechanical properties of poly (polycrystalline) 3C-SiC thin films according to 0%, 7%, and 10% carrier gas (H2) concentrations using nano-indentation. When H2 concentration was 10%, it has been proved that the mechanical properties, Young’s modulus, and hardness of poly 3C-SiC films are the best of them. In the case of 10% H2 concentration, Young’s Modulus and hardness were obtained as 367 and 36 GPa, respectively. The surface roughness according to H2 concentrations was investigated by AFM (atomic force microscope). When H2 concentration was 10%, the roughness of 3C-SiC thins was 9.92 nm, which is also the best of them. Therefore, in order to apply poly 3C-SiC thin films to MEMS (micro-electromechanical system) applications, H2 concentration’s rate should increase to obtain better mechanical properties and surface roughness. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Poly 3C-SiC Nano-indentation AFM Young’s modulus Hardness
1. Introduction 3C-SiC thin film has been an important semiconductor material for high-temperature, high-voltage electronics and harsh environment in the past two decades [1]. Recently, this material has been applied to MEMS (micro-electromechanical system) in harsh environment [2]. 3C-SiC thin film is more suitable for harsh environment application due to the outstanding mechanical and chemical properties of 3C-SiC compared to Si. Although SiC exists in numerous polytypes, only three types are commercially used for device fabrication. The three types are the cubic 3C-SiC, hexagonal 6H-SiC, and 4H-SiC. It is difficult to etch bulk SiC because 6H- and 4H-SiC subsist in single crystal wafer form. Consequently, it is hard to fabricate micro-mechanical structures from them. However, 3C-SiC is the only polytype that can be epitaxially grown in single crystal form on Si substrates [3]. Fabricating micro-mechanical structures from single crystal films is possible, since conventional Si bulk micromachining techniques can selectively remove the substrate [4]. For MEMS applications, the mechanical properties of 3C-SiC thin film, such as the elastic modulus and hardness, are as important as surface roughness. In a growth process, temperature, pressure, gas flow rate and carrier gas (H2) concentration have influence on the quality of 3C-SiC thin film. Above all, the mechanical properties are dependent on carrier gas (H2) concentration. However, previously the research did not measure mechanical properties such as elastic modulus
Corresponding author. Tel.: +82 52 259 1248; fax: +82 52 259 1686.
E-mail address: [email protected] (G.-S. Chung). 0026-2692/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2008.06.062
and hardness. 3C-SiC thin film’s mechanical properties are required in the MEMS designing stage, because it is needed in accurately measuring elastic modulus and hardness. The elastic modulus has influence on mechanical strength and hardness is related to abrasion. Several methods have been developed to evaluate the mechanical properties of thin film. Among them, bulge test was applied to determine residual stress and elastic modulus of 3C-SiC thin film [5]. The measurement of deflection or resonant frequencies of micro-cantilever beams was determined by the elastic modulus of 3C-SiC thin film [6]. Micro-tensile test was performed to determine both elastic modulus and Poisson’s ratio of 3C-SiC thin film [7]. Nano-indentation has also been used for the elastic modulus and hardness of 3C-SiC thin film. But, these methods have not been used to work the 3C-SiC thin films according to growth conditions. In this paper, the mechanical properties of the grown poly (polycrystalline) 3C-SiC thin films according to the carrier gas (H2) concentration were measured by nano-indentation test, as well as roughness of 3C-SiC thin films by AFM (atomic force microscope) and both have been compared.
2. Experiment 3C-SiC thin films were grown on Si(1 0 0) wafers by APCVD (atmospheric pressure chemical vapor deposition) at 1100 1C. HMDS((CH3)6Si2, purity: 99.99%) were used as Si- and C-containing precursors, and H2 and Ar were used as carrier gases. 3C-SiC thin films were grown by the carrier gas (H2) concentrations
ARTICLE IN PRESS 1414
G.-S. Chung, K.-B. Han / Microelectronics Journal 39 (2008) 1413–1415
Fig. 1. Surface photography of poly 3C-SiC thin films grown on thermally oxidized Si wafer.
Fig. 3. Cross-section SEM images of the grown polycrystalline 3C-SiC thin films according to H2 concentrations of (a) 0%, (b) 70%, and (c) 100%.
