JPS598949B2 - ion source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention enables a conventional ion source equipped with a porous extraction electrode system to obtain a high-current, high-purity ion beam by coupling a magnetic quadrupole lens to the conventional ion source. This changes the beam shape.

FIG. 1 shows an ion source device according to the prior art.

A in the figure is a schematic diagram of a method for extracting ions from plasma.

That is, ions in the plasma 2 existing in the plasma chamber 1 are transferred to an extraction electrode system 3 consisting of a porous extraction electrode 5 and a multi-slit extraction electrode 6, respectively shown in B or C in the figure.
The ion beam is extracted as an ion beam 4.

Until now, using this method, a circular beam with a diameter of 40 mm has been continuously obtained with a current of 200 to 600 mA.

7 is a power source for extracting ions.

Now, when plasma is generated using a compound gas or the like as a sample gas, the ion beam will contain ions of various types of elements.

To obtain an ion beam of a specific element, the ion beam must be mass-separated.

In the case of large current ion beams, a mass separator that uses only a magnetic field without using an electrostatic field is used to enable mass separation.

However, the mass resolution of the separator deteriorates in inverse proportion to the increase in the width of the incident ion beam.

Therefore, even if a circular beam with a diameter of 40 m as described above is placed in a magnetic field mass separator, mass separation cannot actually be performed.

From the practical point of view of coupling with a separator with a magnetic field radius of approximately 70 cm (for example, when considering an arsenic ion beam, it is sufficient to separate A35), the width of the incident ion beam must be approximately 5 or less. It is.

Therefore, when it is desired to obtain a high purity ion beam, an ion beam with a narrow width is obtained as shown in FIG.

FIG. 2 is a diagram illustrating an ion source device according to the prior art in which connection with a mass separator is considered.

A in FIG. 2 indicates an extraction electrode system 3' provided in the plasma chamber 1.
The shape is made into one small slit.

Further, in FIG. 1B, an ion beam with a narrow width is obtained by inserting a slit 8 through which only a part of the thick beam extracted from the porous or multi-slit extraction electrode system 3 passes.

It is obvious that in the conventional techniques A and B, the amount of ion beam current that can be provided by the ion source is small.

Furthermore, in these conventional techniques, the ion beam current amount after mass separation was on the order of several mA.

In contrast, the present invention makes it possible to perform mass separation without impairing the current amount of a large current ion beam extracted by a porous type or multi-slit type extraction electrode system.
The present invention provides an ion source device capable of producing a high-purity, large-current ion beam of mA or more.

This will be explained below. FIG. 3 is a diagram explaining the principle of the present invention.

In the figure, A shows one magnetic quadrupole lens after the extraction electrode system 3.
A magnetic quadrupole lens system 9 consisting of at least four magnetic quadrupole lenses is provided to explain changes in beam shape.

By suitably adjusting the combination of magnetic quadrupole lenses and the strength of their magnetic fields, a high-current ion beam 4' with a circular cross section can be transformed into an ion beam with a narrow rectangular cross section at a certain position, as shown in FIG. 3A. It is transformed into beam 4''.

Therefore, if this ion beam 4'' having a rectangular cross section is introduced into a mass separator, a high purity, large current ion beam can be obtained after separation.

FIG. 3B is a diagram illustrating the combination with the mass separator 16.

That is, in FIG. 3B, a magnetic quadrupole lens system 9 is placed between the extraction electrode system 3 and the mass separator 16.

When the object point position of the mass separator 16 is P, this P
Adjust 9 so that the width of the ion beam shape becomes the narrowest on the point.

As a result, the large current ion beam 4'' can be mass separated under conditions where the mass separator 160 has the maximum resolution.

Note that with a quadrupole lens, the horizontal and vertical focusing positions can be changed independently, so the focusing position in the y direction (see A) can be changed by mass separator 1.
6, the so-called image point position Q, and the object point P in the X direction.
If the beam is focused at the image point Q, the shape of the high-purity, large-current ion beam 4'' obtained at the image point Q will also be a spot shape.

FIG. 3C is a diagram illustrating another usage example of the quadrupole lens system 9.

That is, at B, the ion beam 4'' was once focused on the object point P.

In C, the ion beam 4" coming out from 9 degrees is the quadrupole lens 9.
It is made to look like a virtual image.

However, in this case, the position of the virtual image coincides with the object point position P of the mass separator 16.

In the case of C, the position of the quadrupole lens 9 can be between the point P and the mass separator 160, and therefore the distance between the extraction electrode systems 3 and 16 becomes short.

Therefore, it is possible to provide an ion source device that is smaller than that shown in FIG. 3B.

FIG. 4 is a diagram showing the principle of a magnetic quadrupole lens.

In the figure, a quadrupole lens is one in which the excitation current values flowing through the four solenoid coils 12 are all the same, and the resulting magnetic poles 10 have the same polarity in the diagonal direction.

Reference numeral 11 denotes a magnetic path, which is usually made of a magnetic material such as soft iron.

In this case, within the inscribed circle 13, the magnetic fields on the X and Y axes increase in proportion to the distance from the central axis.

Ions running from the front of the paper toward the back of the paper are focused by the Lorentzker in the X-axis direction toward the central axis, while in the Y-axis direction they diverge.

