JP6124709B2 - Microwave ion source - Google Patents

Description

  The present invention relates to a microwave ion source.

  Ion sources that use microwaves for plasma generation are known. Microwave is introduced into the vacuum plasma chamber. The source gas supplied to the plasma chamber is excited by microwaves to generate plasma. Ions are extracted from the plasma. The ions thus extracted from the ion source are used, for example, for an ion implantation process.

JP-A-1-219161 JP-A-60-140635

  The microwave ion source is generally provided with a coil surrounding the periphery of the plasma chamber. The coil generates an axial magnetic field distribution on its central axis that is symmetric with respect to the center of the coil. However, in actual applications, in order to generate high-density plasma, an asymmetric magnetic field distribution having different magnetic field strengths on the microwave incident side and the ion extraction side of the plasma chamber may be desired. One method for obtaining such an asymmetric distribution is to arrange a plurality of coils side by side in the axial direction, generate different magnetic fields in each coil, and adjust each coil to achieve the desired asymmetric distribution when these individual magnetic fields are superimposed. It is to be. However, such a configuration is complicated and expensive.

  One exemplary object of an aspect of the present invention is to provide a microwave ion source that can generate a desired magnetic field distribution in a plasma chamber with a simple configuration.

  A microwave ion source according to an aspect of the present invention includes a window for receiving a microwave, an opening for extracting ions, a plasma chamber defining a plasma generation space, and an axially oriented coil. A coil device disposed to generate a magnetic field in the plasma generation space from the window to the opening; and a magnetic body for adjusting a coil magnetic field intensity on a plasma chamber central axis in the plasma generation space. . The magnetic body is disposed on at least one of the window side and the opening side so as to be asymmetric between the window side and the opening side with respect to the axial center of the coil device.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to the present invention, a desired magnetic field distribution can be generated in the plasma chamber with a simple configuration.

It is a figure showing roughly composition of a microwave ion source concerning an embodiment with the present invention. It is a figure which shows schematically the principal part of the microwave ion source which concerns on one embodiment of this invention. It is a figure which shows schematically the principal part of the microwave ion source which concerns on other embodiment of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate.

  FIG. 1 is a diagram schematically showing a configuration of a microwave ion source 10 according to an embodiment of the present invention. A microwave ion source 10 generates high-density plasma by inputting microwave power in the direction of magnetic field into a plasma chamber 12 to which a magnetic field satisfying electron cyclotron resonance (ECR) or a magnetic field higher than the magnetic field is applied to generate ions with high density. Ion source to be extracted. The microwave ion source 10 is configured to generate a plasma of a source gas by the interaction between a magnetic field and a microwave, and to extract ions from the plasma to the outside of the plasma chamber 12.

  As is well known, the strength of the magnetic field that satisfies the ECR condition is uniquely determined with respect to the microwave frequency used, and a magnetic field of 87.5 mT (875 gauss) is required when the microwave frequency is 2.45 GHz. It is. Hereinafter, for convenience of explanation, a magnetic field that satisfies the ECR condition may be referred to as a resonance magnetic field.

  The microwave ion source 10 is used, for example, as an ion source for an ion implantation apparatus or a particle beam therapy apparatus. The microwave ion source 10 is used as a monovalent ion source, for example. The microwave ion source 10 can also be used as an ion source for a proton accelerator or an X-ray source.

  The microwave ion source 10 includes an ion source body 14. The ion source body 14 includes a plasma chamber 12, a coil device 16 that is a magnetic field generator, and a vacuum vessel 18.

  The plasma chamber 12 has a cylindrical shape having both ends. Hereinafter, the direction from one end to the other end of the plasma chamber 12 may be referred to as an axial direction for convenience. In addition, a direction orthogonal to the axial direction may be referred to as a radial direction, and a direction surrounding the axial direction may be referred to as a circumferential direction. However, these do not necessarily mean that the plasma chamber 12 has a rotationally symmetric shape. In the illustrated example, the plasma chamber 12 has a cylindrical shape, but the plasma chamber 12 may have any shape as long as it can appropriately accommodate plasma. The axial length of the plasma chamber 12 may be longer or shorter than the radial length of the end portion of the plasma chamber 12.

