JPH02216734A - Microwave ion source - Google Patents

Abstract

PURPOSE:To make it possible to operate in a high vacuum condition by forming a discharge chamber into two chambers of a high pressure and a low pressure linking by a specific size of holes. CONSTITUTION:A discharge chamber is formed of auxiliary discharge chambers 2a and a main discharge chamber 2b, and at the borders of both chambers, holes 9 to allow the passage of plasma but to restrict the passage of a fresh gas not ionized are provided. The auxiliary discharge chambers are arranged symmetric to the ion beam injection direction to symmetrize the ion distribution in the ion beams 7. The material gas is made into plasma in the auxiliary discharge chambers 2a and 2a through a leading pipe 8, passes through the holes 9 into the main discharge chamber 2b, and there it is ionized. The gas pressure inside the main discharge chamber 2b is made lower than in the auxiliary discharge chambers 2a, and the microwave discharge is made possible at a high vacuum degree. As a result, the contamination in the ion source by the fresh gas is reduced, and the gas consumption can be also reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to microwave ion sources.

[Conventional technology]

The conventional microwave ion source is disclosed in Japanese Patent Application Laid-Open No. 51-119287.
As described in the publication, there is one discharge chamber and a source gas is introduced into the discharge chamber.

[Problem to be solved by the invention]

In the prior art described above, as with other ion sources, most of the source gas is exhausted without being ionized. Therefore, there are problems as described below.

(1) When the so-called raw gas, which is exhausted without being ionized, is blown onto ion source parts, it forms a film on the surfaces of these parts and contaminates them. When this film adheres to the electrode, pieces of the film peel off, triggering abnormal discharge. Furthermore, if it adheres to an insulator such as an insulator, it lowers the dielectric strength and similarly causes abnormal discharge. In particular, since the raw gas is ejected from the ion beam exit slit in the discharge chamber, it is likely to hit the electrodes near where the beam passes, contaminating them and inducing abnormal discharge.Furthermore, near the exit slit, the gas is emitted into a strong electric field. It is in a state where it is easy to discharge.

(2) When a large amount of raw gas is released into the ion source from the discharge chamber, the ion beam hits this raw gas, destroying the molecular ion beam and increasing the number of metastable ions. In addition, secondary electrons generated simultaneously with the ionization of the raw gas accelerate and rise toward the high voltage side of the ion source, and are likely to be irradiated onto electrodes and the like, causing melting and damage.

(3) Source gas is wasted by the amount of raw gas being exhausted, and vacuum pump oil and other vacuum equipment deteriorate due to exhausting raw gas.

accelerates damage.

The present invention has been made in view of the above points.

The purpose of this invention is to provide a microwave ion source that can be operated in high vacuum.

[Means to solve the problem]

The above purpose is to form a discharge chamber with a main discharge chamber and a sub-discharge chamber by providing a sub-discharge chamber in the discharge chamber, to communicate the main discharge chamber and the sub-discharge chamber, and to create a gas pressure lower than that of the sub-discharge chamber. This is achieved by extracting the ion beam from the main discharge chamber.

[Effect]

With the provision of the above means, the ion beam is emitted from the main discharge chamber with low gas pressure, making stable operation possible even in high vacuum. source is obtained.

〔Example〕

The present invention will be explained below based on the illustrated embodiments. An embodiment of the invention is shown in FIGS. 1 and 2. FIG. As shown in the figure, the microwave ion source includes a discharge chamber 2 into which microwaves 1 are introduced and a source gas is ionized by interaction with a magnetic field. That is, the microwave 1 emitted from the magnetron 3 is guided into the discharge chamber 2 through the waveguide 4. In the discharge chamber 2, a microwave discharge occurs due to the interaction between the microwave 1 and the magnetic field generated by the excitation coil 5. The gas is ionized by the microwave discharge and extracted as an ion beam 7 by the electric field applied near the exit slit 6. In this embodiment of the microwave ion source configured as described above, the discharge chamber 2 is formed by providing a sub-discharge chamber 2a in the discharge chamber 2, a main discharge chamber 2b and a sub-discharge chamber 2a, and the main discharge chamber 2b and the sub-discharge chamber 2a. Sub-discharge chamber 2a
At the same time, the ion beam 7 is drawn out from the main discharge chamber 2b, which has a lower gas pressure than the sub-discharge chamber 2a. By doing this, the main discharge chamber 2 has a low gas pressure.
The ion beam 7 is now emitted from b, making it possible to operate stably even in a high vacuum, making it possible to obtain a microwave ion source capable of operating in a high vacuum.

