JPH02148539A - Ion source - Google Patents

Abstract

PURPOSE:To make the facility smaller and enhance the efficiency of utilization of microwaves, by directly attaching a magnetron to the side wall of an ion source chamber, and causing a part of the space of the ion source chamber to be occupied by a dielectric. CONSTITUTION:A magnetron 8 is attached on the cylindrical face of an ion source chamber 1. The magnetron 8 generates microwaves, which are emitted as electric waves from a high frequency dome 12. The grounded part of the magnetron is connected to the wall of the ion source chamber 1. A dielectric 10 is inserted into the ion source chamber 1 in such a manner that it occupies a larger part of the inside of the chamber in the direction of length thereof. The axial length of the chamber 1 is L. The outside diameter of the dielectric 10 is approximately the same as the inside diameter of the chamber 1, so that they are fitted to each other well. The axial length of the dielectric 10 is q. The remaining part d is a plasma production space 13. A wave guide, etc., is not thus connected to the external of the chamber 1 so that the chamber can be made smaller. In addition, the depth of the plasma production space is small, so that high plasma can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (G) Technical Field The present invention relates to an ion source that generates plasma using microwaves and a magnetic field, which is capable of generating higher-density plasma.

ECR (Electron Cyclctron R) generates plasma using microwaves and magnetic fields.
e5onance) type. There is an axial static magnetic field B, and the electron cyclotron frequency qB/
2πm is approximately equal to the microwave frequency.

Electrons rotate around magnetic field lines. This is called cyclotron motion. Since it has the same period as the microwave frequency, it is accelerated in synchronization with this.

An accelerated object has a larger radius of rotation and a higher speed.

In this way, when electrons moving at high speed collide with gas molecules, they excite them into positive ions, electrons, or neutral active species. Secondary electrons are emitted, which act in a similar manner, quickly turning into a plasma state.

Ion sources that use hot cathodes to generate electrons have been used for a long time, but the filament breaks when a reactive gas is introduced.

Since the ECR type ion source does not have a filament, it has a long life even with highly reactive gases.

ECR type ion sources are used for reactive ion beam etching and ECR (:VD (thin film deposition)).

(b) Conventional technology FIG. 2 shows a conventional ion source.

The ion source chamber 1 is a cylindrical container that can be evacuated. It has a coil 2 along the outer circumference of the cylinder. The coil 2 generates an axial magnetic field.

Microwaves are generated in the microwave oscillator 6. This consists of a waveguide 4, a three-stub tuner 5, a waveguide 4
, and enters the ion source chamber 1 via the dielectric 3 .

A gas to be ionized is introduced into the ion source chamber 1 from a gas introduction system 17 . These gas molecules are excited into plasma by the action of microwaves and a magnetic field.

An extraction electrode system 7 is provided on the other end face of the ion source chamber 1 . This is a superposition of an accelerating electrode and a decelerating electrode. Both are porous plate electrodes. Thereby, it is extracted as an ion beam.

To the left of the ion source chamber 1 is a vacuum chamber (not shown) that holds a sample (not shown), and the ion beam impinges on the sample to perform an etching action or a thin film forming action.

The ion source chamber 1 is filled with plasma. In other words, it is a collection of positive ions and electrons. Other types include gas molecules (ground state) and neutral active species.

Due to the action of the magnetic field, charged particles undergo cyclotron movement, but due to thermal movement and scattering, positive ions and electrons move toward chamber 1.
You can fly anywhere inside.

Ions are extracted from only one end face. Some ions hit the wall and become neutralized before being extracted as ions.

Of the microwave power, the energy extracted as ions is about 100 to 50 W. The rest is dissipated as heat.

(1) Problems to be Solved by the Invention Microwaves are transmitted from a microwave oscillator through an ion source chamber gusset and a waveguide. Since the waveguide is large in size, the equipment becomes bulky.

The size of the ion source chamber is largely determined by the frequency of the microwave. Since t=large waveguides are connected, the overall size of the equipment is large. Also, a three-stub tuner must be inserted in the middle for matching.

