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O2 gas pressure dependence of atomic concentration of zirconia prepared by zirconium pulse arc PBII&D
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 242 (2006) 318–320 www.elsevier.com/locate/nimb
Ar/O2 gas pressure dependence of atomic concentration of zirconia prepared by zirconium pulse arc PBII&D Ken Yukimura
a,*
, Hiroaki Yoshinaga a, Yasunori Ohtsu b, Hiroharu Fujita b, Keiji Nakamura c, Xinxin Ma d
a
c
Department of Electrical Engineering, Doshisha University, 1-3 Tatara-Miyakodani, Kyotanabe, Kyoto 610-0321, Japan b Department of Electrical and Electronic Engineering, Saga University, Honjo-machi1, Saga 840-8502, Japan Department of Electrical Engineering, College of Engineering, Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan d School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China Available online 19 September 2005
Abstract Zirconium oxide films were prepared by plasma-based ion implantation and deposition (PBII&D), where a zirconium pulse arc discharge was generated in O2/Ar gas mixture. The plasma was maintained for approximately 3 ms, and the ion current at the substrate was detected in a time range from 1 to 10 ms after the arc initiation. At O2/Ar pressures of 2.6–3.0 Pa, a stoichiometric film was obtained, while at a pressure lower than 2.2 Pa, the film also contained ZrOx (x < 2) phase as well as ZrO2 phase. In the absence of argon gas, the plasma became unstable, which resulted in shortage of zirconium ions in the plasma, and hence, a stoichiometric condition was not found. 2005 Elsevier B.V. All rights reserved. PACS: 52.77.Dq; 52.80.Mg; 81.05.Je Keywords: PBII&D; Zirconia; Coating; X-ray photoelectron spectroscopy; Pulsed cathodic arc
1. Introduction Using plasma-based ion implantation and metallic arc deposition, referred as PBII&D, three-dimensional components are easily modified. It has been well known that the metallic arc strongly affects the film characteristics due to the plasma species, plasma stability and directivity of the plasma expansion and so on. Conventionally, the deposition of zirconium oxide films have been performed using plasma jet [1], rf magnetron sputtering [2], microwave discharge [3] and rf plasma [4]. In the present study, a pulsed zirconium arc plasma was repetitively generated, and was used to make zirconium ions. Substrates were immersed in the plasma. The purpose
*
Corresponding author. Tel.: +81 774 65 6266; fax: +81 774 65 6816. E-mail address: [email protected] (K. Yukimura).
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.08.052
of this article is to investigate the influence of the background gas and its pressure during the deposition process on the film composition and structure. 2. Experimental The details of the experimental facility are described elsewhere [5]. The vacuum chamber had inner dimensions of 340 mm · 550 mm · 380 mm, and a zirconium cathode with a diameter of 100 mm was set on one of the walls of the vacuum chamber. The zirconium arc was generated by separating a movable pin electrode from the zirconium cathode. The arc was repetitively generated with a rate of 0.25 Hz. A disk-shaped target was 60 mm in diameter and 10 mm in thickness, and (1 1 1)-oriented silicon substrates with a size of 10 mm · 10 mm were pasted on it. The target was set at the same height as the cathodic arc source, and
K. Yukimura et al. / Nucl. Instr. and Meth. in Phys. Res. B 242 (2006) 318–320
was located at a distance of 150 mm from the arc source. A train of negative 5 kV pulse voltage with a duration of 20 ls was applied to the target with a rate of 400 Hz. The timing of the voltage application was not synchronized with the arc generation. Oxygen gas in the presence of argon gas (Ar:O2 = 4:1) or in the absence of argon gas was used as a background gas. The mixed gas pressure was varied from 1.9 to 3.6 Pa, by varying a flow rate from 100 to 500 sccm. The process time was 3.5 min. In order to analyze the composition and the chemical state of the prepared films, X-ray photoelectron spectroscopy (XPS) was employed. Before analyzing, the films were etched by argon ions for 2 min. 3. Results 3.1. Plasma parameters The arc current was approximately 20 A, and the sum of a series resistance and arc resistance is 1.65 X. The electric power consumed in the plasma was approximately 290 W. The average life time of the arc was approximately 3.1 ms. Hence, the energy consumed in the plasma was 0.86 J per shot. The average plasma density at the target over a time range of 1–10 ms after the arc initiation was approximately 1010 cm 3, which is derived by the temporal behavior of the target voltage [6]. Fig. 1 shows a waveform of the ion current at an applied target voltage of 1 kV. The voltage waveform was in a rectangular shape. The current has a sharp peak at the initial stage due to charging the stray- and ion sheath-capacitances, and then is in a stationary state. The ion current was detected for approximately 1–10 ms after the arc initiation. It was found that the stationary ion current was typically 0.5 A at a pressure of 2.2 Pa, and tends to decrease with increasing the gas pressure.
