JP2552697B2 - Ion source - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for forming thin films of various materials on a sample substrate, or for extracting ions for etching or surface modification of the thin film surface. In particular, the present invention relates to a novel ion source for continuously extracting various ions with high current density, high efficiency, and continuously for a long time by utilizing sputtering by high-density plasma.

[Prior Art] Conventionally, a so-called ion source for extracting ions generated in plasma by using an extraction mechanism such as a grid has been widely used in various fields for etching or processing various materials and thin films. Among them, a Kauffman type ion source equipped with a thermionic emission filament as shown in FIG. 15 is most commonly used. The Kauffman type ion source has a filament 2 for emitting thermoelectrons inside a plasma generation chamber 1.
Plasma is generated by causing discharge in the magnetic field generated by the electromagnet 3 using the filament 2 as a cathode, and the ions in the plasma 4 are converted into an ion beam 6 by using several extraction grids 5. It is a drawer.

Since an ion source typified by a conventional Kauffman type ion source takes out thermoelectrons for plasma generation using a filament, the filament material is included in the ions extracted as impurities by sputtering. Further, when a reactive gas such as oxygen is used as the plasma generating gas, the reactive gas reacts with the filament, and there is a great drawback that continuous ion extraction cannot be performed for a long time. Moreover, the extracted ions were limited to those using a gas such as Ar as a raw material. As a metal ion source, there is an antenna type microwave metal ion source, but it is impossible to continuously extract ions for a long time due to the consumption of the antenna due to sputtering, and it is impossible to extract ions over a large area.

Further, in the conventional ion source, the gas and particles in the plasma are not sufficiently ionized, and most of the electric power supplied to the plasma is consumed as thermal energy, and it is used for plasma formation (ionization) to reach the supplied power. It had the drawback of low power consumption.

As an ion source using sputtering, a sputtering type ion source (Japanese Patent Laid-Open No. 62-224686) by microwave discharge using electron cyclotron resonance (ECR) has been proposed, and it has various features as a highly efficient ion source. have.

In order to realize a high-current ion source using sputtering, it is necessary to keep the plasma density high and highly efficient. For that purpose, it is important to efficiently confine the secondary electrons (γ electrons) emitted from the target, but with the above technique, the confinement of the secondary electrons is insufficient, and the energy of high-energy electrons is reduced. It cannot be effectively transmitted to the plasma, and it cannot be said to be sufficient as a high-current sputtering type ion source technology.

[Problems to be Solved by the Invention] The conditions desired as an ion source are summarized as follows: (1) Large yield (large ion current), (2) Impurities are small, (3) Ion energy range is wide. (4) Not only the inert gas but also various ions such as metal ions can be taken out.

However, an ion source satisfying such conditions has not been realized so far.

It is an object of the present invention to provide an ion source that overcomes the conventional drawbacks and can satisfy the above-mentioned conditions.

[Means for Solving the Problems] In order to achieve the above object, the ion source of the present invention has a plasma generation chamber for introducing gas to generate plasma, a microwave introduction window at one end, and the other end. At a vacuum waveguide coupled to the plasma generation chamber, an ion extraction mechanism provided at an end of the plasma generation chamber, and first and first sputtering materials provided at both ends of the plasma generation chamber. Second target, at least one power source for applying a negative voltage to the plasma generation chamber to the first and second targets, and a magnetic field formed inside the plasma generation chamber, and the first and second targets. Two
Means for forming a magnetic flux from one of the targets and entering the other, the vacuum waveguide being arranged perpendicular to the direction of said magnetic flux.

Further, the ion source of the present invention, a plasma generation chamber for introducing a gas to generate plasma, a microwave waveguide having a microwave introduction window at one end, and a vacuum waveguide coupled to the plasma generation chamber at the other end, An ion extraction mechanism provided at the end of the plasma generation chamber, a cylindrical target made of sputtering material provided along the inner surface of the plasma generation chamber, and a negative potential applied to the target with respect to the plasma generation chamber And a means for generating a magnetic field inside the plasma generation chamber and generating a magnetic flux from one end of the target to the other end, the vacuum waveguide being arranged perpendicular to the direction of the magnetic flux. It is characterized by

[Operation] In the present invention, high-density plasma with high activity is generated, and sputtering is performed using the plasma. The reactivity of the generated ions and the conductivity of the obtained film do not hinder the extraction of ions, and the energy consumption is low. Ions can be continuously extracted at high speed and high efficiency. That is, the present invention generates and heats plasma by electron cyclotron resonance (ECR), and uses the high density plasma to perform sputtering.
Both extraction of low energy ions of several eV to several keV and generation of highly active plasma are compatible. Moreover, since the vacuum waveguide is connected perpendicularly to the magnetic flux direction, plasma acceleration in the vacuum waveguide direction is suppressed. As a result, the reflection of microwaves due to the adhesion of the conductive material film to the microwave introduction window can be ignored, and it becomes possible to continuously and stably form metal ions. Moreover, since the target is arranged so that the electrons are reflected in the plasma, high-speed sputtering is possible, and therefore high current density ions can be extracted.

