CVD apparatus and method for forming CVD film

Heretofore, silicon nitride film formed by low pressure plasma CVD has been used for an antireflection film of a solar battery. But it is difficult to reduce the production cost of a solar battery, because, in a low pressure process, facility cost and process cost are expensive. As disclosed, a nitride film is formed by atmospheric pressure plasma CVD using dielectric barrier discharge generated by a plasma head where a plurality of plasma head unit parts is installed in parallel to generate plasma by applying electric field or magnetic field via a dielectric member. Stable glow discharge is formed even under atmospheric pressure by dielectric barrier discharge. And nitride film deposition under atmospheric pressure and low cost production of a solar battery is materialized by using dielectric barrier discharge and by reacting different plasmas generated from plasma supply openings laying side-by-side.

TECHNICAL FIELD

The present invention relates to an atmospheric CVD apparatus using dielectric-barrier discharge plasma and a method for forming CVD film using the plasma, and more particularly, a method for forming a nitride film using an atmospheric CVD apparatus.

CITATION LIST

Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. 1983-220477

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-110671

Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-176119

Patent Document 4: Japanese Unexamined Patent Application Publication No. 2008-98128

Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-39993

Patent Document 6: Japanese Unexamined Patent Application Publication No. 1988-50025

BACKGROUND ART

In recent years, solar power generation has been widely used as clean energy serving as a substitute for oil-based energy having many problems such as resource depletion and the emission of greenhouse gases. Patent document 1 discloses a method to enhance energy conversion efficiency by using silicon nitride film for an antireflection film of a silicon solar battery. Previously, in plasma CVD processing to forma silicon nitride film, a deposition process has been done under reduced pressure of 10−2to several Torr in order to create stable plasma. Therefore, production cost reduction has been difficult because an expensive equipment and pressure reduction process in a deposition chamber are necessary. For more widespread use of solar power generation, it has been desired to develop a CVD apparatus and a production method to produce solar battery at lower cost.

Patent document 2 discloses a technology to produce a thin film by atmospheric CVD.FIG. 12shows a cross-sectional diagram of an existing atmospheric CVD apparatus disclosed in patent document 2. In general, it is known that stable plasma state cannot be kept under atmospheric pressure when most gases are used except specific gases such as helium, and the plasma state instantly moves into an arc discharge state. In a CVD apparatus as illustrated inFIG. 12, a pair of electrodes114and115are placed facing each other in a chamber111. And material gases are introduced from gas inlets111and plasma118is generated via solid dielectric members116,117by applying electric field on electrodes114,115. Then a thin film120is formed on a substrate121by the plasma118being sprayed from a supply opening119. Stable glow discharge plasma can be generated regardless of the difference of gas by applying electric field of the electrode via solid dielectric body. A method to form a nitride film is described in embodiment 3 of Patent Document 2. In this method, plasma is generated by introducing a mixture gas of silane gas and ammonia gas diluted by argon gas into a container111. However, silicon plasma and nitrogen plasma do not react on the substrate but mainly react in the container according to this method. Therefore almost no nitride film can be formed on the substrate.

In Patent Document 3, a technology to produce thin film by atmospheric CVD is also disclosed. The deposition method disclosed in Patent Document 3 is film deposition in discharged space, while the deposition method disclosed in Patent Document 2 is film deposition by plasma spray. Accordingly, a nitride film deposition on the substrate becomes possible, but a difference of film deposition rate between regions around gas inlet and gas outlet becomes notable. This has lowered the film deposition uniformity when several different gases are introduced in those cases such as a nitride film deposition. And a substrate is subject to damage from plasma because the substrate is placed in a discharged space.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

The object of this invention is to provide an atmospheric CVD apparatus which enables film formation with high deposition rate and high uniformity. The object of this invention is mainly to provide a CVD apparatus which enables nitride film formation under atmospheric pressure.

Means for Solving Problem

Present invention (1) is a plasma CVD apparatus wherein a desired number of flow passage plates are stacked and discharge electrodes are placed at the gas outlet side of the flow passage plates, each discharge electrode composed of a ceramic member having a hollow portion where an electrode wire is placed without contact with the ceramic member.

In one embodiment, a gas flow passage is formed along the side of the flow passage plate.

Present invention (3) is the plasma CVD apparatus wherein the hollow portion is in a vacuum state.

In a different embodiment, gas is enclosed in the hollow portion and the gas is noble gas.

In another embodiment, the pressure in the hollow portion is reduced to less than or equal to 250 Torr.

In a further embodiment, the noble gas is Ar or Ne.

In a further embodiment, one terminal of the electrode wire was connected to a metal foil, the end of the metal foil functions as an external extraction terminal, and the metal foil is sealed in contact with narrowed part of the ceramic member.

In another embodiment, the electrode wire is made of Ni or Ni alloy.

In yet another embodiment, the electrode wire is made of W including Th or ThO.

In yet a further embodiment, the content of Th is less than or equal to 4 weight %.

In a further embodiment, the electrode wire is formed with coil-like shape.

In another embodiment, a layer made of emitter material is formed on the surface of the electrode wire, and the emitter material is material with smaller work function than the material of the electrode.

In yet another embodiment, the emitter material is material with perovskite-type crystal structure.

In yet a further embodiment, the emitter material is more than or equal to one chemical compound selected from the chemical compound group comprising TiSrO, MgO, TiO.

In a further embodiment, the emitter layer is formed by a process wherein material of emitter layer is torn into pieces in a mortar, and resultant powder is solved in water, and the solution mixed with glue is coated on the surface of the electrode wire, and emitter layer is formed by sintering of coated wire.

In another embodiment, the emitter layer is formed by MOCVD.

In yet another embodiment, the metal foil is made of Mo or Mo alloy.

Present invention (18) is a plasma CVD apparatus wherein a desired number of flow passage plates are stacked and discharge electrodes are placed at the gas outlet side of the flow passage plates, each discharge electrode composed of a ceramic member where an electrode wire or a metal foil are enclosed inside the ceramic member.

In yet a further embodiment, a gas flow passage is formed along the side of the flow passage plate.

In a further embodiment, the metal foil is made of Mo or Mo alloy.

In another embodiment, the ceramic member is made of quartz.

In yet another embodiment, the ceramic member is made of translucent alumina.

