JPH0837100A - Ion accelerating device - Google Patents

Abstract

PURPOSE:To extract a large current beam having low energy from a tandem accelerator. CONSTITUTION:A high accelerating voltage is applied to the low-energy side accelerating tube 7 and high-energy side accelerating tube 9 of a tandem accelerator 4 from an accelerating voltage source 5 via a high-voltage terminal 6 even when low-energy ions are extracted. A charge conversion section having a stripper canal 8 can be changed to the charge conversion mode and the charge nonconversion mode, and no stripper gas is fed to the stripper canal 8 when low-energy ions are extracted. The negative ions from a negative-ion source 1 are focused and accelerated by a low-energy side accelerating tube 7 via a mass spectrometric electromagnet 2 and a Q-lens 3, and they enter the high- energy side accelerating tube 9 and are accelerated without being charge- converted. No energy is given to ions in the tandem accelerator 4, and an ion beam can be extracted in the same low-energy state as that when it is guided into the tandem accelerator 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion accelerator equipped with an electrostatic tandem accelerator capable of obtaining a low energy beam of 200 keV or less at a high current.

[0002]

2. Description of the Related Art FIG. 6 is a basic configuration diagram of an example of a high energy ion accelerator using an electrostatic tandem accelerator.
The ion beam extracted from the negative ion source 1 is passed through the magnetic field of the mass analysis electromagnet 2 to separate and extract negative ions having a desired mass. Next, the negative ion beam passes through the Q lens 3 on the low energy side and is introduced into the tandem accelerator (main body) 4.
The accelerator body is configured to be housed in a pressure tank filled with high-voltage insulating gas, and the negative ion beam introduced is applied with a high positive acceleration voltage from an acceleration voltage source 5 via a high voltage terminal 6. Low energy side accelerating tube 7
The first acceleration is carried out, and the charge is converted into a positive ion beam in the charge conversion section having the stripper canal 8 into which the stripper gas for charge conversion is introduced. The positive ion beam is accelerated again in the high energy side accelerating tube 9 toward the ground potential. Then, positive ions having a desired valence and energy are extracted by the energy analyzing electromagnet 11 via the high energy side Q lens 10 and injected into the sample 12, for example, a semiconductor wafer.

FIG. 7 is a schematic configuration diagram of a charge conversion section having a stripper canal 8, and the stripper canal 8 is
It is arranged inside a terminal duct 13 that connects the low energy side accelerating tube 7 and the high energy side accelerating tube 9. In the center of the stripper canal 8, a gas cylinder 14
The stripper gas from is supplied through the leak valve 15 and the stripper gas supply passage 16. In order to prevent the stripper gas from entering the both acceleration tubes 7 and 9, a baffle 17 having a cylindrical portion through which an ion beam passes is provided between the stripper canal 8 and both acceleration tubes, and a space for disposing the stripper canal 8 is provided. Is connected to the terminal duct 13, and an exhaust passage 19 of the pump is connected to the stripper gas supply passage 16 to circulate and reuse the stripper gas contained in the exhaust.

An attempt is made to obtain a low-energy ion beam by using the equipment of the high-energy ion accelerator using the tandem accelerator as it is, and an attempt is made to extend the range of use of the accelerator so that low-energy ions can be injected into the sample 12. Has been. FIG. 8 is a diagram showing an example of beam energy vs. beam current characteristics for a megaelectron volt (MeV) class tandem accelerator. The beam current Ib on the vertical axis is the% value of the outgoing beam current to the incoming beam current. is there. When the beam energy is 200 keV, the beam current drops to 20%. This is because in the low energy region, the beam introduced into the stripper canal is reduced and the efficiency of charge conversion from negative ions to positive ions is reduced.

