JPH08138894A - High frequency charge particle accelerator - Google Patents

Abstract

PURPOSE: To hardly cause diffusion due to spatial charge of beam itself. CONSTITUTION: An electron suppressor electrode 9 is installed near a beam coming inlet of a RFQ accelerator 6 and it becomes potential barrier to captured electrons in ion beam and thus electrons are prevented from being separated from the ion beam and being sucked to the RFQ accelerator 6. Consequently, in the upper stream side of the RFQ accelerator 6, electrons stay in the ion beam and the ion beam can be kept electrically neutral.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency charged particle accelerator for use in an apparatus for high-energy ion implantation, surface modification, etc., which resonates when receiving high-frequency power and accelerates charged particles by an electric field. is there.

[0002]

2. Description of the Related Art An ion implantation apparatus is an important apparatus for manufacturing integrated circuits at present, because it can control the impurities that determine the characteristics of the device in a semiconductor process to an arbitrary amount and depth with good controllability. In recent years, semiconductor device makers have been increasingly required to have high-energy MeV class ion implanters. This is the formation of retrograde wells in the C-MOS device manufacturing process, R
This is because the advantages of performing high energy ion implantation for post-OM writing and the like have become clear.

As shown in FIG. 3, one of the above high-energy ion implanters uses a high frequency 4 as an ion accelerating means.
A quadrupole linear accelerator (hereinafter RFQ (Radio Frequency Qu
There is one using an adrupole) 56).
This high-energy ion implanter ionizes an ion source material and extracts it as a beam, an ion source 52, an analysis magnet 53 that selectively extracts only desired ions by mass spectrometry using a magnetic field, and sharply shapes the ion beam. Converging lens system 54 and each of the above parts 52 to 5
4 is provided with an ion beam generator 51 having a high-voltage power supply 55 for supplying electric power. Then, the RFQ accelerator 56 is provided at the subsequent stage of the ion beam generator 51, so that the ions emitted from the ion beam generator 51 are R
The FQ accelerator 56 accelerates to a predetermined energy.

The RFQ accelerator 56 includes a vacuum chamber 5
A quadrupole electrode 56b is provided in 6a. Modulation is formed on the facing surface of the quadrupole electrode 56b, and a bunch portion for bunching is formed near the beam entrance portion of the quadrupole electrode 56b so as to facilitate beam acceleration. There is. By supplying high-frequency power of a predetermined frequency from a high-frequency power source (not shown) to the RFQ accelerator 56, a quadrupole electric field is formed in a direction perpendicular to the traveling direction of the ions, and the bunched beam is focused at the beam entrance portion. While being accelerated.

In the beam accelerated by the RFQ accelerator 56, only an ion having a desired energy is selected by the energy filter 57, and the ion implantation target such as a semiconductor wafer (not shown) set in the end station 58 is irradiated with the ion. It

[0006]

The ion beam transport system from the ion source 52 to the beam entrance of the RFQ accelerator 56 (hereinafter simply referred to as the entrance) is the ion entrance portion of the RFQ accelerator 56. It must be properly designed for maximum performance. This is particularly important when accelerating a low-speed and high-current ion beam.

When the RFQ accelerator 56 is incorporated into an ion implanter for industrial use as described above, it is necessary to enhance the purity of the ion beam to be accelerated. Therefore, the analysis magnet having a large mass resolution, that is, a large radius of curvature. 53 should be used. As a result, the ion source 52
The distance of the beam optical axis from to the entrance of the RFQ accelerator 56 inevitably becomes long.