In yet a further embodiment, the flow passage plate is made of heat resisting metal.

In a further embodiment, the flow passage plate was made of ceramic.

In another embodiment, the flow passage plate is equipped with a mortise at the gas outlet side, the discharge electrode is equipped with a tenon at one side, and the discharge electrode is connected with the flow passage plate by setting in using tenon and mortise.

In yet another embodiment, the discharge electrode is connected with the flow passage plate using a retainer.

In yet a further embodiment, the flow passage plate and the discharge electrode are fabricated by integral molding.

In a further embodiment, the gas flow passage the flow passage plate is processed after the integral molding of the flow passage plate and the discharge electrode.

In another embodiment, the gas flow passage the flow passage plate is processed at the same time as the integral molding of the flow passage plate and the discharge electrode.

In yet another embodiment, a substrate is placed facing to the discharge electrode.

In yet a further embodiment, the substrate can be conveyed.

In a further embodiment, the substrate is a substrate with band-like shape which is conveyed by roll-to-roll process.

In another embodiment, the apparatus is an apparatus for the deposition of silicon nitride film.

In yet another embodiment, the apparatus is an apparatus for the deposition of silicon film.

In yet a further embodiment, at least nitrogen source gas and silicon source gas are supplied through the flow passage plates, and nitrogen source gas and silicon source gas are respectively supplied through different flow passage plates.

In a further embodiment, at least mixed gas of nitrogen source gas and silicon source gas is supplied through the flow passage plates.

In another embodiment, the silicon nitride film or silicon film is deposited consecutively.

In yet another embodiment, the gas outlet is placed downward.

In yet a further embodiment, the gas outlet is placed toward lateral direction.

In a further embodiment, deposition process is carried out while positive bias voltages and negative bias voltages are alternatively applied to a plurality of neighboring discharge electrodes and negative voltage is applied to the substrate.

In another embodiment, deposition process is carried out while positive bias voltages and negative bias voltages are alternatively applied to a plurality of neighboring discharge electrodes and the substrate is set to be floating potential.

In yet another embodiment, deposition process is carried out while positive bias voltage is applied to a plurality of discharge electrodes and negative voltage is applied to the substrate.

In yet a further embodiment, deposition process is carried out while a dielectric substrate is placed under the substrate, and positive bias voltage is applied to the dielectric substrate.

In a further embodiment, deposition process is carried out while the discharge electrode is cooled down by noble gas or inert gas.

In another embodiment, plasma was generated under RF or pulse electric field at lower or higher frequency than 13.56 MHz.

In yet another embodiment, a movable quartz member is fit in a space in the gas passage.

Present invention (47) is a discharge electrode composed of a ceramic member having a hollow portion where an electrode wire is placed without contact with the ceramic member

In yet a further embodiment, the hollow portion is in vacuum state.

In a further embodiment, gas is enclosed in the hollow portion and the gas is noble gas.

In another embodiment, the pressure in the hollow portion is reduced to less than or equal to 250 Torr.

In yet another embodiment, the noble gas is Ar or Ne

In yet a further embodiment, one terminal of the electrode wire was connected to a metal foil, the end of the metal foil functions as an external extraction terminal, and the metal foil is sealed in contact with narrowed part of the ceramic member.

In a further embodiment, the electrode wire is made of Ni or Ni alloy.

In another embodiment, the electrode wire is made of W including Th or ThO.

In yet another embodiment, the content of Th is less than or equal to 4 weight %.

In yet a further embodiment, the electrode wire is formed with coil-like shape.

In a further embodiment, a layer made of emitter material is formed on the surface of the electrode wire, and the emitter material is material with smaller work function than the material of the electrode.

In another embodiment, the emitter material is material with perovskite-type crystal structure.

In yet another embodiment, the emitter material is more than or equal to one chemical compound selected from the chemical compound group comprising TiSrO, MgO, TiO.

In yet a further embodiment, the emitter layer is formed by a process wherein material of emitter layer is torn into pieces in a mortar, and resultant powder is solved in water, and the solution mixed with glue is coated on the surface of the electrode wire, and emitter layer is formed by sintering of coated wire.

In a further embodiment, the emitter layer is formed by MOCVD.

In another embodiment, the metal foil is made of Mo or Mo alloy.

Present invention (63) is a method for forming CVD film using the plasma CVD apparatus according to any of the previously described embodiments.

Effect of the Invention

According to present invention (1), (6), (7), (47), (51), (52), (63), stable glow discharge plasma can be generated even under atmospheric pressure, then high rate deposition of nitride film with excellent uniformity in film thickness. Low cost mass production of solar battery can be achieved.

According to present invention (2)-(5), (48)-(50), stable plasma generation due to glow discharge can be more easily achieved.

According to present invention (8)-(10), (53)-(55), the work function of an electrode wire can be reduced so as to enhance thermal electron emission.

According to present invention (11), (56), discharge area can be enlarged due to the increase in the surface area of an electrode wire.

According to present invention (12)-(15), (57)-(60), electrons are emitted not only from an electrode wire but also from emitter material so that discharge starts by lower power supply and discharge state after the start becomes more stable.

According to present invention (16), (61), the space in a coil can be sufficiently filled by emitter material. And emitter material can be formed more densely, and its compositional ratio can be improved.

According to present invention (17), (62), adhesion of the metal foil with ceramic member can be improved.

According to present invention (18), stable glow discharge plasma can be generated even under atmospheric pressure, then high rate deposition of nitride film with excellent uniformity in film thickness. Low cost mass production of solar battery can be achieved. And the electrode does not have a hollow portion so that it is easier to fabricate a CVD apparatus.

According to present invention (19)-(22), stable plasma generation due to glow discharge can be more easily achieved.

According to present invention (23), thermal deformation of the flow passage plate can be prevented due to heat producing electrode.

According to present invention (24), ceramic is excellent heat resisting material and the difference of its coefficient of thermal expansion from that of an electrode is small.

According to present invention (25), existing flow passage plates can be utilized.

According to present invention (26), tenon and mortise processing is not necessary and quick-release is possible.

According to present invention (27)-(29), it becomes easier to fabricate the apparatus.

According to present invention (30), stable glow discharge plasma can be generated more easily.

