JP2940197B2 - Ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source, and more particularly to an ion source used for surface modification or beam machining of a semiconductor or metal.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing the configuration of a conventional ion source disclosed in, for example, Japanese Patent Application Laid-Open No. 1-307145. In the figure, 1 is a disk-shaped self-heating type hot cathode, which is a material having a high thermoelectron emission capability at a relatively low temperature, for example, La.
It is formed of B ₆ (lanthanum hexaboride). 2 is a cathode structure made of a high melting point metal material (for example, tungsten, tantalum, molybdenum, etc.) holding the self-heating type hot cathode 1, and 3 is made of a ferromagnetic material. An intermediate electrode pinched by an electric field and a strong magnetic field, 4 is a cooling part of the intermediate electrode 3 made of a non-magnetic material, and 5 is made of a high melting point metal material (for example, tungsten, tantalum, molybdenum, etc.) for protecting the intermediate electrode from plasma. Electrode nozzle part having a liner,
An anode for generating a discharge at an applied voltage between the electrodes, 7 is an opening of an anode 6 made of a refractory metal material (for example, tungsten, tantalum, molybdenum, etc.), 8 is a magnet coil for generating a strong magnetic field, and 9 is an ion source. A discharge gas inlet for introducing a gas for generating a discharge to the material, 10 is a material gas inlet for introducing a gas to be ionized, 11 is a power source for discharging an ion source, and 12 is for applying a potential to the intermediate electrode 3. , And is connected to the positive electrode of the discharge power supply 11. Reference numeral 13 denotes an insulator for insulating the cathode potential portion and the intermediate electrode potential portion, 14 denotes an insulator for insulating the anode from the intermediate electrode potential portion, 15 denotes a discharge plasma generated by low pressure arc discharge, and 16 denotes a discharge plasma. A high-density electron beam in which the plasma 15 is pinched by a strong magnetic field generated by the intermediate electrode nozzle portion 5 and the magnet coil 8, an ion extraction electrode 17 for extracting ions ionized by the high-density electron beam 16, and a high electrode 18 for extracting ions A voltage power supply 19 is an extracted ion beam.

Next, the operation will be described. For example, argon gas is introduced from the discharge gas inlet 9 so that the pressure in the intermediate electrode 3 becomes, for example, about 0.5 Torr. In this state, when a voltage of about 500 V is applied by the discharge power supply 11 with the hot cathode 1 being negative and the anode 6 being positive, a positive voltage is applied to the intermediate electrode 3 through the floating resistor 12. At this time, if the distance between the intermediate electrode nozzle portion 5 and the cathode structure 2 is set to about 2 cm, dielectric breakdown occurs near the hot cathode 1 and the central axis between the cathode structure 2 and the intermediate electrode 3, and glow discharge occurs. I do. The intermediate electrode 3 is a floating resistor 1
2, a voltage is generated across the resistor 12 by the discharge current, and the potential of the intermediate electrode 3 approaches the potential of the cathode. Therefore, a voltage is generated between the intermediate electrode 3 and the anode 6, and the discharge between the hot cathode 1 and the intermediate electrode 3 progresses to the discharge between the hot cathode 1 and the anode 6. Hot cathode 1 and anode 6
The self-heating type hot cathode 1 is heated to a high temperature by the inter-glow discharge, starts to emit thermionic electrons, transitions to arc discharge, and generates discharge plasma 15. This discharge plasma 15
Is pinched by the intermediate electrode 3 and narrowed down,
By generating a strong magnetic field between the intermediate electrode 3 and the anode 6 by the magnet coil 8, the pinch is further pinched to form a high-density electron beam 16. When the thermionic emission from the hot cathode 1 is stabilized, the material gas is introduced from the material gas inlet 10 and the flow rate of the argon gas from the discharge gas inlet 9 is reduced. The material gas collides with the high-density electron beam 16 and is ionized. Next, a high voltage of about several tens of kV is applied to the anode 6 from the discharge plasma 14 passing through the opening of the anode 6 by applying a high voltage of about several tens of kV so that the ion extraction electrode 17 has a negative potential. 19 is withdrawn. The ion beam 19 is used, for example, for modifying the surface of a metal.

