JP4336780B2 - Ion source - Google Patents

Description

  The present invention relates to an ion source used in an ion beam irradiation apparatus or the like that irradiates an irradiation object with an ion beam and performs processes such as ion implantation and ion doping (registered trademark).

  In order to increase the generated plasma density, an ion source using a magnetic field and a reflective electrode has been conventionally proposed (see, for example, Patent Document 1).

  This will be described with reference to FIG. 12. This ion source is called a Bernas ion source, and is provided on the plasma generation container 2 into which the source gas 6 is introduced and on one side of the plasma generation container 2. The U-shaped filament 8 for electron emission, the reflection electrode 10 for electron reflection provided on the other side in the plasma generation container 2, and the ion extraction hole 4 provided on the front wall surface of the plasma generation container 2. And. In the vicinity of the front of the ion extraction hole 4, an extraction electrode 14 for extracting an ion beam 16 from the plasma 12 generated in the plasma generation container 2 is provided.

  A filament power supply 20 for heating is connected to the filament 8, and an arc power supply 22 for arc discharge is connected between one end of the filament 8 and the plasma generation vessel 2 with the filament 8 being on the negative electrode side. . The reflective electrode 10 may have a floating potential without being connected anywhere as in the illustrated example, or may be connected to one end of the filament 8 to have a filament potential. In either case, the reflective electrode 10 has a negative potential with respect to the plasma generation container 2. This is because even if the reflective electrode 10 is set to a floating potential, the reflective electrode 10 is charged with a high energy equivalent to the arc voltage emitted from the filament 8, and thus is charged to a negative potential.

  An electromagnet (not shown) that generates a magnetic field 24 in a direction along a line connecting the filament 8 and the reflective electrode 10 is disposed outside the plasma generation container 2. The direction of the magnetic field 24 may be opposite to that illustrated.

  In this ion source, in order to increase the density of the plasma 12, a magnetic field 24 is applied in a direction perpendicular to the extraction direction of the ion beam 16, the electrons emitted from the filament 8 are constrained by magnetic field lines by Larmor motion, and negative. Electrons are reflected by the potential reflecting electrode 10 (in other words, pushed back, the same applies hereinafter) to increase the collision probability between the electrons and the source gas molecules, thereby increasing the generation efficiency of the plasma 12.

JP 2001-176409 A (paragraphs 0016-0021, FIG. 1)

  In the ion source, due to the output voltage of the arc power source 22 and the negative potential of the reflective electrode 10, the potential distribution is high in the plasma generation vessel 2 near its center and low in the vicinity of the filament 8 and the reflective electrode 10. Occurs. A schematic example of the equipotential surface 26 is shown in FIG. Due to this potential distribution, an electric field 28 in the direction intersecting with the extraction direction of the ion beam 16 is generated in the plasma generation container 2, particularly in a region from the ion extraction hole 4 to the vicinity of the filament 8. The same applies to the vicinity of the reflective electrode 10.

  Therefore, ions in the plasma 12 receive a kinetic energy component in a direction different from the traveling direction of the ion beam 16. This energy component remains even after being extracted as the ion beam 16 and becomes a divergence factor of the ion beam 16. That is, it becomes a factor of reducing the parallelism of the ion beam 16. This problem becomes more prominent when the ion beam 16 is extracted with low energy (for example, about 5 keV or less). This is because the influence of energy components in a direction different from the traveling direction becomes relatively large.

  The ion beam 16 having poor parallelism has an unfavorable result in the processing of the irradiated object. For example, when a semiconductor device is formed on the surface of an object to be irradiated, the surface of the object to be irradiated usually has irregularities such as an insulating film or a conductive film constituting the semiconductor device. When the parallelism of the ion beam 16 is poor, a shadow portion where the ion beam 16 is not incident is generated on the side of the unevenness, and the size of the shadow portion is different from each other in the plane of the irradiation object, and accordingly. The desired ion implantation cannot be performed. This shadow problem becomes more serious as the irradiated object becomes larger and the semiconductor device formed on the surface thereof becomes finer.

  Therefore, the main object of the present invention is to provide an ion source that can extract an ion beam with good parallelism.

