Ion generator and ion implanter

Abstract

To provide an ion generator capable of generating more multivalent ions under a low arc condition.SOLUTION: An ion generator 10 includes an arc chamber 50, a magnetic field generator 52 for generating a magnetic field B applied in an axial direction in an internal space S of the arc chamber 50, and a first cathode 54 configured to supply thermal electrons to the internal space S. The first cathode 54 includes a first cathode cap 72 that emits thermal electrons toward the internal space S. The first cathode 54 includes a first thermal shield 76 having a first extending portion that extends in a tubular shape in the axial direction on the radially outer side of the first cathode cap 72 and is adjacent to the first cathode cap 72 with a gap in the radial direction orthogonal to the axial direction, a first front end portion that protrudes toward the inside of the arc chamber, and a first front end opening that opens in the axial direction at the first front end portion. The first front end portion protrudes in the axial direction from the first cathode cap toward the inside of the arc chamber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to ion generating devices and ion implanters. [Background technology]

[0002] In semiconductor manufacturing processes, a standard process involves implanting ions into semiconductor wafers to change the conductivity or crystalline structure of the semiconductor. The equipment used in this process is generally called an ion implanter. In such an ion implanter, ions are generated by an ion generator equipped with an indirectly heated cathode (IHC) and an arc chamber. The generated ions are extracted to the outside of the arc chamber through an extraction electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-225139 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been an increasing demand for generating high-energy ion beams in order to implant ions deeper into the wafer surface. To generate high-energy ion beams, it is effective to generate multiply charged ions in an ion generator and accelerate the generated multiply charged ions using a DC acceleration mechanism or a radio frequency acceleration mechanism (e.g., a linear acceleration mechanism). To generate a sufficient amount of multiply charged ions using an ion generator, high arc conditions with increased arc voltage and arc current are required, which can result in significant wear on the arc chamber. Under such high arc conditions, the life of the ion generator is shortened, leading to a decrease in the productivity of the ion implanter.

[0005] The present disclosure provides an ion generator capable of generating a larger number of multiply charged ions under low arc conditions. [Means for solving the problem]

[0006] An ion generation device according to one embodiment of the present disclosure includes an arc chamber having an internal space and a front slit for extracting an ion beam from plasma generated in the internal space, a magnetic field generator for generating a magnetic field applied in an axial direction in the internal space, and a first cathode configured to supply thermoelectrons to the internal space. The first cathode includes a first cathode cap that protrudes axially toward the interior of the arc chamber and emits the thermoelectrons to be supplied to the internal space, a first heating source that heats the first cathode cap, a first extension portion that extends axially in a cylindrical shape radially outside the first cathode cap and is adjacent to the first cathode cap with a gap in a radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the interior of the arc chamber, and a first tip opening that opens axially at the first tip portion. The first tip portion protrudes axially toward the interior of the arc chamber further than the first cathode cap.

[0007] Another aspect of the present disclosure is an ion implantation apparatus including an ion generator according to an aspect, a beam accelerator that accelerates an ion beam extracted from the ion generator, and an implantation processing chamber in which the ion beam output from the beam accelerator is irradiated onto a wafer.

[0008] Any combination of the above components or mutual substitution of the components or expressions of the present disclosure between methods, devices, systems, etc. are also valid aspects of the present disclosure. [Effects of the Invention]

[0009] According to a non-limiting exemplary embodiment of the present disclosure, an ion generator capable of generating a larger number of multiply charged ions under lower arc conditions can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a top view showing a schematic configuration of an ion implantation apparatus according to an embodiment; [Figure 2] 1 is a cross-sectional view showing a schematic configuration of an ion generating device according to a first embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing in detail the configuration of a first cathode according to the first embodiment. [Figure 4] 4 is a plan view showing the configuration of the first cathode of FIG. 3 when viewed in the axial direction. FIG. [Figure 5] 5(a) and 5(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 6] 6(a) and 6(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 7] 7(a) and (b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 8] 8(a) and 8(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 9] 9(a) and 9(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 10] 10(a) and 10(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the first embodiment. [Figure 11] 11(a) to 11(o) are cross-sectional views schematically showing the shape of a first cathode cap according to a modification of the first embodiment. [Figure 12] FIG. 10 is a cross-sectional view showing in detail the configuration of a first cathode according to a second embodiment. [Figure 13] 13(a) to 13(c) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the second embodiment. [Figure 14] 14(a) to 14(c) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the second embodiment. [Figure 15] 15(a) and 15(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the second embodiment. [Figure 16] 16(a) and 16(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the second embodiment. [Figure 17] FIG. 10 is a cross-sectional view showing in detail the configuration of a first cathode according to a third embodiment. [Figure 18] 18(a) and 18(b) are cross-sectional views schematically showing the configuration of a first cathode according to a modification of the third embodiment. [Figure 19] FIG. 10 is a cross-sectional view showing in detail the configuration of a first cathode according to a fourth embodiment. [Figure 20] FIG. 13 is a cross-sectional view showing in detail the configuration of a first cathode according to a modified example of the fourth embodiment. [Figure 21] FIG. 10 is a cross-sectional view showing a schematic configuration of an ion generating device according to a fifth embodiment. [Figure 22] FIG. 10 is a cross-sectional view showing in detail the configuration of a repeller according to a fifth embodiment. [Figure 23] FIG. 13 is a cross-sectional view showing in detail the configuration of a repeller according to a modified example of the fifth embodiment. [Figure 24] FIG. 13 is a cross-sectional view showing in detail the configuration of a repeller according to a sixth embodiment. [Figure 25] FIG. 13 is a cross-sectional view showing in detail the configuration of a repeller according to a modified example of the sixth embodiment. [Figure 26] FIG. 13 is a cross-sectional view showing in detail the configuration of a repeller according to a seventh embodiment. [Figure 27] FIG. 13 is a cross-sectional view showing in detail the configuration of a repeller according to an eighth embodiment. [Figure 28] FIG. 13 is a cross-sectional view showing a schematic configuration of an ion generating device according to a ninth embodiment. [Figure 29] FIG. 20 is a cross-sectional view showing a schematic configuration of an ion generating device according to a tenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an ion generation device and an ion implantation device according to an embodiment will be described in detail with reference to the drawings. Note that in the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted as appropriate. Furthermore, the configurations described below are examples and do not limit the scope of the present disclosure in any way.

[0012] 1 is a top view showing a schematic configuration of an ion implantation apparatus 100 according to an embodiment. The ion implantation apparatus 100 is a so-called high-energy ion implantation apparatus. The ion implantation apparatus 100 generates an ion beam IB by extracting and accelerating ions generated in an ion generation apparatus 10, transports the ion beam IB along a beam line to a workpiece (e.g., a substrate or wafer W), and implants ions into the workpiece.

[0013] The ion implantation apparatus 100 includes a beam generation unit 12 that generates ions and separates them by mass, a beam acceleration unit 14 that further accelerates the ion beam IB to form a high-energy ion beam, a beam deflection unit 16 that performs energy analysis of the high-energy ion beam, control of energy dispersion, and trajectory correction, a beam transport unit 18 that transports the high-energy ion beam to a wafer W, and a substrate transfer processing unit 20 that implants the high-energy ion beam into the wafer W.

[0014] The beam generating unit 12 has an ion generator 10, an extraction electrode 11, and a mass analyzer 22. In the beam generating unit 12, ions are extracted from the ion generator 10 through the extraction electrode 11 and simultaneously accelerated, and the extracted and accelerated ion beam is mass analyzed by the mass analyzer 22. The mass analyzer 22 has a mass analysis magnet 22a and a mass analysis slit 22b. As a result of mass analysis by the mass analyzer 22, the ion species required for implantation are selected, and the ion beam of the selected ion species is guided to the next beam acceleration unit 14.

[0015] The beam acceleration unit 14 includes multiple linear accelerators, i.e., one or more radio frequency resonators, for accelerating the ion beam. The beam acceleration unit 14 is a radio frequency (RF) acceleration mechanism that accelerates ions by the action of a radio frequency (RF) electric field. The beam acceleration unit 14 includes a first linear accelerator 15a having a basic multi-stage RF resonator and a second linear accelerator 15b having an additional multi-stage RF resonator for ultra-high energy ion implantation. The direction of the ion beam accelerated by the beam acceleration unit 14 is changed by the beam deflection unit 16.

[0016] The high-energy ion beam extracted from the beam acceleration unit 14 has a certain range of energy distribution. Therefore, in order to scan the high-energy ion beam back and forth and collimate it downstream of the beam acceleration unit 14 and irradiate the wafer, it is necessary to perform highly accurate energy analysis, control of energy dispersion, trajectory correction, and adjustment of beam convergence / divergence in advance.

[0017] The beam deflection unit 16 performs energy analysis of the high-energy ion beam, controls energy dispersion, and corrects the trajectory. The beam deflection unit 16 includes at least two high-precision bending electromagnets, at least one energy width limiting slit, at least one energy analysis slit, and at least one lateral focusing device. The bending electromagnets are configured to perform energy analysis of the high-energy ion beam and precisely correct the ion implantation angle onto the wafer W.

[0018] The beam deflection unit 16 includes an energy analyzing electromagnet 24, a transverse focusing quadrupole lens 26 that suppresses energy dispersion, an energy analyzing slit 28, and a deflection electromagnet 30 that provides steering (correction of the ion beam trajectory). The energy analyzing electromagnet 24 is sometimes called an energy filter electromagnet (EFM). The high-energy ion beam is deflected by the beam deflection unit 16 and directed toward the wafer W.

[0019] The beam transport unit 18 is a beamline device that transports the ion beam IB emitted from the beam deflection unit 16, and includes a beam shaper 32 composed of a group of converging / diverging lenses, a beam scanner 34, a beam collimator 36, and a final energy filter 38 (including a final energy separation slit). The length of the beam transport unit 18 is designed to match the combined length of the beam generating unit 12 and the beam acceleration unit 14. The beam acceleration unit 14 and the beam transport unit 18 are connected by the beam deflection unit 16 to form a U-shaped layout overall.

[0020] A substrate transfer processing unit 20 is provided at the downstream end of the beam transport unit 18. The substrate transfer processing unit 20 includes an implantation processing chamber 42 and a substrate transfer section 44. The implantation processing chamber 42 is provided with a platen drive device 40 that holds a wafer W undergoing ion implantation and moves the wafer W in a direction perpendicular to the beam scanning direction. The substrate transfer section 44 is provided with a wafer transfer mechanism such as a transfer robot that transfers a wafer W before ion implantation into the implantation processing chamber 42 and transfers a wafer W after ion implantation out of the implantation processing chamber 42.

[0021] The ion generator 10 is configured to generate multiply charged ions of a dopant, such as boron (B), phosphorus (P), or arsenic (As). The beam acceleration unit 14 accelerates the multiply charged ions extracted from the ion generator 10 to generate a high-energy ion beam of 1 MeV or more, 4 MeV or more, or 12 MeV or more. By accelerating multiply charged ions (e.g., doubly, triply, quadruply, or more), a higher energy ion beam can be generated compared to accelerating singly charged ions.

[0022] The beam acceleration unit 14 may not be a two-stage linear accelerator as shown in the figure, but may be configured as a single linear accelerator as a whole, or may be implemented as a three or more stage linear accelerator. The beam acceleration unit 14 may also be configured as any other type of accelerator, for example, it may include a DC acceleration mechanism. This embodiment is not limited to a specific ion acceleration method, and any beam accelerator capable of generating a high-energy ion beam of 1 MeV or more, 4 MeV or more, or 12 MeV or more may be employed.

[0023] High-energy ion implantation drives the desired dopant ions into the wafer surface at higher energies than ion implantation with energies less than 1 MeV, thereby enabling the desired dopant to be implanted deeper into the wafer surface (e.g., to a depth of 5 μm or more). An application of high-energy ion implantation is, for example, the formation of P-type and / or N-type regions in the fabrication of semiconductor devices such as advanced image sensors.

[0024] Note that various configurations of the components of the ion implantation apparatus 100 of the present disclosure are possible. The ion implantation apparatus of the present disclosure is not limited by the configuration of the components other than the ion generator, as long as the ion generator described below can be applied. Furthermore, it should be noted that the ion generator and ion implantation apparatus of the present disclosure are suitable for generating an ion beam composed of multivalent ions, but can also be applied to generating an ion beam composed of monovalent ions.

[0025] The ion generator 10 according to this embodiment generates an arc discharge in the internal space of an arc chamber to generate plasma containing multiply charged ions. The ion generator 10 uses a so-called indirectly heated cathode and generates plasma by colliding thermoelectrons emitted from a cathode cap with a source gas. Generally, to strip more electrons from atoms contained in the source gas to generate multiply charged ions, high arc conditions, such as higher arc voltage and arc current, are required. Under such high arc conditions, the arc chamber is subject to severe wear and tear, shortening the life of the ion generator and necessitating frequent maintenance of the apparatus. This reduces the operating rate of the ion implantation apparatus 100 and the production efficiency of semiconductor devices.

[0026] Therefore, in this embodiment, an ion generator capable of generating a larger number of multicharged ions under low arc conditions is provided. The "low arc conditions" referred to here refer to arc conditions in which the arc voltage and arc current are relatively lower than the "high arc conditions" required to generate multicharged ions in conventional ion generators. In this embodiment, by employing at least one of the following features (1) to (7), high-density plasma can be efficiently generated even under low arc conditions, and a larger number of multicharged ions can be extracted from the high-density plasma. (1) A thermal shield provided around the cathode cap is used to narrow the range over which thermal electrons are emitted from the cathode cap toward the internal space of the arc chamber. (2) Multiple thermal shields are provided around the cathode cap to promote temperature rise of the cathode cap. (3) A voltage is applied to the thermal shield provided around the cathode cap to extract thermions. (4) A thermal shield is provided around the repeller head to promote the temperature rise of the repeller head. (5) A thermal shield provided around the repeller head is used to narrow the range in which thermoelectrons are emitted from the repeller head toward the internal space of the arc chamber. (6) Multiple thermal shields are provided around the repeller head to further promote the temperature rise of the repeller head. (7) A voltage is applied to the thermal shield provided around the repeller head to draw out thermions.

[0027] (First embodiment) 2 is a diagram showing a schematic configuration of an ion generator 10 according to the first embodiment. The ion generator 10 includes an arc chamber 50, a magnetic field generator 52, a first cathode 54, a repeller 56, a first filament power supply 58a, a first cathode power supply 58b, a first arc power supply 58c, an extraction power supply 58d, and a repeller power supply 58e.

[0028] An extraction electrode 11 is arranged near the ion generator 10 to extract the ion beam IB through a front slit 60 of the arc chamber 50. The extraction electrode 11 includes a first extraction electrode 11a and a second extraction electrode 11b. The first extraction electrode 11a is connected to a suppression power supply 11c, and a negative suppression voltage is applied to it. A ground voltage is applied to the second extraction electrode 11b. An extraction power supply 58d is connected to the arc chamber 50, and a positive extraction voltage is applied to it.

[0029] The arc chamber 50 has an internal space S where plasma is generated. The arc chamber 50 has a substantially rectangular box shape that defines the internal space S. The arc chamber 50 has a front slit 60 for extracting an ion beam IB from the plasma generated in the internal space S. The front slit 60 has an elongated shape that extends in a direction (also referred to as the axial direction) from the first cathode 54 toward the repeller 56. In the drawing, a plasma generation region P where high-density plasma is generated is schematically shown by a dashed line.

[0030] The arc chamber 50 has four side walls, including a front wall 50a and a rear wall 50b, as well as a first end wall 50c and a second end wall 50d. The front wall 50a has a front slit 60. A protrusion 50e protruding toward the interior of the arc chamber 50 is provided in the center of the front wall 50a, and the front slit 60 is formed in the protrusion 50e. By forming the front slit 60 in the protrusion 50e, an ion beam IB can be extracted from a higher-density plasma. The rear wall 50b faces the front wall 50a across the internal space S. A gas inlet 62 for introducing a source gas is provided in the rear wall 50b. The first end wall 50c and the second end wall 50d are arranged axially opposite each other across the internal space S. The first end wall 50c has a first cathode insertion hole 50f extending axially. The second end wall 50d has a repeller insertion hole 50g extending in the axial direction.

[0031] The arc chamber 50 is made of a high-melting-point material, such as a high-melting-point metal such as tungsten (W), molybdenum (Mo), or tantalum (Ta), or an alloy thereof. A portion or the entire arc chamber 50 may be made of graphite (C). For example, the front wall 50a or the protrusion 50e may be made of graphite, and the side walls other than the front wall 50a or the protrusion 50e (e.g., the rear wall 50b), the first end wall 50c, and the second end wall 50d may be made of a high-melting-point metal such as tungsten.

[0032] The magnetic field generator 52 is provided outside the arc chamber 50 and generates a magnetic field B that is applied in the axial direction in the internal space S of the arc chamber 50. The magnetic field generator 52 has a first magnetic pole 52a and a second magnetic pole 52b, and generates the magnetic field B in the axial direction, for example, from the first magnetic pole 52a to the second magnetic pole 52b. The direction of the magnetic field B may be the opposite direction, or may be from the second magnetic pole 52b to the first magnetic pole 52a. The arc chamber 50 is disposed between the first magnetic pole 52a and the second magnetic pole 52b.

