JP5725304B2 - Surface treatment method - Google Patents

Description

The present invention relates to a surface treatment how articles having a hydrophilic surface.

  For example, the following methods are known as methods for decomposing or removing organic substances using plasma.

  (I) A method in which oxygen gas or argon gas is changed to a plasma state under atmospheric pressure, and the plasma is sprayed onto the surface of a substrate such as a silicon wafer or a liquid crystal glass substrate to remove organic substances adhering to the substrate surface. Known (see Patent Documents 1 and 2). Also, an atmospheric pressure plasma surface treatment apparatus that has put this method to practical use has already been commercialized.

  (II) irradiating a liquid such as an organic solvent containing an organic substance with ultrasonic waves to generate bubbles in the liquid; then irradiating the bubbles with electromagnetic waves to generate plasma in the bubbles to form plasma bubbles; A method of decomposing organic substances dispersed in a liquid by using plasma bubbles has been proposed (see Patent Document 3).

  (III) Bubbles are generated in the water by supplying a gas such as oxygen or air to the water, and a high voltage pulse is applied to the bubbles to instantaneously change the inside of the bubbles to a plasma state. Patent Documents 4 to 9 describe techniques for decomposing by the above.

  (IV) Technology for generating high-temperature plasma bubbles in a liquid, attaching a compound generated from the plasma bubbles to the surface of the fiber, and performing surface modification such as uneven shape on the surface of the fiber, and functions obtained from the technology Patent Document 10 describes a modified fiber.

  In the method (I), (1) organic substances on the surface of heat-resistant articles such as inorganic materials can be decomposed or removed by plasma, but decomposed substances or unreacted organic substances drift in the atmosphere. (2) high energy plasma Although gas can be generated, there is a problem that application to an organic polymer material is difficult because the surface temperature of the article becomes very high.

  In the method (II), (1) the organic matter dispersed in the liquid can be decomposed, but it is unclear whether it can be applied to the removal of the organic matter adhering to the surface of the article. (2) Even if the organic substance is decomposed by bringing the plasma into contact with the article, the surface temperature of the article becomes high as in the method (I), so that it is considered difficult to apply the organic polymer material.

  In the method (III), as in (II) above, (1) the organic matter dispersed in the liquid can be decomposed, but it is unclear whether it can be applied to the removal of the organic matter adhering to the surface of the article. (2) Since the plasma state lasts only for a short time, effective decomposition is unlikely to occur when the frequency of contact between bubbles in the plasma state (hereinafter referred to as plasma bubbles) and the organic substance to be decomposed is low.

  In the specification of Patent Document 10 of (IV), it is described that the surface modification of the fiber can be performed by bringing the plasma bubbles into contact with the fiber. The material of the fiber is not particularly limited. However, as described in Patent Document 3 of (II), the temperature of plasma bubbles is as high as about 5000 K, whereas organic polymer materials generally have sufficient heat resistance to withstand such high temperatures. I don't have it. Also, if the melting point or softening point of the material is lower than the temperature of the plasma bubble, it is expected that the material will melt and flow when it comes into contact with the plasma bubble, or it will lead to thermal decomposition and destruction. It is difficult to apply plasma bubbles to the fibers used. Moreover, when using such a material inferior in heat resistance, it is expected that the fiber form itself will be destroyed rather than providing the surface with an uneven function. In addition, although carbon fibers are mentioned in the examples, carbon fibers are very thin, and depending on the shape of wrinkles on the fiber surface, the degree of graphite structure on the surface, and the degree of flame resistance, It is conceivable that the fiber portion in contact with the high-temperature plasma bubbles is excessively graphitized by heat, the fiber becomes locally brittle, and the mechanical properties of the entire fiber are lowered. In addition, there is no description as to whether or not cleaning can be performed without changing the surface form when using a material having poor heat resistance. As described above, the specification of Patent Document 10 has no description regarding selection of materials.

JP 2002-143895 A JP 2004-311838 A JP 2004-306029 A Special table 2005-502456 gazette JP 2005-58887 A JP 2005-21869 A Japanese Patent Laid-Open No. 2005-13858 JP 2004-268003 A JP 2002-272825 A JP 2005-105465 A

  An object of the present invention is to provide a surface treatment method capable of decomposing or removing organic matter such as dirt adhering to an article without scattering it into the atmosphere and suppressing damage to the article, It is an object of the present invention to provide a surface treatment method for etching and to provide an article that is not damaged while highly cleaning the surface and etching an article or surface that is hardly damaged.

In the surface treatment method of the present invention, thermal plasma generated in water vapor bubbles in a liquid containing water is brought into contact with an organic substance attached to a material having a contact angle with respect to water of 90 degrees or less in the liquid. A surface treatment method for removing the organic substance from the material , wherein the material is a polymer electrolyte membrane, glass, or ceramics .
The contact angle of the material with water is not preferable in the range of 70 degrees to 0 degrees.

According to the surface treatment method of the present invention, it is possible to decompose or remove an organic substance or the like adhering to an article without scattering it into the atmosphere, and to suppress damage to the article. In addition, the surface of the article can be etched while suppressing damage to the article.
The article obtained by the surface treatment method of the present invention has a highly cleaned or etched surface and is hardly damaged.

It is a schematic block diagram which shows an example of a plasma generator. It is a figure which shows the contact angle of the water with respect to the article | item surface. It is a graph which shows the contact angle dependence of the etching rate by the water vapor bubble (henceforth water vapor bubble plasma) in a plasma state. It is a schematic diagram of a multilayer wiring damascene process. It is a figure which shows the emission spectrum from water vapor bubble plasma. (Example 1) It is an electron micrograph of the surface of a clogged hollow fiber membrane sample. It is an electron micrograph of the hollow fiber membrane sample surface after surface treatment.

(Surface treatment method)
The surface treatment method of the present invention is a method in which plasma generated in water vapor bubbles in a liquid containing water is brought into contact with an article having a hydrophilic surface in the liquid. The index of the hydrophilic material in the present invention is a material having a contact angle with water of 90 degrees or less.

  As the plasma generator used in the present invention, the plasma generators described in JP-A Nos. 2003-297598 and 2004-152523 may be used.

