JP6344973B2 - Microwave ion source - Google Patents

Description

  The present invention relates to a microwave ion source and a method for controlling 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.

JP-A-2-162638

  Ions generated in the plasma chamber are extracted out of the plasma chamber by the extraction electrode. Some of the extracted ions adhere to the surface of the extraction electrode, and depending on the ion species, an insulating film is formed on the surface of the extraction electrode. The insulating film is charged by the electric field between the plasma chamber and the extraction electrode, and can induce a discharge between the plasma chamber and the extraction electrode. When discharge occurs, it may affect the stable operation of the microwave ion source.

  One exemplary objective of certain aspects of the present invention is to increase the reliability of a microwave ion source.

  A microwave ion source according to an aspect of the present invention includes a plasma chamber having an ion extraction portion in which an extraction opening is provided, and an extraction electrode provided to face the ion extraction portion. The extraction electrode includes a base member having a main surface facing the ion extraction unit, an opening provided at a position communicating with the extraction opening, and an ion extraction unit between the ion extraction unit and the main surface so as to cover the periphery of the opening. A cover member provided, and a spacer member provided between the base member and the cover member.

  Another aspect of the present invention is a method for controlling a microwave ion source. This method is a control method of a microwave ion source including a plasma chamber having an ion extraction portion provided with an extraction opening and an extraction electrode facing the ion extraction portion, and the extraction electrode faces the ion extraction portion. A base member having an opening provided at a position communicating with the extraction opening, a cover member provided between the ion extraction portion and the main surface so as to cover the periphery of the opening, and a base member And a spacer member provided between the cover members. Extracting ions from the extraction opening in the first aspect, and extracting ions from the extraction opening in the second aspect in which ions extracted from the extraction opening are more likely to collide with the cover member than in the first aspect. In the preparation period before ions are extracted in the first mode, ions are extracted in the second mode.

  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, the reliability of the microwave ion source can be increased.

It is a figure which shows typically the structure of the microwave ion source which concerns on embodiment. It is a front view which shows the structure of an extraction electrode typically. It is sectional drawing which shows the structure of an extraction electrode typically. It is a figure which shows typically the deposit adhering to the extraction electrode which concerns on a comparative example. It is a figure which shows typically the deposit adhering to the extraction electrode which concerns on embodiment. It is a figure which shows typically the ion extracted in the 1st aspect. It is a figure which shows typically the ion extracted in a 2nd aspect. It is sectional drawing which shows typically the structure of the extraction electrode which concerns on a modification.

  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 schematically shows a configuration of a microwave ion source 10 according to an embodiment.

  The microwave ion source 10 is configured to generate a plasma of a source gas in the plasma chamber 12 by microwaves and extract ions from the plasma to the outside of the plasma chamber 12. 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 plasma chamber 12 is a container that surrounds a plasma generation space 14 that is a space in which plasma is generated.

  The microwave ion source 10 includes a plasma chamber 12. The plasma chamber 12 is a vacuum chamber configured to generate and maintain plasma in its internal space. 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. 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 plasma chamber 12 includes a side wall part 20, an ion extraction part 22, an extraction opening 24, and a microwave introduction part 26. The ion extraction unit 22 and the microwave introduction unit 26 are opposed to each other with the plasma generation space 14 interposed therebetween.

  The side wall portion 20 connects the ion extraction portion 22 and the microwave introduction portion 26 and surrounds the plasma generation space 14. The side wall portion 20 is fixed to the outer peripheral portions of the ion extraction portion 22 and the microwave introduction portion 26. The side wall portion 20 is formed of a nonmagnetic metal material such as stainless steel or aluminum.

  The side wall part 20 may include a cooling part for cooling the side wall part 20. This cooling part may be built in the side wall part 20 or may be attached outside the side wall part 20. Moreover, in order to protect the side wall part 20 from a plasma, the liner which coat | covers the inner surface of the side wall part 20 may be provided. The liner may be made of, for example, boron nitride (BN).