A first ion source according to the present invention is an ion source that extracts an ion beam in a direction along an x axis, where three axes orthogonal to each other at one point are an x axis, a y axis, and a z axis.
A container that also serves as an anode and generates plasma inside thereof, and a plasma generation container that is open at the front when the ion beam extraction direction is forward; and
A hot cathode that is electrically insulated from the plasma generation container in the rear part of the plasma generation container, spreads in a plane substantially parallel to the yz plane, and emits electrons;
It is provided in the front part of the plasma generation vessel so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, and is maintained at substantially the same potential as one end of the hot cathode. A porous reflective electrode that reflects electrons and draws ions from the plasma;
A porous shape that is provided in the plasma generation vessel and in the vicinity of the back of the reflective electrode, has a plane substantially parallel to the yz plane, and is maintained at substantially the same potential as the plasma generation vessel. A control electrode of
The reflective electrode is provided in the vicinity of the front of the reflective electrode so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, and is maintained at a positive potential more than the reflective electrode. A porous deceleration electrode that decelerates and passes ions passing through
A first coil for generating a magnetic field substantially parallel to the x-axis in the plasma generation vessel;
An extraction electrode system which is provided in front of the deceleration electrode and accelerates ions passing through the deceleration electrode to draw out as an ion beam;
A magnetic field substantially parallel to the x-axis is generated in the region including the extraction electrode system, and in cooperation with the first coil, the region between the deceleration electrode and the extraction electrode system is And a second coil that generates a magnetic field that is attenuated in the direction along which ions travel.

  By arranging the hot cathode, reflection electrode, control electrode, and deceleration electrode as described above for the plasma generation vessel, the electric field generated in the plasma generation vessel is generated, particularly in the vicinity of the front part, which is the ion extraction port. The electric field can be made parallel to the x-axis. In addition, the first coil can generate a magnetic field substantially parallel to the x-axis. Thus, since the electric field and the magnetic field can be made parallel to the x-axis, the electric field and the magnetic field that cause the divergence of the ion beam in the plasma generation container can be reduced. As a result, the ion beam parallelism can be improved.

  Furthermore, the first coil and the second coil cooperate to generate a magnetic field that is attenuated in the direction along the x-axis in the direction of ion travel in the region between the deceleration electrode and the extraction electrode system. Thus, the divergence rate component of the ions can be reduced by utilizing the phenomenon that the magnetic moment of the ions is preserved. As a result, the parallelism of the ion beam can be improved also for this reason.

  The plasma generation vessel is divided into a first part at the rear part and a second part at the front part through an insulator, and the first part has substantially the same potential as one end of the hot cathode. In the rear part of the second part, a porous second control electrode having a surface shape substantially parallel to the yz plane and maintained at substantially the same potential as the second part is provided. Also good.

  The hot cathode may be a filament or an indirectly heated cathode.

A second ion source according to the present invention is an ion source for extracting an ion beam in a direction along the x-axis, assuming that three axes orthogonal to each other at one point are an x-axis, a y-axis, and a z-axis.
A container that also serves as an anode and generates plasma inside thereof, and a plasma generation container that is open at the front when the ion beam extraction direction is forward; and
An electrode that is electrically insulated from the plasma generation container in the front portion of the plasma generation container, extends in a plane substantially parallel to the yz plane, emits electrons, and extracts ions from the plasma A porous filament that doubles as
A porous shape that is provided in the plasma generation vessel and in the vicinity of the rear of the filament, has a plane substantially parallel to the yz plane, and is maintained at the same potential as the plasma generation vessel. A control electrode;
A reflective electrode that is electrically insulated from the plasma generation container in the rear part of the plasma generation container, has a surface shape substantially parallel to the yz plane, and reflects electrons;
It is provided in the vicinity of the front of the filament so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, is maintained at a positive potential than the filament, and passes through the filament. A porous deceleration electrode that decelerates and passes incoming ions;
A first coil for generating a magnetic field substantially parallel to the x-axis in the plasma generation vessel;
An extraction electrode system which is provided in front of the deceleration electrode and accelerates ions passing through the deceleration electrode to draw out as an ion beam;
A magnetic field substantially parallel to the x-axis is generated in the region including the extraction electrode system, and in cooperation with the first coil, the region between the deceleration electrode and the extraction electrode system is And a second coil that generates a magnetic field that is attenuated in the direction along which ions travel.

  This second ion source can also improve ion beam parallelism basically by the same action as the first ion source.

  According to the first aspect of the present invention, the electric field and magnetic field generated in the plasma generation container can be made parallel to the ion beam extraction direction, so that the electric field and magnetic field that cause the ion beam divergence are reduced. Thus, the parallelism of the ion beam can be improved. Furthermore, since the divergent velocity component of the ions can be reduced by generating a magnetic field that is attenuated in the direction of ion travel, the parallelism of the ion beam can also be improved for this reason. . Combined with the above two effects, an ion beam with good parallelism can be extracted.

  According to the second aspect of the present invention, the hot cathode and the second control electrode are disposed substantially parallel to each other, and electrons emitted from the hot cathode are parallel to the ion beam extraction direction. Since they can be close to each other, it is possible to improve the uniformity of plasma in a direction orthogonal to the ion beam extraction direction. As a result, there is a further effect that the uniformity of the ion beam can be improved.

  According to invention of Claim 5, in addition to the effect similar to the said effect of Claim 1, there exist the following effects further. That is, ions can be extracted from a region with a high plasma density near the filament, and the electrons emitted from the filament neutralize the space charge of the ions to obtain a large ion saturation current. You can draw a lot. Furthermore, since the filament and the control electrode are arranged substantially in parallel with each other, the electrons emitted from the filament can be made parallel to the ion beam extraction direction, so that they are orthogonal to the ion beam extraction direction. It becomes possible to improve the uniformity of the plasma in the direction. As a result, the uniformity of the ion beam can be improved.

