JP2879662B2 - Charged particle beam generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam generator for extracting charged particles from plasma using an electrostatic field.

[0002]

2. Description of the Related Art In a conventional charged particle beam generator, a circular screen electrode hole and a circular accelerating electrode hole form a pair, and a voltage is applied between them to generate plasma from a plasma in a plasma generation chamber. A charged particle beamlet is created by extracting and accelerating the charged particles. A plurality of these electrode holes are two-dimensionally present at each electrode, and each pair forms a pair of charged particle beamlets, and forms a charged particle beam by synthesizing the charged particle beamlets. I have.

[0003]

In the above-mentioned conventional charged particle beam generator, the diameter and the interval of the screen electrode holes and the degree of the plasma density, or the distortion of the electrode holes during the production of the electrodes, cause the problem. The cross section of the charged particle beamlet becomes non-circular, and the accelerating electrode hole wears unevenly, and charged particles collide with the accelerating and decelerating electrodes, causing them to be worn away. In addition to shortening the operation time, problems such as contamination of the surroundings by scattered substances generated by wear of the acceleration electrode and the deceleration electrode may occur. In addition, the charged particle beam, which is an aggregate of charged particle beamlets, is also non-circular.If there is a circular gate valve or the like on the path of the charged particle beam, the charged particles collide with this and wear it, causing In addition to shortening the service life, problems such as contamination of the surroundings due to scattered substances generated by wear of the gate valve etc. may occur, and normal operation cannot be performed with a charged particle beam amount in a specific range. was there.

Accordingly, the present invention is to solve the above-mentioned problems in the conventional charged particle generator, and minimizes the degree to which the cross-sectional shape of the charged particle beamlet becomes non-circular, or By shifting the non-circular phase, the charged particle beamlet or charged particle beam
It is an object of the present invention to provide a charged particle generator capable of increasing the circularity of the cross-sectional shape of a system and extending the life and maintenance-free operation time of the charged particle beam generator. However, the circle mentioned here includes a perfect circle, an ellipse, and an ellipse.

[0005]

SUMMARY OF THE INVENTION A cross section of a charged particle beamlet emerging from a single electrode hole is considered to be circular under all conditions, but a screen electrode and an acceleration electrode having a large number of electrode holes. The cross-sectional shape of the charged particle beamlet exiting from is non-circular. In order to investigate the cause, the present inventor used a charged particle beam generation experiment apparatus 20 shown in FIG.
Was manufactured, and thereby the cross-sectional shape of the ion beamlet (that is, the ion current density in the cross section of the ion beamlet) was measured. A typical charged particle generator has hundreds of thousands or more of a large number of electrode holes. In the experimental apparatus, the circular electrode hole 23 of the screen electrode 22 and the circular electrode hole 25 of the accelerating electrode 24 are each located at the center. Circular electrode hole 23
₁ , ₇ and six electrode holes 23 ₂ , 25 ₂ arranged at equal intervals around the opening are only seven in total. Further, downstream of the acceleration electrode placed a conical separator 26, and only the ions emitted from the center of the electrode holes 23 _1, 25 ₁ to pass to the downstream side.

In this charged particle beam generation experiment apparatus, ions generated in the cylindrical discharge chamber 21 are extracted from the discharge chamber by an electric field between the two electrodes, and only ions emitted from the central electrode hole are separated and passed. And 2 from the accelerating electrode
As a result of measuring the cross-sectional shape of the ion beamlet on a plane of 31 cm × 31 cm separated by 5 cm, an ion current density distribution as shown in FIG. 8 was obtained. The isoionic current density line ranges from 5 × 0.0001 A / m ² to 1 × 0.01 A / m ^2.
m ² are drawn at 5 × 0.0001 A / m ² intervals, and the total beamlet current is 106 μA. As is clear from this figure, in the ion beamlet immediately after exiting from the electrode hole, a phenomenon is observed in which the contour line of the ion current density protrudes remarkably outward at approximately every 60 °.

When the protruding portion is compared with the position of the electrode hole of the experimental apparatus, the portion where the contour lines protrude outward has no adjacent electrode hole, and the contour line is depressed in the portion having the electrode holes. It has been found. One of the causes of such a phenomenon is considered to be "territory" of each electrode hole, that is, each electrode hole affects another electrode hole within a certain range. The ions that have reached the vicinity of the screen electrode surface are eventually extracted from any of the electrode holes, or collide with the screen electrode itself to be neutralized. Now, with a constant amount of ion generation,
Or considering that the extraction voltage is gradually increased,
The territory of each electrode hole was initially circular, but as it became larger, it came into contact with the territory of the adjacent electrode hole, and eventually became a regular hexagon. It is considered that the result of this shape being emphasized through the drawer was the shape shown in FIG.