For example, if the frequency of microwave is 2.45 GHz, the inner dimensions of a standard waveguide used therefor are 54.6 mm x 109.2++ m. The flanges at both ends of the waveguide are 106.5mm x 161m+x
It is.

This is a waveguide designed to pass only the TE1o mode of microwaves near 2.45 GHz. The long side of the rectangle is twice as long as the short side.

The half size waveguide has an inner diameter of 27mm x 96mm.
mrv.

The flange dimensions are 60mru x 130+++m, which is about half of the previously described one.

In any case, the waveguide must be straight,
Since it is bulky, it makes the equipment bloated.

Since a waveguide is used, various restrictions arise when installing the ion source. This is because the waveguide is an elongated rigid body.

Since it is a microwave, it can be transmitted through coaxial lines. In this case, current flows through the internal wire, insulation coating, external wire area, and between the internal wire and the external wire. The electric field created in the insulation sheath is radial and perpendicular to the axis.

The magnetic field draws concentric circles around the axis. Both the electric and magnetic fields are perpendicular to the direction of travel. This is called TEM mode.

With coaxial wires, there is no need to keep them straight; they are flexible and can be bent.

However, since current flows through the coaxial line and the electric and magnetic fields are maintained by the action of the current, Joule heat loss naturally occurs.

This is proportional to the frequency, so the higher the frequency, the greater the loss.

At about 2.45 GHz, the microwave power that can be transmitted through a coaxial line is about 100 W at most.

In the conventional example shown in FIG. 2, the microwave power generated by the microwave oscillator 6 is usually 1.0 to 1.5 kW. This attenuates and enters the ion source chamber, but the power that enters is still considered to be about 1 kW.

Microwaves of about 100 W are of little use.

Therefore, transmitting microwaves using coaxial lines is not an effective method.

There is another problem with the ion source shown in Figure 2.

This means that the efficiency of using microwaves is low.

This is because the ion source chamber 1 is long in the axial direction. This is because even once it becomes plasma, many gas molecules recombine and become neutralized before being extracted.

As described above, the problems with the ion source shown in FIG. 2 include installation restrictions due to the bulky waveguide and low microwave utilization efficiency.

) configuration Two improvements are made to the ion source of the present invention.

One method is to attach a magnetron directly to the side wall of the ion source chamber, from which microwaves are generated and supplied into the ion source chamber.

The microwave oscillator is external and is not transmitted through a waveguide or coaxial line. It is attached directly to the ion source chamber. Therefore, no transmission line is required.

Another is that a portion of the space in the ion source chamber is occupied by a dielectric material, thereby narrowing the space in which the gas exists. Make the gas existence space narrower in the axial direction, and do not make the extraction electrodes smaller.

Then, the effective depth l obtained by dividing the plasma existence space V by the effective area S of the extraction electrode becomes shorter, and the plasma is more easily extracted. In other words, the efficiency of using microwaves increases.

FIG. 1 is a longitudinal sectional view showing an example of the ion source of the present invention.

The ion source chamber 1 has a cylindrical shape. This means that microwave standing waves exist. Acts as a cavity resonator. This is no different from the one in Figure 2. However, rather than the microwave entering from one end face, the end face is a blind plate.

Instead, a magnetron 8 is attached to the cylindrical surface of the ion source chamber 1. The magnetron 8 generates microwaves, which are radiated from the high frequency dome 12 as radio waves. The ground side of the magnetron is connected to the ion source chamber 1 wall.

If the tube wavelength of this microwave is λg, the high frequency dome 12 of the magnetron 8 is preferably located at a point λg/4 from the end face of the ion source chamber 1.

This means that when a microwave standing wave is generated, the high frequency dome 12 is located at the antinode of the microwave standing wave. This increases the coupling efficiency.

The outer periphery of the magnetron 8 is covered with a magnetic shield 9 made of ferromagnetic material. The purpose of this is to prevent the magnetic field generated inside the magnetron from leaking to the outside.
The purpose is to prevent external magnetic fields from interfering with the operation of the magnetron.