  The coil device 16 is provided for applying a magnetic field to the plasma chamber 12. The coil device 16 is disposed around the plasma chamber 12. The coil device 16 is configured to generate a coil magnetic field along the central axis of the plasma chamber 12. The direction of the line of magnetic force is indicated by an arrow M in FIG. The coil device 16 is configured to generate a resonance magnetic field or a magnetic field having a higher strength than that in at least a part of the axis of the plasma chamber 12. The coil device 16 can also generate a magnetic field lower than the resonance magnetic field in at least a part of the axis of the plasma chamber 12.

  The vacuum container 18 is a housing for accommodating the plasma chamber 12 in a vacuum environment. The plasma chamber 12 has a vacuum window 24 for receiving microwaves therein. The vacuum vessel 18 is also a structure for holding the coil device 16. The plasma chamber 12, the coil device 16, and the vacuum vessel 18 will be described in more detail later.

  The microwave ion source 10 includes a microwave supply system 26. The microwave supply system 26 is configured to input microwave power to the plasma chamber 12 through the vacuum window 24. The microwave supply system 26 includes a microwave source 28, a waveguide 30, and a matching section 32. The microwave source 28 is, for example, a magnetron. The microwave source 28 outputs a microwave having a frequency of 2.45 GHz, for example. The waveguide 30 is a three-dimensional circuit for transmitting the microwave output from the microwave source 28 to the plasma chamber 12. One end of the waveguide 30 is connected to the microwave source 28, and the other end is connected to the vacuum window 24 via the matching section 32. A matching section 32 is provided for microwave matching.

  In this way, microwaves are introduced from the microwave supply system 26 into the plasma chamber 12 through the vacuum window 24. The introduced microwave propagates inside the plasma chamber 12 toward the end of the plasma chamber 12 facing the vacuum window 24. The propagation direction of the microwave is indicated by an arrow P in FIG. The propagation direction P of the microwave is the same direction as the magnetic force line direction M by the coil device 16. Therefore, the propagation direction P of the microwave coincides with the axial direction of the plasma chamber 12.

  The microwave supply system 26 includes a microwave detector 33 provided in the waveguide 30. The microwave detector 33 includes, for example, a directional coupler for monitoring the incident power to the plasma chamber 12 and the reflected power from the plasma chamber 12. The microwave detector 33 is configured to output the measurement result to the control device C.

  The microwave ion source 10 includes a gas supply system 34. The gas supply system 34 is configured to supply a plasma source gas to the plasma chamber 12. The gas supply system 34 includes a gas cylinder 36 that is a gas source and a gas flow rate controller 38. The front end of the gas pipe 40 of the gas supply system 34 is connected to the plasma chamber 12 through the vacuum vessel 18. For example, the gas pipe 40 is connected to the side wall 64 of the plasma chamber 12. The gas flow rate controller 38 includes an on-off valve for connecting or blocking the gas cylinder 36 to or from the plasma chamber 12 or a flow rate control valve for adjusting the gas flow rate from the gas cylinder 36 to the plasma chamber 12. In this way, the source gas is supplied from the gas cylinder 36 to the plasma chamber 12 at a controlled flow rate.

  The ion source body 14 includes an extraction electrode system 42. The extraction electrode system 42 is configured to extract ions from the plasma through the ion extraction opening 66 of the plasma chamber 12. The extraction electrode system 42 includes a first electrode 44 and a second electrode 46. The first electrode 44 is provided between the plasma chamber 12 and the second electrode 46. The terminal portion 62 having the ion extraction opening 66 and the first electrode 44 are arranged with a gap therebetween, and the first electrode 44 and the second electrode 46 are arranged with a gap therebetween. Each of the first electrode 44 and the second electrode 46 is formed, for example, in an annular shape, and has an opening at the center for allowing ions extracted from the plasma chamber 12 to pass therethrough.