[0033] The first cathode 54 supplies thermoelectrons to the internal space S of the arc chamber 50. The first cathode 54 is inserted through the first cathode insertion hole 50f and fixed to a first cathode support member 64 while being electrically insulated from the arc chamber 50. The first cathode support member 64 is provided outside the arc chamber 50. The first cathode 54 includes a first heat source 70, a first cathode cap 72, a first thermal break 74, and a first thermal shield 76.

[0034] The first heating source 70 is a heat source for heating the first cathode cap 72. The first heating source 70 is, for example, a filament connected to the first filament power supply 58a. The first heating source 70 is disposed inside the first thermal break 74 so as to face the first cathode cap 72. The first cathode power supply 58b is connected between the first heating source 70 and the first cathode cap 72, and a cathode voltage is applied thereto.

[0035] The first cathode cap 72 is a solid member that protrudes axially toward the inside of the arc chamber 50. The first cathode cap 72 has a shape that is rotationally symmetric about a central axis C that extends axially, for example, a truncated cone shape. The first cathode cap 72 emits thermoelectrons toward the internal space S when heated by the first heating source 70. A first arc power supply 58c is connected between the first cathode cap 72 and the arc chamber 50, and an arc voltage is applied thereto.

[0036] The first thermal break 74 is a cylindrical member that supports the first cathode cap 72 and extends axially from the first cathode support member 64 toward the first cathode cap 72. The first thermal shield 76 extends axially in a cylindrical shape radially outward from the first cathode cap 72 and the first thermal break 74. The first thermal shield 76 reflects heat radiation from the first cathode cap 72 and the first thermal break 74, which become hot, and suppresses heat loss from the first cathode cap 72 and the first thermal break 74, thereby promoting a temperature increase in the first cathode cap 72 and the first thermal break 74.

[0037] The first cathode cap 72, the first thermal break 74, and the first thermal shield 76 are made of a high-melting-point material, such as a high-melting-point metal such as tungsten, molybdenum, or tantalum, an alloy thereof, or graphite. As an example, the first cathode cap 72 and the first thermal shield 76 are made of tungsten, and the first thermal break 74 is made of tantalum.

[0038] The repeller 56 is provided on the axially opposite side of the first cathode 54, across the internal space S. The repeller 56 repels electrons in the vicinity of the repeller 56, causing the electrons to remain in the plasma generation region P, thereby increasing plasma generation efficiency. The repeller 56 is inserted into the repeller insertion hole 50g and fixed to a repeller support member 66 while being electrically insulated from the arc chamber 50. The repeller support member 66 is provided outside the arc chamber 50. A repeller power supply 58e is connected between the repeller 56 and the arc chamber 50, and a repeller voltage is applied to the repeller 56. Note that the repeller power supply 58e does not necessarily have to be provided, and the repeller 56 may be configured to have a floating potential. Furthermore, in a configuration where the repeller power supply 58e is not provided, an arc voltage may be applied to the repeller 56 by connecting the repeller 56 to an arc power supply 58c.

[0039] The repeller 56 includes a repeller head 80 and a repeller shaft 82. The repeller head 80 is a solid member that protrudes axially toward the inside of the arc chamber 50, and is disposed so as to be exposed to the internal space S. The repeller head 80 is provided at a position axially opposite the first cathode cap 72. The repeller shaft 82 is a columnar member that supports the repeller head 80, and extends axially from the repeller support member 66 toward the repeller head 80.

[0040] The repeller head 80 and the repeller shaft 82 are made of a high-melting-point material, such as a high-melting-point metal such as tungsten, molybdenum, or tantalum, an alloy thereof, or graphite. The repeller 56 may be made partially or entirely of graphite. For example, the repeller shaft 82 may be made of graphite, and the repeller head 80 may be made of a high-melting-point metal such as tungsten.

[0041] Next, the operation of the ion generator 10 will be described. The filament constituting the first heating source 70 is heated by the first filament power supply 58a and emits primary thermoelectrons. The primary thermoelectrons emitted by the first heating source 70 are accelerated by the cathode voltage (e.g., 200V to 600V) from the first cathode power supply 58b and collide with the first cathode cap 72, heating the first cathode cap 72 with the heat generated by the collision. The first cathode cap 72 heated by the first heating source 70 emits secondary thermoelectrons into the internal space S. The secondary thermoelectrons emitted by the first cathode cap 72 are accelerated by the arc voltage (e.g., 50V to 150V) from the first arc power supply 58c. The accelerated secondary thermoelectrons are supplied to the plasma generation region P as electrons with sufficient energy to generate plasma containing multiply charged ions. Electrons supplied to the plasma generation region P are bound by a magnetic field B applied in the axial direction in the internal space S, and move in a spiral along the magnetic field B. The repeller 56 repels the electrons to the plasma generation region P by a repeller voltage (e.g., 120 V to 200 V) from the repeller power supply 58e. As a result, the movement of the electrons is restricted to the plasma generation region P, thereby improving the plasma generation efficiency. The electrons moving in a spiral in the plasma generation region P ionize the source gas introduced from the gas inlet 62, generating plasma containing multivalent ions in the internal space S.

[0042] In the first embodiment, by adopting the above-described feature (1), a larger number of multiply charged ions are generated under low arc conditions. Specifically, a first thermal shield 76 provided around the first cathode cap 72 is used to narrow the range in which thermoelectrons are emitted from the first cathode cap 72 toward the internal space S of the arc chamber 50. By narrowing the range in which thermoelectrons are emitted, the range of the plasma generation region P (the width w in the radial direction perpendicular to the axial direction) is narrowed, and higher density plasma is generated in a narrower range. The configuration of such a first cathode 54 will be described in detail with reference to FIG. 3.

[0043] FIG. 3 is a cross-sectional view showing in detail the configuration of the first cathode 54 according to the first embodiment, and is an enlarged view of the first cathode 54 shown in FIG. 3. In FIG. 3, arrow A1 indicates the direction extending axially from the outside to the inside of the arc chamber 50, based on the first end wall 50c. Arrow A1 indicates the direction toward the inside of the arc chamber 50 along the axial direction. Arrow A2 indicates the direction opposite to arrow A1, that is, the direction toward the outside of the arc chamber 50 along the axial direction. In the first embodiment, the potential of the first thermal shield 76 is the same as the potential of the first cathode cap 72.

[0044] The first cathode cap 72 protrudes in the axial direction toward the inside of the arc chamber 50. The first cathode cap 72 has a tapered shape in which the radial width decreases toward the inside of the arc chamber 50, and has, for example, a trapezoidal shape that is symmetrical in the cross section of Fig. 3. The first cathode cap 72 has a thermionic emission surface 72a, a heat input surface 72b, and a flange 72c.

[0045] The thermionic emission surface 72a is a surface that protrudes toward the inside of the arc chamber 50 and emits thermionic electrons to be supplied to the internal space S. The thermionic emission surface 72a has a tip surface 72d that is a flat surface exposed in the axial direction toward the inside of the arc chamber 50, and a side surface 72e that is a curved surface (e.g., a truncated cone surface) exposed in a direction oblique to the axial direction. The radial width wb of the tip surface 72d is smaller than the maximum radial width wa of the thermionic emission surface 72a (the outer diameter of the side surface 72e), and is, for example, 10% to 95% of the maximum width wa, and preferably 50% to 80% of the maximum width wa.

[0046] The heat input surface 72b is a flat surface facing the first heating source 70 and is exposed axially toward the outside of the arc chamber 50. The first cathode cap 72 is heated mainly by primary thermoelectrons from the first heating source 70 directed toward the heat input surface 72b. The flange 72c is provided at or near the heat input surface 72b so as to protrude radially outward (e.g., in a direction radially away from the central axis C). The flange 72c engages with the engaging end 74a of the first thermal break 74.

[0047] The first thermal break 74 has a locking end 74a that protrudes in the direction of arrow A1 toward the inside of the arc chamber 50 and an attachment end 74b that protrudes in the direction of arrow A2 toward the outside of the arc chamber 50. The first thermal break 74 extends cylindrically in the axial direction from the attachment end 74b toward the locking end 74a. The locking end 74a engages with a flange 72c of the first cathode cap 72 to secure the first cathode cap 72. The attachment end 74b is attached to the first cathode support member 64.

[0048] The first thermal shield 76 is provided radially outward of the first cathode cap 72 and the first thermal break 74. The first thermal shield 76 has a first leading end 76a that protrudes in the direction of arrow A1 toward the interior of the arc chamber 50 and a first trailing end 76b that protrudes in the direction of arrow A2 toward the exterior of the arc chamber 50. The first leading end 76a protrudes further toward the interior of the arc chamber 50 than the first cathode cap 72. In other words, the axial position of the first leading end 76a is closer to the interior of the arc chamber 50 than the axial position of the tip (tip surface 72d) of the first cathode cap 72. The first trailing end 76b is attached to the first cathode support member 64. In a modified example, the first trailing end 76b may be attached to the first thermal break 74.

[0049] The first thermal shield 76 has a first tip opening 76c that opens in the axial direction at the first tip portion 76a. The first tip opening 76c allows thermions supplied from the first cathode cap 72 toward the internal space S to pass through. The first tip opening 76c is configured to narrow the passage range of thermions emitted from the thermion emission surface 72a. A first radial opening width w1 of the first tip opening 76c is smaller than the maximum radial width of the first cathode cap 72 (the radial width at the position of the flange 72c) and smaller than the maximum radial width wa of the thermion emission surface 72a. The first opening width w1 of the first tip opening 76c is 5% to 95% of the maximum width wa of the thermion emission surface 72a, for example, 50% to 90%. A radial tip width wb of the thermion emission surface 72a (the radial width wb of the tip surface 72d) is smaller than the first opening width w1 of the first tip opening 76c. The radial width wb of the tip surface 72d is, for example, 5% to 95% of the first opening width w1 of the first tip opening 76c, for example, 10% to 90%.

[0050] The first thermal shield 76 has a first extending portion 76d that extends axially in a cylindrical shape from the first end portion 76b to the first tip portion 76a. The first extending portion 76d is adjacent to the first cathode cap 72 and the first thermal break 74 with a radial gap between them. The first extending portion 76d has a first cylindrical portion 76f and a first tapered portion 76g.

[0051] The first cylindrical portion 76f is a portion of the first extending portion 76d where the radial width of the inner surface 76e is constant, and is disposed adjacent to the first thermal break 74 with a radial gap therebetween. The first cylindrical portion 76f is configured so that at least the inner surface 76e is cylindrical. The first cylindrical portion 76f is configured, for example, so that the distance d1 from the inner surface 76e of the first extending portion 76d to the first thermal break 74 is constant. Although the first cylindrical portion 76f shown in FIG. 3 is not adjacent to the first cathode cap 72 with a radial gap therebetween, in a modified example, the first cylindrical portion 76f may be configured so that it is adjacent to the first cathode cap 72 with a radial gap therebetween.

[0052] The first tapered portion 76g is a portion where the radial width of the inner surface 76e of the first extending portion 76d changes in the axial direction, and the radial width of the inner surface 76e of the first extending portion 76d decreases toward the interior of the arc chamber 50. The first tapered portion 76g is disposed adjacent to the first cathode cap 72 with a radial gap therebetween and is disposed along the thermionic emission surface 72a (side surface 72e) of the first cathode cap 72. The first tapered portion 76g is configured so that at least the inner surface 76e has a truncated cone shape. The first tapered portion 76g is configured, for example, so that the distance d2 from the inner surface 76e of the first extending portion 76d to the first cathode cap 72 is constant. For example, the inclination angle θ2 of the inner surface 76e of the first tapered portion 76g relative to the radial direction is the same as the inclination angle θ1 of the side surface 72e of the first cathode cap 72 relative to the radial direction. The first tapered portion 76g may be configured so that the outer surface 76h of the first extending portion 76d has a truncated cone shape. Although the first tapered portion 76g shown in Fig. 3 is adjacent to the first thermal break 74 (engaging end portion 74a) with a radial gap therebetween, the first tapered portion 76g may be configured so that there is no radial gap between the first thermal break 74 and the first thermal break 74.

[0053] FIG. 4 is a plan view showing the configuration of the first cathode 54 of FIG. 3 as viewed in the axial direction, viewing the first cathode 54 from the inside to the outside of the arc chamber 50. In FIG. 4, the first thermal shield 76 is shaded for ease of understanding. As shown in FIG. 4, the first cathode cap 72 and the first thermal shield 76 have shapes that are rotationally symmetric about the central axis C that extends in the axial direction and are arranged coaxially with each other. Although the first thermal break 74 is not visible in FIG. 4, the first thermal break 74 also has a shape that is rotationally symmetric about the central axis C and is arranged coaxially with the first cathode cap 72 and the first thermal shield 76.

[0054] As described above, the first radial opening width w1 of the first tip opening 76c is smaller than the maximum radial width wa of the thermionic emission surface 72a of the first cathode cap 72 and is larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). Therefore, at least a portion of the first thermal shield 76 is disposed so as to overlap with the first cathode cap 72 in the axial direction. More specifically, at least a portion of the edge of the first tip opening 76c of the first thermal shield 76 overlaps with the thermionic emission surface 72a of the first cathode cap 72 in the axial direction (specifically, the side surface 72e).

[0055] According to the first embodiment, by making the first opening width w1 of the first tip opening 76c of the first thermal shield 76 smaller than the maximum radial width of the first cathode cap 72, it is possible to narrow the radial range over which thermoelectrons are emitted from the first cathode cap 72 toward the inside of the arc chamber 50. As a result, it is possible to supply thermoelectrons intensively to a radially limited range, and it is possible to generate high-density plasma in the plasma generation region P even under low arc conditions.

[0056] According to the first embodiment, because the first cathode cap 72 has a tapered shape, thermoelectrons emitted from the side surface 72e of the first cathode cap 72 can be supplied toward the inside of the arc chamber 50. Furthermore, because the first thermal shield 76 has the first tapered portion 76g, the inner surface 76e of the first extension portion 76d is positioned closer to the side surface 72e of the first cathode cap 72, suppressing heat loss from the first cathode cap 72 and promoting a temperature increase in the first cathode cap 72. As a result, it becomes easier to maintain a high temperature in the first cathode cap 72 even under low arc conditions, and more thermoelectrons can be supplied to the plasma generation region P.

[0057] (Modification of the first embodiment) 5(a) to 10(b), modified examples of the first cathode 54 according to the first embodiment will be described. Below, while showing the structures of the first cathode cap 72 and the first thermal shield 76, differences from the first embodiment will be mainly described, and explanations of commonalities will be omitted as appropriate.

[0058] 5(a) and 5(b) are cross-sectional views schematically illustrating the configurations of first cathodes 54A and 54B according to modified examples. In the first cathode 54A shown in FIG. 5(a), the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the interior of the arc chamber than the first tip portion 76a of the first thermal shield 76. That is, the axial position of the tip (tip surface 72d) of the first cathode cap 72 is closer to the interior of the arc chamber than the axial position of the first tip portion 76a. In FIG. 5(a), the axial length of the first cathode cap 72 is longer than that shown in FIG. 3. In a further modified example, the axial length of the first extension portion 76d (e.g., the first tapered portion 76g) may be shorter than that shown in FIG. 3. In the first cathode 54B shown in FIG. 5(b), the axial position of the tip (tip surface 72d) of the first cathode cap 72 is the same as the axial position of the first tip portion 76a of the first thermal shield 76.

[0059] 6(a) and 6(b) are cross-sectional views schematically illustrating the configurations of first cathodes 54C and 54D according to modified examples. In the first cathode 54C shown in FIG. 6(a), the distance d2 from the inner surface 76e of the first extension portion 76d to the first cathode cap 72 varies depending on the axial position, and the distance d2 becomes smaller toward the inside of the arc chamber. In FIG. 6(a), the inclination angle θ2 of the inner surface 76e of the first tapered portion 76g relative to the radial direction is smaller than the inclination angle θ1 of the side surface 72e of the first cathode cap 72 relative to the radial direction.

[0060] 6(b), a first cathode 54D is configured such that a distance d2 from an inner surface 76e of a first extension portion 76d to the first cathode cap 72 increases toward the inside of the arc chamber, as opposed to the distance d2 in FIG. 6(b), an inclination angle θ2 of an inner surface 76e of a first tapered portion 76g with respect to the radial direction is greater than an inclination angle θ1 of a side surface 72e of the first cathode cap 72 with respect to the radial direction.

[0061] 7(a) and 7(b) are cross-sectional views schematically illustrating the configurations of first cathodes 54E and 54F according to modified examples. In the first cathode 54E shown in FIG. 7(a), the radial first opening width w1 of the first tip opening 76c is smaller than the radial maximum width wa of the thermionic emission surface 72a of the first cathode cap 72 and is the same as the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). In the first cathode 54F shown in FIG. 7(b), the radial first opening width w1 of the first tip opening 76c is smaller than the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d).

