JPH07211654A - Plasma generating system and operating method thereof - Google Patents

Abstract

PURPOSE:To generate plasma in a gap between an insulator and a central electrode by feeding the gap with a gas, principally composed of a rare gas, under a pressure within a specified range and then applying an AC electric field between the electrodes thereby ionizing the gas principally composed of a rare gas. CONSTITUTION:A tubular insulator 13 is disposed between a central conductor 11 and an outer conductor 12 and an AC electric field is applied between the conductors 11, 12, i.e., the electrodes, from an AC power supply 14. A gas principally comprising a rare gas, i.e., helium, is then fed into a discharge space 15 from a cylinder 17 through a flow rate controller 16 thus sustaining the discharge space in a pressure state of 5-150Torr. Consequently, a plasma generated in the discharge space 15 is introduced to a region of substantially atmospheric pressure where various plasma processing can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma generator for performing film formation, etching, and various plasma treatments under a moderately reduced pressure of 10 to 150 Torr, and a method of using the plasma generator.

[0002]

2. Description of the Related Art Generally, there is known a technique for activating (plasma) a gas by high-frequency energy, microwave energy, thermal energy or light energy when reducing the pressure to 1 Torr or less, and performing a plasma treatment such as film formation or etching. Has been. However, various plasma treatments at a reduced pressure of 1 Torr or less require (1) a large-scale vacuum exhaust system, which is costly. (2) When processing a large area, the vacuum evacuation system must be upsized, which causes technical and cost difficulties. (3) It takes time to handle and maintain the device. (4) Since the high vacuum state is handled, the adjustment is delicate and the characteristics of each device vary widely.

On the other hand, in order to enable various plasma treatments at atmospheric pressure, 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 electrodes (in the discharge path) (3) at least one electrode is needle-shaped Alternatively, it should be brush-like (4) It is known as a necessary condition that the frequency of the applied electric field is 3 kHz or more. The insulator has an applied electric field frequency of 3k in order to prevent the discharge from shifting to arc discharge.
The frequency of Hz or more is for passing a current through the insulator, and the electrode shape is needle-like or brush-like for the purpose of facilitating the initiation of discharge by making the electric field non-uniform.

It has also been attempted to subject the surface of an organic substance such as polyimide or an inorganic substance such as silicon to etching or the like by these methods. However, although these methods are carried out at atmospheric pressure, they must undergo a step of (1) once depressurizing the reaction space to a vacuum and then filling it with a gas such as helium. (2) The substrate is uniformly processed on the substrate, and it is impossible to selectively process a minute area. (3) Discharge is not stable. (4) The plasma generation region is small, and large-area processing cannot be performed.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma generator capable of performing processing on a large area without using a vacuum exhaust system on a large scale and a method of using the plasma generator. .

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, electrodes made of a conductor such as metal are arranged in a concentric cylindrical shape, and a cylindrical insulator is formed in a concentric circle in the gap between the electrodes. And a gas containing a rare gas (for example, helium) as a main component in the gap between the insulator and the center electrode.
Pressure condition of Torr, preferably 10-100 Torr
It is characterized in that the pressure is maintained at a pressure of r, and an alternating electric field is applied between the electrodes to ionize the gas mainly composed of the rare gas to generate plasma in the gap between the insulator and the center electrode. And The term “flow” as used herein means a state in which gas flows, and does not mean laminar flow. That is, the flow may be turbulent.

The plasma is used to perform plasma processing such as film formation, etching, surface treatment, and ashing. As rare gas, He, Ar, Ne,
Xe and Kr can be used. Particularly, it is preferable to use He and Ar.

FIG. 1 shows a conceptual diagram of a plasma generator utilizing the present invention. In FIG. 1, a cross section taken along line AA ′ is a lower coaxial drawing. In Figure 1, the center conductor
A cylindrical insulator (13) is placed between the (11) and the outer conductor (12), and an AC electric field is applied from the AC power supply (14) to the center conductor (11) and the outer conductor (12) as electrodes. To do. In the discharge space (15), a gas containing a rare gas, helium as a main component, is introduced into the cylinder (17).
It is supplied in a flow state through a flow controller (16). Figure 1
In the configuration shown in (1), the cylindrical insulator (13) and the outer electrode (1
There is also a gap in 2), and gas also flows into this gap. Therefore, discharge is also performed in this gap. However, the discharge in the gap between the cylindrical insulator (13) and the outer electrode (12) is such that the gas in this gap is weaker than the discharge in the gap between the cylindrical insulator (13) and the inner electrode (12). Becomes This is because the electric field strength becomes small.