  Hereinafter, the surface treatment method of the present invention will be described using a specific plasma generator as an example.

  FIG. 1 is a schematic configuration diagram showing an example of a plasma generator used in the surface treatment method of the present invention. The plasma generator 10 includes a container 12 that contains a liquid 11, an electrode 13 that is disposed in the container 12 for emitting electromagnetic waves, a counter electrode 14 that is disposed to face the electrode 13, A support 16 for fixing the article 15 between the electrode 13 and the counter electrode 14, an electromagnetic wave power source (for example, a high frequency power source) (not shown) connected to the electrode 13 and the counter electrode 14, and the liquid 11 in the container 12 A vacuum pump (not shown) for adjusting the pressure of the upper air phase 19 (gas phase) is provided and is generally configured.

  In the plasma generating apparatus 10, the electrode 13 is connected to an electromagnetic wave power source that can supply a high frequency and a high voltage. When the electromagnetic energy of this power source is supplied to the electrode 13, the electrode is heated, the liquid 11 around the electrode is vaporized, and the water vapor bubbles 17 containing water vapor as a main component are attached around the electrode.

  When high frequency and high voltage are applied to the water vapor bubbles attached to the electrode, the molecular motion of water molecules inside the bubbles becomes intense, and electrons are knocked out from the atoms that make up the water molecules. And electrons are generated. A chain reaction in which the knocked-out electrons sequentially attack another water vapor occurs, positively charged gas and electrons are successively generated, and the inside of the water vapor bubbles becomes a plasma state.

  From water vapor bubbles in a plasma state (hereinafter referred to as water vapor bubble plasma), light emission appears in a specific wavelength region. From this emission spectrum, the gas species generated inside the plasma bubbles can be known. Table 1 shows the wavelength of the emission spectrum of water vapor bubble plasma and the attribution of the type of gas that is the cause of light emission.

  When the water vapor bubble plasma around the electrode comes into contact with dirt made of organic matter on the surface of the article 15 immersed in the liquid 11, (1) thermal decomposition due to heat of the water vapor bubble plasma, and (2) oxidation by OH radicals in the water vapor bubble plasma. Dirt is decomposed or removed by two actions.

  Although details will be described later, in this surface treatment, if the article is hydrophilic, the water around the article is evaporated, the article surface is cooled due to latent heat of vaporization, and the heat generated by the heat of the water vapor bubble plasma in (1). Decomposition is reduced.

  The liquid 11 may be a liquid containing water, and examples thereof include water, an aqueous solution containing an organic solvent mixed with water, and an aqueous solution in which electrolyte ions are dissolved in water.

Examples of the organic solvent mixed with water include alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; acetone and the like. Examples of the electrolyte ions include Mg ²⁺ , Ca ²⁺ , Na ⁺ , Fe ²⁺ , Fe ³⁺ , Cl ⁻ , NO ³⁻ , NO ²⁻ , OH ^{− and the} like.

  The presence of electrolyte ions in the liquid 11 improves the electrical conductivity of water, and an arc discharge current easily flows from the electrode 13 that emits electromagnetic waves to the counter electrode 14 when plasma is generated. The organic solvent may be carbonized by plasma, and the carbide may adhere to the article 15. Moreover, when the volume fraction of water falls among liquid compositions, the cooling effect of the surface of the article | item 15 by water will fall as mentioned later, and the article | item 15 surface becomes easy to be damaged. Therefore, it is preferable that the liquid 11 does not contain an organic solvent as much as possible, and it is especially preferable that it does not contain at all. More preferably, it is desirable to use pure water or ultrapure water used in a semiconductor manufacturing process or the like.

  The generation of the water vapor bubbles 17 is not limited to the method by heating the electrode 13, and an ultrasonic generator is provided separately, and cavitation bubbles are generated in the liquid 11 by ultrasonic waves from the ultrasonic generator, Alternatively, the surrounding liquid 11 may be vaporized as a vapor to form the water vapor bubbles 17.

  The frequency of the electromagnetic wave irradiated to the water vapor bubbles 17 is selected according to the application in the range of 1 MHz to 100 GHz.

  When the water vapor bubbles 17 are generated, the air phase 19 in the container 12 may be decompressed by a vacuum pump. When the air phase 19 in the container 12 is depressurized, the boiling point of the liquid 11 is lowered, water vapor is easily generated, the vapor pressure inside the water vapor bubbles is increased, and the number of water vapor molecules leading to plasma generation is increased. Plasma discharge becomes easy. Once the inside of the water vapor bubbles reaches a plasma state, plasma generation inside the bubbles continues even after the vacuum pump is stopped and the pressure of the air phase 19 is returned to atmospheric pressure.

  As the article 15, an article having a hydrophilic surface is suitable. Specifically, a hydrophilic organic polymer material, glass, ceramics, silicon wafer, metal (for example, aluminum, copper, tungsten, etc.), graphite, carbon fiber, etc. Is mentioned.

  In the present invention, the “hydrophilic surface” is defined with the value of the contact angle θ defined in FIG. The “hydrophilic surface” in the present invention is a surface having a contact angle θ of water (water droplets 18) with respect to the surface of the article 15 at 25 ° C. of 90 degrees or less. The contact angle of water with the hydrophilic surface is preferably as low as possible, specifically 80 degrees or less is more preferable, and the range of 70 degrees to 0 degrees is more preferable.

  The definition of the contact angle θ in the present invention is the same as the contact angle, which is a general index of material wetting with respect to water. As a reference book on contact angles, Ikuo Murakawa, “Metallic Functional Surface”, published by Modern Editing Co., 1984, p. The matter described in 133 is cited. According to the same document, when a droplet that does not react with the surface is dropped on a smooth surface and the droplet is in an equilibrium state with a certain contact angle with the surface, the following equation (1) is established in FIG.

γ _SV = γ _SL + γ _LV cos θ (1)
γ- _SV Liquid and vapor adsorption surface tension of solid in parallel γ _SL solid-liquid interface tension γ _LV surface tension of liquid in equilibrium

  When the equation (1) is written as the following equation (2), the left side shows a decrease in surface energy when the solid surface is wetted with a liquid.

