JPH046262A - Thin film forming device - Google Patents

Abstract

PURPOSE:To generate stable plasma at a high density ;and to stably form a uniform thin film on a substrate by enclosing the outside circumference of a plasms injecting gun with a guard electrode of an earth potential at the time of forming thin films consisting of various kinds of raw materials on a substrate by plasma spraying. CONSTITUTION:A gaseous atmosphere, such as H2 or O2, is supplied from an introducing port 10 in a vacuum vessel 1 and after the gas is regulated to a specified atmosphere pressure, an injecting gas, such as Ar, is introduced from a gas introducing port 6 into the vessel. The plasma is generated between an earth electrode 4a and feed electrode 4b of the injecting by a high-frequency power source 2 for generating plasma gun 3 to melt the raw materials5a for film forming, such as Si, Ge and SiC supplied from a supplying port 5b, by which the thin film is formed on the surface of the substrate 9 in the form of a plasma jet. The outside circumference of the plasma gun 3 is enclosed by the guard electrode 12 of the earth potential in this case, by which the generation of the wasteful plasma between the feed electrode 4b and the vacuum vessel 1 is prevented. The good-quality thin film is th;us stably formed on the substrate 9 by the high-density and stable normal plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a thin film forming apparatus using a reduced pressure plasma injection method.

(B) Conventional Technology Conventionally, a plasma injection device using a capacitively coupled direct current plasma method has been used as a surface coating technology for heat-resistant and environment-resistant devices such as jet engines or for surface stabilization of artificial bones and the like. In recent years, such methods have
lid Films, 151 (1987) p343-3
As disclosed in No. 53, it has come to be applied to the formation of semiconductor thin films.

However, film formation using a plasma injection device using a capacitively coupled direct current plasma method was not originally developed as a film formation method for semiconductors, etc., and therefore, with this method, for example, large grain size polycrystalline silicon cannot be formed. Although obtained, in this state, the film quality was poor and could not be used as a semiconductor thin film for devices.

Therefore, as shown in Japanese Patent Application No. 1-100777, improvements have been made to the film forming method, such as mixing atomic elements during film formation by plasma injection to improve film quality, and "Thermal Spraying Technology" No. 8 Vol., No., lp.

The use of a plasma injection device using an inductively coupled high frequency plasma method as disclosed in Nos. 78-83 has been considered. However, in either method, the decomposition or melting of the raw materials is insufficient, and there remains room for further improvement in terms of uniformity of film quality.

In the present invention, decomposition or melting in the plasma injection device: For example, when a solid is used as a raw material, the solid is decomposed or melted into molecules or atoms by the active species of the gas that contributes to plasma generation or the heat of the plasma. This means that the gas is melted into a liquid phase, and in the case of a gas, it means that the gas is decomposed into molecules and atoms by the energy of the plasma.

(c) Problems to be solved by the invention As mentioned above, in the capacitively coupled DC plasma method, the decomposition or melting of the raw materials was insufficient, so even if atomic elements were added during film formation, However, the film quality could not be improved significantly. The reason for this is that the plasma used for decomposition or melting is generated by direct current. For example, if the raw material is solid, the degree of decomposition or melting will vary depending on the degree of electrical resistance of the raw material. In other words, in the case of a solid with low resistance, a stable DC plasma can be obtained, but in the case of a high resistance, it is not stable.

For this reason, when a plurality of solids are mixed, the degree of decomposition or melting differs depending on the type of each solid, resulting in a significantly non-uniform film quality.

Furthermore, if the raw material is a white gas and the final product is an insulator, as long as the capacitively coupled direct current plasma method is used, the film quality will be non-uniform for the same reason as described above.

Furthermore, although film formation using a plasma injection device for the inductively coupled high-frequency plasma method described above is not affected by the electrical resistance of the raw materials, the plasma temperature of the inductively coupled high-frequency plasma method is inherently low. ), it was not possible to form a good film.

In view of this problem, the present invention provides an apparatus for forming a thin film using high-density and stable plasma.

