JP3772192B2 - Wall-contact type electrode in phase control multi-electrode type AC discharge device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a new discharge device that efficiently and stably generates high-density, large-capacity, weakly ionized low-temperature plasma, and more particularly to a discharge electrode thereof.
[0002]
[Problems to be solved by the invention]
In a weakly ionized low temperature plasma under a low gas pressure, the neutral gas temperature is about room temperature, which makes it possible to treat various materials with plasma without causing thermal deformation or alteration. This feature is very useful in the treatment of particularly heat-sensitive materials such as fibers and plastics and the formation of a film on the surface.
[0003]
In these film formation technologies using low temperature plasma, increasing the density of low temperature plasma occupies an important position. This is because if high-density plasma is obtained, discharge can be maintained under a lower pressure, and the film quality of various coatings and the deposition rate can be improved.
[0004]
Therefore, conventionally, as seen in magnetron discharge devices, a separate magnetic field has been applied to increase the density of low-temperature plasma.
The magnetron discharge device is intended to improve the ionization efficiency by causing the electron to drift by applying a magnetic field orthogonal to the electric field and increasing the probability of collision with gas atoms. Thus, it is possible to maintain the discharge and realize high speed and low temperature of the film formation.
[0005]
The shape and arrangement of electrodes for generating low-temperature plasma in conventional discharge devices, including this magnetron discharge device, vary depending on the requirements of the application target, but a flat or cylindrical electrode group is arranged in a circle or a straight line. It was common to place.
[0006]
These electrodes have low cooling efficiency due to their shape and arrangement, and are not cooled so much so that a large amount of power cannot be input and the discharge area is small, so that a high-density plasma is uniformly generated between the electrodes over a wide range. It was difficult.
[0007]
In the case of a magnetron discharge device, it is necessary to cool the magnet attached to the electrode so that the temperature of the magnet is kept below the Curie temperature even when the electrode is heated by discharge. In addition, moving the magnet to rotate the outer periphery of the circumferentially arranged electrode or sliding the back of the linearly arranged electrode has the effect of making the plasma uniform. It was difficult to move the magnet by the mounting method.
[0008]
Therefore, the applicant divides the discharge electrode into a plurality of electrode pieces, and closes and fixes the discharge electrode to the inner wall of the discharge chamber via a thin-film insulating sheet, thereby increasing the cooling efficiency of the electrode and increasing the discharge area. An application for a wall-contact type electrode having the feature of facilitating the use of a magnet was first filed.
[0009]
This wall-contact type electrode supplies a phase control (array) AC power source to an electrode attached in close contact with the wall, so that there is a potential difference between adjacent electrodes.
If a conductive thin film or the like adheres to the insulating sheet in the gap between the electrodes by sputtering during discharge, the electrodes are short-circuited.
Accordingly, in order to always maintain the electrical insulation on the insulating sheet in the gap during discharge, it is necessary to provide some protection to the gap.
[0010]
Accordingly, the present invention has been made for the purpose of protecting the insulating sheet exposed to the gap between the electrodes from adhesion of sputtered particles by devising the shape and arrangement of the discharge electrodes.
[0011]
[Means for Solving the Problems]
In order to achieve this object, the present invention is configured as follows.
[0012]
That is, in a phase control multi-electrode type AC discharge device in which a plurality of electrode pieces are closely attached and fixed to a discharge chamber wall via a thin-film insulating sheet, and a phase control multi-output AC power source is supplied to each electrode piece. ,
Concavities and convexities are formed on the side surfaces of the electrode pieces, and the concavities and convexities are combined so that adjacent electrode pieces are not in contact with each other, and the insulating sheet exposed in the gap between the electrode pieces is covered with the electrode pieces. This is a wall-contact electrode.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
1 and 2 are a cross-sectional view (A-A 'plane in FIG. 2) and a vertical cross-sectional view (B-B' plane in FIG. 1) of a cylindrical discharge device embodying the present invention.
In the discharge device 1, six pieces of cross-sectional arc-shaped divided electrodes 2 are arranged concentrically with a slight gap 2 a, and are closely fixed to an inner wall of a cylindrical vacuum vessel 4 through an insulating sheet 3.
As shown in FIG. 1, the side surface of the divided electrode 2 is inclined so that the insulating sheet 3 exposed to the gap 2a does not directly face the discharge region.
Thereby, the insulating sheet 3 exposed to the gap 2a is protected from adhesion of sputtered particles and the like.
[0015]
The vacuum vessel 4 forms a water-cooled double tube, and the cooling water 5 is flowed to cool the six pieces of divided electrodes 2 that are in close contact with the inner wall of the vacuum vessel 4.