Since the central conductor (11) is directly exposed to plasma, metals such as tungsten and tantalum which are strong against sputtering are effective. When a gas containing a halogen-based element such as fluorine or chlorine that has a strong etching action is added to a gas mainly containing helium, it should be composed of a metal that is difficult to be etched by a halogen-based element such as gold or platinum, or coated on the surface. Good to do. It is desirable that the outer diameter of the central conductor (11) and the inner diameter of the outer conductor (12) satisfy the following equation. (Inner diameter of outer conductor / outer diameter of center conductor) ≧ 3 This is a condition (corona generation condition) where the electric field between the center conductor (11) and the outer conductor (12) becomes unequal, and the discharge start This is an easy condition. The above conditions are only desirable conditions, and even if the ratio of the previous equation is smaller than 3 and is close to 1, it is actually
(Since the cylindrical insulator (13) is inserted between the two, it does not become 1), the discharge only causes the glow discharge without passing through the corona discharge, and the content of the present invention is limited as long as the discharge is generated. Not a thing.

The cylindrical insulator (13) is provided so that the discharge does not transfer to an arc discharge between the electrodes and is made of an inorganic substance such as quartz glass or alumina, or an organic substance such as Teflon, polyimide, polyethylene or polyethylene terephthalate. Can be used. Since there is a possibility that the temperature will rise to some extent when exposed to electric discharge, quartz glass, alumina, etc., which have high heat resistance, are 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 cylindrical insulator (13) changes depending on the relative permittivity of the insulator, and if the gap between the center conductor and the insulator is too large, it exceeds the practical output voltage of the AC power source. It is appropriate to set the range to. That is,
The value of the gap is preferably 5 mm or more and 50 mm or less.

The lower limit of the frequency of the AC power supply is determined by the capacitive susceptance generated by the insulator inserted in the discharge path. That is, the capacitance C per unit length is represented by the series combined capacitance of the gap capacitance Cg between the central conductor and the insulator and the insulator capacitance Ci, and Cg = 2πε ₀ / log (b / a) Ci = 2 It becomes πε / log (c / b). However, the radius of the central conductor (11) is a, and the insulator (13)
Is b, the inner diameter of the outer electrode (12) is c, the dielectric constant (13) of the insulator is ε, and the dielectric constant of the vacuum is ε ₀ .

The electric field applied between the concentric cylindrical electrodes is C
It is divided by the ratio of g and Ci. It has been confirmed by experiments that the discharge is stable if the susceptance value ωC due to the insulator is 10 ^-6 [S] or more.

It has been experimentally proved that the power density per unit area of the electrode needs to be 0.1 W / cm ² or more, so that the power density per unit area of the electrode is 0.1.
W / child at a helium ionization or excitation,該Reiki helium atoms remain in a metastable state long life _{^{(2 3 S 1, 2 1}} S 0). Since the lifetime is long and the energy of the metastable state is as high as 19.8 and 20.96 eV, other additive gas can be ionized and excited. Therefore, when helium is used, excited helium atoms can be carried out to the outside of the discharge region, and the high energy of the excited helium atoms can be used to cause a reaction outside the discharge region.

As rare gases, Ar, Ne, Kr, X
Similar effects can be obtained when e is used. Further, as the additive gas, SiH is used as a reactive gas for film formation.
_{It is possible to use 4} or CH ₄ , a gas containing halogen such as CF ₄ , CCl _4, or NF ₃ as an etching gas, or other H ₂ . Ashing can be performed by using O ₂ gas.

