JP4525203B2 - Ion mass separation method and apparatus - Google Patents

Description

  The present invention relates to an ion mass separation method and apparatus, and more particularly to an ion mass separation method and apparatus capable of stably deriving an ion beam of a desired ion species from an ion mass separation apparatus.

  Conventionally, when an electrically active element is added to a semiconductor or an atom of an adhesive material is added to a substrate in order to adhere a material that is difficult to adhere to the substrate, ion doping is performed. An (injection) device is used.

  In an ion doping apparatus, a material gas is converted into plasma by a plasma generator, plasma ions (charged particles) are accelerated, and the ions are injected into a material to be processed.

  In recent years, as the size of liquid crystal displays has increased, an ion implantation apparatus for producing liquid crystal is required to have a large area and uniform ion implantation. Usually, when ion implantation is performed on a liquid crystal glass substrate, a linear or rectangular ion beam that is slightly wider than the short side of the substrate is generated and moved in a longitudinal direction of the liquid crystal glass substrate (scanning) to implant a large area. The method of doing is taken.

  Further, for the purpose of improving the performance of TFT characteristics (Thin FiLm Transistor) of a liquid crystal display, mass separation performance capable of selectively implanting only a desired ion species is required for an ion implantation apparatus for liquid crystal production. In particular, in order to remove hydrogen contained in the material gas, there is one in which ion mass separation is performed using a permanent stone or an electromagnet.

As a material gas for generating an ion beam, hydrogen diluted phosphine (PH ₃ ), diborane (B ₂ H ₆ ), or the like is used. In the plasma generator, in addition to the desired ion species PH _x and B ₂ H _x , _{, H x, P 2 H x} , also unwanted ions of different ion species of such BH _x occurs, mixed beam of these ions species are drawn from the plasma generator.

  The presence of such unnecessary ion species other than the desired ion species has a problem of non-uniform P and B implantation depth distributions due to ion doping, and a problem that an extra heat load is applied to the material to be processed. There is a need to remove it.

  For this reason, an ion mass separation apparatus has been proposed in which a stable ion beam is generated by performing ion mass separation of a large aperture, particularly a wide ion beam (see, for example, Patent Document 1).

  FIG. 5 is an oblique side view showing an outline of the ion mass separator 1 in Patent Document 1, and FIG. 6 is a side view of FIG. 5. The ion mass separator 1 has an inlet portion 2 and an outlet portion 3 at both ends. The ion deflection casing 5 is curved and has a mass separation space 4 formed therein, and the ion deflection casing 5 is curved outside the ion deflection casing 5 so as to pass through the inlet portion 2 and the outlet portion 3. A conductor 6x is wound along the width direction of the ion deflection casing 5 to form an air core exciting current path 6, and a magnet current is supplied to the air core exciting current path 6 to form a magnetic field. The ion deflection casing 5 is curved at a large angle so that the entrance 2 and the exit 3 are at an angle of 90 °. Further, for example, neutralization electron supply for smoothly moving the ion beam by supplying space to the inner surface of, for example, the widthwise end portion of the ion deflection casing 5 by space charge effect (neutralizing ions). A filament is arranged along the inner surface as the body 7.

  The ion beam introduced into the mass separation space 4 diverges due to the space charge effect of the beam itself, and there is a possibility that the beam trajectory changes and the beam is lost. When the adverse effect due to the space charge effect cannot be ignored in this way, electrons and the like are supplied to the mass separation space 4 in order to neutralize the space charge effect. A filament or the like is generally used as a source for supplying the neutralized electrons.

  A plasma generator 8 is provided in front of the outside of the inlet portion 2, and the plasma generator 8 converts the material gas into plasma by an arc filament 15 to generate ions. An extraction electrode 9 is disposed between the inlet 2 and the plasma generator 8 at a position overlapping with the conductor 6a of the inlet 2 and the extraction electrode 9 mass-separates ions of the plasma generator 8. The ion beam is accelerated to a necessary speed and introduced into the mass separation space 4 through the conductors 6a as an ion beam having a wide width in the width direction of the ion deflection casing 5 (perpendicular to the plane of FIG. 6).