The high frequency dome 12 serves as an antenna and radiates microwaves. This and the cavity resonance mode may be E coupling (electrostatic coupling: coupling with an electric field) or H coupling (electromagnetic coupling: coupling with a magnetic field).

A dielectric body 10 is inserted into the ion source chamber 1 so as to occupy most of the length thereof.

Let L be the axial length of the ion source chamber 1.

Since the outer diameter of the dielectric 10 is approximately the same as the inner diameter of the ion source chamber 1, it is a tight fit. dielectric 10
Let the length in the axial direction be q. The remaining (Lq)=d portion is the plasma generation space 13.

A gas introduction system (not shown) is provided in the plasma generation space 13 having a depth of d, through which gas is introduced.

A coil 2 is provided around the plasma generation space 13 to generate an axial magnetic field.

The inner circumference of the coil 2 is open, but the outer circumference and both end faces are covered with a magnetic shield 9'. Magnetic shield 9'
is made of ferromagnetic material. This is because there is no magnetic interaction with the magnetron 8.

Further, in the middle of the circumferential wall of the ion source chamber 1, a matching device and mode converter 11 is provided.

This allows three stubs to be moved in and out. The stubs are separated by λg/8. The stubs are moved in and out to specify the modes that can exist within the chamber.

Although three stubs are provided on the wall facing the magnetron 8, several more stubs may be provided in the circumferential direction.

Even though it is called a mode, it is an axial mode. The mode in the in-plane direction is fixed, for example, the TFI:11 mode. Specify the axial mode order m written as Tellm.

There is an extraction electrode system 7 on the exit side of the ion source chamber 1, which extracts the ion beam from the plasma.

This is a perforated plate electrode in which an accelerating electrode and a decelerating electrode are superimposed.

(2) Production Microwaves are generated in the magnetron 8.

A magnetron with an output of about 2 kW can be used if it is air-cooled or water-cooled. This microwave is fed into the ion source chamber 1 from the high frequency dome 12 .

The high frequency dome 12 is, for example, E-coupled (electrostatically coupled) and is located at a distance of λg/4 from the end face of the chamber, so that power can be efficiently supplied.

In the ion source chamber 1, which is a cavity resonator, only microwaves in a certain fixed mode are present.

Microwaves emitted from the high-frequency dome are converted into a cavity resonance mode.

Matching box and mode converter 1 to match the cavity resonance mode
Adjust stub 1.

The microwave exists across the dielectric 10 and the plasma generation space 13. Since the dielectric constants of both are different, the wavelengths are different.

A portion of the light is reflected at the interface 14 due to the difference in dielectric constant.

However, if the depth d of the plasma generation space 13 is smaller than λg/2, no unique standing wave can exist here. For this reason, the reflected wave cannot create a stable mode.

In other words, reflection at the interface 14 does not pose much of a problem.

Dielectric 10 occupies a large volume. Plasma generation space 1
3 is narrow. Even though it is narrower, the diametrical dimensions are the same. Therefore, the microwave supply energy Q per unit volume of the plasma generation space increases.

Let me explain in more detail. Let W be the total energy of the microwave, and S be the cross-sectional area of the ion source chamber. The amount of microwave supplied per unit area is W/S.

In the conventional device shown in FIG. 2, the microwave supply energy Q2 per unit volume is as follows, where L is the length of the chamber. Since L is large, Q2 is small.

However, in the present invention, the microwave supply energy Q1 per unit volume is. It is clear that Ql is greater than Q2.

Plasma generation is approximately proportional to the micro-liquid supply energy Q per unit volume. Therefore, the ion source of the present invention can generate higher density plasma.

Since a high-density plasma can be generated, when the ion beam is extracted using an extraction electrode system, the ion beam current becomes stronger. In other words, since a high-density ion beam is obtained, the efficiency of ion processing increases when a sample (not shown) is irradiated.

However, since the energy W/S per unit area of microwaves is the same, Q
ld 1Q2L are the same. Therefore, it may be thought that the ion beam current is the same.