EXAMPLES The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the ion source according to the present invention. The plasma generation chamber 7 includes a plasma generation chamber 7P and a target holding unit 7T. A gas for generating plasma is introduced into the plasma generation chamber 7 from an inlet 8. A vacuum waveguide 9 having a microwave introduction window 10 at one end is connected to the plasma generation chamber 7. The microwave introduction window 10 is a microwave introduction window.
Microwaves are supplied to the plasma generation chamber 7 from a microwave source connected to a microwave introduction mechanism such as a matching box, a microwave power meter, and an isolator (not shown). In this embodiment, a quartz glass plate is used for the microwave introduction window 10 arranged in a portion that is not directly visible from the target placed in the plasma generation chamber 7. The microwave source, for example, using a magnetron of 2.45 GHz _Z.

An ion extraction grid 12 is provided at one end of the plasma generation chamber 7. In the present embodiment, the grid 12 is composed of two perforated grids 12A and 12B, each grid is attached to the bottom of the target holding portion 7T via an insulator 13, and the grids 12A and 12B are connected to plasma from power supplies 14A and 14B, respectively. A negative voltage is applied to the generation chamber 7. A flat plate-shaped target 15 is provided at the other end inside the plasma generation chamber 7, and a cylindrical target 16 is provided near the grid 12.

A method of attaching the targets 15 and 16 to the plasma generation chamber is shown in FIGS. 2A and 2B. As shown, the target 15 is detachably fixed to a water-coolable metal support 15A, and the support 15A is fixed to the upper wall 7A of the plasma generation chamber 7 by a screw lid 15B. Support 15A is insulator 1
Insulated by 5C. Similarly, the target 16 is removably fixed to a water-coolable metal support 16A, which is fixed to the wall 7B by a screw lid 16B via an insulator 16C. The protruding ends 15 of each of the supports 15A and 16A
D and 16D also serve as electrodes, and DC power supplies 17 and 18 respectively
Therefore, a negative voltage can be applied to the targets 15 and 16 with respect to the plasma generation chamber. It is preferable to apply a positive potential to the plasma generation chamber 7. If a voltage of −tens to −200V is applied to the plasma generation chamber 7 to the grid 12A on the plasma generation chamber side, the ions accelerated in the grid have an effect of removing the film deposited on the grid. .

At least one pair of electromagnets 19A and 19B are provided at both ends of the outer periphery of the plasma generation chamber 7 to generate a magnetic field in the plasma generation chamber. At that time, each constituent condition is determined so that the condition of electron cyclotron resonance (ECR) by microwaves is satisfied inside the plasma generation unit 7P. For example, for microwave frequency 2.45 GHz _Z, for conditions for ECR is the flux density 875 G, both ends of the electromagnet 19A, 19B is configured as a magnetic flux density of up to 2000G is obtained for example, magnetic flux density 875 G is It is realized somewhere inside the plasma generator 7P. In addition to efficiently energizing electrons by the ECR inside the plasma generating section 7P, this magnetic field also prevents generated ions and electrons from being dissipated in the direction perpendicular to the magnetic field, and as a result, the A density plasma is generated.

The plasma generation unit 7P adopts, as an example, a circular cavity resonance mode TE ₁₁₃ as a condition of the microwave cavity resonator, and increases the electric field strength of the microwave by using a cylindrical shape having a diameter of 20 cm and a height of 20 cm in the inner ring, It is desirable to increase the efficiency of microwave discharge.

The flat plate target 15 and the cylindrical target 16 have electromagnets 19A and 19A on the surfaces of the flat plate target 15 and the cylindrical target 16, respectively.
The magnetic flux 20 due to B is installed so that the magnetic flux exits from one of the targets and enters the other target.

It is desirable that the plasma generation chamber be water-coolable. In order to protect the side surfaces of the targets 15 and 16 from the plasma, it is preferable to provide shields 7C and 7D on the inner surface of the plasma generation chamber.