The ion beam introduced into the mass separation space 4 is bent according to the mass of the ion by the action of the magnetic field by the air-core excitation current path 6, and the ion beam of the desired ion species is centered in the front-rear direction (left-right direction in FIG. 6). And is led out from between the conductors 6 b provided at the outlet 3. FIG. 5 shows a case where phosphine (PH ₃ ) diluted with hydrogen is used as a material gas. Desired ions (PH _x ⁺ ) are converged and guided to the outlet portion 3, and other masses such as H ⁺ and H ₂ having small masses. Unnecessary ions such as ⁺ and H ₃ ⁺ are quickly bent and neutralized by hitting the inner wall of the ion deflection casing, and unnecessary ions of P ₂ H _x ^{+ having} a mass larger than the desired ion species are not bent and are ionized. It is neutralized by hitting the inner wall of the deflection casing.

  Shielding members 10 are provided on both front and rear side portions (left and right side portions in FIG. 6) of the outlet portion 3 to form an ion outlet 11 at the front and rear central portion, whereby ions made of the focused desired ions are formed. The beam is led out from the ion outlet 11 of the outlet 3.

  Further, the ion beam converged and taken out from the ion extraction port 11 is accelerated to a speed necessary for ion doping by the acceleration electrode 12 which is a rectangular large-diameter single-port electrode. The ion beam separated by the ion mass separator 1 and further accelerated by the conductor 6b and the accelerating electrode 12 is disposed in the process chamber 13 communicating with the mass separation space 4 of the ion mass separator 1. Injected into.

In the ion mass separator 1, the magnetic field intensity of the air-core excitation current path 6 is obtained by calculation from the beam energy and ion mass of the ion beam taken into the ion deflection casing 5 by the extraction electrode 9 from the plasma of the plasma generator 8, and is desired. The magnetic field strength is set so that the ion beam of the ion species is derived from the center position of the exit portion 3.
Japanese Patent Laid-Open No. 2002-203805

  However, even if the ion mass separator 1 is operated with the magnetic field intensity of the air-core excitation current path 6 set to a predetermined value, the beam energy of the ion beam, the beam current amount, and the supply amount of space charge effect neutralized electrons When these change, there is a problem that beam characteristics such as beam current density and ion species ratio after mass separation change.

  That is, the magnet current in the air-core exciting current path 6 is set to a predetermined value so that an ion beam of a desired ion species is suitably derived from the outlet 3, and the current supplied to the neutralizing electron supplier 7 and the plasma Even if each of the arc current supplied to the arc filament 15 of the generator 8 and the extraction current supplied to the extraction electrode 9 is set to a predetermined value, the neutralized electron supplier 7 is consumed in the case of a filament, for example. The supply amount of neutralizing electrons changes with time, so that the magnitude of the space charge effect of the ion beam in the ion deflection casing 5 changes and the trajectory of the ion beam changes. Further, when the properties and temperature of the source gas of the plasma generator 8 are changed, or the generated compound adheres to the extraction electrode 9 and is contaminated, the beam current density and beam energy of the ion beam led out from the outlet portion 3 are increased. Will change. When the characteristics of the ion beam change in this way, there arises a problem that the amount of do pink with respect to the material to be processed 14 changes and the reproducibility deteriorates.

  In addition, as described above, when the characteristics of the ion beam change, it takes time to adjust to the initial state, and therefore, there is a problem that the work efficiency when irradiating the material to be processed with the ion beam decreases. is there.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an ion mass separation method and apparatus capable of stably deriving an ion beam of a desired ion species from an ion mass separation apparatus. It is.

The invention according to claim 1 is an air-core excitation current in which a conductor is wound in the width direction along the curve on the outer periphery of the ion deflection casing so as to pass through the inlet portion at one end and the outlet portion at the other end of the curved ion deflection casing. A magnetic field is formed by the path, and an ion beam is extracted from the plasma generated by the arc in the plasma generator by the extraction electrode and introduced into the inlet portion of the ion deflection casing. At the same time, the ion beam is bent according to the mass by the magnetic field. An ion mass separation method in which neutralizing electrons are supplied by a neutralizing electron supply body in an ion deflection casing to derive an ion beam of a desired ion species from the outlet portion,
The current of the neutralizing electron supplier, the arc current of the plasma generator, and the extraction current of the extraction electrode are set so that the beam current density of the ion beam derived from the outlet becomes a predetermined required irradiation density. In the adjusted state, the magnetic field intensity is changed by changing the magnet current in the air-core excitation current path, and the beam current density of the ion beam derived from the exit portion when the magnetic field intensity changes is measured, and the measured beam measuring a desired ion species density peak position from the distribution of current density, determine the reference magnet current from the measured density peak position, by performing an initial setting for setting a magnet current so that the beam current density is irradiated request density said Ion mass separation operation,
The density peak position of the desired ion species is measured every predetermined period during the operation of the ion mass separation, and when the measured density peak position is outside the allowable range of the reference magnet current, the density peak position is The ion mass separation method is characterized in that the current of the neutralized electron supplier is controlled so as to be within an allowable range of the magnet current .