319
3.2. Zirconia film deposition in argon diluted oxygen gas The atomic concentration of the deposited films was changed by O2/Ar mixed gas pressures of 1.9–3.6 Pa. With increasing the pressure, the rate of oxygen in the films increases from 65 to 70 at.% with the pressure from 1.9 to 3.6 Pa. The zirconium atomic ratio decreases from 35 to 30 at.%, and hence, the element ratio of O to Zr increases from 1.9 to 2.3. A stoichiometric film is prepared at pressures of 2.6–3.0 Pa. The rate of O content in the deposited films increases with the pressure due to increase of oxygen particles, the suppression of the plasma diffusion, and the collision between the zirconium ions and neutrals in the plasma. Fig. 2 shows XPS spectra of 3d3/2 and 3d5/2 of zirconia film deposited at O2/Ar mixed gas pressures of 1.9 to 3.6 Pa. Each spectrum is curve-fitted using Gaussian functions peaking at binding energies of 186 eV of Zr 3d3/2 and 184 eV of Zr 3d5/2, corresponding to ZrO2. At pressures of 1.9 and 2.2 Pa, one more Gaussian function with a peak at 182 eV is added, which corresponds to ZrOx 3d5/2. It is seen from Fig. 2 that only ZrO2 component is observed in a high pressure region from 2.6 to 3.6 Pa, while ZrOx phase is also observed at pressures lower than 2.2 Pa in addition to the ZrO2 component. This shows a shortage of oxygen particles. A zirconium oxide film was prepared in pure oxygen circumstance. In this case, the plasma was unstable probably due to both electron attachment with oxygen and decrease of the sputtering rate at the cathode surface to remove zirconium oxide layer. The stationary ion current in this case became lower by a factor of 3 compared to that of the mixed gas condition under the identical pressure. The
10000
ZrO2 3d3/2
8000
ZrO2 3d5/2
ZrOx 3d5/2
6000 4000 2000 2.0
Intensity [cps]
2.2 Pa 1.5
Ion current [A]
1.9Pa
0 4000
1.0
2000
2.2 Pa
0 4000 2000
2.6Pa
0 4000
0.5
2000
-0.5 -10
3.0 Pa
0 4000
0
0
10
20
30
40
Time [µs] Fig. 1. A waveform of the ion current at a pressure of 2.2 Pa for a delay time of 5.4 ms after the arc initiation and an applied voltage of 1 kV.
2000 0
3.6 Pa
190
185
180
175
Binding energy [eV] Fig. 2. XPS spectra of ZrO2 3d3/2 and ZrO2 3d5/2 at an etching time of 2 min for the zirconia film prepared in Ar/O2 mixtures.
320
K. Yukimura et al. / Nucl. Instr. and Meth. in Phys. Res. B 242 (2006) 318–320
element ratio of O to Zr is only approximately 1.5, showing the shortage of oxygen. The prepared film included silicon spectra, which is observed in a wide scan of the XPS spectra. In a narrow scan of O 1s spectrum, a peak at 532.75 eV, caused by SiO2 was also observed. This suggests that the deposited film thickness is too thin to cover the entire area of the substrate.
Acknowledgments
4. Summary
References
A zirconium oxide film was prepared by PBII&D using a zirconium pulse arc discharge plasma in oxygen gas circumstance with and without argon. The average life time of the arc was approximately 3 ms, while the ion current was observed for 1–10 ms. At a proper O2/Ar mixed gas pressure, the prepared film is stoichiometric at a pressure of 2.6–3.0 Pa. With decreasing the O2/Ar pressure, oxygen is in shortage, which results in appearing ZrOx (x < 2) components. In the absence of argon gas, the plasma is unstable, and as a result, SiO2 components is found.
[1] Y. Ando, S. Tobe, H. Tahara, T. Yoshikawa, in: Conference Proceedings of International Thermal Spray Conference 2002, p. 112. [2] D.H. Kuo, C.H. Chien, C.H. Huang, Thin Solid Films 420–421 (2002) 47. [3] B. Pre´auchat, S. Drain, Surf. Coat. Technol. 142–144 (2001) 835. [4] Y. Ohtsu, M. Egami, T. Misawa, H. Fujita, K. Yukimura, Surf. Coat. Technol. 196 (2005) 81. [5] M. Sano, T. Teramoto, K. Yukimura, T. Maruyama, Surf. Coat. Technol. 128–129 (2000) 245. [6] S. Watanabe, T. Tanaka, T. Takagi, K. Yukimura, Surf. Coat. Technol. 186 (2004) 53.
The authors wish to thank Dr. T. Nakamura (Kyoto Prefectual Comprehensive Center For Small and Medium Enterprises) and Dr. M. Sasaki (Industrial Research Center of Shiga Prefecture) for excellent evaluation of the prepared films.
