JPH07118860A - Counter electrode type microwave plasma treating device and treating method therefor - Google Patents

Abstract

PURPOSE:To provide the microwave plasma treating device which lowers a substrate temp., decreases impurities, does not drop a formation speed, has high adhesion strength to the substrate and has a high nucleus formation density as well. CONSTITUTION:This microwave plasma treating device is.vertically installed with metallic circular pipes 2, 2' with hermetic caps orthogonally with the broad surface of a waveguide 1 and has a flat planar counter electrode 13 facing the substrate 7 and a terminal 14 for impressing a bias voltage to the lower circular pipe 2'. A microwave electric field is impressed perpendicularly to the substrate 7 by using this device, and further, a bias DC voltage is impressed between this counter electrode 13 and a sample stage 6, by which control of ions and electrons is executed. The rise of the temp. and forming speed are thus controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a counter electrode type microstructure for the purpose of synthesizing high density and high quality diamond which is used in a wide range of fields including the semiconductor field, optical members, tools and medical fields. TECHNICAL FIELD The present invention relates to a wave plasma processing apparatus and a processing method using the apparatus.

[0002]

2. Description of the Related Art Various methods for synthesizing diamond by a vapor phase method have been tried, but none have been completed yet. Among them, the microwave plasma CVD method has an advantage that the structure of the apparatus is simple, less impurities are mixed, and stable synthesis can be performed for a long time, but a point that the nucleation density is low is a disadvantage. There is. Further, since the substrate temperature on the sample stage that affects nucleation depends on the gas temperature of plasma and the high frequency loss characteristics of the insulator used for the sample stage, the microwave applied power and the substrate temperature are linked. There is a problem. That is, it is difficult to maintain the substrate temperature at a desired value because the substrate temperature rises as the applied microwave power increases.

In the microwave plasma CVD method, when a positive potential is applied to the silicon substrate to irradiate electrons in the plasma, diamond growth is promoted. Conversely, when a negative potential is applied to irradiate cations, β-SiC is used.
Are co-deposited.

[0004]

As described above, in the conventional diamond synthesis by the microwave plasma CVD method, the production rate is 1 when the substrate temperature is lower than 500 ° C.
It becomes 0 or more times slower, the nucleus generation density is low, and it becomes difficult to adjust the substrate temperature. The object of the present invention is to solve these problems by increasing the plasma density on the substrate surface.

[0005]

A counter electrode type microwave plasma processing apparatus according to the present invention for attaining the above object has metal circular pipes with hermetically sealed lids provided vertically above and below a wide surface of a waveguide. A microwave plasma processing apparatus, wherein a flat plate-shaped counter electrode is provided to face a substrate mounted on a sample table,
The lower electrode has a bias voltage application terminal.

According to the present invention, in the above microwave plasma processing apparatus, a flat plate-shaped counter electrode is provided so as to face a substrate mounted on a sample table, and a microwave electric field is applied vertically to the substrate. In the microwave plasma processing method, a bias DC voltage is applied between the counter electrode and the sample stage to control ions and electrons to adjust the substrate temperature and the generation rate.

The general characteristics of the microwave plasma CVD method are that, since microwaves are used, the electron density per unit volume of the plasma is high and a strong plasma can be locally generated, which is higher than that of the high frequency plasma. That is, the maximum kinetic energy of ions is extremely low. However, when the microwave electric field is parallel to the substrate, the plasma density on the substrate surface does not increase. On the other hand, when the microwave electric field is perpendicular to the substrate, the plasma density on the surface of the substrate becomes high, and the characteristics of the microwave plasma CVD method are sufficiently exhibited. Since the plasma processing apparatus according to the present invention is provided with the counter electrode, it is considered that the effect of superimposing the action of the bias DC voltage and the microwave electric field is obtained.

