JP3333110B2 - Surface treatment method using discharge plasma - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge plasma processing method under a pressure near atmospheric pressure.

[0002]

2. Description of the Related Art Conventionally, a method of generating a glow discharge plasma under a low pressure condition to perform surface modification has been put to practical use. However, treatment under low-pressure conditions is industrially disadvantageous, and is therefore applied only to expensive treated products such as electronic components. For this reason, a method of generating discharge plasma under a pressure near the atmospheric pressure has been proposed. For example, a method of performing treatment in a helium atmosphere is disclosed in
Japanese Patent No. 48626 discloses a method of performing a treatment in an atmosphere comprising argon, acetone and / or helium.
No. 74525.

However, all of the above methods generate plasma in a gas atmosphere containing helium or ketone, and the gas atmosphere is limited. Helium is expensive and is industrially disadvantageous. When ketone is contained, the ketone itself often reacts with the object to be treated, and a desired surface modification treatment may not be performed in some cases.

Further, in order to effectively utilize electrons and ions existing in the discharge space for surface treatment, not only a positive / negative symmetric sine wave centered on a normal ground potential but also a balance between positive and negative potentials is changed. A method of applying an electric field is performed. In this case, under a low pressure, a method is adopted in which a grid is inserted between the two electrodes sandwiching the discharge space and an appropriate potential is applied to the grid. However, a new power source is required for the control potential of the grid, and this control is not only complicated, but also under a pressure near the atmospheric pressure, the presence of the grid prevents uniform glow discharge or discharges from the grid. The method using the grid was not suitable because the impurities to be formed affect the treated surface.

As described above, under a pressure close to the atmospheric pressure, a method of applying an electric field in which the balance between positive and negative potentials is not realized, and there is a limit to speeding up the processing.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and is intended to be uniform and stable under a pressure near the atmospheric pressure regardless of the type of the atmosphere gas. An object of the present invention is to provide a method for generating a discharge plasma to further speed up the surface treatment.

[0007]

According to a surface treatment method using discharge plasma of the present invention, a solid dielectric is provided on at least one of the opposing surfaces of a pair of electrodes facing each other under a pressure near atmospheric pressure. In a gas discharge obtained by applying a pulsed electric field between a pair of opposed electrodes, the magnitude of the positive potential of the pulsed electric field is 1.5 times or more the magnitude of the negative potential.

The above-mentioned "making the magnitude of the positive potential of the pulse electric field 1.5 times or more the magnitude of the negative potential" means that the absolute value of the positive electric field is 1.5 times or more the absolute value of the negative electric field. This means that the surface treatment can be performed at a higher speed under the above conditions.

At a pressure near atmospheric pressure, the helium,
It is known that the plasma discharge state is not stably maintained except for a specific gas such as ketone, and the state is instantaneously shifted to an arc discharge state, but by applying a pulse electric field,
It is considered that a cycle in which the discharge is stopped before the transition to the arc discharge and the discharge is started again is realized.

Under a pressure near the atmospheric pressure, the method of applying a pulsed electric field according to the present invention can be used for the first time in an atmosphere that does not contain a component that takes a long time to change from a plasma discharge state such as helium or ketone to an arc discharge state. As a result, discharge plasma can be generated.

According to the method of the present invention, it is also possible to generate discharge plasma in air. In the plasma treatment under the atmospheric pressure condition containing a specific gas as well as the plasma treatment under the known low pressure condition, it is essential to perform the treatment in a closed container shielded from the outside air. According to the surface treatment method, treatment in an open system becomes possible. Furthermore, according to the method of applying a pulsed electric field, a high-density plasma state can be realized as compared with the method of applying a normal sine wave, which is of great significance in performing an industrial process such as continuous processing.

The above-mentioned pressure near the atmospheric pressure is defined as 100 to 8
Refers to a pressure of 00 Torr. The pressure is preferably in the range of 700 to 780 Torr, which facilitates pressure adjustment and makes the apparatus simple.