FIG. 9 shows an example of a computer analysis result of a beam orbit in a high energy region of a high energy ion accelerator using such a tandem accelerator.
The trajectory a to the right of the center line in the figure shows the horizontal portion of the beam, and the trajectory a'to the left shows the vertical portion of the beam. In this case, the ion accelerator has a slit immediately in front of the low energy side Q lens 3. It is provided. For the accelerating tube of the tandem accelerator, the focal length of the beam optical system is f
[M], the accelerating electric field is E [V / m], and the incident voltage of the beam is Vi [V], a high beam transport efficiency can be obtained at a high accelerating voltage based on the lens action formula f = 4Vi / E. The beam optical system is configured so that The energy of the beam extracted from the negative ion source 1 and entering the tandem accelerator is 50 keV, and the accelerating voltage of the high voltage terminal unit 6, the low energy side and high energy side accelerating tubes 7 and 9 is 0.5 MV, The positive ion beam obtained from the accelerator body has a total energy of 1.05 MeV. The low energy side accelerating tube 7 has a strong lens action at the entrance thereof to direct the beam in the converging direction, so that the beam also has a converging action in the accelerating tube. Therefore, a beam with a diverging tendency is introduced into the low energy side accelerating tube 7 so that the beam is most narrowed in the central part of the stripper canal 8.
Increases charge conversion efficiency.

To obtain a low energy ion beam,
For example, if the accelerating voltage is set to 0 V,
Trajectories b, b'of the computer analysis results when a beam having an energy of 0 keV is passed through the accelerator body 4
Indicated by Since the low-energy accelerating tube 7 has no lens action, the beam introduced into the accelerating tube diverges, and the beam entering the stripper canal 8 is 1/5 of the total beam diameter, and the beam amount is 1/25 or less. Actually, the beam transfer efficiency of the tandem accelerator body remains at most about 3%.

[0007]

DISCLOSURE OF THE INVENTION The present invention is 200 ke
It is an object of the present invention to provide an ion accelerator equipped with a tandem accelerator, which can obtain a low energy beam of V or less with a large current.

[0008]

The ion accelerating device of the present invention is arranged in tandem, in which a high voltage terminal connected to an accelerating voltage source and an accelerating voltage are applied via the high voltage terminal. And a high-energy-side accelerating tube and a high-energy-side accelerating tube, which are provided in the high-voltage terminal, are located between the accelerating tubes, and are capable of changing into a charge conversion mode and a non-charge conversion mode. And is configured so that the ions accelerated by the low energy side acceleration tube can be decelerated by the high energy side acceleration tube without charge conversion.

Further, in the ion accelerator of the present invention, a high voltage terminal connected to an accelerating voltage source, and an accelerating voltage is applied through the high voltage terminal, respectively, and low energy arranged in tandem. Side acceleration tube and high energy side acceleration tube, a stripper canal for charge conversion arranged between the two acceleration tubes in the high voltage terminal, and a stripper gas supply path to the stripper canal for the charge conversion.
A stripper gas source connected through a valve in
A first vacuum pump connected to the stripper canal arrangement space and having an exhaust passage communicating with the stripper gas supply passage; a second valve for opening and closing the stripper gas supply passage; and a stripper gas supply passage. A second vacuum pump that is connected and has an exhaust passage communicating with the inside of the high-energy-side acceleration tube through a third valve, without charge conversion of ions accelerated in the low-energy-side acceleration tube. The high energy side accelerating tube is configured to be able to decelerate.

Further, in the ion accelerator of the present invention, a high voltage terminal connected to an accelerating voltage source, and an accelerating voltage is applied via the high voltage terminal, respectively, and low energy is arranged in tandem. Side accelerating tube and high energy side accelerating tube, the stripper canal for charge conversion, which is arranged between the accelerating tubes in the high voltage terminal and is detachable from the ion beam passage, and to this stripper canal. A stripper gas supply source connected to the stripper gas supply path via a first valve, a second valve for opening and closing the stripper gas supply path, and a stripper canal connecting space, and an exhaust path connected to the stripper. A vacuum pump communicating with the gas supply path and communicating with the acceleration tube on the high energy side through a third valve, It is characterized in that it has configured to allow reduced at the high energy side accelerating tube with the accelerated ions with over side acceleration tube without charge exchange.