γ _SV −γ _SL = γ _LV cos θ (2)

Since this energy is surface free energy, the larger the amount of decrease γ _LV cos θ, the easier it is to wet. If γ _LV is constant, the smaller θ is, the better the wettability is. The reason why the contact angle θ of the water droplet is used to quantify the wettability is based on the formula (2). In the present invention, the liquid is water, and γ _LV is 72.8 dyn / cm (“Science Chronology”, Maruzen Co., Ltd., 1993, p.449) at 20 ° C.

  In the present invention, a smooth material surface is prepared, this surface is kept horizontal, a water droplet is dropped on the surface, (θ / 2) is measured with a contact angle meter, and the contact angle θ in FIG. 2 is obtained. . When the material surface is porous or has irregularities, a smooth surface is prepared using the same material, and θ is obtained on the smooth surface. In an organic polymer, metal, glass, or ceramic, when the surface has irregularities, a smooth surface can be obtained by melting the same material. In the case of a material that cannot be melted, such as carbon fiber, a smooth sheet made of a precursor material (for example, polyacrylonitrile or polyimide) is prepared in advance, and this is fired to have a smooth surface made of a carbon material. Get. A water drop is dropped on this sheet, and the contact angle is measured. The water used in the measurement of the contact angle is clean water such as ultrapure water or ion exchange water.

  Tables 2 and 3 show contact angles θ (25 ° C.) of water with typical organic polymer materials and inorganic materials (Document a: “Chemical Handbook 4th edition, basic edition II”, Maruzen Co., Ltd., 1993, II-83 7.1.3 Contact angle, literature b: Ikuo Ishii, Masumi Koishi, Mitsuo Tsunoda, “Wetting Technology Handbook”, Techno System Co., Ltd., 2001, b1: p.418, b2: p.92, b3: p.96, b4: p.102-103, b5: p.161, b6: p.198).

  In addition, “Metal Surface Handbook”, Nikkan Kogyo Shimbun, 1988, p. 183 states that “the surface of a clean metal is wet with water and the contact angle is zero. If there is dirt, the portion becomes wet with water”. Murakawa Ikuo, “Metallic Functional Surface”, Modern Editor, 1984, p. According to 134-136, the solid surface tension of γ-Fe is 1670-2127 dyn / cm based on the measurement result of the molten state at high temperature, and the solid surface tension of copper is about 1500 dyn based on the measurement result of the molten state at high temperature. / Cm, which is described as being much greater than the surface tension of the polymer. On the other hand, the surface tension of water is 72.8 dyn / cm. That is, the surface of a clean metal is a surface that is very easy to wet with water. A clean metal material having a high surface energy can also apply the surface treatment of the present invention.

  In the present invention, any material such as an organic polymer material, glass, ceramics, metal, graphitic carbon material, and carbon fiber can be used as long as it satisfies θ ≦ 90 degrees.

When the wavelength of atomic hydrogen (H _α : 656 nm) in the plasma in the water vapor bubbles is converted into temperature, the temperature is as high as about 5000 K, and the above-described high-temperature plasma gas is applied to an article made of a general organic polymer material. It will be destroyed instantly without a trace. Here, when an article made of a hydrophilic material satisfying θ ≦ 90 degrees is used, the present inventors can clean the organic substance on the article surface by decomposing or removing it with almost no damage to the article surface. It was found that the surface can be etched without destroying an article cleaned by washing.

  The concept of the present invention for avoiding thermal decomposition is schematically shown in FIG. As shown in FIG. 3, when the material is brought into contact with water vapor bubbles in water, if the contact angle θ of the material with respect to water is 90 degrees or less, the contribution of thermal decomposition etching due to heat is reduced, and 90 degrees When it exceeded, it discovered that the contribution of thermal decomposition etching became large. The reason is given as follows.

  For materials whose θ is 90 degrees or less, the surface of the material is covered with a layer of water in a water-containing liquid, and even if water vapor bubble plasma approaches, the water on the surface of the material evaporates and evaporates from the surroundings of the material. Since it takes away latent heat and water is constantly supplied to the hydrophilic surface, a permanent cooling effect acts on the material surface and the temperature rise of the article is suppressed. As a result, the surface temperature of the article does not exceed the heat resistance temperature of the material, the contribution of etching by thermal decomposition is reduced, and damage to the material is suppressed. This effect is also effective in preventing local excessive graphitization due to the heat of plasma in the surface treatment of carbon fiber.

  It is known that when an organic substance such as dirt adheres to the surface of a hydrophilic article, the water wettability changes to be hydrophobic compared to the original hydrophilic surface. For example, Ishii Ikuo, Koishi Masumi, Tsunoda Mitsuo, “Wet Technology Handbook”, Techno System Co., Ltd., 2001, p. According to 83-84, pure metal surfaces are easily wetted by water, but if left in an atmosphere where organic substances are present, the organic substances gradually adhere to the metal surfaces, so that the hydrophobicity of the metal surface proceeds with time. It is described to do. Similarly, hydrophilic organic materials and ceramic surfaces tend to be hydrophobized by contamination with organic matter.

  According to FIG. 3, the dirt on the surface of the material is decomposed under the action of thermal decomposition by heat of water vapor bubble plasma and oxidative decomposition by OH radicals. When the dirt disappears, a more hydrophilic material surface appears, and the above-described cooling effect of water suppresses thermal decomposition and provides a material surface with low damage.

  In the case of a hydrophilic material having a contact angle of 90 or less, etching by thermal decomposition can be suppressed, and the material can be gradually etched by oxidative decomposition by OH radicals. By this etching, various materials exhibiting hydrophilicity can be etched. For example, hydrophilic polymer materials, metal materials, ceramics, hydrophilic glass, hydrophilic carbon materials, and the like can be etched.

  In the surface treatment of the present invention, the time for which the article 15 is brought into contact with the water vapor bubble plasma (hereinafter referred to as the contact time) is the heat resistance temperature of the article 15, the temperature inside the bubble plasma, the cooling effect of water generated on the article surface, and dirt. It may be adjusted as appropriate in consideration of the degree of.

  If the contact time is too long, the water vapor bubble plasma causes the water on the surface of the article 15 to evaporate too much, resulting in insufficient water on the surface of the article 15, the temperature of the material surface temporarily exceeds the heat resistance temperature, or The oxidation action is too strong and damages the article.