In the present invention, the discharge space is 5 to 150.
Since it suffices to set the pressure state to Torr, it is a necessary condition that the discharge space (15) is within the above pressure range in the configuration shown in FIG. Therefore, it is possible to guide the plasma generated in the discharge space (15) to a region having a pressure close to the atmospheric pressure and perform various plasma treatments there. For example, various plasma treatments can be performed by using a simple operating exhaust system. Such an operation utilizes the fact that the metastable excited state of a rare gas has a long life.

It is also possible to transport the rare gas radicals to a region such as the substrate surface where a reaction is desired by a gas flow and supply the reaction gas to the region through a nozzle or the like.

In the structure of the present invention, the ions do not reach the region to be reacted, and only the radicals can be supplied, so that no current flows through the reactant. Therefore, a living body can be selected as the reaction target. That is, it is possible to scrape the teeth and nails with the radicals or the radicals of the etching gas supplied as needed.

Further, in the plasma generator of the present invention, the reaching distance of radicals can be controlled by controlling the supply gas flow rate. That is, if the flow rate of the supply gas is increased, the flow velocity is increased in proportion to the increase of the flow rate of the supply gas, and the reaching distance of radicals can be lengthened. Further, not only the substrate outside the discharge region but also the electrode itself in the discharge space may be the object to be etched. It can also be used to form needles with very sharp tips.

[0020]

【Example】

[Embodiment 1] In this embodiment, an example in which a coaxial cylindrical discharge region is formed, helium is introduced, an AC electric field is applied, and plasma is formed, the dimensions and the like will be specifically described.

FIG. 2 shows a sectional view of the plasma generator of the present invention. The coaxial cylindrical electrode is the central conductor (11), cylindrical insulator
(13) and outer conductor (29). This central conductor (11)
Plasma is generated in the gap between the cylindrical insulator (13) and the cylindrical insulator (13).
In this example, the central conductor (11) was made of tungsten, the cylindrical insulator (13) was made of quartz glass, and the outer conductor (29) was made of stainless steel. The central conductor (11) is connected to the MHV coaxial connector (21),
An AC electric field is applied from an AC power source through a coaxial cable (not shown) connected to the HV coaxial connector (21). Helium supplied between the central conductor (11) and the cylindrical insulator (13) was supplied from the gas inlet (20), and the helium insulator (2
It flows in between 2) and (27). Teflon insulator (2
2) and (27) also have a role of preventing discharge in unnecessary places.
The cases (23) and (28) are fixed by tightening jigs (25) and (26). The casings (23) and (28) and the fastening jigs (25) and (26) are made of stainless steel, and are kept at the ground potential together with the outer conductor (29). The introduced helium is sealed with an O-ring (24) so that it does not leak from the gaps between the parts. The gap between the cylindrical insulator (13) and the outer conductor (29) is filled with a conductive metal foil. (Not shown).

The overall appearance is shown in FIG. A plasma generator is held on the frame (33). The discharge part (31) can be seen at the bottom. The device described above is placed in a simple vacuum chamber. The inside of this decompression chamber is 100 Tor
Adjust the gas supply and exhaust to maintain r. This chamber can be simple, and a slight leak is not a problem.

2000sccm of helium was supplied to the above apparatus,
It was observed that a stable discharge was obtained when 500 W of high frequency power of 13.56 MHz was applied at a pressure of 100 Torr. The diameter of the central conductor (11) is 5 mm and its length is 30 mm. The outer shape of the cylindrical insulator (13) is 20 mm, and the thickness of the cylindrical insulator (13) is 1 mm. The gap between the central conductor (11) and the cylindrical insulator (13) is 7.5.
mm.

In the structure of this embodiment, the pressure is set to 2
When it is more than 00 Torr, stable discharge does not occur, and the generation of plasma becomes unstable. Therefore, in order to perform stable discharge, the pressure needs to be 150 Torr or less.

[Embodiment 2] In this embodiment, an etching effect in the case of etching silicon and alumina by adding 1 to 3% of CF ₄ to helium as an etching gas will be described. The same plasma generator as in [Example 1] was used. Power frequency is 13.56MHz, power is 50
0 W, the total flow rate of gas is 3 (liter / min), and the distance from the discharge region to the substrate (from the end face of the cylindrical insulator) is 1 mm. The experiment was conducted so that the pressure inside the chamber was 100 Torr. Table 1 below shows the etching effect when the amount of CF ₄ added and the reaction time were changed.