(d) Means for Solving the Problems The thin film forming apparatus according to the present invention is characterized by comprising a vacuum holding container made of a conductive material, a power supply electrode and a ground electrode disposed inside the vacuum holding container, and a plasma The apparatus includes an injection gun that decomposes or melts raw materials such as solids and liquids and sprays them in the form of a jet, a plasma generation power source connected to the power supply electrode and the ground electrode, and a substrate holder placed in the vacuum holding container. In the thin film forming apparatus that forms a thin film by exposing the surface of a substrate placed in the substrate holder to the spray, the plasma generation power source is configured with a high frequency power source, and the plasma generation power source is configured to be a high frequency power source, and the plasma generation power source is configured to be a high frequency power source, and the plasma generating power source is configured to be a high frequency power source, and the plasma generating power source is configured to be a high frequency power source, and the plasma generation power source is configured to be a high frequency power source, and the plasma generating power source is configured to be a high frequency power source, and the plasma generation power source is configured to be a high frequency power source, and the plasma generating power source is configured to be a high frequency power source. The reason is that a surrounding guard electrode is provided.

(E) Function In the present invention, in order to solve the respective problems of the conventional capacitively coupled DC plasma method and the inductively coupled high frequency plasma temperature wave plasma method, we have developed a plasma injection device using the capacitively coupled high frequency plasma method. It was adopted. As can be seen from the fact that such a device is also used to form an insulating film as a sputter deposition method, even if an insulating material is present in the discharge space,
It will not be an unstable plus 7. Furthermore, since it is a capacitively coupled method, it is possible to generate a higher density plasma compared to an inductively coupled high frequency plasma method.

However, only by replacing the plasma generation power source of the plasma injection device in the conventional capacitively coupled direct current plasma method with a high frequency source, stable +7 cannot be generated.

The reason for this is due to the plasma generation mechanism in the capacitively coupled high frequency plasma method.

The characteristics of the generation mechanism of capacitively coupled high-frequency plasma are as follows:
It is as follows. Although the plasma is maintained by an alternating electric field, there is a large difference in the mobility of electrons and ions in the plasma due to the high frequency. That is,
At frequencies of several MHz or more, electrons can follow changes in the alternating electric field, but ions, on the other hand, have a large mass and cannot do so.

Ions that can no longer be followed remain stationary in the plasma. This means that high frequency plasma cannot be maintained.

That is, in the capacitively coupled high frequency plasma method, such ions collide with the electrode and emit electrons from the electrode, thereby contributing to sustaining the plasma.

In capacitively coupled high-frequency plasma, the collision is generated by making the areas of the two electrodes asymmetric. In other words, ion sheaths are generated near the picture electrodes, and the potential difference between the two ends of the ion sheaths is originally
Although it is the same for each electrode, by making the area asymmetric, it is possible to increase only the potential at both ends of the ion sheath in the electrode with a small area. This causes the ions to travel towards the poles and collide.

Since the electrode that is bombarded by ions has a lower potential than the other electrode, the power supply electrode generally functions as the ion bombardment electrode.

The above mechanism cannot be generated simply by replacing the plasma generation power source of the conventional capacitively coupled DC plasma method plasma injection apparatus with a high frequency power source.

The present invention provides a thin film forming apparatus using a capacitively coupled high frequency plasma method that can generate such a mechanism.

(f) Example diagram shows a schematic cross section of a thin film forming apparatus using a capacitively coupled high frequency plasma method of the present invention. ( ) is a vacuum container made of conductive material capable of maintaining reduced pressure, (2N is a high-frequency plasma generation power source for generating plasma, and the frequency is I
MHz or higher, and is itself similar to the conventional one. (3) is an injection gun that generates high-frequency plasma, and the injection gun includes a high-frequency plasma ground electrode (4a) and a power supply electrode (4b). These electrodes are electrically connected to the high frequency plasma generation power source (2).

(13) is an opening through which the decomposed or melted material is injected from the injection gun (3).