  The plasma generation space 14 is defined in the plasma chamber 12 by the side wall portion 20, the ion extraction portion 22, and the microwave introduction portion 26. Since the plasma chamber 12 is configured such that the side wall 20, the ion extraction unit 22, and the microwave introduction unit 26 integrally surround the plasma generation space 14, the end of the side wall 20 connected to the ion extraction unit 22 is an ion. It can also be regarded as a part of the drawer 22. Similarly, the end of the side wall part 20 connected to the microwave introduction part 26 can also be regarded as a part of the microwave introduction part 26.

  The plasma chamber 12 has, for example, a cylindrical shape. In this case, the microwave introduction part 26 and the ion extraction part 22 are substantially disk-shaped, and the side wall part 20 is substantially cylindrical. The plasma chamber 12 may have any shape as long as plasma can be appropriately accommodated.

  The microwave introduction unit 26 includes a vacuum window 32. The vacuum window 32 seals the inside of the plasma chamber 12 to a vacuum. One side of the vacuum window 32 faces the plasma generation space 14, and the other side of the vacuum window 32 is directed to the microwave supply system or the microwave waveguide 30. The propagation direction P of the microwave is perpendicular to the vacuum window 32. In the present embodiment, the vacuum window 32 occupies the entire microwave introduction part 26, but the vacuum window 32 may be formed in a part (for example, the center part) of the microwave introduction part 26.

  The microwave incident power to the plasma chamber 12 is greater than about 100 W, for example. Alternatively, the microwave incident power to the plasma chamber 12 may be about 500 W or more, or about 1 kW or more. The microwave waveguide 30 and the vacuum window 32 are suitable for supplying such a high-power microwave compared to other supply means such as a coaxial line.

The vacuum window 32 is made of a dielectric such as alumina (Al ₂ O ₃ ) or boron nitride (BN). The vacuum window 32 includes a window body 34 and a window protector 36. The window body 34 is made of alumina, for example, and the window protection member 36 is made of boron nitride. As a result, the window protection member 36 protects the window main body 34 against electrons flowing back from the outside of the plasma chamber 12 to the plasma chamber 12 through the extraction opening 24.

  The ion extraction portion 22 has at least one extraction opening 24 formed therein. The drawer opening 24 is, for example, a slit elongated in a direction perpendicular to the paper surface. The extraction opening 24 is formed in the central portion of the ion extraction portion 22. The extraction opening 24 is formed at a position facing the vacuum window 32 across the plasma generation space 14. The vacuum window 32, the plasma generation space 14, and the extraction opening 24 are arranged along the central axis of the plasma chamber 12.

  The plasma chamber 12 is connected to a first power supply 38 for applying a positive high voltage. When a high voltage is applied to the plasma chamber 12, the same high voltage is also applied to the ion extraction part 22, which is a part of the plasma chamber 12. Therefore, the ion extraction part 22 may be called a plasma electrode.

  The microwave ion source 10 includes a magnetic field generator 16. The magnetic field generator 16 is disposed so as to surround the side wall portion 20 of the plasma chamber 12 in order to generate a magnetic field directed in the axial direction on the central axis of the plasma chamber 12. The direction of the line of magnetic force is indicated by an arrow B in FIG. The magnetic force line direction B by the magnetic field generator 16 is the same direction as the propagation direction P of the microwave. Further, the magnetic field B has a resonance magnetic field or higher intensity at least at a part on the central axis of the plasma chamber 12. The magnetic field generator 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 magnetic field generator 16 has an annular coil, and a conducting wire is wound around the plasma chamber 12 in the circumferential direction. The magnetic field generator 16 has a coil power supply (not shown) for flowing a current through the coil. A plurality of the magnetic field generators 16 may be arranged along the axial direction of the plasma chamber 12 and may include a permanent magnet instead of the coil.

The microwave ion source 10 includes a gas supply system (not shown) for supplying a plasma source gas to the plasma generation space 14. The gas supply system supplies an appropriate source gas to the plasma generation space 14 according to the ion species to be generated. For example, boron trifluoride (BF ₃ ), diborane (B ₂ H ₆ ), arsine (AsH ₃ ), phosphine (PH ₃ ), or the like is used as the source gas. The gas supply system may supply a rare gas such as helium (He), neon (Ne), or argon (Ar) as a source gas to the plasma generation space 14.

