JP2002075691A - Plasma generating equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a life of a cathode and stability of plasma by lessening electric power of a whole plasma generating equipment, by reducing quantity of a material spattered by the ion impact from the cathode, and by lessening contamination of the discharging caused with this. SOLUTION: The plasma generating equipment has an anode 2 and the cathode 1, and the cathode is built or included with the material having a wide band gap. The anode is a pipe, and is detached to the cathode in axis direction, and an insulated sheath 5 is surrounding the cathode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma generator. In a plasma generator, the cathode and the anode are separated from each other in a conditioned environment containing a low-pressure discharge gas or mixed gas. If sufficient heat and voltage are applied between these two electrodes, electron emission occurs in the gas, causing discharge and radiation. Usually, radiation is mainly U
Occurs in the V or VUV range.

[0002]

BACKGROUND OF THE INVENTION Prior art in the field of plasma displays includes U.S. Pat. No. 5,705,886, U.S. Pat. No. 5,663,611 and EP-A-07649.
There is No. 65.

Referring to FIG. The plasma generator comprises a circular tubular anode envelope 2, a cathode 1, and an outer solenoidal magnetic coil 3, reference numeral 4 indicating a reaction gas inlet. The anode 2 directly surrounds the cathode 1. All plasma generators are inside the coating chamber. The discharge gas or mixed gas flowing in the direction of arrow A is selected from inert gases such as argon, neon, and helium. The main drawback of this device is that the close proximity of the anode to the cathode causes considerable bombardment of the cathode by direct bombardment of positively charged ions. This device is very similar to a cathodic arc deposition device using a cathode as the deposition material.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the direct impact of positively charged ions on cathode 1.

[0005]

The plasma generator of the present invention includes an anode and a cathode. The cathode is made of a material having a wide band gap, and the anode is tubular and is formed in an axial direction with respect to the cathode. A remote, at least a major portion of the anode does not surround the cathode, and an insulating sheath surrounds the cathode, wherein the plasma generator is in a coating chamber.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The plasma generator of the present invention has a wide bandgap material, such as doped diamond, AIN, G, with a bandgap greater than 2 eV.
A cathode made from or containing an aN or AIGaInN alloy is used.

[0007] Dopings particularly suitable for diamond include the simultaneous doping of nitrogen, sulfur, phosphorus or boron and nitrogen. AlN, GaN or AlGaIn
Suitable doping for N alloys includes codoping of silicon, zinc or silicon + zinc.

[0008] To make such cathodes, there are, for example, chemical vapor deposition (CVD), sputtering, molecular beam epoxy techniques or physical evaporation of hydride vapors, other large crystal fabrication techniques and, for example, resistive heating or Direct or indirect heating is performed using induction heating (AC or RF), and electrons are emitted from the cathode mainly by heat emission.

A voltage is applied to such a cathode and an anode to emit electrons from the cathode mainly by field emission. In contrast to metal cathode electrodes, ion bombardment of the cathode in the device of the present invention results in enhanced secondary emission of electrons.

The magnitude of the physical properties of diamond, as compared to most other materials, represents either a minimum or a maximum of a known value for a given property. The effectiveness of diamond for electrical applications results from a selective combination of these maximums or minimums. The following table lists selected properties of diamond that are suitable for electrical applications. CVD diamond has almost the same properties as large single crystal diamonds, and at the same time has shown the potential for commercial mass production, and such CVD diamonds have a large potential for increasing the marketability of diamonds for electrical applications. Indicates an opportunity.

[0011]

[Table 1]

