JPH0635661B2 - Thin film forming equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for forming a thin film by decomposing and combining raw material gases by discharge plasma.

2. Description of the Related Art In the glow discharge decomposition method of forming an amorphous thin film on a conductive substrate, a raw material gas is introduced into a vacuum chamber as a reaction container that maintains a high vacuum, and the raw material gas is placed opposite to the conductive substrate in the vacuum chamber. Plasma is generated by applying DC or AC power to the electrodes to perform glow discharge, and this plasma is brought into contact with a conductive substrate to form an amorphous thin film on the substrate. At this time, a cold cathode is generally used as an electrode for generating glow discharge, and the pressure of gas to be introduced is 0.1 to 1 T in order to obtain stable discharge plasma.
It is said to be orr.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In a conventional thin film forming apparatus using a high frequency discharge method, which has been most commonly used, the discharge gas pressure is 0.1 to several Torr.
Therefore, there is a drawback that a large amount of powder is generated in the process of forming an amorphous silicon film, for example. Generation of a large amount of powder mixes in the formed film, not only deteriorates the characteristics of the formed film, but also accumulates on the electrode surface and in the vacuum device, so it must be removed frequently. It was inconvenient. Furthermore, since a large amount of the raw material gas is exhausted without reacting, the utilization rate of the raw material gas is 10% or less, which is significantly expensive in terms of cost.

Means for solving the problem A hot cathode and an anode are linearly arranged in the center of a pair of plasma reflectors arranged in parallel, a magnetic field is applied in the same direction as the electric field, and a source gas is introduced to discharge. Then, the substrate is arranged around the discharge region to form a thin film.

The electrons emitted from the working hot cathode are accelerated by the positive voltage applied to the anode, and when a mesh-shaped or fine wire anode is used, most of the electrons pass through the gap between the anodes and a pair of plasmas facing each other. It is reflected by the reflector and reciprocates. At this time, since the magnetic field is applied almost parallel to the electric field direction,
The electrons reciprocate while spiraling. During this time, the electrons collide with the raw material gas and are ionized into a plasma state.
The applied magnetic field has the function of suppressing the diffusion of the generated plasma and generating a high density plasma, and at the same time 10 ^-3 To
It has the function of maintaining discharge at a low gas pressure of about rr. By placing the substrate around the generated plasma, a good quality film can be formed.

Embodiment 1 Embodiment 1 FIG. 1 shows a sectional view of an embodiment of the present invention. Each component is configured to extend in a direction perpendicular to the plane of the drawing over a predetermined length. One of 1a and 1b serves as a cathode and the other serves as an anode. The cathode and the anodes 1a and 1b are composed of fine wires of refractory metal such as tungsten wire.
In the present embodiment, three tungsten wires containing thorium were stretched substantially in parallel. Reference numerals 2a and 2b denote a pair of electron reflection plates, which are arranged substantially parallel to the cathode 1a and the anode 1b. A metal plate or an insulating plate can be used as the reflection plates 2a and 2b. Solenoid coils 3a and 3b are arranged so that the magnetic field B is applied substantially perpendicularly to the cathode 1a and the anode 1b. The solenoid coil can be replaced by a permanent magnet. Reference numerals 4a and 4b are substrates for forming a thin film. The electron reflectors 2a and 2b may be part of a vacuum container.

In such a configuration, the inside of the container is evacuated and the cathode 1a
An electric current is applied to both ends of the electrode to raise the temperature to about 2000 ° K, causing electron emission. A cathode voltage or a voltage lower than that is applied to the electron reflectors 1a and 1b. Or electrically disconnected, or electrically connected via an extremely high resistance,
By making substantially no current flow, it can serve as an electron reflector. Further, the same effect can be obtained by forming the electron reflection plate with an insulating material such as glass or ceramics. In such a structure, when a voltage of 300 to 500 V is applied to the anode 1b, electrons are emitted from the cathode 1a, and electrons are reflected while spirally moving along the magnetic force lines of the magnetic field B of about 300 gauss created by the solenoid coils 3a and 3b. Boards 2a, 2b
Reciprocate between. At this time, since the cathode 1a and the anode 1b are composed of thin wires, there are very few opportunities for electrons to flow into the anode, and therefore the traveling distance of the electron beam becomes extremely long. When the source gas is introduced under such a driving condition and the vacuum degree is kept at 10 ^-4 Torr to 10 ^-1 Torr, plasma can be generated by accelerated electron collision. In such a thin film forming apparatus, the traveling distance of electrons can be made extremely long, and therefore, even if the vacuum is extremely low compared with the conventional CVD apparatus, 10 ¹⁰ to 10 ¹¹ pieces / cm 2 can be obtained.
High density plasma of ³ can be generated.

