JPH08106877A - Ion implanting device - Google Patents

Abstract

PURPOSE: To provide an ion implanting device in which the space charge of an ion beam can be sufficiently suppressed to improve beam transporting efficiency without depending on an electron supplying source for supplying electrons to the ion beam from the outside. CONSTITUTION: A solenoid 14 is arranged on the outside of a connecting pipe 12 for connecting an ion source 2 to a mass spectrometric electromagnet 6 along it. The solenoid 14 is excited by a DC power source 16 to generate a magnetic field B in the direction laid along the axis of an ion beam 4 passing its inside. Further, in positions within the connecting pipe 12 situated near both end parts of the solenoid 14, first and second electron confining electrodes 20, 22 for surrounding the ion beam 4 passing these positions so as not to touch it are arranged, and a negative voltage is applied to these electrodes from a DC power source 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus for irradiating a target with an ion beam in a vacuum to perform ion implantation, and more specifically, it suppresses divergence of the ion beam due to space charge and transports the beam. It relates to means for improving efficiency.

[0002]

2. Description of the Related Art FIG. 4 is a schematic view showing an example of a conventional ion implantation apparatus. This ion implanter uses an ion source 2
The ion beam 4 extracted from the ion beam 4 is deflected through the mass analysis electromagnet 6 and passes through the analysis slit 8 provided at the beam focusing point on the downstream side of the ion analysis beam. The beam 4 is selectively extracted and is made incident on a target (for example, a wafer) 10. The path of the ion beam 4 is all vacuum.

[0003]

In the ion implantation apparatus as described above, in order to increase the beam current in the target 10, it is effective to increase the transport efficiency of the ion beam 4 from the ion source 2 to the target 10. is there.

One of the major factors that lower the beam transport efficiency is the divergence of the ion beam 4 due to the space charge.
This is because the ions in the ion beam 4 repel each other due to the same polarity charge, which causes the ion beam 4 to diverge.

Ion beam 4 by such space charge
Divergence becomes larger as the ion beam 4 has lower energy and larger current. This is because when the current is large, the density of the ions is high, and when the energy is low, the velocity of the ions is low and the density of the ions per unit time is high, which increases the repulsive force between the ions.

Although no ion implanter has been provided with a means for positively neutralizing the space charge of such an ion beam, an electron supply source for supplying electrons to the ion beam from the outside has been used in the ion beam path. It is considered to install it in an appropriate place.

As the electron supply source, it is considered to simply supply only electrons or to supply electrons in the form of plasma.

However, even if an electron supply source for supplying only electrons is simply provided, the electrons are not sufficiently supplied to the central portion of the ion beam, and the space charge of the ion beam is not sufficiently neutralized. This is because when an electron is supplied to the ion beam from the outside, the potential of the ion beam is the highest in the central part, so the electrons are accelerated toward the central part, and the momentum passes through the central part, and then toward the central part again. The electrons reciprocate around the center of the ion beam, such as being accelerated, so that the existence probability of the electrons is low in the center of the ion beam, contrary to the potential distribution of the ion beam. This is because it becomes higher in the peripheral area.

Further, in order for the electrons to be supplied to the ion beam to be successfully trapped in the ion beam by its potential, it is necessary that the electrons have low energy, but an electron supply source that simply extracts the electrons is sufficient. If you try to get low energy of the amount of electrons, the amount of electrons is 3 / of the extraction voltage.
There is also a problem in that the device becomes very large because it decreases sharply as the extraction voltage decreases in proportion to the square.

On the other hand, although the electron supply source for supplying electrons in the form of plasma has a high electron supply capacity, it is necessary to supply a gas for plasma generation to this type of electron supply source, and this gas is an ion beam. Since the gas leaks into the path together with the plasma, it is necessary to add a new vacuum exhaust device or the like in order to maintain the degree of vacuum in the ion beam path. If this is not done, the ion beam collides with gas molecules existing in the ion beam path to become neutral particles, and the particle collision reaction becomes violent, resulting in increased ion beam loss and injection of neutral particles that are not measured as current into the target. As a result, the injection amount becomes abnormal.

As described above, there are various problems in using any electron supply source, and the divergence due to the space charge of the ion beam cannot be well suppressed.