The structure of the injection gun (3) will be explained in detail below. A cylindrical conductive material such as stainless steel is cut out from one end into a cylindrical shape, and the bottom part of the conductive material is cut out into a larger cylindrical shape, and the conductive material is used as a power supply electrode (4b). Further, a needle-shaped ground electrode (4a) is arranged coaxially with the power supply electrode (4b) in a space at the bottom of the power supply electrode (4b). A constant space is maintained between the earth electrode (4a) and the power supply electrode (4b) so that plasma can be stably generated.

Although not shown, the bottom of the power supply electrode (4b) maintains such a structure between it and the earth electrode (4a), and
A spacer made of an insulating material is placed to maintain insulation between the electrodes.

(5a) is the raw material for the thin film to be formed, for example, a particle size of several μm.
Silicon (Si), germanium (G e
), silicon carbide (SiC), silicon nitride (SiN)
(5b) is a reservoir containing powdered materials such as hydrogen (H8), a cylinder containing gas such as hydrogen (H8), argon (Argon), methane (CH,), etc. It is a supply port for tied raw materials. Supply port (5b
) is decomposed or melted by the plasma generated between the earth electrode (4a) and the power supply electrode (4b), and e (6) is used to inject the decomposed or melted raw material into the injection gun (3). Helium (He), argon (A r ) for more external injection.

At the injection gas introduction port for introducing injection gas such as hydrogen (H7), the injection gas is supplied from the outside via piping (not shown).

(7, is the plasma-like jet injected from the injection gun (3), (81 is a substrate holder made of stainless steel or the like, which is placed opposite to the injection gun (3), and (9) is the substrate holder (8).
There is also a substrate installed above, (10) an atmospheric gas inlet for introducing atmospheric gas into the vacuum container (1), and (11) an exhaust port for the atmospheric gas.

The above structure is basically the same as the apparatus for the conventional capacitively coupled direct current plasma method, except that a high frequency plasma power source is used.

(12) is a guard electrode provided to stabilize plasma generation by the capacitively coupled high-frequency plasma method, and is a feature of the present invention. Guard electrode (1
2) is a supply unit that is at ground potential and spouts out the decomposed melt.
l~S mm from the diameter of the opening (13) of the pole (4b)
It surrounds the injection gun (3) close to its outer periphery, leaving a large opening.

When high-frequency plasma is generated using a one-note plasma injection device that does not have a guard electrode (12) installed, the plasma will:
It is more likely to occur between the power supply electrode (4b) and the vacuum vessel (1) than between the power supply electrode (4b) and the ground electrode (4a). That is, this cause is due to the asymmetry of the area mentioned above, and the power supply electrode (4b) and the earth electrode (
The area ratio between the power supply electrode (4b) and the vacuum vessel (
1゛) is much larger, so the feeding electrode (
This is because the plasma between 4b) and the vacuum vessel (1) is more stable. That is, the guard electrode (12) is
This is to suppress plasma generation between the supply electrode (4b) and the vacuum vessel (11).The distance between the guard electrode (12) and the power supply electrode (4b) is preferably about 3 to 10 mm. The reason is that if the distance becomes larger, the vacuum container (1)
Similarly, the guard electrode (12) and the power supply are connected to the pole (
This is because plasma is also generated between the two and 4b).

In addition, the present inventors have provided the following information: @pole (4b) and ground electrode (
4a) and the area ratio between the power supply electrode (4b) and the vacuum vessel (1)
A plasma injection gun (3) larger than any of the others was manufactured, and experiments were also carried out in the case where the forced electrode (12) was not provided.

However, in such a structure, the earth electrode (4a) must be made extremely small, so that the electrode (4a) is deteriorated by the heat of the plasma.

Through the above experiments, the inventors confirmed that the use of the guard electrode (12) is unavoidable.

A specific example of thin film formation using the thin film forming apparatus of the above embodiment employing a capacitively coupled high frequency plasma method will be shown below.

After initially evacuating the vacuum container Yamauchi to about 1 o-'torr, hydrogen (H2), oxygen (Ot), or a mixture thereof is introduced as an atmospheric gas through the atmospheric gas inlet (10). ) is maintained at a constant pressure. After that, the injection gas is introduced from the injection gas inlet (6),
For example, while introducing argon (A r ), hydrogen (H8) gas, or a mixture thereof, the vacuum vessel 111
) is maintained at a constant pressure. Next, high frequency power supply (2)
to generate plasma in the injection gun (3).