On the outer wall of the vacuum vessel 4, six rod-shaped magnets 6 arranged with the polarities adjacent to each other are fixed in close contact with the outer wall at the back of the gap 2 a, and the outer periphery thereof is a cylindrical magnetic shield tube 7. Cover with.
[0016]
Six phase-controlled AC power supplies (not shown) having phases that are shifted by 1/6 period and having the same amplitude are connected to the six pieces of divided electrodes 2 via feeder lines (not shown).
[0017]
The discharge device of the present invention is configured as described above, and the inside of the vacuum vessel 4 is evacuated by an exhaust device (not shown), and phase control alternating current is supplied to the six pieces of divided electrodes 2 to supply discharge electric energy.
As a result, as shown in FIG. 3, a stable AC glow discharge is generated along the inner wall of the vacuum vessel 4.
[0018]
FIG. 3 shows a state of confinement of magnetic field lines and discharge (plasma) in a cross section (A-A ′ plane in FIG. 2) of the cylindrical discharge device of the present invention.
In the drawing, a straight line with an arrow and a symbol indicating the vertical direction indicate the direction of a circumferential magnetic field and a radial electric field in the vicinity of the central portion of the divided electrode 2, and a indicates a discharge (plasma) region.
Since the polarities of the adjacent magnets 6 are opposite, the lines of magnetic force can cover the divided electrodes 2.
Accordingly, the discharge is confined in the central portion in the vicinity of the surface of each divided electrode 2.
The direction of the alternating electric field in the vicinity of the divided electrode 2 is the positive or negative direction (radial direction) substantially perpendicular to the surface of the divided electrode 2 because the potential difference with the divided electrode 2 at the opposite side is the largest.
[0019]
FIG. 4 shows an example of a cross-sectional view of the wall-contact type electrode of the present invention.
In this wall-contact type electrode, concavities and convexities provided on the side surfaces of the electrodes 2 are combined so that adjacent electrodes 2 are not in contact with each other, and the insulating sheet 3 exposed in the gap between the electrodes 2 is covered with the electrodes 2.
This prevents the insulating sheet 3 exposed in the gap 2a between the planar view electrodes 2 from directly facing the discharge region.
[0020]
Since this wall-contact type electrode looks like there is no gap between the electrodes 2 when the wall surface of the discharge chamber 4 is viewed from the center of the discharge region, the ratio of the total area of the electrode 2 to the wall area is substantially 100%. it can. Accordingly, it is possible to generate a discharge uniformly along the surface of the electrode 2 or to discharge sputtered particles uniformly to the discharge chamber 4 side of the electrode 2 using the electrode 2 as a target.
[0021]
Here, there is a concern about the occurrence of discharge (sustainment) in the gap 2a of the narrow electrode 2, but there is no concern if the electron ionization avalanche cannot grow sufficiently in the distance between the gaps 2a.
In general, the distance between the gaps 2a where the electron ionization avalanche grows sufficiently and the sustained discharge occurs depends on the gas pressure and can be obtained from Paschen's experimental law.
In the case of a low gas pressure, the distance between the gaps 2a for generating the sustained discharge becomes large. Therefore, the smaller the gap 2a between the adjacent electrodes 2 in FIG.
[0022]
When the gas pressure is high and discharge in the gap 2a of the electrode 2 becomes a problem, an insulating film (SiO2 or the like) is applied to the surface of the electrode 2 on both sides of the gap 2a to prevent the occurrence of discharge.
[0023]
5, 6, and 7 show a modification of the practical electrode 2.
As the unevenness of the gap 2a from the discharge region to the insulating sheet 3 becomes more complicated, the inflow of sputtered particles or radical particles into the insulating sheet 3 can be suppressed, but it takes time to manufacture and is not practical.
[0024]
FIG. 5A is an example in which a U-shaped unevenness is provided at the center of the side surface of the electrode 2, and FIG. 5B is an example in which the side surface of the electrode 2 is taken in and out in a stepped manner.
FIG. 6A is an example in which a concave and convex shape is provided at the center of the side surface of the electrode 2, and FIG. 6B is an example in which the side surface of the electrode 2 is inclined.
FIG. 7A is an example in which a semicircular unevenness is provided in the center of the side surface of the electrode 2, and FIG. 7B is an example in which the side surface of the electrode 2 is taken in and out in an arc shape.
However, the rounded portion of the electrode 2 is appropriately rounded so that the electric field is not concentrated.
Among the electrodes 2 described above, practicality of the form in which the gap 2a of the electrode 2 in FIG.