[0013] The plasma generation method in the method of the present invention is performed in an apparatus having a pair of opposing electrodes, and a solid dielectric placed on at least one of opposing surfaces of the electrodes. When a solid dielectric is installed on one of the electrodes, the portion where the plasma is generated, between the solid dielectric and the electrode,
When a solid dielectric is provided on both of the electrodes, it is a space between the solid dielectrics.

Examples of the electrode include those made of a simple metal such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds. It is preferable that the counter electrode has a structure in which the distance between the counter electrodes is substantially constant in order to avoid occurrence of arc discharge due to electric field concentration. Examples of an electrode structure that satisfies this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid opposed plate type, and a coaxial cylindrical structure.

The solid dielectric is provided on one or both of the opposing surfaces of the electrode. At this time, the electrode on the side on which the solid dielectric is placed is in close contact with the electrode, and the opposing surface of the contacting electrode is completely covered. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, an arc discharge occurs therefrom.

Examples of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. No.

The shape of the solid dielectric may be a sheet or a film, but preferably has a thickness of 0.05 to 4 mm. If the thickness is too large, a high voltage is required to generate discharge plasma. If the thickness is too small, dielectric breakdown occurs when a voltage is applied, and arc discharge occurs.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm.
If it is less than 1 mm, it is not enough to place the electrodes at intervals. If it exceeds 50 mm, it is difficult to generate uniform discharge plasma.

FIG. 1 shows an example of a pulse voltage waveform. Waveforms (A) and (B) are impulse waveforms, waveform (C) is a square waveform, and waveform (D) is a modulation waveform. Although the pulse voltage waveform in the present invention is not limited to the waveforms shown in FIG. 1, the shorter the rise time and the fall time of the pulse, the more efficiently the ionization of the gas during the plasma generation.

In particular, it is preferable that the rise time and / or the fall time of the pulse is 40 ns to 100 μs. If it is less than 40 ns, it is not realistic, and if it exceeds 100 μs, the discharge state easily shifts to an arc and becomes unstable. More preferably, it is 50 ns to 5 μs. Here, the rise time refers to the time during which the voltage change is continuously positive, and the fall time refers to the time during which the voltage change is continuously negative.

Further, modulation may be performed using pulses having different pulse waveforms, rise times, and frequencies. Such modulation is suitable for performing high-speed continuous surface treatment.

In the present invention, when a pulsed electric field is applied to the electrode, the intensity of the electric field due to the positive potential is 0.5 to 50 k.
V / cm, and a value (peak-peak value) from the maximum value of the positive potential to the maximum value of the negative potential is preferably 0.6 kV or more. If the intensity of the pulse electric field due to the positive potential is less than 0.5 kV / cm, it takes too much time for the surface treatment of the substrate, and if it exceeds 50 kV / cm, arc discharge is likely to occur. If the value (peak-peak value) from the maximum value of the positive potential to the maximum value of the negative potential is less than 0.6 kV, the surface treatment speed becomes insufficient. In applying the pulse voltage, a direct current may be superimposed.

The frequency of the pulse electric field is 1 kHz to 100
Preferably, it is kHz. If it is less than 1 kHz, it takes too much time for the treatment, and if it exceeds 100 kHz, arc discharge is likely to occur.

The formation time of one pulse electric field is 1 μm.
It is preferably from s to 1000 μs, and more preferably from 3 to 200 μs. If it is less than 1 μs, the discharge becomes unstable, and if it exceeds 1000 μs, it is easy to shift to arc discharge. Here, the formation time of one pulse electric field means ON, OFF, as illustrated in FIG.
Is repeated duration of one pulse waveform in a pulse electric field, in other words, a pulse duty time.

Further, in the present invention, the intensity of the pulse electric field is appropriately selected depending on the purpose of use of the discharge plasma and the like, but is preferably 1 to 100 kV / cm. 1
If it is less than kV / cm, the surface treatment speed becomes low,
If it exceeds 00 kV / cm, an arc discharge occurs, which is not preferable.