  The microwave ion source 10 includes an extraction electrode system 40 for extracting ions out of the plasma chamber 12. The extraction electrode system 40 is configured to extract ions from the plasma through the extraction opening 24 of the plasma chamber 12. The extraction electrode system 40 includes a first electrode 42 and a second electrode 52. The first electrode 42 is provided between the plasma chamber 12 and the second electrode 52. The ion extraction part 22 having the extraction opening 24 and the first electrode 42 are arranged with a gap therebetween, and the first electrode 42 and the second electrode 52 are arranged with a gap therebetween. The first electrode 42 and the second electrode 52 are each formed, for example, in an annular shape, and have a first opening 44 and a second opening 54 for allowing ions extracted from the plasma chamber 12 to pass in the center.

  The first electrode 42 is provided for extracting positive ions from the plasma and preventing electrons from returning from the plasma chamber 12 to the plasma chamber 12. Therefore, a negative high voltage is applied to the first electrode 42. A second power supply 48 is provided to apply a negative high voltage to the first electrode 42. The second electrode 52 is grounded. The absolute value of the positive high voltage applied to the plasma chamber 12 by the first power supply 38 is larger than the absolute value of the negative high voltage applied to the first electrode 42 by the second power supply 48. In this way, a positive ion beam is extracted from the plasma chamber 12. The ion beam extraction direction from the plasma chamber 12 is the same as the microwave propagation direction P.

  The first electrode 42 includes a base member 60, a cover member 62, and a spacer member 64. The base member 60 is a base part that constitutes the first electrode 42 and is made of a nonmagnetic metal material such as stainless steel. The base member 60 is provided with a first opening 44 at a position communicating with the drawer opening 24. The cover member 62 is a protective member that covers at least a part of the main surface 61 facing the ion extraction portion 22 of the base member 60, and is made of a high melting point material such as tungsten (W). The cover member 62 has a function of protecting the base member 60 from ions extracted from the plasma chamber 12. A spacer member 64 is provided between the main surface 61 of the base member 60 and the cover member 62 so that the base member 60 and the cover member 62 are not in direct contact with each other. Thereby, the thermal insulation between the base member 60 and the cover member 62 is enhanced.

  A driving mechanism 46 that changes the facing distance between the plasma chamber 12 and the first electrode 42 is connected to the first electrode 42. The operation of the drive mechanism 46 is controlled by the control unit 80 provided in the microwave ion source 10. The controller 80 controls the overall operation of the microwave ion source 10. The control unit 80 controls the voltage value applied by the first power supply 38 and the second power supply 48, the facing distance between the plasma chamber 12 and the first electrode 42 defined by the drive mechanism 46, and the like from the plasma chamber 12. The extraction mode of extracted ions is adjusted. The control unit 80 switches the source gas introduced into the plasma chamber 12 by controlling the gas supply system, and switches the ion species drawn from the plasma chamber 12.

  Next, the configuration of the first electrode 42 as the extraction electrode will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a front view schematically showing the configuration of the first electrode 42, and FIG. 3 is a cross-sectional view schematically showing the configuration of the first electrode 42. 3 shows a cross section taken along the line CC in FIG. 2, and the cross section taken along the line AA in FIG. 2 corresponds to FIG.

  The first electrode 42 includes an opening protection member 66. The opening protection member 66 is a member that defines the first opening 44 having an elongated slit shape, and is made of a high melting point material such as graphite (C). The opening protection member 66 is fitted into the base opening 60a of the base member 60, and is screwed to the base member 60 via the mounting member 70 (see FIG. 3). The attachment member 70 is a member that connects the base member 60 and the opening protection member 66 and is made of stainless steel or the like. The attachment member 70 is fixed to the opening protection member 66 by the second screw 68b, and is fixed to the base member 60 by the third screw 68c.

  The position where the opening protection member 66 is provided is a location where some of the ions extracted from the plasma chamber 12 are likely to collide, and is a location where wear is greater than other locations of the first electrode 42. By providing the opening protection member 66 at such a location and fixing the opening protection member 66 to the base member 60 by screwing, the ease of replacement of the opening protection member 66 that is easily worn out is enhanced.

