JP2815078B2 - DC plasma generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC plasma generator suitable for applying plasma treatment to the surface of a linear or rod-shaped substrate, and more particularly to a DC plasma generator suitable for forming a CVD film on the surface of a linear or rod-shaped substrate. The present invention relates to a plasma generation device.

[0002]

2. Description of the Related Art Conventionally, a plasma generation apparatus has been used for plasma processing or thin film formation by plasma CVD, and various apparatuses using a DC discharge, an AC discharge, a high frequency, a microwave, or the like in combination with a magnetic field are practically used. Has been

[0003]

In the case where the surface of a substrate is treated by using plasma or a thin film is to be formed on the surface, plasma is applied between opposed electrode plates by using a high frequency as conventionally used. The device that generates
Although suitable for treating the surface of a flat substrate, it is difficult to uniformly treat the surface of a linear or rod-shaped substrate, and the problem of high frequency noise is great.

[0004] Further, in a device in which a high-frequency current is caused to flow through a coil wound outside the tubular discharge chamber to generate plasma at the axial center of the tubular discharge chamber, there is a problem of high-frequency noise, and a linear or rod-shaped base is insulated. When the substrate is an object, the surface of the substrate can be treated, but when the substrate is a conductor, the amount of high-frequency power injected into the plasma tends to change, and there is a problem that stable plasma is difficult to maintain.

Further, if the substrate has conductivity, the substrate itself becomes a discharge electrode and is susceptible to damage. In particular, plasma is uniformly contacted with the surface of a long linear or rod-shaped substrate. Therefore, it is necessary to take measures such as applying a bias voltage to the substrate to reduce damage. In addition, it is necessary to apply an external magnetic field to reduce energy loss due to plasma diffusion, and there is a problem that the apparatus itself becomes large and expensive.

Accordingly, the present invention is capable of contacting a linear or rod-shaped substrate surface with a plasma having a uniform density regardless of the properties of the substrate. An object of the present invention is to provide a plasma generating apparatus capable of efficiently forming a uniform thin film by plasma CVD.

[0007]

In order to achieve the above object, the apparatus of the present invention has a cylindrical mesh anode surrounded by a larger-diameter cylindrical cathode and is coaxially arranged in a closed space, and the anode is connected to the anode. It is configured such that a DC voltage is applied between the cathode and the cathode.

The cathode in the DC plasma generator of the present invention may be a cold cathode or a hot cathode.
When the cathode is a hot cathode, it is preferable that the cathode be provided with a high melting point heating wire. For example, as shown in FIG. 1, such a cathode is formed in a tubular shape by stretching a plurality of heating wires 1b between two opposed annular electrodes 1a, and is heated to a high temperature by a heating current. Emit thermoelectrons. The diameter, length,
The number and the like can be appropriately selected according to the capacity of the cathode power supply to be used. Further, the material of the heating wire can be usually tungsten, a tungsten alloy, carbon, or the like, but is not particularly limited.

The cathode of FIG. 1 can efficiently generate plasma in order to suppress the generation of a magnetic field due to a heating current parallel to the axis in the azimuthal direction and the loss of plasma particles in the radial direction. . However, since the heating current flows in the same direction, tension is applied to the heating wires by the electromagnetic force in the radial direction, which tends to shorten the life of the heating wires. For example, as shown in FIG. 2 or FIG. Such a phenomenon can be prevented by making the current directions of the adjacent heating wires alternate. Also in this case, the magnetic field generated by the heating current can suppress the loss of plasma.

The anode in the DC plasma generating apparatus of the present invention is, for example, as shown in FIG. 4, in which annular bodies 2a, 2a smaller in diameter than the annular electrode used for the cathode are opposed to each other, and a mesh of conductive fibers is interposed therebetween. A body formed by winding the body 2b into a cylindrical shape or the like can be used. The material of the material constituting the anode is not particularly limited. However, when the apparatus is used for CVD, it is desirable that the anode be formed of a metal having corrosion resistance to the source gas used.

In the DC plasma generating apparatus of the present invention, the cylindrical anode and the cylindrical cathode are sealed in a sealed container that can be sealed and evacuated so that the anode is enclosed inside the cathode while being insulated from each other. They are arranged coaxially as shown in FIG. At this time, the distance between the anode and the cathode can be appropriately selected so as to be adapted to the voltage applied to the discharge power supply 3, and can be usually about 5 to 10 mm regardless of the diameter of the anode or the like. Reference numeral 4 denotes a heating power supply.

The above-mentioned closed container can withstand a vacuum pressure of at least 10 ^-6 Torr or less, and a member for supporting a linear or rod-shaped substrate is provided at the center axis position of the anode.
Further, it is desirable to provide a means for introducing a gas material for CVD film formation and to be formed of a material having sufficient corrosion resistance to such a gas.

[0013]

According to the DC plasma generating apparatus of the present invention, thermoelectrons are emitted from the heated cathode as necessary.
The thermoelectrons are accelerated by the DC voltage applied to the anode, and are concentrated near the axis of the cylindrical anode to ionize the atmospheric gas, thereby obtaining a columnar DC discharge plasma having an open end. Such a plasma is dense and is distributed at a uniform density in the longitudinal direction, so that it is suitable for performing a uniform treatment on the surface of a linear or rod-like substrate, and a uniform thin film formed by plasma CVD is uniformly formed. It is suitable for forming.