According to present invention (31), (32), a large area film with excellent uniformity in thickness can be deposited.

According to present invention (33), (34), low cost production of useful electronic devices such as a solar battery.

According to present invention (35), silicon nitride film and silicon film with high purity can be deposited using a single apparatus.

According to present invention (36), the configuration of an apparatus can be simplified.

According to present invention (37), a large area film with excellent uniformity in thickness can be deposited.

According to present invention (38), the uniformity of deposited film can be improved.

According to present invention (39), installation area of an apparatus can be minimized.

According to present invention (40), stable glow discharge plasma can be generated more easily. Deposition rate can be enhanced because plasma can be generated in larger region. And the collision damage to the substrate by positive ions such as Ar ions can be weakened. The damage of deposited thin film on the substrate can be reduced so that denser thin film can be formed.

According to present invention (41), (42), stable glow discharge plasma can be generated more easily.

According to present invention (43), the collision damage to the substrate by positive ions such as Ar ions can be weakened. The damage of deposited thin film on the substrate can be reduced so that denser thin film can be formed.

According to present invention (44), the over-heat of the discharge electrode can be prevented.

According to present invention (45), power supply at frequency other than 13.56 MHz which is commonly used in a plasma apparatus can be utilized for a deposition process. By controlling the frequency, it is possible to minimize the damage to a thin film on the substrate.

According to present invention (46), it is possible to control the cross-sectional area of a gas passage so that plasma state or film deposition state can be optimized.

DESCRIPTION OF THE SYMBOLS

1,2,3: plasma head unit member

5,12,16: dielectric member

6,13,17: plasma generation passage

7,14,18: plasma supply opening

10: shock absorbing member

21,22,23: plasma head unit member

24,35: gas distribution passage

25,33: dielectric member

26,36: plasma generation passage

27,37: plasma supply opening

30: shock absorbing member

31: gas distribution passage region

32: plasma generation passage region

34: gas supply pipe

41,47,51: gas introduction opening

42,48,52: dielectric member

43,49,53: plasma generation passage

44,50,54: plasma supply opening

61,66,71: gas introduction opening

62,67,72: dielectric member

63,68,73: plasma generation passage

65,70,75: plasma supply opening

81,88,95: gas introduction opening

82,89,96: dielectric member

83,90,97: plasma generation passage

85,91,98: plasma supply opening

101,102: source gas supply unit

103: power source

104: plasma head

107: plasma reaction region

108: thin film

110: substrate conveyance unit

111: gas introduction opening

112: power source

116,117: solid dielectric body

119: plasma supply opening

120: thin film

201,202: flow passage plate

203,204: quartz member

207,208: gas flow direction

210: support member

211,215: quartz member

213,217: electrode lead wire

218: enclosing member

301,306,311,321: flow passage plate

326: electrode for applying bias voltage

327: power source for applying bias voltage

328: positive argon ion

331,335,339: flow passage plate

332,336,340: flow passage

333,334,337,338,341,342: dielectric member

BEST MODE EMBODIMENTS FOR CARRYING OUT THE INVENTION

Best mode embodiments for carrying out the present invention are described in detail as follows.

Inventors of the present invention have earnestly studied plasma deposition for realization of silicon nitride CVD under atmospheric pressure. First they have employed plasma-blowing deposition for preventing plasma damage on a substrate, and have employed plasma formation by dielectric-barrier discharge for stable glow discharge. In order to prevent plasma reaction in a plasma generation chamber which was a problem of conventional method, a plasma head, which is a plasma generation member, is composed of a plurality of unit parts respectively having an independent plasma blow opening. For example, silicon plasma and nitrogen plasma are generated separately in each unit part in silicon nitride CVD process. Furthermore inventors have discovered that the parallel configuration wherein a unit part for silicon plasma generation is placed next to a unit part for nitrogen plasma generation is effective for improvement in uniformity of deposited film. Plasma supplied from a blow opening does not react in a plasma head, but it reacts in a space between a blow opening and a substrate to deposit silicon nitride film. Therefore highly effective silicon nitride deposition on a substrate becomes possible. And also, material gases are supplied independently to each unit parts of the plasma head, and electrodes are placed so that electrical energy can be controlled independently which is applied for plasma generation. By these arrangements, thin film deposition becomes possible using best conditions for each plasma generation.

And also, in conventional method, there is a problem that it is difficult to generate continuously stable plasma when plasma is generated under atmospheric pressure. Inventors of the present invention have taken notice of the structure of an electrode and the structure of apart where a substrate is placed. And they have discovered that stable plasma generation, the enhancement of nitride film deposition rate, and the improvement of reproducibility in film thickness and film quality become possible by the arrangement wherein an electrode is enclosed in a quartz member, and the electrode is separated from the quartz member by empty space, and a substrate is placed on a quartz supporting member, and plasma is supplied from a plasma head to the substrate.

In addition, “atmospheric pressure” in this specification specifically means pressure between 8×104and 12×104Pa, while it depends on the atmospheric pressure and the altitude of the place where the CVD apparatus is placed. When the pressure of CVD process is within this range, it is possible to reduce facility cost because expensive equipment for compression and decompression is not needed.

(Specific Example of an Electrode Structure)

FIG. 1is a diagram of the structure in a CVD apparatus according to the present invention. Quartz members203,204are placed in the gas blowout openings of flow passage plates201,202where process gas flows, and electrode wires205,206are placed in the hollow portion of the quartz members203,204. Electrical energy due to discharge between electrode wires205,206and a substrate209is applied to gas molecules of process gas which blows out from the gas blowout openings of flow passage plates201,202. Then the molecules are transformed into plasma which is supplied to the substrate209, and silicon nitride film is deposited on the substrate209by the reaction of ions in the plasma. Electrode wires205,206are preferably placed in the hollow portion of the quartz members203,204without direct contact between them. The ambient of the hollow portion is preferably vacuum state or low-pressure state. When the ambient is low-pressure state, gas enclosed in the hollow portion is preferably noble gas such as Ar, or Ne. Preferable range of the low pressure is less than or equal to 250 Torr. Plasma is spontaneously generated by less power supply, and stable plasma generation becomes possible by uniform discharge when the hollow portion is evacuated or depressurized at the pressure less than or equal to 250 Torr with the ambient of noble gas. Flow passage plates201,202are fabricated, for example, by processing aluminum plate. The substrate209is preferably placed on a quartz supporting member210. Then the stability of plasma is enhanced. The shape of the quartz members203,204is not limited to the specific shape if they have long hollow part so that linear electrode can be placed inside. The cross-sectional shape of the hollow portion is not limited to the specific shape, but it is preferably a circle. And the quartz members are preferably equipped with convex parts so that they can be set in the flow passage plates. The flow passage plates are equipped with concave parts corresponding to the convex parts. Alternatively, the quartz members can be equipped with concave parts and the flow passage plates can be equipped with convex parts corresponding to the concave parts.