  The first electrode 44 is provided for extracting positive ions from the plasma and preventing electrons from returning from the beam line 52 to the plasma chamber 12. Therefore, a negative high voltage is applied to the first electrode 44. In order to apply a negative high voltage to the first electrode 44, a first extraction power supply 48 is provided. The second electrode 46 is grounded. A positive high voltage is applied to the vacuum vessel 18. In order to apply a positive high voltage to the vacuum vessel 18, a second extraction power source 50 is provided. In this manner, a positive ion beam 20 is extracted from the plasma chamber 12. The extraction direction of the ion beam 20 from the plasma chamber 12 is the same as the propagation direction P of the microwave.

  The microwave ion source 10 is provided with a beam line 52 for transporting the ion beam 20 extracted by the extraction electrode system 42. The beam line 52 is connected to the ion source main body 14 on the side opposite to the microwave supply system 26. The beam line 52 is a vacuum vessel communicating with the vacuum vessel 18. The beam line 52 is insulated from the vacuum vessel 18 of the ion source body 14 and attached to the vacuum vessel 18. For this purpose, a bushing 54 is provided between the beam line 52 and the vacuum vessel 18.

  The bushing 54 maintains the withstand voltage between the vacuum vessel 18 and the ground side while maintaining the vacuum in the beam line 52 and the vacuum vessel 18. The bushing 54 is made of an insulating material. The bushing 54 has an annular shape and surrounds the extraction electrode system 42. The bushing 54 is attached by being sandwiched between the attachment flanges of the vacuum vessels of the beam line 52 and the ion source main body 14.

  A vacuum exhaust system 56 for providing a vacuum environment to the vacuum vessel 18 and the plasma chamber 12 is provided. In the illustrated example, the evacuation system 56 is provided in the beam line 52. Since the beam line 52 communicates with the vacuum vessel 18 and the plasma chamber 12, the vacuum exhaust system 56 can evacuate the vacuum vessel 18 and the plasma chamber 12. The vacuum exhaust system 56 includes a high vacuum pump such as a cryopump or a turbo molecular pump.

  The microwave ion source 10 may include a control device C for controlling the output of the ion beam 20. The control device C controls each component of the microwave ion source 10 to control the plasma generated in the plasma chamber 12, thereby controlling the output of the ion beam 20. The control device C is configured to control the operation of the microwave supply system 26, the gas supply system 34, and the coil power supply 76, for example. For example, the control device C may control the output of the ion beam 20 by adjusting at least one of the flow rate of the source gas, the microwave power, and the magnetic field strength.

  The plasma chamber 12 is configured to generate and maintain plasma in its internal space. Hereinafter, the internal space of the plasma chamber 12 may be referred to as a plasma generation space 58.

  The plasma chamber 12 includes a start end portion 60, a termination end portion 62, and a side wall 64. The start end portion 60 and the end end portion 62 face each other with the plasma generation space 58 interposed therebetween. The side wall 64 surrounds the plasma generation space 58 and connects the start end 60 and the end end 62. In this way, the plasma generation space 58 is defined inside the vacuum vessel 18 by the start end portion 60, the end end portion 62, and the side wall 64. When the plasma chamber 12 has a cylindrical shape, the start end portion 60 and the end portion 62 have a disk shape, the side wall 64 has a cylindrical shape, and the ends of the side walls 64 are fixed to the outer peripheral portions of the start end portion 60 and the end portion 62. Yes.

  The start end 60 has a vacuum window 24. The vacuum window 24 may occupy the entire start end 60 or may be formed at a part (for example, the center) of the start end 60. One side of the vacuum window 24 faces the plasma generation space 58, and the other side of the vacuum window 24 is directed to the microwave supply system 26. The vacuum window 24 seals the inside of the plasma chamber 12 to a vacuum. The propagation direction P of the microwave is perpendicular to the vacuum window 24. The vacuum window 24 is formed of a dielectric having a low dielectric loss (for example, alumina or boron nitride). The portions other than the vacuum window 24 of the plasma chamber 12 are formed of a nonmagnetic metal material such as stainless steel or aluminum.