[0026]

[Table 1]

The evaluation rank of the etching effect was determined as follows. Good: An effect was observed in surface roughness measurement. Δ: Some effect was observed in surface roughness measurement. X: No effect was observed in surface roughness measurement.

[Comparative Example] In this comparative example, an etching effect in the case of etching silicon with only helium will be described. The same plasma generator as in [Example 1] was used. Power supply frequency is 13.56MHz, power is 500
W, the flow rate of helium gas is 3 (liter / minute), and the distance from the discharge region to the substrate (from the end face of the cylindrical insulator) is 1 m.
m or 2 mm. The pressure in the chamber is 1
It was set to 00 Torr. The results are shown in Table 2 below.

[0029]

[Table 2]

[Embodiment 3] This embodiment is an example of forming a carbon coating by using the plasma generator shown in FIG. 2 described in Embodiment 1. In this embodiment, methane is used as a source gas for forming the carbon film.

Further, in the present embodiment, the central conductor (11) is formed in a pipe shape, and the source gas is made to flow in the pipe. Argon is used as the rare gas. Argon flows into the gap between the central conductor (11) and the cylindrical insulator (13), where it is turned into plasma. The raw material gas is coaxially wrapped in argon gas that has been turned into plasma at the place of exit from the apparatus, and is activated by plasma energy from argon. Then, the activated raw material gas forms a film on the surface to be formed.

The film forming conditions are shown below. Raw material gas CH ₄ + H ₂ = 1: 4 100 scc
m Argon 3 liter / min High frequency power 500 W Pressure 100 Torr High frequency power has a power density per unit area of electrode.
It is a value of 0.1 W or more. The dimensions of other parts of the apparatus are the same as those in the first embodiment.

In the case of adopting the configuration of this embodiment, the source gas is guided to the surface to be formed so as to be wrapped by the rare gas which is turned into plasma, so that the efficiency of collecting the source gas can be made extremely high. Although methane was used as the source gas in this example, the source gas may be selected according to the type of the film to be formed. For example, if a silicon film is formed, silane or disilane may be used.
In addition, it is naturally possible to use the required additive gas and diluting gas together.

When a plurality of kinds of gases are used as the etching gas and the source gas, at least one gas is supplied from the pipe-shaped central conductor (11), and at least another gas is supplied to the central conductor (11) and the cylinder. It may be supplied from a gap with the insulator (13). In this case, the central conductor (11)
The gas supplied from the gap between the cylindrical insulator (13) and the insulator is directly plasmatized or activated by the high frequency energy supplied from the electrode. That is,
The gas supplied from the gap between the central conductor (11) and the cylindrical insulator (13) is more strongly activated or turned into plasma than the gas supplied from the pipe-shaped central conductor (11). Will be. By utilizing this, it is possible to selectively apply the high frequency energy only to the specific gas. That is, by supplying a specific gas from the gap between the central conductor (11) and the cylindrical insulator (13), high-frequency energy is directly applied only to this gas, and other gases are pipe-shaped central conductor (11). ), The energy can be supplied by the rare gas after the gas is discharged from the device. Such a configuration can be used when it is desired to make only the added gas a strong active state.

The structure of this embodiment is also effective for various plasma treatments such as etching and ashing.

[0036]

As described above, when the plasma generator of the present invention is used, stable plasma can be generated in a large area and can be effectively used for various plasma treatments. Alternatively, since the pressure can be increased to about 100 Torr, the device can be configured with a simple exhaust system.

[Brief description of drawings]

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

FIG. 2 shows a specific example of the plasma generator of the present invention.

FIG. 3 shows an external view of a plasma generator of the present invention.

[Explanation of symbols]

 11 ... Central conductor 12 ... Outer conductor 13 ... Cylindrical insulator 14 ... AC power supply 15 ... Discharge space 16 ... Flow rate control Container 17 ... Cylinder 29 ... Outer conductor 21 ... MHV coaxial plug 22, 27 ... Teflon insulator 23, 28 ... Housing 25, 26 ... Tightening jig 33 ... Stand 31 ... Discharge unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01L 21/3065 H05H 1/46 M 9014-2G (72) Inventor Shunpei Yamazaki Hase, Atsugi, Kanagawa Prefecture No. 398 Inside Semiconductor Energy Laboratory Co., Ltd.