  If the contact time is too short, the oxidizing action of OH radicals becomes weak, and cleaning and etching of the article surface tends to be insufficient.

The “contact time” in the present invention is defined as the time during which plasma is generated in the water vapor bubbles 17 by applying a voltage to the electrode 13 and the counter electrode 14 when the article 15 is stationary. When moving in a certain direction, define as follows.
Contact time (s) = length in the moving direction of the article 15 (mm) / moving speed of the article 15 (mm / s) in the region where the plasma is generated

  The index of the heat resistant temperature of a material varies depending on the type of material, but in the present invention, the heat resistant temperature is defined as the temperature at which the form of the material can be maintained.

  In the organic polymer material, the crystalline material has a melting point, and the amorphous polymer material has a glass transition temperature as a heat resistant temperature index. Table 4 shows the glass transition temperature (Tg) and melting point (Tm) of typical crystalline organic polymer materials. (Joel R. Fried, “Polymer Science and Technology”, Prentice Hall, 1995, p. 140).

  In ceramics, the melting point is used as an index of heat-resistant temperature. Table 5 shows melting points (Tm) of typical ceramics. (Marcel Mulder, “Basic Principles of Membrane Technology”, 2nd Edition, Kluwer Academic Publishers, 1996, p. 60)

  For optical glass materials, the glass transition temperature is used as an index of heat resistance. Table 6 shows the glass transition temperatures of typical optical glass types. (Optical Application Technology Workshop Text, “Optical Materials III-9”, Japan Opto-Mechatronics Association, 1988, p. 30)

  For optical crystal materials, the melting point of the material is used as an index of heat resistance. Table 7 shows melting points of typical optical crystal materials. (Optical Application Technology Workshop Text, “Optical Materials III-9”, Japan Opto-Mechatronics Association, 1988, p. 55)

  For metals, silicon wafers (silicon), etc., the melting point is used as an index of the heat resistant temperature. Table 8 shows melting points of typical metals. (National Astronomical Observatory, “Science Chronology”, Maruzen Co., Ltd., 1993, p.469)

  In carbon materials, carbonization-graphitization has already progressed with temperature, and it is difficult to determine a clear heat-resistant temperature. Therefore, 3550 ° C., the melting point of the graphite single crystal of the related material, is used as an indicator of the structural phase transition of the carbon material To do. In the case of carbon fibers, the degree of crystallinity is low, and it is difficult to clearly distinguish between amorphous and crystalline parts, and it is often difficult to determine the structural phase transition point of clear crystals. The temperature up to the temperature is the heat resistant temperature.

(application)
The surface treatment method of the present invention includes (1) cleaning an article in which organic matter such as dirt adheres (deposits) on the material surface, (2) processing for etching the hydrophilic material surface, and (3) irregularities on the material surface. It can be applied to processing that gives

  The cleaning (1) will be described. Organic substances include viruses, bacteria, yeasts, molds, algae, protozoa, proteins, blood and blood components, animal or plant cells, hair, household waste, garbage, wastewater, etc. Organic materials commonly found in daily life are listed.

  Examples of the cleaning of the article based on the surface treatment method of the present invention include the following examples. The object of cleaning is not limited to the following example, and any hydrophilic material having a water contact angle θ of 90 degrees or less can be used, and a process suitable for the temperature of the plasma bubbles and the cooling effect condition can be used. If it is selected appropriately, it can be washed.

  (A) Plasma is brought into contact with the porous membrane having a hydrophilic surface used for the filtration treatment, and the filtered deposit made of organic matter adhering to the membrane surface is decomposed and removed by thermal decomposition (or carbonization) or oxidation action by OH radicals. Then, the porous membrane is regenerated.

  (B) After being embedded in the human body, the plasma is brought into contact with the biocompatible material having a hydrophilic surface, which is taken out of the human body, and the organic matter adhering to the surface of the biocompatible material is thermally decomposed (or carbonized) or OH radicals. The biocompatible material is regenerated by decomposing and removing it by the oxidizing action. Examples of the biocompatible material include polymethyl methacrylate resin, polylactic acid resin, polyurethane, hydrogel, cellulose, polyvinyl alcohol, and hydroxyapatite.

  (C) Plasma is brought into contact with an organ having a hydrophilic surface taken out from the human body, and cancer cells existing in the organ are decomposed and removed by thermal decomposition (or carbonization) or oxidation action by OH radicals.

  (D) Plasma is brought into contact with a contact lens having a hydrophilic surface, and organic substances such as proteins adhering to the contact lens are decomposed and removed by thermal decomposition (or carbonization) or oxidation action by OH radicals.

  (E) Plasma is applied to a catheter or an artificial blood vessel having a hydrophilic surface, which is brought into contact with a catheter or an artificial blood vessel having a hydrophilic surface before being embedded in the human body, to sterilize the catheter or the artificial blood vessel, or to be removed from the human body. And are decomposed and removed by thermal decomposition (or carbonization) or oxidation by OH radicals. After disassembly and removal, safely discard the catheter or artificial blood vessel.

  (F) A plasma is brought into contact with a DNA specimen detection device having a hydrophilic surface before or after use, and organic substances on the surface of the device are decomposed and removed by thermal decomposition (or carbonization) or oxidation action by OH radicals.

  (G) Plasma is brought into contact with a nonwoven fabric having a hydrophilic surface, and organic substances adhering to the nonwoven fabric surface are decomposed and removed by thermal decomposition (or carbonization) or oxidation action by OH radicals.

  (H) A lithographic material, such as a photoresist thin film, contacts the surface of the silicon wafer coated on the surface with water vapor bubble plasma to remove the thin film. Alternatively, the dust on the surface is brought into contact with the water vapor bubble plasma to clean the dirt on the silicon wafer.

  (I) When cleaning the surface of a glass plate, particularly a glass plate used in a liquid crystal cell or a glass master used in a mastering process of an optical disk, high cleanliness is required. Conventionally, RCA cleaning technology using a chemical solution has been performed, but since the cost of wastewater treatment of the chemical solution is high, cleaning without using a chemical solution is required. When the glass plate is cleaned by this technology, dirt can be decomposed without damaging the surface of the glass plate by bringing the OH radicals generated from the plasma bubbles into contact with the glass plate and appropriately setting the contact time. . The decomposition products become carbide, carbon dioxide and water, and no harmful waste liquid is generated.