[0004]

Since the conventional ion source is constructed as described above, the material gas introduced from the material gas inlet 10 passes through the intermediate electrode nozzle portion 5 to the region of the hot cathode 1. The structure is easy to flow backward. In particular, when the material gas is a material gas having a high reactivity with the hot cathode 1 such as oxygen or nitrogen, the cathode is excessively consumed and the emission of thermoelectrons from the cathode is prevented, so that ions cannot be generated stably. was there. Further, in order to operate the self-heating type hot cathode 1 stably, it is necessary to keep the pressure inside the ion source high. Therefore, it is necessary to make the opening 7 of the anode 6 small and to narrow the high-density electron beam 16 very finely. Was. Therefore, the ion source becomes an extremely small point source, and the extraction sheath surface of the ion beam is not ideally formed, which causes a problem that the ion beam diverges. In addition, in order to uniformly extract the high-current ion beam 19, it is necessary to uniformly expand the narrowed high-density electron beam 16, which results in a problem that the shape of the cup in the extraction portion and the shape of the magnetic field become complicated. There was a point.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and suppresses the backflow of the material gas to the region of the hot cathode 1, thereby preventing the cathode from being damaged and expanding the discharge plasma uniformly. To obtain an ion source capable of extracting a high-brightness ion beam. Further, it is an object of the present invention to provide a plurality of extraction holes by expanding discharge plasma and to obtain a large current ion source.

[0006]

The ion source according to the present invention has an opening smaller than the nozzle opening of the intermediate electrode through which all or a part of the electron beam narrowed down by the intermediate electrode can pass . Second with floating resistance
The intermediate electrode is provided so that the opening is located where the magnetic field intensity between the intermediate electrode and the anode is maximized, and the opening has an inner surface that expands on the anode side, so that the material gas is introduced from the inner surface, Further, an electrode for reflecting the electron beam is provided at a position facing the anode of the intermediate electrode, and the strength of the magnetic field for confining the electrons decreases from the second intermediate electrode toward the reflection electrode.

[0007]

In the ion source according to the present invention, the backflow of the material gas to the cathode region is suppressed by the second intermediate electrode having an opening smaller than the nozzle opening of the intermediate electrode to prevent the cathode from being damaged. In the ion source according to the present invention, the plasma is uniformly expanded by the second intermediate electrode, the anode, the reflective electrode, and the magnetic field shape in the area thereof, so that the current of the ion source can be increased.

[0008]

[Embodiment 1] An embodiment of the present invention will be described below with reference to the drawings. FIG.
In the above, 20 is a second intermediate electrode provided between the intermediate electrode and the anode, and 21 is an opening of the second intermediate electrode having an opening smaller than the nozzle opening of the intermediate electrode and a conical enlarged portion. And has a material gas inlet 10 on the inner surface.
Reference numeral 22 denotes a floating resistor for applying a potential to the second intermediate electrode 20, which is connected to the positive electrode of the discharge power supply 11. Reference numeral 23 denotes a reflection electrode for reflecting electrons made of a ferromagnetic material.
As a result, a magnetic field distribution is formed such that the magnetic field intensity increases once from the tip of the intermediate electrode to the reflection electrode, and gradually decreases after the maximum magnetic field intensity is obtained. FIG. 2 is a sectional view (a) near the central axis of the ion source and a distribution diagram (b) showing the magnetic field strength on the central axis in this embodiment. The opening of the second intermediate electrode has the maximum magnetic field strength. It is arranged to be located as shown. 24 is a ion beam extraction portion of the reflective electrode formed of a non-magnetic refractory metal material (e.g. tungsten, tantalum, molybdenum, etc.), one Oh <br/> Rui provided a plurality of ion beam extraction port Have been. Reference numeral 25 denotes a floating resistor for applying a potential to the reflective electrode 23, which is connected to the positive electrode of the power supply 11 for discharge. The anode 6 has the same function as the conventional one, but has an opening with a large cross-sectional area according to the expanded plasma diameter. The ion extraction electrode 17 has the same function as the conventional one, but has one or a plurality of holes according to the ion beam extraction part 24 of the reflection electrode. Reference numeral 26 denotes an extended ion source plasma containing desired ions. Reference numeral 27 denotes an ion deceleration electrode provided to prevent electrons from flowing back into the ion source through the ion beam 19, and has one or a plurality of holes according to the ion beam extraction portion 21 of the reflection electrode. 28 is an ion on the deceleration electrode 27
This is a deceleration power supply that applies a positive potential to the extraction electrode 17 .