Therefore, according to the present invention, it is possible to sufficiently suppress the space charge of the ion beam and improve the beam transport efficiency without relying on an electron supply source for supplying electrons to the ion beam from the outside. The main purpose is to provide an injection device.

[0013]

In order to achieve the above object, the ion implantation apparatus of the present invention is provided near the ion beam path between the ion source and the target so as not to hit the ion beam. , Magnetic field generating means for generating a magnetic field in the direction along the axis of the ion beam passing therethrough, and surrounding the ion beam passing therethrough so as not to hit the magnetic field generating means, which are respectively disposed near both ends of this magnetic field generating means. It is characterized by comprising first and second electron confinement electrodes and a DC power supply for applying a negative voltage to the first and second electron confinement electrodes, respectively.

[0014]

The residual gas always exists in the ion beam path, although the amount thereof varies, and electrons are generated by the collision between the residual gas and the ion beam. By trapping such electrons in the ion beam by the positive potential of the ion beam, the ion beam is neutralized to some extent. However, the trapping of electrons in the ion beam is insufficient because the electrons have kinetic energy and move easily in the radial or axial direction of the ion beam to escape from the ion beam simply by trapping with the positive potential of the ion beam. Therefore, the space charge of the ion beam cannot be made sufficiently small.

On the other hand, according to the magnetic field generating means, the electrons are wound around the magnetic field in the direction along the axis of the ion beam, so that the electrons can be prevented from escaping in the radial direction of the ion beam. Electrons can be magnetically confined in the radial direction of the ion beam.

According to the first and second electron confinement electrodes, the negative voltage applied from the DC power supply can push back the electrons that try to escape in the axial direction of the ion beam from both sides toward the center. Therefore, electrons can be confined electrostatically in the axial direction of the ion beam.

According to the above structure, the electrons can be well confined in the ion beam in this way,
Even if it does not rely on an electron supply source that supplies electrons to the ion beam from the outside, the confined electrons can sufficiently suppress the space charge of the ion beam, suppress the beam divergence due to the space charge, and improve the beam transport efficiency. it can.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an ion implantation apparatus according to an embodiment of the present invention. The same or corresponding portions as those of the conventional example in FIG. 4 are denoted by the same reference numerals, and the differences from the conventional example will be mainly described below.

In this embodiment, in the vicinity of the ion beam path between the ion source 2 and the mass analysis electromagnet 6 described above, a solenoid is wound along the ion beam path so as to wrap the ion beam 4 without hitting it. 14 are arranged. More specifically, the ion source 2 and the mass analysis electromagnet 6 are connected to each other by a connecting pipe 12 as a vacuum container, and in this embodiment, a cylindrical solenoid 14 is provided outside the connecting pipe 12 along the same. It is arranged.

A direct current power supply 16 is connected to the solenoid 14, and the solenoid 14 is excited by the direct current power supply 16 to generate a magnetic field B in the direction along the axis of the ion beam 4 passing therethrough. That is, in this embodiment, by the solenoid 14 and the DC power source 16,
It constitutes a magnetic field generating means. The direction of the magnetic field B is
Contrary to the illustration, it may be directed to the ion source 2 side, and the point is that the direction is along the axis of the ion beam 4 passing therethrough.

The strength of the magnetic field B generated by the solenoid 14 may be, for example, about several tens gauss. This is because the Larmor radius of the electrons wrapped around the magnetic field B is about 3 mm at a magnetic field B of 10 Gauss, which is sufficiently small even if the electron temperature is about 1 eV.

Further, inside the connecting pipe 12 and in the vicinity of both ends of the solenoid 14, first and second electron confinement electrodes 20 for surrounding the ion beam 4 passing therethrough so as not to hit it, and 22 are arranged respectively. Then, both electron confinement electrodes 20, 22
A DC power supply 26 is connected to the above through the current introduction terminal 24, and from this DC power supply 26, both electron confinement electrodes 20, 2 are connected.
A negative voltage is applied to 2.

The magnitude of the negative voltage applied to both electron confinement electrodes 20 and 22 depends on the electric field of the negative voltage.
It is necessary to make it large enough to push back the electrons trying to escape in the axial direction of, but specifically, it may be about −several hundreds of volts.