  In this specification and the drawings, three axes orthogonal to each other at one point, that is, the x axis, the y axis, and the z axis are used in order to represent the direction of each component, the traveling direction of the ion beam, and the like. The x-axis, y-axis, and z-axis need only be axes that are orthogonal to each other at a single point, and are not necessarily limited to the illustrated example. For example, the x-axis may be taken in the horizontal direction, the vertical direction, or a direction inclined therefrom.

  FIG. 1 is a sectional view showing an embodiment of an ion source according to the present invention. This ion source is an ion source that extracts the ion beam 90 in the direction along the x-axis. The direction along is, for example, a parallel or substantially parallel direction.

  This ion source also serves as an anode, and includes a plasma generation container 30 into which a source gas 34 is introduced and for generating a plasma 40 therein. The plasma generation container 30 has, for example, a cylindrical shape such as a cylindrical shape or a rectangular tube shape, or a box shape, and a front portion 32 thereof is open. In this specification, the extraction direction of the ion beam 90 is referred to as the front, and the opposite direction is referred to as the rear. The plasma generation vessel 30, the ion transport vessel 74 described later, and the path of the ion beam 90 are evacuated by a vacuum evacuation device (not shown).

  In this embodiment, the plasma generation container 30 is divided into a first portion 36 at the rear portion and a second portion 38 at the front portion thereof via an insulator 61. However, such a configuration is not essential. The first portion 36 is electrically connected to one end of a filament 42 described later, and is maintained at substantially the same potential as that. Note that in this specification, “substantially the same potential” includes a state of the same potential.

  As an example of a hot cathode, a filament that is electrically insulated from the plasma generation vessel 30 (more specifically, the first portion 36 thereof) by an insulator 60 in the rear portion of the plasma generation vessel 30 and emits electrons. 42 is provided. For example, as illustrated in FIG. 3, the filament 42 extends in a plane substantially parallel to the yz plane. In the example shown in FIG. 3, the filament 42 has a structure in which a number of thin rod-like filaments are folded back along the yz plane, but a structure in which a thin plate-like filament is folded in the same manner may be used. Alternatively, the filament 42 may be, for example, a flat plate having the same outer shape as the filament 42 of FIG.

For example, a DC filament power supply 68 for heating the filament 42 is connected. The output voltage V ₁ of the filament power supply 68 is, for example, about 10V to 15V, but is not limited thereto.

A direct-current arc power source between the one end of the filament 42 and the plasma generation vessel 30 (more specifically, the second portion 38), with the former being on the negative electrode side and generating arc discharge between the two 42 and 30. 70 is connected. Output voltage V ₂ of the arc power supply 70 is, for example, is about 40V～120V, not limited thereto. With this output voltage V ₂ , electrons emitted from the filament 42 are accelerated and collide with the source gas molecules to ionize the source gas 34 to generate the plasma 40.

  A surface that is electrically insulated from the plasma generation vessel 30 (more specifically, the second portion 38 thereof) by an insulator 62 in the front portion 32 of the plasma generation vessel 30 and is substantially parallel to the yz plane. A porous reflective electrode 48 is provided. The term “porous” means, for example, a plate shape or a mesh shape having a large number of small holes. The same applies to other electrodes described later. The reflective electrode 48 is electrically connected to one end of the filament 42 and is maintained at substantially the same potential as that. The reflective electrode 48 reflects electrons (mainly electrons emitted from the filament 42) in the plasma generation container 30 and has a porous shape to extract ions 52 from the plasma 40.

  A porous control electrode 46 having a planar shape substantially parallel to the yz plane is provided in the plasma generation container 30 (more specifically, the second portion 38) and in the vicinity of the rear of the reflective electrode 48. Is provided. The control electrode 46 is electrically connected to the plasma generation container 30 (more specifically, the second portion 38), and is maintained at substantially the same potential as that.

  Furthermore, in this embodiment, a porous second control electrode 44 having a planar shape substantially parallel to the yz plane is provided in the rear part of the second portion 38 of the plasma generation container 30. The second control electrode 44 is electrically connected to the second portion 38 and is maintained at substantially the same potential as that.

  In the vicinity of the front side of the reflective electrode 48, the insulator 62 is electrically insulated from the plasma generation vessel 30 (more specifically, the second portion 38), and has a surface shape substantially parallel to the yz plane. A porous deceleration electrode 50 is provided. The deceleration electrode 50 is maintained at a positive potential with respect to the reflection electrode 48 by a deceleration power source 72 to be described later, and decelerates and passes the ions 52 passing through the reflection electrode 48.