  At least one ion extraction opening 66 is formed in the end portion 62. The ion extraction opening 66 is formed at a position facing the vacuum window 24 with the plasma generation space 58 interposed therebetween. That is, the vacuum window 24, the plasma generation space 58, and the ion extraction opening 66 are arranged along the axial direction of the plasma chamber 12.

  The vacuum vessel 18 has a double cylinder structure in which the plasma chamber 12 is integrally formed. That is, the plasma chamber 12 is an inner cylinder of the vacuum vessel 18, and an outer cylinder 68 that accommodates the plasma chamber 12 is provided outside the plasma chamber 12. The outer cylinder 68 may have a cylindrical shape that is coaxial with the plasma chamber 12. There is a gap between the outer cylinder 68 and the side wall 64 of the plasma chamber 12, and the tip of the gas pipe 40 of the gas supply system 34 enters the gap and is attached to the side wall 64. The vacuum vessel 18 is made of, for example, a nonmagnetic metal material.

  The vacuum vessel 18 may not be formed integrally with the plasma chamber 12. The vacuum vessel 18 and the plasma chamber 12 may be separate and separable. Further, the vacuum vessel 18 itself may form the plasma chamber 12. Thus, when the vacuum vessel 18 also serves as the plasma chamber 12, an end plate having an ion extraction opening 66 on the beam line 52 side of the outer cylinder 68 may be attached.

  One end of the vacuum vessel 18 is closed by an end plate 70, and the other end is opened toward the beam line 52. A starting end 60 of the plasma chamber 12 is formed at the center of the end plate 70. The outer peripheral portion of the end plate 70 extends to the outside of the outer cylinder 68 in the radial direction. A mounting flange 72 for the bushing 54 is provided at the end of the vacuum vessel 18 on the beam line 52 side. The mounting flange 72 extends radially outward from the outer cylinder 68. The vacuum vessel 18 and the plasma chamber 12 have the same axial length, and the mounting flange 72 and the end portion 62 of the plasma chamber 12 have the same axial position. The vacuum vessel 18 and the plasma chamber 12 may have different axial lengths.

  A coil holding part 74 for holding the coil device 16 is formed in the vacuum container 18. For example, the coil holding portion 74 is formed on the outer surface of the outer cylinder 68 of the vacuum vessel 18. Thus, the coil device 16 is provided outside the vacuum vessel 18 (that is, in the atmosphere). The coil device 16 is disposed so as to surround the vacuum vessel 18. In some embodiments, the coil holding unit 74 may be another member that is separated from the vacuum vessel 18 or the plasma chamber 12. In this case, different potentials may be applied to the coil device 16 and the plasma chamber 12.

  The coil device 16 includes a coil 75 configured to generate a coil magnetic field that faces the axial direction of the plasma chamber 12. In this example, the plasma chamber 12 and the vacuum vessel 18 are cylindrical, the coil 75 is formed in an annular shape, and a conducting wire is wound in the circumferential direction of the plasma chamber 12. The coil device 16 includes a coil power supply 76 for causing a current to flow through the coil 75. The coil device 16 may include a plurality of coils arranged along the axial direction of the plasma chamber 12 instead of including one coil 75 as illustrated.

  As will be described later in detail with reference to FIGS. 2 and 3, the microwave ion source 10 is provided with a magnetic body 80. The magnetic body 80 includes, for example, a shield member provided around the plasma chamber 12 and / or a yoke member provided around the coil 75.

  The magnetic body 80 is disposed between the vacuum window 24 and the ion extraction opening 66 in the axial direction. In this way, since the magnetic body 80 can be brought close to the plasma generation space 58, the coil magnetic field in the plasma generation space 58 can be effectively adjusted by the magnetic body 80. Further, with such an arrangement, it is easy to secure an installation space for the magnetic body 80. Since the microwave supply system 26 is provided upstream of the vacuum window 24 and the extraction electrode system 42 is provided downstream of the ion extraction opening 66, the spatial margin is small.

