TWI405608B - Surface modification method and surface-modified article - Google Patents

Abstract

Plasma generated in water vapor bubbles present in a water-containing liquid is brought into contact, in the liquid, with an article having a contact angle with water of 90° or less. The plasma is contacted with an organic substance adhering to the article to thereby remove the organic substance from the article. By bringing the plasma into contact with the article, the surface of the article is etched without breaking the article. The article may comprise a material composed of both a hydrophobic part having a contact angle with water exceeding 90° and a hydrophilic part having a contact angle with water of 90° or less. In this case only the hydrophobic part is etched by bringing the plasma into contact with the article.

Description

Surface treatment method and surface treated article

The present invention relates to a surface treatment method for an article having a hydrophilic surface, and an article surface treated by the method.

The present application claims priority from Japanese Patent Application No. 2005-089631, filed on March 25, 2005, the content of which is incorporated herein.

As a method of decomposing or removing organic substances by plasma, for example, the following methods are known.

(I) It is known that the oxygen or argon gas is in a plasma state at atmospheric pressure, and the plasma is sprayed on the surface of a substrate such as a silicon wafer or a liquid crystal glass substrate to remove the surface attached to the substrate. Organic matter (see Patent Documents 1 and 2). Moreover, the normal piezoelectric slurry surface treatment apparatus which puts this method practical has been manufactured.

(II) A method is proposed in which a liquid such as an organic solvent containing an organic substance is irradiated with an ultrasonic wave to generate a bubble in the liquid, and then the electromagnetic wave is irradiated to the bubble to generate a plasma in the bubble to serve as a plasma bubble, and the plasma is used. The bubbles decompose the organic matter dispersed in the liquid (see Patent Document 3).

(III) Patent Literatures 4 to 9 disclose a technique of supplying a gas such as oxygen or air to water to generate bubbles in the water, and applying a high voltage pulse to the bubble to instantaneously become a plasma state inside the bubble. Use plasma to break down organic matter in water.

(IV) Patent Document 10 discloses that a high-temperature plasma bubble is generated in a liquid, and a compound generated by the plasma bubble is adhered to the surface of the fiber, and surface re-formation such as a concavo-convex shape is applied to the surface of the fiber. Technology, and functionalized fibers obtained by this technology.

In the method of (I), there are the following problems: (1) Although the plasma can be used to decompose or remove organic substances on the surface of a heat-resistant article such as an inorganic material, the decomposition product or unreacted organic matter floats in the atmosphere; (2) Although a high-energy plasma gas can be produced, it is difficult to apply to an organic polymer material because the surface temperature of the article is extremely high.

In the method of (II), (1) although the organic substance dispersed in the liquid can be decomposed, it is not clear whether it is suitable for removing the organic substance attached to the surface of the article, and (2) conversely, even if the plasma in the bubble contacts the article In the same manner as in the method of (1), the decomposition of the organic substance is difficult to apply to the organic polymer material because the surface temperature of the article becomes high.

In the method of (III), similarly to the above (II), (1) although the organic substance dispersed in the liquid can be decomposed, it is not clear whether it is suitable for removing the organic substance adhering to the surface of the article. Further, (2) since the plasma state is maintained only for a short period of time, when the frequency of contact between the bubbles in the plasma state (hereinafter referred to as plasma bubbles) and the organic substance to be decomposed is low, it is difficult to effectively decompose.

The specification of Patent Document 10 of (IV) discloses that the surface recombination of the fibers can be carried out by bringing the plasma bubbles into contact with the fibers. The fiber material is not particularly limited. However, as described in Patent Document 3 of (II), for a high temperature at which the plasma bubble temperature is about 5000 K, the organic polymer material generally does not have sufficient heat resistance to withstand such a high temperature. Moreover, when the melting point or softening point of the material is lower than the temperature of the plasma bubble, it is expected that when the plasma bubble is contacted, the material dissolves and generates a flow, or causes thermal decomposition or destruction, so that it is difficult to make the plasma bubble suitable for use of such a material. In the fiber. Further, when such a material having poor heat resistance is used, it is expected that the surface unevenness function is imparted thereto, as the fiber form itself is damaged. Further, carbon fibers are exemplified in the examples, but in view of the fact that the carbon fibers are very fine, and depending on the wrinkle shape of the fiber surface or the degree of construction of the surface graphite and the degree of flame resistance, the fiber portion partially contacting the high-temperature plasma bubbles is The heat causes excessive graphitization, causing the fibers to become locally brittle, and the mechanical properties of the entire fiber are degraded. Further, when a material having poor heat resistance is used, there is no disclosure as to whether or not the surface can be cleaned without changing its surface morphology. In the specification of Patent Document 10, there is no disclosure as far as the material selection is concerned.

[Patent Document 1] Japanese Patent Laid-Open Publication No. JP-A No. 2004-311838 (Patent Document 2) Japanese Patent Laid-Open No. 2004-311838 (Patent Document 3) Japanese Patent Laid-Open Publication No. 2004-306029 (Patent Document 4) [Patent Document 5] Japanese Patent Laid-Open Publication No. 2005-58887 [Patent Document 6] Japanese Patent Laid-Open Publication No. 2005-21869 (Patent Document 7) Japanese Patent Laid-Open Publication No. 2005-13858 Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. Hei. No. 2002-272825.

An object of the present invention is to provide a surface treatment method for decomposing or removing an organic substance such as dirt attached to an article without scattering it to the atmosphere and suppressing damage of the article; and a surface treatment method for etching the surface of the article while suppressing damage of the article; And items that are highly cleaned on the surface, etched on almost undamaged items or surfaces, and are not damaged.

The surface treatment method of the present invention is characterized in that a plasma generated in a water vapor bubble in an aqueous liquid is brought into contact with a material having a contact angle with water of 90 degrees or less in the liquid.

Further, the article of the present invention is an article which is surface-treated by the above surface treatment method.

According to the surface treatment method of the present invention, the organic matter attached to the article can be decomposed or removed without being scattered to the atmosphere, and the article is prevented from being damaged. Moreover, the surface of the article can be etched while suppressing damage to the article. The article obtained by the surface treatment method according to the present invention has a surface which is highly cleaned or etched and which is almost free from damage.