Connected between the deceleration electrode 50 and the reflective electrode 48 is a direct current deceleration power source 72 that keeps the deceleration electrode 50 at a positive potential relative to the reflective electrode 48 with the former being on the positive electrode side. The output voltage V ₃ of the deceleration power source 72 is, for example, a voltage that is several tens of volts higher than the output voltage V ₂ , more specifically about 70 V to 150 V, but is not limited thereto. What is necessary is just to determine according to the energy of the required ion 52. FIG.

  A first coil 54 that generates a magnetic field substantially parallel to the x-axis is provided in the plasma generation container 30 around the outside of the plasma generation container 30. An outline of this magnetic field is indicated by magnetic lines of force 58. The direction of the magnetic field may be opposite to that shown in the figure. In this embodiment, the first coil 54 has two coils 54a and 54b connected in series with each other, and both the coils 54a and 54b have an excitation current for generating the magnetic field from a DC excitation power source 56. Is supplied. Both coils 54a and 54b are Helmholtz coils, for example. The first coil 54 may be composed of a single solenoid coil or the like instead of the coils 54a and 54b.

  In front of the deceleration electrode 50, an extraction electrode system 76 that accelerates and extracts the ions 52 passing through the deceleration electrode 50 as an ion beam 90 is provided. In this embodiment, a cylindrical ion transport container 74 larger than the plasma generation container 30 for transporting ions 52 is provided in front of the deceleration electrode 50, and is drawn out to the front part of the ion transport container 74. An electrode system 76 is provided. The deceleration electrode 50, the ion transport container 74, and the extraction electrode 78 of the extraction electrode system 76 are electrically connected to each other and maintained at substantially the same potential. However, the ions 52 may be transported in another vacuum container (such as a beam line container) without specially providing the ion transport container 74.

In this embodiment, the extraction electrode system 76 includes an extraction electrode 78, a suppression electrode 79, and a ground electrode 80. Each of the electrodes 78 to 80 is a porous electrode in this example, but may have a slit-shaped ion extraction hole. A positive acceleration voltage V ₄ for accelerating the ion beam 90 is applied to the extraction electrode 78 from a DC acceleration power supply 82. A negative suppression voltage V ₅ for suppressing backflow electrons is applied to the suppression electrode 79 from a DC suppression power supply 84. The ground electrode 80 is electrically grounded. The electrodes 78, 79, 80 are electrically insulated by insulators 63, 64. However, the configuration of the extraction electrode system 76 is not limited to this example.

The acceleration voltage V ₄ is, for example, about 1 kV to 40 kV, but is not limited to this, and may be determined according to the required energy of the ion beam 90. Inhibit voltage V ₅ it is, for example, is about 1KV～2kV, not limited to this.

  In the vicinity of the outer periphery of the extraction electrode system 76, a magnetic field substantially parallel to the x axis is generated in a region including the extraction electrode system 76, and in cooperation with the first coil 54, the deceleration electrode 50 and the extraction electrode In a region between the system 76 (more specifically, its extraction electrode 78), a second coil 86 is provided that generates a magnetic field that is attenuated in the direction of travel of the ions 52 in the direction along the x-axis. ing. The second coil 86 generates a magnetic field in the same direction as the first coil 54. The outline of this magnetic field is indicated by the magnetic field lines 58.

  In this embodiment, the second coil 86 includes three ring-shaped coils 86a to 86c that are excited by DC excitation power supplies 88a to 88c, respectively, and the coils 86a to 86c generate magnetic fields in the same direction. generate. The second coil 86 is not necessarily limited to that of this embodiment, but from the viewpoint of generating the magnetic field as described above, the second coil 86 is composed of a plurality of coils and independently supplies an excitation current to each coil. A direct current excitation power source is preferably provided.

  In this ion source, when the predetermined portion is evacuated, a desired source gas 34 is introduced into the plasma generation vessel 30 and a voltage is applied to the predetermined portion, arc discharge is generated in the plasma generation vessel 30. Is generated, the source gas 34 is ionized, and the plasma 40 is generated. Then, the ions 52 are extracted from the plasma 40, transported to the extraction electrode system 76 along the magnetic field lines 58, accelerated by the extraction electrode system 76, and extracted as the ion beam 90.

An example of the potential distribution in the direction along the x-axis during operation of this ion source is shown in FIG. In this figure, the output voltage V ₁ of the filament power supply 68 is small and neglected because it is not necessary for explanation. The same applies to FIG. 5 described later. The plasma 40 (see FIG. 1) generated in the plasma generation container 30 usually has a plasma potential V _p slightly higher (for example, about several tens of volts) than the potential of the plasma generation container 30. An ion sheath is formed in the vicinity of the second control electrode 44, the control electrode 46, the reflective electrode 48, and the like that are close to the plasma 40. This is why the potential is lowered in the vicinity of the second control electrode 44 and the control electrode 46 which are substantially the same potential as the plasma generation vessel 30.

