REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02C306 (2014)
Development of microwave ion source for industrial applicationsa) N. Takahashi,1,b) H. Murata,1 H. Mitsubori,1 J. Sakuraba,1 T. Soga,1 Y. Aoki,1 T. Katoh,1 Y. Saitoh,2 K. Yamada,2 N. Ikenaga,3 and N. Sakudo3 1
Sumitomo Heavy Industries, Ltd., 19 Natsushima-cho, Yokosuka, Kanagawa 237-8555, Japan Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan 3 Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan 2
(Presented 10 September 2013; received 5 September 2013; accepted 2 October 2013; published online 31 October 2013) A microwave ion source is one of the long-life ion sources. In this paper, we report on the characteristics of the extracted Ar ion beam produced by a microwave ion source under various conditions, in terms of magnetic flux distribution and mass flow, and the stability of the ion beam. The measured spectra show that, under the experimental condition, almost all of produced ions were Ar+ ions. For more than 6 h, the ion beam was stable. © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4826675] I. INTRODUCTION
A microwave ion source is expected to be a maintenancefree and long-life ion source, because of fewer consumable items such as filaments. In addition, highly density plasma has been produced,1 and applied to an ion implantation system.2 Many kinds of ion sources are applied to industrial products, such as film-forming devices, particle cancer therapy systems, and ion implantation systems. There is a possibility that microwave ion sources also can be applied to these products. Therefore, we have been developing the microwave ion source for the purpose of application to industrial products. Below, we report on the evaluation of the spectra of the ions extracted under various mass flows and magnetic flux density distributions as well as on the stability of the ion currents. II. EXPERIMENTAL DETAILS
Experiments were performed at Takasaki Advanced Radiation Research Institute of Japan Atomic Energy Agency (JAEA) in which there is an ion source beam line system. Figure 1 shows a schematic diagram of a cross-sectional view of the microwave ion source that was developed for this study. There were two coils, and the magnetic flux density distribution in the plasma chamber could be tuned by changing the currents, the center position, and the length between the two coils. The plasma chamber had a cylindrical structure, whose inner wall was covered with boron nitride (BN) in order to enhance the emission of secondary electrons. In addition, the wall consisted of a double structure for a water-cooling system. The microwave frequency was 2.45 [GHz] and the maximum power was 1 [kW]. A disk made of alumina was used as a microwave-transmission window. A directional coupler was used in order to evaluate the traveling and the reflected
microwave powers. Argon (Ar) gas was used, for which the mass flow could be adjusted using a mass flow controller. Figure 2 shows a photograph of the ion source beam line system. Faraday cups were installed before and after the analyzing magnet in order to evaluate the total ion beam current and separated current, respectively. The maximum extraction voltage was 10 [kV], and an einzel lens was used as a focusing system. The aperture of the electrode and the length between the electrode and the plasma chamber were optimized in order to achieve better transmittance of the Ar+ beam at the entrance of the analyzing magnet. III. RESULTS AND DISCUSSIONS
Figure 3(a) shows the spectra of the extracted ion beam with various magnetic flux distributions. The horizontal axis and the vertical axis represent the mass-to-charge ratio and the ion beam current, respectively. The microwave power was 500 [W], the mass flow was 0.5 [ccm], and the extraction voltage was 10 [kV]. Figure 3(b) shows the calculated axial magnetic flux density distributions in the center of the
a) Contributed paper, published as part of the Proceedings of the 15th
International Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(2)/02C306/3/$30.00
FIG. 1. A cross-sectional view of the ion source. 85, 02C306-1
© 2013 AIP Publishing LLC
02C306-2
Takahashi et al.
Rev. Sci. Instrum. 85, 02C306 (2014)
FIG. 4. The ratio of Ar+ to Ar2+ beam current. FIG. 2. A photograph of ion-source beam line.
plasma chamber. MW and EX represent the position of the microwave-induced side and the beam-extraction electrode side of the plasma chamber, respectively. Thus, all of the magnetic flux density distributions of the MW side were higher than those of the EX side and decreased from MW to EX monotonically. The black, red, and green lines in Fig. 3(a) and 3(b) correspond to each other.
As a result, it was found that almost all the extracted ions were Ar+ ions for all magnetic flux density distributions. It is assumed that, since the magnetic flux density distributions do not have the effect of confining electrons (as, for example, a magnetic mirror structure dose), there are few electrons that have enough energy to produce highly charged ions. Further, when the magnetic flux density distribution was highest, the highest beam current was obtained.
FIG. 3. (a) The spectra of ion beams. (b) Calculated magnetic flux distributions.