And also, electrodes can be placed under the supporting member210for controlling bias voltage applied to the plasma. In this case, electrodes placed above the substrate209, such as electrodes205,206, are called as upper electrodes, and electrodes placed under the substrate209(under the supporting member210) are called as lower electrodes.

As shown inFIG. 1, main body of a flow passage plate and an electrode can be fabricated as separate parts, and can be set in using tenon and mortise. Alternatively, an electrode can be placed under the flow passage plate using a retainer. A process to make mortise trench is not necessary, and it becomes easier to remove and replace these parts. And also, main body of a flow passage plate and an electrode can be fabricated by integral molding. The process to fabricate an apparatus becomes easier. A flow passage can be processed after the integral molding of a flow passage plate and an electrode. Or it can be processed at the same time as the integral molding.

It is found that plasma is not generated when nitrogen or ammonia gas which is process gas for nitride film deposition is introduced from the beginning of the process, but plasma can be generated when Ar gas is introduced. Therefore, it is found that plasma which is necessary for nitride film deposition can be stably generated by process steps characterized in that plasma is generated by introducing Ar gas first, and then the number of electrons is increased, and then the flow rate of nitrogen or ammonia gas is gradually increased.

In the embodiment as shown inFIG. 1, electrode wires are not placed in direct contact with quartz members, and they are placed as floating status in a hollow portion. Alternatively, electrode wires can be placed in direct contact with quartz members without making a hollow portion, which makes fabrication of plasma head easier. The material of electrode wires or metal foil is preferably Mo or Mo alloy. Mo or Mo alloy is highly adhesive with ceramics.

The material of an insulating member of the electrode which corresponds to the above-mentioned members203,204is preferably ceramics in both cases where a hollow portion is prepared or not around the electrode. Furthermore the material is preferably quartz or translucent alumina. And the material of the flow passage plate is preferably heat-resistant metal or ceramics.

The structure of an electrode used in the conventional CVD apparatus is the structure where carbon members are exposed, so there is a leakage problem of impurities included in carbon material. Meanwhile, there is no leakage problem of impurities in the structure of the electrode according to the present invention wherein an electrode wire is covered by a quartz tube.

The material of an electrode wire is preferably W. It is more preferably W which contains Th or ThO. The content of Th is preferably less than or equal to 4% by weight. This arrangement reduces the work function of the electrode wire, and facilitates the emission of thermal electrons so that plasma can be easily generated.

It is preferable that an electrode wire is entirely heated by appropriate external current supply to the wire. When the temperature of the wire is low, nitride or silicon film can be deposited on the surface of the electrode. Then it is not preferable because the flow passage may be reduced in thickness or clogged up. To the contrary, it is possible to prevent the growth of deposited material on the surface of the electrode by heating it. And also, it is possible to control the work function of metal such as Th or PTO which is added to electrode material such as W by controlling the temperature of the electrode. By these arrangements, electron density emitted from metal can be controlled so that CVD process can be controlled more precisely.

And radioactive material is preferably coated on the surface of electrode material. For example, strontium is preferably coated. Plasma can be easily excited by coating radioactive material.

And also, material with smaller work function than the material of the electrode is preferably used as emitter material, and a layer of the emitter material is preferably formed on the surface of the electrode wire. Material with perovskite-type crystal structure is preferably used as the emitter material. And more than or equal to one chemical compound selected from the chemical compound group comprising TiSrO, MgO, TiO is preferably used as the material. Any of these arrangements reduces the work function of the electrode wire, and facilitates the emission of thermal electrons so that plasma can be easily generated.

The emitter layer is formed by a process wherein material of emitter layer is torn into pieces in a mortar, and resultant powder is solved in water, and the solution mixed with glue is coated on the surface of the electrode wire, and emitter layer is formed by sintering of coated wire. Or it can be formed by MOCVD. When the electrode wire is formed with coil-like shape, space formed in the electrode can be sufficiently filled by emitter material. And the emitter layer can be formed more densely, and its composition ratio can be improved.

And also, a quartz electrode placed in a quartz member is preferably used not only for an electrode for high frequency radiation but also used for a heater. The temperature control of a body on which deposition film is formed can be controlled, for example, by heating, by using the quartz electrode as a heater.

(Method for Fabricating an Electrode)

FIGS. 2(a), (b)are diagrams to show process steps to fabricate the electrode in a CVD apparatus according to the present invention. First, as shown inFIG. 2(a), a quartz member214with a hollow portion is prepared having one terminal with an opening214and the other closed terminal. As an electrode wire212, for example, a wire made of Ni or Ni alloy is used. InFIG. 2, a linear electrode wire is shown, but an electrode wire with coil-like shape is preferably used. The surface area of the electrode can be enlarged, and the discharge area can be also enlarged by using an electrode with coil-like shape. A lead wire213is attached on the terminal of an electrode212. As a lead wire, for example, metal foil with a thickness of about 20 μm made of Mo or Mo alloy is used. Next, the inside of the quartz member211is depressurized until the pressure reaches to vacuum or less than or equal to 250 Torr. Then the opening214is enclosed as shown inFIG. 2(b). According to these process steps, an electrode member is completed where an electrode216is supported by a lead wire217in a floating state without contact with a quartz member215.

Noble gas such as Ar or Ne is preferably used for filler gas when a hollow portion is depressurized. It is more preferable that clean gas such as Ar with impurity concentration less than or equal to 10 ppb is introduced as purge gas into the hollow portion before the filler gas is introduced.