FIG. 3 is a block diagram showing an example of the configuration of a power supply circuit for forming a pulse electric field satisfying the above conditions, and FIG. 4 is an equivalent circuit diagram showing the principle of the operation. Indicated by In FIG. 4, SW1 to SW4 are semiconductor elements that function as switches in the switching inverter circuit in FIG.
By using a semiconductor device having a turn-on time and a turn-off time of 0 ns or less, the electric field strength is 1 to 100.
It is possible to realize the formation of a high-voltage and high-speed pulse electric field at kV / cm and a pulse rising and / or falling time of both 40 ns to 100 μs.

Next, the principle of operation will be briefly described with reference to FIG. + E is a positive DC voltage supply unit, and -E is a negative DC voltage supply unit. SW1 to SW4 are switching elements made of the high-speed semiconductor elements described above. D
Numerals 1 to 4 denote diodes, and I1 to I4 indicate the directions in which electric charges move.

First, when SW1 is turned on, the electric charge becomes I1
Then, one side (positive load) of a pair of electrodes placed at both ends of the discharge space is charged. Next, S
By turning off W1 and then turning on SW2 instantaneously, the charge charged to the positive load becomes SW2 and D
4 and move in the direction of I3.

Next, after SW2 is turned off, SW3
Is turned on instantaneously, the charge moves in the direction of I2 and charges the other electrode (negative load). Furthermore, SW3
Is turned off and then the switch SW4 is turned on instantaneously, so that the electric charge charged to the negative load moves in the direction of I4 through the switches SW4 and D2.

By repeating the above operation, an output pulse having the waveform shown in FIG. 5 can be obtained. [Table 1]
The operation table is shown in FIG. The numerical values shown in Table 1 correspond to the numerical values given to the waveforms in FIG.

[0031]

[Table 1]

The advantage of the circuit described above is that even if the load impedance is high, the charged electric charge is transferred to SW
2 and D4 or SW4 and D2 to discharge reliably, and high-speed turn-on switching elements SW1 and SW3 to perform high-speed charging. A pulsed electric field having an extremely short rise time and fall time as shown in FIG. 2 can be applied to a load, that is, between a pair of electrodes. The pulse electric field used in the surface treatment method of the present invention does not prevent superposition of a DC electric field.

The above-described power supply can arbitrarily change the magnitude of the voltage supplied from the positive DC voltage supply section and the magnitude of the voltage supplied from the negative DC voltage supply section. The positive / negative ratio can be easily controlled.

The discharge plasma device used in the present invention is:
As shown in FIG. 6, the base material 7 is placed on a dielectric in contact with the lower electrode 5, and the lower electrode 5 is usually grounded. However, an arbitrary potential may be applied. In this case, the potential of the lower electrode 5 is set to the reference potential for convenience.

When a pulse electric field having a shape in which the absolute value of the positive electric field is larger than the absolute value of the negative electric field is applied between the upper and lower electrodes with respect to the reference electric potential, the electric potential of the upper electrode 4 is biased positively on a time average basis. It is considered that the positive ions generated by the ionization of the gas exist longer on the substrate side above the lower electrode 5, and in this state, more excited species necessary for the surface treatment are present on the substrate. Therefore, it is estimated that the surface treatment speed is further improved.

To clearly increase the processing speed, the magnitude of the positive potential needs to be 1.5 times or more the magnitude of the negative potential. If the ratio of the negative potential / positive potential exceeds 20, the discharge becomes unstable and the transition to arc discharge becomes easy. Therefore, the ratio of negative potential / positive potential is preferably 20 or less.

The discharge plasma generated in the method of the present invention can be applied to various fields. Examples include surface modification using the reaction between the species excited by the discharge plasma and the substrate surface, decomposition and removal of nitrogen oxides by generating discharge plasma in the presence of nitrogen oxides, and light sources. Can be used.