(surface treatment method)

The surface treatment method of the present invention is a method of bringing a plasma generated in a water vapor bubble in an aqueous liquid 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 generating apparatus used in the present invention, a plasma generating apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-297598 and Japanese Patent Laid-Open No. 2004-152523 can be used.

Hereinafter, a surface treatment method of the present invention will be described by taking a specific plasma generating apparatus as an example.

Fig. 1 is a schematic block diagram showing an example of a plasma generating apparatus used in the surface treating method of the present invention. The plasma generating device 10 is a container 12 having a schematic configuration, that is, a container 12 for storing the liquid 11, an electrode 13 disposed in the container 12 for radiating electromagnetic waves, and a counter electrode 14 disposed opposite to the electrode 13; The article 15 is fixed to the support member 16 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 is adjusted. A vacuum pump (not shown) that presses the air phase 19 (gas phase) above.

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

When a high frequency/high voltage is applied to the water vapor bubbles attached to the electrodes, the molecular motion of the water molecules inside the bubbles is intense, and electrons are ejected from the atoms constituting the water molecules, generating positively charged gases and electrons. The evicted electrons generate a chain reaction that continuously attacks other water vapors, and successively generate positively charged gases and electrons, causing the inside of the water vapor bubbles to become a plasma state.

Water vapor bubbles (hereinafter referred to as steam bubble plasma) in a plasma state emit light in a specific wavelength range. From the luminescence spectrum, the type of gas generated inside the plasma bubble can be known. Table 1 records the wavelength of the luminescence spectrum of the vapor bubble plasma and the species of the gas which is the cause of luminescence.

When the water vapor bubble plasma around the electrode contacts the dirt composed of the organic matter immersed in the surface of the article 15 in the liquid 11, the thermal decomposition caused by (1) the heat of the steam bubble plasma, (2) water vapor is utilized. The oxidation of OH radicals in the bubble plasma serves to separate or decompose the dirt.

As will be described in detail below, in the surface treatment, when the article is hydrophilic, water around the article evaporates, and the surface of the article is cooled by the latent heat of vaporization, and thermal decomposition caused by heat of the plasma of the water vapor bubble in (1) is lowered.

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

Examples of the organic solvent that can be mixed with water include alcohols such as methanol, ethanol, isopropanol, and butanol, and acetone. Examples of the electrolyte ions include Mg ^{2 +} , Ca ^{2 +} , Na ⁺ , Fe ^{2 +} , Fe ^{3 +} , Cl ^- , NO ^{3 -} , NO ² , OH ^- and the like.

Since the electrolyte ions are present in the liquid 11, the electrical conductivity of the water discharge is improved, and when the plasma is generated, the arc discharge current easily flows from the electrode 13 for radiating electromagnetic waves to the counter electrode 14. The organic solvent is carbonized by the plasma, and its carbide may adhere to the article 15. Further, when the volume fraction of water in the liquid component is lowered, as described below, the cooling effect of water on the surface of the article 15 is lowered, and the surface of the article 15 is easily damaged. Therefore, the liquid 11 is preferably as free from an organic solvent as possible, and particularly preferably not contained at all. More preferably, pure water or ultrapure water used in a semiconductor manufacturing process or the like is preferable.

The generation of the water vapor bubbles 17 is not limited to the method of heating the electrode 13, and a method may be employed in which an ultrasonic generating device is additionally provided, and cavitation bubbles are generated in the liquid 11 in accordance with the ultrasonic waves from the ultrasonic generating device, and in the bubbles The surrounding liquid 11 is vaporized into a vapor to form a water vapor bubble 17.

The frequency of the electromagnetic wave that is irradiated to the water vapor bubble 17 can be selected in the range of 1 MHz to 100 GHz depending on the application.

When the water vapor bubbles 17 are generated, the air phase 19 in the container 12 can also be decompressed by a vacuum pump. When the air phase 19 in the container 12 is decompressed, the boiling point of the liquid 11 is lowered, so that water vapor is easily generated, and the vapor pressure inside the water vapor bubble is increased, and the number of water vapor molecules generated by the plasma is increased, so the plasma is increased. Easy to discharge. When the inside of the water vapor bubble reaches the plasma state once, even if the vacuum pump is stopped, the pressure of the air phase 19 is returned to the atmospheric pressure, and the plasma continues to be generated inside the bubble.

As the article 15, an article having a hydrophilic surface is preferable, and specific examples thereof include a hydrophilic organic polymer material, glass, ceramics, a ruthenium wafer, a metal (for example, aluminum, copper, tungsten, etc.), graphite, carbon fiber, or the like.

In the present invention, the "hydrophilic surface" is defined by the value of the contact angle θ defined in Fig. 2. In the present invention, the "hydrophilic surface" is a surface at which the contact angle θ of water (water droplets 18) to the surface of the article 15 is 90 or less at 25 °C. The smaller the contact angle of water with respect to the hydrophilic surface, the better. Specifically, it is preferably 80 degrees or less, and more preferably 70 degrees to 0 degrees.

The contact angle θ in the present invention is defined as the same contact angle with the wetting index of the material to ordinary water. As a reference book on the contact angle, the quotation is disclosed in the "Metal Function Surface" by Murakami Hiroshi, published by the Modern Co., Ltd., and 1984 p.133. According to this document, when droplets which do not react with the surface are dropped on the smooth surface, and the droplet maintains a certain contact angle with the surface, the following formula (1) holds.

[Number 1] γ _{S V} = γ _{S L} + γ _{L V} cos θ (1) γ _{S V is} the surface tension of the solid in which the liquid is in vapor adsorption equilibrium γ _{S L} The interfacial tension γ _{L V} between the solid and the liquid is in equilibrium with the vapor Surface tension of liquid

When the formula (1) is represented by the following formula (2), the left side thereof indicates a decrease in surface energy when the solid surface is wetted by the liquid.