[0062] 8(a) and 8(b) are cross-sectional views schematically illustrating the configuration of first cathodes 54G and 54H according to modified examples. In the first cathode 54G shown in FIG. 8(a), the first tip portion 76a of the first thermal shield 76 extends radially inward. The first tip portion 76a extends radially inward from the tip of the first extension portion 76d. The first tip opening 76c in FIG. 8(a) has a tapered shape whose radial width increases toward the interior of the arc chamber. In a further modified example, the first tip opening 76c in FIG. 8(a) may be configured to have a constant radial width or may have an inverse tapered shape whose radial width decreases toward the interior of the arc chamber. In FIG. 8(a), the first radial opening width w1 of the first tip opening 76c is smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). In a further variant, the first radial opening width w1 of the first tip opening 76c may be the same as or larger than the radial tip width wb of the thermoelectron emission surface 72a (the radial width wb of the tip surface 72d).

[0063] In the first cathode 54H shown in FIG. 8(b), similar to FIG. 8(a), the first tip portion 76a of the first thermal shield 76 extends radially inward. In FIG. 8(b), the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the inside of the arc chamber than the first tip portion 76a, and the first tip portion 76a extends radially inward toward the first cathode cap 72. The first tip opening 76c in FIG. 8(b) has a tapered shape in which its radial width decreases toward the inside of the arc chamber. In a further modification, the first tip opening 76c in FIG. 8(b) may be configured to have a constant radial width or may have a tapered shape in which its radial width increases toward the inside of the arc chamber. In FIG. 8(b), the first radial opening width w1 of the first tip opening 76c is greater than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0064] 9(a) and 9(b) are cross-sectional views schematically illustrating the configurations of first cathodes 54I and 54J according to modified examples. In the first cathode 54I shown in FIG. 9(a), only the inner surface 76e of the first tapered portion 76g of the first thermal shield 76 is tapered; the outer surface 76h is not tapered. In FIG. 9(a), the inner surface 76e of the first tapered portion 76g is a truncated cone surface, and the outer surface 76h of the first tapered portion 76g is a cylindrical surface. In FIG. 9(a), the radial first opening width w1 of the first tip opening 76c is larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). In a further variant, the first radial opening width w1 at the first tip opening 76c may be the same as or smaller than the radial tip width wb of the thermoelectron emission surface 72a (the radial width wb of the tip surface 72d).

[0065] In the first cathode 54J shown in FIG. 9(b), the first extension portion 76d of the first thermal shield 76 has a first cylindrical portion 76f but does not have a first tapered portion 76g. In FIG. 9(b), the first cylindrical portion 76f is adjacent to the first cathode 54 with a radial gap therebetween, and a first tip portion 76a is provided at the tip of the first cylindrical portion 76f. The first tip portion 76a extends radially inward from the first cylindrical portion 76f. The first tip opening 76c in FIG. 9(b) has a tapered shape whose radial width increases toward the interior of the arc chamber. In a further variation, the first tip opening 76c in FIG. 9(b) may be configured to have a constant radial width, or may have an inverse tapered shape whose radial width decreases toward the interior of the arc chamber. 9(b), the first radial opening width w1 of the first tip opening 76c is smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). In a further modification, the first radial opening width w1 of the first tip opening 76c may be the same as or larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0066] 9(a) and 9(b), the first tip portion 76a protrudes further into the arc chamber than the tip (tip surface 72d) of the first cathode cap 72. In a further modification, the tip portion (tip surface 72d) of the first cathode cap 72 may be at the same axial position as the first tip portion 76a, or may protrude further into the arc chamber than the first tip portion 76a.

[0067] 10(a) and 10(b) are cross-sectional views schematically illustrating the configuration of first cathodes 54K and 54L according to modified examples. In the first cathodes 54K and 54L shown in FIGS. 10(a) and 10(b), the first tapered portion 76g is configured in a dome shape. Specifically, the inner surface 76e and the outer surface 76h of the first tapered portion 76g are configured as curved surfaces that are convex toward the inside of the arc chamber. The inner surface 76e and the outer surface 76h of the first tapered portion 76g are configured to be, for example, part of a sphere, an elliptical sphere, or a paraboloid of revolution.

[0068] In the first cathode 54K shown in Fig. 10(a), the first tip portion 76a protrudes further toward the inside of the arc chamber than the tip (tip surface 72d) of the first cathode cap 72. In Fig. 10(a), the first radial opening width w1 of the first tip opening 76c is the same as the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). As a further modification, the first radial opening width w1 of the first tip opening 76c may be larger or smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0069] 10(b), the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the inside of the arc chamber than the first tip portion 76a. The first tip portion 76a extends obliquely with respect to the axial direction toward the first cathode cap 72. In FIG. 10(b), the first radial opening width w1 of the first tip opening 76c is larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0070] The features related to the arrangement of the first cathode cap 72 and the first thermal shield 76 shown in FIGS. 3 to 10(b) and the features related to the shape of the first thermal shield 76 shown in FIGS. 3 to 10(b) can be used in any suitable combination. The first cathode cap 72 shown in FIGS. 3 to 10(b) may have a polygonal truncated pyramid shape instead of a truncated cone shape. The first cathode cap 72 shown in FIGS. 3 to 10(b) may have a shape that is rotationally asymmetric with respect to the central axis C of FIG. 3. The shape of the space defined by the inner surface 76e of the first tapered portion 76g shown in FIGS. 3 and 5(a) to 9(a) may be a truncated pyramid shape. The shape of the space defined by the inner surface 76e of the first tapered portion 76g shown in FIG. 9(b) may be a polygonal prism shape. The shape of the space defined by the inner surface 76e of the first tapered portion 76g shown in FIGS. 3 to 10(b) may have a shape that is rotationally asymmetric with respect to the central axis C of FIG.

[0071] 11(a) to 11(o) are cross-sectional views schematically showing the shape of a first cathode cap 72 according to a modified example. FIGS. 11(a) to 11(o) show first cathode caps 72 having a shape different from the truncated cone shape shown in FIGS. 3 to 10. The first cathode caps 72 shown in FIGS. 11(a) to 11(o) can be used in place of the truncated cone-shaped first cathode caps 72 shown in FIGS. 3 to 10. In other words, the first cathode caps 72 shown in FIGS. 11(a) to 11(o) can be used in combination with the first thermal shield 76 shown in FIGS. 3 to 10.

[0072] Fig. 11(a) shows a cylindrical (or polygonal) first cathode cap 72. The thermionic emission surface 72a of the first cathode cap 72 shown in Fig. 11(a) has a tip surface 72d formed by a flat surface exposed in the axial direction toward the inside of the arc chamber, and a side surface 72e formed by a cylindrical surface (or polygonal cylindrical surface) exposed in the radial direction. In Fig. 11(a), the radial width of the thermionic emission surface 72a is constant, and the maximum radial width wa and tip width wb of the thermionic emission surface 72a both correspond to the radial width of the tip surface 72d (the diameter of the side surface 72e).

[0073] FIG. 11(b) shows a first cathode cap 72 having a conical (or polygonal pyramidal) shape. The thermionic emission surface 72a of the first cathode cap 72 shown in FIG. 11(b) is formed of a conical surface (or polygonal pyramidal surface) that protrudes axially toward the inside of the arc chamber. Therefore, the first cathode cap 72 in FIG. 11(b) does not have a tip surface formed of a flat surface that is exposed axially toward the inside of the arc chamber. In FIG. 11(b), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the base of the conical (or polygonal pyramidal) shape, and the radial tip width of the thermionic emission surface 72a is 0.

[0074] FIG. 11(c) shows a dome-shaped first cathode cap 72. The first cathode cap 72 has a shape, for example, a sphere or an ellipsoid cut in half. The thermionic emission surface 72a of the first cathode cap 72 shown in FIG. 11(c) is formed by a curved surface (e.g., a part of a sphere, an ellipsoid, or a paraboloid of revolution) that protrudes axially toward the inside of the arc chamber, and does not have a tip surface formed by a flat surface that is exposed axially toward the inside of the arc chamber. In FIG. 11(c), the maximum radial width wa of the thermionic emission surface 72a corresponds to the radial diameter of the dome shape, and the radial tip width of the thermionic emission surface 72a is zero.

[0075] Figure 11(d) shows a first cathode cap 72 having a shape in which a cylinder and a truncated cone (or a polygonal prism and a truncated polygonal pyramid) are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(d) has a tip surface 72d formed by a flat surface exposed in the axial direction toward the inside of the arc chamber, a first side surface 72e1 formed by a truncated cone surface (or a truncated polygonal pyramid surface), and a second side surface 72e2 formed by a cylindrical surface (or a polygonal cylindrical surface). In Figure 11(d), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the cylinder (or polygonal prism), and the radial tip width wb of the thermionic emission surface 72a corresponds to the radial width of the tip surface 72d.

[0076] Figure 11(e) shows a first cathode cap 72 having a shape in which a cylinder and a cone (or a polygonal prism and a polygonal pyramid) are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(e) has a tip surface 72d consisting of a conical surface (or a polygonal pyramid surface) that protrudes axially toward the inside of the arc chamber, and a side surface 72e consisting of a cylindrical surface (or a polygonal cylindrical surface). In Figure 11(e), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the cylinder (or polygonal prism), and the radial tip width of the thermionic emission surface 72a is 0.

[0077] Figure 11(f) shows a first cathode cap 72 having a shape in which a cylinder and a dome shape are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(f) has a tip surface 72d formed by a curved surface (e.g., a part of a sphere, an ellipsoid, or a paraboloid of revolution) that protrudes axially toward the inside of the arc chamber, and a side surface 72e formed by a cylindrical surface. In Figure 11(f), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the cylinder, and the radial tip width of the thermionic emission surface 72a is 0.

[0078] Figure 11(g) shows a first cathode cap 72 having a shape in which two cylinders (or polygonal prisms) of different diameters are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(g) has a tip surface 72d formed by a flat surface exposed in the axial direction toward the inside of the arc chamber, a first side surface 72e1 formed by a cylindrical surface (or polygonal cylindrical surface) with a small diameter, an intermediate end surface 72f formed by a ring-shaped flat surface exposed in the axial direction toward the inside of the arc chamber, and a second side surface 72e2 formed by a cylindrical surface (or polygonal cylindrical surface) with a large diameter. In Figure 11(g), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the second side surface 72e2, and the radial tip width wb of the thermionic emission surface 72a corresponds to the radial width of the tip surface 72d (the diameter of the first side surface 72e1).

[0079] FIG. 11(h) shows a first cathode cap 72 having a shape in which a cylinder (or polygonal prism) and a cone (or a polygonal pyramid) with a diameter smaller than that of the cylinder are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in FIG. 11(h) has a tip surface 72d formed by a conical surface (or a polygonal pyramid surface) exposed in the axial direction toward the inside of the arc chamber, an intermediate end surface 72f formed by a ring-shaped flat surface exposed in the axial direction toward the inside of the arc chamber, and a side surface 72e formed by a cylindrical surface (or a polygonal cylindrical surface). In FIG. 11(h), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the side surface 72e, and the radial tip width of the thermionic emission surface 72a is 0.

[0080] Figure 11(i) shows a first cathode cap 72 having a shape in which a cylinder (or polygonal prism) and a dome shape with a diameter smaller than that of the cylinder (or polygonal prism) are stacked coaxially. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(i) has a tip surface 72d formed by a curved surface (e.g., a part of a sphere, an ellipsoid, or a paraboloid of revolution) that protrudes axially toward the inside of the arc chamber, an intermediate end surface 72f formed by a ring-shaped flat surface that is exposed axially toward the inside of the arc chamber, and a side surface 72e formed by a cylindrical surface (or a polygonal cylindrical surface). In Figure 11(i), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the side surface 72e, and the radial tip width of the thermionic emission surface 72a is 0.

[0081] 11(j) shows a first cathode cap 72 having a shape in which two cylinders (or two polygonal prisms) of different diameters and one truncated cone (or one polygonal pyramid) are stacked coaxially, with the truncated cone (or one polygonal pyramid) connecting the two cylinders (or two polygonal prisms). The thermionic emission surface 72a of the first cathode cap 72 shown in FIG. 11(j) has a tip surface 72d consisting of a flat surface exposed in the axial direction toward the inside of the arc chamber, a first side surface 72e1 consisting of a cylindrical surface (or polygonal cylindrical surface) with a small diameter, a second side surface 72e2 consisting of a truncated cone surface (or polygonal pyramid surface), and a third side surface 72e3 consisting of a cylindrical surface (or polygonal cylindrical surface) with a large diameter. In Figure 11(j), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the third side surface 72e3, and the radial tip width wb of the thermionic emission surface 72a corresponds to the radial width of the tip surface 72d (the diameter of the first side surface 72e1).

[0082] FIG. 11(k) shows a first cathode cap 72 having a shape in which a cylinder (or polygonal prism), a truncated cone (or polygonal pyramid), and a cone (or polygonal pyramid) are stacked coaxially, with the truncated cone (or polygonal pyramid) connecting the cylinder (or polygonal prism) and the cone (or polygonal pyramid). The thermionic emission surface 72a of the first cathode cap 72 shown in FIG. 11(k) has a tip surface 72d formed by a conical surface (or polygonal pyramid surface) protruding axially toward the inside of the arc chamber, a first side surface 72e1 formed by a truncated cone surface (or polygonal pyramid surface) having an inclination angle different from that of the tip surface 72d, and a second side surface 72e2 formed by a cylindrical surface (or polygonal cylindrical surface). In FIG. 11(k), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the second side surface 72e2, and the radial tip width of the thermionic emission surface 72a is zero.

[0083] Figure 11(l) shows a first cathode cap 72 having a shape in which a cylinder, a truncated cone, and a dome shape are stacked coaxially, with the truncated cone connecting the cylinder and the dome shape. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(l) has a tip surface 72d formed by a curved surface (e.g., a portion of a sphere, an ellipsoid, or a paraboloid of revolution) that protrudes axially toward the inside of the arc chamber, a first side surface 72e1 formed by a truncated cone surface, and a second side surface 72e2 formed by a cylindrical surface. In Figure 11(l), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the second side surface 72e2, and the radial tip width of the thermionic emission surface 72a is zero.

[0084] Figure 11(m) shows a first cathode cap 72 having a cylindrical shape with a chamfered edge at the tip. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(m) has a tip surface 72d formed by a flat surface exposed in the axial direction toward the inside of the arc chamber, a first side surface 72e1 formed by a curved surface protruding obliquely with respect to the axial direction, and a second side surface 72e2 formed by a cylindrical surface. In Figure 11(l), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the second side surface 72e2, and the radial tip width wb of the thermionic emission surface 72a corresponds to the radial width of the tip surface 72d.

[0085] Figure 11(n) shows a first cathode cap 72 having a dome-shaped shape with the tip cut off. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(n) has a tip surface 72d formed by a flat surface exposed in the axial direction toward the inside of the arc chamber, and a side surface 72e formed by a curved surface that is convex radially outward and toward the inside of the arc chamber. In Figure 11(n), the maximum radial width wa of the thermionic emission surface 72a corresponds to the radial diameter of the dome shape, and the radial tip width wb of the thermionic emission surface 72a corresponds to the radial width of the tip surface 72d.

[0086] Figure 11(o) shows a first cathode cap 72 having a shape in which a truncated cone and a dome are coaxially stacked. The thermionic emission surface 72a of the first cathode cap 72 shown in Figure 11(o) has a tip surface 72d formed by a curved surface (e.g., a part of a sphere, an ellipsoid, or a paraboloid of revolution) that protrudes axially toward the inside of the arc chamber, and a side surface 72e formed by a truncated cone surface. In Figure 11(o), the maximum radial width wa of the thermionic emission surface 72a corresponds to the diameter of the truncated cone (side surface 72e), and the radial tip width of the thermionic emission surface 72a is zero.

[0087] (Second embodiment) 12 is a cross-sectional view showing in detail the configuration of a first cathode 154 according to the second embodiment. The first cathode 154 according to the second embodiment differs from the first embodiment in that it further includes a second thermal shield 78. The following description of the second embodiment will focus on the differences with the first embodiment, and will omit a description of the commonalities as appropriate.

[0088] The first cathode 154 includes a first heating source 70, a first cathode cap 72, a first thermal break 74, a first thermal shield 76, and a second thermal shield 78. The first heating source 70, the first cathode cap 72, the first thermal break 74, and the first thermal shield 76 are configured similarly to the first embodiment.

[0089] The second thermal shield 78 extends axially in a cylindrical shape radially outside the first thermal shield 76. The second thermal shield 78 reflects thermal radiation from the first thermal shield 76, which is in a high-temperature state, and suppresses heat escape from the first thermal shield 76, thereby promoting a temperature increase in the first thermal shield 76. The second thermal shield 78 promotes a temperature increase in the first thermal shield 76, thereby promoting a temperature increase in the first cathode cap 72 and the first thermal break 74. In the second embodiment, the potential of the second thermal shield 78 is the same as the potentials of the first cathode cap 72, the first thermal break 74, and the first thermal shield 76.

[0090] Second thermal shield 78 has a shape that is rotationally symmetrical about the axial direction and is disposed, for example, coaxially with central axis C. Second thermal shield 78 has a second leading end 78a that protrudes in the direction of arrow A1 toward the inside of arc chamber 50 and a second trailing end 78b that protrudes in the direction of arrow A2 toward the outside of arc chamber 50.

