JPH01201467A - Ion source - Google Patents

Abstract

PURPOSE:To stably and efficiently extract ions over a long time by installing means of impressing negative potential on targets and a means of forming a magnetic field in a plasma generation chamber and generating magnetic flux between the targets. CONSTITUTION:A flat plate-shaped target 12 is placed at the upper part of a plasma generation chamber 7, a cylindrical target 13 near a grid 9 for extracting ions and negative potential is impressed on the targets 12, 13 from DC power sources 14, 15 in comparison with the chamber 7. An electromagnet 16 is placed around the chamber 7 and an electric field is formed. The electromagnet 16 and the targets 12, 13 are positioned so that magnetic flux generated from the electromagnet 16 intersects the targets 12, 13, emerges from the surface of one of the targets and enters the surface of the other. Plasma is generated in the magnetic field and ions in the plasma are extracted as ion beams 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for extracting ions for forming thin films of various materials on a sample substrate, or for etching or surface modification of the thin film surface. In particular, it relates to a new sputter-type ion source that utilizes sputtering using high-density plasma to continuously and stably extract various ions at high current density and with high efficiency over a long period of time.

[Prior Art] Conventionally, so-called ion sources that extract ions generated in plasma using an extraction mechanism such as a grid have been widely used in various fields for etching or processing various materials and 7G films. Among these, a Kauffman type ion source equipped with a filament for emitting thermionic electrons as shown in FIG. 17 is most commonly used. The Kaufman type ion source has a filament 2 for emitting thermionic electrons inside a plasma generation chamber 1, and generates plasma 4 by causing discharge in a magnetic field generated by an electromagnet 3 using the filament 2 as a cathode. Ions in the plasma 4 are extracted as an ion beam 6 using several extraction grids 5.

Since ion sources such as the conventional Kaufmann ion source use a filament to extract thermal electrons for plasma generation, the filament material is sputtered and included in the extracted ions as impurities. Furthermore, when a reactive gas such as oxygen is used as the plasma generating gas, there is a major drawback in that the reactive gas reacts with the filament, making it impossible to extract ions continuously for a long time. Moreover, the extracted ions are limited to those made from a gas such as Ar. As a metal ion source, there is an antenna-type microwave metal ion source, but ions cannot be extracted continuously for a long time because the antenna is worn out by sputtering, and furthermore, ions cannot be extracted over a large area.

Furthermore, in conventional ion sources, gases and particles in the plasma are not sufficiently ionized, and most of the power input to the plasma is consumed as thermal energy.
There was a drawback that the ratio of the power used for plasma formation (electron 1III) to the input power was low.

As an ion source using sputtering, there is a sputtering type ion source using microwave discharge using electron cyclotron [1% (ECR) (Japanese Patent Application Laid-open No. 224686/1986).
has been proposed and has various features as a highly efficient ion source.

To realize a high-current ion source using sputtering, it is necessary to maintain plasma density at high density and with high efficiency. For this purpose, secondary electrons (γ electrons) emitted from the target
It is important to efficiently confine secondary electrons, but with the above techniques, the confinement of these secondary electrons is insufficient and the energy of high-energy electrons cannot be effectively transferred to the plasma, making it difficult to use high-current sputter-type ion sources. It is hard to say that the technology is sufficient.

[Problems to be solved by the invention] Desirable conditions for an ion source are summarized as: (1) high yield (large ion current), (2) few impurities, (3) wide range of ion energy. (4) The ability to extract not only inert gas but also various ions such as metal ions.

However, an ion source that satisfies these conditions has not been realized to date.

The present invention aims to improve the conventional drawbacks and provide an ion source that can satisfy each of the above conditions.

[Means for Solving the Problems] In order to achieve such an object, the present invention includes a plasma generation chamber that introduces gas to generate plasma, an ion extraction mechanism provided at an end of the plasma generation chamber, and , first and second targets each made of a sputtering material provided at both ends inside the plasma generation chamber;
and at least one power source that applies a negative potential with respect to the plasma generation chamber to the second target, respectively;
and means for generating magnetic flux exiting one of the targets and entering the other.

The present invention includes a plasma generation chamber for introducing gas to generate plasma, a vacuum waveguide having a microwave introduction window at one end and connected to the plasma generation chamber at the other end, and an end of the plasma generation chamber. a cylindrical target made of sputtering material provided along the inner surface of the plasma generation chamber; a power supply that applies a negative potential to the target with respect to the plasma generation chamber; The present invention is characterized by comprising means for forming a magnetic field inside the generation chamber and for generating magnetic flux that exits from one end of the target and enters the other end of the target.