[Number 2] γ _{S V} -γ _{S L} =γ _{L V} cosθ (2)

Since this energy is the surface free energy, the larger the amount of decrease γ _{L V} cos θ is, the easier it is to wet, and the smaller the θ is, the better the wettability is when γ _{L V is} fixed. In order to quantify the wettability, the water droplet contact angle θ used depends on the formula (2). In the present invention, the liquid is water, and when γ _{L V is} 20 ° C, it is 72.8 dyn/cm ("Science chronology", Maruzen Co., Ltd., 1993, p. 449).

In the present invention, a smooth material surface is prepared, and the surface is kept horizontal, water droplets are dropped on the surface, and the contact angle θ in Fig. 2 is obtained by contact angle measurement (θ/2). When the surface of the material is porous or has irregularities, a smooth surface of the same material is prepared, and the angle θ of the smooth surface is obtained. 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 which cannot be melted such as carbon fiber, a smooth sheet containing a precursor material thereof (for example, polyacrylonitrile or polyimide) is previously prepared and fired to obtain a sheet having a smooth surface including a carbon material. Water droplets were dropped on the sheet and the contact angle was measured. The water used for measuring the contact angle is pure water such as ultrapure water or ion exchange water.

The contact angle θ (25 ° C) of water to representative organic polymer materials and inorganic materials is shown in Table 2 and Table 3 (Document a: "Chemical Fact Sheets Revised 4 Edition Basic Series II", Maruzen Co., Ltd., 1993 II -83 7.1.3 Contact angle, document b: Edited by Ishii Shuo, Koishi Shino, and Kakuda Kakuo technology , Techno-System, Inc., 2001, b1: p. 418, b2: p. 92, b3: p. 96, b4: p. 102-103, b5: p. 161, b6: p. 198).

In addition, the "Metal Surface Handbook", Nikkan Kogyo Shimbun, p. 183, 1988, states that "the surface of pure metal is wet with water and the contact angle is zero. If there is dirt, the moisture of this part of the water is poor." According to Murakami Hiroshi's "Metal Functional Surface", the modern compilation society 1984 p.134-136, revealed as follows: γ-Fe solid surface tension, according to the measurement results of the molten state at high temperature, 1670-2127 dyn/cm The solid surface tension of copper is about 1500 dyn/cm according to the measurement result of the molten state at a high temperature, which is much larger than the surface tension of the polymer. On the other hand, the surface tension of water is 72.8 dyn/cm. That is, a pure metal surface is a surface that is very wettable by water. Pure metal materials having a high surface energy can also be applied to the surface treatment of the present invention.

In the present invention, if θ is satisfied For materials of 90 degrees, any material such as organic polymer materials, glass, ceramics, metals, graphite carbon materials, and carbon fibers can also be used.

The wavelength of atomic hydrogen (Hα: 656 nm) in the plasma in the water vapor bubble is converted into a temperature of about 5000 K, and if the high-temperature plasma gas is brought into contact with an article comprising a common organic high-concentration material, Then there is no trace of destruction in an instant. Here, the inventors have found that when the use contains θ In the case of a 90 degree hydrophilic material, only the organic matter on the surface of the article can be decomposed or removed and cleaned, and the surface of the article is hardly damaged, and the surface thereof can be etched without damaging the cleaned article.

Fig. 3 schematically shows the viewpoint of the present invention to avoid thermal decomposition. It can be found that, 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 water is less than or equal to 90 degrees, the effect of etching due to thermal decomposition by heat becomes smaller, if larger than At 90 degrees, the effect of etching due to thermal decomposition increases. The following reasons are attached to this phenomenon.

The material with θ less than or equal to 90 degrees, in the aqueous liquid, the surface is covered by the water layer. Even if the plasma of the water vapor bubble is close, the water on the surface of the material will vaporize and vaporize, and the latent heat of evaporation is taken away from the material, and the hydrophilicity is continuously Water is supplied to the surface, so that a continuous cooling effect acts on the surface of the material to suppress an increase in the temperature of the article. As a result, the surface temperature of the article does not exceed the heat-resistant temperature of the material, and the etching action of thermal decomposition is reduced to suppress the damage of the material. This effect can also effectively prevent the local excessive graphitization caused by the heat of the plasma in the surface treatment of the carbon fiber.

It has been known that when an organic substance such as dirt adheres to the surface of the hydrophilic article, the water wettability of the hydrophobic surface changes as compared with the original hydrophilic surface. For example, according to "Ishii Shuo, Koishi Shino, and Kakuda Kakuo" technology Technology Systems, Inc., 2001 p.83-84 reveals that pure metal surfaces are easily wetted by water, but if they are placed in an environment where organic substances are present, organic substances gradually adhere to the metal surface. The metal surface is hydrophobized over time. Similarly, hydrophilic organic materials and ceramic surfaces also have a tendency to hydrophobize due to contamination of organic matter.

According to Fig. 3, the dirt on the surface of the material is decomposed by the thermal decomposition of the vapor of the water vapor bubble and the oxidative decomposition of the OH radical. When the dirt gradually disappears, the surface of the material is more hydrophilic, and the cooling effect of the water is utilized. , the thermal decomposition is suppressed, and the surface of the material with less damage is obtained.

When it is 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 of OH radicals. By this etching, various materials representing hydrophilicity can be etched. For example, a hydrophilic polymer material, a metal material, a ceramic or a glass exhibiting hydrophilicity, a carbon material exhibiting hydrophilicity, or the like can be etched.

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

When the contact time is too long, the moisture on the surface of the article 15 is excessively evaporated due to the vapor bubble of the water vapor, resulting in insufficient moisture on the surface of the article 15, and the surface temperature of the material temporarily exceeds the heat-resistant temperature, or the oxidation of the OH radical is too strong. Injury to the item.

When the contact time is too short, the oxidation of the OH radical becomes weak, which tends to cause insufficient cleaning or etching of the surface of the article.

In the present invention, the "contact time" is defined as the time during which the voltage is applied to the electrode 13 and the counter electrode 14 when the article 15 is stationary, and the plasma is generated in the water vapor bubble 17, and when the article 15 is moved in the fixed direction, as follows.

When contacting (s) = length of the moving direction of the article 15 in the plasma generating region (mm) / moving speed of the article 15 (mm/s)

The heat-resistant temperature of the material differs depending on the kind of the material. In the present invention, the temperature at which the form of the material can be maintained is defined as the heat-resistant temperature.