Further, in the conventional method, the temperature of the substrate on the sample table depends on the gas temperature of the plasma and the high frequency loss characteristic of the insulator, so that it cannot be freely adjusted. However, in the processing apparatus of the present invention, a flat plate-shaped counter electrode is provided at a position facing the sample table, and a bias DC voltage is applied between the two to adjust the substrate temperature and the generation rate.

As the counter electrode, molybdenum, tantalum, tungsten or the like having a high melting temperature can be used. In the case of diamond synthesis, a mixed gas obtained by diluting a compound containing methane and a methyl group with hydrogen gas is often used as a reaction gas.

[0010]

With the above structure, in the counter electrode type microwave plasma processing apparatus of the present invention and the processing method using the same, since the microwave electric field is perpendicular to the substrate, the plasma density on the substrate surface is higher than that of the conventional one. When a positive DC voltage is applied to the counter electrode and a negative voltage is applied to the substrate,
Electrons in the plasma are concentrated on the counter electrode and hydrogen ions are concentrated on the substrate. Graphitic carbon reacts with hydrogen to become hydrocarbons, which are regasified and their precipitation is suppressed, so that contamination of impurities is reduced. Is possible. Further, due to the carbon ion implantation effect, an intermediate layer of SiC is formed on the substrate surface, and it becomes possible to increase the nucleus generation density.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a counter electrode type microwave plasma processing apparatus according to the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a sectional view showing an example of the plasma processing apparatus of the present invention. In the experiment, a microwave power of 2.45 GHz was used, and an attempt was made to synthesize diamond by a microwave plasma CVD method. In FIG. 1, 2.45G
Metal circular tubes 2 and 2 ′ are attached vertically to the wide surface of the rectangular waveguide 1 for Hz, and a quartz tube 5 is provided inside this, and lids 3 and 4 are fitted on the top and bottom thereof, and the inside is hermetically sealed. And A water-cooled sample table 6 is embedded in the lid 4, and a substrate 7 is attached to the upper part thereof.

The inside of the sample table is cooled with cooling water.
In the figure, 8 is a cooling water inlet and 9 is an outlet. Lid 4
Is further provided with a connection hole 10 for connecting to a vacuum pump, and the inside of the quartz tube is evacuated. If this substrate is a material with good thermal conductivity, it is attached via a thin insulator.

On the other hand, a flat plate-shaped counter electrode 13 which is the feature of the present invention is attached to the upper lid 3 by a shaft 12 via an insulating layer (not shown), and the counter electrode 13 and the sample table 6 are attached. A bias DC voltage is applied between The terminal 14 attached to the lower part is a terminal for this purpose. In this embodiment, a reticulated molybdenum electrode is used as the counter electrode 13. With such a structure, the microwave electric field in the waveguide 1 is applied vertically to the substrate 7, and by applying a bias DC voltage, ions and electrons are controlled.

The upper lid 3 is also provided with a reaction gas injection hole 11 from which a reaction gas is injected.

A microwave 16 of 2.45 GHz is externally applied to the rectangular waveguide 1 by a flange 15 and a plasma 1 near the sample stage is set by a movable short-circuiter 17 at the other end.
8 is adjusted to be excited. Since the inside of the reaction chamber becomes hot due to the generation of this plasma, the water cooling pipe 19 is wound around the outside of the metal circular pipes 2 and 2'for cooling.

Comparative Example In vapor phase synthesis of diamond, the upper limit temperature for depositing diamond is limited to 1200 ° C. or lower, and above that temperature, the deposited diamond transforms into stable graphite. Therefore, a comparative experiment was attempted using the apparatus of FIG. 1 by a normal method without applying a bias voltage.
The film deposited by precipitation at 30 ° C. contained a large amount of impurities including carbon and the like.

EXAMPLE In the present invention, when a microwave electric field is applied perpendicularly to the substrate 7 and a bias DC voltage is applied between the counter electrode 13 and the substrate 7, a cubic crystal having a low impurity content at a substrate temperature of 369 ° C. Diamond (ASTM6-675) was deposited. The data at that time were as follows.