Claims (13)

[Claims] 1. An electrode made of a conductor is arranged in a concentric cylinder shape, and a cylindrical insulator is inserted into a gap between the electrodes so as to form a concentric circle, and is inserted into a gap between the outer electrode and the inner electrode. A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A plasma characterized by maintaining a flow state at a pressure of 50 Torr, and applying an AC electric field between the electrodes to ionize the gas mainly containing the rare gas to generate plasma in the gap between the electrodes. Generator. 2. The plasma generator according to claim 1, wherein the gap between the insulator and the center electrode is 5 mm to 50 mm. 3. The plasma generator according to claim 1, wherein the gap between the insulator and the center electrode is 5 mm to 20 mm. 4. The plasma generator according to claim 1, wherein the plasma is glow discharge or corona discharge plasma. 5. The rare gas according to claim 1, wherein the rare gas is helium,
A plasma generator characterized by using at least one gas selected from argon, krypton, xenon, and neon. 6. An electrode made of a conductor is 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 is inserted into the gap between the outer electrode and the inner electrode. A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A method of operating a plasma generator that maintains a flow state at a pressure of 50 Torr and applies an AC electric field between the electrodes to ionize a gas mainly composed of the rare gas to generate plasma in a gap between the electrodes. In addition, a predetermined reactive gas is added to the gas containing the rare gas as a main component, and the plasma treatment is performed using the plasma generated in the gap between the insulator and the center electrode. How it works. 7. The method of operating a plasma generator according to claim 6, wherein film formation, etching, ashing, or alteration of the surface of the material to be processed is performed as the plasma treatment. 8. An electrode made of a conductor is 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 is inserted into the gap between the outer electrode and the inner electrode. A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A method of operating a plasma generator that maintains a flow state at a pressure of 50 Torr and applies an AC electric field between the electrodes to ionize a gas mainly containing the rare gas to generate plasma in a gap between the electrodes. A method of operating a plasma generator, wherein etching is performed by adding a reactive gas containing a halogen element to a gas mainly containing the rare gas. 9. An electrode made of a conductor is 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 is inserted into the gap between the outer electrode and the inner electrode. A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A method of operating a plasma generator that maintains a flow state at a pressure of 50 Torr and applies an AC electric field between the electrodes to ionize a gas mainly composed of the rare gas to generate plasma in a gap between the electrodes. A method of operating a plasma generator, wherein a thin film containing an element contained in the raw material gas is formed by adding a raw material gas to a gas mainly containing the rare gas. 10. A method of using a plasma generator according to claim 9, wherein a hydrocarbon gas is used as a source gas and a carbon film is formed as a thin film. 11. A method of using a plasma generator according to claim 10, wherein methane is used as the hydrocarbon gas. 12. An electrode made of a conductor is arranged in a concentric cylinder shape, and a cylindrical insulator is inserted into the gap between the electrodes so as to form a concentric circle, and is inserted into the gap between the outer electrode and the inner electrode. A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A plasma generator for maintaining a flow state at a pressure of 50 Torr and applying an AC electric field between the electrodes to ionize a gas mainly containing the rare gas to generate plasma in a gap between the electrodes. The plasma generating device, wherein the center electrode of the concentric circular electrodes has a pipe shape. 13. An electrode made of a conductor is arranged in a concentric cylindrical shape, and a cylindrical insulator is concentrically inserted in the gap between the electrodes, and a gap between the outer electrode and the inner electrode is inserted, A gas consisting mainly of a rare gas is added to the gap between the insulator and the center electrode between 5 and 1
A method of operating a plasma generator that maintains a flow state at a pressure of 50 Torr and applies an AC electric field between the electrodes to ionize a gas mainly composed of the rare gas to generate plasma in a gap between the electrodes. The center electrode of the concentric circular electrodes has a pipe shape, and the gas flowing in the pipe is activated by a gas containing plasma of the rare gas. A method of operating a plasma generator characterized.