JPS5916703B2 - microwave ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ion sources, and more particularly to improvements in microwave ion sources suitable for implanting ions into semiconductor wafers.

Microwave ion sources have a long life and are easy to obtain large currents, so
This is suitable as an ion source for ion implanters and is actually used.

FIG. 1 shows a schematic configuration of a conventional microwave ion source for an ion implanter.

In the figure ζ, microwaves with a frequency of 2.45 GHz generated by a microwave generation source (not shown) such as a magnetron pass through a waveguide 2 having ridges 8, 8 inside and reach a discharge box 1. will be introduced in

The discharge box 1 is connected to a waveguide 2 via a disc 3 made of a dielectric material such as ceramic for vacuum sealing.

The discharge box 1 also includes discharge electrodes 5, 5, a discharge chamber formed between the discharge electrodes 5, 5, an inlet for a gas to be ionized, and a space other than the discharge chamber, such as boron nitride, which is filled with heat. Microwaves introduced into the discharge box 1 generate a strong microwave electric field in the discharge chamber formed between the discharge electrodes 5, 5.

Further, a strong magnetic field is applied to the discharge chamber in a direction (axial direction in FIG. 1) perpendicular to the microwave electric field generated between the discharge electrodes 5, 5.

In order to generate this magnetic field, a solenoid coil (not shown) is installed around the outer periphery of the discharge box 1.

To generate plasma in the discharge chamber, open the leak pulp 9 and introduce a sample gas such as phosphine gas (PH3) into the discharge chamber, and the interaction between the microwave electric field and the magnetic field creates a high density inside the discharge chamber. Generate plasma.

The ion beam 22 is extracted from the high-density plasma thus generated through the ion extraction electrode system 6,7°7'ζ.

4' is a disc made of a dielectric material such as boron nitride with slits, so that the microwave electric field is strongest in the ion beam extraction part, and therefore the highest plasma density is achieved in the extraction part.

In the ion extraction electrode system 6, 7.7', +50 KV is applied to the electrode 6.

A voltage of -2 KV is applied to the electrode 1, and a voltage of Ov is applied to the electrode 7'.

Therefore, the discharge box 1 and the waveguide 2, which are connected to the electrode 6, are also at the same potential as the electrode 6 and form the high voltage side, whereas the electrodes 7, 7' have the low voltage side. It is necessary to form.

Now, it is expected that ion implanters will have higher currents and higher voltage extraction voltages in the future. Conventional microwave ion sources have the following drawbacks:

That is, as mentioned above, a zero potential solenoid coil is placed outside and surrounding the discharge box 1 which is to be held at a high potential, and this solenoid coil is approximately It is necessary to generate a magnetic field of 1 kilogauss.

The microwave ion source mentioned above (slit length 4Q1ml,
For ion extraction voltage 50KV), a solenoid coil with an inner diameter of 180mm and an outer diameter of 350+ ot is used.
In order to increase the current of the ion source (this leads to an increase in the slit length and a large discharge chamber is required), it is necessary to increase the inner diameter of the solenoid coil.

Moreover, in this case, the magnetic field strength in the central part, that is, the discharge chamber, must be kept the same, so the outer diameter of the solenoid coil becomes increasingly large, and the capacity of the power supply to excite this solenoid coil is also extremely large. Is required.

Furthermore, in the above-mentioned microwave ion source, as shown in the schematic diagram shown in FIG. A magnetic field with field lines diverging in direction 22 is required.

For this reason, three solenoid coils 17, 18, and 19 are arranged for the discharge region 20f as shown in FIG.

However, the solenoid coils 17 and 18 need to be placed on the high voltage side 23 as described above, and the solenoid coil 19 also needs to be placed across the high voltage side 23 and the low voltage side 24.

However, with this arrangement, +50K
It is difficult to take insulation measures to prevent discharge between the waveguide 2, discharge box 1, electrode 5 that forms the high voltage side (V) and the ground potential (solenoid coils 17, 18, 19), It is even more difficult to measure.

In order to solve this problem, it is possible to make the distance between them narrower, but in that case, among the solenoid coils 17, 18 and 19,
The outer diameter becomes large and the above-mentioned problems occur.

Therefore, an object of the present invention is to provide a small-sized microwave ion source with low power consumption, which solves the above-mentioned problems.

In order to achieve the above object, in the present invention, an electromagnet is provided on the low voltage side of the extraction W system in the microwave ion source described above, and an electromagnet is provided on the waveguide side (this position does not impede the propagation of microwaves). The present invention is characterized in that a high magnetic permeability member is provided in the region to form a magnetic field having the required magnetic field shape and magnetic field strength in the discharge chamber.