[0014]

【Example】

(First Embodiment) Stainless steel annular electrode 1 having a diameter of 70 mm
a, a cathode 1 having a structure as shown in FIG. 1 formed by using 24 tungsten filaments 1b each having a diameter of 0.2 mm and a length of 50 mm and being uniformly stretched so as to form a cylindrical shape.
And a stainless steel ring 2a, 50 mm in diameter,
The anode 2 having a structure as shown in FIG. 4 formed by winding a 60-mesh stainless steel wire net 2b to a length of 50 mm between a and a is coaxially assembled inside the cathode 1 as shown in FIG. Was installed in a vacuum vessel having a lining, and connected to a discharge power source 3 and a heating power source 4 to assemble a plasma generating apparatus of the present invention.

After the inside of the container is evacuated, hydrogen is introduced to 0.06 Torr, a current of 120 A in total is applied to the cathode to heat the filament to about 2500 ° C., and a positive voltage of 25 V to the cathode is applied to the anode. By applying the voltage, plasma was generated in the internal space of the anode. When the plasma density was measured in the radial direction from the axial position by the Langmuir probe method, the result as shown in FIG. 6 was obtained.

(Second Embodiment) A cathode in which 24 conductive carbon fibers (Nippon Oil Co., Ltd., Granox XN40) are uniformly stretched so as to have a cylindrical shape as in the first embodiment, instead of using a tungsten filament. A plasma generator was assembled in exactly the same manner as in the first embodiment, except that the plasma generator was used. When the plasma density in the internal space of the anode was measured using this apparatus in the same manner as in the first embodiment, the same results as in the first embodiment were obtained.

(Third Embodiment) Eight tungsten filaments 6d having a diameter of 0.2 mm and a length of 50 mm are provided between a stainless steel annular electrode 6a having a diameter of 70 mm and a stainless steel annular electrode 6b having a diameter of 70 mm. To form a cylindrical shape at an equal interval, and 10 times more than the annular electrode 6b.
using eight tungsten filaments 6e having a diameter of 0.2 mm and a length of 60 mm between an annular electrode 6c of stainless steel also having a diameter of 70 mm and an annular electrode 6a having a diameter of 70 mm,
As shown in FIG. The cathode 6 having the structure as described above was formed. Then, an anode having a structure as shown in FIG. 4 was combined, a heating power source was connected between the annular electrode 6b and the annular electrode 6c, and a plasma generating apparatus similar to that of the first embodiment was assembled.

After the inside of the container is evacuated, hydrogen is introduced to
At Torr, a current of 40 A was passed through the cathode to heat the filament to about 2500 ° C., and a positive voltage of 25 V was applied to the anode to the anode to generate plasma in the internal space of the anode. When the plasma density at the axial center was measured by the Langmuir probe method, a value of 10 ⁹ / cm ³ was obtained.

[0019]

According to the plasma generating apparatus of the present invention, a hollow cylindrical reticulated anode is coaxially arranged by surrounding it with a larger-diameter cylindrical cathode, so that the space in the anode has a uniform density in the longitudinal direction. Can be generated. Therefore, a uniform plasma treatment can be applied to the surface of the linear or rod-shaped substrate mounted at the axial position, and any material can be used regardless of whether the substrate is conductive or non-conductive. There is an advantage that plasma processing including CVD can be performed without any problem.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a structure of a cathode in a plasma generation device of the present invention.

FIG. 2 is a diagram showing another example of the structure of the cathode in the plasma generation device of the present invention.

FIG. 3 is a diagram showing another example of the structure of the cathode in the plasma generation device of the present invention.

FIG. 4 is a diagram showing an example of the structure of an anode in the plasma generation device of the present invention.

FIG. 5 is an explanatory diagram showing a combination and wiring of an anode and a cathode in the plasma generation device of the present invention.

FIG. 6 is a graph showing a density distribution of plasma generated in the plasma generation apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode 1a Toroidal electrode 1b Heating wire 2 Anode 2a Toroidal body 2b Reticulated body 3 Discharge power supply 4 Heating power supply 5 Cathode 5a Toroidal body 5b Heating wire 6 Cathode 6a, 6b, 6c Toroidal electrode 6d, 6e Heating wire 6f Ceramic insulation tube

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-88955 (JP, A) JP-A-3-24271 (JP, A) Japanese Utility Model 1983-68958 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) H05H 1/46 C23C 16/50

Claims (4)

(57) [Claims] 1. A structure in which a cylindrical reticulated anode is coaxially arranged in a closed space by surrounding it with a larger-diameter cylindrical cathode, and a DC voltage is applied between the anode and the cathode. Characteristic DC plasma generator. 2. The DC plasma generator according to claim 1, wherein the cathode is a cold cathode. 3. The DC plasma generator according to claim 1, wherein the cathode is a hot cathode. 4. The DC plasma generator according to claim 3, wherein the cathode is provided with a heating wire.