  FIG. 2 is a cross-sectional view schematically showing a main part of the microwave ion source 10 according to an embodiment of the present invention. The upper part of FIG. 2 shows the main part of the microwave ion source 10 shown in FIG. 1, and the lower part of FIG. 2 illustrates the axial magnetic field on the central axis of the plasma chamber 12 generated by the coil device 16. In FIG. 2, the vertical axis represents the axial magnetic flux density B on the central axis of the plasma chamber 12, and the horizontal axis represents the axial position Z on the central axis of the plasma chamber 12. Here, the central position of the plasma chamber 12 in the axial direction is denoted as Zc, and the peak position of the axial magnetic flux density B on the central axis of the plasma chamber 12 is denoted as Zp. Further, the axial positions of the vacuum window 24 and the ion extraction opening 66 are represented as Zw and Za, respectively.

  As described above, the microwave ion source 10 includes the plasma chamber 12 that defines the plasma generation space 58. The plasma chamber 12 includes a start end portion 60 having a vacuum window 24 for receiving microwaves, a termination portion 62 having an ion extraction opening 66 for extracting ions from the plasma generation space 58, a start end portion 60, and a termination portion 62. And a side wall 64 for connecting the two.

  The microwave ion source 10 also includes a coil device 16 that is arranged to generate a coil magnetic field directed in the axial direction in the plasma generation space 58. The coil device 16 generates a magnetic field in the entire plasma generation space 58 in the axial direction from the vacuum window 24 to the ion extraction opening 66. The coil device 16 includes a single coil power source 76 and a single coil 75 that generates a magnetic field in the plasma generation space 58 by feeding from the coil power source 76. The coil 75 generates a single-peak axial magnetic field distribution having an intensity peak at the center thereof. This magnetic field distribution may be larger than the resonance magnetic field (that is, the magnetic field satisfying the ECR condition) at least at the peak and larger than the resonance magnetic field over the entire axial direction of the plasma chamber 12.

  The coil device 16 is configured such that the peak of the coil magnetic field on the central axis of the plasma chamber 12 is located in the plasma chamber 12. The coil device 16 is disposed such that the window side surface and the opening side surface of the coil 75 are positioned between the vacuum window 24 and the ion extraction opening 66 in the axial direction. The coil 75 is a donut-shaped coil surrounding the plasma chamber 12.

  In the present embodiment, the coil device 16 is disposed so that the axial position of the coil device 16 (specifically, the coil 75) is aligned with the center of the plasma chamber 12 in the axial direction. Therefore, if the shield member 82 is not provided, the coil device 16 generates an axial magnetic field distribution having a peak at the central position Zc of the plasma chamber 12. This magnetic field distribution is symmetrical with respect to the axial center position Zc.

  The microwave ion source 10 includes a magnetic body 80 (see FIG. 1) for adjusting the coil magnetic field strength on the plasma chamber central axis in the plasma generation space 58. The magnetic body 80 is disposed on the opening side of the plasma chamber 12. Therefore, the magnetic body 80 is asymmetric between the window side and the opening side with respect to the axial center of the coil device 16.

  Specifically, as shown in FIG. 2, the magnetic body 80 includes a shield member 82. The shield member 82 is a soft magnetic material such as iron. The shield member 82 is disposed along the side wall 64 on the opening side of the plasma chamber 12. The shield member 82 is provided away from the coil 75. The shield member 82 may be a short cylinder surrounding the entire circumference of the plasma chamber 12 or may be a plurality of magnetic pieces arranged along the circumferential direction of the plasma chamber 12. The shield member 82 is disposed symmetrically about the axis.

  The shield member 82 has an effect of deflecting the coil magnetic field on the central axis of the plasma chamber 12 toward the outer peripheral side of the plasma chamber 12. Therefore, as shown in FIG. 2, the shield member 82 reduces the magnetic field on the opening side of the plasma chamber 12 (that is, the Za side in FIG. 2). Since the shield member is not provided on the window side of the plasma chamber 12, the original magnetic field is maintained on the window side (that is, the Zw side). In this way, the peak Zp on the central axis of the magnetic field adjusted by the shield member 82 is still in the plasma chamber 12, but is located at a position off the window side from the peak Zc of the unadjusted coil magnetic field.