If all polarities are reversed, there will be divergence on the X axis and convergence on the Y axis.

If two or more of these magnetic quadrupole lenses are installed vertically at an appropriate distance, it becomes possible to simultaneously converge the X-axis and Y-axis directions.

Further, the image magnification in the X and Y directions of the image formation can be arbitrarily changed by adjusting the solenoid coil current that excites each magnetic quadrupole lens.

Therefore, it is clear that it is possible in principle to transform an ion beam with a circular cross section into an ion beam with a rectangular cross section using these magnetic quadrupole lens systems.

Examples actually carried out will be described below.

FIG. 5 is a diagram illustrating an embodiment based on the principle of the present invention.

Here, it was confirmed whether the circular cross-section ion beam 4' from the porous extraction electrode could be shaped into a slit by the quadrupole lens.

To confirm this, it is sufficient to provide the fluorescent film 15 and observe the cross-sectional shape of the ion beam.

As the plasma, we used argon plasma generated by microwave discharge of argon gas in a magnetic field.

It goes without saying that the plasma source may be a plasma source using other generation methods.

Next, as the porous type extraction electrode system 3, one in which a total of 61 small holes with a diameter of 3 mm were bored in a circle with a diameter of 41 mm was used.

The material is copper and the thickness is 1rrmt.

The electrode gap was 2 m each, and voltages were applied to the extraction electrodes in FIG. 5 from the left to 5 KV, -1 KV, and ground, respectively.

The magnetic quadrupole lens is made by arranging three of the lenses shown in FIG.

At this time, in the X-axis direction, the ions receive a force of divergence, convergence, and divergence as they pass through the lens, and in the Y-axis, they undergo convergence, divergence, and convergence.

According to this experiment, as a result of appropriately adjusting the excitation current of each quadrupole lens, it was possible to transform the argon ion beam into a rectangular cross section with a width of 10 mm and a length of 20 mm.

In this case, the experiment was mainly carried out by applying the same excitation current to the lenses 14, 14'', but the magnetic quadrupole lenses 14, 14', 1
By excitation of 4" completely independently, the width of the beam can be reduced to within 5 gates.

In other words, reducing the current value11 82 The horizontal direction is reduced to less than 1, and the vertical direction is reduced to less than 1. I was able to reduce it.

Next, another embodiment based on the present invention will be described.

When using a two-stage quadrupole lens, an argon ion beam extracted from a single slit with a width of 3 mm and a length of 30 Trtm can be made into a rectangular cross section with three horizontal cylinders and a length of 10 mm without loss of ion beam current. We were able to.

In other words, while maintaining the width of the beam, We were able to reduce the size vertically.

This indicates that the ion beam shape can be maintained and the ion beam can be transported to an arbitrary distance with a small decrease in the amount of ion beam current.

Of the various embodiments, only the porous type extraction electrode system and the case with one slit have been described here, but the extraction electrode system with multiple slits and any other shape can also be described.
The effects of the present invention were obtained by using a magnetic quadrupole lens.

Here, an electromagnet was used as the magnetic quadrupole lens, but
The effects of the present invention can also be obtained by using a magnetic quadrupole lens made of permanent magnets.

In this case, image formation and image magnification can be adjusted by changing the distance between each quadrupole lens.

Next, here, a semicircular cross-sectional shape was used as the magnetic pole 10 of the quadrupole lens.

However, the cross-sectional shape is... It may be hyperbolic or polygonal.

In short, any structure may be used as long as it has a quadrupole structure in which the magnetic field strength increases in proportion to the increase in distance from the central axis, or approximately in direct proportion to the magnetic field strength.

If a mass separator is coupled to the ion source device according to the present invention as described above, it becomes possible to provide a high-purity, large-current ion beam, and the effect is remarkable in practical use.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining an ion source device according to the prior art, FIG. 2 is a diagram explaining an ion source device according to the prior art considering coupling with a mass separator, and FIG. 3 is a diagram explaining the principle of the present invention. Figure 4 is a diagram explaining the magnetic quadrupole lens, Figure 5 is a diagram explaining the magnetic quadrupole lens.
The figure is a diagram illustrating an embodiment carried out based on the principle of the present invention. In the figure, 1... plasma chamber, 2... plasma, 3...
・Ion extraction electrode system, 4, 4/, 4//,
4//jin: ion beam, 5: porous extraction electrode, 6: multi-slit extraction electrode, 7: ion extraction power source, 8: slit, 9: magnetic quadruple Polar lens system, 10... Magnetic pole, 11... Magnetic path, 12...
Lenoid coil, 13...inscribed circle, 14.14',
14″... Quadrupole lens, 15... Fluorescent film, 16.
...Mass separator.

Claims (1)

[Claims] 1. A plasma chamber that converts gas into plasma. In order to extract an ion beam from the plasma generated in this plasma chamber,
In an ion source device consisting of a porous extraction electrode system with multiple small holes or a multi-slit extraction electrode system with multiple slits, by providing one or more magnetic quadrupole lenses after the extraction electrode system. The present invention is characterized in that the cross-sectional shape of the large-diameter, high-current ion beam extracted from the above-mentioned ion source device is changed, thereby making it possible to perform mass separation of the high-current ion beam when using a mass separator. Ion source device.