FIG. 5. (a) The stability from a cold start. (b) The stability of the continuous operation.
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Takahashi et al.
Figure 4 plots the ratio of Ar+ beam current to Ar2+ ion current as a function of mass flow. The microwave power was 500 [W] and the extraction voltage was 10 [kV]. The magnetic flux density distribution was optimized in order to make the reflectance of the microwave reflectance at the surface of source plasma as small as possible and stable. As a result, it was found that the Ar+ current was overwhelmingly high under all mass flow conditions. Figure 5(a) shows the evaluation of the stability of the ion beam current from a cold start. The microwave power and magnetic flux density distribution were equivalent to those in Fig. 3. The mass flow was 0.5 [ccm]. The changes of the Ar+ current in about 20 min and 25 min after turning on the ion source as shown in Fig. 5(a) were because of adjustment of the voltage of the einzel lens and the magnetic flux density distribution of the analyzing magnet. The Ar+ current became stable about 30 min after the cold start. Figure 5(b) shows the result of the continuous operation of the microwave ion source. The Ar+ current was reduced
Rev. Sci. Instrum. 85, 02C306 (2014)
by about 1% after about 6 h. However, the magnetic flux density distribution of the analyzing magnet was also reduced by about 0.1% during this period. Therefore, it is difficult to identify the reason for the decrease of the Ar+ current, which may have been caused by the ion source or by a change of the magnetic flux density distribution of the analyzing magnet. IV. CONCLUSIONS
The spectra of Ar plasma with various magnetic flux density distributions and mass flows were evaluated. It was found that almost all of produced ions were Ar+ ions under all experimental conditions. The ion beam became stable about 30 min after the cold start. As a result of continuous operation, the ion beam was reduced about by 1% after 6 h. In the future, ion beams with various kinds of gases will be evaluated. 1 V.
Kopecky, J. Musil, and F. Zacek, Plasma Phys. 17, 1147 (1975). Sakudo, K. Tokiguchi, H. Koike, and I. Kanomata, Rev. Sci. Instrum. 54, 681 (1983).
2 N.
Review of Scientific Instruments is copyrighted by the American Institute of Physics (AIP). Redistribution of journal material is subject to the AIP online journal license and/or AIP copyright. For more information, see http://ojps.aip.org/rsio/rsicr.jsp
Development of microwave ion source for industrial applicationsa) N. Takahashi,1,b) H. Murata,1 H. Mitsubori,1 J. Sakuraba,1 T. Soga,1 Y. Aoki,1 T. Katoh,1 Y. Saitoh,2 K. Yamada,2 N. Ikenaga,3 and N. Sakudo3 1
Sumitomo Heavy Industries, Ltd., 19 Natsushima-cho, Yokosuka, Kanagawa 237-8555, Japan Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan 3 Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan 2
(Presented 10 September 2013; received 5 September 2013; accepted 2 October 2013; published online 31 October 2013) A microwave ion source is one of the long-life ion sources. In this paper, we report on the characteristics of the extracted Ar ion beam produced by a microwave ion source under various conditions, in terms of magnetic flux distribution and mass flow, and the stability of the ion beam. The measured spectra show that, under the experimental condition, almost all of produced ions were Ar+ ions. For more than 6 h, the ion beam was stable. © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4826675] I. INTRODUCTION
A microwave ion source is expected to be a maintenancefree and long-life ion source, because of fewer consumable items such as filaments. In addition, highly density plasma has been produced,1 and applied to an ion implantation system.2 Many kinds of ion sources are applied to industrial products, such as film-forming devices, particle cancer therapy systems, and ion implantation systems. There is a possibility that microwave ion sources also can be applied to these products. Therefore, we have been developing the microwave ion source for the purpose of application to industrial products. Below, we report on the evaluation of the spectra of the ions extracted under various mass flows and magnetic flux density distributions as well as on the stability of the ion currents. II. EXPERIMENTAL DETAILS
Experiments were performed at Takasaki Advanced Radiation Research Institute of Japan Atomic Energy Agency (JAEA) in which there is an ion source beam line system. Figure 1 shows a schematic diagram of a cross-sectional view of the microwave ion source that was developed for this study. There were two coils, and the magnetic flux density distribution in the plasma chamber could be tuned by changing the currents, the center position, and the length between the two coils. The plasma chamber had a cylindrical structure, whose inner wall was covered with boron nitride (BN) in order to enhance the emission of secondary electrons. In addition, the wall consisted of a double structure for a water-cooling system. The microwave frequency was 2.45 [GHz] and the maximum power was 1 [kW]. A disk made of alumina was used as a microwave-transmission window. A directional coupler was used in order to evaluate the traveling and the reflected
microwave powers. Argon (Ar) gas was used, for which the mass flow could be adjusted using a mass flow controller. Figure 2 shows a photograph of the ion source beam line system. Faraday cups were installed before and after the analyzing magnet in order to evaluate the total ion beam current and separated current, respectively. The maximum extraction voltage was 10 [kV], and an einzel lens was used as a focusing system. The aperture of the electrode and the length between the electrode and the plasma chamber were optimized in order to achieve better transmittance of the Ar+ beam at the entrance of the analyzing magnet. III. RESULTS AND DISCUSSIONS
Figure 3(a) shows the spectra of the extracted ion beam with various magnetic flux distributions. The horizontal axis and the vertical axis represent the mass-to-charge ratio and the ion beam current, respectively. The microwave power was 500 [W], the mass flow was 0.5 [ccm], and the extraction voltage was 10 [kV]. Figure 3(b) shows the calculated axial magnetic flux density distributions in the center of the
a) Contributed paper, published as part of the Proceedings of the 15th
International Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(2)/02C306/3/$30.00
FIG. 1. A cross-sectional view of the ion source. 85, 02C306-1
© 2013 AIP Publishing LLC
02C306-2
Takahashi et al.