Due to the characteristic configuration of the present invention, even if the ion source is made to have a high voltage, the inner and outer diameters of the solenoid coil, which is an electromagnet, will be smaller than the dimensions and shape of the electrode, discharge box, and waveguide that form the high voltage side. Not affected.

As a result, the entire microwave ion source can be downsized, and at the same time, an increase in power consumption can be suppressed.

Furthermore, by arranging the solenoid coil on the low voltage side, insulation from the high voltage section, which was necessary in the conventional configuration, becomes unnecessary, and as a result, insulation becomes very easy.

Further, due to the arrangement of the high magnetic permeability member and the solenoid coil, the shape of the magnetic field formed in the discharge region becomes an ideal mirror shape, and as a result, high-density plasma can be obtained.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 3 shows the basic configuration of the microwave ion source according to the present invention.

The microwave ion source according to the present invention has the same structure as the conventional structure shown in FIG. 1, except for the structure of the magnetic field generating means for forming a magnetic field in the discharge region 20.

Therefore, in FIG. 3, the discharge chamber formed between the discharge electrodes 5, 5 of the discharge box 1 in FIG. 1 is shown as a representative discharge area 20.

As shown in FIG. 3, the microwave ion source according to the present invention has a solenoid coil 25 disposed on the low voltage side 24, and increases the magnetic flux density of the magnetic lines of force 21 generated by the solenoid coil 25 to generate a magnetic field necessary for microwave discharge. In order to form a magnetic field having a specific shape and magnetic field strength in the discharge region 20, a magnetic material 12 with high magnetic permeability, such as pure iron, is arranged on the side where the microwave 26 enters, that is, the waveguide side, with respect to the discharge region 20. This is what I did.

Here, it is desirable that the high magnetic permeability member 12 has a shape and arrangement that does not prevent the microwave 26 from entering.

By adopting such an arrangement, it is possible to realize a microwave ion source having a number of excellent features as described above.

The present invention will be further explained below using specific examples.

Embodiment 1 FIG. 4 shows a cross-sectional structure of an embodiment of a microwave ion source according to the present invention.

The feature of this embodiment is that the ridge 8' is made of a magnetic material such as pure iron, and is provided inside the waveguide 2 to achieve microwave matching between the waveguide and the discharge box.

"Solenoid coil 25 on the low voltage side
This is because we have established the following.

With such a configuration, the waveguide 2, the discharge box,
Even if a weak excitation current is applied to the solenoid coil 25 without changing the extraction electrode system 6, 7, 7', etc., the discharge chamber formed between the discharge electrodes 5.5 has the shape and strength necessary for discharge. Can generate a magnetic field.

Note that 10 is a high voltage insulator. Embodiment 2 FIG. 5 shows a cross-sectional structure of another embodiment of the microwave ion source according to the present invention.

The feature of this embodiment is the discharge box 1'.

The discharge box 1' is an L-shaped rectangular waveguide filled with a dielectric material 4 such as boron nitride, leaving only the discharge area.

The means for generating a suitable magnetic field in the discharge area is comprised of a solenoid coil 25 provided on the low voltage side and a magnetic material 12 such as pure iron provided near the rhombic portion of the discharge box 1'.

It goes without saying that the waveguide in this embodiment also uses the rectangular waveguide 1.

Embodiment 3 FIG. 6 shows a cross-sectional structure of another embodiment of the microwave ion source according to the present invention.

The feature of this embodiment is the discharge box 1.

That is, the discharge box 1 is a rectangular ridge waveguide shaped into an L shape, and a dielectric material 4 such as boron nitride is filled between the ridges of the waveguide, leaving only the discharge region.

This is the discharge box 1' of the second embodiment shown in FIG. 5 with ridges (discharge electrodes) 5, 5 added thereto.

The means for generating an appropriate magnetic field in the discharge region has exactly the same structure as in the second embodiment.

Embodiment 4 FIG. 7 shows a cross-sectional structure of another embodiment of the microwave ion source according to the present invention.

The feature of this embodiment is that a coaxial groove wave tube '2'y is used as a waveguide.
Accordingly, the discharge box was also a coaxial discharge box 1'', and the extraction electrode system was made of porous electrodes 6', γ', and γ''.

The means for generating an appropriate magnetic field in the discharge region are a solenoid coil 25 provided on the low voltage side and a cylindrical magnetic material 12 such as pure iron provided surrounding the coaxial waveguide 1 near the discharge box 1''. ′.