Hereinafter, the method for treating the surface of the substrate will be described in detail. The surface treatment method of the present invention has a pair of counter electrodes,
In a device in which a solid dielectric is provided on at least one of the opposing surfaces of the electrodes, when a solid dielectric is provided on one of the electrodes, a space between the solid dielectric and the electrode, and a solid dielectric is provided on both of the electrodes. When a body is provided, a base material is provided in a space between the solid dielectrics, and the surface of the base material is treated by discharge plasma generated in the space.

Examples of the substrate to be subjected to the surface treatment of the present invention include plastics such as polyethylene, polypropylene, polystyrene, polycarbonate, polyethylene terephthalate, polytetrafluoroethylene, and acrylic resin, glass, ceramic, and metal. Examples of the shape of the substrate include a plate shape and a film shape, but are not particularly limited thereto. According to the surface treatment method of the present invention, it is possible to easily cope with the treatment of substrates having various shapes.

In the surface treatment, any treatment can be performed by selecting a gas (hereinafter referred to as a processing gas) existing in the discharge plasma generation space. By using a fluorine-containing compound gas as the processing gas, a fluorine-containing group can be formed on the surface of the base material to lower the surface energy and obtain a water-repellent surface.

Examples of the fluorine element-containing compounds include carbon tetrafluoride (CF ₄ ), carbon hexafluoride (C ₂ F ₆ ), propylene hexafluoride (CF ₃ CFCF ₂ ), and cyclobutane octafluoride (C ₄ F ₈ ) Fluorine-carbon compounds such as monochloride
Halogen, such as fluorocarbon (CClF ₃₎ - carbon compound,
6 fluoride such as sulfur hexafluoride (SF ₆₎ - sulfur compounds and the like. From the viewpoint of safety, it is preferable to use carbon tetrafluoride, carbon hexafluoride, propylene hexafluoride, and cyclobutane 8-fluoride which do not generate hydrogen fluoride which is a harmful gas.

Further, by using an oxygen element-containing compound, a nitrogen element-containing compound, or a sulfur element-containing compound as a treatment gas as described below, a hydrophilic functional group such as a carbonyl group, a hydroxyl group or an amino group is formed on the substrate surface. It can be formed to increase the surface energy and obtain a hydrophilic surface.

Examples of the oxygen element-containing compound include oxygen,
Contains oxygen elements such as ozone, water, carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, and aldehydes such as methanal and ethanal. Organic compounds and the like can be mentioned. These alone are 2
Mixtures of more than one species may be used. Further, the oxygen element-containing compound and a gas of a hydrocarbon compound such as methane and ethane may be mixed and used. Addition of the fluorine element-containing compound at 50% by volume or less to the oxygen element-containing compound promotes hydrophilicity. As the fluorine-containing compound, the same compounds as those described above may be used.

Examples of the nitrogen element-containing compound include nitrogen,
Ammonia and the like. The nitrogen element-containing compound and hydrogen may be used as a mixture.

Examples of the sulfur-containing compound include sulfur dioxide and sulfur trioxide. Further, sulfuric acid can be used after being vaporized. These may be used alone or in combination of two or more.

By performing the treatment in an atmosphere of a monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule,
A hydrophilic polymer film can be laminated. As the hydrophilic group, a hydroxyl group, a sulfonic acid group, a sulfonate group,
Examples include a hydrophilic group such as a primary, secondary, or tertiary amino group, an amide group, a quaternary ammonium base, a carboxylic acid group, and a carboxylic acid group. Also, a hydrophilic polymer film can be similarly laminated by using a monomer having a polyethylene glycol chain.

The monomers include acrylic acid, methacrylic acid, acrylamide, methacrylamide, N, N
-Dimethylacrylamide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, sodium styrenesulfonate, allyl alcohol, allylamine, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, and the like. These monomers are
Used alone or as a mixture.

Since the above-mentioned hydrophilic monomer is generally a solid, it is used by dissolving it in a solvent and vaporizing it by heating, decompression, or the like. Examples of the solvent include organic solvents such as methanol, ethanol, and acetone, water, and mixtures thereof.