In the invention according to claim 2, in addition to controlling the current of the neutralizing electron supplier so that the measured density peak position is within the allowable range of the reference magnet current, the maximum density value of the beam current density is 2. The ion mass separation method according to claim 1 , wherein at least one of an arc current of a plasma generator or an extraction current of an extraction electrode is controlled so as to be within an allowable range of the required irradiation density.

According to a third aspect of the present invention, there is provided a curved ion deflection casing having an inlet portion at one end and an outlet portion at the other end, and an ion deflection casing so as to pass through the inlet portion and the outlet portion of the ion deflection casing. An air-core excitation current path in which a conductor is wound in the width direction along a curve on the outer periphery, a plasma generator, and a drawer that extracts an ion beam from the plasma generated by the plasma generator and introduces it to the inlet of the ion deflection casing An electrode and a neutralization electron supplier provided inside the ion deflection casing, and the ion beam of a desired ion species is bent by the magnetic field of the air-core excitation current path according to the mass to output the ion beam of a desired ion species An ion mass separator that is derived from the unit,
A Faraday beam characteristic cup for measuring the beam current density of the ion beam derived from the exit portion;
An arithmetic and control unit that measures the density peak position of the desired ion species from the distribution of the beam current density measured by the Faraday cup;
A beam including at least a magnet current setting unit that sets a magnet current of the air-core excitation current path based on a density peak position calculated by the calculation control device and a neutralization current regulator that controls a current of a neutralizing electron supply body A characteristic adjusting device,
The arithmetic and control unit sets the current of the neutralizing electron supplier, the arc current of the plasma generator, and the extraction current of the extraction electrode, and the beam current density of the ion beam derived from the outlet is a predetermined irradiation request. The magnetic field intensity is changed by changing the magnet current in the air-core excitation current path in the state adjusted to the density, and the beam current density of the ion beam derived from the exit part at the time of the change of the magnetic field intensity is measured. Measure the density peak position of the desired ion species from the measured beam current density distribution, determine the reference magnet current from the measured density peak position, and set the magnet current so that the beam current density becomes the required irradiation density Set up
Furthermore, the arithmetic and control unit measures the density peak position of the desired ion species for each predetermined period during the operation of the ion mass separation, and when the measured density peak position is outside the allowable range of the reference magnet current, The ion mass separation apparatus is characterized in that the current of the neutralization electron supplier is controlled so that the density peak position is within an allowable range of the reference magnet current.
The invention according to claim 4 is characterized in that the arithmetic and control unit controls the current of the neutralizing electron supplier so that the measured density peak position is within an allowable range of the reference magnet current, and the beam current. The at least one of the arc current of the plasma generator and the extraction current of the extraction electrode is controlled so that the maximum density value falls within an allowable range of the required irradiation density. This is an ion mass separator .

The invention according to claim 5, wherein the beam characteristic adjustment device is an ion mass separation device according to claim 3, characterized in that it comprises an arc current regulator for varying the arc current of the plasma generator.

The invention according to claim 6 is the ion mass separation apparatus according to claim 3, wherein the beam characteristic adjusting device includes an extraction current adjuster for changing an extraction current of the extraction electrode.

  Measure the beam current density of the ion beam derived from the exit when the magnetic field intensity is changed by changing the magnet current in the air-core excitation current path, and the density peak of the desired ion species from the measured beam current density distribution Since the position is measured, the reference magnet current is obtained from the measured density peak position, and the magnet current is set, the ion beam of the desired ion species can be stably derived from the ion mass separator, and thus the material to be processed This has the effect of stabilizing the amount of do pink against and improving reproducibility.

  In addition, the density peak position of the desired ion species is measured every predetermined period during the operation of the ion mass separator, and the current of the neutralization electron supplier is adjusted so that the measured density peak position is within the allowable range of the reference magnet current. Therefore, there is an effect that an ion beam of a desired ion species can always be reliably derived.