One of the most intriguing properties of diamond is the so-called negative electron affinity (NEA) of its (111) plane. Since the electron affinity is weak, the diamond film emits electrons in a weak electric field of 0.5 V / μm. The (111) plane not only exhibits NEA,
It has a very high resistance to poisoning its cathodic properties when exposed to atomic oxygen, atomic hydrogen, air or water. Intentional arcing of the diamond cathode cannot destroy its NEA properties. The amount of sputtering of the (111) oriented diamond tip is small, and the lifetime as an emission device is long. Diamond is an indirect bandgap semiconductor with minimal energy along the <111> direction, and the emission density of diamond is ten times that of most semiconductors (10 ⁶ A / cm ² ). (11
1) The electrons emitted on the surface have been found to be nearly mono-energy, and this has proven to be very useful in vacuum microelectronics to reduce electron beam noise. It might be. High-field drift velocities (both electron and hole) in diamond
Drift-velocities surpass that of other materials. Electron motility exceeds that of silicon, and only germanium exceeds the momentum of holes. As a high-performance, high-performance plasma-generating cathode due to very high dielectric strength, high thermal conductivity, and high radiant hardness (as a result of low radiation capture cross-sections and unsurpassed charge carrier velocities), diamond compares to metal. Or better than metal.

A plasma generator according to the present invention comprises an anode and a cathode, the cathode being made of a material having a wide band gap, the anode being tubular and being axially spaced from the cathode, and having At least a major portion does not surround the cathode, and an insulating sheath surrounds the cathode, and the plasma generator is in a coating chamber. Preferably, the anode does not surround the cathode.

It is preferable that the material having a wide band gap has a band gap larger than 2 eV.
Doped diamond; or CVD doped diamond; or Zn, Si or Zn + Si
The cathode can be made from GaN, AlN or AlGaInN alloys doped with N; or other doped nitrides, borides or oxides.

[0015] The cathode is a free-standing device made of, or containing, a wide bandgap doped material. The cathode comprises a metal frame and a layer of doped wide bandgap material on the frame. The metal is a heat-resistant metal or a metal that adheres well to a material having a wide band gap. In this case, the wide band gap material is doped diamond and the metal is tungsten, molybdenum or tantalum. The cathode is in the form of a dome, tube or cap.

The plasma generator includes an outer solenoidal magnetic coil and means for supplying a primary discharge gas or mixed gas and a secondary reaction gas or mixed gas. Such plasma generators include a magnetic homogenizer for the plasma to enhance the uniformity of the plasma.

The sheath is made of or contains quartz or a high temperature ceramic material.

The cathode is heated directly by a direct current, or directly by an inductive radio frequency signal, or indirectly by a secondary resistance heater.

When the temperature of the cathode reaches a level at which the electrons exceed the barrier of the material having a wide bandgap, electrons are emitted from the cathode. The electron emission is mainly thermal radiation, and the part with less electron emission is electric field radiation. Is preferred.

The cathode may act as a field emission emitter by applying an effective bias voltage to the anode and the cathode.

The anode and the cathode are connected to a DC power supply to control a discharge voltage and a current.

The magnetic homogenizer is a circular multi-cusp at the top of the plasma outlet.

The plasma generator of the present invention can be used in combination with another material evaporator, for example, an electron beam evaporator, a thermal evaporator or a sputtering device.

Embodiments of the present invention will be described below with reference to the drawings. Please refer to FIG. A plasma generator according to an embodiment of the present invention has a circular tubular anode envelope 2, a cathode 1, and an outer solenoidal magnetic coil 3. The anode is above the cathode and axially spaced from the cathode as shown in the figure (no part of the anode surrounds the cathode), and its insulating sheath 5 is made of quartz or high temperature ceramic material. It is made from All plasma generators are inside the coating chamber.

The cathode can be heated directly by direct current, can be induction heated at radio frequency, or can be heated indirectly using a secondary resistance heater.

When the temperature of the cathode reaches a level at which electrons can exceed the barrier of a material having a wide band gap, electrons are emitted from the cathode. This electron emission is mainly due to thermal radiation, and the electric field radiation is slight. Cathode 1
Emits electric field only by applying a bias voltage to the cathode and the anode. The primary discharge gas or gas mixture flowing in the direction of arrow A is selected from inert gases such as argon, neon, helium, and the pressure is greater than 1 Torr, preferably between about 10 ^-6 Torr and 20 Torr. Between. The electrodes 1 and 2 are connected to a DC power supply for adjusting the discharge voltage and the current. A secondary discharge gas or mixed gas selected from an inert gas such as argon, neon, or helium flows through the opening 10 of the coil 3 and the opening 11 of the anode 2 in the direction of arrow B.