  The cover member 62 is provided away from the main surface 61 of the base member 60 so as to cover the periphery of the first opening 44 of the base member 60. The cover member 62 has a substantially elliptical shape that is long in the longitudinal direction of the first opening 44, for example, corresponding to the first opening 44 having an elongated slit shape. Accordingly, the cover member 62 protects the base member 60 by covering a region close to the first opening 44 in the main surface 61 of the base member 60 where the opening protection member 66 is not provided. Further, the cover member 62 is provided with a cover opening 62 a having an opening range larger than that of the first opening 44. Therefore, the cover member 62 is provided at a position where the first opening 44 is not blocked.

The cover member 62 is screwed to the base member 60 via the spacer member 64. The spacer member 64 has a hollow shape so that the first screw 68a connecting the base member 60 and the cover member 62 can be inserted. The spacer member 64 is composed of a member having low thermal conductivity such as stainless steel or alumina (Al ₂ O ₃ ). The spacer member 64 is partially provided on the main surface 61 at a position where the first screw 68a is provided. For example, as shown in FIG. 2, the spacer member 64 is arranged at three locations above and below the first opening 44 together with the first screw 68 a. By disposing the spacer member 64 in a local region having a sufficiently small area with respect to the total area of the main surface 61, the thermal insulation between the base member 60 and the cover member 62 is enhanced.

  The first screw 68a that connects the base member 60 and the cover member 62 is made of a conductive member such as stainless steel, and the base member 60 and the cover member 62 are electrically connected via the first screw 68a. Thereby, the cover member 62 is kept at the same potential as the base member 60 to which the second power supply 48 is connected.

  Next, the operation of the microwave ion source 10 according to the present embodiment will be described. A source gas that is a raw material for plasma generation is supplied to the plasma generation space 14. An axial magnetic field B is applied to the plasma generation space 14 by the magnetic field generator 16. Microwaves are introduced into the plasma generation space 14 through the vacuum window 32. The source gas is excited by the action of the microwave and the axial magnetic field B, and plasma is generated in the plasma generation space 14. Ions are extracted through the extraction opening 24 to the outside of the plasma generation space 14 by the extraction electrode system 40.

  In the present embodiment, since the cover member 62 that protects the main surface 61 of the base member 60 is thermally insulated from the base member 60, the cover member 62 can be maintained at a high temperature. The cover member 62 is heated by radiant heat from the plasma chamber 12 or ions incident on the cover member 62. As a result, the deposit adhering to the surface of the cover member 62 is sublimated at a high temperature, and a large amount of deposit is prevented from adhering to the surface of the cover member 62. This effect will be described with reference to FIGS.

FIG. 4 is a diagram schematically showing the deposit 90 attached to the extraction electrode 142 according to the comparative example. The extraction electrode 142 according to the comparative example includes the base member 60 and the cover member 62, similarly to the first electrode 42 according to the above-described embodiment, but a spacer member is provided between the base member 60 and the cover member 62. This is different from the first electrode 42 in that it is not. The extraction electrode 142 extracts ions D from the plasma generation space 14 of the plasma chamber 12 through the extraction opening 24. A part of the extracted ions D adheres to the surface of the cover member 62 and forms a deposit 90. For example, when phosphine (PH ₃ ) is used as a source gas to generate an ion beam of phosphorus (P), an insulating phosphorus (P) film is formed as the deposit 90. If an insulating film is formed on the surface of the cover member 62, it becomes easy to discharge between the plasma chamber 12 and the cover member 62, which may affect the stable operation of the microwave ion source.

  It is known as inventor's knowledge that the phosphorus film formed as the deposit 90 sublimes by raising the temperature to about 500 ° C. However, in the comparative example, since the contact area between the base member 60 and the cover member 62 is large, the thermal insulation between them is low, the cover member 62 is radiated through the base member 60, and the temperature of the cover member 62 is unlikely to rise. In particular, the microwave ion source is adjacent to the plasma chamber 12 because the temperature of the plasma chamber is lower than an indirectly heated cathode (IHC) ion source that uses thermal electrons emitted from a high-temperature cathode. The temperature of the extraction electrode 142 is also difficult to increase. Then, the insulating phosphorus film adhering to the extraction electrode 142 cannot be sublimated, and discharge due to the deposition of the phosphorus film is likely to occur. In order to prevent discharge, it is necessary to remove the insulating film attached to the extraction electrode 142. If the maintenance frequency for removal increases, the operation rate of the microwave ion source 110 and the apparatus using the microwave ion source 110 will decrease.