Fig. 4. AFM images of 3C-SiC thin films according to carrier gas (H2) concentrations of (a) 0%, (b) 7%, and (c) 10%. Fig. 2. The position of measured nano-indenter.
of 0%, 7% , and 10%. Fig. 1 shows the poly 3C-SiC thin films grown on Si(1 0 0) wafers. The mechanical properties, elastic modulus and hardness of the poly 3C-SiC thin film were measured using the CSM (continuous stiffness measurement) model of nano-indentor DCM. The indentor tip used for this experiment was a Diamond Berkovich tip. Fig. 2 shows the measurement position of nanoindentor and how to obtain the mechanical properties, Young’s modulus and Hardness, which are calculated by the average values of nano intents of 9 points on a thin film sample. The interval of position of nano-indentor is 80 mm in order to minimize influence of near indent depths. From the mechanical data of 3C-SiC, it was assumed that Poisson ratio of the poly 3C-SiC is 0.16. In this paper, elastic modulus and hardness by nano-indentation are measured in order to understand the mechanical properties of 3C-SiC thin films according to carrier gas (H2) concentration of 0%, 7%, and 10%. So, SEM and AFM images were analyzed in order to investigate the surfaces of 3C-SiC according to carrier gas (H2) concentrations.
3. Results and discussion Fig. 3 shows the cross-section of SEM images of the grown polycrystalline 3C-SiC thin films according to H2 concentration. In the case of high carrier gas (H2) rate, the density and uniformity of 3C-SiC thin film is better than others. AFM images are used to measure the roughness of the poly 3C-SiC thin films. AFM images of 3C-SiC thin film according to H2 concentration are shown in Fig. 4. We have measured the roughness of ploy 3C-SiC thin films and their values are 61.7 nm for 0%, 10.65 nm for 7%, and 9.92 nm for 10% carrier gas (H2) concentrations, respectively. In the case of high carrier gas (H2) rate, the roughness of 3C-SiC thin films is smaller than others. Fig. 5 shows that Young’s modulus values were measured by the nano-indentation for the 3C-SiC thin films according to H2
Fig. 5. Young’s modulus values according to H2 concentrations of (a) 0%, (b) 7% and (c) 10%.
concentration of (a) 0%, (b) 7% and (c) 10%. As shown in Fig. 5, their values are 276 GPa for 0%, 304 GPa for 7%, and 367 GPa for 10% carrier gas (H2) concentrations, respectively. We know that Young’s modulus of the 3C-SiC thin films is improved by increasing in carrier gas (H2) concentration. Fig. 6 shows that the hardness was measured by the nanoindentation for the 3C-SiC thin films according to H2 concentration each (a) 0, (b) 7 and (c) 10%. As shown in Fig. 5, their values are 28.3 GPa for 0%, 30.65 GPa for 7%, and 36 GPa for 10% carrier gas (H2) concentrations, respectively. Also, we know that the hardness of the 3C-SiC thin film is improved by increase in carrier gas (H2) concentration. From nano-indentation measurement of the SEM and AFM analyses, it can be proved that the mechanical properties of the poly 3C-SiC thin film are improved by the increase in carrier gas
ARTICLE IN PRESS G.-S. Chung, K.-B. Han / Microelectronics Journal 39 (2008) 1413–1415
1415
hardness increase because the more the carrier gas (H2) concentration increases, the more improved is combined Si and C. Thus, the mechanical properties and roughness of 3C-SiC thin film can be improved by the carrier gas (H2) concentration. It is applied to RF and Bio-material in micro-/nano-electronic mechanical systems (M/NEMS) in harsh environment.
Acknowledgments This research was supported by the Program for the Training of Graduate Students in Regional Innovation, which was conducted by the Ministry of Commerce, Industry, and Energy of the Korean Government, and post-BK (Brain Korea) 21 program, MOE (Ministry of Education and Human Resources Development), and MOCIE (Ministry of Commerce, Industry and Energy), respectively. Fig. 6. Hardness values according to H2 concentrations of (a) 0%, (b) 7% and (c) 10%.
(H2) concentration and they are consistent with the expectation of SEM and AFM analyses.