(J) Cleaning of the surface of ceramic products such as Al ₂ O ₃ ceramic tiles having a hydrophilic surface by this technique.

  (K) The surface of the photocatalytic tile product coated with titanium oxide particles having a hydrophilic surface is cleaned by this technique. If the surface of the photocatalyst is so stained that ultraviolet rays do not reach it, it can be washed to regenerate the photocatalytic function.

  (L) The surface of the carbon electrode modified to a hydrophilic surface is cleaned by this technique. In particular, in the electrode of the secondary battery using electrolyte ions, a hydrophilic electrode is used in some cases. Due to repeated charging and discharging, dirt may be generated in the electrolyte solution, and dirt may be generated on the electrode surface. According to the present invention, it is possible to clean a carbon electrode to which dirt is attached.

  (M) A fluorine-based electrolyte membrane (for example, Nafion membrane manufactured by DuPont) used as a solid electrolyte membrane is highly hydrophobic. In this case, when the electrolyte membrane is immersed in water and swollen with water, the moisture content of the membrane increases and the contact angle with water decreases. A membrane surface having a contact angle of 90 degrees or less can be cleaned by the technique of the present invention.

  Examples of the above-described (2) processing for etching the surface of the hydrophilic material include the following examples.

(n) In a semiconductor multi-layer wiring process, a damascene process is provided in which a trench 20 is provided on an insulating film 23 , a metal film 21 such as copper, aluminum, tungsten, or titanium is embedded, and an unnecessary metal film 21 on the insulating film 23 is removed. It can also be used for (Damascene process). FIG. 4 shows a schematic diagram of the damascene process. In FIG. 4, the process proceeds from a.fwdarw.b.fwdarw.c, and patterning of the wiring metal is formed at c.

  Since the clean metal film is hydrophilic as described above, the metal atoms are removed at the atomic level by the electrochemical reaction between atomic hydrogen and OH radicals generated from the water vapor bubble plasma and the metal atoms. Can be processed precisely. In that case, it is necessary to appropriately control the etching rate by OH radicals.

Already, Graduate School of Engineering, Osaka University Hidekazu Goto, Kikuharu Hirose, Takashi Inada, Yuzo Mori et al., Journal of Precision Engineering, VOL. 69, no. 9, 2003, p. In 1332-1336, water molecules in ultrapure water are dissociated into H and OH by a catalyst to form OH negative ions, and a new ultra-precise type using chemical reaction between the OH negative ions and workpiece surface atoms. The development of ultra-clean processing method is reported. When Al (001) is used as the cathode, the report on the surface reaction process shows that (1) When OH is bonded to the Al (001) surface atom, the bond strength between the surface first layer and second layer atoms (2) When OH and H act on the H-terminated Al (001) surface, all bonds between Al surface atoms are broken, and Al surface atoms are removed as AlH ₂ (OH) molecules. To be reported. In this document, H and OH are generated by a catalyst, and an electrochemical reaction using this OH is used. However, research results by OH radicals generated from water vapor bubble plasma are not reported. On the other hand, the present inventors have found that clean metals are hydrophilic with respect to water, and by causing OH radicals generated by the water vapor bubble plasma of the present invention to act on the metal, as in the above-mentioned publication of the Japan Society for Precision Engineering. It is claimed that this technique can be applied to a precision etching process in which a metal is removed from a material while breaking chemical bonds of atoms on the metal surface.

  (O) Kaoru Hattori, “Electronic Materials”, separate volume, December 2005, p. No. 93-101 describes a silicon wafer cleaning technique. This document introduces wet cleaning of a silicon wafer in which the surface is cleaned by RCA cleaning, and wet cleaning in which the wafer is cleaned with acid, alkali, diluted hydrogen fluoride water, and ozone water while the wafer is rotated. On the other hand, when the technique of the present invention is used, the wafer can be cleaned with OH radicals having a stronger oxidizing power than ozone water cleaning. According to Chobe Yamabe, “Improvement of water quality environment by discharge in submerged microbubbles”, Grants-in-Aid for Scientific Research, 2000-2014, (A) (2) Research report, March 2003 For example, the standard oxidation potential of OH radicals is 2.84 eV, while the standard oxidation potential of ozone is 2.07 eV, indicating that OH radicals have a stronger oxidation ability than ozone.

  Specifically, the silicon wafer can be cleaned by immersing a dirty silicon wafer in the water of the reactor shown in FIG. 1 and bringing the silicon wafer into contact with the water vapor bubble plasma while rotating the silicon wafer in the water. it can.

  Hereinafter, as an example of cleaning an article, cleaning of a porous film clogged after being used for the filtration treatment described in (a) above will be described. Examples of the porous membrane include a hydrophilic hollow fiber membrane made of polyethylene, a flat membrane, and a tubular membrane.

  A dirty porous membrane is immersed in water and fixed in the vicinity of an electrode that emits electromagnetic waves. When electromagnetic waves are radiated from the electrodes, water vapor bubbles are generated around the electrodes, and at the same time, plasma is generated in the water vapor bubbles. When the plasma generated in the water vapor bubbles is brought into contact with the membrane surface of the porous membrane for a predetermined contact time, the organic matter adhering to the membrane surface is thermally decomposed by the plasma and blown off. The hydrophilic surface that is exposed after the organic matter is blown away is covered with a water layer because it is easily wetted with water, and is not easily damaged by plasma, and the pore structure formed in the porous film is almost maintained. . The contact time is preferably 1 to 5 minutes. If the contact time is less than 1 minute, organic substances such as dirt attached to the porous membrane surface may not be sufficiently removed. If the contact time exceeds 5 minutes, a part of the porous membrane surface starts to melt. Although the specific example of (a) has been described above, the dirt can be similarly cleaned for each of the cases (a) to (m). The present invention can also be applied to the etchings (n) to (o).