[0011]

The accelerating voltage is applied to both the low energy side and the high energy side accelerating tubes, and both accelerating tubes work as a normal tandem accelerator when the charge conversion section is operated in the ion charge conversion mode. When the charge conversion section is operated in the non-conversion mode, the ions introduced into the low energy side accelerating tube having the lens action by the application of the acceleration voltage are converged and accelerated, and then enter the high energy side accelerating tube as they are and are decelerated. The ions introduced into the low energy side acceleration tube are taken out from the high energy side acceleration tube in the low energy state of the energy as it is. The tandem accelerator acts as an Einzel lens as a whole.

When extracting the low energy beam, the first
The valve and the second valve are closed to cut off the supply of the stripper gas, the operation of the first vacuum pump is stopped, the second vacuum pump is operated, and the third valve is opened. As a result, the degree of vacuum in the stripper canal through which the ion beam passes increases, and the ions from the low energy side acceleration tube can be sent to the high energy side acceleration tube as they are.

When the low energy beam is taken out, the supply of the stripper gas to the stripper canal is stopped and the canal is separated from the ion beam passage. The vacuum space of the stripper canal is evacuated by a vacuum pump to increase the degree of vacuum in the ion beam passage.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a basic configuration diagram of the embodiment, and the same reference numerals as those in FIG. 6 denote the same parts. When obtaining ions in the low energy region with an ion accelerator using a tandem accelerator, the acceleration energy of ions can be obtained only by the beam extraction voltage of the ion source. The ion beam extracted from the negative ion source 1 enters the magnetic field of the mass analysis electromagnet 2,
Negative ions of a desired mass are separated and extracted. Then, the negative ion beam passes through the low energy side Q lens 3 and is introduced into the tandem accelerator body 4, and the low energy side acceleration tube 7 to which a positive acceleration voltage is applied from the acceleration voltage source 5 through the high voltage terminal 6. Is accelerated by. The accelerated negative ion beam is introduced into the charge conversion unit having the stripper canal 8, but stripper gas is not supplied to the canal, and the negative ion beam is not subjected to charge conversion and is passed to the high energy side acceleration tube 9. enter. The same acceleration voltage as in the normal tandem acceleration operation, that is, the voltage of the same polarity as in the case of accelerating the charge-converted positive ion beam is applied to the same accelerating tube, and the same negative ion beam without charge conversion is applied. It will be decelerated by the acceleration tube. Then, a desired valence is obtained by the energy analysis electromagnet 11 via the high energy side Q lens 10,
A positive ion beam of energy is extracted and injected into the sample 12, eg a semiconductor wafer.

The basic principle of the present invention is to consider the tandem accelerator as an Einzel lens. Ions are accelerated while being converged in the low energy side accelerating tube 7, and decelerated in the high energy side accelerating tube 9, so that the total energy given to the ions in the tandem accelerator is zero, and the ions introduced into the low energy accelerating tube. Is injected into the sample 12 in the energy state at the time of its introduction.

From the lens action formula f = 4Vi / E, the strength of the lens action at the entrance and exit of the low energy side accelerating tube (LE) 7 and the high energy side accelerating tube (HE) 9 is as follows. However, E = Vt / l, Vt: terminal voltage,
l: Acceleration tube length. When both accelerating tubes are used as a normal-tandem accelerator for acceleration-acceleration, the inlet f (LE, in) of the low energy side is f (LE, in) = 4Vi / E, and the outlet f (LE, out) of the same is -4 (Vi + Vt). / E High-energy-side accelerating tube inlet f (HE, in) = 4 (Vi + Vt) / E Same outlet f (HE, out) =-4 (Vi + 2Vt) / E, and the strength of the lens action is strong. , Medium, weak, roughly, and schematically shown in FIG. 2 (a).