4. Conclusion The elastic modulus and hardness of 3C-SiC thin films according to carrier gas (H2) concentration were measured by nano-indentation method. The density uniformity and the roughness of 3C-SiC thin films have been investigated by SEM and AFM analyses. The roughness size decreases according to the decrease in carrier gas (H2) concentration. In contrast, Young’s modulus and
References [1] J.A. Powell, L.G. Matus, Recent developments in SiC, in: Proceedings of the 1st International Conference on Amorphous & Crystalline Silicon Carbide & Related Materials, 1989, pp. 2–12. [2] K.M. Jackson, J. Dunning, A. Zorman, Fracture strength, elastic modulus and Poisson’s ratio of polycrystalline 3C-SiC thin-film silicon carbide found by micro sample tensile testing, J. Micro Electro Mech. Sys. 14 (2005) 664–672. [3] S. Nishino, J.A. Powell, H.A. Will, Production of large-area single-crystal wafers of cubic SiC for semiconductor devices, Appl. Phys. Lett. 42 (1983) 460–467. [4] J.A. Powell, L.G. Matus, J.B. Petit, Progress in silicon carbide semiconductor technology, Mat. Soc. Symp. Proc. 242 (1992) 495–505. [5] J.J. Vlassak, W.D. Nix, A new bulge test technique for the determination of Young’s modulus and Poisson’s ratio of thin films, J. Mater. Res. 7 (1992) 3242–3249. [6] J. Koskinen, Microtensile testing of free-standing polysilicon fibers of various grain sizes, J. Micromech. Microeng. 3 (1993) 13–17. [7] J.S. Mitchell, C.A. Zorman, T. Kicher, S. Roy, M. Mehregany, Examination of the bulge test for determining residual stress, Young’s modulus and Poisson’s ratio of 3C-SiC thin films, J. Aerospace Eng. 16 (2003) 46–54.
Contents lists available at ScienceDirect
Microelectronics Journal journal homepage: www.elsevier.com/locate/mejo
H2 carrier gas dependence of Young’s modulus and hardness of chemical vapor deposited polycrystalline 3C-SiC thin films Gwiy-Sang Chung , Ki-Bong Han School of Electrical Engineering, University of Ulsan, San 29, Mugerdong, Namgu, Ulsan 680-749, Republic of Korea
a r t i c l e in fo
abstract
Article history: Received 20 March 2008 Accepted 14 June 2008 Available online 5 August 2008
This paper presents the mechanical properties of poly (polycrystalline) 3C-SiC thin films according to 0%, 7%, and 10% carrier gas (H2) concentrations using nano-indentation. When H2 concentration was 10%, it has been proved that the mechanical properties, Young’s modulus, and hardness of poly 3C-SiC films are the best of them. In the case of 10% H2 concentration, Young’s Modulus and hardness were obtained as 367 and 36 GPa, respectively. The surface roughness according to H2 concentrations was investigated by AFM (atomic force microscope). When H2 concentration was 10%, the roughness of 3C-SiC thins was 9.92 nm, which is also the best of them. Therefore, in order to apply poly 3C-SiC thin films to MEMS (micro-electromechanical system) applications, H2 concentration’s rate should increase to obtain better mechanical properties and surface roughness. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Poly 3C-SiC Nano-indentation AFM Young’s modulus Hardness
1. Introduction 3C-SiC thin film has been an important semiconductor material for high-temperature, high-voltage electronics and harsh environment in the past two decades [1]. Recently, this material has been applied to MEMS (micro-electromechanical system) in harsh environment [2]. 3C-SiC thin film is more suitable for harsh environment application due to the outstanding mechanical and chemical properties of 3C-SiC compared to Si. Although SiC exists in numerous polytypes, only three types are commercially used for device fabrication. The three types are the cubic 3C-SiC, hexagonal 6H-SiC, and 4H-SiC. It is difficult to etch bulk SiC because 6H- and 4H-SiC subsist in single crystal wafer form. Consequently, it is hard to fabricate micro-mechanical structures from them. However, 3C-SiC is the only polytype that can be epitaxially grown in single crystal form on Si substrates [3]. Fabricating micro-mechanical structures from single crystal films is possible, since conventional Si bulk micromachining techniques can selectively remove the substrate [4]. For MEMS applications, the mechanical properties of 3C-SiC thin film, such as the elastic modulus and hardness, are as important as surface roughness. In a growth process, temperature, pressure, gas flow rate and carrier gas (H2) concentration have influence on the quality of 3C-SiC thin film. Above all, the mechanical properties are dependent on carrier gas (H2) concentration. However, previously the research did not measure mechanical properties such as elastic modulus
Corresponding author. Tel.: +82 52 259 1248; fax: +82 52 259 1686.