As a result of further research based on the above findings, the present inventor has found that the circularity of the charged particle beamlet is reduced by making the circular electrode hole non-circular in consideration of the “territory” of the electrode hole. Have been found to be able to increase the circularity of the charged particle beam by shifting the phase of the non-circular beamlets, and have reached the present invention.

That is, the charged particle beam generating apparatus of the present invention is characterized in that the shape of the electrode hole of the screen electrode is made non-circular to increase the circularity of the sectional shape of the charged particle beamlet. This problem has been solved by adopting means. Further, as another solution, it is possible to increase the circularity of the cross-sectional shape of the charged particle beamlet by making the shape of the electrode hole of the acceleration electrode non-circular, thereby solving the above problem. it can. further,
By making both the electrode hole of the screen electrode and the electrode hole of the acceleration electrode non-circular, it is possible to more effectively increase the circularity of the cross-sectional shape of the charged particle beamlet. The degree of making the shape of each of the electrode holes non-circular is preferably adjusted according to the degree of non-circularity of the cross-sectional shape of the original charged particle beamlet.

The non-circularity of the electrode hole is such that, in the screen electrode, the diameter becomes maximum at the closest point to the adjacent electrode hole,
It is effective and desirable that the diameter be minimum at the midpoint between the points of closest approach. In the accelerating electrode, it is effective and desirable that the diameter be minimum at the point of closest approach to the adjacent electrode hole and maximized at the midpoint between the points of closest approach.

Further, the charged particle generator according to the present invention increases the circularity of the cross-sectional shape of the charged particle beam by combining two or more two-dimensional arrangements of the electrode hole of the screen electrode and the electrode hole of the acceleration electrode. This solves the non-circularization of the charged particle beam.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a charged particle beam generator according to the present invention will be described with reference to FIGS. FIG. 1 schematically shows a charged particle beam generator according to the present embodiment, in which a screen electrode 2 is attached to a plasma generation chamber 1, and an acceleration electrode 3 is provided via a spacer 5 so as to be electrically insulated therefrom. Is attached. At this time, the deviation of the electrode hole 6 of the screen electrode 2 and the electrode hole 7 of the accelerating electrode 3 to be paired with each other is prevented from being excessively large. Further, the deceleration electrode 4 is attached via the spacer 5 in a similar manner.

In this embodiment, as shown in FIG. 2, the shape of the electrode hole 6 of the screen electrode is a rounded regular hexagon, and the position of the vertex a of each electrode hole is the closest to the adjacent electrode hole 6. It is arranged to be the approaching point. Therefore, in this case, each electrode hole has a maximum diameter at the closest point and a minimum diameter at a middle point between the closest points. On the other hand, as shown in FIG. 3, the shape of the electrode hole 7 of the accelerating electrode 3 is a rounded regular hexagon, and the position on each side b of the electrode hole is the closest point to the adjacent electrode hole 7. Are arranged as follows. Therefore, the diameter of the electrode hole 7 of the accelerating electrode 3 is minimum at the point of closest approach to the adjacent electrode hole, and is maximum at the midpoint (ie, the vertex) between the points of closest approach. The shape of the electrode hole 8 of the deceleration electrode is circular because it hardly acts to increase the circularity of the charged particle beamlet.

The charged particle beam generator of this embodiment is configured as described above, and the technical meaning of making the electrode hole shape of the screen electrode non-circular is to make the territory of the electrode hole close to a circle, By reducing the hole diameter in the direction where there is no electrode hole in advance, the territory can be kept close to a circle up to a higher voltage. Therefore, the charged particle beamlet can be made closer to a circular shape by forming the electrode hole of the screen electrode into a regular hexagon with a rounded corner and the vertex a being the closest point to the adjacent electrode hole 6. In this case, if the extraction voltage is low, the territory may be distorted, but it is most advantageous to select an optimal shape according to the required range of the extraction capability.

On the other hand, considering the electric field formed by the accelerating electrode, the electrode hole 7 of the accelerating electrode has a slightly stronger electric field in a portion having a smaller hole diameter, and has a higher drawing ability. Therefore, if the diameter of the hole is increased corresponding to the portion where the contour lines protrude in the cross-sectional shape of the ion beamlet in FIG. 6, it is effective to suppress the protrusion. According to this principle, as in the present embodiment, the electrode hole 7 of the accelerating electrode is formed into a regular hexagon with a chamfered shape, and the position of the side b is set to the adjacent electrode hole 7.
By making the point closest to the above, the charged particle beamlet can be effectively made close to a circle.