In the ion source configured as described above, for example, argon gas is introduced from the discharge gas inlet 9 so that the pressure in the intermediate electrode 3 becomes, for example, about 0.5 Torr. A voltage of about 500 V is applied by the power supply 11 for discharging, with 6 as positive. Since a positive voltage is also applied to the intermediate electrode 3 through the floating resistor 12, a spark discharge is generated near the central axis between the hot cathode 1 and the cathode structure 2 and the intermediate electrode 3, and transitions to a glow discharge.
Since the intermediate electrode 3 is floated by the floating resistor 12, a voltage is generated across the resistor 12 by the discharge current, and the potential of the intermediate electrode 3 approaches the potential of the cathode. Therefore, a voltage is generated between the intermediate electrode 3 and the anode 6,
The discharge between the hot cathode 1 and the intermediate electrode 3 evolves into a discharge between the hot cathode 1, the second intermediate electrode 20 and the anode 6. Self-heating type hot cathode 1 by glow discharge between hot cathode 1 and intermediate electrode 3
Is heated to a high temperature, starts emitting thermionic electrons, transitions to arc discharge, and generates discharge plasma 15. This discharge plasma 15 is generated by the intermediate electrode 3 and the magnet coil 8,
A high-density electron beam 16 pinched by the strong magnetic field generated between the intermediate electrode 3 and the reflective electrode 21 forms the narrowest high-density electron beam 16 at the position of the opening 21 of the second intermediate electrode showing the maximum magnetic field strength. When the opening 21 of the second intermediate electrode is substantially the same as the opening of the intermediate electrode nozzle portion 5, the entire high-density electron beam 16 is partially provided when the opening 21 of the second intermediate electrode is smaller than the opening of the intermediate electrode nozzle portion 5. It passes through the opening 21 of the intermediate electrode. The electrons passing through the opening 21 of the second intermediate electrode are
, But cannot reach the anode 6 directly because of being constrained by the axial magnetic field.
To reach. Since the reflection electrode 23 is floated by the floating resistor 25, a voltage is generated across the resistor 25 by the flowing electron current to limit the flow of electrons. Therefore, most electrons are reflected and the second intermediate electrode 2 is reflected.
Although it is accelerated in the direction of 0, the second intermediate electrode 20 is similarly reflected because it is floating by the floating resistor 22. Since the electrons oscillate in the anode 6 in this manner, ionization is promoted to form a high-density and uniform ion source plasma 26, and finally reaches the anode 6. At this time,
As the magnetic field distribution is formed so that the magnetic field strength for confining the electrons becomes weaker as the magnetic field distribution goes from the second intermediate electrode to the reflective electrode, the high-density electron beam 16 spreads the magnetic flux from the second intermediate electrode to the reflective electrode. Accordingly, the ion source plasma is diffused into a conical ion source plasma. When the thermionic emission from the hot cathode 1 is stabilized, the material gas is introduced from the material gas inlet 10 and the flow rate of the argon gas from the discharge gas inlet 9 is reduced. Since the material gas is introduced so as to directly collide with the high-density electron beam 16, it is efficiently ionized and forms an ion source plasma 26 containing desired ions which is uniform on the front surface of the ion extraction portion 24 of the reflection electrode. Can be. Since the ion source plasmar 26 is separated from the hot cathode 1 by the second intermediate electrode 20 having a smaller opening in addition to the conventional intermediate electrode nozzle portion 5, the backflow of the material gas can be suppressed. Next, when a high voltage of about several tens of kV is applied from the high-voltage power supply 18 to the reflection electrode 22 so that the ion extraction electrode 17 has a negative potential, a high-density ion beam 19 is extracted from the ion source plasma 26. Since the ion source plasma 26 is sufficiently uniform, an ion beam with high brightness can be extracted ideally. In addition, since the ion source plasma 26 is sufficiently expanded, by providing a plurality of extraction holes in the reflection electrode extraction section 24, It is possible to easily increase the current of the ion beam 19.