After the inside of the plasma generation chamber 7 is evacuated to a high vacuum, a gas is introduced from the gas introduction port 8 to introduce microwaves to cause discharge under ECR conditions and generate high density plasma. Ions in the plasma can be extracted as the ion beam 21. The magnetic flux between the targets has the effect of preventing secondary electrons (γ electrons) generated from the target surface from being dissipated in the direction perpendicular to the magnetic field, and also has the effect of confining the plasma. As a result, high-density plasma can be generated in a low gas pressure. Is generated.

FIG. 3 is a sectional view of an example of a thin film forming apparatus using the ion source shown in FIG. Ion drawer grid 12
A sample chamber 22 is connected to the plasma generation chamber 7 with the sample chamber 22 interposed therebetween. The sample chamber 22 and the plasma generation chamber 7 are preferably insulated. Gas can be introduced into the sample chamber 22 through the gas introduction port 23, and can be evacuated to a high vacuum by the exhaust system 24. A substrate holder for holding a substrate 25 in the sample chamber 22
26 is provided, the substrate holder 26 and the ion extraction grid 12 are provided.
A shutter 27 that can be opened and closed is provided between and. The substrate holder 26 preferably has a heater built therein so that the substrate can be heated, and a DC or AC voltage is applied to the substrate 25 to apply a bias voltage to the substrate during film formation,
It is desirable to configure the substrate so that it can be sputter cleaned.

The energy of the extracted ions is mainly the plasma generation chamber 7
And the acceleration voltage, which is the relative difference between the voltages applied to the ion extraction grid 12.

FIG. 4 shows an example of the magnetic field strength distribution in the magnetic flux direction in the thin film forming apparatus shown in FIG. The magnetic field is a divergent magnetic field.

Here, the principle of high-density plasma generation in the ion source of the present invention will be described in detail with reference to FIG.

By applying a negative potential to the target facing the generated high density plasma, the ions in the high density plasma are efficiently drawn into the cylindrical target 16 and the flat plate target 15 to cause sputtering. Cylindrical target
When the ions attracted by 16 and the flat target 15 collide with the target surface, secondary electrons (γ electrons) 28 are emitted from the target surface. The γ-electrons 28 are accelerated by the electric field created by the respective targets, and are bound by the magnetic flux 20 running on the surfaces of the targets, and move to the opponent's target at high speed while performing spiral motion. The γ-electrons 28 that have reached the opponent's target are also reflected by the electric field created by the target, and as a result, the γ-electrons 28 are trapped in a spiral motion between both targets. The reciprocating motion of the γ-electrons is confined until the energy becomes smaller than the binding energy of the magnetic flux, and during that period ionization is accelerated by collision with neutral particles and interaction with plasma.

In addition, cylindrical target 16 and flat plate target
A portion of the mostly neutral particles sputtered from 15 are ionized in a high density plasma with a high electron temperature. As a result, ions of the target material are formed.

Further, since the plasma is active, the discharge can be stably formed even at a lower gas pressure of the order of 10 ⁻⁵ Torr.

Ions in the plasma generation chamber are the ion extraction grid 12
The low-energy ions of several tens to several keV are obtained by being selectively extracted outside the plasma generation chamber.

In the sputter-type ion source of the present invention, since the plasma has a high ionization rate as described above, the neutral sputtered particles emitted from the target are highly ionized in the plasma. The ionized target constituent particles are also accelerated by the potential of the target, and the so-called self-sputtering rate at which the target is sputtered becomes extremely large. That is, even when the plasma generating gas (for example, Ar) is extremely dilute, or when the gas is not used, the above-mentioned self-sputtering is continued, and therefore high-purity ion extraction can be realized.

When extracting the metal ions, if the microwave introduction window becomes cloudy, plasma cannot be generated for a long time. Therefore, the vacuum waveguide 9 is connected perpendicular to the magnetic flux direction so that the microwave introduction window 10 is not clouded by the adhesion of the conductive material film. This utilizes that the plasma is not accelerated in the direction perpendicular to the magnetic flux. Cylindrical target 16 and flat plate target 15 installed in plasma generation chamber 7
Among the particles sputtered from, the non-ionized neutral particles are not affected by the magnetic field or the electric field and fly almost straight from the target. Therefore, the microwave introduction window
By installing 10 at a position that is not directly visible from the target, it is possible to prevent the microwave introduction window 10 from being fogged by sputtered particles. In this way, regardless of the type of extracted ions and the conductivity of the generated film, and regardless of the film thickness, the microwave introduction window does not become cloudy, and most of the ions remain stable for a long time. It is possible to withdraw.

