JP2007188748A - Remote type plasma processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve plasma processing efficiency, in a remote plasma processing method. <P>SOLUTION: This plasma processing method uses a plasma processing device equipped with a pair of electrodes 4A and 4B facing to each other, and a solid dielectric layer 5 or 6 installed on a facing surface of at least one of the pair of electrodes. A processing gas 9 having a pressure above the atmospheric pressure is introduced into a discharge space 8, the processing gas 9 is activated by using discharge by application of a pulse voltage to the pair of electrodes, and a processing object 11 is exposed to the activated processing gas. A gap interval (d) of the discharge space, the average electric field intensity between the electrodes and the pulse width of the pulse voltage are not greater than 0.3 mm, not smaller than 10 kV/cm and not longer than 5 μsec, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a remote plasma processing method.

  Patent Document 1 discloses a method in which a glow discharge plasma treatment is performed by placing a solid dielectric on at least one opposing surface of a counter electrode and applying an electric field between the counter electrodes under a pressure near atmospheric pressure. ing. Here, the applied electric field is pulsed, the voltage rise time is 100 μs or less, and the electric field strength is 1 to 100 kV / cm. For this reason, it is said that, for example, nitrogen gas was subjected to a glow discharge plasma treatment, and the substrate surface modification was successfully performed.

The method described in Patent Document 1 is a method of performing surface modification by using a processing gas near atmospheric pressure and performing glow discharge between electrodes. When the present inventor examined, when a plasma jet was generated using a pressurized processing gas and the plasma jet was sprayed on an object to be processed (remote plasma method), the processing efficiency was very low. It was.
Patent No. 3040358

  Further, since it is a glow discharge method, the plasma density is low, and a sufficiently high treatment efficiency cannot be obtained by surface modification treatment or the like.

  In Patent Document 1, since an inverter type pulse generator is further used, the pulse current density cannot be increased, and a sufficient processing effect cannot be obtained. Further, a MOS type element such as an IGBT is used as the switching element of the pulse power source. However, the frequency of malfunctioning due to noise in the pulse circuit is high, and in some cases, the element may be destroyed when an arc is generated.

  An object of the present invention is to improve plasma processing efficiency in a remote plasma processing method.

The present invention uses a plasma processing apparatus comprising a pair of electrodes facing each other, and a solid dielectric layer placed on the facing surface of at least one of the pair of electrodes,
A processing gas having a pressure higher than atmospheric pressure is introduced into a discharge space provided between the pair of electrodes, the processing gas is activated using discharge by applying a pulse voltage to the pair of electrodes, and the activated processing gas is When contacting the workpiece, the gap distance of the discharge space is 0.3 mm or less, the average electric field strength between the electrodes is 10 kV / cm or more, and the pulse width of the pulse voltage is 5 microseconds or less. The present invention relates to a remote plasma processing method.

  According to the present invention, during remote plasma processing, the gap interval of the discharge space is narrowed to 0.3 mm or less, and a high energy density streamer discharge is generated in the narrow gap space, thereby generating radicals in the plasma jet. A large amount of plasma treatment with high treatment effect was realized.

  By setting the gap interval d in the discharge space to 0.3 mm or less, the energy density in the processing gas passing through the gap can be increased and the processing efficiency can be improved. From this point of view, the gap interval d of the discharge space is more preferably 0.2 mm or less. In addition, if the gap interval is 0.05 mm or less, it is difficult to keep the entire electrode surface at a uniform interval and the processing effect becomes non-uniform, so from the viewpoint of obtaining an industrially stable plasma processing apparatus. The gap distance d is preferably 0.05 mm or more.

  The average electric field strength between the electrodes is more preferably 40 kV / cm or more from the viewpoint of the present invention.

  In addition, by setting the pulse width of the pulse voltage to 5 microseconds or less, the amount of radicals generated in the flow in the processing gas can be increased, and the processing efficiency can be improved.

  In a preferred embodiment, an induction storage type pulse power supply is used as a pulse power supply for applying a pulse voltage. This makes it possible to generate a streamer discharge with a high current density. As a result, the amount of radicals generated in the plasma jet is large, and the treatment effect can be improved.