Among the organic polymer materials, the material having crystallinity is an index for setting the heat resistance temperature at the melting point, and the amorphous material is an index for setting the heat resistance temperature at the glass transition temperature. The glass transition temperature (Tg) and melting point (Tm) of a representative crystalline organic polymer material are shown in Table 4. (Joel R, Fried, "Polymer Science and Technology" Prentice Hall, 1995, p. 140)

In ceramics, the index of the heat resistance temperature is set at the melting point. Representative ceramic melting points (Tm) are shown in Table 5. (Marcel Mulder, "Basic Principles of Membrane Technology", 2nd Edition, Kluwer Academic Publishers, 1996 p. 60)

In the optical glass material, the index of the heat resistance temperature is set at the glass transition temperature. Representative optical glass-like glass transition temperatures are shown in Table 6. (Light Application Technology Workshop Textbook, "Optical Materials III-9", Corporate Legal Corporation Japan Optomechatronics Association, 1988 p.30)

In the optically crystalline material, the heat resistance temperature index is set at the melting point of the material. The melting points of representative optically crystalline materials are shown in Table 7. (Light Application Technology Workshop Textbook, "Optical Materials III-9", Corporate Optomechatronics Association, 1988 p.55)

In metal, tantalum wafers, etc., the index of the heat resistance temperature is set at the melting point. Representative metal melting points are shown in Table 8. (Edited by the National Astronomical Observatory, "Science Yearbook", Maruzen Co., Ltd., p.469, 1993)

In the carbon material, carbonization-graphitization has been carried out with temperature, and it is difficult to determine a clear heat-resistant temperature. Therefore, the melting point of the graphite single crystal of the related material, that is, 3550 ° C, is used as a structural phase transfer index of the carbon material. In the case of carbon fiber, since the degree of crystallization is low, and it is often difficult to clearly distinguish the amorphous portion from the crystal portion, or it is difficult to specify a clear crystal structure phase transition point, the temperature at which the fiber morphology is maintained is taken as the heat-resistant temperature.

(application)

The surface treatment method of the present invention can be applied to (1) cleaning of an article having an organic substance such as dirt adhered (stacked) on the surface of the material; (2) etching processing of the surface of the hydrophilic material; and (3) processing of the unevenness of the surface of the material. .

The cleaning of (1) will be explained. Examples of the organic substance include organic substances and fertilizer components contained in viruses, bacteria, yeasts, molds, algae, protozoa, proteins, blood and blood components, animals or plant cells, hair, household garbage, kitchen garbage, and drainage. All the organic things that are common in everyday life.

As an example of the article cleaning according to the surface treatment method of the present invention, the following examples are mentioned. The object to be cleaned is not limited to the following examples, and any hydrophilic material having a contact angle θ of water of 90 degrees or less may be selected, and a process suitable for plasma bubble temperature and cooling effect conditions may be appropriately selected to be cleaned.

(a) contacting the plasma with a porous film having a hydrophilic surface used in the filtration treatment, and decomposing and removing the filter deposit composed of organic substances adhering to the membrane surface by thermal decomposition (or carbonization) or oxidation of OH radicals. The porous membrane is regenerated.

(b) contacting the organic suitable material having a hydrophilic surface taken out from the human body after being buried in the human body with the plasma, and decomposing and removing the surface of the suitable material of the organism by thermal decomposition (or carbonization) or oxidation of OH radicals. The organic matter that regenerates the organism's suitability material. Examples of the organic suitable material include polymethyl methacrylate, polylactic acid resin, polyurethane, hydrogel, cellulose, polyvinyl alcohol, hydroxyphosphorus lime, and the like.

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

(d) Contacting the plasma with a contact lens having a hydrophilic surface, and decomposing and removing organic substances such as proteins attached to the contact lens by thermal decomposition (or carbonization) or oxidation of OH radicals.

(e) contacting the plasma with a catheter or an artificial blood vessel having a hydrophilic surface before being buried in the human body, sterilizing the catheter or the artificial blood vessel, or contacting the plasma with a catheter or artificial blood vessel having a hydrophilic surface taken out from the human body, and utilizing Thermal decomposition (or carbonization) or oxidation of OH radicals is removed by decomposition. After disassembly and removal, the catheter or artificial blood vessel is safely discarded.

(f) A DNA sample detecting device having a hydrophilic surface before or after use of the plasma is used to decompose and remove the organic matter on the surface of the device by thermal decomposition (or carbonization) or oxidation of OH radicals.

(g) contacting the plasma with a non-woven fabric having a hydrophilic surface, and decomposing and removing the organic matter adhering to the surface of the nonwoven fabric by thermal decomposition (or carbonization) or oxidation of OH radicals.

(h) The surface of the silicon wafer to which the vapor bubble plasma is applied is coated with a lithographic material such as a photoresist film to remove the film. Alternatively, the vapor bubble plasma is brought into contact with the ruthenium wafer to which the surface is attached, and the dirt on the ruthenium wafer is cleaned.

(i) High purity is required when cleaning the glass plate, especially the surface of the glass master used in the mastering process for cleaning the glass plate or the optical disk for the liquid crystal cell. Previously, the RCA cleaning technique using a chemical solution has been used, but the cost of draining the chemical solution is required, so it is required to wash without using a chemical solution. According to the present technology, when the glass plate is cleaned, the OH radical generated from the plasma bubbles is brought into contact with the glass plate, and the contact time is appropriately set, whereby the scale can be decomposed without damaging the surface of the glass plate. The decomposition product becomes carbide or carbon dioxide, water, and does not produce harmful waste liquid.

(j) Using the present technology, the dirt on the surface of a ceramic article such as an Al ₂ O ₃ ceramic tile having a hydrophilic surface is cleaned.

(k) Using the present technique, the surface of a photocatalytic tile product having a hydrophilic surface and coated with titanium oxide particles is cleaned. When the surface of the photocatalyst is contaminated with dirt and the ultraviolet light cannot be injected, it can be cleaned and regenerated.