[Function] The present invention generates high-density plasma in a low-pressure gas, performs sputtering using the plasma, and continuously extracts the generated ions with high current density and high efficiency. That is, in the present invention, a target made of a sputtering material is installed at both ends of the plasma generation chamber, and a magnet provided around the plasma generation chamber generates a magnetic flux that passes from one side of the target to the other. By applying a negative potential to the target, secondary electrons (γ electrons) emitted from the target are reflected into the plasma using the mirror effect of the electric field, and the confinement of the magnetic field formed between the targets is utilized. can easily generate low acceleration voltage and high density plasma. According to the present invention, the energy of high-speed electrons is more effectively transmitted to the plasma, and as a result, it is possible to generate high-density plasma with higher efficiency and to extract large current ions.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of an embodiment of an ion source according to the invention. Gas for generating plasma is introduced into the plasma generation chamber 7 through an inlet 8. An ion extraction grid 9 is provided at one end of the plasma generation chamber 7. In this embodiment, the grid 9 consists of two porous grids 9A and 9B, each grid is attached with an insulator 10 to the wall 7A forming the bottom of the plasma generation chamber, and the grids 9A and 9B are connected to a power source 11^. and 11B
A negative voltage is applied from A flat target 12 is provided at the other end inside the plasma generation chamber 7 , and a cylindrical target 13 is provided near the grid 9 .

The target 12 is removably fixed to a water-coolable metal support 12A, and the support 128 is fixed to the upper wall 7B of the plasma generation chamber 7 by a screw cap 12B.

The support body 12A and the wall 7B are insulated by an insulator 12C. Similarly, the target 13 is removably fixed to a water-coolable metal support 13A.
is fixed to the wall 7C by a tie-cover 13B via an insulator 13c. The protruding ends 120 and 130 of the supports 12^ and 13A also serve as electrodes, and are connected to the DC power source 14.
A negative voltage can be applied to the targets 12 and 13 from 15 and 15 with respect to the plasma generation chamber 7 . It is preferable to apply a positive voltage to the plasma generation chamber 7. When a voltage of 10 to 1200 V is applied to the grid 9A on the plasma generation chamber side with respect to the plasma generation chamber 7,
The ions accelerated by the grid have the effect of removing the film deposited on the grid.

An electromagnet 16 is provided around the outer periphery of the plasma generation chamber 7 for forming a magnetic field inside the plasma generation chamber. Electromagnet 16 and targets 12 and 13 are positioned so that magnetic flux 17 generated by electromagnet 16 crosses both target surfaces, with the magnetic flux exiting the surface of one target and entering the surface of the other. It is desirable that the plasma generation chamber can be cooled with water. In order to protect the side surfaces of targets 12 and 13 from plasma, shields 7D and 7E are preferably provided on the inner surface of the plasma generation chamber.

After the inside of the plasma generation chamber 7 is evacuated to a high vacuum, gas is introduced from the gas introduction port 8, and when the voltage applied to the target 12, 13 is increased in the magnetic field by the electromagnet 16, discharge occurs and plasma is generated. Ions in the plasma can be extracted as an ion beam 18. The magnetic flux between the targets prevents the secondary electrons (γ electrons) generated from the target surface from dissipating in the direction perpendicular to the magnetic field, and has the effect of confining the plasma, resulting in the generation of high-density plasma in low gas pressure. be done.

FIG. 2 is a sectional view of an example of a thin film forming apparatus using the ion source shown in FIG. A sample chamber 19 is connected to a plasma generation chamber 7 with an ion extraction grid 9 in between.

The sample chamber 19 and the plasma generation chamber 7 are preferably insulated.

Gas can be introduced into the sample chamber 19 through a gas inlet 20, and the sample chamber 19 can be evacuated to a high vacuum using an exhaust system 21. A substrate holder 23 for holding a substrate 22 is provided in the sample chamber 19, and a shutter 24 that can be opened and closed is provided between the substrate holder 23 and the ion extraction grid 9.

It is preferable that the substrate holder 23 has a built-in heater to heat the substrate, and also applies DC or AC voltage to the substrate 22 to apply a bias voltage to the substrate during film formation, and for sputter cleaning of the substrate. It is desirable to configure the system so that it is possible to do so.

Factors that affect plasma generation include gas pressure in the plasma generation chamber, power supplied to the target, magnetic field distribution, and distance between targets.

The energy of the extracted ions can be controlled mainly by the acceleration voltage, which is the relative difference between the voltages applied to the plasma generation chamber 7 and the ion extraction grid 9.

FIG. 3 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 explained in detail with reference to FIG.