On the other hand, the present invention uses two accelerating tubes arranged in tandem for acceleration and deceleration in the low energy region, and the strength of the lens action at each entrance / exit is that of the accelerating tube on the low energy side. Inlet f (LE, in) = 4Vi / E, same outlet f (LE, out) =-4 (Vi + Vt) / E High energy side accelerating tube inlet f (HE, in) =-4 (Vi + Vt) / E The same outlet f (HE, out) = 4Vi / E, and these lens actions are schematically shown in FIG. 3 (b).
As a result, the beam optical system is symmetrical about the high voltage terminal.

FIG. 3 shows an example of a beam trajectory analysis result by a computer when such a tandem accelerator is operated without charge conversion. The trajectory c to the right of the center line is the horizontal portion of the beam, and the left. The orbit c'indicates the horizontal portion. The energy voltage of the beam incident on the low energy side accelerating tube 7 is Vi = 50 keV, and the high voltage target
FIG. 6 is a trajectory diagram when the minal voltage Vt = 0.5 MV. The beam envelope of the high energy side accelerating tube 9 is symmetrical with the envelope of the low energy side accelerating tube 7, and it is found that the ion beam introduced into the low energy side accelerating tube passes through the high energy side accelerating tube. A high-energy beam with low energy can be obtained.

The charge conversion part in which the stripper canal 8 in the tandem accelerator is arranged is finally evacuated through the low-energy side and high-energy side acceleration tubes 7 and 9, but stripper gas is removed. Because it is designed to be confined, the degree of vacuum is not good. In the present invention, when extracting low energy ions from the tandem accelerator, the ions accelerated by the low energy side acceleration tube 7 must be sent to the high energy side acceleration tube 9 without undergoing charge conversion. Therefore, the degree of vacuum in the stripper canal 8 must be increased.

FIG. 4 is a block diagram of an embodiment of such a charge conversion section capable of improving the degree of vacuum. The stripper gas is supplied from the gas cylinder 14 to the central portion of the stripper canal 8 through the first valve, the leak valve 15, and the stripper gas supply passage 16. A first vacuum pump for evacuating the arrangement space of the stripper canal 8, a turbo molecular pump 18, is connected to the terminal duct 13,
The exhaust passage 19 of the pump is connected to the stripper gas supply passage 16 so as to circulate and reuse the residual stripper gas. A second valve 20 for opening and closing the supply path, a second vacuum pump, and a turbo molecular pump 21 for canal exhaust are connected to the gas supply path 16, and an exhaust path 22 of the pump has a third valve 23. It is made to communicate with the inside of the high-energy side accelerating tube 9 via.

When the tandem accelerator is operated in a normal tandem acceleration operation so as to obtain a high-energy ion beam, the first valve, the leak valve 15 and the second valve 2 are used.
0 is opened to supply the stripper gas from the gas cylinder 14 to the stripper canal 8, the first vacuum pump and the turbo molecular pump 18 are operated, the second vacuum pump and the turbo molecular pump 21 are stopped, and the third vacuum pump and the turbo molecular pump 21 are stopped. The valve 23 is closed. The accelerated negative ions from the low energy accelerating tube 7 are converted into positive ions in the stripper canal 8 and are accelerated in the high energy side accelerating tube 9.

When obtaining a low energy ion beam, the first valve, the leak valve 15 and the second valve 20 are closed to stop the supply of the stripper gas, the operation of the first vacuum pump 18 is stopped, and the second vacuum pump 18 is stopped. Of the third valve 2 by operating the vacuum pump and the turbo molecular pump 21 for canal exhaust.
Open 3 Therefore, the stripper canal 8 is evacuated by the second vacuum pump, and the negative ions accelerated in the low energy side acceleration tube 7 are introduced into the high energy side acceleration tube 9 without undergoing charge conversion. It is decelerated, and negative ions can be taken out from the tandem accelerator in the energy state when introduced.