  In addition to controlling the current of the neutralization electron supply, at least one of the arc current of the plasma generator or the extraction current of the extraction electrode is controlled so that the beam current density falls within the allowable range of the required irradiation density. By doing so, an ion beam having a stable beam current density can be always derived.

  The above control can be automatically performed in a short time, so that the efficiency of the work of irradiating the material to be processed with the ion beam can be improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic side view showing an example of an ion mass separation apparatus of the present invention. In the figure, the same components as those in FIGS. As shown in FIG. 1, a material to be processed 14 is movably provided at a lower portion of the outlet portion 3 of the ion deflection casing 5, and a Faraday cup 16 is provided at a lower portion of the movement path of the material 14 to be processed. ing.

  The Faraday cup 16 is for measuring the beam current density of the ion beam led out from the exit 3 of the ion deflection casing 5, and the Faraday cup 16 is, for example, a large number of detection units (see FIG. The beam current (beam current density) flowing in each detection unit by receiving an ion beam is measured by an ammeter 17.

  In FIG. 1, reference numeral 23 denotes a beam characteristic adjusting device for adjusting characteristics such as a beam current density of an ion beam taken out from the exit unit 3. The beam current of each detection unit measured by the ammeter 17 is the beam current. This is input to the arithmetic control device 18 such as a personal computer constituting the characteristic adjusting device 23. The arithmetic and control unit 18 measures the density peak position of the desired ion species from the measured beam current density distribution. That is, since the magnetic field intensity of the air-core exciting current path 6 can be converted into the mass number of ions, the arithmetic control unit 18 determines the density peak position from the distribution of the measured beam current density (current density of each ion species). Is measured.

FIG. 1 shows the case where diborane (B ₂ H ₆ ) is used as the material gas of the plasma generator 8. In this case, if the magnet current is changed as shown in FIG. the ion beam, H _x from the lower of the magnetic field strength (magnetic current), BH _x, the distribution of a plurality of peaks appeared in the beam current density in the order of B ₂ H _x is the desired ion species being measured. Therefore, the arithmetic and control unit 18 can measure the density peak position 20 of the desired ion species B ₂ H _x based on the distribution of FIG.

  In FIG. 1, reference numeral 19 denotes a part of the beam characteristic adjusting device 23, and a magnet current setting device that sets the magnet current of the air-core exciting current path 6 according to a signal from the arithmetic control device 18. It is. In order to set the magnet current by the magnet current setting unit 19, first, the magnetic field intensity is changed by changing the magnet current of the air-core exciting current path 6, and the ion beam led out from the exit 3 at that time is changed. The beam current density is measured using the Faraday cup 16, and the density peak position 20 of the desired ion species shown in FIG. 2 is measured from the distribution of the beam current density at the changed magnet strength. Then, the reference magnet current 21 by the magnet current setting device 19 is calculated from the measured density peak position 20, and the magnet current of the magnet current setting device 19 is set. The reference magnet current 21 has an allowable range 22 as shown in FIG.

  In addition to the magnet current setting device 19 for setting the magnet current, the beam characteristic adjusting device 23 includes a neutralizing current adjuster 24 for adjusting the current of the neutralizing electron supply body 7 and an arc filament for the plasma generator 8. 15 includes an arc current regulator 25 that regulates the arc current of 15 and an extraction current regulator 26 that regulates the extraction current of the extraction electrode 9, and each of the regulators 24, 25, and 26 is also controlled by a signal from the arithmetic and control unit 18. To be controlled.

  The neutralization current regulator 24 changes the neutralization degree of the space charge effect of the ion beam in the ion deflection casing 5 by adjusting the supply amount of the neutralization electrons by the neutralization electron supply body 7. The ion beam trajectory can be changed. Further, the arc current adjuster 25 adjusts the generation of plasma in the plasma generator 8 to mainly adjust the beam current density of the ion beam (the maximum density value at the density peak position 20 measured for the desired ion species in FIG. 2). 27) can be varied. The extraction current adjuster 26 can change the beam current density and beam energy of the ion beam by adjusting the extraction of the ion beam. Further, in the extraction current regulator 26, the ion beam trajectory can be changed in order to change the extraction speed of the ion beam. In FIG. 2, reference numeral 28 denotes an irradiation requirement density at the density peak position 20 of the desired ion species, and the irradiation requirement density 28 has an allowable range 29.