  In a preferred embodiment, an electrostatic induction thyristor element is used as the switching element of the pulse power supply. This is less likely to cause malfunction due to noise and element destruction, and is easy to maintain, so that productivity can be improved.

  FIG. 1 is a diagram schematically showing an embodiment of the present invention. The electrode devices 4A and 4B are electrode devices covered with dielectric solid layers 5, 6, 12, and 13, and a discharge space 8 is formed by facing them. That is, the discharge space 8 is formed at a position so as to be sandwiched between the electrodes. In this example, the discharge space 8 is formed between the two dielectric layers 12 and 13. When the dielectric layer 5 (or 6) is provided only on one electrode, the space formed between the electrode device and the dielectric layer becomes the discharge space 8, but the discharge space 8 is also provided between the pair of electrodes. ing. In this example, the dielectric layers 5 and 6 are also provided on the outer sides of the electrodes 4A and 4B, but these are not essential. The gap interval d of the discharge space 8 is set to 0.3 mm or less according to the present invention. The electrode interval X is defined as the distance between the short surfaces on the discharge space gap side of the electrode devices 4A and 4B.

  A pulse voltage is supplied from the power source 1 to the pair of electrodes 4A and 4B. At the same time, the processing gas is ejected into the space 8 as in the gas pipes 2 to 9, plasma processing is performed, and the treated gas is ejected to the surface 11 a to be processed 11 as indicated by the arrow 10. Let

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

  The solid dielectric is disposed on one or both of the opposing surfaces of the electrode. At this time, the solid dielectric and the electrode on the side to be installed are in close contact with each other, and the opposing surface of the electrode in contact is completely covered. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, arc discharge occurs from there.

  One or both of the electrodes can be coated with a solid dielectric. Examples of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal dioxide such as silicon dioxide, aluminum oxide, zirconium dioxide, and titanium dioxide, and composite oxide such as barium titanate.

  The solid dielectric preferably has a relative dielectric constant of 2 or more (under an environment of 25 ° C.). Specific examples of the dielectric having a relative dielectric constant of 2 or more include polytetrafluoroethylene, glass, and metal oxide film. In order to stably generate a high-density discharge plasma, it is preferable to use a fixed dielectric having a relative dielectric constant of 10 or more. The upper limit of the relative dielectric constant is not particularly limited, but about 18,500 is known as an actual material. The solid dielectric having a relative dielectric constant of 10 or more is composed of a metal oxide film mixed with 5 to 50% by weight of titanium oxide and 50 to 95% by weight of aluminum oxide, or a metal oxide film containing zirconium oxide. It is preferable to use a film having a thickness of 10 to 1000 μm.

  In the present invention, the planar pattern of each electrode is not particularly limited, and can be designed according to the type of catalyst and the type of reaction. For example, the planar pattern of the electrodes can be comb-like or mesh-like.

  In the case where the electrode has a net shape or a comb shape, it is preferable that the through holes are formed in a net shape or regularly formed in the gaps between the comb teeth. In this embodiment, the shape of the mesh is not particularly limited, and may be a circle, an ellipse, a racetrack shape, a quadrangle, a polygon such as a triangle, or the like. The shape of the comb-teeth of the comb-like electrode is not particularly limited, but is preferably a rectangle or a parallelogram.

  In the present invention, a pulse voltage is applied between the counter electrodes to generate plasma. At this time, the waveform of the pulse voltage is not particularly limited, and may be any of an impulse type, a square wave type (rectangular wave type), and a damped oscillation type. A DC bias voltage can be applied simultaneously.

  In the present invention, the pulse width of the pulse voltage is 5 microseconds or less. Pulse width A period of half width where the pulse voltage is half of the voltage peak value. In the pulse of the decay waveform, a series of a plurality of pulses are continuously attenuated. In this case, it means the half width of the initial wave. For example, in the case of the waveform shown in FIG. 2A, since it is one impulse type pulse voltage, the pulse width is the half width of the pulse. In FIG. 2B, since the pulse oscillates damped, the pulse width is the half-value width of the initial wave. Similarly, for the square wave shown in FIG. 2C, the pulse width is defined by the half width of the pulse voltage. Further, the average electric field strength Eav is defined by a value obtained by dividing the voltage peak value Vp by the electrode interval X as shown in the following equation.

