JPS60243952A - Microwave ion source - Google Patents

Abstract

PURPOSE:To obtain a microwave ion source which has a simple structure and can lead out a large current ion beam at a low cost by using a wave guide as a microwave three-dimensional circuit surrounding an electric discharge chamber and providing a slit-like outlet hole. CONSTITUTION:Microwaves produced in a microwave generator 1 is introduced into a discharge electrode 4 through wave guides 2a and 2b and a microwave introduction flange 3 to produce a microwave electric field in an electric discharge chamber 5. A dielectric insulating material 5a is packed into the discharge electrode 4 except its electric discharge chamber 5. Around the discharge chamber 5, a magnetic field perpendicular to the microwave electric field is applied by means of a magnetic field generator 8. Next, a gas to be ionized is introduced through a gas introduction tube 6 into the discharge chamber 5 to produce plasma by the interaction between a microwave electric field and a magnetic field. After that, ion beams 21 are led out from the plasma by means of ion-beam-leading-out electrode systems 7a, 7b and 7c. An ion beam emission slit 7 is narrowest at its center and becomes wider toward the ends.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ion source capable of extracting a milliampere (mA) ion beam, and particularly to a microwave ion source suitable for a large current ion implantation device.

[Background of the invention]

A conventional microwave ion source for an ion implantation device, as described in Japanese Patent Application Laid-open No. 132.754/1983, uses a three-dimensional microwave circuit to form a discharge chamber, and a microwave ion source is used in a discharge chamber. It used a ridge type that could generate a strong and relatively uniform electric field. However, the ridge type microwave circuit has a complicated shape, and there are also restrictions on the shape, such as the need to install a part of the taper in order to reduce impedance mismatching as a microwave circuit. It had become expensive.

[Purpose of the invention]

An object of the present invention is to provide an inexpensive microwave ion source for an ion implanter without degrading the performance of the microwave ion source.

[Summary of the invention]

The easiest way to make the three-dimensional microwave circuit for forming the discharge chamber simple and inexpensive is to replace the conventional ridge waveguide with a rectangular waveguide. However, in the rectangular waveguide, compared to the ridge type.

Since the microwave electric field strength in the discharge chamber is low and its uniformity is poor, if left as is, there is a possibility that the current amount and emittance of the extracted ion beam will drop. However, we confirmed that the ion current could be improved by increasing the length of the ion beam exit loss slit. (When using a ridge-type waveguide, the maximum length of the ion beam exit loss slit can only be the same as the length of the ridge electrode, so the length of the ion beam exit loss slit cannot be simply increased.) It was confirmed that the emitter resistance could be improved by matching the shape of the extraction electrode system and the width of the ion beam output loss slit to the density distribution of the plasma generated in the discharge chamber. It turns out that it can be used for purposes.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

1, 2, and 3 show the structure of a microwave ion source according to the present invention, which includes a microwave generator 1. Waveguide 2. Microwave introduction flange 3
．． Discharge electrode 4. Discharge chamber5. Gas introduction pipe6. Ion beam extraction electrode system 7a.

7b, 7c, and a magnetic field generator 8. In this embodiment, the waveguide 2. Both the microwave introduction flange 3 and the discharge electrode 4 are rectangular. The discharge chamber 5 is
The microwave circuit is installed at the terminal end, that is, at the tip of the discharge electrode 4 (see FIG. 2). In the discharge electrode 4, a portion other than the discharge chamber 5 is filled with a dielectric insulator 5a (boron nitride sintered body in this embodiment) to prevent discharge from occurring in the portion other than the discharge chamber 5.

Waveguide 2. Microwave introduction flange 3. The dimensions of the discharge electrode 4 are as follows.

■Cross-sectional shape (aXb) =...96X27 (mm) ■Characteristic impedance (Rcl)...137.6 (Ω
)Micro introduction flange 3 ■Material: Polyimide resin, Er"3.4 ■Cross-sectional shape (aXb)..."96X27 (mm) ■Thickness (t
)--18 (Tnm) ■Characteristic impedance (R
c2)...82.5 (Ω) Late demon! Tamado ■ Dielectric filler material: boron nitride, 6. =4■4
■Cross section (a x b) - 75X 18 (mm) ■Characteristic impedance (R, c3)...49.5 (Ω) Here, the characteristic impedance of each part can be calculated using the following formula.

Er: relative dielectric constant of the waveguide internal filling λg: wavelength inside the waveguide λ: free space wavelength in the internal filling a, b: waveguide dimensions In this example, the microwave is introduced at the microwave introduction flange 3. wave tube 2
and impedance matching of the discharge electrode 4 (Rc 2 = J Rc 1500i1゜t
=λg/4Xn, n is an odd number (in this example, n=1). In this way, a three-dimensional microwave circuit with less reflection can be constructed, and the microwaves generated by the microwave generator 1 can be efficiently sent into the discharge chamber 5. It is possible to pass microwaves even if the parts are connected appropriately without impedance matching, but in this case, there will be a lot of reflection at each connection, so the power input to the microwave generator will be reduced. It's a waste to need so much.