  Next, the ion mass separation method of the present invention will be described.

  Prior to the operation of the ion mass separator 1, the initial setting shown in FIG. 3 is performed.

  First, the beam characteristic setting I is performed. That is, the setting I of the beam characteristic is performed by adjusting the neutralization current so that the beam current density of the ion beam irradiated from the outlet 3 to the material to be processed 14 becomes a predetermined irradiation required density 28 corresponding to the material to be processed 14. Each of the current by the adjuster 24, the arc current by the arc current adjuster 25, and the draw current by the draw current adjuster 26 is set by inputting a calculated value and an empirical value (S1).

  Subsequently, spectrum measurement II for setting the reference magnet current of the air-core excitation current path 6 is performed as in steps S2 to S5. That is, in the spectrum measurement II, the magnetic current intensity is changed by changing the magnet current of the air-core exciting current path 6 by the magnet current setting device 19 (S2), and the beam current of the ion beam derived from the exit 3 at that time is changed. The density is measured by the arithmetic and control unit 18 using the Faraday cup 16 (S3). After measuring the density peak position 20 of the desired ion species shown in FIG. 2 from the distribution of the beam current density at the changed magnet strength (S4), the reference magnet current 21 of the magnet current setting device 19 is measured from the measured density peak position 20. Is calculated and the magnet current of the magnet current setting unit 19 is set (S5). The spectrum measurement II can be automatically performed by the arithmetic and control unit 18. When the above setting is completed, the ion mass separator 1 is operated.

  Next, during the operation of the ion mass separation apparatus 1, the temporal control shown in FIG. 4 is performed at predetermined intervals as shown in steps S1 to S6. That is, the density peak position 20 of the desired ion species is measured (S2) by performing the spectrum measurement II (S1) by the arithmetic and control unit 18 every predetermined period during the operation of the ion mass separator 1. When the measured density peak position 20 is out of the allowable range 22 of the reference magnet current 21, a magnet current setting device is set so that the density peak position 20 is within the allowable range 22 of the reference magnet current 21. 19 automatically controls the current of the neutralized electron supplier 7.

  Further, as described above, after the density peak position 20 is adjusted within the allowable range 22 of the reference magnet current 21 by the control of the current of the neutralization electron supplier 7, the arithmetic control unit 18 adjusts the beam current density of FIG. The maximum density value 27 is measured from the distribution (S4), and the arc filament 15 of the plasma generator 8 by the arc current regulator 25 is adjusted so that the measured maximum density value 27 falls within the allowable range 29 of the required irradiation density 28. One or both of the control of the arc current to and the control of the extraction current of the extraction electrode 9 by the extraction current regulator 26 are performed (S5). Thereafter, the measurement of the maximum density value 27 (S6) is performed again. If the measured maximum density value 27 is outside the required irradiation density 28, step S5 is performed again.

  The time-dependent control shown in FIG. 4 is based on a command programmed in the arithmetic control device 18 when the material to be processed 14 does not pass through the upper part of the Faraday cup 16 during the operation of the ion mass separator 1. Can be implemented automatically.

  It should be noted that the ion mass separation method and apparatus of the present invention are not limited to the above-described embodiments, and it goes without saying that various changes can be made without departing from the scope of the present invention.

It is a schematic side view which shows an example of the ion mass separator of this invention. It is a diagram which shows the distribution in which the peak of the beam current density in the ion beam derived | led-out when the magnet current was changed appeared. It is a flowchart which shows the initial setting prior to the driving | operation of an ion mass separator. It is a flowchart of time-dependent control performed for every predetermined period during the driving | operation of an ion mass separator. It is an oblique side view which shows the outline | summary of the conventional ion mass separator. FIG. 6 is a side view of FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ion mass separator 2 Inlet part 3 Outlet part 5 Ion deflection casing 6 Air core exciting current path 7 Neutralization electron supply body 8 Plasma generator 9 Extraction electrode 15 Arc filament 16 Faraday cup 18 Arithmetic controller 19 Magnet current setting device 20 Density Peak Position 21 Reference Magnet Current 22 Allowable Range 23 Beam Characteristic Adjusting Device 24 Neutralizing Current Adjuster 25 Arc Current Adjuster 26 Drawer Current Adjuster 27 Maximum Density Value 28 Required Radiation Density 29 Allowable Range

Claims (6)