  Furthermore, the surface treatment method of the present invention can also be applied to partial etching of articles. That is, when plasma is brought into contact with an article having both a hydrophobic surface (θ> 90 degrees) and a hydrophilic surface (θ ≦ 90 degrees) in water, the etching rate of the hydrophobic surface increases and the article surface is uneven. Is formed.

  In order to form an uneven surface, it is necessary to appropriately select the contact time between the material and the water vapor bubble plasma.

  This concavo-convex formation technique is useful for etching a material in a semiconductor lithography process and fine concavo-convex processing of a plastic material (for example, processing for imparting a non-glare function for preventing image reflection on the surface of a transparent resin plate). .

  According to the surface treatment method of the present invention described above, since the article surface is brought into contact with the water vapor bubble plasma in the liquid, the soil decomposition product from the article is not scattered in the atmosphere. In particular, it can be safely decomposed and removed in water without scattering viruses, harmful organic substances, etc. in the atmosphere. The decomposition product that has migrated into water can be safely removed from the water by collecting it with an adsorption filter or the like. In particular, articles handled at medical sites such as hospitals and food manufacturing sites (for example, catheters, artificial blood vessels, DNA specimen detection devices, nonwoven fabrics with a virus-capturing function, dialysis filtration membranes, microfiltration membranes, gas separation membranes, etc.) When discarding, it is necessary to safely detoxify organic substances such as germs and viruses adhering to the surface of the article, and the present invention is effective for this purpose.

  In the etching of the material by the surface treatment of the present invention, chemicals such as electrolyte, sulfuric acid, hydrochloric acid, and hydrogen fluoride water are not used, and OH radicals generated from water are utilized for decomposition. There is no chemical waste. In the case of metal etching, metal hydroxide precipitates, but since it is insoluble in water, it can be separated into solid and liquid, and no waste liquid harmful to the environment is generated.

  When surface treatment is performed using carbon fibers suitable for the present invention, excessive graphitization due to high temperature of water vapor bubble plasma is suppressed, and stable carbonization is maintained, while etching and cleaning with OH radicals, etc. Therefore, it is possible to produce a continuous carbon fiber with high industrial value.

Example 1
A household water purifier (trade name: Clean Sui 02) manufactured by Mitsubishi Rayon Co., Ltd. was prepared. The filtration cartridge of the water purifier uses a hydrophilic hollow fiber membrane made of polyethylene (contact angle of water (25 ° C.) = 55 ° of the hydrophilic material). The hollow fiber membrane is a hollow fiber membrane having an inner diameter of 270 μm and a film thickness of 55 μm manufactured by Mitsubishi Rayon Co., Ltd. The fibrils made of polyethylene are oriented in the fiber direction of the hollow fiber membrane, and many fibrils are arranged in the thickness direction of the membrane. It has a stacked pore-shaped pore structure.

  When this water purifier is attached to a tap water tap at home and tap water (Mikasacho, Iwakuni) is passed through the filter cartridge for 1 year, the filter cartridge becomes clogged and the surface of the hollow fiber membrane in the filter cartridge Turned light gray. The clogged filtration cartridge was removed from the water purifier body, and the activated carbon was removed from the filtration cartridge to obtain a clogged hollow fiber membrane sample. The clogged hollow fiber membrane surface was observed with an electron microscope. An electron micrograph is shown in FIG. In the clogged hollow fiber membrane, the slit-shaped pores on the membrane surface were clogged with organic substances.

The clogged hollow fiber membrane was washed as follows.
Since the clogged hollow fiber membrane sample was as short as about 50 mm, the hollow fiber membrane clogged into the 150 mm long hydrophilized hollow fiber membrane (manufactured by Mitsubishi Rayon, EX-540V polyethylene hollow fiber membrane). A sample for experiment was prepared by attaching samples.

  As the plasma generator, the apparatus shown in FIG. 1 was used. A model T161-5766LQ manufactured by THAMWAY was used as the RF power source, and a model T0202-5766LQ manufactured by THAMWAY was used as the Matching Box.

  First, an experimental sample was immersed in a container filled with water and fixed with a support near the electrode. Water was heated using the heat generated by the electrodes, and this heat generated water vapor bubbles in the water. In FIG. 1, in a reduced pressure environment where the gas phase pressure is 30 hPa, the water vapor bubbles are irradiated with electromagnetic waves (27.1 MHz) with an output of 300 W, the water vapor in the bubbles is turned into plasma, and then the pressure is changed to atmospheric pressure. Generation of water vapor bubble plasma was continued. FIG. 5 shows an emission spectrum from water vapor bubble plasma when the gas phase side is atmospheric pressure. This spectroscopic spectrum is obtained by using a PMA-11 C-7473-36 type Zellnitana type small polychromator and a back-illuminated CCD linear image sensor made by Hamamatsu Photonics in the reactor shown in FIG. The spectral intensity for each wavelength was measured and determined. The number of photodetecting elements was 1024, the wavelength range was 200 to 950 nm, and the exposure time was 19 ms. Measurement was performed using a polychromator and linear image sensor, which had been corrected for wavelength sensitivity unevenness and wavelength axis calibration.

  In a state where the gas phase side is atmospheric pressure, the water vapor bubble plasma was brought into contact with the experimental sample for 3 minutes. The surface of the hollow fiber membrane sample after the surface treatment was observed with an electron microscope. An electron micrograph is shown in FIG. The organic matter that was clogged was almost completely removed. Moreover, almost no damage was observed on the surface of the hollow fiber membrane sample, and the pore structure maintained the original shape.

Example 2
Using the same plasma generator as in Example 1, an experimental sample was immersed in a container filled with water, and fixed with a support near the electrode. Water vapor bubble plasma was generated under the same conditions as in Example 1 except that an ethylene / vinyl alcohol copolymer film (hereinafter also referred to as EVAL film) shown in Table 9 was used as a sample. Was in contact with the sample for 3 minutes. All films had a contact angle with water before plasma contact within a range of 64 to 71 degrees, and exhibited hydrophilicity. All of these films withstood the heat of water vapor bubble plasma and maintained their form.

