JPH0594801A - Ion implantation device - Google Patents

Abstract

PURPOSE:To sufficiently prevent charge up in the peripheral part and the central part of an ion irradiation object. CONSTITUTION:An ion implantation device uses secondary electrons emitted by irradiating an ion irradiation object 5 with an ion beam 1 for newtralization of the ion irradiation object 5. And the ion implantation device has the coils 12, 14 for generating the upper and lower side cusped magnetic fields forming the cusped magnetic field where the ion irradiation object 5 is located in the central part. Secondary electrons emitted from the ion irradiation object 5 and a disk 6 are mainly collected by the cusped magnetic field in the central direction of the ion irradiation object 5. Accordingly, negative potential due to the secondary electrons is applied to the irradiation object 5 so as to increase in the central part direction. Then, an impressing condition of negative potential increasing in this central part direction corresponds to a state where positive potential increases in the central part direction of the ion irradiation objects 5.

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 neutralizing the positive charge of an ion irradiation target by using secondary electrons generated when the ion irradiation target is irradiated with an ion beam. It is about.

[0002]

2. Description of the Related Art Impurity ions used for an ion beam of an ion implanter include, for example, boron ions (positive ions) and arsenic ions (positive ions), and these impurity ions have a polysilicon film, for example. When the ion irradiation target made of a silicon substrate is irradiated, the polysilicon film of the ion irradiation target is positively charged as the impurities are injected into the ion irradiation target. Then, when the potential difference between the positively charged polysilicon film and the silicon substrate exceeds a predetermined value, discharge occurs and charge-up that destroys the circuit of the device occurs.

Therefore, conventionally, in the ion implantation apparatus, charge-up is prevented by, for example, electron shower or disk bias. That is, the electron shower accelerates thermoelectrons emitted from the heated filament 53, as shown in FIG.
2 when it collides with the neutral cup 54
The secondary electron is irradiated onto the ion irradiation target object 51 in a shower shape. In addition, the disk bias causes a potential difference between the ion irradiation target 51 and the neutral cup 54, and the secondary electrons emitted from the ion irradiation target 51 and the disk 55 by the irradiation of the ion beam 52 are ion irradiation target. It is supplied after being inverted to 51.

As a result, in the conventional ion implanter adopting the electron shower and the disk bias, the polysilicon film of the positively charged ion irradiation object 51 is neutralized by the electrons to charge up. It can be prevented.

[0005]

By the way, as shown in FIG. 3, the ion irradiation target 51, which is positively charged by the ion beam 52, is usually the ion irradiation target 51.
Has a potential distribution in which the positive potential increases in the direction of the central portion of the. However, since the secondary electrons of the electron shower reach the ion irradiation target 51 while swinging left and right in the ion beam 52, the moving speed decreases from the central portion of the ion beam 52 toward the outer peripheral portion. Cage,
The irradiation amount of electrons is increased in the outer peripheral direction of the ion beam 52. As a result, the electron shower supplies a large number of electrons to the outer peripheral portion having a lower positive potential than the central portion of the ion irradiation target 51 having a high positive potential, so that the prevention of charge-up in the central portion is insufficient. It has become.

Further, the ion irradiation target 51 having a positive potential which becomes higher toward the central portion, even if the secondary electrons emitted from the ion irradiation target 51 and the disk 55 by the disk bias are supplied. Is not supplied so as to increase toward the central portion of the ion irradiation target 51, so that charge-up prevention at the central portion is insufficient as in the case of the electron shower described above.

As described above, in the conventional ion implantation apparatus, although the positive potential of the ion irradiation target object 51 is increased toward the central portion by the irradiation of the ion beam 52, the electron irradiation amount is adjusted to the ion irradiation target object 51. Since it cannot be increased in the direction of the central part, the charge-up prevention is insufficient. Therefore, it is an object of the present invention to provide an ion implanter capable of sufficiently preventing charge-up by increasing the electron irradiation amount toward the center of the ion irradiation target 51.

[0008]

In order to solve the above-mentioned problems, an ion implantation apparatus of the present invention emits an ion beam by irradiating an ion irradiation target and a supporting member for fixing the ion irradiation target with an ion beam. Secondary electrons are used to neutralize the ion irradiation target. The ion implanter has an upper cusp magnetic field generating coil and a lower cusp magnetic field generating coil that are cusp magnetic field forming means for forming a cusp magnetic field, and an ion irradiation object is located at the center of the cusp magnetic field. It is characterized by doing.

[0009]

According to the above structure, when the ion beam is irradiated on the ion irradiation target and the supporting member, secondary electrons are emitted from the ion irradiation target and the supporting member by the energy of the ion beam. The secondary electrons emitted from the support member are linked with the cusp magnetic field formed by the cusp magnetic field forming means, the traveling direction is bent by the cusp magnetic field, and the ion irradiation target is located in the center of the cusp magnetic field. The traveling direction will be changed toward the center of the object. Further, the secondary electrons emitted from the ion irradiation target are returned to the ion irradiation target because the traveling direction is reversed by the interlinking cusp magnetic field when traveling from the ion irradiation target to the outside. ..