The shape of FIG. 7 is modified by changing the anode 2 and the sheath 5 to reduce the direct impact of positively charged ions on the cathode 1 resulting from the proximity to the positively biased anode 2.

The solenoid magnetic coil 3 effectively acts on the electrons emitted from the cathode 1, and the ionized discharge gas flowing upward from the cathode 1 carries the electrons in a spiral motion. The reaction gas inlet 4 (at the top of the anode 2) emits a reaction gas or a mixed gas such as oxygen or nitrogen and reacts with the ionized inert gas or the mixed gas with high energy electrons. This intense ion flux helps deposit films of materials made from secondary sources. A circular magnetic multi-cusp homogenizer 6 is placed on top of the plasma outlet to enhance plasma uniformity.

One example of a wide bandgap material (bandgap greater than 2 eV) that is suitable for cathode 1 is a doped diamond film, which is a very useful material for making cathodes compared to conventional cathode materials. Creates a large amount of secondary electrons. This means that the cathode voltage drop in the plasma generator is reduced, thereby reducing the overall power of the device. This reduces the amount of material sputtered from the cathode by ion bombardment, thereby reducing discharge contamination. Less cathode material loss due to sputtering improves cathode life and plasma stability. Also, the thermal conductivity of diamond is so high that the heat generated by the indirect or direct heating mechanism is transmitted uniformly and quickly throughout the cathode.

The heat generated by ion bombardment is also quickly transmitted to the entire cathode. This high thermal conductivity results in a uniform electron emission over the entire surface of the cathode.

Referring to FIGS. 2a and 2b. Cathode 1 made from a doped wide band material is in the form of a tube. The cathode is mounted axially within the anode and uses the electrical path between them to apply the desired bias voltage. The cathode 1 of FIGS. 2a, 2b is also made of a metal frame coated with a layer of a doped, wide bandgap material. The metal frame may be a spring-type coil or a braided metal wire.

The cathode 1 can be formed in various shapes, for example, as shown in FIG.
In FIGS. 4a and 4b, the cathode is in the form of a dome and in FIGS. 4a and 4b the cathode is in the form of a dome.

In FIGS. 5a and 5b, the cathode is in the form of a fence with a gap 8 between the square pillars 7 and the pillars 7 arranged in a circle. Attach electrical contacts to the top and bottom ends of the cathode pole. The electrical contacts provide the mechanical support for the cathode.

It will be appreciated that there are other different forms of cathode. Such examples include curved tubes or corrugations.

FIG. 6 shows a magnetic multi-cusp homogenizer 6.
Will be described in detail. The magnetic multi-cusp homogenizer 6 is located between the plasma generator and the substrate. When the electric field of the magnetic multicaps is applied, the plasma distribution is made uniform. The magnetic multi-cusp is a magnetic field created by alternately poled magnets 9 as shown in FIG. This magnet creates a strong magnetic field at the boundary of the multi-cusp, but there is almost no magnetic field in the inner region. The dispersion of the plasma results in a flat plasma profile in its interior region, but the lateral magnetic field is reduced by the strong magnetic field at the edges, whereby the plasma is confined within the multi-cusp. In the example using SmCo having a magnetic field strength of 410 mT and an electron temperature of 1 eV, an ion drift velocity perpendicular to the magnetic field of about 1 m / s was obtained. This is one-fourth of the directed ion velocity and drift velocity in the region without magnetic field, and it can be said that the plasma was very effectively contained in the region inside the magnetic multi-cusp. To make a multi-cusp homogenizer having a diameter of 22 cm, it is sufficient to arrange 30 SmCo magnets.

[0036]

As described above, in the present invention, since the anode is axially separated from the cathode and at least the main portion of the anode does not surround the cathode, positively charged ions directly impact the cathode. This has the effect of suppressing the loss of cathode material and improving the life of the cathode and the stability of plasma.

[Brief description of the drawings]

FIG. 1 is a sectional view of a plasma generator embodying the present invention.

FIG. 2a is a partial longitudinal sectional view of a cathode of the plasma generator of FIG. 1;

FIG. 2b is a cross-sectional view of the cathode of the plasma generator of FIG. 1;

FIG. 3a is a partial longitudinal sectional view of a cathode according to another embodiment of the present invention.