The shapes of both electron confinement electrodes 20 and 22 are
It is preferable that the cross section of the ion beam 4 passing therethrough be matched. For example, if the ion beam 4 has a circular cross section, it has a cylindrical shape as shown in FIG. 2, and if it has an elliptical cross section, it has an elliptic cylindrical shape and a rectangular cross section (sheet shape).
If it is a beam, it may be a thin rectangular tube. This is because the electric field due to the negative voltage applied to the electron confinement electrodes 20 and 22 can efficiently reach the central portion of the ion beam 4 without hitting the ion beam 4.

Further, the length L of the cylindrical electron confinement electrodes 20 and 22 in the beam traveling direction is approximately the same as the diameter R in the case of a cylindrical shape (see FIG. 2), and in the case of an elliptic cylindrical shape. In the case of a rectangular tube shape, it is preferable to make it to the same extent as the shorter diameter, and to the same extent as the inner method of the shorter one. This is because the potential of the electrodes can reach the central portions of the cylindrical electron confinement electrodes 20 and 22.

In the example of FIG. 1, the ion source 2 has a plasma generating portion 2a for generating plasma, and an extraction electrode system 2b for extracting the ion beam 4 by the action of an electric field from the plasma generating portion 2a.
An ion source housing 2c for accommodating them and an ion source magnet 2d for generating a magnetic field for electron confinement in the plasma generator 2a.

A residual gas always exists in the path of the ion beam 4 although the amount thereof is small, and electrons are generated by the collision between the residual gas and the ion beam 4. By capturing such electrons in the ion beam 4 by the positive potential of the ion beam 4, the ion beam 4 is neutralized to some extent even as it is. However, if only the positive potential of the ion beam 4 is trapped, the electrons have kinetic energy and move in the radial or axial direction of the ion beam 4 and easily escape from the ion beam 4, so that the electrons are trapped in the ion beam 4. The confinement is insufficient and the space charge of the ion beam 4 cannot be made sufficiently small.

On the other hand, the solenoid 1 as described above
When the magnetic field B is generated in the direction along the axis of the ion beam 4 by providing the electrons 4, electrons are wound around the magnetic field B, so that the electrons can be prevented from escaping in the radial direction of the ion beam 4. That is, magnetically, in the space inside the solenoid 14,
Electrons can be confined (radial confinement).

The electron confinement electrodes 20 and 2 are also provided.
If 2 is provided and a negative voltage is applied to it, the electrostatic field can push back the electrons trying to escape in the axial direction of the ion beam 4 from both sides toward the center. That is, it is possible to electrostatically confine electrons (axial confinement) in the space between the electron confinement electrodes 20 and 22.

In this way, the electrons can be successfully confined in the ion beam 4 in the space surrounded by the solenoid 14 and the electron confinement electrodes 20 and 22, so that the electrons are supplied to the ion beam 4 from the outside. Even if it does not depend on the source, the space charge of the ion beam 4 can be sufficiently suppressed by the confined electrons, the beam divergence due to the space charge can be suppressed, and the beam transport efficiency can be improved. As a result, the amount of beam transported to the target 10 increases.

In particular, when the ion beam 4 is composed of ion species having low energy, large current, and large mass number,
Since the space charge effect remarkably appears, the effect of providing the above means in the case of such an ion beam is great.

Although the solenoid 14 is arranged in the atmosphere outside the connecting pipe 12 in the example of FIG. 1, it may be arranged in the vacuum inside the connecting pipe 12. In that case, of course, the ion beam 4 is prevented from hitting the solenoid 14. If the solenoid 14 is arranged in a vacuum, the magnetic field B can be applied to the ion beam path from a closer position, so that the efficiency of applying the magnetic field is high, and therefore the solenoid 14 can be made small and simple, and for that purpose. The DC power supply 16 can also have a small capacity.

Further, around the both ends of the solenoid 14, if necessary, for example, as shown in FIG. 3, the magnetic field generated by the solenoid 14 may leak from the both ends to the outside in the axial direction. The suppressing magnetic shields 30 and 32 may be provided respectively. Both magnetic shields 30, 32 are made of a magnetic material, preferably a ferromagnetic material, and have, for example, a ring shape or a cylindrical shape.