Further, when the velocity of the ion beam is relatively high, this is not a serious problem, but from the ion source 52 to RF.
When the velocity of the ion beam passing through the ion beam transport system to the entrance of the Q accelerator 56 is relatively low (for example, in the case of a B ⁺ beam having an energy of 30 keV), its space charge effect cannot be ignored. That is, when the positively charged ions collide with a stationary residual gas in a vacuum (the residual gas seen by the ion beam transported with a certain amount of energy appears to be stationary), the atoms forming the residual gas Alternatively, the molecule is ionized. In this case, if the ions are positively ionized, they are repelled by the space charge of the ion beam, and the electrons generated by the ionization are captured by the positive potential of the beam. If this process occurs naturally and the positive ion beam is kept completely neutralized by the trapped electrons, the divergence due to the space charge of the beam itself can in principle be suppressed to zero. . However, if there are no or almost no electrons in the positive ion beam and the neutralization of the beam is not maintained, the beam will spread greatly during beam transportation.

The phenomenon that the electrons disappear (or almost disappear) in the positive ion beam as described above is due to the following reasons. That is, the energy of the trapped electrons in the beam is as small as a few eV, and it is as if wandering back and forth in the valley of potential created by the fluffy positive ion beam. In such a state, if there is an electric field acceleration type accelerator in principle like the RFQ accelerator 56 in the beam line, the electrode voltage of the accelerator forms a strong electric field enough to pull out trapped electrons in the beam, and Is ejected out of the beam along the electric field and collides with the accelerator electrode. As a result, the ion beam loses the trapped electrons and completely disturbs the electrical neutralization, and diverges due to the space charge of the beam itself.

The space charge effect caused by the RFQ accelerator 56 as described above is remarkably widened in connection with the beam line lengthened by using the analysis magnet 53 having a large radius of curvature as described above. I will end up. As a result, the beam becomes larger than the entrance of the RFQ accelerator 56, and the amount of the beam entering the RFQ accelerator 56 decreases. For example, when the distance from the ion source 52 to the entrance of the RFQ accelerator 56 is 2.5 m and the electrons are completely removed from the ion beam by the RFQ accelerator 56 as described above, the beam diameter is At the entrance of the RFQ accelerator 56, the ion source 52
It is 4 times larger than immediately after being drawn from. This reduces the beam current density by 1/16, and the beam amount that can be accelerated by the RFQ accelerator 56 is significantly reduced.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-frequency charged particle accelerator capable of suppressing the divergence of a beam without disturbing the neutralization of the ion beam before entering the accelerator. It is in.

[0012]

A high-frequency charged particle accelerator according to the present invention accelerates a charged particle beam incident from a beam entrance by an electric field, and has the following means. I am trying.

That is, a negative potential electron suppressor electrode is provided near the beam entrance of the high-frequency charged particle accelerator.

[0014]

According to the above structure, a negative potential electron suppressor electrode is installed in the vicinity of the beam entrance of the high frequency charged particle accelerator, and this serves as a potential barrier for trapped electrons in the ion beam, and the electrons are ionized. Prevents the high-frequency charged particle accelerator from being drawn away from the beam.
As a result, on the upstream side of the high-frequency charged particle accelerator, the electrons remain in the ion beam and the ion beam can maintain electrical neutrality, so that divergence due to the space charge of the beam itself hardly occurs.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

A high frequency quadrupole linear accelerator (hereinafter referred to as RFQ accelerator) as a high frequency charged particle accelerator according to this embodiment is incorporated in a high energy ion implanter and, as shown in FIG. It is installed in the subsequent stage of the ion beam generator 1 of the ion implanter.

The ion beam generator 1 forming an ion beam incident system to the RFQ accelerator 6 ionizes an ion source material and extracts it as a beam, and selects only desired ions by mass spectrometry using a magnetic field. Analysis magnet 3 that is selectively taken out, a focusing lens system 4 that focuses the ion beam after mass analysis in order to increase the efficiency of the amount of beam that enters the RFQ accelerator 6, and a high-voltage power supply that supplies power to each of the above parts 2-4. It has a part 5.

As the ion source 2, a general Freeman type ion source or the like can be used. The analyzing magnet 3 is a 90 ° -deflecting dipole electromagnet, and is provided with a sextupole correction unit so that proper beam characteristics (beam size, spread) can be obtained when the beam enters the RFQ accelerator 6. The focusing lens system 4 is composed of four quadrupole electromagnets and an Einzel lens.