As a result, the secondary electrons emitted from the ion irradiation target and the supporting member are supplied to the ion irradiation target by the cusp magnetic field, and further, the supplied secondary electrons are concentrated in the central portion direction. Therefore, the negative potential due to the secondary electrons is applied in a state of increasing toward the center. The negative potential application state that increases toward the central portion corresponds to the state where the positive potential increases toward the central portion of the ion irradiation target due to the irradiation of the ion beam. Therefore, the neutralization by the secondary electrons bent by the cusp magnetic field is uniformly performed on the entire surface of the ion irradiation target, and the charge is increased in the outer peripheral portion of the ion irradiation target and the center of the ion irradiation target is also increased. It is possible to sufficiently prevent charge-up in the section.

[0011]

EXAMPLE As shown in FIG. 1, an ion implanter according to this example has a neutral cup 2 and a catch plate 3 for measuring the beam amount of an ion beam 1 made of impurity ions. The neutral cup 2 above is
A rising part 2a raised in the incident direction of the ion beam 1.
An inclined portion 2b inclined from the lower end of the rising portion 2a to the outer peripheral direction at an angle of 45 °, and a cup outer peripheral portion 2c formed from the lower end of the inclined surface portion 2b to the outer peripheral direction.
On the other hand, the catch plate 3 is composed of a concave portion 3a irradiated with the ion beam 1, and a plate outer peripheral portion 3b formed in the outer peripheral direction from the upper end portion of the concave portion 3a and having the same diameter as the cup outer peripheral portion 2c. ing.

The neutral cup 2 and the catch plate 3 described above are connected via the current integrator 4 to the G
The current integrator 4 is connected to ND
The beam amount of the ion beam 1 is measured as a beam current. Further, in the space portion 7 formed by the neutral cup 2 and the catch plate 3,
The ion irradiation target 5 is placed and fixed on the disk 6 which is a supporting member, and the cup outer peripheral portion 2c and the plate outer peripheral portion 3 are
It is supposed to be introduced from between b and the disk 6
Is configured to make the irradiation of the ion beam 1 onto the ion irradiation target 5 uniform by reciprocating translational movement at constant speed rotation.

A mask slit 11 connected to GND is provided on the side of the neutral cup 2 from the rising portion 2a in the emitting direction of the ion beam 1. The mask slit 11 is irradiated with ions of the ion beam 1. The irradiation shape on the object 5 is set. An annular front suppressor 8 is disposed between the mask slit 11 and the rising portion 2a of the neutral cup 2 in proximity to the rising portion 2a. The front suppressor 8 is connected to the negative electrode side of a suppressor power supply 9 having a DC voltage of, for example, -600 to -1,000 V, and the ion beam 1 is applied to the catch plate 3, the ion irradiation target 5 and the disk 6. Dispersion of secondary electrons from the rising portion 2a to the outside of the space portion 7 generated when irradiated is prevented.

Further, an annular side suppressor 10a is disposed in the vicinity of the outer peripheral portion 2c of the cup of the neutral cup 2, and the catch plate 3 is provided.
In the outer peripheral direction of the plate outer peripheral portion 3b, the side suppressor 1 having the same shape as the above side suppressor 10a.
0b are arranged close to each other. And these side suppressors 10a and 10b are -100--2, for example.
It is connected to the negative electrode side of the suppressor power supply 13 having a DC voltage of 00V, and prevents secondary electrons from being dissipated to the outside of the space 7 from between the cup outer peripheral portion 2c and the plate outer peripheral portion 3b.

Further, an annular upper cusp magnetic field generating coil 12 (cusp magnetic field forming means) is arranged above the cup outer peripheral portion 2c close to the side suppressor 10a so as to be insulated from the neutral cup 2. A lower cusp magnetic field generating coil 14 (cusp magnetic field forming means) is arranged in an insulated state from the catch plate 3 below the plate outer peripheral portion 3b adjacent to the side suppressor 10b. The upper cusp magnetic field generating coil 12 and the lower cusp magnetic field generating coil 14 are set to have the same diameter, and are connected to a DC power supply with reduced ripples through a feedthrough (not shown).

The upper cusp magnetic field generating coil 12 and the lower cusp magnetic field generating coil 14 are composed of a magnetic field B of the upper cusp magnetic field generating coil 12 and a magnetic field of the lower cusp magnetic field generating coil 14 generated by a direct current. The sheet cusp surface A, which is the interface with B, is set in a position parallel to the surface of the ion irradiation target 5, and the magnetic field axes of both magnetic fields B and B are set in a position that coincides with the central axis of the ion beam 1. Has been done. As a result, the ion irradiation target 5 is positioned at the center of the cusp magnetic field composed of both magnetic fields B and B. It is desirable that the sheet cusp surface A coincides with the surface of the ion irradiation target 5.

The operation of the ion implanter having the above structure will be described.