(The First Specific Example of a Unit Part of a Plasma Head)

FIGS. 5(a), (c)is respectively a front view diagram and a side view diagram of a plasma head according to the first specific example of the present invention. The first specific example of a unit part is a unit part of a plasma head to generate capacitance coupling plasma. The unit part comprises a dielectric member42and a pair of electrodes45,46which hold a dielectric member42. The dielectric member42is equipped with a hole which passes through from top down, and the hole functions as a plasma generation passage. The dielectric member42can be formed as an integral member, or it can be formed by pasting or fitting a plurality of members together. When the dielectric member is composed of a plurality of members, it is preferably processed so that no leakage occurs at a joint part. One end of the hole is used as a gas introduction opening41. Then electrical field is applied to the electrode45,46which provides electrical energy to introduced gas molecules to generate plasma made of radicals, ions, and electrons. Constant, high-frequency, or pulsed electrical field can be preferably applied. Especially, pulsed electrical field can be preferably applied. Electrical field is applied via dielectric member, so even when constant electrical field is applied, accumulation and extinction of charge are repeated one after the other on the surface of dielectric member. Accordingly, plasma discharge state does not reach to be arc discharge but becomes stable glow discharge. Generated plasma blows out from plasma supply opening50which is the other end of the hole. The range where plasma is supplied depends on the condition of plasma generation, but generally speaking, plasma is supplied in the range of several mm-several cm from plasma supply opening50. As shown in the side view diagram ofFIG. 3(b), the unit part can be equipped with one plasma supply opening. And as shown inFIG. 5(c), it can be equipped with a plurality of plasma supply openings. When a deposition process is applied on a small substrate, plasma can be supplied from one plasma supply opening. When a deposition process is applied on a large substrate, plasma is preferably supplied from a plurality of plasma supply openings for better uniformity of deposition.

And also it is not necessary that a hole is prepared for a gas passage in dielectric member as shown inFIG. 5. A space between dielectric members can be used as a gas passage when the dielectric members are placed parallel to each other with a space between them.

Material of dielectric members is preferably plastic, glass, carbon dioxide, metal oxide such as aluminum oxide. Especially, quartz glass is preferably used. Dielectric material with relative permittivity greater than or equal to 2 is preferably used. Dielectric material with relative permittivity greater than or equal to 10 is more preferably used. The thickness of dielectric material is preferably in the range from 0.01 mm to 4 mm. If it is too thick, excessively high voltage is necessary for plasma generation. If it is too thin, arc discharge tends to take place.

Material of electrode is preferably metal such as copper, aluminum, stainless-steel or metal alloy. The distance between electrodes, which depends on the thickness of dielectric member and applied voltage, is preferably in the range from 0.1 mm to 50 mm.

(The Structure of a Plasma Head)

(The First Specific Example of a Plasma Head)

FIG. 3(a)is a front view diagram of a plasma head according to the first specific example of the present invention.FIGS. 3(b), (c)are side view diagrams of a plasma head according to the first specific example of the present invention. Plasma head is formed by sequentially installing one of a plurality of unit parts adjacent to the other including plasma head unit members1,2,3. InFIG. 3(a), plasma head unit parts are placed in parallel by inserting shock absorbing member10between the plasma head unit members. The shock absorbing member is not always an indispensable part for the plasma head structure. But it is useful for preventing the damage of dielectric member5by inserting the shock absorbing member when the dielectric member5is made of material subject to breakage such as glass and a plurality of plasma head unit parts is fixed by clenching. According to the structure of unit parts used, a plasma head can be equipped with one plasma supply opening as shown in the side view diagram inFIG. 3(b), and it can be equipped with a plurality of plasma supply openings as shown inFIG. 3(c).

(The Second Specific Example of a Plasma Head)

FIGS. 4(a), (b)are respectively a front view diagram and a side view diagram of a plasma head according to the second specific example of the present invention. Plasma head is formed by sequentially installing one of a plurality of unit parts adjacent to the other including plasma head unit members21,22,23. As shown in the side view diagram inFIG. 2(b), plasma head is equipped with a plurality of plasma supply openings. A dielectric member35is processed so that it is equipped with a hollow portion inside. This hollow portion functions as a gas distribution passage and a plasma generation passage. A hollow portion can be formed in the dielectric member as an integral part. Or a hollow portion can be formed by that a concave part is formed in one dielectric plate and the other plate is bonded to the former plate. Material gas for plasma generation is supplied from gas supply opening34. A gas distribution passage region is formed is formed in the upper part of the dielectric member35, the region which distributes gas supplied from the gas supply opening34into a plurality of plasma generation pas sages36. According to this structure, material gas can be equally supplied to many plasma generation members using a simple structure so as to contribute downsizing of CVD apparatus.

(The Structure of a CVD Apparatus)

FIG. 8is a cross-sectional diagram of a CVD apparatus according to the embodiment of the present invention. A CVD apparatus consists of a source gas supply unit101supplying the first gas, a source gas supply unit102supplying the second gas, a plasma head104which is formed by sequentially installing a plasma head unit part adjacent to a shock absorbing member, a power supply which supplies electrical power to the plasma head unit part, and a substrate conveyance unit110which conveys substrates. A plasma head unit part consists of a dielectric member equipped with plasma generation passage and an electrode. Material gas is introduced from the upper gas introduction opening, and electric field is applied by an electrode via a dielectric member to excite the material gas for generating plasma comprising radicals, ions, and electrons. Generated plasma is supplied from a plasma supply opening to a substrate109placed on the substrate conveyance unit110. A deposition process is carried out while substrates are conveyed by a substrate conveyance unit which enables consecutive deposition. The shape of the substrate is preferably band-like shape which is conveyed by roll-to-roll process. Or another process can be adopted in which a substrate is placed on a static position during deposition process, and after the deposition is finished, the substrate is conveyed so that the next substrate is in the deposition position by the substrate conveyance unit.

In addition, a lower electrode which is not shown in the diagram is placed under the substrate109, and it can apply bias voltage from under the substrate.

Plasma supply openings can be placed downward as shown inFIG. 8, or they can be placed toward lateral direction. When plasma supply openings are placed downward, the uniformity of deposition can be improved. When they are placed toward lateral direction, the installation area of the apparatus can be minimized.