Kind of reaction gas: CH ₄ + H ₂ Reaction gas flow rate: ₂ CCM (CH ₄ ) + 198 CC
M (H ₂ ) Degree of vacuum: 0.13 torr Bias voltage: 500 V, 0.88 A Bias voltage polarity: Negative polarity on substrate side, counter electrode positive characteristic Microwave power: 700 W Precipitation growth rate: 0.78 μ / When Substrate temperature: 369 ° C Substrate material: Silicon Counter electrode: Reticulated molybdenum

When the diamonds obtained in the above comparative example and the example were compared by X-ray diffraction and Raman spectroscopy, a clear difference was observed in the precipitation growth rate and the impurity content.

That is, the Raman spectrum of the film obtained in the comparative example (conventional method, 830 ° C.) is 1332 cm ^−1.
A sharp diamond peak is observed at
There is also a wide range of impurity amorphous carbon peaks near 0 cm ^-1 . The results of X-ray diffraction were also the same, and the peak of cubic crystal diamond (ASTM6-675) was recognized and the amorphous carbon (ASTM26-1
081, ASTM 26-1082) is also present.

On the other hand, in the Raman spectroscopic spectra of the films obtained in the examples of the present invention, a sharp peak of diamond was observed at 1332 cm ^-1, and no peak of amorphous carbon was observed. Also, as a result of X-ray diffraction, only cubic diamond (ASTM6-675) and hexagonal diamond (ASTM19-268) were observed, and no peak of amorphous carbon was observed.

[0023]

As described above, the counter electrode type microwave plasma processing apparatus and the processing method using the same according to the present invention are provided with a counter electrode in a microwave plasma processing apparatus of 2.45 GHz to generate a microwave electric field. By applying a bias DC voltage between the counter electrode and the sample stage in addition to the vertical direction to the substrate, high-quality diamond can be obtained. It was possible to improve the enlargement, the improvement of the adhesion strength with the substrate, and the decrease of the temperature of the synthetic substrate. . The effects are listed below.

1. Nucleation density increases. 2. Good adhesion to the substrate. 3. Due to the small diameter of the nucleation particles, a very thin film is deposited. 4. Diamond synthesis is possible even at a substrate temperature as low as 100 ° C. or higher. 5. Good thermal conductivity. 6. Very low impurity content. 7. Films can be formed on materials with different thermal expansion, and adhesion is good.

As described above, by using the processing apparatus of the present invention, it is possible to synthesize good quality diamond particles and thin films at a relatively low cost. As its application, it can be used in many fields such as tools utilizing high hardness, high thermal conductivity, and scalpels for living bodies.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a counter electrode type microwave plasma processing apparatus of the present invention.

[Explanation of symbols]

 1 rectangular waveguide 2, 2'metal circular tube 3 upper lid 4 lower lid 5 quartz tube 6 water-cooled sample stage 7 substrate 8 cooling water inlet 9 same outlet 10 vacuum pump connection port 11 reaction gas injection port 12 shaft 13 counter electrode 14 Bias voltage application terminal 15 Waveguide flange 16 Microwave power injection 17 Mobile short circuit 18 Plasma 19 Water cooling tube

Claims (2)

[Claims] 1. A microwave plasma processing apparatus in which metal circular tubes with hermetically-sealed lids are provided vertically above and below a wide surface of a waveguide, wherein a flat plate-shaped counter electrode is provided facing a substrate mounted on a sample table. A counter electrode type microwave plasma processing apparatus provided with a bias voltage application terminal on a lower electrode. 2. In a microwave plasma processing apparatus, a flat plate-shaped counter electrode is provided so as to face a substrate mounted on a sample table so that a microwave electric field is applied perpendicularly to the substrate, and the counter electrode and the sample table are further provided. A microwave plasma processing method, characterized in that a bias DC voltage is applied between the electrodes to control ions and electrons to increase the substrate temperature and adjust the generation rate.