  FIG. 5 is a diagram schematically illustrating the deposit 90 attached to the first electrode 42 according to the embodiment. The temperature of the cover member 62 is increased by the radiation heat from the plasma chamber 12 or the collision of ions D drawn from the extraction opening 24. In the present embodiment, since the thermal insulation between the base member 60 and the cover member 62 is enhanced by the spacer member 64, the cover member 62 can be easily kept at a high temperature. Therefore, even if the deposit 90 adheres to the cover member 62, the cover member 62 can be kept at a high temperature and the deposit 90 can be sublimated and removed. Thereby, generation | occurrence | production of the discharge by the insulating deposit 90 adhering can be prevented, and the reliability of the microwave ion source 10 can be improved. Moreover, since the deposit 90 is difficult to adhere, the maintenance frequency for removal can be reduced, and the operating rate of the microwave ion source 10 can be increased.

  In order to increase the temperature of the cover member 62, the extraction mode of the ions D extracted from the extraction opening 24 may be changed. In addition to the normal ion extraction mode (hereinafter also referred to as the first mode) for supplying an ion beam to the subsequent beam line, the ion extraction that the ions extracted to the cover member 62 collide more easily than the first mode. Aspect (hereinafter also referred to as a second aspect) is used. By extracting ions in the second mode between normal operations, many ions can collide with the cover member 62 and the temperature of the cover member 62 can be further increased.

FIG. 6 is a diagram schematically showing the ions D extracted in the first mode. In the first mode, which is a normal ion extraction mode, the ions D are extracted so that most of the extracted ions D pass through the first opening 44 so that the beam current amount of the extracted ion beam increases. In the first aspect, the ions D are extracted so that the spread angle θ _{1 of the} ions D extracted from the extraction opening 24 becomes small.

FIG. 7 is a diagram schematically showing the ions D extracted in the second mode. In the second aspect, at the expense of the beam current amount of the extracted ion beam, ions are extracted so that most of the extracted ions D collide with the cover member 62. Accordingly, in a second aspect, the spread angle theta ₂ of the ion D drawn from the extraction opening 24 is ion D is drawn to be larger than the angle theta ₁ of the first embodiment.

  In order to change the extraction mode of the ions D, for example, the potential difference between the plasma chamber 12 and the first electrode 42 may be changed, or the distance L between the plasma chamber 12 and the first electrode 42 may be changed. The controller 80 drives the drive mechanism 46 to move the first electrode 42 in order to change the ion extraction mode, and changes the distance between the ion extraction unit 22 of the plasma chamber 12 and the first electrode 42 that is the extraction electrode. May be. Further, the control unit 80 may change the potential difference between the ion extraction unit 22 and the first electrode 42 by changing the applied voltage of the first power supply 38 or the second power supply 48 in order to change the ion extraction mode. In this way, the control unit 80 switches the ion extraction mode between the first mode and the second mode.

  The controller 80 may increase the temperature of the cover member 62 by extracting ions in the second mode at the start of operation of the microwave ion source 10 or during a preparation period. Since the temperature of the cover member 62 is relatively low when the microwave ion source 10 is activated, the temperature of the cover member 62 can be increased in a shorter time by extracting ions in the second mode. Moreover, the control part 80 may be made to maintain the temperature of the cover member 62 at high temperature by switching a drawer | drawing-out aspect from a 1st aspect to a 2nd aspect regularly. For example, the cover member 62 can be kept at a high temperature without restricting the use of the ion beam by setting the extraction mode in the period when the ion beam is not used downstream of the beam line as the second mode. Thereafter, the ion extraction mode is switched to the first mode, and the ion beam is supplied to the subsequent beam line.

Furthermore, the control unit 80 may switch the source gas to a rare gas when the ion extraction mode is the second mode. For example, when the ion extraction mode is switched to the second mode while using phosphine (PH ₃ ) to extract the ion beam of phosphorus (P), a large amount of P ⁺ ions adhere to the cover member 62, There is a risk of increased deposits. Therefore, when switching to the second mode, a rare gas such as argon (Ar) is introduced as a source gas, and Ar ⁺ ions collide with the cover member 62. Thereby, even if it is a case where the microwave ion source 10 is drive | operated in a 2nd aspect, the temperature of the cover member 62 can be raised, preventing the increase in the deposit on the cover member 62. FIG. Thereby, adhesion of the deposit to the cover member 62 can be further reduced.