[0091] 12 protrudes further toward the inside of the arc chamber 50 than the first tip 76a of the first thermal shield 76. In other words, the axial position of the second tip 78a is closer to the inside of the arc chamber 50 than the axial position of the first tip 76a. The second end 78b is attached to the first cathode support member 64. In a modified example, the second end 78b may be attached to the first thermal shield 76 or the first thermal break 74.

[0092] The second thermal shield 78 has a second tip opening 78c that opens in the axial direction at the second tip portion 78a. The second tip opening 78c allows thermions supplied from the first cathode cap 72 toward the internal space S to pass through. The second radial opening width w2 of the second tip opening 78c is larger than the first radial opening width w1 of the first tip opening 76c. The second opening width w2 of the second tip opening 78c shown in FIG. 12 is larger than the maximum radial width wa of the thermion emission surface 72a. The second radial opening width w2 of the second tip opening 78c is smaller than the maximum radial width w1a of the outer surface 76h of the first extension portion 76d of the first thermal shield 76.

[0093] The second thermal shield 78 has a second extending portion 78d that extends axially in a cylindrical shape from the second end portion 78b toward the second tip portion 78a. The second extending portion 78d is adjacent to the first extending portion 76d of the first thermal shield 76 with a radial gap between them. The second extending portion 78d has a second cylindrical portion 78f and a second tapered portion 78g.

[0094] The second cylindrical portion 78f is a portion of the second extending portion 78d in which the radial width of the inner surface 78e is constant, and is disposed adjacent to the first cylindrical portion 76f of the first thermal shield 76 with a radial gap therebetween. The second cylindrical portion 78f is configured so that at least the inner surface 78e is cylindrical. The second cylindrical portion 78f is configured, for example, so that the distance d3 from the inner surface 78e of the second extending portion 78d to the outer surface 76h of the first extending portion 76d is constant. The axial length of the second cylindrical portion 78f shown in FIG. 12 is the same as the axial length of the first cylindrical portion 76f. In a modified example, the axial length of the second cylindrical portion 78f may be greater or smaller than the axial length of the first cylindrical portion 76f.

[0095] The second tapered portion 78g is a portion where the radial width of the inner surface 78e of the second extension portion 78d changes in the axial direction, and the radial width of the inner surface 78e of the second extension portion 78d decreases toward the interior of the arc chamber 50. The second tapered portion 78g is disposed adjacent to the first tapered portion 76g of the first thermal shield 76 with a radial gap therebetween and is disposed along the first tapered portion 76g. The second tapered portion 78g is configured so that at least the inner surface 78e thereof has a conical shape. The second tapered portion 78g shown in FIG. 12 is configured so that a distance d4 from the inner surface 78e of the second extension portion 78d to the outer surface 76h of the first extension portion 76d is constant. In a modified example, the distance d4 may vary depending on the axial position, or may be configured so that the distance d4 decreases toward the interior of the arc chamber 50, or may be configured so that the distance d4 increases toward the interior of the arc chamber 50. 12, the axial length of the second tapered portion 78g is greater than the axial length of the first tapered portion 76g. In a modified example, the axial length of the second tapered portion 78g may be the same as or smaller than the axial length of the first tapered portion 76g.

[0096] In the second embodiment, the above-described features (1) and (2) are combined to generate more multiply charged ions under low arc conditions. Specifically, by using multiple thermal shields 76, 78 in combination, the temperature rise of the first cathode cap 72 can be accelerated compared to when a single thermal shield 76 is used. Furthermore, by using the first thermal shield 76 to narrow the range in which thermoelectrons are emitted from the first cathode cap 72 toward the internal space S of the arc chamber 50, a higher density plasma can be generated in a narrower range.

[0097] (Modification of the second embodiment) 13(a) to 16(b), modified examples of the first cathode 154 according to the second embodiment will be described. Below, while showing the structures of the first cathode cap 72, the first thermal shield 76, and the second thermal shield 78, differences from the contents described in the above embodiment will be mainly described, and explanations of commonalities will be omitted as appropriate.

[0098] 13(a) to 13(c) are cross-sectional views schematically illustrating the configurations of first cathodes 154A, 154B, and 154C according to modifications. In the first cathode 154A shown in FIG. 13(a), the first tip portion 76a and the second tip portion 78a are located at the same axial position, and the first tip portion 76a and the second tip portion 78a protrude further toward the inside of the arc chamber than the tip (tip surface 72d) of the first cathode cap 72. In the first cathode 154B shown in FIG. 13(b), the tip (tip surface 72d) of the first cathode cap 72, the first tip portion 76a, and the second tip portion 78a are located at the same axial position. In the first cathode 154C shown in Figure 13(c), the axial positions of the first tip portion 76a and the second tip portion 78a are the same, and the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the inside of the arc chamber than the first tip portion 76a and the second tip portion 78a.

[0099] 14(a) to 14(c) are cross-sectional views schematically illustrating the configurations of first cathodes 154D, 154E, and 154F according to modified examples. In the first cathode 154D shown in FIG. 14(a), the axial positions of the tip (tip surface 72d) of the first cathode cap 72 and the first tip portion 76a are the same, and the second tip portion 78a protrudes further toward the inside of the arc chamber than the tip (tip surface 72d) and the first tip portion 76a of the first cathode cap 72. In the first cathode 154E shown in FIG. 14(b), the axial positions of the tip (tip surface 72d) of the first cathode cap 72 and the second tip portion 78a are the same, and the tip (tip surface 72d) of the first cathode cap 72 and the second tip portion 78a protrude further toward the inside of the arc chamber than the first tip portion 76a. In the first cathode 154F shown in Figure 14(c), the second tip 78a protrudes further toward the inside of the arc chamber than the first tip 76a, and the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the inside of the arc chamber than the second tip 78a.

[0100] 15(a) and 15(b) are cross-sectional views schematically illustrating the configuration of first cathodes 154G and 154H according to modified examples. In the first cathodes 154G and 154H shown in FIGS. 15(a) and 15(b), the second tip portion 78a of the second thermal shield 78 extends radially inward. The second tip opening 78c has a tapered shape whose radial width increases toward the interior of the arc chamber.

[0101] 15(a), the second radial opening width w2 of the second tip opening 78c is configured to be smaller than the maximum width wa of the thermionic emission surface 72a of the first cathode cap 72 and larger than the first radial opening width w1 of the first tip opening 76c and the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d). Note that in a further modification, the second opening width w2 of the second tip opening 78c may be the same as the first opening width w1 of the first tip opening 76c. In other words, the second opening width w2 of the second tip opening 78c may be greater than or equal to the first opening width w1 of the first tip opening 76c.

[0102] 15(b), the second radial opening width w2 of the second tip opening 78c is configured to be smaller than the maximum width wa of the thermionic emission surface 72a of the first cathode cap 72 and the first radial opening width w1 of the first tip opening 76c, but larger than the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d). In this case, like the first tip opening 76c, the second tip opening 78c is configured to narrow the passage range of thermionic electrons emitted from the thermionic emission surface 72a. In a further variation, the second opening width w2 of the second tip opening 78c may be the same as or smaller than the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d).

[0103] 15(a) and 15(b), the second opening width w2 of the second tip opening 78c is adjusted by the second tip portion 78a extending radially inward. In a further modified example, in a configuration in which the second tip portion 78a does not extend radially inward, that is, in a configuration such as that shown in FIGS. 12 to 14(c), the second opening width w2 may be set to be the same as or smaller than any of the maximum width wa of the thermionic emission surface 72a of the first cathode cap 72, the tip width wb (the radial width wb of the tip surface 72d), and the first opening width w1 of the first tip opening 76c.

[0104] 16(a) and 16(b) are cross-sectional views schematically illustrating the configuration of first cathodes 154I and 154J according to modified examples. In the first cathodes 154I and 154J illustrated in FIGS. 16(a) and 16(b), the second extending portion 78d of the second thermal shield 78 has a second cylindrical portion 78f but does not have a second tapered portion 78g. In FIGS. 16(a) and 16(b), the second cylindrical portion 78f is adjacent to the first tapered portion 76g with a gap therebetween in the radial direction, and a second tip portion 78a is provided at the tip of the second cylindrical portion 78f.

[0105] In FIG. 16(a), the second tip portion 78a extends radially inward from the second cylindrical portion 78f. The second tip opening 78c has a tapered shape whose radial width increases toward the interior of the arc chamber. In FIG. 16(a), the second radial opening width w2 of the second tip opening 78c is smaller than the first radial opening width w1 of the first tip opening 76c and is larger than the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d). In this case, like the first tip opening 76c, the second tip opening 78c is configured to narrow the passage range of thermionic electrons emitted from the thermionic emission surface 72a. In a further modification, the second opening width w2 of the second tip opening 78c may be the same as or smaller than the radial tip width wb of the thermionic emission surface 72a of the first cathode cap 72 (the radial width wb of the tip surface 72d). The second opening width w2 of the second tip opening 78c may be the same as or larger than the first opening width w1 of the first tip opening 76c. In this case, the second opening width w2 of the second tip opening 78c may be smaller than, the same as, or larger than the maximum radial width w1a of the first extension portion 76d of the first thermal shield 76.

[0106] In Fig. 16(b), the second tip portion 78a does not extend radially inward from the second cylindrical portion 78f. Therefore, in Fig. 16(b), the second radial opening width w2 of the second tip opening 78c corresponds to the radial width of the inner surface 78e of the second extension portion 78d and is greater than the maximum radial width w1a of the first extension portion 76d.

[0107] In a further modification of the second embodiment, the second thermal shield 78 may have a shape similar to that of the first thermal shield 76 shown in Figures 9(a), 10(a), and 10(b). The first cathode cap 72 may have a shape similar to that of the first cathode cap 72 shown in Figures 11(a) to 11(o). Furthermore, in the second embodiment as well, the features related to the arrangement of the first cathode cap 72 and the first thermal shield 76 shown in Figures 3 to 10(b) and the features related to the shape of the first thermal shield 76 shown in Figures 3 to 10(b) can be used in any suitable combination.

[0108] (Third embodiment) 17 is a cross-sectional view showing in detail the configuration of a first cathode 254 according to the third embodiment. The first cathode 254 according to the third embodiment differs from the first embodiment in that a first thermal shield 276 is attached to the arc chamber 50. The following description of the third embodiment will focus on the differences from the first embodiment, and will omit a description of the commonalities as appropriate.

[0109] The first cathode 254 includes a first heat source 70, a first cathode cap 72, a first thermal break 74, and a first thermal shield 276. The first heat source 70, the first cathode cap 72, and the first thermal break 74 are configured similarly to the first embodiment.

[0110] The first thermal shield 276 is provided radially outward from the first cathode cap 72. The first thermal shield 276 has a first leading end 276a that protrudes in the direction of arrow A1 toward the interior of the arc chamber 50 and a first terminal end 276b that protrudes in the direction of arrow A2 toward the exterior of the arc chamber 50. The first leading end 276a protrudes further toward the interior of the arc chamber 50 than the first cathode cap 72. That is, the axial position of the first leading end 276a is closer to the interior of the arc chamber 50 than the axial position of the tip (tip surface 72d) of the first cathode cap 72. The first terminal end 276b is attached to the arc chamber 50, for example, to a first end wall 50c of the arc chamber 50. The first thermal shield 276 may be configured to be integral with the first end wall 50c, or may be configured to extend axially from the first end wall 50c toward the interior of the arc chamber 50.

[0111] The first thermal shield 276 has a first tip opening 276c that opens in the axial direction at the first tip portion 276a. The first tip opening 276c allows thermions supplied from the first cathode cap 72 toward the internal space S to pass through. A first radial opening width w1 of the first tip opening 276c is smaller than the maximum radial width of the first cathode cap 72 (the radial width at the position of the flange 72c) and smaller than the maximum radial width wa of the thermion emission surface 72a. The first opening width w1 of the first tip opening 276c is larger than the radial tip width wb of the thermion emission surface 72a (the radial width wb of the tip surface 72d).

[0112] The first thermal shield 276 has a first extending portion 276d extending axially in a cylindrical shape from a first end portion 276b to a first tip portion 276a. The first extending portion 276d is adjacent to the first cathode cap 72 with a radial gap therebetween. The first extending portion 276d has a first tapered portion 276g, in which the radial width of an inner surface 276e of the first extending portion 276d decreases toward the inside of the arc chamber 50. The first extending portion 276d is configured so that its entirety forms the first tapered portion 276g. The first tapered portion 276g is positioned adjacent to the first cathode cap 72 with a radial gap therebetween, and is positioned along the thermionic emission surface 72a (side surface 72e) of the first cathode cap 72. The first tapered portion 276g is configured so that at least the inner surface 276e has a truncated cone shape. The first tapered portion 276g is configured, for example, so that the distance d2 from the inner surface 276e of the first extending portion 276d to the first cathode cap 72 is constant. For example, the inclination angle θ2 of the inner surface 276e of the first tapered portion 276g relative to the radial direction is the same as the inclination angle θ1 of the side surface 72e of the first cathode cap 72 relative to the radial direction. The first tapered portion 276g may be configured so that the outer surface 276h has a truncated cone shape.

[0113] In the third embodiment, the potential of the first thermal shield 276 is the same as the potential of the arc chamber 50. An arc voltage is applied between the arc chamber 50 and the first cathode cap 72 by the first arc power supply 58c. Therefore, the potential of the first thermal shield 276 is different from the potential of the first cathode cap 72 and the first thermal break 74 and is higher than the potential of the first cathode cap 72 and the first thermal break 74 by the arc voltage. The potential of the first thermal shield 276 relative to the first cathode cap 72 and the first thermal break 74 (i.e., the arc voltage) is, for example, +30 V to +150 V.

[0114] In the third embodiment, by employing the above-described feature (3), a larger number of multiply charged ions are generated under low arc conditions. Specifically, by applying a voltage (here, equal to the arc voltage) for extracting thermoelectrons to the first thermal shield 276, thermoelectrons can be more efficiently extracted from the first cathode cap 72 toward the interior of the arc chamber 50. As a result, compared to when the potentials of the first thermal shield 276 and the first cathode cap 72 are the same, a larger number of thermoelectrons can be supplied toward the internal space S of the arc chamber 50, and a higher density plasma can be generated even under low arc conditions.

[0115] According to the third embodiment, by making the first tip portion 276a of the first thermal shield 276 protrude further toward the inside of the arc chamber 50 than the tip (tip surface 72d) of the first cathode cap 72, it is possible to more efficiently extract thermoelectrons emitted from the tip (tip surface 72d) of the first cathode cap 72. This makes it possible to supply more thermoelectrons toward the internal space S of the arc chamber 50 than in a configuration in which the tip (tip surface 72d) of the first cathode cap 72 protrudes further toward the inside of the arc chamber 50 than the first tip portion 276a.

[0116] In the third embodiment, by further combining and adopting the above-described feature (1), it is possible to generate a larger number of multiply charged ions under low arc conditions. Specifically, by making the first radial opening width w1 at the first tip portion 276a of the first thermal shield 276 smaller than the maximum radial width wa of the thermion emission surface 72a, it is possible to supply a larger number of thermions to a narrower range in the internal space S of the arc chamber 50 and generate a higher density plasma.

[0117] (Modification of the third embodiment) The third embodiment can also employ a structure similar to that of the first thermal shield 76 in the modified example of the first embodiment. The first thermal shield 276 may have a distance d2 from the inner surface 276e of the first thermal shield 276 to the first cathode cap 72 that varies depending on the axial position. The distance d2 from the inner surface 276e of the first thermal shield 276 to the first cathode cap 72 may be configured to decrease toward the inside of the arc chamber, as shown in FIG. 6(a). The distance d2 from the inner surface 276e of the first thermal shield 276 to the first cathode cap 72 may be configured to increase toward the inside of the arc chamber, as shown in FIG. 6(b).

[0118] 7(a), the first thermal shield 276 may be configured so that the first radial opening width w1 at the first tip portion 276a is the same as the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). As in FIG. 7(b), the first thermal shield 276 may be configured so that the first radial opening width w1 at the first tip portion 276a is smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0119] 8(a), the first thermal shield 276 may be configured such that the first tip portion 276a extends radially inward. In this case, the first tip opening 276c may have a tapered shape whose radial width increases toward the inside of the arc chamber. The first radial opening width w1 of the first tip opening 276c may be smaller than, equal to, or larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0120] The first thermal shield 276 may be configured such that only the inner surface 276e of the first tapered portion 276g is tapered, and the outer surface of the first tapered portion 276g is not tapered, as shown in FIG. 9(a). The first thermal shield 276 may be configured such that the first extending portion 276d includes only the first cylindrical portion, and does not include the first tapered portion 276g, as shown in FIG. 9(b). In this case, the first tip portion 276a may be configured to extend radially inward. The first tip opening 276c may have a tapered shape whose radial width increases toward the interior of the arc chamber.