Because plasma discharge is dielectric barrier discharge, plasma becomes stable glow discharge, and it becomes non-equilibrium plasma where the temperature of electrons is high and that of radicals and ions is low.

When silicon nitride is deposited, for example, silane gas and ammonia gas are used as material gas. Silane gas and ammonia gas are supplied alternately to adjacent plasma head unit parts, and silicon plasma105and nitrogen plasma106are generated in each plasma generation passage. Silicon plasma and nitrogen plasma reach downward until several mm to several cm from plasma supply opening, then plasma reaction region107is formed.

When silicon nitride is deposited, other silicon source gas or nitrogen source gas can be used. As silicon source gas, silane, disilane, or mixed gas made of these gases attenuated by inert gas can be used. As nitrogen source gas, ammonia, nitrogen, or mixed gas made of these gases attenuated by inert gas can be used.

Silicon nitride film can be deposited by independently supplying silicon source gas and nitrogen source gas through flow passage plates laying side-by-side among a plurality of flow passage plates. During this process, it is possible to flow curtain-enclosed gas made of inert gas such as nitrogen through flow passage plates surrounding the plates for source gases. The flow rate of silicon source gas and nitrogen source gas can be independently controlled, which enables precise control of process conditions.

Alternatively, silicon nitride film can be deposited by supplying a mixed gas made of silicon source gas and nitrogen source gas through identical flow passage plates. The configuration of an apparatus can be simplified.

As another example of deposited film, silicon film can be deposited by not supplying nitrogen source gas but supplying silicon source gas.

During the excitation of plasma for deposition process, it is preferable to cool down an electrode by introducing a mixed gas comprising or including noble gas (for example, Ar and N2) nearby the electrode in the flow passage plate. When an electrode is not cooled down, and the temperature of the electrode itself rises by plasma excitation, a film which is not a dielectric member in use or extraneous material is attached on the surface of the electrode, and the function of the electrode is disabled. To prevent this problem, it is preferable to circulate cooling gas in a temperature of about 20 deg C.

And also, a movable dielectric member is preferably fit in a space in gas passage or flow passage plate through which process gas or carrier gas flows. Quartz is preferably used as a dielectric member. By this arrangement, it is possible to control the cross-sectional area of flow passage so that the controllability of the process can be improved.FIGS. 11(a), (b), (c)are cross-sectional diagrams of a flow passage plate in a CVD apparatus according to the practical example of the present invention. The cross-sectional area of a flow passage332(FIG. 11(a)) surrounded by a flow passage plate331and dielectric members333,334can be controlled by moving the dielectric members333,334as shown in a flow passage336(FIG. 11(b)) and a flow passage340(FIG. 11(c)). The flow rate of process gas can be controlled by controlling the cross-sectional area of a flow passage. For example, the flow rate can be increased by narrowing the cross-sectional area of a flow passage.

Process conditions to generate plasma are appropriately determined according to the purpose to utilize plasma. When capacitance coupling plasma is generated, plasma is generated by applying constant electric field, high frequency electric field, pulsed electric field, micro-wave electric field between a pair of electrodes. When electric field is applied other than constant electric field, the used frequency can be 13.56 MHz which is used in a general plasma apparatus, or it can be higher than or lower than 13.56 MHz. In Patent Document 6, a technology to prevent plasma damage on the deposited film by using high frequency plasma of 100 MHz in a plasma apparatus is disclosed. By controlling the frequency of electric field, characteristics such as deposition rate, the quality of deposited film can be optimized.

Pulsed electric field is preferably used for plasma generation. Its field intensity is preferably in the range from 10 to 1000 kV/cm. Its frequency is preferably higher than or equal to 0.5 kHz.

(The Second Specific Example of a Unit Part of a Plasma Head)

Technical idea concerning plasma head according to the present invention is not limited to be applied for a plasma head for capacitance coupling plasma, but for example, it can be applied for a plasma head for inductive coupling plasma.

FIG. 6(a)is a front view diagram of a plasma head unit member according to the second specific example of the present invention.FIGS. 6(b), (c)is a side view diagram of a plasma head according to the second specific example. The unit part consists of a dielectric members62and an inductive coil64circumferentially placed adjacent to the member. The dielectric members62is equipped with a hole which passes through from top down, and the hole functions as a plasma generation passage. The dielectric member62can be formed as an integral member, or it can be formed by pasting or fitting a plurality of members together. When the dielectric member is composed of a plurality of members, it is preferably processed so that no leakage occurs at a joint part. One end of the hole is used as a gas introduction opening61. Then electrical current is applied to the inductive coil64, and generated magnetic field provides magnetic energy to introduced gas molecules to generate plasma made of radicals, ions, and electrons. Plasma discharge state becomes stable glow discharge. Generated plasma blows out from plasma supply opening65which is the other end of the hole. The range where plasma is supplied depends on the condition of plasma generation, but generally speaking, plasma is supplied in the range of several mm-several cm from plasma supply opening65. As shown in the side view diagram ofFIG. 6(b), the unit part can be equipped with one plasma supply opening. And as shown inFIG. 6(c), it can be equipped with a plurality of plasma supply openings. When a deposition process is applied on a small substrate, plasma can be supplied from one plasma supply opening. When a deposition process is applied on a large substrate, plasma is preferably supplied from a plurality of plasma supply openings for better uniformity of deposition.

(The Third Specific Example of a Plasma Head)

FIG. 7(a)is a front view diagram of a plasma head unit member according to the third specific example of the present invention.FIGS. 7(b), (c)is a side view diagram of a plasma head according to the third specific example. The unit part consists of a dielectric members82and an inductive coil84placed adjacent to the member. The dielectric members82is equipped with a hole which passes through from top down, and the hole functions as a plasma generation passage83. The dielectric member can be formed as an integral member, or it can be formed by pasting or fitting a plurality of members together. When the dielectric member is composed of a plurality of members, it is preferably processed so that no leakage occurs at a joint part. The terminals86,87of the inductive coil84are placed well away from each other so that they are not electrically shorted. One end of the hole is used as a gas introduction opening81. Then electrical current is applied to the inductive coil84, and generated magnetic field provides magnetic energy to introduced gas molecules to generate plasma made of radicals, ions, and electrons. Plasma discharge state becomes stable glow discharge. Generated plasma blows out from plasma supply opening85which is the other end of the hole. The range where plasma is supplied depends on the condition of plasma generation, but generally speaking, plasma is supplied in the range of several mm-several cm from plasma supply opening85. As shown in the side view diagram ofFIG. 7(b), the unit part can be equipped with one plasma supply opening. And as shown inFIG. 7(c), it can be equipped with a plurality of plasma supply openings. When a deposition process is applied on a small substrate, plasma can be supplied from one plasma supply opening. When a deposition process is applied on a large substrate, plasma is preferably supplied from a plurality of plasma supply openings for better uniformity of deposition.