A magnetic field is formed by an air-core excitation current path in which a conductor is wound in the width direction along the curve on the outer periphery of the ion deflection casing so as to pass through the inlet portion at one end and the outlet portion at the other end of the curved ion deflection casing, and the plasma The ion beam is extracted from the plasma generated by the arc in the generator by the extraction electrode and introduced into the inlet of the ion deflection casing, and the ion beam is bent according to the mass by the magnetic field, and at the same time, neutralization in the ion deflection casing is performed. An ion mass separation method in which neutralized electrons are supplied from an electron supplier to derive an ion beam of a desired ion species from the outlet portion,
The current of the neutralizing electron supplier, the arc current of the plasma generator, and the extraction current of the extraction electrode are set so that the beam current density of the ion beam derived from the outlet becomes a predetermined required irradiation density. In the adjusted state, the magnetic field intensity is changed by changing the magnet current in the air-core excitation current path, and the beam current density of the ion beam derived from the exit portion when the magnetic field intensity changes is measured, and the measured beam The density peak position of the desired ion species is measured from the current density distribution, the reference magnet current is obtained from the measured density peak position, and the magnet current is set so that the beam current density becomes the irradiation required density. Ion mass separation operation,
The density peak position of the desired ion species is measured every predetermined period during the operation of the ion mass separation, and when the measured density peak position is outside the allowable range of the reference magnet current, the density peak position is An ion mass separation method, wherein the current of a neutralized electron supply body is controlled to be within an allowable range of a magnet current.   In addition to controlling the current of the neutralizing electron supply so that the measured density peak position is within the allowable range of the reference magnet current, the maximum density of the beam current density is within the allowable range of the required irradiation density. 2. The ion mass separation method according to claim 1, wherein at least one of an arc current of the plasma generator and an extraction current of the extraction electrode is controlled so that A curved ion deflection casing having an inlet portion at one end and an outlet portion at the other end, and a width direction along the curve on the outer periphery of the ion deflection casing so as to pass through the inlet portion and the outlet portion of the ion deflection casing An air-core exciting current path wound with a conductor, a plasma generator, an extraction electrode for extracting an ion beam from the plasma generated by the plasma generator and introducing it into the inlet of the ion deflection casing, and A neutralization electron supply body provided therein, and the ion beam is bent according to the mass by the magnetic field of the air-core excitation current path so that the ion beam of a desired ion species is led out from the exit portion. An ion mass separator comprising:
A Faraday beam characteristic cup for measuring the beam current density of the ion beam derived from the exit portion;
An arithmetic and control unit that measures the density peak position of the desired ion species from the distribution of the beam current density measured by the Faraday cup;
A beam including at least a magnet current setting unit that sets a magnet current of the air-core excitation current path based on a density peak position calculated by the calculation control device and a neutralization current regulator that controls a current of a neutralizing electron supply body A characteristic adjusting device,
The arithmetic and control unit sets the current of the neutralizing electron supplier, the arc current of the plasma generator, and the extraction current of the extraction electrode, and the beam current density of the ion beam derived from the outlet is a predetermined irradiation request. The magnetic field intensity is changed by changing the magnet current in the air-core excitation current path in the state adjusted to the density, and the beam current density of the ion beam derived from the exit part at the time of the change of the magnetic field intensity is measured. Measure the density peak position of the desired ion species from the measured beam current density distribution, determine the reference magnet current from the measured density peak position, and set the magnet current so that the beam current density becomes the required irradiation density Set up
Furthermore, the arithmetic and control unit measures the density peak position of the desired ion species for each predetermined period during the operation of the ion mass separation, and when the measured density peak position is outside the allowable range of the reference magnet current, An ion mass separation apparatus characterized in that the current of the neutralized electron supplier is controlled so that the density peak position falls within an allowable range of the reference magnet current. The arithmetic and control unit controls the current of the neutralizing electron supply so that the measured density peak position is within an allowable range of the reference magnet current, and the maximum value of the beam current density is the irradiation density. 4. The ion mass separator according to claim 3, wherein at least one of an arc current of the plasma generator and an extraction current of the extraction electrode is controlled so as to be within an allowable range of the required density. 4. The ion mass separator according to claim 3, wherein the beam characteristic adjusting device includes an arc current adjuster that changes an arc current of the plasma generator. 4. The ion mass separator according to claim 3, wherein the beam characteristic adjusting device includes an extraction current adjuster for changing an extraction current of the extraction electrode.

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