JPH05275193A - Plasma generating device - Google Patents

Abstract

PURPOSE:To generate sheet-form plasma by furnishing a plate-shaped insulative member in contact with one of a pair of parallel electrode plates, sending into the gap a gas chiefly containing He in atmospheric condition, and applying a high frequency power. CONSTITUTION:In contact with a casing 2 an insulative plate 3 is installed between an electrode plate 1 and the casing 2. An AC field is applied from a power supply 4, and into the discharge space 5 a gas chiefly containing He is fed from a gas container 7 via a rate-of-flow limiter 8. The electrode plate 1 is made of W, etc., and coated, if necessary, with an Au film, while the insulative plate 3 is made of alumina, etc., which prevents transition to arc discharge. Thereby the gas is sent at a uniform speed in a single direction into the gap between the plate 3 and casing 1 to establish a discharging condition by a high frequency power, and active seeds in plasma generated are pushed to outside the electrode with the gas stream. A sheet form plasma uniform in at a radical concentration is produced in the space near the electrodeplate. Therein the gap between the insulative plate and casing is selected to under 1mm and the insulative member is given the ratio of its thickness in mm to specific dielectric factor as below 0.2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is
The present invention relates to a plasma generation device that is sheet-shaped (plate-shaped) and can stably obtain low-temperature discharge plasma.

[0002]

2. Description of the Related Art Atmospheric pressure is an insulator at low electric fields,
When a high electric field such as direct current, alternating current, or impulse is applied, dielectric breakdown occurs and current begins to flow (self-sustaining discharge). Self-sustaining discharge is divided into corona discharge, glow discharge, and arc discharge. In the case of a uniform electric field, when it goes to self-sustaining discharge, all the roads are destroyed immediately, and it goes to glow discharge or arc discharge.
In the case of an unequal electric field, first, only local parts where the electric field is strong are dielectrically broken down, and corona discharge occurs. After that, if the electric field is further increased, the road will be destroyed. In the atmospheric pressure air, when the all-road breakdown usually occurs, the arc discharge often occurs rapidly without the glow discharge. This is because arc discharge is characterized by thermionic emission (existence of cathode luminescent spots) due to electrode heating caused by incident ions, but at high pressure the number of ions incident on the electrode is higher than at low pressure, so it is extremely It is considered that the electrode is heated in a short time and thermions are emitted. It is known that glow discharge occurs when the current is 2 A or less, but there is a problem that the controllability is not good. Generally, arc discharge is used for applications such as welding and cutting.

The arc discharge utilizes the high electrode temperature and positive column temperature (gas temperature) to melt the workpiece,
It is used for fusing. However, when the arc discharge is used, the temperature of the processed portion becomes as high as 2000 to 6000K, so that there is a problem that the processed object cannot be processed without heating.

Therefore, in order to enable substrate treatment and processing at room temperature, attempts have been made to stably generate glow discharge at atmospheric pressure (S. Kanazawa et.al. J. Phys. D: App
L. Phys. 21 (1988) 838-840). In order to achieve stable glow discharge at atmospheric pressure, 1. fill the discharge space with He, 2. insert an insulator between the electrodes (in the discharge path), 3. at least one electrode is needle-shaped or It is known as a necessary condition that it has a brush shape, and that the frequency of the applied electric field is 3 kHz or more. In order to prevent discharge from shifting to arc discharge in the insulator, when the applied electric field frequency is 3 kHz or more, current flows through the insulator, so making the electrode shape needle-shaped or brush-shaped makes the electric field a non-uniform electric field. This is to make it easier to start the discharge. It has also been attempted to subject the surfaces of organic substances such as polyimide and inorganic substances such as silicon to etching and the like by these methods. However, in these methods, although the treatment is carried out at atmospheric pressure, it is necessary to temporarily reduce the pressure in the reaction space to a vacuum and then fill it with a gas such as helium. In addition, the substrate is uniformly processed on the surface of the substrate, and it is not possible to selectively process a minute area.

Therefore, in order to overcome the above-mentioned drawbacks, the present inventors formed stable low-temperature plasma in an open system atmospheric pressure state without temporarily depressurizing it to a minute region. The invention of a plasma generator capable of confining, processing of a minute region, surface treatment, and etching and an etching method using the same was carried out. (Patent application 2-
286883)

In this method, electrodes made of a conductor such as metal are arranged in a concentric cylindrical shape, and a cylindrical insulator is inserted into the gap between the electrodes so as to form a concentric circle and contact the outer electrode. A gas containing helium as a main component is maintained in a flow state under atmospheric pressure in a gap between the insulator and the center electrode, and an AC electric field is applied between the electrodes to ionize the gas containing helium as a main component. Plasma is generated in the gap between the insulator and the center electrode, and an etching gas is further introduced into the plasma for use in etching.