The energy of the ions 52 extracted through the deceleration electrode 50 becomes V _p −V ₃ [eV]. By adjusting the output voltage V ₃ of the deceleration power source 72, the energy of the ions 52 is very small (for example, 1 eV to several eV). The reason for making it smaller will be described later.

  In this ion source, the filament 42, the second control electrode 44, the control electrode 46, the reflection electrode 48, and the deceleration electrode 50 are disposed substantially parallel to the yz plane. 2, equipotential surfaces 92 that are substantially parallel to each other and substantially perpendicular to the x-axis are formed. Therefore, the electric field 94 generated in the plasma generation container 30, particularly the electric field 94 generated in the vicinity of the front portion 32, which is an extraction port for the ions 52, can be made parallel to the x axis. In addition, the first coil 54 can generate a magnetic field substantially parallel to the x-axis. As described above, since the electric field and the magnetic field can be made parallel to the x-axis, the electric field and the magnetic field that cause the divergence of the ion beam 90 in the plasma generation container 30 can be reduced. As a result, the parallelism of the ion beam 90 can be improved. This is the first effect.

  Furthermore, the first coil 54 and the second coil 86 cooperate to attenuate toward the traveling direction of the ions 52 in the direction along the x-axis in the region between the deceleration electrode 50 and the extraction electrode system 76. By generating a magnetic field, the divergence rate component of the ions 52 can be reduced by utilizing the phenomenon that the magnetic moment of the ions 52 described below is preserved. As a result, also for this reason, the parallelism of the ion beam 90 can be improved. This is the second effect.

  Therefore, according to this ion source, the ion beam 90 having good parallelism can be extracted by combining the first and second functions and effects. Further, as can be seen from FIG. 11 described later, the ions 52 extracted from the deceleration electrode 50 can be expanded by a magnetic field, and an ion beam 90 having a larger area than the deceleration electrode 50 can be extracted. Therefore, it is possible to easily cope with a large object to be irradiated.

The preservation of the magnetic moment will be described in detail. As described in Non-Patent Documents 1 and 2 below, when the magnetic field (magnetic flux density) B [T] changes in the ion traveling direction, Formula 1 When the condition (2) is satisfied, the magnetic moment μ of the ion expressed by Equation 2 is preserved. Here, M is the ion mass number [AMU], Z is the load number, U is the energy [eV], and L is the characteristic length of the system (here, the distance in the ion traveling direction of the space in which the magnetic field is attenuated) [m. ], m is the mass of the ion, v _r is a component orthogonal to the magnetic field of the ion velocity.

[Equation 1]
BL >> 1.5 × 10 ⁻⁴ √ (MU) / Z

[Equation 2]
μ = mv _r ² / 2B

By utilizing the property that the magnetic moment μ is conserved, if the ions are transported in the direction in which the magnetic field is attenuated, the component v _r orthogonal to the magnetic field of the ion velocity is reduced, and accordingly, the component v parallel to the magnetic field is reduced. _x increases (in other words, v _r is converted to v _x ). The use of such a property for collimating ions extracted from the ion source is not described in Non-Patent Documents 1 and 2, but in this ion source, focusing on this property, the divergence of ions 52 is included. It is used to reduce the speed component. Therefore, the velocity component v _{x in the} direction orthogonal to the x-axis, that is, the divergence velocity component decreases while the ions 52 pass through the decaying magnetic field in the ion transport container 74.

[Non-Patent Document 1]
Junzo Ishikawa, Ionics Series, “Ion Source Engineering”, First Printing, Ionics Corporation, May 31, 1986, pp. 94-95
[Non-Patent Document 2]
Writer Toshiyoshi Takagi, University of Electrical Engineers, “Electron / Ion Beam Engineering”, First Edition, The Institute of Electrical Engineers of Japan, March 1, 1995, page 99

  Next, an example of the result of simulating the magnetic field generated by the first coil 54 and the second coil 86 and the trajectory of the ions 52 in the magnetic field will be described.

  FIG. 6 is a vector diagram of a magnetic field in the xz plane. When this vector is connected, it corresponds to the magnetic field line 58 shown in FIG. In this example, the magnetomotive force of each of the coils 54a, 54b, 86a, 86b, 86c is set to 10,000A, 10,000A, 1,500A, 1,250A, 2,250A, respectively. The magnetic field is substantially parallel to the x-axis in the region between the coils 54a and 54b constituting the first coil 54, diverges and attenuates in the region between the coil 54b and the coil 86a, and the coil starts from the vicinity of the coil 86b. It can be seen that the region extending to 86c is substantially parallel to the x-axis again.

FIG. 7 shows changes in the magnetic flux density on the x-axis in the example of FIG. The magnetic flux density B _{0 at} x = 0 m is about 0.37 T, and the magnetic flux density B _{1 at} x = 0.1 m is about 0.04 T. Between both points, particularly between x = 0 m and x = 0.02 m, It can be seen that the magnetic field decays rapidly.