[0121] 10(a), the first thermal shield 276 may have a dome-shaped first tapered portion 276g. That is, the inner surface 276e and the outer surface 276h of the first tapered portion 276g may be curved surfaces that are convex radially outward and toward the interior of the arc chamber. The inner surface 276e and the outer surface 276h of the first tapered portion 276g may be configured to be part of a sphere, an elliptical sphere, or a paraboloid of revolution.

[0122] 18(a) and 18(b) are cross-sectional views schematically illustrating the configuration of first cathodes 254A and 254B according to modified examples. In the first cathode 254A illustrated in FIG. 18(a), the first extending portion 276d of the first thermal shield 276 has a first cylindrical portion 276f and a first tapered portion 276g. The first cylindrical portion 276f is a portion of the inner surface 276e of the first extending portion 276d where the radial width is constant. The first cylindrical portion 276f is provided closer to the exterior of the arc chamber than the first tapered portion 276g. The first terminal portion 276b is provided at the end of the first cylindrical portion 276f. The first tapered portion 276g is provided closer to the interior of the arc chamber than the first cylindrical portion 276f. The first tip portion 276a is provided at the tip of the first tapered portion 276g.

[0123] 18(a), the first radial opening width w1 of the first tip opening 276c is smaller than the maximum radial width wa of the thermionic emission surface 72a of the first cathode cap 72 and larger than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d). Note that the first opening width w1 of the first tip opening 276c may be the same as or larger than the maximum radial width wa of the thermionic emission surface 72a. The first opening width w1 of the first tip opening 276c may be the same as or smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip surface 72d).

[0124] In the first cathode 254B shown in FIG. 18(b), the first extension portion 276d of the first thermal shield 276 has a first cylindrical portion 276f but does not have a first tapered portion (e.g., 276g in FIG. 18(a)). The first extension portion 276d is configured so that the radial width of the inner surface 276e of the first extension portion 276d is constant. The first tip portion 276a is provided at the tip of the first cylindrical portion 276f. The first end portion 276b is provided at the end of the first cylindrical portion 276f. In FIG. 18(b), the first radial opening width w1 of the first tip opening 276c is greater than the maximum radial width wa of the thermionic emission surface 72a of the first cathode cap 72.

[0125] In a further modification of the third embodiment, the shape of the first cathode cap 72 may be any of the shapes shown in FIGS. 11(a) to 11(o).

[0126] In a further modification of the third embodiment, the potential of the first thermal shield 276 may be different from the potential of the arc chamber 50. In this case, the first thermal shield 276 may be attached to the first end wall 50c via an electrical insulating member provided between the first thermal shield 276 and the arc chamber 50. The potential of the first thermal shield 276 may be lower than the potential of the arc chamber 50. For example, the potential of the arc chamber 50 relative to the first cathode cap 72 may be +30V to +150V, while the potential of the first thermal shield 276 relative to the first cathode cap 72 may be +5V to +100V.

[0127] (Fourth embodiment) 19 is a cross-sectional view showing in detail the configuration of a first cathode 354 according to the fourth embodiment. The first cathode 354 according to the fourth embodiment differs from the first and second embodiments in that it includes a second thermal shield 378 attached to the arc chamber 50. The following description of the fourth embodiment will focus on the differences from the first embodiment, and will omit a description of the commonalities as appropriate.

[0128] The first cathode 354 includes a first heat source 70, a first cathode cap 72, a first thermal break 74, a first thermal shield 76, and a second thermal shield 378. The first heat source 70, the first cathode cap 72, the first thermal break 74, and the first thermal shield 76 are configured similarly to the first embodiment.

[0129] The second thermal shield 378 extends in the axial direction in a cylindrical shape radially outside the first thermal shield 76. The second thermal shield 378 has a rotationally symmetric shape with respect to the axial direction and is disposed, for example, coaxially with the central axis C shown in FIG. 4. The second thermal shield 378 reflects thermal radiation from the first thermal shield 76, which is in a high-temperature state, and suppresses heat loss from the first thermal shield 76, thereby promoting a temperature increase in the first thermal shield 76. The second thermal shield 378 promotes a temperature increase in the first thermal shield 76, thereby promoting a temperature increase in the first thermal break 74 and the first cathode cap 72.

[0130] In the fourth embodiment, the potential of the second thermal shield 378 is the same as the potential of the arc chamber 50, and the potential of the first thermal shield 76 is the same as the potential of the first cathode cap 72. An arc voltage is applied between the arc chamber 50 and the first cathode cap 72 from the first arc power supply 58c. Therefore, the potential of the second thermal shield 378 is different from the potentials of the first cathode cap 72, the first thermal break 74, and the first thermal shield 76, and is higher than the potentials of the first cathode cap 72, the first thermal break 74, and the first thermal shield 76 by the arc voltage. The potential of the second thermal shield 378 relative to the first cathode cap 72, the first thermal break 74, and the first thermal shield 76 (i.e., the arc voltage) is, for example, +30 V to +150 V.

[0131] The second thermal shield 378 has a second tip portion 378a that protrudes in the direction of arrow A1 toward the inside of the arc chamber 50 and a second end portion 378b that protrudes in the direction of arrow A2 toward the outside of the arc chamber 50. The second tip portion 378a protrudes further toward the inside of the arc chamber 50 than the first cathode cap 72 and the first thermal shield 76. In other words, the axial position of the second tip portion 378a is closer to the inside of the arc chamber 50 than the axial position of the tip (tip surface 72d) of the first cathode cap 72, and is closer to the inside of the arc chamber 50 than the axial position of the first tip portion 76a of the first thermal shield 76. The second end portion 378b is attached to the arc chamber 50, for example, to the first end wall 50c of the arc chamber 50.

[0132] The second thermal shield 378 has a second tip opening 378c that opens in the axial direction at the second tip portion 378a. The second tip opening 378c allows thermions supplied from the first cathode cap 72 toward the internal space S to pass through. The second radial opening width w2 of the second tip opening 378c is smaller than the maximum radial width w1a of the outer surface 76h of the first thermal shield 76. The second opening width w2 of the second tip opening 378c shown in FIG. 19 is larger than the first radial opening width w1 of the first tip opening 76c and larger than the maximum radial width wa of the thermion emission surface 72a. Note that the second opening width w2 of the second tip opening 378c may be the same as the first radial opening width w1 of the first tip opening 76c. In other words, the second opening width w2 of the second tip opening 378c may be equal to or larger than the first radial opening width w1 of the first tip opening 76c.

[0133] The second thermal shield 378 has a second extension portion 378d that extends axially in a cylindrical shape from the second end portion 378b to the second tip portion 378a. The second extension portion 378d is adjacent to the first extension portion 76d of the first thermal shield 76 with a radial gap therebetween. The second extension portion 378d has a second tapered portion 378g, in which the radial width of an inner surface 378e of the second extension portion 378d decreases toward the interior of the arc chamber 50. The second extension portion 378d is configured so that its entirety forms the second tapered portion 378g. The second tapered portion 378g is positioned adjacent to the first tapered portion 76g with a radial gap therebetween and is positioned along the outer surface 76h of the first tapered portion 76g. The second tapered portion 378g is configured so that at least the inner surface 378e has a truncated cone shape. The second tapered portion 378g may be configured so that the outer surface 378h has a truncated cone shape. The second tapered portion 378g is configured, for example, so that the distance d4 from the inner surface 378e of the second extending portion 378d to the outer surface 76h of the first extending portion 76d is constant.

[0134] In the fourth embodiment, the above-described features (1) to (3) are combined to generate a larger number of multiply charged ions under low arc conditions. Specifically, the first thermal shield 76 is used to narrow the range in which thermoelectrons are emitted from the first cathode cap 72 toward the internal space S of the arc chamber 50, thereby generating a higher density plasma in a narrower range. Furthermore, by using multiple thermal shields 76, 378, the temperature rise of the first cathode cap 72 can be accelerated compared to when a single thermal shield 76 is used. Furthermore, by applying a voltage (here, equal to the arc voltage) for extracting thermoelectrons to the second thermal shield 378, thermoelectrons can be more efficiently extracted from the first cathode cap 72 toward the interior of the arc chamber 50.

[0135] According to the fourth embodiment, the second opening width w2 of the second tip opening 378c is equal to or greater than the first opening width w1 in the radial direction of the first tip opening 76c, and therefore the range over which thermoelectrons are emitted from the first cathode cap 72 toward the internal space S of the arc chamber 50 is limited by the first opening width w1 of the first tip opening 76c. As a result, the above-described feature (1) can be achieved by the first thermal shield 76, and feature (3) can be achieved by the second thermal shield 378. By achieving the two features (1) and (3) using the individual thermal shields 76 and 378, the shapes of the thermal shields 76 and 378 can be determined to be optimal for each of the features (1) and (3).

[0136] (Modification of the Fourth Embodiment) Fig. 20 is a cross-sectional view showing in detail the configuration of a first cathode 354A according to a modified example. In the first cathode 354A shown in Fig. 20, the second thermal shield 378 is configured to be integrated with the first end wall 50c of the arc chamber 50. In other words, the first end wall 50c of the arc chamber 50 has the second thermal shield 378 configured to extend axially inside the arc chamber 50.

[0137] The second thermal shield 378 has a second end portion 378b joined to the first end wall 50c. The second thermal shield 378 has a second extension portion 378d extending axially from the second end portion 378b toward the second tip portion 378a. The second extension portion 378d has a second cylindrical portion 378f configured so that the radial widths of the inner surface 378e and the outer surface 378h of the second extension portion 378d are constant. The second extension portion 378d is composed only of the second cylindrical portion 378f and does not have a second tapered portion (e.g., 378g in FIG. 19). The second tip portion 378a is configured to extend radially inward from the tip of the second extension portion 378d. The second tip opening 378c has a tapered shape whose radial width increases toward the interior of the arc chamber 50.

[0138] The second extension portion 378d shown in FIG. 20 may have only the second tapered portion 378g as shown in FIG. 19. The second extension portion 378d shown in FIG. 20 may have both the second cylindrical portion 378f and the second tapered portion 378g, similar to the first thermal shield 276 shown in FIG. 18(a). The second opening width w2 of the second tip opening 378c may be greater than, equal to, or smaller than the maximum radial width w1a of the outer surface 76h of the first thermal shield 76. The second opening width w2 of the second tip opening 378c may be greater than, equal to, or smaller than the maximum radial width wa of the thermionic emission surface 72a. The second opening width w2 of the second tip opening 378c may be larger than, the same as, or smaller than the first opening width w1 of the first tip opening 76c. The second opening width w2 of the second tip opening 378c may be larger than, the same as, or smaller than the radial tip width wb of the thermionic emission surface 72a (the radial width wb of the tip face 72d).

[0139] The above-described modifications of the first embodiment can also be applied to the fourth embodiment. The first cathode cap 72 and the first thermal shield 76 of the fourth embodiment can have the structures shown in FIGS. 3 to 10(b). The first cathode cap 72 of the fourth embodiment can have the shape shown in FIGS. 11(a) to 11(o). The second thermal shield 378 of the fourth embodiment can have the same structure as the second thermal shield 78 shown in FIGS. 12 to 16(b).

[0140] (Fifth embodiment) 21 is a cross-sectional view showing a schematic configuration of an ion generator 410 according to a fifth embodiment. The fifth embodiment differs from the first embodiment in that a repeller 456 includes a thermal shield 86 (hereinafter also referred to as a third thermal shield 86). The following description of the fifth embodiment will focus on the differences from the first embodiment, and a description of the commonalities will be omitted as appropriate.

[0141] The ion generation device 410 includes an arc chamber 50, a magnetic field generator 52, a first cathode 54, a repeller 456, a first filament power supply 58a, a first cathode power supply 58b, a first arc power supply 58c, an extraction power supply 58d, and a repeller power supply 58e. The arc chamber 50, the magnetic field generator 52, the first cathode 54, and the various power supplies 58a to 58e are configured similarly to those in the first embodiment. Note that the repeller power supply 58e does not necessarily have to be provided, and the repeller 456 may be configured to have a floating potential. Furthermore, in a configuration in which the repeller power supply 58e is not provided, an arc voltage may be applied to the repeller 456 by connecting the repeller 456 to an arc power supply 58c.

[0142] The repeller 456 includes a repeller head 80, a repeller shaft 82, a repeller connection portion 84, and a third thermal shield 86. The repeller head 80 and the repeller shaft 82 are configured in the same manner as in the first embodiment described above.

[0143] The repeller connection part 84 is provided between the repeller head 80 and the repeller shaft 82 and has a disk shape extending radially. The third thermal shield 86 is provided radially outside the repeller head 80 and extends axially in a cylindrical shape from the outer periphery of the repeller connection part 84 toward the inside of the arc chamber 50. The third thermal shield 86 reflects heat radiation from the repeller head 80, which becomes hot, and suppresses heat loss from the repeller head 80, thereby promoting a temperature increase in the repeller head 80. The repeller connection part 84 and the third thermal shield 86 are made of a high-melting-point material, such as a high-melting-point metal such as tungsten, molybdenum, or tantalum, an alloy thereof, or graphite.

[0144] FIG. 22 is a cross-sectional view showing in detail the configuration of a repeller 456 according to the fifth embodiment, and is an enlarged view of the repeller 456 shown in FIG. 21. In FIG. 22, arrow A3 indicates a direction extending axially from the outside to the inside of the arc chamber 50 with respect to second end wall 50d. Arrow A3 is a direction toward the inside of the arc chamber 50 along the axial direction. Arrow A4 is a direction opposite to arrow A3 and is a direction toward the outside of the arc chamber 50 along the axial direction.

[0145] The repeller head 80 is a solid member that protrudes axially toward the interior of the arc chamber 50 and is disposed so as to be exposed to the internal space S. The repeller head 80 has a shape that is rotationally symmetrical about a central axis C that extends axially, e.g., a cylindrical shape with chamfered edges on the upper and lower surfaces. The repeller head 80 has a leading end surface 80a that is a flat surface that is axially exposed toward the interior of the arc chamber 50, a terminal end surface 80b that is a flat surface that faces the outside of the arc chamber 50, and a side surface 80c that is a cylindrical surface that faces radially outward. The repeller connection portion 84 has a shape that is rotationally symmetrical about the central axis C that extends axially, and is disposed so as to be coaxial with the repeller head 80 and the repeller shaft 82.

[0146] The third thermal shield 86 has a third tip portion 86a that protrudes in the direction of arrow A3 toward the inside of the arc chamber 50. The third thermal shield 86 has a third tip opening 86c that opens axially at the third tip portion 86a. The third thermal shield 86 has a third extension portion 86d that extends axially in a cylindrical shape from the repeller connecting portion 84 toward the third tip portion 86a. The third extension portion 86d is adjacent to the repeller head 80 with a radial gap between them. The third thermal shield 86 has a shape that is rotationally symmetrical with respect to a central axis C that extends axially. The third thermal shield 86 is arranged, for example, coaxially with the repeller head 80, the repeller shaft 82, and the repeller connecting portion 84.

[0147] The axial position of the third tip portion 86a of the third thermal shield 86 is the same as the axial position of the tip (tip surface 80a) of the repeller head 80. In a modified example, the third tip portion 86a of the third thermal shield 86 may protrude further toward the inside of the arc chamber than the tip (tip surface 80a) of the repeller head 80. In another modified example, the tip (tip surface 80a) of the repeller head 80 may protrude further toward the inside of the arc chamber than the third tip portion 86a of the third thermal shield 86.

[0148] The third extension portion 86d has a third cylindrical portion 86f. The third cylindrical portion 86f is a portion where the radial width of the inner surface 86e of the third extension portion 86d is constant. The third cylindrical portion 86f is configured so that at least the inner surface 86e is cylindrical. The third cylindrical portion 86f is configured, for example, so that the distance d5 from the inner surface 86e of the third extension portion 86d to the side surface 80c of the repeller head 80 is constant. The third extension portion 86d shown in FIG. 22 is configured so that it is composed only of the third cylindrical portion 86f and does not have a tapered portion. Note that in a modified example, the third extension portion 86d of the third thermal shield 86 may have a third tapered portion. The third tapered portion is configured so that the radial width of the inner surface 86e of the third extension portion 86d changes depending on the axial position. For example, the radial width of inner surface 86e of third extension portion 86d may be configured to increase toward the inside of the arc chamber, or conversely, may be configured to decrease toward the inside of the arc chamber. In other words, distance d5 from inner surface 86e of third extension portion 86d to side surface 80c of repeller head 80 may be configured to increase toward the inside of the arc chamber, or conversely, may be configured to decrease toward the inside of the arc chamber.

[0149] In the fifth embodiment, the above-described feature (4) is adopted to generate a larger number of multiply charged ions under low arc conditions. The repeller head 80 is heated by interaction with the plasma generated in the plasma generation region P and reaches a high temperature. The third thermal shield 86 reflects thermal radiation from the repeller head 80, which is in a high temperature state, and suppresses heat loss from the repeller head 80, thereby promoting a temperature increase in the repeller head 80. Since the repeller head 80, which is maintained in a high temperature state, emits thermoelectrons, this promotion of temperature increase allows more thermoelectrons to be supplied from the repeller head 80 toward the internal space S of the arc chamber 50. Therefore, according to this embodiment, by providing the third thermal shield 86 around the repeller head 80, the plasma generation efficiency in the plasma generation region P can be improved.