That is, the gas introduction pipe 8 communicates with the sub-discharge chamber 2a, and the source gas from the cylinder is first introduced into the sub-discharge chamber 2a. In order to make the ion distribution in the ion beam 7 symmetrical, the sub-discharge chambers 2a are provided symmetrically, one on each side.
The main discharge chamber 2b is located in the center thereof. The source gas once fills the sub-discharge chamber 2a, partially becomes plasma, and the sub-discharge chamber 2a
It is led to the main discharge chamber 2b through a small hole 9 provided in the main discharge chamber 2b.

Since the gas flow rate is restricted by the small hole 9, the sub-discharge chamber 2a
Microwave discharge is performed in the main discharge chamber 2b at a lower gas pressure, that is, at a higher degree of vacuum. On the contrary, in the sub-discharge chamber 2a, the gas pressure can be kept sufficiently high, the ignition performance can also be improved, and stable microwave discharge can be performed. The source gas that has come out through the small hole 9 has passed through the plasma in the sub-discharge chamber 2a, and may be at a high temperature and may also be partially excited. Since plasma is emitted from the smaller hole 9, stable microwave discharge is maintained in the main discharge chamber 2b even at low gas pressure.

In this way, according to this embodiment, the ion source can be operated in high vacuum, which reduces contamination inside the ion source due to raw gas, and further lengthens the maintenance cycle of the microwave ion source, which is characterized by a long life. Can be done. Additionally, since there is little dirt and the degree of vacuum is high, there is little discharge and a stable ion beam can be supplied.

Since microwave discharge can be maintained stably even at low gas pressures, more multivalent ions can be generated by increasing the microwave power. Furthermore, since the vacuum level of the beam line can be increased, there is no problem of metastable ions that overlap with the peak of multivalent ions due to molecular ions colliding with residual gas and decomposing during flight.
It becomes possible to use multivalent ions with peace of mind. Also.

The ion beam collides with the residual gas in the beam line.

The risk that electrons generated at the same time as ionizing the gas flow back through the ion source and hit the electrodes of the ion source and cause damage due to dissolution is reliably reduced.

Furthermore, the high degree of vacuum reduces the burden on the vacuum pump, reducing oil deterioration and corrosion damage to the pump, etc. Furthermore, since the amount of source gas used is reduced, very economical operation becomes possible. Even by simple calculations, by improving the vacuum level of the ion source by one order of magnitude, the gas in the cylinder can last about 10 times longer.

As described above, the ripple effects of the present invention are wide-ranging and may significantly change the concept of conventional ion sources.

〔Effect of the invention〕

As described above, the present invention enables a microwave ion source to operate in a high vacuum, thereby providing a microwave ion source capable of operating in a high vacuum.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the microwave ion source of the present invention, and FIG. 2 is an enlarged view of the discharge chamber in FIG. 1. DESCRIPTION OF SYMBOLS 1...Microwave, 2...Discharge chamber, 2a...Sub-discharge chamber, 2b...Main discharge chamber, 7...Ion beam, 9
...hole. Tail 1 figure q-1 complete

Claims (1)

[Claims] 1. In a microwave ion source equipped with a discharge chamber that introduces microwaves and ionizes a source gas by interaction with a magnetic field, the discharge chamber is provided with an auxiliary discharge chamber. The main discharge chamber is formed by a main discharge chamber and the sub-discharge chamber, and the main discharge chamber and the sub-discharge chamber are communicated with each other, and the ion beam is drawn out from the main discharge chamber with a gas pressure lower than that of the sub-discharge chamber. A microwave ion source characterized by the following. 2. The discharge chamber ignites plasma in a sub-discharge chamber into which the source gas is introduced, and transfers the plasma and source gas to the main discharge chamber through a hole provided in the sub-discharge chamber;
2. The microwave ion source according to claim 1, wherein only ions are extracted as an ion beam through microwave discharge in the main discharge chamber. 3. The microwave ion source according to claim 1 or 2, wherein the sub-discharge chamber is arranged symmetrically with respect to the emission direction of the ion beam. 4. The sub-discharge chamber is arranged in a position symmetrical with respect to the emission direction of the ion beam, with holes in the sub-discharge chamber disposed in symmetrical positions with respect to the emission direction of the ion beam, according to claim 1, 2, or 3. microwave ion source. 5. A patent claim in which the sub-discharge chamber is formed with the hole having a size that allows plasma generated by plasma discharge in the sub-discharge chamber to pass therethrough and suppresses passage of raw gas that is not ionized as the source gas. The microwave ion source according to any one of the ranges 1 to 4.