1) Ethylene: ethylene content 2) θ / 2: Reading value with a contact angle meter.
CA-DT made by Kyowa Interface Science is used for the contact angle meter.
The pure water droplet volume was 1 μL.
3) θ: contact angle 4) T: temperature of the measurement chamber 5) RH: humidity of the measurement chamber 6) “Plasma durability” means durability against water vapor bubble plasma in water.
7) “The gas phase is atmospheric pressure” in FIG. 1 means that the gas phase above the water surface is air at atmospheric pressure, and water vapor bubble plasma is generated in this state.
8) “Durable” means that the original form was maintained without breaking.
9) “No durability” means that the sample was thermally decomposed after being broken by the heat of the plasma.
In Table 10 and Table 11 below, the same symbols or terms as 1) to 9) have the same meaning.

  In addition, the surface of the film of sample DC3203F was marked with oil-based ink. When the marked part was applied to the plasma, the oil-based ink was decomposed by the plasma and did not remain on the film. The film surface after washing was smooth by visual observation.

Example 3
When the Nafion 112 and Nafion 1035 films made by DuPont were immersed in 25 ° C. ion exchange water for 5 minutes and the membrane was swollen with water, the contact angle was measured. The contact angles shown in Table 10 were obtained. Nafion 112 and Nafion 1035 shown in Table 10 were used as samples for plasma treatment.
Using the same plasma generator as in Example 1, the sample was immersed in a container filled with water, and the sample was fixed with a support near the electrode. Next, water vapor bubble plasma was generated under the same conditions as in Example 1, and the plasma was brought into contact with the sample for 3 minutes. As shown in Table 10, both Nafion 112 and Nafion 1035 swollen with water withstood the heat of water vapor bubble plasma and maintained their form.

  Further, the surface of the Nafion 112 film was marked with oil-based ink. The marking was firmly attached to the film. When the marked portion was contacted with water vapor bubble plasma in water for 3 minutes and then visually observed, the oil-based ink was decomposed by the plasma and did not remain on the sample. The film surface after washing was smooth by visual observation.

Example 4
Using the same plasma generator as in Example 1, the sample was immersed in a container filled with water, and fixed in the vicinity of the electrode with a support. Water vapor bubble plasma was generated under the same conditions as in Example 1 except that an optically polished glass plate (thickness 5 mm, 100 mm × 100 mm) was used as a sample, and the plasma was brought into contact with the glass plate for 3 minutes. . The glass plate withstood the heat of water vapor bubble plasma and maintained its form. The contact angle of the glass plate before water contact with water was about 35 degrees.
In addition, the surface of the glass plate was marked with oil-based ink, and the marked portion was visually observed after being contacted with water vapor bubble plasma in water for 3 minutes. The oil-based ink was decomposed by the plasma and did not remain on the glass plate. The glass plate after washing was smooth by visual observation.

Example 5
Using the same plasma generator as in Example 1, an experimental sample was immersed in a container filled with water, and fixed with a support near the electrode. A vapor bubble plasma was generated under the same conditions as in Example 1 except that an alumina ceramic sheet (γ-Al ₂ O ₃ sheet thickness 3 mm, 100 mm × 100 mm) was used as a sample, and the plasma was applied to the alumina ceramic sheet. Touch for 3 minutes. The contacted alumina ceramic sheet withstood the heat of the water vapor bubble plasma and maintained its original form. The contact angle with respect to the water of the alumina ceramic sheet before contacting with plasma was about 55 degrees.
Further, the surface of the alumina ceramic sheet was marked with oil-based ink, and the marked portion was contacted with water vapor bubble plasma in water for 3 minutes and then visually observed. The oil-based ink was decomposed by the plasma and did not remain on the alumina ceramic sheet. The alumina ceramic sheet surface after washing was smooth by visual observation.

Example 6
Using the same plasma generator as in Example 1, an experimental sample was immersed in a container filled with water, and fixed with a support near the electrode.
An ethylene-vinyl alcohol copolymer film (ethylene content 32 mol%) is used as a base material (thickness 3 mm, 100 mm × 100 mm), and a 5 mm wide polyethylene film (thickness 0.5 mm, 100 mm × 100 mm) is separated by 5 mm from this base material. Then, a sample made of a hydrophilic surface / hydrophobic surface having a hydrophilic part width of 5 mm and a hydrophobic part width of 5 mm was prepared. The contact angle with water of the ethylene-vinyl alcohol copolymer film (ethylene content 32 mol%) was 67 degrees, and the contact angle with water of the polyethylene film was 95 degrees.
A vapor bubble plasma was generated in the same manner as in Example 1 except that the prepared sample was used, and the plasma was brought into contact with the entire sample for 3 minutes. After contact, when the sample was taken out from the reaction vessel, the polyethylene film, which is a hydrophobic part, was etched by plasma, and the average thickness was 0.1 mm, but the ethylene-vinyl alcohol copolymer film substrate was The initial surface was smooth and maintained. Only the hydrophobic part was the result of being etched by the plasma.

Comparative Example 1
As an article, a 100 μm thick polytetrafluoroethylene film (contact angle with water (25 ° C.) = 110 degrees), polyethylene film (contact angle with water (25 ° C.) = 95 degrees), which has not been hydrophilized, A polypropylene film (contact angle with water (25 ° C.) = 96 degrees) was prepared. No organic matter such as dirt adhered to the surface of these films. These films were subjected to surface treatment in the same manner as in Example 1. All the films were thermally decomposed by the high temperature of the plasma at the moment when the plasma contacted and broke.

Comparative Example 2
As an article, a 50 μm-thick organic polymer porous flat membrane (made by Millipore, hydrophobic polytetrafluoroethylene membrane, water contact angle (25 ° C.) = 110 degrees, average pore diameter, not hydrophilized 1 μm), 100 μm thick organic polymer porous flat membrane (manufactured by Millipore, hydrophobic polyethylene membrane, water contact angle (25 ° C.) = 94 degrees, average pore diameter 1 μm). No organic matter such as dirt adhered to the surface of these high-molecular porous flat membranes. These polymer porous flat membranes were subjected to surface treatment in the same manner as in Example 1. All the flat films were thermally decomposed by the high temperature of the plasma at the moment when the plasma contacted, and were broken.