The cross-sectional shape of the ion beam extraction loss slit 7 (included in the ion beam extraction electrode 7a in FIG. 1) is narrowest at the center and widens toward both ends (see FIG. 3). ). This is done in accordance with the density distribution of the plasma generated in the discharge chamber 5 (the slit width is narrow in the central part where the density is high, and the slit width is widened in the low end parts), and the ion beam is extracted from each part of the ion beam output loss slit 7. The amount of ion current applied is made to be the same. The plasma density distribution occurs because the strength of the microwave electric field generated in the discharge chamber 5 differs in each part.

Next, the operation of the microwave ion source will be explained. In FIG. 1, microwaves generated by a microwave generator 1 are introduced into a discharge electrode 4 via waveguides 2a, 2b and a microwave introduction flange 3, and create a microwave electric field in a discharge chamber 5. generate. Furthermore, near the discharge chamber, a magnetic field generator 8 (
In this embodiment, a magnetic field is applied by a solenoid coil in a direction perpendicular to the microwave electric field. In this state, the gas to be ionized is introduced into the discharge chamber 5 through the gas introduction tube 6,
Plasma is generated by the interaction of a microwave electric field and a magnetic field, and the ion beam extraction electrode type 7a.

7b and 7c, the ion beam 21 is extracted from the plasma.
is brought out.

According to this embodiment, a rectangular waveguide with a simple structure can be used as the discharge electrode 4 for forming the discharge chamber 5, and its length in the axial direction can be freely adjusted without worrying about impedance matching. Therefore, it is possible to create an inexpensive microwave ion source as a whole. Furthermore, since the dimensions of the discharge chamber 5 can be increased to the limit of one dimension of the discharge electrode 4, it is possible to draw out a larger current than before.

In this example, a rectangular waveguide was used as the discharge electrode d, but a cylindrical waveguide or a coaxial waveguide could be used instead of the rectangular waveguide without increasing the overall size of the ion source. It is clear that the same performance can be achieved with a simpler structure. Furthermore, although a single slit was used as the ion beam exit loss slit 7, it is clear that the same effect can be obtained even if multiple slits are used, or if small holes are arranged in the slit direction (multi-aperture). .

Further, FIG. 4 shows another embodiment. In this embodiment, the discharge chamber 5
The density distribution of the plasma generated inside is corrected by changing the shape of the ion beam extraction electrode 7b (in the previous embodiment, this was done by changing the width of the ion beam extraction loss slit 7). In other words, in this embodiment, the slit width of the ion beam extraction loss slit 7 is constant, and instead, the shape of the ion beam extraction electrode 7b is such that the central part is the highest in the shape of a mountain, and the height of the mountain decreases toward the edges. It is. As a result, the ion beam extraction electric field strength at the ion beam output loss slit portion is reduced to the discharge chamber 5.
Since it can be adjusted to the distribution of plasma density within
As a result, a parallel ion beam 21 can be extracted.

As a countermeasure against the density distribution of plasma generated in the discharge chamber 5, two embodiments have been shown in which the width of the ion beam exit loss slit 7 is changed and the shape of the ion beam extraction electrode 7b is changed. It is clear that similar effects can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to provide a microwave ion source capable of extracting a large current ion beam with a simpler structure than the conventional one and at a lower cost than the conventional one.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an embodiment based on the present invention, and Figure 2 is a diagram showing an example of the invention.
FIG. 1 is a sectional view taken along line AA in FIG. 1, FIG. 4 is a sectional view taken along line BB in FIG. 1, and FIG. 4 is a diagram showing another embodiment based on the present invention. l...Microwave generator, 2a, 2b... Waveguide,
3...Microwave introduction flange, 4...Discharge electrode,
5...Discharge chamber, 5a...Dielectric filling for forming a discharge chamber in the discharge electrode, 6...Gas introduction tube, 7...
・Ion beam output loss slip 1~. 7a+7bt7c...
・Ion beam extraction electrode system, 8...magnetic field generator,
11...1st (2) Mouth 4th figure

Claims (1)

[Claims] (1) In a microwave ion source that uses microwave discharge in a magnetic field to create a plasma of an introduced gas and extracts an ion beam from this plasma, the portion surrounding the discharge chamber for forming the plasma. A microwave ion source characterized by using a waveguide as a three-dimensional microwave circuit and having a slit-shaped exit hole as a hole for ejecting ions from plasma. 2. The microwave ion source according to claim 1, characterized in that a rectangular waveguide is used as the microwave three-dimensional circuit surrounding the discharge chamber. 3. The microwave ion source according to claim 1, wherein a cylindrical waveguide is used as the microwave three-dimensional circuit surrounding the discharge chamber. 4. The microwave ion source according to claim 1, wherein a coaxial waveguide is used as the microwave three-dimensional circuit surrounding the discharge chamber. 5. Any one of claims 1 to 4, characterized in that the slit-shaped exit hole has a slit whose width is changed in accordance with the density distribution of plasma generated within the discharge chamber. Microwave ion source as described in Crab. 6. Claims 1 to 6 include an ion beam extraction electrode system whose shape is changed in accordance with the density distribution of the plasma. The microwave ion source according to any of paragraph 4.