[0150] The repeller 456 of the fifth embodiment may be used in combination with a first cathode of a modified example of the first embodiment, or in combination with a first cathode of the second, third or fourth embodiment, or a modified example thereof.

[0151] (Modification of the fifth embodiment) 23 is a cross-sectional view showing in detail the configuration of a repeller 456A according to a modified example. The repeller 456A includes a repeller head 480, a repeller shaft 82, a repeller connecting portion 84, and a third thermal shield 86. This modified example employs the above-described feature (5) and uses the third thermal shield 86 provided around the repeller head 480 to narrow the range over which thermoelectrons are emitted from the repeller head 480 toward the internal space S of the arc chamber 50. This modified example will be described mainly focusing on the differences from the fifth embodiment described above, and a description of the commonalities will be omitted as appropriate.

[0152] The repeller head 480 has a tapered shape whose radial width decreases toward the interior of the arc chamber 50, and has, for example, a trapezoidal shape that is symmetrical on the left and right sides in the cross section of FIG. 23 . The repeller head 480 has a shape that is rotationally symmetric with respect to a central axis C extending in the axial direction, and has, for example, a truncated cone shape. The repeller head 480 has a tip surface 480a formed of a flat surface that is exposed in the axial direction toward the interior of the arc chamber 50, and a side surface 480c that is exposed in a direction oblique to the axial direction. The tip surface 480a and the side surface 480c of the repeller head 480 are thermionic emission surfaces that emit thermionic electrons toward the internal space S of the arc chamber 50. The radial width wd of the tip surface 480a of the repeller head 480 is smaller than the maximum radial width wc of the repeller head 480.

[0153] The third extension portion 86d of the third thermal shield 86 has a third tapered portion 86g configured so that the radial width of the inner surface 86e decreases toward the inside of the arc chamber. The third tapered portion 86g is disposed adjacent to the repeller head 480 with a radial gap therebetween and is disposed along the side surface 480c of the repeller head 480. The third tapered portion 86g is configured so that the space defined by at least the inner surface 86e has a truncated cone shape. The third tapered portion 86g is configured so that, for example, the distance d5 from the inner surface 86e to the side surface 480c of the repeller head 480 is constant.

[0154] A third radial opening width w3 of the third tip opening 86c of the third thermal shield 86 is smaller than the maximum radial width wc of the repeller head 480 and larger than the radial tip width wd of the repeller head 480 (the radial width wd of the tip surface 480a). Therefore, at least a portion of the third thermal shield 86 is disposed so as to overlap with the repeller head 480 in the axial direction. More specifically, at least a portion of the edge of the third tip opening 86c of the third thermal shield 86 axially overlaps with the side surface 480c, which is the thermionic emission surface of the repeller head 480.

[0155] The repeller head 480 and the third thermal shield 86 may have the same structure as the first cathode cap 72 and the first thermal shield 76 shown in Figures 3 to 10(b). More specifically, the third extension portion 86d of the third thermal shield 86 may have the same structure as the first extension portion 76d (or the first tapered portion 76g) shown in Figures 3 to 10(b). The repeller head 480 may have the same shape as the first cathode cap 72 shown in Figures 11(a) to 11(o).

[0156] (Sixth embodiment) FIG. 24 is a cross-sectional view showing in detail the configuration of a repeller 556 according to the sixth embodiment. The repeller 556 differs from the fifth embodiment shown in FIG. 22 in that it further includes an additional thermal shield 88 (also referred to as a fourth thermal shield 88). The sixth embodiment employs the above-described feature (6), and provides multiple thermal shields 86, 88 around the repeller head 80 to further promote temperature rise in the repeller head 80. The sixth embodiment will be described focusing on the differences from the fifth embodiment, and a description of the commonalities will be omitted as appropriate.

[0157] The repeller 556 includes a repeller head 80, a repeller shaft 82, a repeller connecting portion 84, a third thermal shield 86, and a fourth thermal shield 88. The repeller head 80, the repeller shaft 82, the repeller connecting portion 84, and the third thermal shield 86 are configured in the same manner as in the fifth embodiment, but the diameter of the repeller connecting portion 84 is larger than that in FIG.

[0158] The fourth thermal shield 88 is disposed radially outward of the third thermal shield 86 and extends axially from the outer periphery of the repeller connecting portion 84 in a cylindrical shape. The fourth thermal shield 88 has a fourth tip portion 88a that protrudes toward the interior of the arc chamber 50 in the direction of arrow A3. The fourth thermal shield 88 has a fourth tip opening 88c that opens axially at the fourth tip portion 88a. The fourth thermal shield 88 has a fourth extension portion 88d that extends axially in a cylindrical shape from the repeller connecting portion 84 toward the fourth tip portion 88a. The fourth extension portion 88d is adjacent to the third extension portion 86d with a radial gap therebetween. The fourth thermal shield 88 has a rotationally symmetric shape with respect to the central axis C that extends axially. The fourth thermal shield 88 is disposed, for example, coaxially with the repeller head 80, the repeller shaft 82, the repeller connecting portion 84, and the third thermal shield 86.

[0159] The fourth tip portion 88a of the fourth thermal shield 88 protrudes toward the inside of the arc chamber further than the tip (tip surface 80a) of the repeller head 80 and the third tip portion 86a of the third thermal shield 86. In a modified example, the axial position of the fourth tip portion 88a of the fourth thermal shield 88 may be the same as the axial position of the tip (tip surface 80a) of the repeller head 80, or may be the same as the axial position of the third tip portion 86a of the third thermal shield 86. In another modified example, at least one of the tip (tip surface 80a) of the repeller head 80 and the third tip portion 86a of the third thermal shield 86 may protrude toward the inside of the arc chamber further than the fourth tip portion 88a of the fourth thermal shield 88.

[0160] The fourth extension portion 88d has a fourth cylindrical portion 88f. The fourth cylindrical portion 88f is a portion where the radial width of the inner surface 88e of the fourth extension portion 88d is constant. The fourth cylindrical portion 88f is configured so that at least the inner surface 88e is cylindrical. The fourth cylindrical portion 88f is configured, for example, so that the distance d6 from the inner surface 88e of the fourth extension portion 88d to the outer surface 86h of the third extension portion 86d is constant. The fourth extension portion 88d shown in FIG. 24 is configured so that it is composed only of the fourth cylindrical portion 88f and does not have a tapered portion. Note that in a modified example, the fourth extension portion 88d of the fourth thermal shield 88 may have a fourth tapered portion. The fourth tapered portion is configured so that the radial width of the inner surface 88e of the fourth extension portion 88d changes depending on the axial position. For example, the radial width of inner surface 488e of fourth extension portion 88d may be configured to increase toward the inside of the arc chamber, or conversely, may be configured to decrease toward the inside of the arc chamber. In other words, distance d6 from inner surface 88e of fourth extension portion 88d to outer surface 86h of third extension portion 86d may be configured to increase toward the inside of the arc chamber, or conversely, may be configured to decrease toward the inside of the arc chamber.

[0161] The fourth thermal shield 88 reflects heat radiation from the third thermal shield 86, which is in a high temperature state, and suppresses heat escape from the third thermal shield 86, thereby promoting a temperature rise in the third thermal shield 86. The fourth thermal shield 88 promotes a temperature rise in the third thermal shield 86, and as a result, promotes a temperature rise in the repeller head 80.

[0162] The repeller 556 of the sixth embodiment may be used in combination with a first cathode of a modified example of the first embodiment, or may be used in combination with a first cathode of the second, third or fourth embodiment, or a modified example thereof.

[0163] (Modification of the Sixth Embodiment) Fig. 25 is a cross-sectional view showing in detail the configuration of a repeller 556A according to a modified example. The repeller 556A includes a repeller head 480, a repeller shaft 82, a repeller connecting portion 84, a third thermal shield 86, and a fourth thermal shield 88. In this modified example, similar to the modified example shown in Fig. 23, the repeller head 480 has a truncated cone shape, and the third extension portion 86d of the third thermal shield 86 has a third tapered portion 86g. Furthermore, the fourth extension portion 88d of the fourth thermal shield 88 has a fourth tapered portion 88g.

[0164] In this modification, the above-described features (5) and (6) are combined to generate more multiply charged ions under low arc conditions. Specifically, the combination of the third thermal shield 86 and the fourth thermal shield 88 can further promote the temperature rise of the repeller head 480. Furthermore, by using the third thermal shield 86 to narrow the range in which thermoelectrons are emitted from the repeller head 480 toward the internal space S of the arc chamber 50, a higher density plasma can be generated in a narrower range.

[0165] The repeller 556A may have a structure similar to that of the first cathode 154 shown in FIG. 12. The third extension portion 86d (or the third tapered portion 86g) may be configured similarly to the first extension portion 76d (or the first tapered portion 76g) shown in FIGS. 3 to 16(b). The fourth extension portion 88d (the fourth tapered portion 88g) may be configured similarly to the second extension portion 78d (or the second tapered portion 78g) shown in FIGS. 12 to 16(b). The repeller head 480 may have a shape similar to that of the first cathode cap 72 shown in FIGS. 11(a) to 11(o).

[0166] 25, the fourth radial opening width w4 of the fourth tip opening 88c is larger than the third opening width w3 of the third tip opening 86c, the maximum width wc of the repeller head 480, and the tip width wd of the repeller head 480. In a further modification, the fourth radial opening width w4 of the fourth tip opening 88c may be the same as or smaller than any of the third opening width w3 of the third tip opening 86c, the maximum width wc of the repeller head 480, and the tip width wd of the repeller head 480.

[0167] (Seventh embodiment) 26 is a cross-sectional view showing in detail the configuration of a repeller 656 according to the seventh embodiment. The repeller 656 according to the seventh embodiment includes a repeller head 80, a repeller shaft 82, and a third thermal shield 286. The seventh embodiment differs from the fifth embodiment in that the third thermal shield 286 is attached to the arc chamber 50. The following description of the seventh embodiment will focus on the differences from the fifth embodiment, and will omit a description of the commonalities as appropriate.

[0168] The third thermal shield 286 has a third tip portion 286a that protrudes toward the inside of the arc chamber in the direction of arrow A3 and a third end portion 286b that protrudes toward the outside of the arc chamber in the direction of arrow A4. The third tip portion 286a protrudes toward the inside of the arc chamber 50 further than the repeller head 80. That is, the axial position of the third tip portion 286a is closer to the inside of the arc chamber 50 than the axial position of the tip (tip surface 80a) of the repeller head 80. The third thermal shield 286 has a third tip opening 286c that opens in the axial direction at the third tip portion 286a. The third end portion 286b is attached to the arc chamber 50, for example, to the second end wall 50d of the arc chamber 50. The third thermal shield 286 may be configured to be integral with the second end wall 50d or to extend axially from the second end wall 50d toward the inside of the arc chamber 50.

[0169] The third thermal shield 286 has a third extension portion 286d that extends axially in a cylindrical shape from the third end portion 286b toward the third end portion 286a. The third extension portion 286d is adjacent to the repeller head 80 with a radial gap therebetween. The third extension portion 286d has a third cylindrical portion 286f configured so that the radial width of the inner surface 286e of the third extension portion 286d is constant. The third extension portion 286d shown in FIG. 26 is configured only with the third cylindrical portion 286f and does not have a tapered portion. Note that in a modified example, the third extension portion 286d of the third thermal shield 286 may have a third tapered portion.

[0170] In the seventh embodiment, by employing the above-described feature (7), a larger number of multiply charged ions are generated under low arc conditions. Specifically, by applying a voltage (here, equal to the repeller voltage) for extracting thermoelectrons to the third thermal shield 286, thermoelectrons can be more efficiently extracted from the repeller head 80 toward the inside of the arc chamber 50. As a result, compared to when the repeller head 80 and the thermal shield 286 have the same potential, a larger number of thermoelectrons can be supplied toward the internal space S of the arc chamber 50, and a higher density plasma can be generated even under low arc conditions.

[0171] The third thermal shield 286 according to the seventh embodiment has a configuration similar to the first thermal shield 276 shown in FIG. 18(b). In a modified example, the third thermal shield 286 may have a configuration similar to the first thermal shield 276 shown in FIG. 17 or FIG. 18(a). More specifically, the third extension portion 286d of the third thermal shield 286 may have the same structure as the first extension portion 276d shown in FIGS. 17 to 18(b). The third thermal shield 286 according to the seventh embodiment may have a configuration similar to the first thermal shield 76 shown in FIGS. 3 to 10(b). The shape of the repeller head 80 may be a truncated cone shape similar to the first cathode cap 72 shown in FIGS. 17 to 18(b), or the shape of the first cathode cap 72 shown in FIGS. 11(a) to 11(o).

[0172] The repeller 656 of the seventh embodiment may be used in combination with a first cathode of a modified example of the first embodiment, or in combination with a first cathode of the second, third or fourth embodiment, or a modified example thereof.

[0173] (Eighth embodiment) 27 is a cross-sectional view showing in detail the configuration of a repeller 756 according to the eighth embodiment. The repeller 756 according to the eighth embodiment includes a repeller head 80, a repeller shaft 82, a repeller connecting portion 84, a third thermal shield 86, and a fourth thermal shield 388. The eighth embodiment differs from the sixth embodiment in that the fourth thermal shield 388 is attached to the arc chamber 50. The following description of the eighth embodiment will focus on the differences from the sixth embodiment, and a description of the commonalities will be omitted as appropriate.

[0174] The fourth thermal shield 388 has a fourth tip portion 388a that protrudes toward the inside of the arc chamber in the direction of arrow A3 and a fourth end portion 388b that protrudes toward the outside of the arc chamber in the direction of arrow A4. The fourth tip portion 388a protrudes further toward the inside of the arc chamber 50 than the tip (tip surface 80a) of the repeller head 80 and the third tip portion 86a of the third thermal shield 86. In other words, the axial position of the fourth tip portion 388a is closer to the inside of the arc chamber 50 than the axial positions of the tip (tip surface 80a) of the repeller head 80 and the third tip portion 86a of the third thermal shield 86. The fourth thermal shield 388 has a fourth tip opening 388c that opens in the axial direction at the fourth tip portion 388a. The fourth end portion 388b is attached to the arc chamber 50, for example, to the second end wall 50d of the arc chamber 50. The fourth thermal shield 388 may be configured to be integral with the second end wall 50d or to extend axially from the second end wall 50d toward the interior of the arc chamber 50.

[0175] The fourth thermal shield 388 has a fourth extension portion 388d that extends axially in a cylindrical shape from a fourth end portion 388b toward a fourth end portion 388a. The fourth extension portion 388d is adjacent to the third extension portion 86d with a radial gap therebetween. The fourth extension portion 388d has a fourth cylindrical portion 388f configured so that the radial width of the inner surface 388e of the fourth extension portion 388d is constant. The fourth extension portion 388d shown in FIG. 27 is configured solely with the fourth cylindrical portion 388f and does not have a tapered portion. Note that in a modified example, the fourth extension portion 388d of the fourth thermal shield 388 may have a fourth tapered portion.

[0176] In the eighth embodiment, by adopting the above-mentioned features (6) and (7), a larger number of multiply charged ions are generated under low arc conditions. Specifically, by providing multiple thermal shields 86, 388 around the repeller head 80, the temperature rise of the repeller head 80 can be promoted. Furthermore, by applying a voltage for extracting thermoelectrons (here, equal to the repeller voltage) to the fourth thermal shield 388, thermoelectrons can be more efficiently extracted from the repeller head 80 toward the inside of the arc chamber 50.

[0177] The repeller 756 according to the eighth embodiment may be configured similarly to the first cathodes 354, 354A shown in FIGS. 19 and 20. The third extension portion 86d of the third thermal shield 86 may have the same structure as the first extension portion 76d (or the first tapered portion 76g) shown in FIGS. 19 and 20. The fourth extension portion 388d of the fourth thermal shield 388 may have the same structure as the second extension portion 378d (or the second tapered portion 378g) shown in FIGS. 19 and 20. The third thermal shield 86 may have the same structure as the first thermal shield 76 shown in FIGS. 3 to 10(b), and the fourth thermal shield 388 may have the same structure as the second thermal shield 78 shown in FIGS. 12 to 16(b). The shape of the repeller head 80 may be a truncated cone shape similar to that of the first cathode cap 72 shown in FIGS. 19 and 20, or may be the shape of the first cathode cap 72 shown in FIGS. 11(a) to 11(o).

[0178] The repeller 756 of the eighth embodiment may be used in combination with a first cathode of a modified example of the first embodiment, or may be used in combination with a first cathode of the second, third or fourth embodiment, or a modified example thereof.

[0179] (Ninth embodiment) 28 is a cross-sectional view showing a schematic configuration of an ion generator 810 according to a ninth embodiment. The ninth embodiment differs from the first embodiment in that a second cathode 55 is provided instead of the repeller 56. The ninth embodiment is a dual-cathode ion generator provided with two cathodes, a first cathode 54 and a second cathode 55. The following description of the ninth embodiment will focus on the differences from the first embodiment, and will omit a description of the commonalities as appropriate.