FIG. 9 and FIG. 11 show the trajectory of the ion 52 when the ion 52 is emitted at an initial divergence angle θ ₀ = 60 degrees from the vicinity of the middle of the coils 54a and 54b in the case of the magnetic field distribution of FIG. At this time, the ions 52 are boron ions ¹¹ B ⁺ having a mass number of 11, and the energy U is 0.5 eV.

As shown in FIG. 8, the ions 52 were discharged from the point P in six directions in a conical shape at an initial divergence angle θ ₀ = 60 degrees (only two directions are shown in FIG. 8). Note that the initial divergence angle θ ₀ = 60 degrees does not mean that the ions 52 extracted from the deceleration electrode 50 have such a large divergence angle, and the divergence angle is reduced by preserving the magnetic moment. This is an example of a great exaggeration to clarify that.

  In the above case, when the characteristic length L of the system shown in Equation 1 is 0.02 m, the mass number M is 11, the ion energy U is 0.5 eV, and the load number Z is 1. The formula is derived.

[Equation 3]
B >> 0.012 [T]

  Similarly, when the characteristic length L of the system shown in the above equation 1 is 0.15 m, the mass number M is 11, the ion energy U is 0.5 eV, and the load number Z is 1. The formula is derived.

[Equation 4]
B >> 0.0023 [T]

  As shown in FIG. 7, since the magnetic flux density B is sufficiently large at x = 0 to 0.15 m, it can be seen that the conditions of the above equations 3 and 4 are satisfied in this example. In this case, if the energy U of the ions 52 is large, the magnetic flux density B in the attenuation region increases to satisfy the condition of Equation 1. In order to avoid this, the ion source of this embodiment is provided with a decelerating electrode 50 to decelerate ions 52 and reduce their energy U.

Therefore, in this ion source, the magnetic moment μ is preserved, and as can be seen from FIG. 9, the divergence angle θ of the ions 52 is rapidly reduced between the coil 54b and the coil 86a. Specifically, as shown in FIG. 10, the initial divergence angle θ ₀ = 60 degrees is reduced to about 17 degrees, and the divergence angle θ _{1 at} the point of x = 0.1 m is reduced to be parallelized. I understand that Actually, since the initial divergence angle θ ₀ of the ions 52 extracted from the deceleration electrode 50 is much smaller than 60 degrees, they are parallelized so that the divergence angle θ ₁ is very close to 0 degrees.

  Although the ion 52 shown in FIG. 9 seems to move up and down in the z-axis direction at first glance, the ion 52 has a radius of Larmor around the axis in the traveling direction. It moves so as to draw an envelope circle, and takes a spiral orbit while maintaining a constant inclination with respect to its traveling direction (direction of magnetic field B). The pitch is inversely proportional to the magnetic field. The same applies to the case of FIG.

In FIG. 9, the ions 52 diverge after passing through the second coil 86. However, in the example of FIG. 9, the acceleration voltage V ₄ is not applied to the extraction electrode system 76 and the ions 52 are 0. This is because it has an energy of .5 eV, and when the acceleration voltage V ₄ is applied, the ions 52 are extracted as an ion beam 90 substantially parallel to the x-axis as in the example shown in FIG. FIG. 11 shows an example in which the acceleration voltage V ₄ is 5 kV. In this case, the ion beam 90 is collimated to a divergence angle of 1.7 × 10 ⁻³ degrees. Even with an acceleration voltage V ₄ lower than this, that is, with an ion beam 90 having an energy lower than 5 keV, the parallelism can be made very good.

  As can also be seen from FIG. 11, the ions 52 extracted from the deceleration electrode 50 can be expanded by a magnetic field, and an ion beam 90 having a larger area than the deceleration electrode 50 can be extracted. Therefore, it is possible to easily cope with a large object to be irradiated.

  Referring to FIG. 1 again, as in this embodiment, the plasma generation container 30 is divided into a first portion 36 and a second portion 38, and a second control electrode 44 is provided in the rear portion of the second portion 38. The filament 42 and the second control electrode 44 are disposed substantially in parallel with each other, and the electrons emitted from the filament 42 can be made parallel to the ion beam extraction direction. It becomes possible to improve the uniformity of the plasma 40 in the direction orthogonal to the direction. As a result, the uniformity of the ion beam 90 can be improved.

  As the hot cathode, instead of the filament 42, for example, a plate-like cathode substantially parallel to the yz plane may be used, and an indirectly heated cathode that is heated from behind by a filament or the like may be used.

  Next, another embodiment of the ion source according to the present invention will be described with reference to FIGS. Portions that are the same as or correspond to those in the above-described embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals, and differences from the above-described embodiment will be mainly described below.