From the viewpoint of microwave introduction efficiency, it is better to set the magnetic field strength of the microwave incident part of the plasma generation chamber to be stronger than the magnetic field strength for ECR, in this case 875G.

Next, results of forming Al films by extracting Al ions using the apparatus shown in FIG. 3 will be described.

FIG. 6 shows an example of the discharge characteristics of the target. Here, the voltage Va ^P applied to the flat target 15 is fixed at -500 V, the microwave power Pμ is fixed at 300 W and 80 W, and the gas pressure is fixed at 0.3 mTorr and 3 mTorr. Even if the voltages applied to the flat plate target 15 and the cylindrical target 16 are different as shown in FIG. 6, it is possible to realize plasma generation with a sufficiently high density. If the voltage is the same,
That is, similar high-efficiency plasma generation can be performed even when both targets are electrically connected.

After evacuating the vacuum of the sample chamber 22 to 5 × 10 ^-7 Torr,
Gas was introduced at a flow rate of 1 cc / min, the gas pressure in the plasma generation chamber was set to 2 × 10 ^-4 Torr, and microwave power was 100 to 5
00W, the electric power input to the cylindrical Al target 16 is 300 to 60
A film was formed with 0 W.

FIG. 7 shows an example of ion extraction characteristics at this time. The ion extraction voltage on the horizontal axis is the plasma generation chamber 7 and the grid 12
It is the relative voltage difference from A. At this time, the film was formed at room temperature without heating the substrate holder. As a result, 1-10
The Al film could be deposited stably and efficiently continuously for a long time at the deposition rate of nm / min.

The ion source of the present embodiment can be used not only for forming a film by extracting Al ions, but also for extracting almost all ions and forming a film, and can use almost any reactive gas as a gas to be introduced, Thereby, formation of a compound film using reactive sputtering can be realized.

FIG. 8 shows a thin film forming apparatus to which another embodiment of the present invention is applied. The difference between this apparatus and the apparatus shown in FIG. 3 is the shape of the plasma generation chamber and the arrangement of the cylindrical target 16.
That is, the plasma generation chamber 7 in the present embodiment includes only a plasma generation unit, and is not provided with a special target holding unit. The cylindrical target 16 is provided on the inner surface of the lower portion of the plasma generation chamber. The ion source of this embodiment also operates similarly to the ion source shown in FIG.

FIG. 9 is a sectional view of another embodiment of the ion source of the present invention. In this embodiment, two cylindrical targets 16 and 29 are used instead of a combination of a flat plate target and a cylindrical target. The magnetic flux generated by the magnetic field generating electromagnet 19 exits from one target and enters the other target. The strength of the magnetic field is the same as that of the embodiment shown in FIG. The target 29 is detachably fixed to a water-coolable metal support 29A, and a negative power source is applied to the plasma generation chamber 7 by a power source 17. 29C is an insulator.

As shown in FIG. 10, even in this embodiment, the negative voltage Va, V
When fast ions collide with a target to which a'is applied, fast secondary electrons (γ electrons) from the target surface
28 is released. Γ-electrons emitted from this target
28 is reflected by the electric fields of both targets, and reciprocates between the targets while performing cyclotron motion around the magnetic flux 20 running between both targets. In the same manner as described above, the high density plasma can be generated in the low gas pressure also in this embodiment.

FIG. 11 shows an example of a thin film forming apparatus to which the ion source shown in FIG. 9 is applied. With this apparatus, it is possible to form a thin film at a high speed similarly to the apparatus shown in FIG. The plasma generation chamber may be composed of a plasma generation unit and a target holding unit as shown in FIG. 1, and one target 16 may be provided in the target holding unit.

FIG. 12 shows a thin film forming apparatus to which still another embodiment of the ion source of the present invention is applied. The ion source of this embodiment includes one cylindrical target 30. The target 30 is supported by a water-coolable metal target support 30A, and a power source 18
A negative voltage is applied to the plasma generating chamber 7. 30C is an insulator. The magnetic flux generated by the electromagnet 19 exits from one end of the target 30 and enters the other end. This ion source can extract a high-power ion beam similarly to the ion source shown in FIG. 9, and can form a film at high speed by using the thin film forming apparatus shown in FIG.

FIG. 13 shows a sectional view of still another embodiment of the present invention.
In this embodiment, a second ion extraction mechanism is added to the embodiment shown in FIG. An ion extraction grid 31 composed of two grids 31A and 32A is provided at the end of the plasma generation chamber 7 opposite to the ion extraction grid 12, and the power supply 3
A negative voltage is applied to the plasma generation chamber 7 from 2A and 32B to the grids 31A and 31B. In this way, ions can be extracted from both sides of the plasma generation chamber.