[0180] Ion generation device 810 includes arc chamber 50, magnetic field generator 52, first cathode 54, second cathode 55, first filament power supply 58a, first cathode power supply 58b, first arc power supply 58c, extraction power supply 58d, second filament power supply 58f, second cathode power supply 58g, and second arc power supply 58h. Arc chamber 50, magnetic field generator 52, first cathode 54, first filament power supply 58a, first cathode power supply 58b, first arc power supply 58c, and extraction power supply 58d are configured in the same manner as in the first embodiment.

[0181] The second cathode 55 supplies thermoelectrons to the internal space S of the arc chamber 50. The second cathode 55 is provided on the axially opposite side of the internal space S from the first cathode 54. The second cathode 55 is inserted into a second cathode insertion hole 50h provided in the second end wall 50d and fixed to a second cathode support member 65 while being electrically insulated from the arc chamber 50. The second cathode support member 65 is provided outside the arc chamber 50. The second cathode 55 includes a second heating source 90, a second cathode cap 92, a second thermal break 94, and a second thermal shield 96.

[0182] The second heating source 90 is a heat source for heating the second cathode cap 92. The second heating source 90 is, for example, a filament connected to a second filament power supply 58f. The second heating source 90 is disposed inside the second thermal break 94 so as to face the second cathode cap 92. A second cathode power supply 58g is connected between the second heating source 90 and the second cathode cap 92, and a cathode voltage is applied thereto.

[0183] The second cathode cap 92 is a solid member that protrudes axially toward the inside of the arc chamber 50. The second cathode cap 92 has, for example, a truncated cone shape. When heated by the second heating source 90, the second cathode cap 92 emits thermoelectrons toward the internal space S. A second arc power supply 58h is connected between the second cathode cap 92 and the arc chamber 50, and an arc voltage is applied thereto. Note that the first arc power supply 58c and the second arc power supply 58h may be a common power supply. For example, the second arc power supply 58h may not be provided, and the arc voltage may be applied to the second cathode cap 92 by connecting the first arc power supply 58c to the second cathode cap 92.

[0184] The second thermal break 94 is a cylindrical member that supports the second cathode cap 92 and extends axially from the second cathode support member 65 toward the second cathode cap 92. The second thermal shield 96 extends axially in a cylindrical shape radially outward from the second cathode cap 92 and the second thermal break 94. The second thermal shield 96 reflects heat radiation from the second cathode cap 92 and the second thermal break 94, which are in a high-temperature state, and suppresses heat loss from the second cathode cap 92 and the second thermal break 94, thereby promoting a temperature increase in the second cathode cap 92 and the second thermal break 94.

[0185] The second cathode cap 92, the second thermal break 94, and the second thermal shield 96 are made of a high-melting-point material, such as a high-melting-point metal such as tungsten, molybdenum, or tantalum, an alloy thereof, or graphite. As an example, the second cathode cap 92 and the second thermal shield 96 are made of tungsten, and the second thermal break 94 is made of tantalum.

[0186] The second cathode 55 has a configuration similar to that of the first cathode 54 according to the first embodiment shown in FIG. 3. The second cathode 55 includes the same configuration as the first cathode 54, except that the "first" in the components of the first cathode 54 is replaced with "second." For example, the second thermal shield 96 extends cylindrically in the axial direction radially outside the second cathode cap 92 and has a second extension portion adjacent to the second cathode cap 92 with a radial gap therebetween, a second tip portion protruding toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion. The second radial opening width of the second tip opening is smaller than the maximum radial width of the thermionic emission surface of the second cathode cap 92.

[0187] According to the ninth embodiment, by using the first cathode 54 and the second cathode 55 together, a larger number of thermoelectrons can be supplied to the internal space S of the arc chamber 50. Also, in the second cathode 55, the second radial opening width of the second tip opening is smaller than the maximum radial width of the thermoelectron emission surface of the second cathode cap 92, so that the radial range over which thermoelectrons are emitted from the second cathode cap 92 toward the inside of the arc chamber 50 can be narrowed. As a result, thermoelectrons can be supplied intensively to a radially limited range, and high-density plasma can be generated in the plasma generation region P even under low arc conditions.

[0188] The second cathode 55 of the ninth embodiment may be used in combination with the first cathode of a variant of the first embodiment, or in combination with the first cathode of the second, third or fourth embodiment, or a variant thereof.

[0189] (Modification of the ninth embodiment) The second cathode 55 may be configured similarly to the first cathodes 54A to 54L according to the modified examples shown in Figures 5(a) to 10(b). The second cathode cap 92 of the second cathode 55 may have a shape similar to the first cathode cap 72 according to the modified examples shown in Figures 11(a) to 11(o).

[0190] The second cathode 55 may be configured similarly to the first cathode 154 according to the second embodiment. In this case, the second cathode 55 includes a configuration similar to that of the first cathode 154, except that the "first heat source 70, first cathode cap 72, first thermal break 74, first thermal shield 76, and second thermal shield 78" are replaced with "second heat source, second cathode cap, second thermal break, third thermal shield, and fourth thermal shield." In other words, the second cathode 55 includes a second heat source, a second cathode cap, a second thermal break, a third thermal shield, and a fourth thermal shield. The third thermal shield extends axially in a cylindrical shape radially outward from the second cathode cap and second thermal break. It has a third extension adjacent to the second cathode cap and second thermal break with a radial gap, a third tip protruding toward the interior of the arc chamber, and a third tip opening opening in the axial direction at the third tip. The fourth thermal shield extends axially in a cylindrical shape radially outward from the third thermal shield. It has a fourth extension adjacent to the third extension with a radial gap, a fourth tip protruding toward the interior of the arc chamber, and a fourth tip opening opening in the axial direction at the fourth tip. The third radial opening width of the third tip opening is greater than the maximum radial width of the thermionic emission surface of the second cathode cap. The second cathode 55 may be configured similarly to the first cathodes 154A to 154J according to the modified second embodiment.

[0191] The second cathode 55, which is configured in the same manner as the first cathodes 154 to 154J according to the second embodiment or a variant of the second embodiment, may be used in combination with a first cathode according to a variant of the first embodiment, or may be used in combination with a first cathode according to the second, third or fourth embodiment, or a variant thereof.

[0192] The second cathode 55 may be configured similarly to the first cathode 254 according to the third embodiment. In this case, the second cathode 55 includes a configuration similar to that of the first cathode 254, except that the "first heat source 70, first cathode cap 72, first thermal break 74, and first thermal shield 276" of the first cathode 254 are replaced with "second heat source, second cathode cap, second thermal break, and second thermal shield." That is, the second cathode 55 includes a second heat source, a second cathode cap, a second thermal break, and a second thermal shield. The second thermal shield extends axially in a cylindrical shape radially outward of the second cathode cap and second thermal break and has a second extension portion adjacent to the second cathode cap and second thermal break with a radial gap therebetween, a second tip portion protruding toward the interior of the arc chamber, and a second tip opening that opens axially at the second tip portion. The second thermal shield has a higher potential than the second cathode cap, and the second tip protrudes axially beyond the second cathode cap toward the inside of the arc chamber. The second cathode 55 may be configured similarly to the first cathodes 254A and 254B according to the modified example of the third embodiment.

[0193] The second cathode 55, which is configured in the same manner as the first cathodes 254 to 254B according to the third embodiment or a variant of the third embodiment, may be used in combination with a first cathode according to a variant of the first embodiment, or may be used in combination with a first cathode according to the second, third or fourth embodiment, or a variant thereof.

[0194] The second cathode 55 may be configured similarly to the first cathode 354 according to the fourth embodiment. In this case, the second cathode 55 includes a configuration similar to that of the first cathode 354, except that the "first heat source 70, first cathode cap 72, first thermal break 74, first thermal shield 76, and second thermal shield 378" are replaced with "second heat source, second cathode cap, second thermal break, third thermal shield, and fourth thermal shield." In other words, the second cathode 55 includes a second heat source, a second cathode cap, a second thermal break, a third thermal shield, and a fourth thermal shield. The third thermal shield extends axially in a cylindrical shape radially outward from the second cathode cap and second thermal break. It has a third extension adjacent to the second cathode cap and second thermal break with a radial gap, a third tip protruding toward the interior of the arc chamber, and a third tip opening opening in the axial direction at the third tip. The fourth thermal shield extends axially in a cylindrical shape radially outward from the third thermal shield. It has a fourth extension adjacent to the third extension with a radial gap, a fourth tip protruding toward the interior of the arc chamber, and a fourth tip opening opening in the axial direction at the fourth tip. The fourth radial opening width of the fourth tip opening is equal to or greater than the third radial opening width of the third tip opening. The second cathode 55 may be configured similarly to the first cathode 354A according to the modified fourth embodiment.

[0195] The second cathode 55, which is configured in the same manner as the first cathodes 354 to 354A according to the fourth embodiment or a variant of the fourth embodiment, may be used in combination with a first cathode according to a variant of the first embodiment, or may be used in combination with a first cathode according to the second, third or fourth embodiment, or a variant thereof.

[0196] (Tenth embodiment) 29 is a cross-sectional view showing a schematic configuration of an ion generator 910 according to a tenth embodiment. The tenth embodiment differs from the above-described embodiments in that a repeller 956 has a structure similar to that of the second cathode 55. The following description of the tenth embodiment will focus on the differences from the above-described embodiments, and will omit a description of the commonalities as appropriate.

[0197] The ion generation device 910 includes an arc chamber 50, a magnetic field generator 52, a first cathode 54, a repeller 956, a first filament power supply 58a, a first cathode power supply 58b, a first arc power supply 58c, an extraction power supply 58d, and a repeller power supply 58e. The arc chamber 50, the magnetic field generator 52, the first cathode 54, the first filament power supply 58a, the first cathode power supply 58b, the first arc power supply 58c, the extraction power supply 58d, and the repeller power supply 58e are configured in the same manner as in the first embodiment.

[0198] The repeller 956 includes a repeller head 992, a second thermal break 994, and a second thermal shield 996. The repeller 956 has a configuration similar to that of the second cathode 55 in FIG. 28 , except that the second heating source 90 is removed. The repeller 956 includes a configuration similar to that of the second cathode 55, except that the "second cathode cap 92, second thermal break 94, and second thermal shield 96" are replaced with "a repeller head 992, a second thermal break 994, and a second thermal shield 996." The repeller 956 differs from the second cathode 55 in that it does not include the second heating source 90. The repeller head 992 is heated by interaction with the plasma generated in the plasma generation region P.

[0199] (Modification of the Tenth Embodiment) The repeller 956 may be configured similarly to the first cathodes 54A to 54L according to the modified examples shown in Figures 5(a) to 10(b) except that the first heating source is removed. The repeller head 992 of the repeller 956 may have a shape similar to the first cathode cap 72 according to the modified examples shown in Figures 11(a) to 11(o).

[0200] The repeller 956 may be configured similarly to the first cathode 154 according to the second embodiment, except that the first heating source is removed. In this case, the repeller 956 includes a configuration similar to that of the first cathode 154, except that the "first cathode cap 72, first thermal break 74, first thermal shield 76, and second thermal shield 78" are replaced with "a repeller head, a second thermal break, a third thermal shield, and a fourth thermal shield." In other words, the repeller 956 includes a repeller head, a second thermal break, a third thermal shield, and a fourth thermal shield. The repeller 956 may be configured similarly to the first cathodes 154A to 154J according to the modified second embodiment, except that the first heating source is removed.

[0201] The repeller 956 may be configured similarly to the first cathode 254 according to the third embodiment, except that the first heating source is removed. In this case, the repeller 956 includes a configuration similar to that of the first cathode 254, except that the "first cathode cap 72, first thermal break 74, and first thermal shield 276" are replaced with a "repeller head, second thermal break, and second thermal shield." In other words, the repeller 956 includes a repeller head, a second thermal break, and a second thermal shield. The repeller 956 may be configured similarly to the first cathodes 254A, 254B according to the modified third embodiment, except that the first heating source is removed.

[0202] The repeller 956 may be configured similarly to the first cathode 354 according to the fourth embodiment, except that the first heating source is removed. In this case, the repeller 956 includes a configuration similar to that of the first cathode 354, except that the "first cathode cap 72, first thermal break 74, first thermal shield 76, and second thermal shield 378" are replaced with "a repeller head, a second thermal break, a third thermal shield, and a fourth thermal shield." In other words, the repeller 956 includes a repeller head, a second thermal break, a third thermal shield, and a fourth thermal shield. The repeller 956 may be configured similarly to the first cathode 354A according to the modified fourth embodiment.

[0203] While the present disclosure has been described above with reference to the above-described embodiments, the present disclosure is not limited to the above-described embodiments, and the configurations of the embodiments may be appropriately combined or substituted. Furthermore, based on the knowledge of a person skilled in the art, it is also possible to appropriately rearrange the combinations and processing orders in the embodiments, and to apply various design changes and other modifications to the embodiments. Such rearrangements and modifications may also be included in the scope of the ion generation device and ion implantation device according to the present disclosure.

[0204] In the above-described embodiment and modifications, the cathode cap is heated by a filament. In a further modification, a heat source other than a filament may be used. For example, a laser may be used as the heat source, and the cathode cap may be heated by irradiating the heat input surface of the cathode cap with laser light.

[0205] In the above-described embodiment and modified examples, one or two thermal shields are provided radially outward from the cathode cap or repeller head. In a further modified example, three or more thermal shields may be provided radially outward from the cathode cap or repeller head. For example, an additional thermal shield may be provided radially outward from the second thermal shield included in the first cathode, or an additional thermal shield may be provided radially outward from the fourth thermal shield included in the repeller or second cathode.

[0206] In the above-described embodiment and modified examples, a repeller used in combination with a first cathode according to the present disclosure has been described. The repeller according to the present disclosure is applicable to any ion generator and ion implanter equipped with a repeller, and is not limited to a combination with a first cathode including a tapered first cathode cap and a tapered first thermal shield according to the present disclosure. The repeller according to the present disclosure may be used in combination with a first cathode in which at least one of the first cathode cap and the first thermal shield does not have a tapered shape, or may be used in combination with a first cathode without a first thermal shield. The repeller according to the present disclosure may be used in combination with any indirectly heated first cathode.

[0207] Several aspects of the present disclosure are described below.

[0208] [Aspect 1] an arc chamber having an internal space and a front slit for extracting an ion beam from plasma generated in the internal space; a magnetic field generator for generating an axially applied magnetic field in the interior space; a first cathode configured to supply thermoelectrons to the interior space; The first cathode is a first cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons to be supplied to the internal space; a first heating source that heats the first cathode cap; a first thermal shield having a first extending portion that extends cylindrically in the axial direction radially outside the first cathode cap and is adjacent to the first cathode cap with a gap in a radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the inside of the arc chamber, and a first tip opening that opens in the axial direction at the first tip portion, The ion generating device, wherein a first opening width in the radial direction of the first tip opening is smaller than a maximum width in the radial direction of the first cathode cap. [Aspect 2] 2. The ion generating device according to aspect 1, wherein at least a portion of an edge of the first tip opening is provided at a position overlapping with the first cathode cap in the axial direction. [Aspect 3] 3. The ion generating device according to aspect 1 or 2, wherein the first cathode cap has a tapered shape in which the width in the radial direction decreases toward the inside of the arc chamber. [Aspect 4] The ion generation device according to any one of aspects 1 to 3, wherein the first extension portion has a first tapered portion configured such that the radial width of the inner surface of the first extension portion decreases toward the inside of the arc chamber. [Aspect 5] 5. The ion generating device according to any one of aspects 1 to 4, wherein the distance between the first extension and the first cathode cap is constant. [Aspect 6] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 6. The ion generator according to any one of aspects 1 to 5, wherein the first opening width is larger than the width of the tip surface in the radial direction. [Aspect 7] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 6. The ion generator according to any one of aspects 1 to 5, wherein the first opening width is equal to or smaller than the width of the tip surface in the radial direction. [Aspect 8] The ion generation device according to any one of aspects 1 to 7, wherein the first tip portion protrudes in the axial direction toward the inside of the arc chamber further than a tip of the first cathode cap protruding in the axial direction toward the inside of the arc chamber. [Aspect 9] The ion generation device according to any one of aspects 1 to 6, wherein a tip of the first cathode cap protruding in the axial direction toward the inside of the arc chamber is at the same axial position as the first tip portion, or protrudes further toward the inside of the arc chamber than the first tip portion. [Aspect 10] 10. The ion generator according to any one of aspects 1 to 9, wherein the potential of the first thermal shield is the same as the potential of the first cathode cap. [Aspect 11] 11. The ion generating device according to any one of aspects 1 to 10, wherein the first tip portion extends radially inward from the first extension portion. [Aspect 12] 12. The ion generation device according to any one of aspects 1 to 11, wherein the first end opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber. [Aspect 13] a second cathode disposed on the opposite side of the internal space from the first cathode in the axial direction and configured to supply thermoelectrons to the internal space; The second cathode is a second cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a second heating source for heating the second cathode cap; a second thermal shield having a second extending portion that extends cylindrically in the axial direction radially outside the second cathode cap and is adjacent to the second cathode cap with a gap in the radial direction, a second tip portion that protrudes toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion, 13. The ion generator according to any one of aspects 1 to 12, wherein a second opening width in the radial direction of the second tip opening is smaller than a maximum width in the radial direction of the second cathode cap. [Aspect 14] a repeller provided on the opposite side of the internal space from the first cathode in the axial direction, The repeller is a repeller head projecting in the axial direction toward the interior of the arc chamber; 13. The ion generation device according to any one of aspects 1 to 12, further comprising: a thermal shield extending cylindrically in the axial direction radially outside the repeller head.