E-mail address: [email protected] (G.-S. Chung). 0026-2692/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2008.06.062
and hardness. 3C-SiC thin film’s mechanical properties are required in the MEMS designing stage, because it is needed in accurately measuring elastic modulus and hardness. The elastic modulus has influence on mechanical strength and hardness is related to abrasion. Several methods have been developed to evaluate the mechanical properties of thin film. Among them, bulge test was applied to determine residual stress and elastic modulus of 3C-SiC thin film [5]. The measurement of deflection or resonant frequencies of micro-cantilever beams was determined by the elastic modulus of 3C-SiC thin film [6]. Micro-tensile test was performed to determine both elastic modulus and Poisson’s ratio of 3C-SiC thin film [7]. Nano-indentation has also been used for the elastic modulus and hardness of 3C-SiC thin film. But, these methods have not been used to work the 3C-SiC thin films according to growth conditions. In this paper, the mechanical properties of the grown poly (polycrystalline) 3C-SiC thin films according to the carrier gas (H2) concentration were measured by nano-indentation test, as well as roughness of 3C-SiC thin films by AFM (atomic force microscope) and both have been compared.
2. Experiment 3C-SiC thin films were grown on Si(1 0 0) wafers by APCVD (atmospheric pressure chemical vapor deposition) at 1100 1C. HMDS((CH3)6Si2, purity: 99.99%) were used as Si- and C-containing precursors, and H2 and Ar were used as carrier gases. 3C-SiC thin films were grown by the carrier gas (H2) concentrations
ARTICLE IN PRESS 1414
G.-S. Chung, K.-B. Han / Microelectronics Journal 39 (2008) 1413–1415
Fig. 1. Surface photography of poly 3C-SiC thin films grown on thermally oxidized Si wafer.
Fig. 3. Cross-section SEM images of the grown polycrystalline 3C-SiC thin films according to H2 concentrations of (a) 0%, (b) 70%, and (c) 100%.
Fig. 4. AFM images of 3C-SiC thin films according to carrier gas (H2) concentrations of (a) 0%, (b) 7%, and (c) 10%. Fig. 2. The position of measured nano-indenter.
of 0%, 7% , and 10%. Fig. 1 shows the poly 3C-SiC thin films grown on Si(1 0 0) wafers. The mechanical properties, elastic modulus and hardness of the poly 3C-SiC thin film were measured using the CSM (continuous stiffness measurement) model of nano-indentor DCM. The indentor tip used for this experiment was a Diamond Berkovich tip. Fig. 2 shows the measurement position of nanoindentor and how to obtain the mechanical properties, Young’s modulus and Hardness, which are calculated by the average values of nano intents of 9 points on a thin film sample. The interval of position of nano-indentor is 80 mm in order to minimize influence of near indent depths. From the mechanical data of 3C-SiC, it was assumed that Poisson ratio of the poly 3C-SiC is 0.16. In this paper, elastic modulus and hardness by nano-indentation are measured in order to understand the mechanical properties of 3C-SiC thin films according to carrier gas (H2) concentration of 0%, 7%, and 10%. So, SEM and AFM images were analyzed in order to investigate the surfaces of 3C-SiC according to carrier gas (H2) concentrations.