As described above, the charged particle beam generating apparatus of the present invention has a different phase from the effect of making the cross-sectional shape of the charged particle beamlet originally possessed by the apparatus itself non-circular. The effect of non-circularization is multiplied and canceled out,
The charged particle beamlets serve to increase the circularity of the cross-sectional shape. As the circularity of the charged particle beam rate increases, the diameter of the cross section becomes the smallest circle,
The degree to which charged particles collide with the accelerating electrode and the decelerating electrode serving as the path of the charged particle beamlet and are worn out is reduced. Therefore, the degree of contamination of the surroundings by the scattering of the electrode material generated due to the wear of the electrodes is reduced. Furthermore, the degree of wear and contamination is reduced, resulting in charged particle beads.
This has the effect of extending the life of the system and the maintenance-free operation period.

FIG. 4 shows an embodiment of the charged particle beam generator of the present invention in which the circularity of the cross-sectional shape of the charged particle beam is increased, and FIG. 4 shows the arrangement of the electrode holes of the screen electrode. The electrode holes of the electrodes have the same arrangement.

In this embodiment, the screen electrode 9
The electrode holes 13 are arranged so that the arrangement directions are different between the central part 10 and the peripheral part 12 of the central part 10. The electrode holes in the central part 10 are arranged in a hexagonal close-packed type in the horizontal direction in FIG.
One electrode group is arranged in a hexagonal close-packed type in the vertical direction. As described above, by combining two or more kinds of the two-dimensional arrangement of the electrode holes of the screen electrode and the acceleration electrode, the non-circularization due to the phase shift of the non-circularization of the cross-sectional shape of the charged particle beamlets is canceled out by the cancellation of the non-circularization. Work to increase the degree.

Therefore, according to the present invention, as shown in FIG. 4, the circularity of the charged particle beam can be improved even when the shape of each electrode hole is the same as the conventional one.
However, by combining the shape of the individual electrode holes with the shape shown in, for example, FIG. 2 or FIG. 3, it is more effective in combination with the improvement of the circularity of the cross-sectional shape of each charged particle beamlet. . Further, the two-dimensional arrangement of the electrode holes is not limited to the arrangement shown in FIG. 4, but may be a combination of a simple vertical / horizontal arrangement type and a hexagonal close-packed type, for example.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various design changes can be made within the scope of the technical idea. For example, although the embodiment shown in FIG. 1 shows an example of a charged particle beam generator having a three-electrode structure, the number of electrodes is not limited to three. 2 and 3 show the hexagonal close-packed type hole arrangement method, but the present invention is not limited to the hexagonal close-packed type hole arrangement method. An optimal arrangement may be adopted according to conditions such as capacity and use. Further, in the embodiment of FIG. 1, each electrode has a planar shape, but is not limited to a planar shape.

Further, the charged particle beam generator of the present invention comprises:
The supply of charged particle beams such as an ion beam and an electron beam is not limited to the ultimate target, and a supply source of charged particles converted into neutral particles in a neutral particle beam generator, Alternatively, the present invention may be applied to a supply source of charged particles which collide with a target of a charged particle deposition apparatus, or an ion engine utilizing a reaction force of a charged particle beam.

[0022]

EXAMPLE In order to confirm the effect when the shape of the electrode hole of the screen electrode was made regular hexagon, in the charged particle beam generation experiment apparatus shown in FIG.
Instead of having a regular hexagonal electrode hole shape shown in
The sectional shape of the ion beamlet was measured under the same conditions as described in the sixth column. As a result, an ion current density distribution as shown in FIG. 7 was obtained.

FIG. 8 shows a case of a circular electrode hole shape (comparative example), and FIG. 7 shows a case of a regular hexagonal electrode hole shape (example).
In the case of the embodiment shown in FIG.
It can be seen that the sharp corners in the comparative example are rounded and the circularity is increased. In order to quantitatively show this, the following measures such as “distortion rate” and “divergence angle” are introduced and expressed.

The “distortion rate” is obtained by calculating the area S _{0 of} a figure surrounded by constant current density lines as shown in FIG.
A circle having an area S ₀ is superimposed on the original figure so that the center of the circle overlaps the peak of the current density as shown in FIG. 3B, and the area of a portion outside the circle shown by oblique lines in FIG. S ₁ is obtained and represents the ratio S ₁ / S ₀ between the two, and represents the degree of distortion with respect to a circle. Therefore, the distortion rate is 0 in the case of a perfect circle, and the distortion rate increases as the shape becomes non-circular.
Further, the divergence angle is expected as an effect of reducing the distortion rate, and of the total ion beamlet current,
It is a half vertex angle of a cone containing 95%, and a smaller divergence angle indicates a higher circularity.

In the above experiment, the distortion rate with respect to the ion beamlet current and the divergence angle with respect to the ion beamlet current were measured when the electrode hole was hexagonal (Example) and circular (Comparative Example). The results are shown in FIGS. From these graphs, it can be understood that the distortion rate and the divergence angle of the example are smaller than those of the comparative example, and that the example clearly has higher circularity and better convergence, confirming the effect of the present invention. Was.