[0209] [Aspect 15] The ion generation device according to any one of aspects 1 to 12, wherein the first cathode further includes a second thermal shield that extends cylindrically in the axial direction radially outside the first thermal shield and has a second extension portion that is adjacent to the first extension portion with a gap in the radial direction, a second tip portion that protrudes toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion. [Aspect 16] The ion generating device described in aspect 15, wherein the second tip portion is at the same position in the axial direction as the first tip portion, or protrudes further toward the inside of the arc chamber than the first tip portion. [Aspect 17] The ion generating device according to aspect 15 or 16, wherein in a cross section along the axial direction, the second radial opening width of the second tip opening is smaller than the maximum radial width of the outer surface of the first extension portion. [Aspect 18] 18. The ion generating device according to aspect 17, wherein the second opening width is equal to or greater than the first opening width. [Aspect 19] 18. The ion generating device according to aspect 17, wherein the second opening width is smaller than the first opening width. [Aspect 20] 20. An ion generation device according to any one of aspects 15 to 19, wherein the second extension portion has a second tapered portion configured so that the radial width of the inner surface of the second extension portion becomes smaller toward the inside of the arc chamber. [Aspect 21] 21. The ion generator according to any one of aspects 15 to 20, wherein the second thermal shield has the same potential as the first thermal shield. [Aspect 22] 22. The ion generating device according to any one of aspects 15 to 21, wherein the second tip portion extends inward in the radial direction from the second extension portion. [Aspect 23] 23. The ion generation device according to any one of aspects 15 to 22, wherein the second tip opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber. [Aspect 24] a second cathode disposed on the opposite side of the internal space from the first cathode in the axial direction and configured to supply thermoelectrons to the internal space; The second cathode is a second cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a second heating source for heating the second cathode cap; a third thermal shield that extends cylindrically in the axial direction radially outside the second cathode cap and has a third extension portion that is adjacent to the second cathode cap with a gap in a radial direction perpendicular to the axial direction, a third tip portion that protrudes toward the inside of the arc chamber, and a third tip opening that opens in the axial direction at the third tip portion; a fourth thermal shield that extends cylindrically in the axial direction radially outside the third thermal shield and has a fourth extension portion that is adjacent to the third extension portion with a gap in the radial direction, a fourth tip portion that protrudes toward the inside of the arc chamber, and a fourth tip opening that opens in the axial direction at the fourth tip portion, 24. The ion generator according to any one of aspects 15 to 23, wherein a third opening width in the radial direction of the third tip opening is smaller than a maximum width in the radial direction of the second cathode cap. [Aspect 25] a repeller provided on the opposite side of the internal space from the first cathode in the axial direction, The repeller is a repeller head projecting in the axial direction toward the interior of the arc chamber; 24. The ion generation device according to any one of aspects 15 to 23, further comprising: a thermal shield extending cylindrically in the axial direction radially outside the repeller head.

[0210] [Aspect 26] an arc chamber having an internal space and a front slit for extracting an ion beam from plasma generated in the internal space; a magnetic field generator for generating an axially applied magnetic field in the interior space; a first cathode configured to supply thermoelectrons to the interior space; The first cathode is a first cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons to be supplied to the internal space; a first heating source that heats the first cathode cap; a first thermal shield having a first extending portion that extends cylindrically in the axial direction radially outside the first cathode cap and is adjacent to the first cathode cap with a gap in a radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the inside of the arc chamber, and a first tip opening that opens in the axial direction at the first tip portion, the potential of the first thermal shield is higher than the potential of the first cathode cap; The ion generating device, wherein the first tip portion protrudes in the axial direction toward the inside of the arc chamber beyond the first cathode cap. [Aspect 27] 27. The ion generating device according to aspect 26, wherein a first opening width in the radial direction of the first tip opening is smaller than a maximum width in the radial direction of the first cathode cap. [Aspect 28] 28. The ion generating device according to aspect 26 or 27, wherein at least a part of the edge of the first tip opening is provided at a position overlapping with the first cathode cap in the axial direction. [Aspect 29] 29. The ion generation device according to any one of aspects 26 to 28, wherein the first cathode cap has a tapered shape in which the width in the radial direction decreases toward the inside of the arc chamber. [Aspect 30] 30. An ion generation device according to any one of aspects 26 to 29, wherein the first extension portion has a first tapered portion configured so that the radial width of the inner surface of the first extension portion becomes smaller toward the inside of the arc chamber. [Aspect 31] 31. The ion generating device according to any one of aspects 26 to 30, wherein the distance between the first extension and the first cathode cap is constant. [Aspect 32] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 32. The ion generator according to any one of aspects 26 to 31, wherein a first opening width in the radial direction of the first tip opening is larger than a width in the radial direction of the tip surface. [Aspect 33] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 32. The ion generator according to any one of aspects 26 to 31, wherein a first opening width in the radial direction of the first tip opening is equal to or smaller than a width in the radial direction of the tip surface. [Aspect 34] 34. The ion generator according to any one of aspects 26 to 33, wherein the first tip portion extends radially inward from the first extension portion. [Aspect 35] 35. The ion generation device according to any one of aspects 26 to 34, wherein the first tip opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber. [Aspect 36] a second cathode disposed on the opposite side of the internal space from the first cathode in the axial direction and configured to supply thermoelectrons to the internal space; The second cathode is a second cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a second heating source for heating the second cathode cap; a second thermal shield having a second extending portion that extends cylindrically in the axial direction radially outside the second cathode cap and is adjacent to the second cathode cap with a gap in the radial direction, a second tip portion that protrudes toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion, the potential of the second thermal shield is higher than the potential of the second cathode cap; 36. The ion generating device according to any one of aspects 26 to 35, wherein the second tip portion protrudes in the axial direction further toward the inside of the arc chamber than the second cathode cap. [Aspect 37] a repeller provided on the opposite side of the internal space from the first cathode in the axial direction, The repeller is a repeller head projecting in the axial direction toward the interior of the arc chamber; 36. The ion generator according to any one of aspects 26 to 35, further comprising: a thermal shield extending cylindrically in the axial direction radially outside the repeller head.

[0211] [Aspect 38] an arc chamber having an internal space and a front slit for extracting an ion beam from plasma generated in the internal space; a magnetic field generator for generating an axially applied magnetic field in the interior space; a first cathode configured to supply thermoelectrons to the interior space; The first cathode is a first cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons to be supplied to the internal space; a first heating source that heats the first cathode cap; a first thermal shield that extends cylindrically in the axial direction radially outside the first cathode cap and has a first extending portion that is adjacent to the first cathode cap with a gap in a radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the inside of the arc chamber, and a first tip opening that opens in the axial direction at the first tip portion; a second thermal shield that extends cylindrically in the axial direction radially outside the first thermal shield and has a second extension portion that is adjacent to the first extension portion with a gap in the radial direction, a second tip portion that protrudes toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion, An ion generating device, wherein a second opening width in the radial direction of the second tip opening is equal to or greater than a first opening width in the radial direction of the first tip opening. [Aspect 39] The ion generating device according to aspect 38, wherein the second tip portion protrudes in the axial direction further toward the inside of the arc chamber than the first cathode cap and the first tip portion. [Aspect 40] 40. The ion generator according to aspect 38 or 39, wherein the second thermal shield has a higher potential than the first cathode cap or the first thermal shield. [Aspect 41] 40. The ion generator according to aspect 38 or 39, wherein the second thermal shield has a higher potential than the first cathode cap and the first thermal shield. [Aspect 42] 42. The ion generator according to aspect 40 or 41, wherein the first opening width is smaller than the maximum width of the first cathode cap in the radial direction. [Aspect 43] 43. The ion generator according to any one of aspects 40 to 42, wherein at least a portion of an edge of the first tip opening is provided at a position overlapping with the first cathode cap in the axial direction. [Aspect 44] 44. The ion generation device according to any one of aspects 40 to 43, wherein the first cathode cap has a tapered shape in which the width in the radial direction decreases toward the inside of the arc chamber. [Aspect 45] An ion generation device described in any one of aspects 40 to 44, characterized in that the first extension portion has a first tapered portion configured so that the radial width of the inner surface of the first extension portion becomes smaller toward the inside of the arc chamber. [Aspect 46] 46. ​​The ion generator according to any one of aspects 40 to 45, wherein the distance between the first extension and the cathode cap is constant. [Aspect 47] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 47. The ion generator according to any one of aspects 40 to 46, wherein the first opening width is larger than the width of the tip surface in the radial direction. [Aspect 48] the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 47. The ion generator according to any one of aspects 40 to 46, wherein the first opening width is equal to or smaller than the width of the tip surface in the radial direction. [Aspect 49] 49. The ion generating device according to any one of aspects 40 to 48, wherein the first tip portion protrudes in the axial direction further toward the inside of the arc chamber than the first cathode cap. [Aspect 50] An ion generation device described in any one of aspects 40 to 47, characterized in that the tip of the first cathode cap protruding in the axial direction toward the inside of the arc chamber is at the same axial position as the first tip portion, or protrudes further toward the inside of the arc chamber than the first tip portion. [Aspect 51] 51. The ion generator according to any one of aspects 40 to 50, wherein the potential of the first thermal shield is the same as the potential of the first cathode cap. [Aspect 52] 52. The ion generator according to any one of aspects 40 to 51, wherein the first tip portion extends radially inward from the first extension portion. [Aspect 53] 53. The ion generation device according to any one of aspects 40 to 52, wherein the first tip opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber. [Aspect 54] An ion generating device described in any one of aspects 40 or 53, characterized in that in a cross section along the axial direction, the second radial opening width at the second tip opening is smaller than the maximum radial width of the outer surface of the first extension portion. [Aspect 55] An ion generation device described in any one of aspects 40 to 54, characterized in that the second extension portion has a second tapered portion configured so that the radial width of the inner surface of the second extension portion decreases toward the inside of the arc chamber. [Aspect 56] 56. The ion generator according to any one of aspects 40 to 55, wherein the second tip portion extends radially inward from the second extension portion. [Aspect 57] 57. The ion generating device according to any one of aspects 40 to 56, wherein the second tip opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber. [Aspect 58] a second cathode disposed on the opposite side of the internal space from the first cathode in the axial direction and configured to supply thermoelectrons to the internal space; The second cathode is a second cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a second heating source for heating the second cathode cap; a third thermal shield that extends cylindrically in the axial direction radially outside the second cathode cap and has a third extension portion that is adjacent to the second cathode cap with a gap in a radial direction perpendicular to the axial direction, a third tip portion that protrudes toward the inside of the arc chamber, and a third tip opening that opens in the axial direction at the third tip portion; a fourth thermal shield that extends cylindrically in the axial direction radially outside the third thermal shield and has a fourth extension portion that is adjacent to the third extension portion with a gap in the radial direction, a fourth tip portion that protrudes toward the inside of the arc chamber, and a fourth tip opening that opens in the axial direction at the fourth tip portion, 58. The ion generator according to any one of aspects 38 to 57, wherein a fourth opening width in the radial direction of the fourth tip opening is equal to or greater than a third opening width in the radial direction of the third tip opening. [Aspect 59] a repeller provided on the opposite side of the internal space from the first cathode in the axial direction, The repeller is a repeller head projecting in the axial direction toward the interior of the arc chamber; 58. The ion generator according to any one of aspects 38 to 57, further comprising: a thermal shield extending cylindrically in the axial direction radially outside the repeller head.

[0212] [Aspect 60] An ion generator according to any one of aspects 1 to 59; a beam accelerator that accelerates the ion beam extracted from the ion generator; an implantation processing chamber in which the ion beam output from the beam accelerator is irradiated onto a wafer. [Industrial Applicability]

[0213] According to a non-limiting exemplary embodiment of the present disclosure, an ion generator capable of generating a larger number of multiply charged ions under lower arc conditions can be provided. [Explanation of symbols]

[0214] 10...Ion generator, 12...Beam generation unit, 14...Beam acceleration unit, 16...Beam deflection unit, 18...Beam transport unit, 20...Substrate transfer processing unit, 42...Implantation processing chamber, 50...Arc chamber, 52...Magnetic field generator, 54...First cathode, 56...Repeller, 60...Front slit, 70...First heating source, 72...First cathode cap, 76...First thermal seal d, 76a...first tip portion, 76c...first tip opening, 76d...first extension portion, 76e...inner surface, 76g...first tapered portion, 76h...outer surface, 78...second thermal shield, 78a...second tip portion, 78c...second tip opening, 78d...second extension portion, 78e...inner surface, 78g...second tapered portion, 78h...outer surface, 100...ion implantation device, B...magnetic field, P...plasma generation region, S...internal space, W...wafer.

Claims

1. an arc chamber having an internal space and a front slit for extracting an ion beam from plasma generated in the internal space; a magnetic field generator for generating an axially applied magnetic field in the interior space; a first cathode configured to supply thermoelectrons to the interior space; The first cathode is a first cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a first heating source for heating the first cathode cap; a first thermal shield having a first extending portion that extends cylindrically in the axial direction radially outside the first cathode cap and is adjacent to the first cathode cap with a gap in a radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the inside of the arc chamber, and a first tip opening that opens in the axial direction at the first tip portion, The ion generating device, wherein the first tip portion protrudes in the axial direction toward the inside of the arc chamber beyond the first cathode cap.

2. 2. The ion generating device according to claim 1, wherein the potential of the first thermal shield is higher than the potential of the first cathode cap.

3. 2. The ion generating device according to claim 1, wherein the potential of the first thermal shield is the same as the potential of the first cathode cap.

4. 2. The ion generating device according to claim 1, wherein the first opening width in the radial direction of the first tip opening is 5% to 95% of the maximum width in the radial direction of the first cathode cap.

5. 5. The ion generating device according to claim 4, wherein the first opening width is 50% to 90% of the maximum width of the first cathode cap in the radial direction.

6. The ion generating device according to claim 1 , wherein at least a portion of an edge of the first tip opening is provided at a position overlapping with the first cathode cap in the axial direction.

7. The ion generating device according to claim 1 , wherein the first cathode cap has a tapered shape in which the width in the radial direction decreases toward the inside of the arc chamber.

8. 2. The ion generating device according to claim 1, wherein the first extension portion has a first tapered portion configured such that the radial width of the inner surface of the first extension portion decreases toward the inside of the arc chamber.

9. The ion generating device according to claim 1 , wherein the distance between the first extension and the first cathode cap is constant.

10. the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, The ion generating device according to claim 1 , wherein a first opening width in the radial direction of the first tip opening is larger than a width in the radial direction of the tip surface.

11. The ion generating device according to claim 10, wherein the width of the tip surface in the radial direction is 5% to 95% of the first opening width.

12. The ion generating device according to claim 11, wherein the width of the tip surface in the radial direction is 10% to 90% of the first opening width.

13. the first cathode cap includes a tip surface exposed in the axial direction toward the inside of the arc chamber, 2. The ion generating device according to claim 1, wherein a first opening width in the radial direction of the first tip opening is equal to or smaller than a width in the radial direction of the tip surface.

14. The ion generating device according to claim 1 , wherein the first tip portion extends radially inward from the first extension portion.

15. 2. The ion generating device according to claim 1, wherein the first tip opening has a tapered shape in which the width in the radial direction increases toward the inside of the arc chamber.

16. a second cathode disposed on the opposite side of the internal space from the first cathode in the axial direction and configured to supply thermoelectrons to the internal space; The second cathode is a second cathode cap that protrudes in the axial direction toward the interior of the arc chamber and emits thermoelectrons that are supplied to the internal space; a second heating source for heating the second cathode cap; a second thermal shield having a second extending portion that extends cylindrically in the axial direction radially outside the second cathode cap and that is adjacent to the second cathode cap with a gap in the radial direction, a second tip portion that protrudes toward the inside of the arc chamber, and a second tip opening that opens in the axial direction at the second tip portion, 2. The ion generating device according to claim 1, wherein the second tip portion protrudes in the axial direction further toward the inside of the arc chamber than the second cathode cap.

17. a repeller provided on the opposite side of the internal space from the first cathode in the axial direction, The repeller is a repeller head projecting in the axial direction toward the interior of the arc chamber; 2. The ion generating device according to claim 1, further comprising: a thermal shield extending cylindrically in the axial direction radially outside the repeller head.

18. The ion generating device according to claim 1 , wherein the first thermal shield is made of a high-melting-point material selected from the group consisting of a high-melting-point metal, an alloy of a high-melting-point metal, and graphite.

19. An ion generator according to any one of claims 1 to 18; a beam accelerator that accelerates the ion beam extracted from the ion generator; an implantation processing chamber in which the ion beam output from the beam accelerator is irradiated onto a wafer; An ion implantation apparatus comprising:

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