As described above, the inventors of the present invention have researched / developed a plasma generator under an open atmospheric pressure condition, and have realized the possibility of practical application of low-temperature plasma at atmospheric pressure. There are many problems to be solved. One of them is the problem of the discharge area of plasma drawn into the atmosphere = the processing area of the plasma.

Including the inventions of the present inventors, the conventionally proposed low-temperature plasma discharge types under atmospheric pressure conditions can be roughly classified into the following two types.

1. Application of parallel plate discharge device Some proposals have been made in the past. The basic structure is such that a discharge space is formed by two parallel electrode plates with a dielectric plate installed on one side, and these are stored in a discharge vessel kept at atmospheric pressure by a plasma source gas to discharge atmospheric pressure discharge. To do. A sample to be film-formed / etched is placed on the electrode. The plasma exists only in the gaps between the facing electrode plates.

2. Utilizing Needle / Beam Plasma The past inventions of the present inventors described in the above description are typical. That is, a needle-shaped electrode is provided at the center of the void of a cylindrical electrode, and electric discharge is performed under atmospheric pressure. Beam-shaped plasma is obtained not only by the electrode gap but also by the gas flow.

The above two cases are not practical in terms of discharge area. First, in the case of the conventional parallel plate type, the discharge is a non-open system inside the container, and a container and an exhaust device are required. It is not practical in terms of applying plasma to film formation / processing etc. in a completely open system, which the present inventors have tried so far, and storing the sample together in the container provides flexibility even if the discharge area is large. Lacks.

It has been proposed in the past to perform film formation / processing in an open system by using a needle-shaped / beam-shaped plasma generator. That is, needle-shaped / beam-shaped plasma generators are arranged in series to approximate a discharge state similar to a sheet-shaped plasma. However, in the case of this method, as described above, the radical density inside the needle-shaped / beam-shaped plasma is extremely different between the central portion and the outer portion, and the difference is the difference in radical density inside the sheet depending on the position of the electrode. And appears. Therefore, it has not been realized to obtain a uniform sheet-like plasma in an open atmospheric pressure state.

[0013]

DISCLOSURE OF THE INVENTION The present invention provides a device for generating a large area sheet-like plasma in an open system at atmospheric pressure without the need for a reaction vessel and an exhaust device, thereby providing a large area in the open system. The purpose is to enable film formation or etching processing of.

[0014]

SUMMARY OF THE INVENTION The present invention provides two adjacent devices.
Gas is made to flow in a single direction and at a uniform speed between the electrode plates, and a high-frequency power applied between the electrodes creates a discharge state.The active species in the plasma generated by this discharge are pushed out of the electrode by the gas flow, and the radical concentration Relates to a structure for generating uniform sheet-shaped (plate-shaped) plasma in the space near the electrode plate.

According to the present invention, a pair of electrode plates made of parallel and opposed conductors, and a plate-shaped insulator provided in contact with one electrode in a gap formed by the pair of electrode plates, A structure in which a gas containing helium or argon as a main component is held in the gap between the insulator and the exposed electrode plate at atmospheric pressure and in a unidirectional flow state, and an AC electric field is applied between the electrodes It is characterized by having.

FIG. 1 shows a conceptual diagram of the plasma generator of the present invention. An insulator plate (3) is placed between the electrode plate (1) and the outer casing (2) in close contact with the outer casing (2), and the electrode plate (1) and the outer casing (2) are respectively arranged. An AC electric field is applied to them as an electrode from an AC power supply (4). A gas containing a rare gas such as helium as a main component is supplied to the discharge space (5) from a cylinder (7) through a flow rate controller (8) in a flow state. Further, (9) is a substrate when film formation or etching is performed, and (10) is a substrate holder. However, the configuration for installing the substrate is not limited to the format shown in the figure.

Since the electrode plate (1) is directly exposed to plasma, metals such as tungsten and tantalum which are strong against sputtering are effective. Further, when etching is carried out by adding a gas containing a halogen-based element having a strong etching action such as fluorine or chlorine to a gas mainly composed of a rare gas such as helium, gold,
The electrode plate (1) is made of a metal that is difficult to be etched by halogen-based elements such as platinum, or the surface of the electrode plate (1) is made of
It is better to coat with platinum or the like.