FIGS. 7 and 8 show the ion current density lines of the example and the comparative example in which the ion beamlet current was 106 μA in this experiment. In this case, the distortion rate was 8.75% in the example. Example 10.85%, the divergence angle is 20.2 ° in the example and 25.0 ° in the comparative example, and the distortion rate and the divergence angle in the example are clearly smaller than those in the comparative example. Has become. In addition, as the isocurrent density line used for obtaining the distortion rate of the experimental result, a line having a peak current density of 2.5% was selected.

[0027]

As apparent from the above description, the present invention has the following effects. By making the electrode hole non-circular, the circularity of the cross section of the charged particle beamlet is increased and the diameter is likely to be minimized, and the charged particles are charged to the accelerating electrode and decelerating electrode serving as the path of the charged particle beamlet. Impact and wear is reduced.

As a result, the degree of contamination of the surroundings due to the scattering of the electrode material generated due to wear of the electrodes is reduced,
Furthermore, the life of the charged particle beam generator and the maintenance-free operation period can be extended by reducing the degree of electrode wear and contamination.

Further, by combining two or more kinds of two-dimensional arrangement of the electrode holes, the circularity of the charged particle beam can be increased and the diameter of the cross section can be minimized. In the case where there is a circular gate valve or the like, it is possible to reduce the degree to which charged particles collide and are worn.

As a result, the degree of contamination of the surroundings due to scattering of substances generated due to wear of the gate valve and the like is reduced,
Further reduction in wear and contamination,
The service life and maintenance-free operation time of the valve can be extended.

Also, since the charged particle beam can be concentrated within the circle having the minimum diameter, the amount of gas and the like which are the source of the charged particles for obtaining the required amount of charged particle beam and the amount of electric power can be reduced. Can be done. Further, the required capacity of the vacuum exhaust device and the like required to operate the charged particle beam device is minimized, and if this is kept constant, the pressure of the surrounding environment can be minimized.

Further, since the density distribution of the charged particle beam is a function only of the distance from the center and it is not necessary to consider the change in the circumferential density, it is possible to irradiate a fixed amount of the charged particle beam. It will be easier. Further, when the apparatus of the present invention is used in an ion engine, the divergence angle is minimized, and thus there is an effect that the degree of freedom in mounting is increased.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a charged particle beam generator according to an embodiment of the present invention.

FIG. 2 is a schematic view showing an embodiment of a shape and an arrangement of an electrode hole of a screen electrode.

FIG. 3 is a schematic diagram showing an embodiment of the shape and arrangement of the electrode holes of the acceleration electrode holes.

FIG. 4 is a cross-sectional view showing an embodiment of the arrangement of the electrode holes of the screen electrode.

FIG. 5 is a partially cutaway perspective view of the charged particle beam generation experiment apparatus.

FIG. 6 is a schematic diagram showing the shape and arrangement of electrode holes in an example.

FIG. 7 is a diagram illustrating an ion current density in an example.

FIG. 8 is a diagram illustrating an ion current density in a comparative example.

FIG. 9 is a graph showing a relationship between an ion beamlet current and a distortion rate with respect to an electrode hole shape.

FIG. 10 is a graph showing a relationship between an ion beamlet current and a divergence angle with respect to an electrode hole shape.

FIGS. 11A to 11C are explanatory diagrams of distortion rates.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma generation chamber 2, 9 Screen electrode 3 Acceleration electrode 4 Deceleration electrode 5 Spacer 6-8, 13 Electrode hole 10 Central part 11 Peripheral part 20 Charged particle beam generation experimental apparatus 21 Discharge chamber 22 Screen electrode 24 Acceleration electrode 23, 25 Electrode hole 26 Separator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G21K 1/00-5/10 H01J 27/00-27/26 H01J 37/08

Claims (5)

(57) [Claims] 1. A charged particle beam generator, wherein a shape of an electrode hole of a screen electrode is made non-circular to increase the circularity of a sectional shape of a charged particle beamlet. 2. A charged particle beam generator, wherein the shape of the electrode hole of the screen electrode and the shape of the electrode hole of the acceleration electrode are made non-circular to increase the circularity of the sectional shape of the charged particle beamlet. Electrode hole shape wherein the screen electrode, the diameter closest point of approach between the adjacent electrode holes up, according to claim 1 or 2, wherein the diameter at the midpoint between the points of closest approach is at the minimum Charged particle beam generator. Wherein the electrode hole shape of the accelerating electrode, the diameter closest point of approach between the adjacent electrode holes minimum, according to claim 2, wherein the diameter at the midpoint between the points of closest approach is the largest charge Particle beam generator. 5. A charged particle beam generation characterized by increasing the circularity of the cross section of a charged particle beam by combining two or more kinds of two-dimensional arrangement of an electrode hole of a screen electrode and an electrode hole of an acceleration electrode. apparatus.