But that's not the case. Only a part of the nearby plasma can be extracted by the extraction electrode system 7.

Plasma in a portion away from the extraction electrode system 7 often recombines and disappears. In other words, what determines the size of the ion beam is not the integral value of the plasma in the axial direction, but the plasma density near the extraction electrode system.

In the present invention, the plasma generation space 13 is narrowed by inserting the dielectric 10, thereby achieving high plasma density.

The dielectric 10 has several functions in addition to simply acting as a filler.

A high frequency dome 12 of the magnetron 8 is surrounded by a dielectric 10. Do not come into contact with reactive gases.

Therefore, the high frequency dome 12 is not corroded by the reactive gas.

The stub of the matching box/mode converter 11 is also protected by the dielectric 10. Therefore, it is not corroded by reactive gases.

Furthermore, the parts that come into contact with the plasma are heated and therefore need to be cooled. The high frequency dome 1 is formed by the dielectric 10.
2. Since the stubs are shielded from the plasma, they cannot be heated too much. No need for cooling.

Since no waveguide or the like extends from the ion source chamber, the ion source is smaller overall and installation is less space-intensive.

This is because the magnetron 8 was directly attached. A magnetron with a large output of 1.5 kW to 2 kW can also be used.

However, as described above, in the present invention, since the depth d of the plasma generation space is small, the microwave supply energy Q1 per unit volume becomes large. Therefore, the microwave power W can be made smaller.

For a magnetron with lower power, for example 500 W, the dimensions are 100mm x 100mm x 100mm.
It's about my level. Extremely small. Since the combination of the waveguide 4, three-stub tuner 5, and microwave oscillator 6 in FIG. 2 is replaced with the magnetron 8,
This can be said to be a significant miniaturization.

Of course, the magnetron 8 is connected to a cord for supplying power. Cords are thinner than waveguides and can be bent freely, so there are no restrictions on installation.

(2) Effect Since the waveguide, three-stub tuner, microwave oscillator, etc. are not connected to the outside of the ion source chamber,
It is smaller overall. There are fewer restrictions on installation. It can be installed even in narrow spaces.

Since the plasma generation space is a shallow space, the microwave supply energy per unit volume is large and high-density plasma can be generated.

As a result, a high-power ion beam can be obtained. Improves ion processing capacity.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an ion source according to an example of the present invention. FIG. 2 is a longitudinal cross-sectional view of a conventional ion source. 1... Ion source chamber 2... Coil 3... Dielectric 4... Waveguide 5... Three stub tuner 6...・・・・・・
Microwave oscillator 7... Extraction electrode system 8... Macnetron 9.9... Magnetic shield 10... Dielectric 11... Matching lid Combined mode converter 12...
・High frequency dome 13...Plasma generation space 14...Interface 17...Gas introduction system inventor Yoshitaka Sasamura

Claims (1)

[Claims] It is an ion source that generates plasma using microwaves and a magnetic field, and includes a cylindrical ion source chamber 1 that can be evacuated, one end is open and the other end is closed, and the inner diameter of the ion source chamber 1 is approximately the same as the inner diameter of the ion source chamber 1. A dielectric body 10 having the same outer diameter and a length smaller than that of the ion source chamber 1 and inserted toward the closed end of the ion source chamber 1, and a magnetron attached to the wall of the ion source chamber 1 and generating microwaves. 8 and a dielectric material 1 inside the ion source chamber 1 to radiate microwaves generated by the magnetron 8.
0, and a plurality of stubs attached to the wall of the ion source chamber 1 and inserted into and out of the dielectric 10 inside the ion source chamber 1. a coil 2 that is provided around the plasma generation space 13 inside the ion source chamber 1 and without the dielectric 10 and generates an axial magnetic field, and a magnetic shield that surrounds the outer periphery of the magnetron 8. 9, a magnetic shield 9' surrounding the outer periphery of the coil 2, and an extraction electrode system 7 provided outside the plasma generation space 13 of the ion source chamber 1 for extracting ions from the plasma. .