(l) Using the present technique, the surface of the carbon electrode recombined into a hydrophilic surface is cleaned. In particular, when a secondary battery electrode using electrolyte ions is used, a hydrophilic electrode is used depending on some cases. Due to the reverse charging and discharging, dirt may be generated in the electrolyte to cause fouling on the surface of the electrode. With the present invention, the carbon electrode to which the dirt is attached can be cleaned.

(m) A fluorine-based electrolyte membrane (for example, a Nafion membrane of Dupont Co., Ltd.) used as a solid electrolyte membrane, which is highly hydrophobic. In this case, when the electrolyte membrane is immersed in water and swelled with water, the moisture content of the membrane increases, and the contact angle with water decreases. With the technique of the present invention, the surface of the film having a contact angle of 90 degrees or less can be cleaned.

As an example of the surface etching processing of the above (2) hydrophilic material, the following examples are mentioned.

(n) In the multilayer wiring step of the semiconductor, the following damascene process may be utilized: a trench is provided on the insulating film, and a metal film such as copper, aluminum, tungsten, or titanium is buried, and the insulating film is not required. Metal film. A schematic view of the damascene process is shown in FIG. In Fig. 4, the process is advanced by a → b → c, and a pattern of a metal for wiring is formed at c.

As described above, since the pure metal film is hydrophilic, in the present invention, the atomic acid is removed at the atomic level by electrochemical reaction of atomic hydrogen and OH radical generated from the vapor plasma of the water vapor with the metal atom. And carry out precision machining. At this time, the speed of etching due to OH radicals must be appropriately controlled.

The University of Osaka Graduate School of Engineering, Goto Hideyoshi, Hiroaki Hiroshi, Inada, Mori, and others, have been revealed in the Journal of Precision Engineering, VOL.69, No.9, 2003, p.1332-1336 A new ultra-precision/ultra-cleaning method developed by using a catalyst to dissociate water molecules in ultrapure water into H and OH, forming OH anions, and utilizing the chemical reaction of the OH anions with the atoms on the surface of the workpiece. When Al(001) is used for the cathode, the literature report on the elementary process reveals: (1) when the OH is bonded to the surface of the Al(001) surface, the first layer to the second layer of the surface are inter The bonding strength decreases, and (2) on the H-terminated Al(001) surface, the interaction between the atoms on the Al surface is completely cut by the action of OH and H, and the Al surface atoms are removed and processed as AlH ₂ (OH) molecules. In this document, H and OH are generated from a catalyst, and the electrochemical reaction of the OH is utilized, but the research results of the OH radical generated by the vapor bubble plasma are not mentioned. On the other hand, the present inventors have claimed that a pure metal is hydrophilic to water, and the OH radical generated by the steam bubble plasma of the present invention acts on the metal, thereby being similar to the literature published by the Society of Precision Engineering. This technique can also be applied to the precise etching step of cutting off the chemical bonding of atoms on the metal surface and gradually removing the metal from the material.

(o) Hattori is in the "Electronic Materials" supplement, December 2005 p.93-101, which discloses the cleaning technology for silicon wafers. In this document, wet cleaning for cleaning the surface of a silicon wafer by RCA cleaning and wet cleaning using an acid, alkali, dilute hydrofluoric acid or ozone water for rotating the wafer while rotating the wafer are described. On the other hand, using the technique of the present invention, it is possible to clean the wafer by cleaning the OH radical having a stronger oxidizing power than ozone water. According to the Minister of the Mountain, the guardian of the water Water quality environment "Improvement", the basic research of the research grants of the 12-14 years of the research, the report of the research results of the March (A) (2) study shows that the standard oxidation potential of OH radicals is 2.84 eV, on the other hand, ozone The standard oxidation potential is 2.07 eV, and OH radicals have stronger oxidizing power than ozone.

Specifically, the contaminated germanium wafer is immersed in the water of the reaction device shown in FIG. 1 to rotate the germanium wafer in water, and the germanium wafer is contacted with the vapor bubble plasma, thereby cleaning the germanium wafer. .

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

The contaminated porous membrane is immersed in water and fixed near the electrode that emits electromagnetic waves. When the electromagnetic wave is radiated from the electrode, water vapor bubbles are generated around the electrode, and plasma is generated in the water vapor bubble. When the plasma generated in the water vapor bubbles contacts the film surface of the porous film at a specific contact time, the organic substances adhering to the film surface are thermally decomposed by the plasma and scattered around. Since the hydrophilic surface exposed by the organic matter is easily wetted by water, it is covered by the water layer and is hardly damaged by the plasma, so that the pore structure formed in the porous film can be maintained substantially. The contact time is preferably 1 to 5 minutes. When the contact time is less than 1 minute, organic substances such as dirt adhering to the surface of the porous film may not be sufficiently removed, and when the contact time exceeds 5 minutes, a part of the surface of the porous film starts to melt. The above is a specific example of (a), and the stains can be cleaned in the same manner for each of the examples (a) to (m). Further, the present invention is also applicable to the etching of (n) to (o).

Further, the surface treatment method of the present invention can also be applied to partial etching of articles. That is, the plasma is brought into contact with water having a hydrophobic surface (θ>90 degrees) and a hydrophilic surface (θ At 90 degrees), the etching speed of the hydrophobic surface becomes large, and irregularities are formed on the surface of the article.

In order to form the uneven surface, the contact time of the material with the vapor bubble plasma must be appropriately selected.

This unevenness forming technique is used for material etching in the semiconductor lithography step and fine uneven processing of the plastic material (for example, processing for preventing the glare-free function from being reflected on the surface of the transparent resin sheet).

According to the surface treatment method of the present invention described above, the vapor bubble plasma is brought into contact with the surface of the article in the liquid, so that the scale decomposition product from the article does not fly to the atmosphere. In particular, it can be safely decomposed and removed in water without causing viruses, harmful organic substances, etc. to fly into the atmosphere. The decomposition product transferred to the water is recovered by an adsorption filter or the like and can be safely taken out from the water. In particular, items used in medical sites such as abandoned hospitals and food manufacturing sites (for example, catheters, artificial blood vessels, DNA sample detection devices, non-woven fabrics with virus-capturing functions, dialysis filter membranes, precision filtration membranes, gas separation membranes, etc.) At the time, it is necessary to make the organic matter such as bacteria and viruses attached to the surface of the article safe and harmless, and the present invention is effective for achieving this object.