Note that 11 is an antenna.

Embodiment 5 FIG. 8 shows a cross-sectional structure of another embodiment of the microwave ion source according to the present invention.

The feature of this embodiment is that the solenoid coil 25 used in the first embodiment is eliminated and replaced with other excitation means.

The excitation means in place of the solenoid coil 25 is such that the electrode 6 of the ion extraction electrode system 6, 7.7' is an electrode C made of a magnetic material such as pure iron, and the ridges 8' and 8' are made of a similar magnetic material. The electrode 6 is connected with external magnetic paths 13, 13, and a permanent magnet or coil 14 is provided between the external magnetic paths 13, 13.

By using such an excitation mechanism, the discharge electrodes 5, 5
A magnetic field necessary for causing a discharge can be created in the discharge chamber formed between the two.

Of course, the above-described excitation mechanism can be provided in place of the solenoid coil 25 in the second to fourth embodiments as well.

Embodiment 6 FIG. 9 shows a cross-sectional structure of another embodiment of the microwave ion source according to the present invention.

The feature of this embodiment is that the solenoid coil 25 used in the first embodiment is eliminated and replaced with other excitation means.

Furthermore, in this embodiment, the direction in which the magnetic field is applied is not in the axial direction but in the direction perpendicular to the axis between the discharge electrodes 5, 5, and the magnetic field application portion is localized only between the discharge electrodes 5, 5.

That is, in the conventional structure shown in FIG.
5, a magnetic path 13 is provided outside it, and it is excited by a coil 14.

With this configuration, the magnetic field is
15, and the microwave electric field and its magnetic field direction B (!: are perpendicular to each other).

In this case, since the magnetic permeability of the ferrites 15, 15 is high, even if the excitation by the coil 14 is small, the ferrites 15.1
5 hours (a strong magnetic field is generated).

Further, instead of the coil 140, a permanent magnet may be provided in the middle of the magnetic path 13.

Note that the ferrite 15.degree. 15 is not semicircular and may be provided only in a portion corresponding to the width of the discharge chamber formed between the discharge electrodes 5, 5.

Of course, in this case it is necessary to fill the remaining space with a dielectric such as boron nitride.

It goes without saying that the above-described excitation mechanism can also be applied to the rectangular waveguide discharge boxes in Examples 2 and 3.

As described above, the present invention has made it possible to realize a microwave ion source that is smaller in size and consumes less power.

In addition to the above-mentioned pure iron, suitable magnetic materials include fxFe-Ni alloys such as permalloy, ferrite, and silicon steel.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional microwave ion source, Figure 2
The figure is a schematic diagram for explaining the magnetic field generation mechanism of the conventional microwave ion source shown in Figure 1, and Figure 3 is a principle explanatory diagram for explaining the magnetic field generation mechanism of the microwave ion source according to the present invention. , and FIGS. 4 to 9 are schematic configuration diagrams showing embodiments of the microwave ion source according to the present invention. DESCRIPTION OF SYMBOLS 1... Discharge box, 2... Waveguide, 3... Ceramic disc for vacuum sealing, 4... Dielectric, 5... Discharge electrode,
6, 7... Extraction electrode system, 8... Ridge, 9...
Leak valve, 10... Insulator, 12... High magnetic permeability member, 11... Antenna, 14... Coil or permanent magnet, 15... Ferrite, 17, 18, 19,
25...Solenoid coil, 20...Discharge area.

Claims (1)

[Claims] 1. A source for generating microwaves, a waveguide connected to the source for propagating the microwaves, and a waveguide provided at the end of the waveguide and located indoors. a discharge chamber that forms plasma by applying an electric field and a magnetic field generated by the microwave to the introduced discharge gas bottle; an extraction electrode system provided adjacent to the discharge chamber for extracting ions from the plasma; The discharge chamber 1 includes an electromagnet installed on the low voltage side of the extraction electrode system to form the magnetic field, and an electromagnet placed on the waveguide side to adjust the shape of the magnetic field and to prevent the propagation of the microwave. A microwave ion source comprising a high magnetic permeability member provided with an unobstructed region. 2. The microwave ion according to claim 1, wherein the waveguide is a ridge waveguide, and the high magnetic permeability member is provided so as to constitute the ridge. source. 3. Claim 1, wherein the waveguide is a coaxial waveguide, and the high magnetic permeability member is provided to surround the coaxial waveguide. microwave ion source. 4. The microwave ion source according to any one of claims 1 to 3, wherein the high magnetic permeability member is made of pure iron.