In the above embodiment, the description has been given of the case where the material gas for obtaining the desired ions and the rare gas for maintaining the discharge are used. However, when extracting the ions of the rare gas, the discharge gas inlet 9 is used. Alternatively, the gas may be introduced from both the discharge gas inlet 9 and the material gas inlet 10. Also,
The source gas may be a metal vapor or a reactive gas that promotes metal sputtering.

[0011]

As described above, according to the present invention , the floating electrode having the opening smaller than the opening of the intermediate electrode nozzle is provided.
By providing a second intermediate electrode having a switching resistance and introducing the material gas to the anode side from this opening, there is an effect that the backflow of the material gas to the cathode region can be suppressed and the cathode can be prevented from being damaged. Further, by providing a reflecting electrode for reflecting the electrons passing through the second intermediate electrode and an electron confining magnetic field in which the magnetic field intensity in the axial direction becomes weaker from the second intermediate electrode to the reflecting electrode, the aperture is narrowed down. The generated discharge plasma is expanded again to produce an ion source plasma capable of extracting a large current ion beam.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an ion source according to an embodiment of the present invention.

FIGS. 2A and 2B are a cross-sectional view near the central axis of the ion source in the embodiment shown in FIG. 1A and a distribution diagram showing a magnetic field intensity on the central axis.

FIG. 3 is a sectional view showing a conventional duoplasmatron ion source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot cathode 3 Intermediate electrode 5 Intermediate electrode nozzle part 6 Anode 8 Magnet coil 10 Material gas inlet 16 High-density electron beam 20 Second intermediate electrode 21 Opening of second intermediate electrode 23 Reflecting electrode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-44935 (JP, A) JP-A-2-5331 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 27/00-27/26 H01J 37/08

Claims (4)

(57) [Claims] A hot cathode held by a cathode structure, an intermediate electrode having a nozzle portion, and an anode, wherein a spark discharge between the hot cathode and the intermediate electrode causes dielectric breakdown,
In the ion source which generates the discharge plasma by arc discharge between the hot cathode and the anode by heating the hot cathode by the glow discharge, the ion source has an axial magnetic field for confining electrons near the anode, and the intermediate electrode and Located between the anodes, all of the electron beam emitted from the cathode and narrowed down by the intermediate electrode, or located on the side of the anode facing the intermediate electrode of the second intermediate electrode and the anode through which a part passes, has a reflection electrode for reflecting electrons from the cathode, the
The second intermediate electrode has a floating resistance, and
An opening provided in the intermediate electrode for passing an electron beam is smaller than the opening of the intermediate electrode nozzle. 2. The ion source according to claim 1, wherein a coil for forming an axial magnetic field for confining electrons is provided on the intermediate electrode, further comprising an intermediate electrode made of a ferromagnetic material and a nonmagnetic high melting point metal. With the use of a reflective electrode made of ferromagnetic material with an ion extraction part made of a material, the axial magnetic field strength that confines electrons becomes stronger as it goes from the tip of the intermediate electrode to the reflective electrode, and then gradually weakens after taking the maximum magnetic field strength An ion source having a structure, wherein the second intermediate electrode is arranged such that an opening for passing an electron beam provided in the second intermediate electrode is located at a position where the maximum magnetic field intensity is exhibited. 3. The ion source according to claim 2, wherein an opening provided in the second intermediate electrode for passing an electron beam has the smallest cross-sectional area on the intermediate electrode side and the opening area on the anode side. An ion source comprising a second intermediate electrode having a shape that expands so that a product of magnetic field strengths becomes substantially constant. 4. The ion source according to claim 3, wherein said sustaining gas supply means supplies a rare gas for maintaining a discharge to said cathode portion, and is surrounded by said second intermediate electrode, anode and reflective electrode. A material gas supply means for supplying a gas to be ionized to a region for generating the ions,
An ion source, which is located on the inner surface of the intermediate electrode having an enlarged shape and is provided so that the material gas directly collides with the electron beam.