FIG. 5 is a block diagram of another embodiment of the charge conversion section. The stripper canal 8 of the charge conversion section arranged in the terminal duct 13 is configured to be detachable from the beam passage. The gas supply pipe 16 _{1 which} is connected to the central portion of the stripper canal 8 and forms a part of the stripper gas supply passage 16 is provided with a cylindrical pipe 24 attached to the terminal duct 13 and an O-ring 25 for vacuum sealing.
It is inserted by interposing. An operation shaft 26 is attached to the stripper canal 8, and the coaxial shaft is axially supported by a sliding seal bearing 27 provided in the terminal duct 13.
By extending the stripper canal from the minal duct and operating from outside the duct, the stripper canal can be moved to the beam passage and a position separated from the passage. The gas supply pipe 16 ₂ which is connected to the cylindrical pipe 24 and forms a part of the stripper gas supply passage 16 is provided with a second valve 20, and the supply pipe 16 ₂ is provided with a first valve and a leak valve. Stripper gas is supplied from the bus cylinder 14 via 15. Exhaust path 19 of the vacuum pump, a turbo molecular pump 18 for evacuating the terminal duct 13 is in communication with the gas supply pipe 16 _2, and further communicates through a third valve 23 to the high energy side accelerating tube 9 . The cylindrical tube 2
The four and two operating shafts 26 are arranged at the same angular position of the terminal duct 13, and this arrangement angle and the terminal of the vacuum pump 18 are arranged.
The arrangement angle in the minal duct is different.

When obtaining a high-energy ion beam from the tandem accelerator, the stripper canal 8 is arranged at the position shown in the drawing, and the first valve, the leak valve 15 and the second valve 19 are opened to stripper gas from the gas cylinder 14 to the stripper canal 8. The vacuum pump and the turbo molecular pump 18 are operated, and the third valve 21 is closed. The accelerated negative ions from the low energy accelerating tube 7 are converted into positive ions in the stripper canal 8 and are accelerated in the high energy side accelerating tube 9.

When obtaining a low energy ion beam, the stripper canal 8 is lowered in the direction of arrow a and moved to a position separated from the passage of the ion beam. The first valve and the leak valve 15 are closed to stop the supply of stripper gas, the vacuum pump 18 is operated, and the third valve 21
open. Therefore, the beam passage space is evacuated by the turbo molecular pump 18, and the low energy side acceleration tube 7
The negative ions accelerated by are introduced into the high energy side acceleration tube 9 without undergoing charge conversion, and are decelerated by the acceleration tube. Negative ions have the same energy as when the tandem accelerator body was introduced and are taken out from the accelerator.

In the above-mentioned embodiment, the tandem accelerator has been described in which negative ions are introduced from the negative ion source 1. However, a positive ion source such as a PIG ion source is used as the ion source, and the positive ions from the same ion source are metalized. Negative ions may be obtained through a vapor charge conversion cell. Alternatively, the positive ions from the positive ion source may be directly introduced into the tandem accelerator. In this case, the voltage polarity of the accelerating voltage source 5 is reversed and the low energy side accelerating tube is passed through the high voltage terminal 6. 7 and the high energy side acceleration tube 9 are given a high negative acceleration voltage.

[0027]

Since the present invention is configured as described above, by operating the charge conversion section in the non-conversion mode, an acceleration voltage similar to that in the normal operation of the tandem accelerator is applied to cause the lens action. The ions introduced into the low energy side accelerating tube are converged and accelerated, enter the high energy side accelerating tube as they are, and are decelerated. Ions introduced into the low energy side accelerator tube can be taken out from the high energy side accelerator tube in the low energy state with the energy at the time of introduction, and a high current ion beam in the low energy state can be taken out from the tandem accelerator.