The RFQ accelerator 6 has a resonance structure for forming an accelerating electric field in the vicinity of the beam optical axis, and is provided in the vacuum chamber 6a and the vacuum chamber 6a.
And a quadrupole electrode 6b arranged at equal intervals around the beam optical axis. Modulation for forming a quadrupole electric field is formed on the facing surface of each electrode of the quadrupole electrode 6b in a direction perpendicular to the ion traveling direction (the facing surface of each electrode is processed into a wavy shape). ing). In addition, a bunch portion for bunching is formed near the beam incident portion of the quadrupole electrode 6b so as to easily accelerate the beam.

Further, the RFQ accelerator 6 is supplied with high frequency power of a predetermined frequency from a high frequency power source (not shown). When high-frequency power is supplied to the RFQ accelerator 6, resonance occurs, a quadrupole electric field is formed in a direction perpendicular to the ion traveling direction, and the bunched beam is accelerated while being focused at the beam entrance portion.

An electron suppressor electrode 9 to which a negative suppressor voltage is applied from a power source 10 and which is held at a negative potential is provided in the vicinity of a beam entrance (hereinafter simply referred to as an entrance) of the RFQ accelerator 6. . The electron suppressor electrode 9 is a ring-shaped electrode having a beam passage hole at the center. The electron suppressor electrode 9 is preferably provided as close as possible to the entrance of the RFQ accelerator 6, and is attached to the entrance of the electron suppressor electrode 9 by an insulating support member. This electron suppressor electrode 9 is
The electrons existing in the space upstream of the RFQ accelerator 6 are R
It serves as a potential barrier that prevents the FQ accelerator 6 from being sucked.

On the downstream side of the RFQ accelerator 6, there are an energy filter 7 for selecting ions having a desired energy, and an end station 8 in which an ion implantation target such as a semiconductor wafer is set and implantation processing is performed. They are provided in order.

The operation of the high energy ion implanter to which the RFQ accelerator 6 of the above structure is applied will be described below.

The positive ion beam extracted by the electric field from the ion source 2 is subjected to mass analysis by the analyzing magnet 3 to be a beam of specific ions, which is then focused by the focusing lens system 4 and then the RFQ accelerator 6 Incident on.

A negative potential electron suppressor electrode 9 is installed on the entrance side of the RFQ accelerator 6, which serves as a potential barrier for trapped electrons in the ion beam, and the electron moves away from the ion beam and the RFQ accelerator 6 4 It is prevented from being sucked into the heavy electrode 6b. This allows RFQ
On the upstream side of the accelerator 6, the electrons remain in the ion beam, and the ion beam can maintain electrical neutrality, so that divergence due to the space charge of the beam itself hardly occurs. As a result, the ion beam enters the RFQ accelerator 6 in a properly focused state.

After that, among the ions accelerated by the RFQ accelerator 6, only the ions having a desired energy are selected by the energy filter 7, and the ion implantation target such as a semiconductor wafer (not shown) set in the end station 8 is set. Is irradiated.

Since the electron suppressor electrode is not provided on the beam exit side of the RFQ accelerator 6, electrons existing in the space on the downstream side of the RFQ accelerator 6 are sucked into the RFQ accelerator 6, but the RFQ accelerator 6 Since the beam emitted from 6 is accelerated to have a high speed, it is hardly affected by the space charge effect.

Here, it will be shown how the envelope of the ion beam (outermost boundary line when viewed as a whole, not as individual beam particles) differs depending on the presence or absence of electrons in the beam. As shown in FIG. 2, if the radius of the beam at a certain position on the beam optical axis z is r ₀ and the radius of the beam on the downstream side of this position is r _m , then r _m / r ₀ = 1 + 0.48k (z / R ₀ ) ² (1) Here, β in the above equation (1) is (the velocity of ions /
The speed of light), k is a constant having the relationship of the following expression (2) (I is the beam current).