By providing such magnetic shields 30 and 32, mutual interference between the magnetic field of the solenoid 14 and another magnetic field, for example, the magnetic field of the mass analysis electromagnet 6 or the magnetic field of the ion source magnet 2d can be avoided. This is the ion source 2
This is particularly effective when the solenoid 14 is arranged in a narrow space between the electromagnet 6 and the mass analysis electromagnet 6.

In addition, since the magnetic force lines 15 generated by the solenoid 14 come in and out from the magnetic shields 30 and 32 in the form of being sharply bent near the both ends of the solenoid 14, when the magnetic force lines 15 spread loosely. As compared with the above, it is possible to reduce the spread and twist of the ion beam 4 due to the magnetic field of the solenoid 14.

A negative voltage may be applied to both electron confinement electrodes 20 and 22 from a common DC power source 26 as in the example of FIG. 1, or a negative voltage may be applied from another DC power source. You can In the latter case, since negative voltages having different magnitudes can be applied to the electron confinement electrodes 20 and 22, a more appropriate negative voltage can be applied.

Although the solenoid 14 and the electron confinement electrodes 20 and 22 as described above can be provided anywhere as long as they are the ion beam paths between the ion source 2 and the target 10, the above-mentioned effects can be obtained. For example, the ion beam 4 may be provided between the mass analysis electromagnet 6 and the analysis slit 8 or between the analysis slit 8 and the target 10.
The more the effect of suppressing the divergence on the upstream side, the smaller the solid angle with respect to the target 10, so that a larger effect can be obtained.
Therefore, for this reason, as in the embodiment of FIG.
It is preferably provided between the electromagnet 6 and the mass analysis electromagnet 6.

Further, instead of the solenoid 14 and the DC power source 16, a plurality of permanent magnets are provided outside or inside the connecting pipe 12 to generate the magnetic field B as described above, thereby constituting the magnetic field generating means. You may.

[0039]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, the electrons generated by the collision of the ion beam with the residual gas are generated in the ion beam in the space surrounded by the magnetic field generating means and the first and second electron confinement electrodes. Since it can be confined magnetically and electrostatically well, the space charge of the ion beam can be sufficiently suppressed by the confined electrons without depending on the electron source that supplies electrons to the ion beam from the outside. Beam divergence due to electric charges can be suppressed and beam transport efficiency can be improved.

According to the second aspect of the present invention, the divergence of the ion beam can be suppressed at a position closest to the upstream side of the ion beam path, so that a greater effect can be obtained in improving the beam transport efficiency.

According to the third aspect of the invention, mutual interference between the magnetic field generated by the magnetic field generating means and another magnetic field can be avoided, and the spread and twist of the ion beam due to the magnetic field of the magnetic field generating means can be reduced. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing an ion implantation apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an example of an electron confinement electrode.

FIG. 3 is a cross-sectional view showing an example in which magnetic shields are provided near both ends of a solenoid coil.

FIG. 4 is a schematic view showing an example of a conventional ion implantation apparatus.

[Explanation of symbols]

 2 Ion source 4 Ion beam 6 Mass analysis electromagnet 8 Analysis slit 10 Target 12 Connection tube 14 Solenoid 16 DC power source 20,22 Electron confinement electrode 26 DC power source 30,32 Magnetic shield

Claims (3)

[Claims] 1. An ion implanter configured to cause an ion beam extracted from an ion source to enter a target through a mass analysis electromagnet so that the ion beam does not hit the vicinity of an ion beam path between the ion source and the target. Magnetic field generating means which is provided and generates a magnetic field in a direction along the axis of the ion beam passing therethrough;
First and second electron confinement electrodes, which are respectively disposed near both ends of the magnetic field generating means and surround an ion beam passing therethrough so as not to hit the ion beam, and the first and second electron confinement electrodes. An ion implantation apparatus comprising: a DC power supply for applying a negative voltage. 2. The ion implanter according to claim 1, wherein the magnetic field generating means and the first and second electron confinement electrodes are arranged between the ion source and the mass analysis electromagnet. 3. The magnetic shields are provided near both ends of the magnetic field generating means to prevent the magnetic field generated by the magnetic field generating means from leaking to the outside in the axial direction from the both ends. Or the ion implantation apparatus according to 2.