(Method for Producing a Plasma Head)

To fabricate dielectric members making up a plasma head according to the present invention, it is necessary to process a hollow portion with a complicated shape such as a plasma generation passage and a gas distribution passage. Such a dielectric member with a hollow portion can be fabricated by bonding dielectric members with a hollow portion or by bonding a dielectric member with a hollow portion and a flat dielectric member after forming a hollow portion on the surface of a plurality of dielectric members.

A plasma head unit part is formed by stacking an electrode or an inductive coil on the dielectric member with a hollow portion formed by this way. Furthermore, a plasma head is formed by stacking a plurality of plasma head unit parts via a shock absorbing member made of material such as Teflon™.

A plasma head unit part can be fabricated by an injection molding method. A hydraulic core and an electrode or an inductive coil are placed in a mold, and material of a dielectric member is injected in the mold, then a fabricated part is unmolded and the hydraulic core is removed with the electrode or the inductive coil left behind. Furthermore, a plasma head is formed by stacking a plurality of plasma head unit parts via a shock absorbing member made of material such as Teflon™.

(Points of Difference with Similar Technologies)

In Patent Document 4, a process to reform the property or sterilize on the surface of an object by blowing out plasma to the object is disclosed, the plasma generated by dielectric discharge from a plasma head formed by bundling a plurality of dielectric thin tubes. A plurality of plasma supply openings is equipped in the technology disclosed in Patent Document 4, but gas inlets and electrodes to generate plasma of each thin tube do not function independently. And there is no description to suggest a technology where gas inlets and electrodes are independently equipped in each thin tube. Therefore it is not easy to invent a technology according to the present invention wherein a plurality of different plasmas is generated in a plurality of plasma generation units, and plasma reaction is carried out in a space between a plasma head and a substrate by referring to this document.

In Patent Document 5, a process to form an organic thin film including metal such as silicon oxide by a reaction of gas including metal such as TEOS and oxygen is disclosed. But the technology described in Patent Document 5 is a technology wherein a thin film is formed by mixing and reacting reaction gas which is in plasma state and metal-including gas which is not in plasma state. Therefore this technology is different from the technology of the present invention wherein a plasma head is composed of a plurality of unit parts installed in parallel, and different plasmas are generated in each unit part, and film deposition is carried out by the reaction between the different plasmas. The technology according to the present invention is a technology wherein a plurality of plasma supply openings to generate different plasmas can be very closely and densely placed by stacking alternately a plurality of dielectric members and electrodes. Therefore it is not easy to invent a technology according to the present invention by referring to this document.

INDUSTRIAL APPLICABILITY

As above mentioned, by using a CVD apparatus and a method for forming CVD film according to the present invention, low cost production of a high quality nitride film can be materialized for the purpose of, for example, forming antireflection film of a solar battery, which makes a huge contribution to the field of electronics.

PREFERRED EMBODIMENTS

Several embodiments of a method for forming CVD film according to the present invention are described in detail as follows, but the present invention is not limited to these embodiments.

(The First Test on Electrodes)

Minimum supply voltage necessary to spontaneously generate plasma was measured by setting different several conditions for the ambient of a hollow portion and gas which flows in the flow passage plate in order to investigate optimum conditions for plasma generation for an electrode (upper electrode) with a hollow portion according to the present invention. For comparison, the voltage was measured for an electrode without a hollow portion. And also, a flow passage plate was formed using ceramic members, and a gas flow passage was formed on the lateral side of the flow passage plate.

TABLE 1Minimum RF power (W) necessary for spontaneously generating plasmaGas (carrier gas)which flows in a flow passage plateAr 70%Ambient in a hollow portionAr 100%Ar 85% N215%N230%Ar gas enclosed at 50 Torr5009002000(W)Ar gas enclosed at 250 Torr70011001800Ar gas enclosed at 500 Torr80016002000Ne gas enclosed at 50 Torr40010002200Ne gas enclosed at 250 Torr60011001700Ne gas enclosed at 500 Torr90015002100Atmospheric pressure60015001300Vacuum50015002100Without a hollow portion60010002100

In addition, members as follows were used for the components of a discharge electrode.

An electrode wire: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was not used

It was found that an optimum CVD condition was when RF power necessary for spontaneously generating plasma was less than or equal to 700 W because spark discharge was not generated and plasma state was stable. And it was found that Ar gas not including N2was preferable for carrier gas flowing in a flow passage plate to maintain stable plasma. And it was found that vacuum or Ar gas enclosed at less than or equal to 250 Torr was preferable as an ambient of a hollow portion. And according to the other experiment using other gases as enclosed gas, excellent result was obtained when noble gas such as Ne was used as carrier gas and enclosed gas in the hollow portion, the result being similar to the result when Ar was used.

(The Second Test on Electrodes)

Next, minimum RF power necessary for spontaneous plasma generation was measured using an electrode formed according to the present invention by changing the material of members and the condition of gas which flows in a flow passage plate. Discharge electrodes were equipped with hollow portions filled with noble gas at a pressure of 250 Torr. The flow passage plate was made of heat resisting metal and flow passages were formed along the side of the plate.

TABLE 2Minimum RF power (W) necessary for spontaneously generating plasmaGas (carrier gas)Ambientwhich flows in a flow passage platein a hollow portionAr 100%Ar 85% N215%Ar 70% N230%Condition 170010001700(W)Condition 280011001800Condition 36009001600Condition 480010001800Condition 5100013002100Condition 670010001700Condition 770011001600Condition 860010001600
Condition 1: a linear electrode wire made of Ni alloy, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz, Ni—W alloy was used as Ni alloy.
Condition 2: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo alloy, emitter material was not used, ceramic member was made of quartz, Mo—W alloy was used as Mo alloy.
Condition 3: a linear electrode wire made of W including 1 weight % of Th, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.
Condition 4: a linear electrode wire made of W including 4 weight % of Th, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.
Condition 5: a linear electrode wire made of W including 10 weight % of Th, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.
Condition 6: a linear electrode wire made of W including 4 weight % of ThO, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.
Condition 7: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of translucent alumina.
Condition 8: a coiled electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.