Introduce gas into the plasma generation chamber and target 12.13
A negative voltage is applied to create an electrical discharge in the gas, ionizing the gas. When high-speed ions collide with a target to which negative voltages Va and Va' are applied, high-speed secondary electrons (γ electrons) 25 are emitted from the target surface. The γ electrons 25 emitted from this target are reflected by the electric field of both targets, and the γ electrons move back and forth between the targets while making a cycloton movement around the magnetic flux 17 running between the two targets. acts as a mirror for The γ electrons are confined between the two targets until their energy becomes smaller than the binding energy of the magnetic flux, during which time their ionization is promoted by collisions with neutral particles. Furthermore, the high-speed electron flow (electron beam) that travels back and forth between the targets further accelerates the ionization of neutral particles through interaction with plasma. As described above, high-density plasma can be generated even at low gas pressure.

In the apparatus of the present invention, a discharge can be stably formed even at a lower gas pressure on the order of 10"" Torr, and high-speed ion extraction can be achieved.

Next, the results of forming a film by extracting Aj2 ions using the ion source of the example will be described. After evacuating the sample chamber 19 to a vacuum level of 5 X 10-' Torr, Ar gas was introduced at flow rates of 2.5 cc and 5 cc per minute to reduce the gas pressure in the plasma generation chamber 7 to 5 X 10-' Torr. T
FIG. 5 shows the discharge characteristics when discharged at 10-3 Torr and 10-3 Torr. Here, the voltage applied to the flat target 12 is fixed at -300V.

All of them exhibit constant current discharge characteristics in which the discharge current increases like an avalanche from a certain voltage, indicating that high-density plasma is multiplying. In the ion source of the present invention, sufficiently high-density plasma can be generated even when the voltages applied to the cylindrical target 13 and the flat target 12 are different, as in the example shown in FIG. 5. Further, even when those voltages are the same, sufficiently highly efficient plasma generation can be realized. Sputtering was performed with a power input to the cylindrical A1 target 13 of 300 to 600 W. FIG. 6 shows an example of ion extraction characteristics. The ion extraction voltage on the horizontal axis is the relative voltage difference between the plasma generation chamber 7 and the grid 9A. As a result of fixing the energy of the extracted ions at 300 eV and forming the film at room temperature without heating the substrate holder,
The film could be deposited stably and efficiently continuously for a long time at a deposition rate of 1 to 100 m/min.

FIG. 7 shows a sectional view of another embodiment of the ion source according to the present invention, and FIG. 8 shows a sectional view of an example of a thin film forming apparatus using this ion source.

The ion source of this embodiment differs from the embodiment shown in FIG. 1 in that the targets for sputtering are two cylindrical targets 13 and 26. target 26
is removably fixed to a water-coolable metal support 26A, which is fixed to wall 7C by screw M26B and insulated from wall 7C by insulator 26C. The protruding end 26D of the support 26^ also serves as an electrode, and a negative voltage is applied to the target 26 from the power source 27 with respect to the plasma generation chamber. The magnetic flux due to electromagnet 16 exits one surface of targets 26 and 13 and enters the other surface.

FIG. 9 shows an example of the magnetic field strength distribution in the magnetic flux direction in this embodiment. The magnetic field is a divergent magnetic field.

As shown in FIG. 10, also in this embodiment, the negative voltage Va
When high-speed ions collide with a target to which , Va' are applied, high-speed secondary electrons (γ electrons) 25 are emitted from the target surface. The γ electrons 25 emitted from the targets are reflected by the electric fields of both targets, and reciprocate between the targets while making a cycloton movement around the magnetic flux 17 running between the targets. In the same way as described above, high-density plasma can be generated in a low gas pressure in this embodiment as well.

Next, the results of forming a film by extracting A4 ions using the sputter type ion source of the present invention will be described. Sample chamber 19
After evacuating the vacuum to 5 x 10-'Torr,
A: Gas is introduced at a flow rate of 5 cc and lcc per minute, and the gas pressure in the plasma generation chamber 7 is set to 5 x 1 O-3 Torr.
FIG. 11 shows the discharge characteristics when discharged at 8×10 Torr and 8×10 Torr. Here, the voltage applied to the cylindrical target on both days is set to the same value. All of them exhibit constant current discharge characteristics in which the discharge current increases like an avalanche from a certain voltage, indicating that high-density plasma is multiplying. In the sputter type ion source of the present invention, sufficiently high-density plasma can be generated even when the voltages applied to the cylindrical targets 13 and 26 are the same as in the example shown in FIG. 11, or when they are different. can.

FIG. 12 shows an example of the extraction characteristics of A1 ions.

Sputtering was performed at a power input of 300 to 600 W to the cylindrical A pattern targets 13 and 2B. The energy of extracted ions was fixed at 30θev and the film was formed at room temperature without heating the substrate holder.
The F film could be deposited stably and efficiently continuously for a long time at a deposition rate of min.