FIG. 3b is a cross-sectional view of a cathode according to another embodiment of the present invention.

FIG. 4a is a partial longitudinal sectional view of a cathode according to another embodiment of the present invention.

FIG. 4b is a cross-sectional view of a cathode according to another embodiment of the present invention.

FIG. 5a is a partial longitudinal sectional view of a cathode according to another embodiment of the present invention.

FIG. 5b is a cross-sectional view of a cathode according to another embodiment of the present invention.

6 is a top sectional view of a magnetic multi-cusp homogenizer located between the substrate and the anode in the plasma generator of FIG. 1;

FIG. 7 is a sectional view of a conventional plasma generator.

[Explanation of symbols]

 1: Cathode 2: Anode 3: Solenoid magnetic coil 4: Opening 5: Insulating sheath 6: Multi-cusp homogenizer

Continued on the front page (72) Inventor Wang Nang Wang United Kingdom BIA3 6 Jedabrow Bath, Limpley Stoke, Midford Lane, Mart Let's (no address) F-term (reference) 4G075 AA24 BC02 CA13 CA15 CA25 DA02 EB21 EB41 EC10 EC21 EE23 FB02 FB03 FB04 FC11

Claims (21)

[Claims] An anode and a cathode, wherein the cathode is made of a wide bandgap material, the anode is tubular and is axially spaced from the cathode, and at least a major portion of the anode is a cathode. , And an insulating sheath surrounding the cathode, wherein the plasma generator is in a coating chamber. 2. The plasma generator according to claim 1, wherein the anode does not surround the cathode. 3. The plasma generator according to claim 1, wherein a band gap of the wide band gap material is larger than 2 eV. 4. Doped diamond; or CV
D-doped diamond; or GaN, AlN or AlG doped with Zn, Si or Zn + Si
The plasma generator of claim 1, wherein the cathode is made from an aInN alloy; or another doped nitride, boride or oxide. 5. The plasma generator according to claim 1, wherein the cathode is a free-standing device made of a doped wide bandgap material or containing such a material. 6. The plasma generator of claim 1, wherein the cathode comprises a metal frame and a layer of a wide bandgap material doped on the frame. 7. The metal according to claim 6, wherein the metal is a heat-resistant metal or a metal which adheres well to a material having a wide band gap.
3. The plasma generator according to claim 1. 8. The plasma generator according to claim 7, wherein the material having a wide band gap is doped diamond, and the metal is tungsten, molybdenum or tantalum. 9. The plasma generator according to claim 1, wherein the cathode has a dome shape. 10. The plasma generator according to claim 1, wherein the cathode is in the form of a tube. 11. The plasma generator according to claim 1, wherein the cathode is in the form of a cap. 12. The plasma generating apparatus according to claim 1, further comprising an outer solenoid magnetic coil, and means for supplying a primary discharge gas or a mixed gas and a secondary reaction gas or a mixed gas. 13. The plasma generating apparatus according to claim 12, further comprising a magnetic homogenizer for plasma for improving plasma uniformity. 14. The plasma generator according to claim 1, wherein the sheath is made of or includes quartz or a high temperature ceramic material. 15. The plasma generator according to claim 1, wherein the cathode is directly heated by a direct current. 16. The plasma generator according to claim 1, wherein the cathode is directly heated by the induction radio frequency signal. 17. The plasma generator according to claim 1, wherein the cathode is indirectly heated by a secondary resistance heater. 18. The cathode emits electrons when the temperature of the cathode reaches a level at which the electrons cross a barrier of a material having a wide bandgap. The electrons are mainly emitted by heat, and a portion having less electron emission is emitted by electric field emission. The plasma generator according to claim 1, wherein 19. The plasma generator according to claim 1, wherein the cathode acts as a field emission emitter by applying an effective bias voltage to the anode and the cathode. 20. The plasma generator according to claim 1, wherein the anode and the cathode are connected to a DC power supply to control a discharge voltage and a current. 21. The plasma generator according to claim 13, wherein the magnetic homogenizer is a circular multi-cusp at the top of the plasma outlet.