  In this manner, the magnetic body 80 is disposed on the opening side in the axial direction and between the coil 75 and the plasma generation space 58 in the radial direction, thereby generating plasma on the central axis of the plasma chamber 12. The magnetic field in the window side region of the space 58 is stronger than the magnetic field in the opening side region of the plasma generation space 58. The magnetic field distribution that is asymmetric with respect to the axial center serves to generate and maintain a high density plasma in the plasma generation space 58.

  The plasma chamber 12 includes a cooling unit 78 that cools the shield member 82. The cooling unit 78 is disposed between the shield member 82 and the plasma generation space 58 in the radial direction. The cooling unit 78 includes, for example, a cooling pipe built in the side wall 64 of the plasma chamber 12 in order to cool the plasma chamber 12. Thus, it is possible to prevent an excessive temperature rise of the shield member 82 due to the plasma generation space 58 that becomes high temperature during operation.

  The cooling unit 78 may be installed on the outer surface of the side wall 64 of the plasma chamber 12. The cooling unit 78 shown in the figure cools the shield member 82 from the radially inner side. However, a cooling unit for cooling the shield member 82 from the radially outer side may be provided together with or instead of the cooling unit 78. Good. For example, the cooling unit may be provided on the protection member 84.

  A protective member 84 that protects the shield member 82 may be provided. The protective member 84 forms a protective layer that covers the surface of the shield member 82. For example, the protection member 84 may be formed of a nonmagnetic material such as aluminum. In this way, the material of the shield member 82 can be prevented from being released to the environment, and contamination of the ion beam 20 can be prevented. Note that the protective member 84 may not be provided in applications where such contamination problems are not important. In this case, the surface of the magnetic body 80 (for example, the shield member 82 and / or the yoke member 86) may be exposed (see FIG. 3).

  FIG. 3 is a cross-sectional view schematically showing a main part of a microwave ion source 10 according to another embodiment of the present invention. The microwave ion source 10 according to this embodiment is different from the above-described embodiment with respect to the arrangement and function of the magnetic body 80. For the remainder, the embodiment shown in FIG. 3 is the same as the embodiment described with reference to FIGS. In the following description, the description of similar parts will be omitted as appropriate to avoid redundancy.

  The magnetic body 80 is disposed on the window side of the plasma chamber 12. Therefore, the magnetic body 80 is asymmetric between the window side and the opening side with respect to the axial center of the coil device 16. The magnetic body 80 includes a yoke member 86 attached to the coil 75 as shown in FIG. 3 instead of the shield member 82 shown in FIG. The yoke member 86 is a soft magnetic material such as an iron material. The yoke member 86 is disposed symmetrically with respect to the axis, and is provided away from the plasma chamber 12.

  The yoke member 86 includes a first portion 88 disposed along the window side surface of the coil 75 and a second portion 90 disposed along the radially outer peripheral surface of the coil 75. The first portion 88 is a flat plate having a through hole through which the plasma chamber 12 passes. The second portion 90 is a short cylinder extending in the axial direction adjacent to the radially outer peripheral end of the first portion 88. The second portion 90 covers the window side portion of the radially outer peripheral surface of the coil 75, but may cover the entire radially outer peripheral surface of the coil 75. The yoke member 86 is not provided on the opening side surface of the coil 75.

  The yoke member 86 may include at least the first portion 88, or only one of the first portion 88 and the second portion 90. The yoke member 86 may surround the entire circumference of the coil 75, or may be a plurality of magnetic body pieces arranged along the circumferential direction of the coil 75.