  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.

  FIG. 8 schematically shows a configuration of the first electrode 42 according to the modification. This modification is described above in that the second spacer member 64b is provided between the attachment member 70 and the opening protection member 66 separately from the first spacer member 64a provided between the base member 60 and the cover member 62. This is different from the embodiment. Therefore, the opening protection member 66 is fixed to the base member 60 via the second spacer member 64b, and the thermal insulation between the base member 60 and the opening protection member 66 is enhanced. This makes it easier to keep the opening protection member 66 at a higher temperature than when the second spacer member 64 b is not provided, and makes it difficult for deposits to adhere to the opening protection member 66.

  In the above-described embodiment, the temperature of the cover member 62 is increased using radiant heat from the plasma chamber 12 or ions extracted from the extraction opening 24. In a modification, the cover member 62 may be provided with a heating mechanism to heat the cover member 62. For example, the heater may be attached so as to be embedded in the back surface of the cover member 62 facing the main surface of the base member 60 or in the cover member 62. Thereby, the cover member 62 can be kept at a high temperature without switching the ion extraction mode to the second mode. Even when the heating mechanism is provided, the spacer member 64 is provided between the base member 60 and the cover member 62, so that the cover member 62 can be easily maintained at a high temperature.

  In the above-described embodiment, a configuration in which the first electrode 42 and the second electrode 52 are combined as the extraction electrode system 40 is used. In the modification, only one extraction electrode facing the ion extraction portion 22 of the plasma chamber 12 may be used as the extraction electrode system, or three or more electrodes may be used as the extraction electrode system. In addition, the cover member that protects the surface of the extraction electrode may be provided only on the extraction electrode adjacent to the ion extraction portion 22, or when the extraction electrode system has a plurality of extraction electrodes, each of the plurality of extraction electrodes A cover member may be provided.

  In the above-described embodiment, phosphine is used as the source gas and phosphorus is attached as the deposit 90. However, in the present embodiment, the deposit is attached even when other source gases are used. Can be suppressed. For example, when arsine is used as the source gas, adhesion of arsenic (As) deposits can be suppressed.

  DESCRIPTION OF SYMBOLS 10 ... Microwave ion source, 12 ... Plasma chamber, 22 ... Ion extraction part, 24 ... Extraction opening, 60 ... Base member, 61 ... Main surface, 62 ... Cover member, 64 ... Spacer member, 66 ... Opening protection member

Claims (5)

A plasma chamber having an ion extraction portion provided with an extraction opening;
An extraction electrode provided outside the plasma chamber so as to face the ion extraction unit,
The extraction electrode is
A base member having a main surface facing the ion extraction portion and an opening portion provided at a position communicating with the extraction opening;
A cover member provided between the ion extraction portion and the main surface so as to cover the periphery of the opening;
A spacer member provided between the base member and the cover member,
The spacer member is partially provided on the main surface so as to provide a gap between the base member and the cover member, and thermally insulates the cover member from the base member. A microwave ion source. A plasma chamber having an ion extraction portion provided with an extraction opening;
An extraction electrode provided outside the plasma chamber so as to face the ion extraction unit,
The extraction electrode is
A base member having a main surface facing the ion extraction portion and an opening portion provided at a position communicating with the extraction opening;
A cover member provided between the ion extraction portion and the main surface so as to cover the periphery of the opening;
A spacer member provided between the base member and the cover member,
It said base member is composed of stainless steel, features and to luma microwave ion source that said cover member is composed of tungsten.   3. The cover member according to claim 1, wherein the cover member is screwed to the base member by a screw that penetrates the spacer member, and is electrically connected to the base member through the screw. A microwave ion source as described. The extraction electrode further includes an opening protection member fixed to the base member and defining the opening,
The microwave ion source according to any one of claims 1 to 3 , wherein the opening protection member is made of graphite. The microwave ion source according to claim 4 , wherein the opening protection member is fixed to the base member via a spacer member different from the spacer member.

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