[0025]
In FIG. 8, gas is supplied from the insulating sheet 3 in the gap 2a of the electrode 2 to the inside of the apparatus, and the sputtered particles and radical particles that attempt to flow into the gap 2a of the electrode 2 from the discharge region are repelled (blocked) by the supply flow. A method for protecting the insulating sheet 3 in the gap 2a will be described.
In this method, an insulating pipe (ceramic or the like) 2b having small holes at equal intervals on the surface is mounted on an insulating sheet 3 in the gap 2a, and gas is allowed to flow out of the small holes in the pipe 2b to discharge the inside of the discharge vessel 4 To supply gas. At this time, the gas is exhausted to the outside of the discharge vessel 4 by a pump, and the gas pressure inside the discharge vessel 4 is maintained at a necessary pressure.
This method is effective when the gas flow is large to some extent and it is easy to install a device that uniformly supplies gas along the gap 2a of the electrode 2.
[0026]
FIG. 9 shows a method for protecting the insulating sheet 3 in the gap 2a by providing a pedestal 2c between adjacent electrodes 2 and installing a cover 2d.
This method is a direct method. Regardless of the material of the cover 2d being conductive or non-conductive, a gap is maintained between the cover 2d and the electrode 2, and the electrical insulation between the cover 2d and the electrode 2 is maintained. Keep. This is because even in the case of the nonconductive cover 2d, a conductive thin film or the like may adhere to the surface.
[0027]
The cover 2d is configured to be detachable so that it can be removed and replaced after sputter particles or the like have accumulated to some extent.
The covers 2d installed between the electrodes 2 may be removed one by one. For example, as shown in FIG. 10, a plurality of covers 2d are formed into a bowl shape, and the electrodes 2 are detachable. You may attach to the gap | interval 2a.
[0028]
As the material of the cover 2d, a heat-resistant material (such as molybdenum) that hardly generates gas or spatters even when exposed to electric discharge is used. Here, if the structure of the cover 2d is made mesh-like (net-like), the gap 2a can be easily evacuated, and dust generated inside the apparatus can be taken into the mesh gap.
[0029]
【The invention's effect】
The wall-contact type electrode of the present invention has the above-described configuration, and forms irregularities on the side surfaces of the electrode pieces, and these irregularities are combined in a gap between the electrode pieces so that adjacent electrode pieces are non-contacting and overlapping. The exposed insulating sheet is covered with this electrode piece.
Therefore, according to the present invention, since the insulating sheet exposed in the gap between the electrodes does not directly face the discharge region in plan view, the insulating sheet exposed in the gap between the electrodes is protected from adhesion of sputtered particles and the like.
In addition, when the wall-contact type electrode according to the present invention is viewed from the center of the discharge region, there is no gap between the electrodes, so the ratio of the total area of the electrode to the wall area is substantially 100%. Can be.
For this reason, discharge can be uniformly generated along the electrode surface, or sputtered particles can be uniformly discharged to the discharge chamber side of the electrode using the electrode as a target.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cylindrical discharge device of the present invention.
FIG. 2 is a longitudinal sectional view of a cylindrical discharge device of the present invention.
FIG. 3 is a diagram showing lines of magnetic force and a state of discharge of a cylindrical discharge device.
FIG. 4 is a cross-sectional view of a wall-contact type electrode of the present invention.
FIG. 5 is a cross-sectional view of a modification of the wall-contact type electrode of the present invention.
FIG. 6 is a cross-sectional view of another modification of the wall-contact type electrode of the present invention.
FIG. 7 is a cross-sectional view of another modification of the wall-contact electrode of the present invention.
FIG. 8 is a diagram showing a method for protecting an insulating sheet in an electrode gap by a gas flow.
FIG. 9 is a diagram showing a method for protecting an insulating sheet in an electrode gap with a cover.
FIG. 10 is a view showing a cover formed in a bowl shape.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Discharge device 2 Divided electrode 3 Insulation sheet 4 Vacuum vessel 5 Cooling water 6 Magnet 7 Magnetic shield

Claims (1)

In a phase control multi-electrode type AC discharge device in which a plurality of electrode pieces are closely attached and fixed to a discharge chamber wall via a thin film insulating sheet, and a phase control multi-output AC power supply is supplied to each electrode piece.
Concavities and convexities are formed on the side surfaces of the electrode pieces, and the concavities and convexities are combined so that adjacent electrode pieces are not in contact with each other, and the insulating sheet exposed in the gap between the electrode pieces is covered with the electrode pieces. A wall-contact type electrode characterized by that.

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