FIG. 14 shows a thin film forming apparatus to which still another embodiment of the present invention is applied. In the ion source of this embodiment, the electromagnets 19A and 19B shown in FIG. 1 are replaced by permanent magnets 33 and 34, respectively. By forming a magnetic field having an intensity satisfying the ECR condition in the plasma generation chamber and generating a magnetic flux from one target to enter the other target, the ion source of this embodiment has a large magnetic field as in the embodiment of FIG. High-speed film formation is possible using the apparatus shown in FIG. 14 by generating an ion beam of electric current.

Also in the embodiments shown in FIGS. 8, 9, 12 and 13, it is possible to use a permanent magnet instead of the electromagnet.

[Effects of the Invention] As described above, the present invention realizes highly efficient ion extraction in a low gas pressure by using sputtering using microwave plasma generated by electron cyclotron resonance. It is possible to realize continuous and stable extraction of ions for a long time regardless of the type of ions and the conductivity and film thickness of the film obtained thereby.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an ion source according to the present invention, FIGS. 2A and 2B are views showing details of target attachment, and FIG. 3 is a thin film formation to which the embodiment shown in FIG. 1 is applied. FIG. 4 is a sectional view of the apparatus, FIG. 4 is a view showing a magnetic field strength distribution in the magnetic flux direction in the apparatus of FIG. 3, FIG. 5 is a view for explaining a high-density plasma generation mechanism according to the embodiment shown in FIG. FIG. 6 is a diagram showing an example of discharge characteristics in an embodiment of the present invention, FIG. 7 is a diagram showing an example of ion extraction characteristics, and FIG. 8 is a sectional view of a thin film forming apparatus to which another embodiment of the present invention is applied. FIG. 9 is a cross-sectional view of still another embodiment of the present invention, FIG. 10 is a view for explaining a high-density plasma generation mechanism in the embodiment of FIG. 9, and FIGS. 11, 12 and 13 are 14 is a sectional view of a thin film forming apparatus to which still another embodiment of the ion source of the present invention is applied, respectively. FIG. 15 is a sectional view of another embodiment of the ion source of the invention, and FIG. 15 is a sectional view of a conventional Kauffman type ion source. 1 ... plasma generation chamber, 2 ... filament, 3 ... electromagnet, 4 ... plasma, 5 ... ion extraction grid, 6 ... ion beam, 7 ... plasma generation chamber, 7P ... plasma generation part, 7T: Target holding part, 8 ... Gas inlet, 9 ... Vacuum waveguide, 10 ... Microwave inlet window, 11 ... Microwave waveguide, 12 ... Ion extraction grid, 14,17, 18,29,30 …… Power supply, 15 …… Flat target, 16,29,30 …… Cylindrical target, 19,19A, 19B …… Electromagnet, 20 …… Magnetic flux, 21 …… Ion beam, 22 …… Sample chamber, 25 …… Substrate, 26 …… Substrate holder, 28 …… Secondary electron, 33,34 …… Permanent magnet.

Claims (3)

(57) [Claims] 1. A plasma generation chamber for introducing a gas to generate plasma; a vacuum waveguide having a microwave introduction window at one end and coupled to the plasma generation chamber at the other end; Ion extraction mechanism provided at the end of the generation chamber, first and second targets made of sputtering material provided at both ends of the plasma generation chamber, and the first and second targets respectively. At least one power supply that applies a negative voltage to the plasma generation chamber, and a magnetic flux that forms a magnetic field inside the plasma generation chamber and that enters from one of the first and second targets to the other. An ion source, wherein the vacuum waveguide is arranged perpendicular to the direction of the magnetic flux. 2. A plasma generation chamber for introducing a gas to generate plasma, a vacuum wave conduit having a microwave introduction window at one end and coupled to the plasma generation chamber at the other end, the plasma generation An ion extraction mechanism provided at the end of the chamber, a cylindrical target made of a sputtering material provided along the inner surface of the plasma generation chamber, and a negative potential with respect to the plasma generation chamber applied to the target. The vacuum waveguide includes a power source to be applied and a means for forming a magnetic field inside the plasma generation chamber and generating a magnetic flux from one end of the target to enter the other end, wherein the vacuum waveguide is in the direction of the magnetic flux. An ion source characterized in that the ion source is arranged vertically. 3. The plasma generation chamber comprises a plasma generation unit and a target holding unit.
Or the ion source according to 2.