  The yoke member 86 has the effect of concentrating the magnetic field at the axial position. Therefore, as shown in FIG. 3, the yoke member 86 strengthens the magnetic field on the window side of the plasma chamber 12. Since the yoke member is not provided on the opening side of the plasma chamber 12, the original magnetic field is maintained on the opening side. In this way, the peak Zp on the central axis of the magnetic field adjusted by the yoke member 86 is still in the plasma chamber 12, but is located at a position off the window side from the peak Zc of the unadjusted coil magnetic field.

  In this way, the magnetic body 80 is arranged on the window side in the axial direction and on the side and outside of the coil 75 in the radial direction, so that the window side of the plasma generation space 58 on the central axis of the plasma chamber 12 is arranged. The magnetic field in the region is stronger than the magnetic field in the opening side region of the plasma generation space 58. The magnetic field distribution that is asymmetric with respect to the axial center in this way is useful for generating and maintaining a high-density plasma in the plasma generation space 58.

  As described above, the microwave ion source 10 according to the present embodiment includes the plasma chamber 12, one coil power source 76, and a coil that generates a symmetric magnetic field in the axial direction of the plasma chamber 12 by the one coil power source 76. 75. In addition, the microwave ion source 10 includes a magnetic body 80 disposed on the outer peripheral side of the plasma chamber 12 and on the entry side or the exit side of the plasma chamber 12. The microwave ion source 10 forms an asymmetric magnetic field distribution in the plasma chamber 12 by the coil 75 and the magnetic body 80.

  Therefore, according to the present embodiment, an asymmetric magnetic field suitable for generating high-density plasma can be realized with a simple configuration in which the magnetic body 80 is combined with the coil device 16 including one set of the coil 75 and the coil power source 76. There is an advantage that a complicated configuration is not required in which a plurality of coils are provided in the axial direction and different currents are applied to the coils.

  In addition, the fact that there is only one coil power supply 76 is useful for cost reduction. In particular, the magnetic field for plasma generation is generally generated by a large coil current of, for example, several hundred amperes, and such a power source is expensive. Reducing the number of power supplies greatly contributes to configuring the system at a low cost.

  In addition, since the peak portion of the coil magnetic field is applied to the plasma generation space 58, the current supplied to the coil 75 by the coil power supply 76 can be reduced. This is useful for reducing the size and cost of the power supply. On the other hand, if the peak portion of the coil magnetic field is located outside the plasma chamber 12 and the tail portion of the coil magnetic field is given to the plasma generation space 58, a magnetic field having the same strength is brought to the plasma generation space 58. A large current is required.

  In the above, this invention was demonstrated based on the Example. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiment, and various design changes are possible, various modifications are possible, and such modifications are within the scope of the present invention. By the way.

  In the above-described embodiment, the magnetic body 80 is disposed on one of the window side and the opening side of the plasma chamber 12. However, the magnetic body 80 may be disposed on both the window side and the opening side so as to be asymmetric between the window side and the opening side with respect to the axial center of the coil device 16. Therefore, the microwave ion source 10 according to an embodiment may include both the shield member 82 and the yoke member 86.

  In the above-described embodiment, the microwave ion source 10 is configured to generate an asymmetric magnetic field that is biased toward the window with respect to the axial center of the coil device 16. However, on the contrary, an asymmetric magnetic field biased toward the opening side is also possible. In one embodiment, the microwave ion source 10 is configured such that the peak on the central axis of the magnetic field adjusted by the magnetic body 80 is located at a position off the opening side from the peak of the original coil magnetic field. Also good. The magnetic body 80 generates plasma with the coil 75 in the axial direction on the window side and in the radial direction so that the magnetic field in the opening side region of the plasma generation space 58 is stronger than the magnetic field in the window side region of the plasma generation space 58 on the central axis. It may be arranged between the space 58 and / or on the opening side in the axial direction and on the side or outside of the coil 75 in the radial direction. For example, the magnetic body 80 may include a shield member disposed along the side wall 64 on the window side. Alternatively, the magnetic body 80 may include a yoke member disposed along the opening side surface of the coil 75 or the radial outer peripheral surface of the coil 75.