Further, in the etching of the surface-treated material of the present invention, the electrolyte solution or a chemical such as sulfuric acid, hydrochloric acid or hydrogen fluoride water is not used, but the decomposition of the OH radical generated by the water is used, so that no chemical waste liquid is generated after the reaction. Further, in the case of metal etching, the metal hydroxide precipitates, but since it is insoluble in water, solid-liquid separation can be performed, and waste liquid harmful to the environment is not generated.

When the surface treatment is carried out using carbon fibers suitable for the present invention, excessive graphitization due to high temperature of the steam bubble plasma can be suppressed, and carbon fibers can be continuously produced, and the carbon fibers are fibers which maintain stable carbonization and are uniformly distributed throughout the fibers. Industrial added value is high in surface treatment such as etching or cleaning caused by OH radicals.

[Examples] Example 1

Prepared a household water purifier (trade name: CLEANSUI 02) manufactured by Mitsubishi Rayon (trade name). In the filter cartridge of the water purifier, a hydrophilized polyethylene hollow fiber membrane (contact angle of hydrophilic material to water (25 ° C) = 55 °) was used. The hollow fiber membrane is a hollow membrane having an inner diameter of 270 μm and a membrane thickness of 55 μm manufactured by Mitsubishi Rayon Co., Ltd., and has a slit-like pore structure in which a fiber composed of polyethylene is aligned with a hollow fiber membrane. In the fiber direction, a plurality of the fibers are stacked in the thickness direction of the film.

The water purifier was installed on a household tap, and the tap water was passed to the filter box (Sanke-cho, Iwakuni City) for a period of one year. The filter box was clogged, and the surface of the hollow fiber membrane in the filter box changed to light gray. The filter box causing the clogging is removed from the water purifier body, and the activated carbon is removed from the filter cartridge to obtain a blocked hollow fiber membrane sample. The surface of the blocked hollow fiber membrane was observed with an electron microscope. An electron microscope photograph is shown in Fig. 6. In the blocked hollow fiber membrane, the slit-shaped pores on the surface of the membrane are blocked by the organic matter.

The blocked hollow fiber membrane was washed in the following manner.

The length of the hollow fiber membrane sample that was blocked was about 50 mm, so it was bundled on a 150 mm long hollow fiber membrane (manufactured by Mitsubishi Rayon, EX-540V polyethylene hollow fiber membrane). The blocked hollow mesangial sample was prepared for the experimental sample.

As the plasma generating device, the device shown in Fig. 1 was used. As the RF power source, the T161-5766LQ model manufactured by THAMWAY Co., Ltd. was used as the matching box, and the T0202-5766LQ model manufactured by THAMWAY Co., Ltd. was used.

First, the experimental sample was immersed in a container filled with water so that the support member was fixed near the electrode. The electrode is used to heat the water, which causes water vapor bubbles to be generated in the water. In Fig. 1, an electromagnetic wave (27.1 MHz) is irradiated to a water vapor bubble at a discharge power of 300 W at a gas pressure of 30 hPa to vaporize water vapor in the bubble, and secondly, the pressure is atmospheric pressure. And make the vapor bubble plasma continue to be produced. When the gas phase side is at atmospheric pressure, the luminescence spectrum from the water vapor bubble plasma is as shown in FIG. The spectroscopic spectrum was carried out in the reaction apparatus of Fig. 1 using a PZ-11 C-7473-36 Czerney-Turner type small polychromator manufactured by PHOTONICS and a back-illuminated CCD line image sensor for light from the luminescent bubble. The spectral intensity is determined by measuring in wavelength. The number of photodetecting elements is 1024, the wavelength range is 200 to 950 mn, and the exposure time is 19 ms. Measurements were performed using a polychromator with a wavelength sensitivity unevenness correction and a wavelength axis correction and a line image sensor.

The vapor bubble plasma was brought into contact with the experimental sample for 3 minutes while the gas phase side was at atmospheric pressure. The surface of the surface treated hollow fiber membrane sample was observed with an electron microscope. The electron micrograph is shown in Figure 7. The blocked organic matter is almost completely removed. Moreover, the surface of the hollow fiber membrane sample was hardly damaged, so the pore structure maintained its original shape.

Example 2

Using the same plasma generating apparatus as in Example 1, the test sample was immersed in a container filled with water so that the support member was fixed in the vicinity of the electrode. The vapor-bubble plasma was generated under the same conditions as in Example 1 except that the ethylene-vinyl alcohol copolymer film (hereinafter sometimes referred to as EVAL film) shown in Table 9 was used as the sample, and the electricity was generated. The slurry was contacted with the sample for 3 minutes. The contact angle of any film to water before the plasma contact is in the range of 64 to 71 degrees, showing hydrophilicity. The plurality of films can withstand the heat of the vapor bubble plasma and maintain its morphology.

1) Ethylene: ethylene content rate 2) θ/2 = reading value of the contact angle meter. In the contact angle meter, CA-DT manufactured by Concord Interface Science was used. The droplet volume of pure water is 1 μL. 3) θ: contact angle 4) T: temperature of measurement chamber 5) RH: humidity of measurement chamber 6) "plasma durability" means durability of water vapor plasma in water. 7) The term "gas phase is atmospheric pressure" means that the gas phase above the water surface is atmospheric pressure, and the water vapor bubble plasma is generated in this state. 8) The term "having durability" means not breaking and maintaining the original form. 9) The term "no durability" refers to thermal decomposition caused by the heat of plasma after rupture.

In Tables 10 and 11 shown below, the same symbols or terms as those of 1) to 9) have the same meanings.

Further, the surface of the film of the sample DC3203F was marked with an oily ink. When the marked portion is brought into contact with the plasma, the oily ink is decomposed by the plasma and does not remain on the film. The surface of the film after washing was smoother when visually observed.

Example 3

The Nafion 112 and Nafion 1035 films manufactured by DuPont were immersed in ion-exchanged water at 25 ° C for 5 minutes, and the film was swollen with water, and then taken out, and the contact angle was measured as the contact angle shown in Table 10. Nafion 112 and Nafion 1035 shown in Table 10 were used as samples for plasma treatment.