  In the ion source shown in FIG. 4, the plasma generation container 30 is not divided. A porous filament 42 that is electrically insulated from the plasma generation container 30 by an insulator 62 and extends in a plane substantially parallel to the yz plane is provided in the front portion 32 of the plasma generation container 30. It has been. For example, as shown in FIG. 3, the filament 42 has a structure in which a thin rod-like or thin plate-like filament is folded back many times along the yz plane. Since such a filament 42 has a large number of gaps 43, it is also included in the porous category in this specification. In addition, the filament 42 may be a flat plate having a large number of small holes or a mesh.

  The filament 42 is heated by the filament power source 68 to emit electrons, and has a porous shape to extract the ions 52 from the plasma 40.

  The control electrode 46 and the deceleration electrode 50 are provided near the rear and front of the filament 42, respectively. In this case, the control electrode 46 also serves as a discharge anode that generates arc discharge with the filament 42. The deceleration electrode 50 decelerates and passes the ions 52 passing through the filament 42.

  A reflective electrode 49 that is electrically insulated from the plasma generation container 30 by the insulator 65 and has a surface shape substantially parallel to the yz plane is provided in the rear part of the plasma generation container 30. Unlike the reflective electrode 48, the reflective electrode 49 need not allow the ions 52 to pass therethrough, and may be a simple flat plate or the like.

  As shown in the example shown in FIG. 4, the reflective electrode 49 may be connected to one end of the filament 42 to have a filament potential, or may not be connected anywhere and may have a floating potential. As described above, even when the floating potential is used, the negative potential is charged. In either case, the reflective electrode 49 has a negative potential with respect to the plasma generation container 30 and functions to reflect electrons (mainly electrons from the filament 42) in the plasma generation container 30.

  The various power sources 68 and 70, the first coil 54, the second coil 86, the extraction electrode system 76, and the like are the same as in the above embodiment.

  An example of the potential distribution in the direction along the x-axis during the operation of the ion source of this embodiment is shown in FIG. Except for the second control electrode 44, the potential distribution is the same as the potential distribution shown in FIG.

  The ion source of this embodiment also basically has the same effects as the ion source of the above embodiment. That is, in this ion source, the reflective electrode 49, the control electrode 46, the filament 42, and the deceleration electrode 50 are disposed substantially parallel to the yz plane. As shown in a representative example, equipotential surfaces 92 that are substantially parallel to each other and substantially perpendicular to the x-axis are formed. Therefore, the electric field 94 generated in the plasma generation container 30, particularly the electric field 94 generated in the vicinity of the front portion 32, which is an extraction port for the ions 52, can be made parallel to the x axis. In addition, the first coil 54 can generate a magnetic field substantially parallel to the x-axis. As described above, since the electric field and the magnetic field can be made parallel to the x-axis, the electric field and the magnetic field that cause the ion beam 90 to diverge can be reduced in the plasma generation container 30. As a result, the parallelism of the ion beam 90 can be improved. This is the first effect.

  Furthermore, the first coil 54 and the second coil 86 cooperate to attenuate toward the traveling direction of the ions 52 in the direction along the x-axis in the region between the deceleration electrode 50 and the extraction electrode system 76. By generating a magnetic field, the divergence rate component of the ions 52 can be reduced by utilizing the phenomenon that the magnetic moment of the ions 52 described above is preserved. As a result, also for this reason, the parallelism of the ion beam 90 can be improved. This is the second effect.

  Therefore, according to this ion source, the ion beam 90 having good parallelism can be extracted by combining the first and second functions and effects. As can be seen from FIG. 11 described above, the ions 52 extracted from the deceleration electrode 50 can be expanded by a magnetic field, and an ion beam 90 having a larger area than the deceleration electrode 50 can be extracted. Therefore, it is possible to easily cope with a large object to be irradiated.

  In addition, the ion source of this embodiment has the following further effects. That is, since the plasma 40 has a high density near the filament 42 and ions 52 can be extracted from the high plasma density region, the electrons emitted from the filament 42 neutralize the space charge of the ions 52 and ion saturation. Since a large electric current can be taken, ions 52 and hence ion beam 90 can be extracted more. Furthermore, the filament 42 and the control electrode 46 are disposed substantially in parallel with each other, and the electrons emitted from the filament 42 can be brought close to parallel to the ion beam extraction direction. It is possible to improve the uniformity of the plasma 40 in the direction orthogonal to the direction. As a result, the uniformity of the ion beam 90 can be improved.