The surface of the electrode plate (1) has a depth of 1 to
Brush-shaped or comb-shaped irregularities of about 2 mm may be provided. This is to make the electric field between the electrode plate (1) and the outer body (2) unequal to facilitate the initiation of discharge. However, the above conditions are only desirable conditions, and the contents of the present invention are not limited as long as a discharge is generated even with a simple flat plate.

The insulator (3) is provided so that the discharge does not transfer to an arc discharge between the electrodes, and an inorganic substance such as quartz glass or alumina, or an organic substance such as Teflon, polyimide, polyethylene or polyethylene terephthalate is used. You can In addition, since there is a possibility that the temperature will rise to some extent when exposed to electric discharge, quartz glass with high heat resistance,
Alumina or the like is effective. Further, the larger the dielectric constant of the insulator is, the higher the voltage applied to the gap between the central conductor and the insulator is, so that the discharge is more easily started. Therefore, alumina and soda glass are effective. The thickness of the insulator changes according to the relative permittivity of the insulator, and if the gap between the electrode plate and the insulator is too large, it exceeds the practical output voltage of the AC power supply. is there. That is, the gap between the insulator and the center electrode is 5 mm or less, preferably 1 mm or less, and the relationship between the relative permittivity and the thickness of the insulator is as follows: thickness (mm) / relative permittivity = 1 or less, preferably 0 It is better to be less than or equal to 2.

The frequency of the high frequency power applied to the electrode plate-insulator plate can be set widely. In the present invention, a general industrial frequency of 13.56 MHz is used. However, since the composition and density of plasma differ depending on the frequency, the frequency can be selected according to the purpose.

The gas introduced into the apparatus will be described below. In the conventional atmospheric pressure discharge including the past inventions of the present inventors, it has been required that the gas containing noble gas as the main component supplied to the discharge space (5) contains 70% or more of helium. However, in the device of the present invention, the discharge by argon is slightly higher than that of helium, that is, 50 W +.
It was possible by turning on the power of several W. In addition to rare gases such as Ne, Ar, Kr, Xe, CF ₄ and CC as additive gas
It is also possible to use a gas containing halogen such as l ₄ , NF ₃ or the like, and by using the halogen-based gas, it becomes possible to perform etching on a silicon substrate or the like. When CF ₄ is used as the additive gas, there is an experimental fact that no discharge occurs when the CF ₄ concentration is 4% or more. When the target of etching is an organic substrate material, the additive gas may be oxygen. Also, CH
It is also possible to form a carbon film by adding a hydrocarbon gas such as ₄ , C ₂ H ₄ or the like. It is possible to form a silicon film by using SiH ₄ or the like, but it is highly dangerous because the film is formed in an open state.

It is desirable that the supply of the reaction gas be as uniform as possible in flow rate / velocity in the discharge space (5) of the plasma generator of the present invention. The flow velocity / flow rate is one of the factors that determine the length / uniformity of the sheet-like plasma, and the reaching distance of radicals can be controlled by controlling the supply gas flow rate. In the plasma generator of the present invention, the groove extending to the discharge space (5) is provided inside the device to make the supply gas uniform. When the cross-sectional area of the electrode-insulator gap is 8 mm ² , the gas flow rate of 200 sccm gives a flow rate of about 40 mm / sec. When the flow rate of the supply gas is increased, the flow velocity is increased in proportion to the flow rate, and the reaching distance of the radicals is also increased.

In addition to mixing the reaction gas with the rare gas and introducing it into the discharge space as described above, for example, when helium is used, the fact that metastable excited helium atoms have a long life makes it possible to use helium in a gas flow. There is also a method in which radicals are transported to a region such as the substrate surface where a reaction is desired and a reaction gas is separately supplied to the region by an external nozzle or the like. In this case, since ions do not reach the region to be reacted and only radicals can be supplied, current does not flow to the reaction target. Therefore, living organisms (human body / or animals / plants / microorganisms) are to be reacted.
You can also choose.