Nuclear Instruments and Methods in Physics Research B 242 (2006) 318–320 www.elsevier.com/locate/nimb
Ar/O2 gas pressure dependence of atomic concentration of zirconia prepared by zirconium pulse arc PBII&D Ken Yukimura
a,*
, Hiroaki Yoshinaga a, Yasunori Ohtsu b, Hiroharu Fujita b, Keiji Nakamura c, Xinxin Ma d
a
c
Department of Electrical Engineering, Doshisha University, 1-3 Tatara-Miyakodani, Kyotanabe, Kyoto 610-0321, Japan b Department of Electrical and Electronic Engineering, Saga University, Honjo-machi1, Saga 840-8502, Japan Department of Electrical Engineering, College of Engineering, Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan d School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China Available online 19 September 2005
Abstract Zirconium oxide films were prepared by plasma-based ion implantation and deposition (PBII&D), where a zirconium pulse arc discharge was generated in O2/Ar gas mixture. The plasma was maintained for approximately 3 ms, and the ion current at the substrate was detected in a time range from 1 to 10 ms after the arc initiation. At O2/Ar pressures of 2.6–3.0 Pa, a stoichiometric film was obtained, while at a pressure lower than 2.2 Pa, the film also contained ZrOx (x < 2) phase as well as ZrO2 phase. In the absence of argon gas, the plasma became unstable, which resulted in shortage of zirconium ions in the plasma, and hence, a stoichiometric condition was not found. 2005 Elsevier B.V. All rights reserved. PACS: 52.77.Dq; 52.80.Mg; 81.05.Je Keywords: PBII&D; Zirconia; Coating; X-ray photoelectron spectroscopy; Pulsed cathodic arc
1. Introduction Using plasma-based ion implantation and metallic arc deposition, referred as PBII&D, three-dimensional components are easily modified. It has been well known that the metallic arc strongly affects the film characteristics due to the plasma species, plasma stability and directivity of the plasma expansion and so on. Conventionally, the deposition of zirconium oxide films have been performed using plasma jet [1], rf magnetron sputtering [2], microwave discharge [3] and rf plasma [4]. In the present study, a pulsed zirconium arc plasma was repetitively generated, and was used to make zirconium ions. Substrates were immersed in the plasma. The purpose
*
Corresponding author. Tel.: +81 774 65 6266; fax: +81 774 65 6816. E-mail address: [email protected] (K. Yukimura).
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.08.052
of this article is to investigate the influence of the background gas and its pressure during the deposition process on the film composition and structure. 2. Experimental The details of the experimental facility are described elsewhere [5]. The vacuum chamber had inner dimensions of 340 mm · 550 mm · 380 mm, and a zirconium cathode with a diameter of 100 mm was set on one of the walls of the vacuum chamber. The zirconium arc was generated by separating a movable pin electrode from the zirconium cathode. The arc was repetitively generated with a rate of 0.25 Hz. A disk-shaped target was 60 mm in diameter and 10 mm in thickness, and (1 1 1)-oriented silicon substrates with a size of 10 mm · 10 mm were pasted on it. The target was set at the same height as the cathodic arc source, and
K. Yukimura et al. / Nucl. Instr. and Meth. in Phys. Res. B 242 (2006) 318–320
was located at a distance of 150 mm from the arc source. A train of negative 5 kV pulse voltage with a duration of 20 ls was applied to the target with a rate of 400 Hz. The timing of the voltage application was not synchronized with the arc generation. Oxygen gas in the presence of argon gas (Ar:O2 = 4:1) or in the absence of argon gas was used as a background gas. The mixed gas pressure was varied from 1.9 to 3.6 Pa, by varying a flow rate from 100 to 500 sccm. The process time was 3.5 min. In order to analyze the composition and the chemical state of the prepared films, X-ray photoelectron spectroscopy (XPS) was employed. Before analyzing, the films were etched by argon ions for 2 min. 3. Results 3.1. Plasma parameters The arc current was approximately 20 A, and the sum of a series resistance and arc resistance is 1.65 X. The electric power consumed in the plasma was approximately 290 W. The average life time of the arc was approximately 3.1 ms. Hence, the energy consumed in the plasma was 0.86 J per shot. The average plasma density at the target over a time range of 1–10 ms after the arc initiation was approximately 1010 cm 3, which is derived by the temporal behavior of the target voltage [6]. Fig. 1 shows a waveform of the ion current at an applied target voltage of 1 kV. The voltage waveform was in a rectangular shape. The current has a sharp peak at the initial stage due to charging the stray- and ion sheath-capacitances, and then is in a stationary state. The ion current was detected for approximately 1–10 ms after the arc initiation. It was found that the stationary ion current was typically 0.5 A at a pressure of 2.2 Pa, and tends to decrease with increasing the gas pressure.