K ∝ (I / β ³ ) (1- _fe ) ... (2) _fe = 0: when there are no electrons in the ion beam _fe = 1: when the ion beam is in a completely neutralized state For example, in the case of a B ⁺ beam with a radius r ₀ = 1 cm, a beam current I = 1 mA, and an energy = 30 keV, when there is no neutralization by electrons (when f _e = 0), while traveling in a 1 m non-electric field space. The beam diameter is doubled. In general, when the velocity of the ion beam is slow and relativity is not taken into consideration, the beam diameter expands in proportion to β ^-3 regardless of its mass, so neutralization of the beam is important. Is recognized.

As described above, the RFQ accelerator 6 according to this embodiment accelerates the ion beam incident from the beam entrance by the electric field, and the electron suppressor electrode 9 of negative potential is provided near the beam entrance. This is the configuration provided.

As a result, on the upstream side of the RFQ accelerator 6, electrons remain in the ion beam and the ion beam maintains electrical neutrality, so that divergence due to the space charge of the beam itself can be prevented, and the RFQ accelerator 6 can be prevented. It is possible to avoid a reduction in the amount of incident beam on the.

Further, the ion implantation apparatus according to this embodiment is
The RFQ accelerator 6 having the electron suppressor electrode 9 is provided.

As described above, when the RFQ accelerator, which has been conventionally used for physical experiments, is incorporated into an ion implantation apparatus for industrial use, it is necessary to increase the purity of the ion beam to be accelerated, and an analysis magnet having a large radius of curvature is used. The distance of the beam optic axis used and from the ion source to the entrance of the RFQ accelerator will be longer than that used in normal experiments. Further, since the ion implanter is required to accelerate heavy ions having a large current, it is particularly important to neutralize the ion beam before it is incident on the RFQ accelerator 6, and the ions of the RFQ accelerator 6 of the present embodiment are important. The application to the injection device is very effective.

RF used in conventional physical experiments
In order to incorporate the Q accelerator into the ion implantation apparatus as in this embodiment and develop it for industrial use, it is essential that a high beam current value is required. An ion implantation system to which an RFQ accelerator is applied is extremely effective as a system particularly suitable for ion implantation in the MeV energy region. If the RFQ accelerator 6 of this embodiment is applied to this ion implantation system, the RFQ will be applied to the beam line. The beam current loss due to the provision of the accelerator 6 is minimized.
Beam transmittance is high, a high beam current value can be obtained at the implantation position (target position), and a system suitable for high dose ion implantation can be constructed.

The above-mentioned embodiments are intended to clarify the technical contents of the present invention, and should not be construed in a narrow sense by limiting to such specific examples. Various modifications can be made within the scope of the claims.

[0036]

As described above, the high-frequency charged particle accelerator of the present invention accelerates the charged particle beam incident from the beam entrance by an electric field, and the electron of negative potential is provided in the vicinity of the beam entrance. In this configuration, a suppressor electrode is provided.

Therefore, on the upstream side of the high-frequency charged particle accelerator, electrons can be prevented from being sucked into the accelerator away from the ion beam, so that the ion beam can be prevented from being neutralized before entering the accelerator. The effect that can suppress the divergence of.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, and is a schematic configuration diagram of a high energy ion implantation apparatus to which an RFQ accelerator is applied.

FIG. 2 is an explanatory diagram for explaining an envelope of an ion beam.

FIG. 3 is a schematic configuration diagram of a high energy ion implanter to which a conventional RFQ accelerator is applied.

[Explanation of symbols] 1 ion beam generator 2 ion source 3 analysis magnet 4 focusing lens system 6 RFQ accelerator (high-frequency charged particle accelerator) 9 electron suppressor electrode 10 power supply

Claims (1)

[Claims] 1. A high frequency charged particle accelerator for accelerating a charged particle beam incident from a beam entrance by an electric field, wherein a negative potential electron suppressor electrode is provided in the vicinity of the beam entrance. Type charged particle accelerator.