Further, using a processing gas such as a metal-hydrogen compound, a metal-halogen compound, or a metal alcoholate of a metal such as Si, Ti, or Sn, SiO ₂ , TiO ₂ , Sn
By forming a metal oxide thin film such as O ₂ , electrical and optical functions can be given to the substrate surface.

From the viewpoint of economy and safety, it is preferable to carry out the treatment in an atmosphere in which the above-mentioned treatment gas is diluted with an inert gas. Helium, as an inert gas,
Rare gases such as neon, argon, and xenon, and nitrogen gas are exemplified. These may be used alone or in combination of two or more. Conventionally, processing was performed in the presence of helium under a pressure near the atmospheric pressure. However, according to the method of the present invention, stable processing in argon and nitrogen gas, which is cheaper than helium, can be performed. And has great industrial advantages.

FIG. 6 shows an example of an apparatus for performing the surface treatment method of the present invention. In this device, a solid dielectric 6 is provided on a lower electrode 5, and a solid dielectric 6 and an upper electrode 4 are provided.
A discharge plasma is generated in the space 3 between the two. The container 2 includes a gas introduction pipe 8, a gas exhaust port 10, and a gas exhaust port 11, and the processing gas is supplied from the gas introduction pipe 8 to the discharge plasma generation space 3. In the present invention, since the part in contact with the generated discharge plasma is processed, FIG.
In the example, the upper surface of the substrate 7 is processed. If it is desired to treat both surfaces of the base material, the base material may be set up in the discharge plasma generation space 3.

It is preferable that the processing gas is uniformly supplied to the plasma generation space. When processing in a mixed gas of a processing gas and an inert gas, since the inert gas is lighter than the processing gas, a device must be devised to avoid non-uniformity during supply. In particular, when treating a substrate having a large area, care must be taken since the substrate tends to be uneven. In the example shown in the apparatus of FIG. 6, a gas introduction tube 8 is connected to the electrode 4 having a porous structure, and a processing gas is supplied to the plasma generation space 3 from above the substrate through the hole of the electrode 4. The inert gas is separately supplied through an inert gas introduction pipe 9. The structure is not limited to such a structure as long as the gas can be supplied uniformly, and a means such as stirring or blowing the gas at a high speed may be used.

The material of the container 2 includes, for example, resin and glass, but is not particularly limited. Metals such as stainless steel and aluminum can also be used as long as they have a structure insulated from the electrodes.

The discharge plasma treatment of the present invention may be carried out by heating or cooling the substrate, but is sufficiently possible at room temperature. The time required for the discharge plasma treatment is the applied voltage,
It is appropriately determined in consideration of the type of the processing gas, the ratio in the mixed gas, and the like.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to further clarify the surface treatment method using discharge plasma of the present invention, an embodiment of an optical surface treatment will be described below as an example of the surface treatment. In the following embodiment, a power supply (manufactured by Heiden, semiconductor element: IXYS, model number TO-247) according to the equivalent circuit diagram of FIG.
AD).

Example 1 In a discharge plasma processing apparatus (chamber: Pyrex glass container 2, capacity: 8 liter) shown in FIG. 6, a grounded lower electrode 5 (diameter: 140 mm, surface: relative dielectric constant: 16)
A soda glass substrate 7 is disposed on the zirconium dioxide dielectric of the above, and the upper electrode 4 (holes of 80 mm in diameter and 1 mm in diameter are disposed at 5 mm intervals at 2 mm above the substrate surface. Was coated with a zirconium dioxide dielectric having a relative dielectric constant of 16), and a polymer film was formed under the following conditions.

The inside of the apparatus is set to 0.1 Torr by an oil rotary pump.
Evacuation was performed until. Next, nitrogen gas was introduced from the inert gas introduction pipe 9 until the inside of the apparatus reached 760 Torr. Thereafter, a mixed gas of propylene hexafluoride at a flow rate of 20 sccm and argon gas at a flow rate of 980 sccm was introduced from a (reaction) gas introduction gas pipe 8 connected to the upper electrode 4. After introducing the mixed gas for one minute, a positive potential of 12.5 was applied between the upper electrode 4 and the lower electrode 5 at a frequency of 8 kHz.
A pulse electric field of kV and a negative potential of 1.5 kV was applied, and discharge was performed for 30 seconds to form a fluorocarbon polymer film on the surface of the glass substrate. The discharge current density was 40 mA / cm ² .