Using the same plasma generating apparatus as in Example 1, the sample was immersed in a container containing water to support the sample to be fixed near the electrode. Next, under the same conditions as in Example 1, steam bubble plasma was generated, and the plasma was brought into contact with the sample for 3 minutes. As shown in Table 10, the water-swelled Nafion 112 and Nafion 1035 were subjected to the heat of the steam bubble plasma to maintain their morphology.

Further, the surface of the Nafion 112 film was marked with an oil-based ink. The markings can be placed against and secured to the film. The marked portion was exposed to water vapor bubble plasma in water for 3 minutes, and visually observed, at which time the oily ink was decomposed by the plasma and did not remain on the sample. The cleaned film surface was smoothed by visual observation.

Example 4

Using the same plasma generating apparatus as in Example 1, the sample was immersed in a container filled with water so that the support member was fixed in the vicinity of the electrode. A water vapor bubble 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 the sample, and the plasma was brought into contact with the glass plate. 3 minutes. The glass plate is subjected to the heat of the water vapor bubble plasma and maintains its shape. The contact angle of the glass plate before contact with the plasma to water is about 35 degrees.

Further, the surface of the glass plate was marked with oily ink, and the marked portion was exposed to water vapor bubble plasma in water for 3 minutes, and then visually observed. The oily ink is decomposed by the plasma and does not remain on the glass plate. The cleaned glass plate is smoother when viewed visually.

Example 5

Using the same plasma generating apparatus as in Example 1, the test sample was immersed in a container filled with water so that the support member was fixed in the vicinity of the electrode. The vapor bubble plasma was generated under the same conditions as in Example 1 except that an alumina ceramic thin plate (γ-Al ₂ O ₃ thin plate, thickness: 3 mm, 100 mm × 100 mm) was used as the sample, and The plasma was in contact with the glass for 3 minutes. The contacted alumina ceramic sheet is subjected to the heat of the water vapor bubble plasma to maintain the original shape. The contact angle of the alumina ceramic sheet before contact with the plasma is about 55 degrees.

Further, the surface of the alumina ceramic thin plate was marked with an oil-based ink, and the mark portion was exposed to water vapor bubble plasma in water for 3 minutes, and then visually observed. The oily ink is decomposed by the plasma and does not remain on the alumina ceramic sheet. The cleaned alumina ceramic sheet was smoother when viewed visually.

Example 6

Using the same plasma generating apparatus as in Example 1, the test sample was immersed in a container filled with water so that the support member was fixed in the vicinity of the electrode.

A polyethylene-vinyl alcohol copolymer film (ethylene content: 32 mol%) was used as a substrate (thickness: 3 mm, 100 mm × 100 mm), and a polyethylene was attached to the substrate at a distance of 5 mm by heat fusion. A film (thickness 0.5 mm, 100 mm x 100 mm) was prepared and included a sample having a hydrophilic portion having a 5 mm width and a hydrophobic portion having a hydrophilic surface/hydrophobic surface of 5 mm width. The ethylene-vinyl alcohol copolymer film (ethylene content: 32 mol%) had a contact angle with water of 67 degrees, and the polyethylene film had a contact angle with water of 95 degrees.

A steam 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 sample for 3 minutes. After the contact, the sample was taken out from the reaction vessel, and the polyethylene film as a hydrophobic portion was etched by plasma to have an average thickness of 0.1 mm, but the ethylene-vinyl alcohol copolymer film substrate maintained the initial smooth surface. As a result, only the hydrophobic portion is etched by the plasma.

Comparative example 1

As an article, a 100 μm thick polytetrafluoroethylene film (contact angle to water (25 ° C) = 110 °) and a polyethylene film (contact angle to water (25 ° C) = 95) were prepared without hydrophilization. Degree), polypropylene film (contact angle to water (25 ° C) = 96 degrees). Organic substances such as dirt are not adhered to the surface of the plurality of films. The above-mentioned plurality of films were subjected to surface treatment in the same manner as in Example 1. Any film, at the moment of contact with the plasma, thermally decomposes due to the high temperature of the plasma, causing cracking.

Comparative example 2

As an article, an organic polymer porous flat membrane (manufactured by Millipore Co., Ltd., hydrophobic polytetrafluoroethylene film, having a hydrophilicity of 50 μm) was prepared, and the contact angle with water (25 ° C) was 1,10 °, average. Organic polymer porous flat membrane with a pore diameter of 1 μm and a thickness of 100 μm (manufactured by Millipore, a hydrophobic polyethylene film with a contact angle to water (25 ° C) = 94 ° and an average pore diameter of 1 μm) . On the surface of the plurality of polymer porous flat membranes, organic substances such as dirt are not adhered. The above-mentioned plurality of polymer porous flat films were subjected to surface treatment in the same manner as in Example 1. Any flat film is thermally decomposed due to the high temperature of the plasma at the moment of contact with the plasma, resulting in cracking.

Comparative example 3

Water vapor bubble plasma was used under the same conditions as in Example 3 except that two Nafion films (Nafion 112, Nafion 1035) manufactured by DuPont Co., Ltd., which were left in a 25 ° C, 55% RH atmosphere, were used as the sample. Contact the sample.

The contact angles of Nafion 112 and Nafion 1035 for water before the plasma contact were as shown in Table 11. At the moment of contact with the plasma, both Nafion films are thermally decomposed by the high temperature of the plasma to cause cracking.

Comparative example 4

Prepare 200 mL of pure water in a 300 mL-capacity beaker, immerse the blocked hollow fiber membrane used in Example 1 in pure water at 25 ° C, and clean the hollow fiber membrane with an ultrasonic cleaner with an output of 100 W and 20 KHz. 1 hour. The cleaned film was observed with an electron microscope, and it was found that the organic substances clogged on the film surface were not removed.

Comparative Example 5

In Example 1, the electrode of the reaction apparatus was superheated to generate a water vapor bubble in a non-plasma state, and the water vapor bubble was brought into contact with the blocked hollow fiber membrane sample for 3 minutes, at which time the organic matter blocked on the membrane surface was not Was removed.