[0024]

【Example】

"Embodiment 1" FIG. 2 shows a sectional view of a plasma generator of an embodiment utilizing the present invention. The parallel plate electrode portion is composed of an electrode plate (1), an insulator plate (3), and an outer casing (2). The insulator plate (3) is provided in close contact with the outer casing (2). In this example, the electrode plate (1) was made of stainless steel, the insulator plate (3) was made of quartz glass, and the outer casing (2) was made of stainless steel. The electrode plate (1) is insulated from the other by three Teflon shields (20), (21) and (22).
It is connected to the V coaxial plug (11). An AC electric field (13.56 NHz) is applied to the electrode plate (1) via a coaxial cable (not shown) connected to the MHV coaxial plug (11). The helium supplied during (3) is supplied from the gas inlet (12) and through the gas groove carved in the Teflon insulator (13), which does not require the Teflon insulator (13). It also has the role of preventing electric discharge in various places.
The electrode plate holder (16) is screwed to the top plate (17). The electrode plate holder (16) and the top plate (17) are made of stainless steel and are kept at the ground potential together with the outer casing (2). The width of the electrode plate and the opposing insulator plate, that is, the width of the discharge portion is 8 mm, and the insulator thickness is 1.0 mm. Further, (9) is a substrate for etching and film formation, and (10) is a substrate holder.

When 100 sccm of helium was supplied to the above apparatus and 50 W of high frequency power of 13.56 MHz was applied, stable discharge was obtained over the entire width of the discharge part, and this state was maintained for 10 minutes or more. However, there was no trouble on the device such as overheating.

The temperature of the plasma formed by the discharge was measured by blowing the plasma on a thermocouple, and the temperature was about room temperature to 70 ° C.

Example 2 In this example, the plasma generator of the present invention was used, and argon was used as another noble gas.
This is an example of attempting discharge. As described above, in the atmospheric pressure discharge including the beam-shaped plasma generator proposed by the present inventors, it was necessary to contain 70% or more of helium gas as a raw material gas. In the generator, a helium concentration of 70% or less, or stable discharge was possible without using helium. In this example, argon gas was supplied at 100 sccm instead of the helium gas in Example 1, and an attempt was made to discharge.

When an attempt was made to discharge under the same conditions as in Example 1, it was confirmed that a stable discharge similar to that of helium was obtained at an input power of 54 W, which was slightly higher than that of helium.
In the beam-shaped plasma generator, a high electric power (100 W or more) was applied and the minute arc discharge as in the case where the argon gas was forcibly discharged was not recognized, and the overheat failure did not occur.

Although the drawing does not show the substrate to be processed or film-formed using plasma,
When using the plasma obtained by the plasma generator of this embodiment, the atmospheric pressure low temperature plasma generated in 5 may be blown onto the substrate. The plasma generator of the present embodiment shown in FIG. 2 has a size that fits in the palm of the hand, and plasma can be irradiated onto the surface of the substrate while being brought close to the substrate.

[0030]

As described above, by using the plasma generator of the present invention, it is possible to stably generate a sheet-shaped plasma discharge under atmospheric pressure conditions, and it is possible to generate a sheet-shaped plasma discharge more than conventional ones such as a beam-shaped plasma. We were able to open the way to a substrate surface treatment system where large-area etching or film formation effects are expected.

[Brief description of drawings]

FIG. 1 shows a schematic view of a plasma generator of the present invention.

FIG. 2 shows an embodiment of the plasma generator of the present invention.

[Explanation of symbols]

 1 Electrode Plate 2 External Enclosure 3 Insulator Plate 4 AC Power Supply 5 Discharge Space 7 Cylinder 8 Flow Controller 9 Substrate 10 Substrate Holder 20 Teflon Shield 21 Teflon Shield 22 Teflon Shield 11 MHV Coaxial Plug 13 Teflon Insulator 16 Electrode Plate Holder 17 Ceiling board

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigenori Hayashi, 398 Hase, Atsugi City, Kanagawa Prefecture, Semiconducting Energy Laboratory Co., Ltd. 72) Inventor Shunpei Yamazaki 398 Hase, Atsugi City, Kanagawa Prefecture Semiconductor Energy Laboratory Co., Ltd.

Claims (1)

[Claims] 1. A pair of electrode plates composed of parallel opposing conductors, a plate-shaped insulator provided in contact with one electrode in a gap formed by the pair of electrode plates, and the insulation. A configuration in which a gas containing helium or argon as a main component is maintained in the gap between the body and the exposed electrode plate in an atmospheric pressure state and in a flow direction in one direction, and a configuration in which an AC electric field is applied between the electrodes are provided. A plasma generator characterized by having.