Example 2 A fluorocarbon polymer film was formed on the surface of a glass substrate in the same manner as in Example 1 except that the applied electric field was 8.4 kV for the positive potential and 5.6 kV for the negative potential. The discharge current density is 40 mA
/ Cm ² .

Comparative Example 1 A fluorocarbon polymer film was formed on the surface of a glass substrate in the same manner as in Example 1 except that the applied pulse electric field was set to 7 kV for both the positive potential and the negative potential. The discharge current density is 40 mA
/ Cm ² .

As described above, the transparent polymer films on the glass substrates obtained in Examples 1 and 2 and Comparative Example 1
Ellipsometer (DVA-, manufactured by Mizojiri Optical Industrial Co., Ltd.)
36 VW), and measured at five points to obtain an average value.

[0061]

[Table 2]

From the above Examples and Comparative Examples, it can be confirmed that when the positive potential is set to 1.5 times or more of the negative potential, a high-speed processing effect is exhibited, and the higher the ratio, the higher the speed.

[0063]

The surface treatment method using discharge plasma according to the present invention is configured as described above, so that only the output of the discharge electrode according to the present invention is controlled without changing other discharge conditions. The surface treatment capacity can be further increased. or,
Since the present invention can be carried out in the vicinity of the atmospheric pressure, the discharge conditions can be changed even during the continuous processing, so that the present invention has a great industrial advantage. Furthermore, in the plasma generation space,
Unlike the conventional glow discharge, there is no need to insert a control grid electrode, so that no impurities are mixed into the surface treatment film.

[0064]

[Brief description of the drawings]

FIG. 1 is a voltage waveform diagram showing an example of a pulse electric field.

FIG. 2 is an explanatory diagram of a formation time of one pulse electric field.

FIG. 3 is a block diagram of a power supply that generates a pulse electric field.

FIG. 4 is an equivalent circuit diagram of a power supply that generates a pulse electric field.

FIG. 5 is a diagram of an output pulse signal corresponding to an operation table of a pulse electric field.

FIG. 6 is a schematic view showing one example of a discharge plasma processing apparatus of the present invention.

[Explanation of symbols]

 1-1 AC power supply (high voltage pulse power supply) 1-2 DC power supply 2 Pyrex glass container 3 Discharge plasma generation space 4 Upper electrode 5 Lower electrode 6 Solid dielectric 7 Base material 8 (Reaction) gas introduction pipe 9 Inert gas Inlet pipe 10 Gas outlet 11 Exhaust port

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-10-287757 (JP, A) JP-A-9-302118 (JP, A) JP-A-3-236475 (JP, A) JP-A-6-302 336529 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J ⁷ /00-7/18 H05H 1/46

Claims (3)

(57) [Claims] At least one opposing surface of a pair of opposing electrodes is provided with a solid dielectric under a pressure near the atmospheric pressure,
In a gas discharge obtained by applying a pulsed electric field between the pair of opposed electrodes, a discharge plasma characterized in that the magnitude of the positive potential of the pulsed electric field is 1.5 times or more the magnitude of the negative potential. Surface treatment method used. 2. The method according to claim 1, wherein the rise time and / or the fall time is 40 ns to 100 μs, the electric field strength due to the negative potential is 0.5 to 50 kV / cm, and the maximum potential of the positive potential is from the maximum value of the negative potential. The surface treatment method using discharge plasma according to claim 1, wherein a pulse electric field having a value (peak-peak value) of 0.6 kV or more is applied. 3. A pulse electric field has a pulse electric field formation time of 1 μs to 1000 μs and a frequency of 1 kHz.
The surface treatment method using discharge plasma according to claim 1 or 2, wherein the frequency is set to 100 kHz.