When the low energy beam is extracted from the tandem accelerator, the charge conversion stripper canal in which the supply of the stripper gas is cut off is evacuated,
The degree of vacuum in the stripper canal through which the ion beam passes is increased, and the ions from the low energy side acceleration tube can be directly sent to the high energy side acceleration tube.

Further, when the low-energy beam is taken out, the stripper canal whose supply of the stripper gas is cut off is separated from the ion beam passage, so that the vacuum degree of the passage can be increased by one vacuum pump. it can.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram when a low energy ion beam is extracted in an example.

FIG. 2 is a schematic explanatory view of a lens action of an accelerating tube in a tandem accelerator.

FIG. 3 is a beam trajectory analysis diagram at the time of extracting a low energy ion beam in the tandem accelerator.

FIG. 4 is a configuration diagram of an embodiment of a charge conversion unit.

FIG. 5 is a configuration diagram of another embodiment of the charge conversion unit.

FIG. 6 is a basic configuration diagram of an example of an ion accelerator using a tandem accelerator.

FIG. 7 is a schematic configuration diagram of a charge conversion unit having a stripper canal.

FIG. 8 is a characteristic diagram showing an example of beam energy versus beam current of a tandem accelerator.

FIG. 9 is a beam trajectory analysis diagram of the tandem accelerator.

[Explanation of symbols] 1 ion source 5 accelerating voltage source 6 high voltage terminal 7 low energy side accelerating tube 8 stripper canal 9 high energy side accelerating tube 13 terminal duct 14 stripper gas cylinder 15 first valve 16 stripper gas supply path 18 First Vacuum Pump 19, 22 Vacuum Pump Exhaust Path 20 Second Valve 21 Second Vacuum Pump 23 Third Valve

Claims (3)

[Claims] 1. A high-voltage terminal connected to an accelerating voltage source, and a low-energy side accelerating tube and a high-energy side acceleration arranged in tandem, to which an accelerating voltage is applied respectively via the high-voltage terminal. A tube and a charge converter provided in the high-voltage terminal, located between the two accelerating tubes, and capable of changing between a charge conversion mode and a non-charge conversion mode. An ion accelerator, wherein the accelerated ions can be decelerated by the high energy side accelerating tube without charge conversion. 2. A high-voltage terminal connected to an accelerating voltage source, and a low-energy side acceleration tube and a high-energy side acceleration arranged in tandem, to which an accelerating voltage is applied respectively via the high-voltage terminal. Tube, a stripper canal for charge conversion arranged in the high-voltage terminal between the two accelerating tubes, and a stripper connected to a stripper gas supply path to the stripper canal via a first valve. A gas supply source, a first vacuum pump connected to the stripper canal disposition space, and an exhaust passage communicating with the stripper gas supply passage; a second valve for opening and closing the stripper gas supply passage; A second vacuum pump connected to the stripper gas supply path and having an exhaust path communicating with the high-energy-side acceleration pipe through a third valve; An ion accelerating device characterized in that it is configured such that the ions accelerated by the Rugey side accelerating tube can be decelerated by the high energy side accelerating tube without charge conversion. 3. A high-voltage terminal connected to an accelerating voltage source, and an accelerating voltage is applied via the high-voltage terminal, respectively, and a low-energy side accelerating tube and a high-energy side accelerating arranged in tandem. A tube and a stripper canal for charge conversion, which is arranged between the two accelerating tubes in the high voltage terminal and is detachable from the ion beam passage, and a stripper gas supply path to the stripper canal for the charge conversion.
A stripper gas source connected through a valve in
A second valve for opening and closing the stripper gas supply passage;
The stripper canal is connected to the arrangement space, and the exhaust passage communicates with the stripper gas supply passage.
And a vacuum pump communicating with the high energy side accelerating tube through the valve, and the ions accelerated by the low energy side accelerating tube can be decelerated by the high energy side accelerating tube without charge conversion. An ion accelerator which is configured as described above.