After the plasma state has stabilized, when the solid or gaseous material for the thin film to be formed, or a mixture thereof, is fed into the injection gun C3 from the raw material supply port (5+), a jet-like injection (71 occurs, and a thin film is formed on the surface of the substrate (9) exposed to this spray.

Tables 1 and 2 show specific conditions for forming the thin film according to the present invention.
Shown below. In the following experiments, all experiments were conducted under the condition that the frequency and power of high-frequency power were 13,543MH2 and 3W, respectively. Table 1 shows raw materials in powder form,
In particular, in cases ■ to ■ in the same table, polycrystalline silicon films are each formed to a thickness of 2 μm on a stainless steel substrate, in case ■ an alumina film is formed, and in case ■ a yttrium-based oxide film, which is a superconducting material, is formed to a thickness of 4 μm each on a ceramic substrate. -It's something.

The pressure in the same table indicates the degree of vacuum inside the vacuum container after the injection gas and the atmospheric gas are respectively introduced into the vacuum container.

Table 1 Table 2 is not used.

On the other hand, Table 2 shows argon (Ar) and hydrogen (H,).

The figure shows the case where a diamond thin film is formed using one gas of methane (CH1) as the raw material. , is formed using only source gas.However, the atmospheric gas exhaust port is opened to suppress the pressure increase inside the vacuum container Q+ during film formation.The substrate is made of glass, and the film thickness is as follows. It is 1 μm.

All of these films are difficult to form using the above-mentioned inductively coupled high-frequency plasma method, and can be stably formed using the plasma injection apparatus using the capacitively coupled high-frequency plasma method of the present invention. It turned out that.

Table 3 shows typical physical property values of the polycrystalline silicon of Examples 1 to 1 above. In a conventional thin film forming apparatus using a capacitively coupled direct current plasma method, the film thickness unevenness, which is a measure of film uniformity, is within ±30% of the average value.
Even though it is 96, in Examples ■～■, it is 3 Q6
It was very good. Further, the alumina film according to Example (2) had a peel strength of 5 kgf, and the ytnoum-based superconducting film of Example (2) exhibited a high Tc temperature of 85. The diamond film in Table 2 had an optical gap of 5.5 eV and a good Raman shift of 1349 crn-'.

Table 3 (G) Effects of the Invention The thin film forming apparatus of the present invention uses a capacitively coupled high frequency 7 raz?
Since the raw material is decomposed or melted using the plasma method, the plasma is not affected by the electrical properties of the raw material, making it possible to form a uniform film. Furthermore, because of the high heat generated by such plasma, it is possible to obtain high thermal decomposition efficiency even for gaseous raw materials.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view of the thin film forming apparatus of the present invention. (1) Vacuum container (2) Power source for high frequency plasma generation (3)
Injection gun (4a) Earth electrode (4b) Power supply electrode
(5a) Raw materials (5b) Raw material supply port (6/Injection gas inlet (81 Substrate holder (91 Substrate (10) Atmosphere gas inlet (11) Atmosphere gas exhaust port (12)
guard to extreme

Claims (1)

[Claims] (1) A vacuum holding container made of a conductive material, disposed within the vacuum holding container, and comprising a power supply electrode and a ground electrode,
An injection gun that decomposes or melts raw materials such as solids and liquids and sprays them in a jet shape by generating plasma, a power source for plasma generation connected to the power supply electrode and the earth electrode, and a substrate holder placed in the vacuum holding container. Equipped with
In the thin film forming apparatus that forms a thin film on the surface of a substrate placed in the substrate holder by exposing the surface to the spray, the plasma generation power source is a high frequency power source, and the plasma generating power source is configured to be a high frequency power source, and the plasma generating power source is configured to be a high frequency power source, and the A thin film forming apparatus characterized in that a guard electrode is provided to surround the thin film forming apparatus.