Comparative Example 3
As a sample, the same conditions as in Example 3 were used except that two types of Nafion membranes (Nafion 112, Nafion 1035) manufactured by DuPont, which were left in an atmosphere of 25 ° C. and 55% RH for one week, were used as samples. The sample was brought into contact with water vapor bubble plasma.
The contact angles of Nafion 112 and Nafion 1035 with respect to water before the plasma contact were the values shown in Table 11. At the moment of contact with the plasma, both types of Nafion membranes were thermally decomposed by the high temperature of the plasma and broke.

Comparative Example 4
Prepare 200 mL of pure water in a 300 mL capacity beaker, immerse the clogged hollow fiber membrane used in Example 1 in 25 ° C. pure water, and use an ultrasonic cleaner with an output of 100 W and 20 KHz to output the hollow fiber membrane. Was washed for 1 hour. When the washed film was observed with an electron microscope, organic substances clogged on the film surface were not removed.

Comparative Example 5
In Example 1, the electrode of the reactor was heated to generate water vapor bubbles that were not in a plasma state, and when the water vapor bubbles were clogged for 3 minutes, the membrane surface was clogged. Organic matter was not removed.

  The present invention provides a surface that decomposes or removes organic substances adhering to an article without damaging the article by bringing the plasma generated in water vapor bubbles into contact with the article having a hydrophilic surface in water. Processing technology. This surface treatment technique is useful, for example, for household water purifiers, industrial wastewater filtration, organic polymer porous membranes used for air filtration, ceramic porous membrane regeneration, and safe disposal of porous membranes. In particular, membranes that are contaminated or clogged with substances containing bacteria, such as filtration membranes for hospital hand-washing water, air filtration membranes for hospital infection prevention in hospitals, and air filtration membranes for biohazard rooms, can be safely regenerated or It is an effective method for disposal.

  Moreover, the surface treatment method of the present invention uses a biocompatible material embedded in the body, and after the use, organic matter such as bacteria on the surface of the material is thermally decomposed or carbonized to safely dispose of the material; Treatment for cancer cells that coexist with organs to be thermally decomposed or carbonized to be useful for life safety; Organic substances such as bacteria, blood, and proteins attached to used contact lenses are thermally decomposed or carbonized for safe disposal It can be applied to the processing. Furthermore, the surface treatment method of the present invention includes sterilization before embedding catheters, artificial blood vessels and the like in the body, sterilization of fungi adhering after removal from the living body, and the like. Processing to remove; Processing to safely dispose of used DNA specimen detection devices; To dispose of fungi adhering to non-woven fabric used in air filters, masks, etc. by pyrolyzing or carbonizing them safely It can also be applied to processing.

  In addition, the etching technique of the present invention gives fine irregularities to the surface of the hydrophilic transparent organic material, reveals an antireflection function in optical applications, or reveals visibility only at a specific viewing angle. It can also be used for processing into privacy filters. In addition, the surface of the metal film can be etched only with chemical species derived from water molecules, and the cost of waste liquid treatment can be reduced in the damascene process of high-density multilayer wiring in semiconductor devices, which is effective in reducing manufacturing costs. It is.

  Also, in recent semiconductor multilayer wiring devices, the wiring density has increased and finer processing is required. In that case, a low dielectric constant material consisting of a porous silicon film as an insulating film has been proposed. Yes. Since this insulating film has a large pore volume, and the material has a hydrophobic contact angle with water, the polishing liquid is repelled by the insulating film in the normal chemical mechanical polishing process, and the metal film is scraped off. Later, it is difficult to flatten the whole. On the other hand, when the method of the present invention is used, by selecting a material having a contact angle with water of 90 degrees or less as the low dielectric constant film, OH radicals in the water vapor bubble plasma etch the low dielectric constant film. A flat insulating film / multilayer wiring metal structure can be obtained.

  In the etching technique of the present invention, only the hydrophobic portion can be selectively etched by controlling the contact time with the water vapor bubble plasma to be a short time. This technique can be applied when selectively etching a hydrophobic portion with respect to various materials such as an organic material, an inorganic material, and a carbon material having both a hydrophilic surface and a hydrophobic surface portion. In particular, materials such as carbon materials and silicon wafers are difficult to surface-process due to their high heat-resistant temperature, but can be easily etched using this technique.

DESCRIPTION OF SYMBOLS 11 Liquid 12 Container 13 Electrode 14 Counter electrode 15 Article 16 Support 17 Water vapor bubble 18 Water drop 19 Air phase γ _SV Surface tension of solid in adsorption equilibrium with liquid (water) vapor (room temperature, atmospheric pressure)
γ _SL Interfacial tension between solid and liquid γ _LV Surface tension of liquid (water) in equilibrium with its vapor (water vapor)

Claims (6)

The thermal plasma generated in the water vapor bubbles in the liquid containing water is brought into contact with the organic matter attached to the material having a contact angle with respect to water of 90 degrees or less in the liquid to remove the organic matter from the material. A surface treatment method , wherein the material is a polymer electrolyte membrane . The thermal plasma generated in the water vapor bubbles in the liquid containing water is brought into contact with the organic matter attached to the material having a contact angle with respect to water of 90 degrees or less in the liquid to remove the organic matter from the material. A surface treatment method, wherein the material is glass. The thermal plasma generated in the water vapor bubbles in the liquid containing water is brought into contact with the organic matter attached to the material having a contact angle with respect to water of 90 degrees or less in the liquid to remove the organic matter from the material. A surface treatment method, wherein the material is ceramic. A thermal plasma generated in water vapor bubbles in a liquid containing water is brought into contact with an organic substance adhering to a material having a contact angle with respect to water in the range of 70 degrees to 0 degrees in the liquid. A surface treatment method for removing from a material, wherein the material is a polymer electrolyte membrane . A thermal plasma generated in water vapor bubbles in a liquid containing water is brought into contact with an organic substance adhering to a material having a contact angle with respect to water in the range of 70 degrees to 0 degrees in the liquid. A surface treatment method for removing from a material, wherein the material is glass . A thermal plasma generated in water vapor bubbles in a liquid containing water is brought into contact with an organic substance adhering to a material having a contact angle with respect to water in the range of 70 degrees to 0 degrees in the liquid. A surface treatment method for removing from a material, wherein the material is ceramic .