When SiH ₄ gas diluted with hydrogen of 30% was introduced as a source gas and the gas was held at a gas pressure of 10 ⁻³ Torr for discharge, the substrates 4 a, 4 b
An amorphous silicon film can be formed on the surface of the substrate at a deposition rate of about 10 μm / min.

Example 2 The electrode structure was the same as that of Example 1, and both the cathode 1a and the anode 1b were made of thorium tungsten wire, the container was evacuated, and the same source gas as in Example 1 was introduced to the cathode and anode. Apply voltage from different power supply to both ends of
Heat to about 2000 ° K and 300-500V between both electrodes
When an AC voltage of 2 was applied, discharge was generated in the source gas as in Example 1, and an amorphous silicon film could be formed on the substrates 4a and 4b. In the present embodiment, both the cathode 1b and the anode 1b are heated and an AC voltage is applied, so that the cathode and the anode are alternately replaced in both electrodes, and uniform plasma can be generated over the entire discharge region. Further, since both electrodes alternately serve as anodes, they are heated by the discharge current, and under appropriate driving conditions, self-heating is maintained and the discharge is maintained without applying a heating voltage to both ends of the tungsten wire. There are also features. As the metal wire used for the cathode and the anode, a high melting point metal wire such as a tungsten wire, a tantalum wire, a molybdenum wire can be used. Thorium-containing tungsten wire that emits electrons at a relatively low temperature is the most suitable. Similar effects can be obtained by using a mesh-shaped refractory metal as the cathode and the anode.

In addition, SiH ₄ and Si ₂ H ₆ hydrogenated silicon and N were used as source gases.
By introducing a mixed gas of ₂ or NH _{3 and} a mixed gas of silicon hydride and O _2, a Si ₃ N ₄ film and a SiO ₂ film can be formed, respectively. A necessary film can be deposited on the surface of the substrate by introducing another source gas.

Effects of the Invention A cathode and an anode are linearly arranged in the central portion of a pair of plasma reflectors arranged substantially in parallel, and a magnetic field is applied in a direction substantially the same as an electric field, and a raw material gas is introduced to cause an electric discharge, resulting in extremely low gas Since a high-density plasma can be stably generated by pressure, a thin film of good quality can be formed at high speed without generating a large amount of powdery deposits, and it is a thin-film forming device with excellent mass productivity. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of a main part of a thin film forming apparatus in an embodiment of the present invention. 1a ... Cathode, 1b ... Anode, 2a, 2b ... Electron reflector, 3a, 3b ... Solenoid coil, 4a, 4b ...
substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Akiyama 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. A cathode and an anode are arranged in the center of a pair of electron reflectors arranged substantially parallel to each other, a magnetic field is applied in a direction substantially the same as the electric field between the both electrodes, and a source gas is introduced to discharge by the both electrodes. A thin film forming apparatus characterized by forming a thin film by disposing a substrate around the discharge region. 2. The thin film forming apparatus according to claim 1, wherein at least one of the cathode and the anode is a hot cathode. 3. The thin film forming apparatus according to claim 1, wherein the cathode and the anode are composed of a mesh or a thin wire. 4. The thin film forming apparatus according to claim 1, wherein the cathode and the anode are made of a refractory metal. 5. The thin film forming apparatus according to claim 1, wherein the hot cathode is composed of a tungsten wire. 6. The thin film forming apparatus according to claim 1, wherein the hot cathode is composed of a plurality of thin wires. 7. The thin film forming apparatus according to claim 1, wherein the hot cathode is composed of a thorium tungsten wire. 8. The thin film forming apparatus according to claim 1, wherein the hot cathode is arranged at the center of the two anodes. 9. The thin film forming apparatus according to claim 1, wherein the electron reflecting plate is electrically floated. 10. The thin film forming apparatus according to claim 1 or 9, wherein the electron reflection plate is made of an insulating material.