FIG. 13 shows still another embodiment of the present invention. In this embodiment, the sputtering target consists of one cylindrical target 28. The target 28 is removably fixed to a water-coolable metal support 28A. Support 28A is fixed to wall 7C by screw cap 28B and insulated from wall 7C by insulator 28C. The protruding end 28D of the support 28A also serves as an electrode,
A negative voltage can be applied to the target 28 from the power source 15 with respect to the plasma generation chamber 7 . The magnetic flux 17 generated by the electromagnet 16 exits from the surface of one end of the target 28 and enters the surface of the other end. The ion source of this embodiment operates in the same manner as the embodiment shown in FIG.

FIG. 14 shows a sectional view of still another embodiment of the ion source according to the present invention. In this embodiment, ion extraction grids 9 and 29 are provided at both ends of the ion source shown in FIG. 7, so that the ion beam is extracted from both sides of the ion source. In this embodiment, the ion extraction grid 29 consists of two porous grids 29A and 29B, to which a negative voltage is applied by power supplies 30^ and 30B, respectively.

In each of the embodiments described above, it is sufficient for the maximum value of the magnetic field formed within the plasma generation chamber by the electromagnet 16 to be approximately 100G.

A permanent magnet can also be used instead of the electromagnet 16. FIG. 15 is a cross-sectional view of an ion source in which the electromagnets in the ion source shown in FIG. 1 are replaced with two permanent magnets 31 and 32, and FIG. 3 is a cross-sectional view of an ion source in which the ion source is replaced by two permanent magnets 32 and 33. FIG. Target 12 and 1
By generating magnetic flux exiting one surface of targets 26 and 13 and entering the other surface, a high-density plasma is generated and a high-current ion beam is generated, similar to the embodiments of FIGS. 1 and 7, respectively. It can be used as a source. It is also possible to replace the electromagnets in the embodiments shown in FIGS. 13 and 14 with permanent magnets.

[Effects of the Invention] As explained above, according to the present invention, high-efficiency ion extraction can be achieved continuously and stably for a long time in low gas pressure by using sputtering using high-density plasma. . The ion source according to the present invention can be applied to continuous formation of high-quality films with little damage at high speed and high stability at low substrate temperatures, material surface modification, or etching.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the ion source of the present invention, FIG. 2 is a sectional view of an example of a thin film forming apparatus to which the ion source of FIG. A diagram showing the magnetic field strength distribution in the magnetic flux direction. Figure 4 is a diagram explaining the high-density plasma generation mechanism of the ion source of the present invention. Figure 5 is a diagram showing the discharge characteristics of the ion source in Figure 1 when the target is set to +l. FIG. 6 is a diagram showing an example of ion extraction characteristics, FIG. 7 is a cross-sectional view of another embodiment of the ion source of the present invention, and FIG. 8 is a diagram showing an example of the ion source of FIG. 7. A cross-sectional view of an example of a thin film forming apparatus, FIG. 9 is a diagram showing the magnetic field strength distribution in the magnetic flux direction in the apparatus shown in FIG. 8, and FIG. 1θ illustrates the high-density plasma generation mechanism of the ion source shown in FIG. 7. Figure 11 shows the target in the ion source of Figure 7 using AI.
Figure 12 is a diagram showing an example of the discharge characteristics when L, Figure 12 is a diagram showing an example of ion extraction characteristics, Figures 13 to 16 are
The figures are cross-sectional views showing other embodiments of the present invention, and FIG. 17 is a cross-sectional view showing an outline of a conventional Kauffman type ion source. DESCRIPTION OF SYMBOLS 1... Plasma generation chamber, 2... Filament, 3... Electromagnet, 4... Plasma, 5... Ion extraction grid, 6... Ion beam, 7... Plasma generation chamber, 8... Gas inlet, 9.29... Grid for ion extraction, 11A, 11
B, 14, 15, 27.3OA, 30t...Power supply, 12
...Flat-shaped target! 3, 21t, 2B...Cylindrical target, 16...
- Electromagnet, 17... Magnetic flux, 18... Ion beam, 19... Sample chamber, 22... Substrate, 23... Substrate holder, 25... Secondary electron, 31.32.33. ··permanent magnet. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1) A plasma generation chamber that introduces gas to generate plasma; an ion extraction mechanism provided at an end of the plasma generation chamber; and an ion extraction mechanism provided at both ends inside the plasma generation chamber. first and second targets each made of a sputtering material; at least one power source that applies a negative potential to the first and second targets, respectively, with respect to the plasma generation chamber; and an interior of the plasma generation chamber. and means for generating a magnetic field at the target and generating a magnetic flux exiting one of the first and second targets and entering the other. an ion extraction mechanism provided at an end of the plasma generation chamber; a cylindrical target made of a sputtering material provided along an inner surface of the plasma generation chamber; an ion source, comprising: a power source for applying a potential of .