First, a direct current is passed through the upper cusp magnetic field generating coil 12 and the lower cusp magnetic field generating coil 14, and the upper and lower cusp magnetic field generating coils 12.1.
A magnetic field B · B is formed around 4. Next, positively charged ions are extracted from the ion source by the extraction electrode, and an ion beam 1 of impurity ions composed of a specific ion species mass-analyzed by the mass spectrometer is formed. Then, the shape of the ion beam 1 is shaped by the mask slit 11 and then introduced into the space 7 in the neutral cup 2.

At this time, the ion irradiation target 5 is placed on the disk 6 and introduced into the space 7 between the cup outer peripheral portion 2c and the plate outer peripheral portion 3b. It is moving together with the disk 6 that is reciprocally translated at a constant speed. As a result, the ion beam 1 introduced into the space 7 is evenly applied to the entire surface of the ion irradiation target 5 and also to the disk 6.

When the ion beam 1 is irradiated on the ion irradiation target 5 and the disk 6, secondary energy is emitted from the ion irradiation target 5 and the disk 6 by the energy of the ion beam 1 as shown by a broken line. Become. The inclined portion 2 of the neutral cup 2 is released from the disc 6
The secondary electrons traveling in the b direction are interlinked with the cusp magnetic fields formed by the above-described upper and lower cusp magnetic field generating coils 12 and 14, and the traveling direction is bent by the cusp magnetic field, and the ion irradiation target The traveling direction is changed to the central portion of the object 5. In addition, the secondary electrons emitted from the ion irradiation target 5 are neutral cups 2
When traveling in the direction, the traveling direction is reversed by the interlinking cusp magnetic field, and thus the ion irradiation target 5 is returned.

As a result, the secondary electrons emitted from the ion irradiation target 5 and the disk 6 are supplied to the ion irradiation target 5 by the cusp magnetic field, and the supplied secondary electrons are directed toward the central portion. Since many are assembled, the negative potential due to the secondary electrons is applied to the entire surface and in a state of increasing toward the central portion. The state of application of the negative potential increasing toward the center corresponds to the state of increasing the positive potential toward the center of the ion-irradiated object 5 due to the irradiation of the ion beam 1. Since the ionization is uniformly performed on the entire surface of the ion irradiation target 5, it is possible to sufficiently prevent charge-up in the outer peripheral part of the ion irradiation target 5 and charge-up in the central part of the ion irradiation target 5. It has become.

Although the magnetic fields B and B are formed by the upper and lower cusp magnetic field generating coils 12 and 14 in this embodiment, the present invention is not limited to this and is formed by permanent magnets. May be. Further, the magnetic fields B and B formed by the upper and lower cusp magnetic field generating coils 12 and 14 may be adjustable in intensity in accordance with the beam shape of the ion beam 1. In this case, By cooperating with the beam shape automatic adjusting system, it becomes possible to more efficiently collect secondary electrons in the central direction.

[0023]

INDUSTRIAL APPLICABILITY As described above, the ion implantation apparatus of the present invention ion-irradiates secondary electrons emitted by irradiating an ion-irradiated object and a supporting member for fixing the ion-irradiated object with an ion beam. It is used for neutralizing an object, and has a configuration in which the ion irradiation object has a cusp magnetic field forming means for forming a cusp magnetic field located at the center.

As a result, the secondary electrons emitted from the ion-irradiated object and the supporting member are supplied to the ion-irradiated object by the cusp magnetic field, and more of the supplied secondary electrons are gathered toward the central portion. Therefore, the negative potential due to the secondary electrons increases in the direction of the central portion and is applied. And, the application state of the negative potential that increases in the central portion direction corresponds to the state in which the positive potential increases in the central portion direction of the ion irradiation target by the irradiation of the ion beam,
It is possible to sufficiently prevent charge-up in the outer peripheral portion and the central portion of the ion irradiation target.

[Brief description of drawings]

FIG. 1 illustrates the present invention and is an explanatory diagram showing a moving state of secondary electrons bent by a cusp magnetic field.

FIG. 2 illustrates a conventional example and is an explanatory diagram of an electron shower.

FIG. 3 is an explanatory diagram showing a potential distribution of an ion irradiation target and a moving state of electrons in an electron shower.

[Explanation of symbols]

1 Ion Beam 2 Neutral Cup 3 Catch Plate 4 Current Integrator 5 Ion Irradiation Target 6 Disk (Supporting Member) 7 Space 8 Front Suppressor 9 Suppressor Power Supply 10a Side Suppressor 10b Side Suppressor 11 Mask Slit 12 Upper Casp Magnetic Field Generation Coil (cusp) Magnetic field forming means) 13 Suppressor power supply 14 Lower cusp magnetic field generating coil (cusp magnetic field forming means)

Claims (1)

[Claims] 1. An ion implanter for using secondary electrons emitted by irradiating an ion irradiation target and a support member for fixing the ion irradiation target with an ion beam to neutralize the ion irradiation target. An ion implantation apparatus characterized in that it has a cusp magnetic field forming means for forming a cusp magnetic field located at the center of the ion irradiation target.