It is sectional drawing which shows one Embodiment of the ion source which concerns on this invention. It is a figure which shows an example of the electric potential distribution in the direction in alignment with the x-axis at the time of operation | movement of the ion source of FIG. It is a front view which shows an example of a filament. It is sectional drawing which shows other embodiment of the ion source which concerns on this invention. FIG. 5 is a diagram illustrating an example of a potential distribution in a direction along the x axis when the ion source of FIG. 4 is operated. FIG. 5 is a diagram illustrating an example of a result of simulating a magnetic field vector in the xz plane in the ion source of FIGS. 1 and 4. It is a figure which shows the mode of the change of the magnetic flux density on the x-axis in the example of FIG. It is a figure which shows the initial divergence angle of ion. FIG. 7 is a diagram showing an example of simulation results of ion trajectories when ions are emitted at an initial divergence angle of 60 degrees in the case of the magnetic field distribution of FIG. 6. In this example, no acceleration voltage is applied to the extraction electrode system. It is a figure which shows the mode of the change of the divergence angle of the ion in the example of FIG. FIG. 7 is a diagram showing another example of simulation results of ion trajectories when ions are emitted at an initial divergence angle of 60 degrees in the case of the magnetic field distribution of FIG. 6. In this example, an acceleration voltage of 5 kV is applied to the extraction electrode system. is doing. It is sectional drawing which shows an example of the conventional ion source.

Explanation of symbols

30 Plasma generation vessel 32 Front portion 36 First portion 38 Second portion 40 Plasma 42 Filament (hot cathode)
44 Second control electrode 46 Control electrode 48, 49 Reflection electrode 50 Deceleration electrode 52 Ion 54 First coil 58 Magnetic field line 76 Extraction electrode system 86 Second coil 90 Ion beam

Claims (5)

An ion source for extracting an ion beam in a direction along the x-axis when three axes orthogonal to each other at one point are defined as an x-axis, a y-axis, and a z-axis,
A container that also serves as an anode and generates plasma inside thereof, and a plasma generation container that is open at the front when the ion beam extraction direction is forward; and
A hot cathode that is electrically insulated from the plasma generation container in the rear part of the plasma generation container, spreads in a plane substantially parallel to the yz plane, and emits electrons;
It is provided in the front part of the plasma generation vessel so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, and is maintained at substantially the same potential as one end of the hot cathode. A porous reflective electrode that reflects electrons and draws ions from the plasma;
A porous shape that is provided in the plasma generation vessel and in the vicinity of the back of the reflective electrode, has a plane substantially parallel to the yz plane, and is maintained at substantially the same potential as the plasma generation vessel. A control electrode of
The reflective electrode is provided in the vicinity of the front of the reflective electrode so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, and is maintained at a positive potential more than the reflective electrode. A porous deceleration electrode that decelerates and passes ions passing through
A first coil for generating a magnetic field substantially parallel to the x-axis in the plasma generation vessel;
An extraction electrode system which is provided in front of the deceleration electrode and accelerates ions passing through the deceleration electrode to draw out as an ion beam;
A magnetic field substantially parallel to the x-axis is generated in the region including the extraction electrode system, and in cooperation with the first coil, the region between the deceleration electrode and the extraction electrode system is An ion source comprising: a second coil that generates a magnetic field that is attenuated in a direction along which ions travel in a direction along the direction.   The plasma generation vessel is divided into a first part at the rear part and a second part at the front part through an insulator, and the first part has substantially the same potential as one end of the hot cathode. A porous second control electrode is provided in the rear part of the second part, and has a planar shape substantially parallel to the yz plane and is maintained at substantially the same potential as the second part. The ion source according to claim 1.   The ion source according to claim 1, wherein the hot cathode is a filament.   The ion source according to claim 1, wherein the hot cathode is an indirectly heated cathode. An ion source for extracting an ion beam in a direction along the x-axis when three axes orthogonal to each other at one point are defined as an x-axis, a y-axis, and a z-axis,
A container that also serves as an anode and generates plasma inside thereof, and a plasma generation container that is open at the front when the ion beam extraction direction is forward; and
An electrode that is electrically insulated from the plasma generation container in the front portion of the plasma generation container, extends in a plane substantially parallel to the yz plane, emits electrons, and extracts ions from the plasma A porous filament that doubles as
A porous shape that is provided in the plasma generation vessel and in the vicinity of the rear of the filament, has a plane substantially parallel to the yz plane, and is maintained at the same potential as the plasma generation vessel. A control electrode;
A reflective electrode that is electrically insulated from the plasma generation container in the rear part of the plasma generation container, has a surface shape substantially parallel to the yz plane, and reflects electrons;
It is provided in the vicinity of the front of the filament so as to be electrically insulated from the plasma generation vessel, has a surface shape substantially parallel to the yz plane, is maintained at a positive potential than the filament, and passes through the filament. A porous deceleration electrode that decelerates and passes incoming ions;
A first coil for generating a magnetic field substantially parallel to the x-axis in the plasma generation vessel;
An extraction electrode system which is provided in front of the deceleration electrode and accelerates ions passing through the deceleration electrode to draw out as an ion beam;
A magnetic field substantially parallel to the x-axis is generated in the region including the extraction electrode system, and in cooperation with the first coil, the region between the deceleration electrode and the extraction electrode system is An ion source comprising: a second coil that generates a magnetic field that is attenuated in a direction along which ions travel in a direction along the direction.

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