(The Third Test on Electrodes)

Next, minimum RF power necessary for spontaneous plasma generation was measured using an electrode formed according to the present invention by changing a layer made of emitter material formed on the surface of an electrode wire and the condition of gas which flows in a flow passage plate. Discharge electrodes were equipped with hollow portions filled with noble gas at a pressure of 250 Torr.

TABLE 3Minimum RF power (W) necessary for spontaneously generating plasmaGas (carrier gas)Atmospherewhich flows in a flow passage platein a hollow portionAr 100%Ar 85% N215%Ar 70% N230%Condition 980011001800(W)Condition 106009001500Condition 1170010001400Condition 127009001600Condition 136009001600Condition 1470010001500Condition 157009001400
Condition 9: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz, Ni—W alloy was used as Ni alloy.
Condition 10: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of TiSrO having perovskite type crystal structure formed by glue coating and firing, ceramic member was made of quartz.
Condition 11: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of MgO having perovskite type crystal structure formed by glue coating and firing, ceramic member was made of quartz.
Condition 12: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of TiO having perovskite type crystal structure formed by glue coating and firing, ceramic member was made of quartz.
Condition 13: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of TiSrO having perovskite type crystal structure formed by MOCVD, ceramic member was made of quartz.
Condition 14: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of MgO having perovskite type crystal structure formed by MOCVD, ceramic member was made of quartz.
Condition 15: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was made of TiO having perovskite type crystal structure formed by MOCVD, ceramic member was made of quartz.

(The First Evaluation of Nitride Film)

When atmospheric pressure plasma is generated by supplying power from RF or LF power source via electrodes prepared for dielectric-barrier discharge, it is possible to soften the collision energy of electrons or charged reactive molecules which collide the surface of a substrate so as to control substrate damage and enhance desired reaction by, for example, applying bias voltage to the lower electrode in addition to simply applying appropriate effective voltage between the upper electrode and the lower electrode. The film quality of silicon nitride film was evaluated which was deposited by applying bias voltage so that plasma was generated not only between an electrode and a substrate but also between an electrode and other electrode.

FIGS. 9(a), (b), (c)are cross-sectional diagrams of a plasma head in a CVD apparatus according to of the embodiment of the present invention.FIG. 9(a)is a diagram which shows a plasma generation state when a substrate was connected to ground potential and positive bias voltages and negative bias voltages were alternatively applied to a plurality of electrodes.FIG. 9(b)is a diagram which shows a plasma generation state when a substrate was connected to floating potential inFIG. 9(a).FIG. 9(c)is a diagram which shows a plasma generation state when a substrate was connected to ground potential and positive bias voltages were applied to all electrodes.

Film quality was evaluated. In the case ofFIG. 9(a), stable plasma was generated by glow discharge and a dense film was obtained. By contrast, in the case ofFIGS. 9(b) and (c), stable plasma was generated by glow discharge but a less dense film was obtained in comparison toFIG. 9(a). In the case ofFIG. 9(a), plasma is generated between neighboring electrodes, plasma region is wide, and deposition rate is large. And deposited film presumably receives less damage because collision of positive ions to a substrate is weakened.

TABLE 4The deposition rate of silicon nitride film andits film quality evaluation (relative value)ConventionalFilm depsitedthermalaccording to the present inventionCVD filmFIG. 9(a)FIG. 9(b)FIG. 9(c)Upper electrode (+)200 (V)200200voltageUpper electrode (−)00NAvoltageLower electrode (−)0float0voltageDeposition rate1020~4015~3510~30Etching rate1010~3040~6040~60
Discharge electrode was made of the following members. Plasma excitation frequency was 13.56 MHz.
Electrode wires were placed in the hollow portion. The ambient of the hollow portion is vacuum state.
Electrode wire: a linear electrode wire made of Ni, one terminal was connected to a metal foil made of Mo, emitter material was not used, ceramic member was made of quartz.

The technology according to the present invention was compared with nitride film deposition by conventional thermal CVD. In all the case of bias voltage application as shown inFIGS. 9(a), (b), (c), the increase of deposition rate was observed in the deposition method according to the present invention in comparison to the conventional method. Among these cases, especially high deposition rate was observed in the method as shown inFIG. 9(a). In addition, etching rate using buffered hydrofluoric acid for evaluation of the film quality of deposited film. When etching rate is lower, film quality is shown as being denser. By thermal CVD, the deposition of denser film is possible though deposition rate is low. Among CVD methods according to the present invention using a plasma head as shown inFIGS. 9(a), (b), (c), especially the film quality was found to be the densest by the method as shown inFIG. 9(a).

(The Second Evaluation of Nitride Film

The experiment of deposition and evaluation similar to the embodiment 4 was done by changing plasma excitation frequency.

In order to relax the damage of a substrate due to the collision of positive ions such as Ar ions, the effect of a method was evaluated, the method wherein a positive bias voltage was applied to the substrate.FIG. 10is a cross-sectional diagram of a plasma head in a CVD apparatus according to the embodiment of the present invention. A dielectric substrate325was placed under the substrate324, and an electrode for applying bias voltage326was placed under the dielectric substrate. Positive bias voltage was applied by a power source327to the electrode326. And deposited film presumably receives less damage because collision of Ar positive ions328which moves from an electrode322to a substrate324is presumably weakened. The experiment showed that the quality of the deposited film was denser when positive bias voltage was applied by a power source327in comparison to the case when it was not applied.

In order to investigate a cooling effect by a discharge electrode, an electrode temperature was measured after Ar gas plasma was generated for one hour under RF power of 2000 W applied at 13.56 MHz. The electrode temperature was 150° C. when cooling down was not done. On the other hand, when cooling down was done using Ar gas or nitrogen gas, the temperature was 50° C. and 60° C. respectively, which showed that adequate cooling effect was obtained.