3. Results and discussion Fig. 3 shows the cross-section of SEM images of the grown polycrystalline 3C-SiC thin films according to H2 concentration. In the case of high carrier gas (H2) rate, the density and uniformity of 3C-SiC thin film is better than others. AFM images are used to measure the roughness of the poly 3C-SiC thin films. AFM images of 3C-SiC thin film according to H2 concentration are shown in Fig. 4. We have measured the roughness of ploy 3C-SiC thin films and their values are 61.7 nm for 0%, 10.65 nm for 7%, and 9.92 nm for 10% carrier gas (H2) concentrations, respectively. In the case of high carrier gas (H2) rate, the roughness of 3C-SiC thin films is smaller than others. Fig. 5 shows that Young’s modulus values were measured by the nano-indentation for the 3C-SiC thin films according to H2
Fig. 5. Young’s modulus values according to H2 concentrations of (a) 0%, (b) 7% and (c) 10%.
concentration of (a) 0%, (b) 7% and (c) 10%. As shown in Fig. 5, their values are 276 GPa for 0%, 304 GPa for 7%, and 367 GPa for 10% carrier gas (H2) concentrations, respectively. We know that Young’s modulus of the 3C-SiC thin films is improved by increasing in carrier gas (H2) concentration. Fig. 6 shows that the hardness was measured by the nanoindentation for the 3C-SiC thin films according to H2 concentration each (a) 0, (b) 7 and (c) 10%. As shown in Fig. 5, their values are 28.3 GPa for 0%, 30.65 GPa for 7%, and 36 GPa for 10% carrier gas (H2) concentrations, respectively. Also, we know that the hardness of the 3C-SiC thin film is improved by increase in carrier gas (H2) concentration. From nano-indentation measurement of the SEM and AFM analyses, it can be proved that the mechanical properties of the poly 3C-SiC thin film are improved by the increase in carrier gas
ARTICLE IN PRESS G.-S. Chung, K.-B. Han / Microelectronics Journal 39 (2008) 1413–1415
1415
hardness increase because the more the carrier gas (H2) concentration increases, the more improved is combined Si and C. Thus, the mechanical properties and roughness of 3C-SiC thin film can be improved by the carrier gas (H2) concentration. It is applied to RF and Bio-material in micro-/nano-electronic mechanical systems (M/NEMS) in harsh environment.
Acknowledgments This research was supported by the Program for the Training of Graduate Students in Regional Innovation, which was conducted by the Ministry of Commerce, Industry, and Energy of the Korean Government, and post-BK (Brain Korea) 21 program, MOE (Ministry of Education and Human Resources Development), and MOCIE (Ministry of Commerce, Industry and Energy), respectively. Fig. 6. Hardness values according to H2 concentrations of (a) 0%, (b) 7% and (c) 10%.
(H2) concentration and they are consistent with the expectation of SEM and AFM analyses.
4. Conclusion The elastic modulus and hardness of 3C-SiC thin films according to carrier gas (H2) concentration were measured by nano-indentation method. The density uniformity and the roughness of 3C-SiC thin films have been investigated by SEM and AFM analyses. The roughness size decreases according to the decrease in carrier gas (H2) concentration. In contrast, Young’s modulus and
References [1] J.A. Powell, L.G. Matus, Recent developments in SiC, in: Proceedings of the 1st International Conference on Amorphous & Crystalline Silicon Carbide & Related Materials, 1989, pp. 2–12. [2] K.M. Jackson, J. Dunning, A. Zorman, Fracture strength, elastic modulus and Poisson’s ratio of polycrystalline 3C-SiC thin-film silicon carbide found by micro sample tensile testing, J. Micro Electro Mech. Sys. 14 (2005) 664–672. [3] S. Nishino, J.A. Powell, H.A. Will, Production of large-area single-crystal wafers of cubic SiC for semiconductor devices, Appl. Phys. Lett. 42 (1983) 460–467. [4] J.A. Powell, L.G. Matus, J.B. Petit, Progress in silicon carbide semiconductor technology, Mat. Soc. Symp. Proc. 242 (1992) 495–505. [5] J.J. Vlassak, W.D. Nix, A new bulge test technique for the determination of Young’s modulus and Poisson’s ratio of thin films, J. Mater. Res. 7 (1992) 3242–3249. [6] J. Koskinen, Microtensile testing of free-standing polysilicon fibers of various grain sizes, J. Micromech. Microeng. 3 (1993) 13–17. [7] J.S. Mitchell, C.A. Zorman, T. Kicher, S. Roy, M. Mehregany, Examination of the bulge test for determining residual stress, Young’s modulus and Poisson’s ratio of 3C-SiC thin films, J. Aerospace Eng. 16 (2003) 46–54.