Rev. Sci. Instrum. 85, 02C306 (2014)
FIG. 4. The ratio of Ar+ to Ar2+ beam current. FIG. 2. A photograph of ion-source beam line.
plasma chamber. MW and EX represent the position of the microwave-induced side and the beam-extraction electrode side of the plasma chamber, respectively. Thus, all of the magnetic flux density distributions of the MW side were higher than those of the EX side and decreased from MW to EX monotonically. The black, red, and green lines in Fig. 3(a) and 3(b) correspond to each other.
As a result, it was found that almost all the extracted ions were Ar+ ions for all magnetic flux density distributions. It is assumed that, since the magnetic flux density distributions do not have the effect of confining electrons (as, for example, a magnetic mirror structure dose), there are few electrons that have enough energy to produce highly charged ions. Further, when the magnetic flux density distribution was highest, the highest beam current was obtained.
FIG. 3. (a) The spectra of ion beams. (b) Calculated magnetic flux distributions.
FIG. 5. (a) The stability from a cold start. (b) The stability of the continuous operation.
02C306-3
Takahashi et al.
Figure 4 plots the ratio of Ar+ beam current to Ar2+ ion current as a function of mass flow. The microwave power was 500 [W] and the extraction voltage was 10 [kV]. The magnetic flux density distribution was optimized in order to make the reflectance of the microwave reflectance at the surface of source plasma as small as possible and stable. As a result, it was found that the Ar+ current was overwhelmingly high under all mass flow conditions. Figure 5(a) shows the evaluation of the stability of the ion beam current from a cold start. The microwave power and magnetic flux density distribution were equivalent to those in Fig. 3. The mass flow was 0.5 [ccm]. The changes of the Ar+ current in about 20 min and 25 min after turning on the ion source as shown in Fig. 5(a) were because of adjustment of the voltage of the einzel lens and the magnetic flux density distribution of the analyzing magnet. The Ar+ current became stable about 30 min after the cold start. Figure 5(b) shows the result of the continuous operation of the microwave ion source. The Ar+ current was reduced
Rev. Sci. Instrum. 85, 02C306 (2014)
by about 1% after about 6 h. However, the magnetic flux density distribution of the analyzing magnet was also reduced by about 0.1% during this period. Therefore, it is difficult to identify the reason for the decrease of the Ar+ current, which may have been caused by the ion source or by a change of the magnetic flux density distribution of the analyzing magnet. IV. CONCLUSIONS
The spectra of Ar plasma with various magnetic flux density distributions and mass flows were evaluated. It was found that almost all of produced ions were Ar+ ions under all experimental conditions. The ion beam became stable about 30 min after the cold start. As a result of continuous operation, the ion beam was reduced about by 1% after 6 h. In the future, ion beams with various kinds of gases will be evaluated. 1 V.
Kopecky, J. Musil, and F. Zacek, Plasma Phys. 17, 1147 (1975). Sakudo, K. Tokiguchi, H. Koike, and I. Kanomata, Rev. Sci. Instrum. 54, 681 (1983).
2 N.
Review of Scientific Instruments is copyrighted by the American Institute of Physics (AIP). Redistribution of journal material is subject to the AIP online journal license and/or AIP copyright. For more information, see http://ojps.aip.org/rsio/rsicr.jsp