319
3.2. Zirconia film deposition in argon diluted oxygen gas The atomic concentration of the deposited films was changed by O2/Ar mixed gas pressures of 1.9–3.6 Pa. With increasing the pressure, the rate of oxygen in the films increases from 65 to 70 at.% with the pressure from 1.9 to 3.6 Pa. The zirconium atomic ratio decreases from 35 to 30 at.%, and hence, the element ratio of O to Zr increases from 1.9 to 2.3. A stoichiometric film is prepared at pressures of 2.6–3.0 Pa. The rate of O content in the deposited films increases with the pressure due to increase of oxygen particles, the suppression of the plasma diffusion, and the collision between the zirconium ions and neutrals in the plasma. Fig. 2 shows XPS spectra of 3d3/2 and 3d5/2 of zirconia film deposited at O2/Ar mixed gas pressures of 1.9 to 3.6 Pa. Each spectrum is curve-fitted using Gaussian functions peaking at binding energies of 186 eV of Zr 3d3/2 and 184 eV of Zr 3d5/2, corresponding to ZrO2. At pressures of 1.9 and 2.2 Pa, one more Gaussian function with a peak at 182 eV is added, which corresponds to ZrOx 3d5/2. It is seen from Fig. 2 that only ZrO2 component is observed in a high pressure region from 2.6 to 3.6 Pa, while ZrOx phase is also observed at pressures lower than 2.2 Pa in addition to the ZrO2 component. This shows a shortage of oxygen particles. A zirconium oxide film was prepared in pure oxygen circumstance. In this case, the plasma was unstable probably due to both electron attachment with oxygen and decrease of the sputtering rate at the cathode surface to remove zirconium oxide layer. The stationary ion current in this case became lower by a factor of 3 compared to that of the mixed gas condition under the identical pressure. The
10000
ZrO2 3d3/2
8000
ZrO2 3d5/2
ZrOx 3d5/2
6000 4000 2000 2.0
Intensity [cps]
2.2 Pa 1.5
Ion current [A]
1.9Pa
0 4000
1.0
2000
2.2 Pa
0 4000 2000
2.6Pa
0 4000
0.5
2000
-0.5 -10
3.0 Pa
0 4000
0
0
10
20
30
40
Time [µs] Fig. 1. A waveform of the ion current at a pressure of 2.2 Pa for a delay time of 5.4 ms after the arc initiation and an applied voltage of 1 kV.
2000 0
3.6 Pa
190
185
180
175
Binding energy [eV] Fig. 2. XPS spectra of ZrO2 3d3/2 and ZrO2 3d5/2 at an etching time of 2 min for the zirconia film prepared in Ar/O2 mixtures.
320
K. Yukimura et al. / Nucl. Instr. and Meth. in Phys. Res. B 242 (2006) 318–320
element ratio of O to Zr is only approximately 1.5, showing the shortage of oxygen. The prepared film included silicon spectra, which is observed in a wide scan of the XPS spectra. In a narrow scan of O 1s spectrum, a peak at 532.75 eV, caused by SiO2 was also observed. This suggests that the deposited film thickness is too thin to cover the entire area of the substrate.
Acknowledgments
4. Summary
References
A zirconium oxide film was prepared by PBII&D using a zirconium pulse arc discharge plasma in oxygen gas circumstance with and without argon. The average life time of the arc was approximately 3 ms, while the ion current was observed for 1–10 ms. At a proper O2/Ar mixed gas pressure, the prepared film is stoichiometric at a pressure of 2.6–3.0 Pa. With decreasing the O2/Ar pressure, oxygen is in shortage, which results in appearing ZrOx (x < 2) components. In the absence of argon gas, the plasma is unstable, and as a result, SiO2 components is found.
[1] Y. Ando, S. Tobe, H. Tahara, T. Yoshikawa, in: Conference Proceedings of International Thermal Spray Conference 2002, p. 112. [2] D.H. Kuo, C.H. Chien, C.H. Huang, Thin Solid Films 420–421 (2002) 47. [3] B. Pre´auchat, S. Drain, Surf. Coat. Technol. 142–144 (2001) 835. [4] Y. Ohtsu, M. Egami, T. Misawa, H. Fujita, K. Yukimura, Surf. Coat. Technol. 196 (2005) 81. [5] M. Sano, T. Teramoto, K. Yukimura, T. Maruyama, Surf. Coat. Technol. 128–129 (2000) 245. [6] S. Watanabe, T. Tanaka, T. Takagi, K. Yukimura, Surf. Coat. Technol. 186 (2004) 53.
The authors wish to thank Dr. T. Nakamura (Kyoto Prefectual Comprehensive Center For Small and Medium Enterprises) and Dr. M. Sasaki (Industrial Research Center of Shiga Prefecture) for excellent evaluation of the prepared films.