The present invention is a surface treatment technique which causes a plasma generated in a water vapor bubble to come into contact with an article having a hydrophilic surface in water, whereby the organic matter attached to the article can be decomposed or removed without causing damage to the article. This surface treatment technique is useful, for example, in the regeneration of the organic polymer porous membrane and the ceramic porous membrane used in household water purifiers, industrial drainage filters, air filtration, and safety disposal of porous membranes. In particular, it is effective as a method of safely regenerating or discarding the following membranes: a filter membrane for hand washing water in a hospital, an air filter membrane for in-hospital infection prevention in a hospital, an air filter membrane for a disinfection chamber, and the like, and is contained by a substance containing bacteria. Contaminated or clogged membrane.

Further, the surface treatment method of the present invention is suitably applied to a method in which an organism-suitable material is embedded in a body and used, and after use, an organic substance such as bacteria on the surface of the material is thermally decomposed or carbonized for safe disposal of the material; The cancer cells coexisting with the organs are thermally decomposed or carbonized for safe and effective treatment; the organic substances such as bacteria, blood, and proteins attached to the used contact lenses are thermally decomposed or carbonized for safe disposal. Wait. Furthermore, the surface treatment method of the present invention can also be applied to a treatment in which a catheter, an artificial blood vessel, or the like is immersed in a body before sterilization, and bacteria adhering to the organism after being taken out from the organism are sterilized; Removal of bacteria other than the target; treatment for safely discarding the used DNA sample detection device; thermal decomposition or carbonization of fungi attached to the nonwoven fabric used in air filters, masks, etc., for safe disposal Processing and so on.

Further, the etching technique of the present invention can also be applied to the processing of an anti-slip goggle which imparts fine irregularities to the surface of the hydrophilic transparent organic material, and exhibits an anti-reflection function for optical use, or finds that only Visibility at a specific viewing angle. Further, the surface of the metal film can be etched only by the chemical substance derived from the water molecules, and the cost of the waste liquid processing can be reduced in the damascene process of the high-density multilayer wiring in the semiconductor device, so that the manufacturing cost can be effectively reduced.

Further, in the semiconductor multilayer wiring device in recent years, the wiring density is increased, and it is necessary to perform finer processing. In this case, a low dielectric constant material containing a porous tantalum film is proposed as the insulating film. The insulating film has a large pore volume, and the contact angle of the material with water is hydrophobic. Therefore, in a usual chemical mechanical polishing process, the polishing liquid is repelled by the insulating film, and after the metal film is cut, it is difficult to make the whole flat. On the other hand, by using the method of the present invention, a material having a contact angle of water of 90 degrees or less can be selected as the low dielectric constant film, whereby the OH radical in the vapor bubble plasma etches the low dielectric constant film, so that A structure of a flat insulating film/multilayer wiring metal is obtained.

Further, the etching technique of the present invention can control the contact time with the vapor bubble plasma and set it as a short time, so that only the hydrophobic portion can be selectively etched. This technique is applicable to various materials such as an organic material, an inorganic material, and a carbon material which have both a hydrophilic surface and a hydrophobic surface, and can selectively etch a hydrophobic portion. In particular, materials such as carbon materials and tantalum wafers have high heat resistance temperatures, so surface processing is difficult, but etching can be easily performed by this technique.

10. . . Plasma generating device

11. . . liquid

12. . . container

13. . . electrode

14. . . Counter electrode

15. . . article

16. . . Support

17. . . Water vapor bubble

18. . . Water droplets

19. . . Air phase

γ _{S V} . . . Surface tension of solids in equilibrium with liquid (water) vapor (room temperature, atmospheric pressure)

γ _{S L} . . . Interfacial tension between solid and liquid

γ _{L v} . . . Surface tension of liquid (water) in equilibrium with the vapor (water vapor)

Fig. 1 is a schematic block diagram showing an example of a plasma generating apparatus.

Figure 2 is a representation of the contact angle of water on the surface of the article.

Fig. 3 is a graph showing the dependence of the contact angle of the etching rate of water vapor bubbles (hereinafter referred to as steam bubble plasma) in a plasma state.

4 is a schematic view of a multilayer wiring damascene process.

Fig. 5 is a graph showing the luminescence spectrum of a slurry of water vapor bubbles. (Example 1)

Figure 6 is an electron micrograph of the surface of a blocked hollow fiber membrane sample.

Fig. 7 is an electron micrograph of the surface of the hollow fiber membrane sample after surface treatment.

10. . . Plasma generating device

11. . . liquid

12. . . container

13. . . electrode

14. . . Counter electrode

15. . . article

16. . . Support

17. . . Water vapor bubble

19. . . Air phase

Claims (14)

A surface treatment method for causing a plasma generated in a water vapor bubble in an aqueous liquid to contact a material having a contact angle with water of 90 degrees or less in the liquid. An article which is surface-treated according to the surface treatment method described in claim 1 of the patent application. A surface treatment method for causing a plasma generated in a water vapor bubble in an aqueous liquid to contact an organic substance adhering to a material having a contact angle with water of 90 degrees or less in the liquid, and removing the organic substance from the material. The surface treatment method according to claim 3, wherein the material is a porous polymer membrane. The surface treatment method according to claim 3, wherein the material is a polymer electrolyte membrane. The surface treatment method according to claim 3, wherein the material is glass. The surface treatment method according to claim 3, wherein the material is ceramic. An article which is surface-treated according to the surface treatment method according to any one of claims 3 to 7. An etching method is a plasma generated in a water vapor bubble in an aqueous liquid, in which a material having a contact angle with water of 90 degrees or less is contacted, and the surface of the material is etched without damaging the material. Such as the etching method described in claim 9 of the patent scope, the above materials For metal. The etching method according to claim 10, wherein the metal is at least one selected from the group consisting of copper, aluminum, and tungsten. An article which is etched according to the etching method according to any one of claims 9 to 11. An etching method for causing a plasma generated in a water vapor bubble in an aqueous liquid to contact both a hydrophobic portion having a contact angle with water of more than 90 degrees and a hydrophilic portion having a contact angle of 90 degrees or more in the liquid. Material and etch the hydrophobic portion. An article which is etched according to the etching method described in claim 13 of the patent application.