  In the above-described embodiment, the shield member 82 is in close contact with the plasma chamber 12. However, the shield member 82 may have a gap with the plasma chamber 12. Similarly, in the above-described embodiment, the yoke member 86 is in close contact with the coil 75, but a gap may be provided between the yoke member 86 and the coil 75.

  In an embodiment, a permanent magnet may be provided instead of the shield member 82. In this case, the permanent magnet is oriented between the coil 75 and the plasma generation space 58 so that the magnetic field is at least partially canceled by the magnetic field.

  10 microwave ion source, 12 plasma chamber, 16 coil device, 58 plasma generation space, 60 start end, 62 end, 64 side wall, 66 ion extraction opening, 75 coil, 76 coil power supply, 78 cooling unit, 80 magnetic body, 82 shield member, 84 protective member, 86 yoke member.

Claims (10)

A plasma chamber comprising a window for receiving microwaves and an opening for extracting ions, and defining a plasma generation space;
A coil device arranged to generate an axially oriented coil magnetic field in the plasma generation space from the window across the opening;
A magnetic body for adjusting the coil magnetic field strength on the plasma chamber central axis in the plasma generation space,
The magnetic body is disposed on at least one of the window side and the opening side so as to be asymmetric between the window side and the opening side with respect to the axial center of the coil device ,
The coil device includes a coil disposed around the plasma chamber,
The magnetic body has an axial direction on the window side in the axial direction and a radial direction of the coil so that the magnetic field in the window side region of the plasma generation space is stronger than the magnetic field in the opening side region of the plasma generation space on the central axis. Placed on the side or outside,
The magnetic body includes a yoke member disposed along a window side surface of the coil or a radially outer peripheral surface of the coil, and the yoke member is not provided on a side surface of the coil on the opening side. A microwave ion source characterized by The said yoke member is provided with the 1st part arrange | positioned along the side surface by the side of the window of the said coil, and the 2nd part arrange | positioned along the radial direction outer peripheral surface of the said coil. Item 2. The microwave ion source according to Item 1. The microwave ion source according to claim 2, wherein the second portion of the yoke member is provided on the window side and is not provided on the opening side. A plasma chamber comprising a window for receiving microwaves and an opening for extracting ions, and defining a plasma generation space;
A coil device arranged to generate an axially oriented coil magnetic field in the plasma generation space from the window across the opening;
A magnetic body for adjusting the coil magnetic field strength on the plasma chamber central axis in the plasma generation space,
The magnetic body is disposed on at least one of the window side and the opening side so as to be asymmetric between the window side and the opening side with respect to the axial center of the coil device,
The plasma chamber includes a start end provided with the window, a terminal end provided with the opening, and a side wall connecting the start end and the terminal end,
The microwave body according to claim 1, wherein the magnetic body includes a shield member disposed along the side wall on the opening side, and the shield member is not provided on the window side . The coil device includes a coil disposed around the plasma chamber,
The shield member has an axial direction on the opening side and a radial direction on the coil such that the magnetic field in the window side region of the plasma generation space is stronger than the magnetic field in the opening side region of the plasma generation space on the central axis. Microwave ion source according to claim 4, characterized in that it is placed between the plasma generating space with. The microwave ion source according to claim 4 , wherein the plasma chamber includes a cooling unit that cools the shield member. The said coil apparatus is provided with the single coil power supply and the single coil which produces | generates a magnetic field in the said plasma production space by the electric power feeding from this power supply , The any one of Claim 1 to 6 characterized by the above-mentioned. Microwave ion source. The peak on the central axis of the coil magnetic field is located in the plasma chamber,
The peak on the center axis of the adjusted magnetic field by a magnetic body, from claim 1, characterized in that positioned outside the location in the window side from the peak of the coil magnetic field there is within the plasma chamber 7 The microwave ion source according to any one of the above. The magnetic material, microwave ion source according to claim 1, characterized in that it is disposed between the opening and the window in the axial direction 8. Microwave ion source according to any of claims 1 9, characterized by further comprising a protective member covering the surface of the magnetic body.

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