  Eav = Vp / X

  The shorter the rise time of the pulse, the more efficiently ionization of the gas during plasma generation. From this point of view, the pulse rise time is preferably 0.05 microseconds or less. In reality, the rise time of the pulse is 0.1 microsecond or more due to the transient time due to the operation time of the switching element used in the pulse generation circuit and the circuit impedance. The rise time is a time during which the voltage change is continuously positive.

  Further, the falling time of the pulse electric field is preferably steep, and is preferably 0.05 microseconds or less.

  The frequency of the pulse electric field is preferably 0.5 kHz to 100 kHz. If it is less than 0.5 kHz, the plasma density is low, so that the process takes too much time. If it exceeds 100 kHz, arc discharge tends to occur.

  The pulse voltage as described above can be applied by a steep pulse generating power source. As such a power source, an induction accumulation type pulse power source using an electrostatic induction thyristor element that does not require a magnetic compression mechanism, a thyratron equipped with a magnetic compression mechanism, a gap switch, an IGBT element, a MOF-FET element, an electrostatic induction A capacity storage type pulse power source using a thyristor element can be exemplified. As the pulse power source for applying the pulse voltage, an induction accumulation type pulse power source is particularly preferable.

  The object to be processed by the plasma generated by the present invention is not particularly limited. Hereinafter, the surface treatment method of the substrate will be described in detail.

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

  By using a fluorine-containing compound gas as the treatment gas, it is possible to form a fluorine-containing group on the surface of the substrate to reduce the surface energy and obtain a water-repellent surface.

  Fluorine-containing compounds such as carbon tetrafluoride (CF4), carbon hexafluoride (C2 F6), propylene hexafluoride (CF3 CFCF2), cyclobutane octafluoride (C4 F8), monochloride Examples thereof include halogen-carbon compounds such as carbon trifluoride (CClF3), fluorine-sulfur compounds such as sulfur hexafluoride (SF6), and the like. From the viewpoint of safety, it is preferable to use carbon tetrafluoride, carbon hexafluoride, hexafluoropropylene, and octafluorocyclobutane that do not generate hydrogen fluoride, which is a harmful gas.

  Using the following oxygen element-containing compounds, nitrogen element-containing compounds, and sulfur element-containing compounds as processing gases, surface functional energy is formed by forming hydrophilic functional groups such as carbonyl groups, hydroxyl groups, and amino groups on the substrate surface. The surface can be increased to obtain a hydrophilic surface.

  Examples of the oxygen element-containing compound include oxygen, ozone, water, carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, metanal, and ethanal. Examples include organic compounds containing oxygen elements such as aldehydes. These may be used alone or in admixture of two or more. Further, the oxygen element-containing compound may be mixed with a gas of a hydrocarbon compound such as methane or ethane. Moreover, hydrophilization is accelerated | stimulated by adding a fluorine element containing compound in 50 volume% or less of the said oxygen element containing compound. What is necessary is just to use the same thing as the said illustration as a fluorine element containing compound.

  Nitrogen, ammonia, etc. are mentioned as a nitrogen element containing compound. You may mix and use the said nitrogen element containing compound and hydrogen.

  Examples of the sulfur element-containing compound include sulfur dioxide and sulfur trioxide. Moreover, sulfuric acid can be vaporized and used. These may be used alone or in admixture of two or more.

  A hydrophilic polymer film can also be deposited by performing the treatment in an atmosphere of a monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule. Examples of the hydrophilic group include a hydroxyl group, a sulfonic acid group, a sulfonate group, a primary or secondary or tertiary amino group, an amide group, a quaternary ammonium base, a carboxylic acid group, and a carboxylic acid group. Can be mentioned. Similarly, a hydrophilic polymer film can be deposited using a monomer having a polyethylene glycol chain.

  Examples of the monomer include acrylic acid, methacrylic acid, acrylamide, methacrylamide, N, N-dimethylacrylamide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, sodium styrenesulfonate, allyl alcohol, allylamine, polyethylene. Examples include glycol dimethacrylic acid ester and polyethylene glycol diacrylic acid ester. These monomers are used alone or in combination.

  Since the hydrophilic monomer is generally a solid, a substance dissolved in a solvent is vaporized by means such as reduced pressure. Examples of the solvent include organic solvents such as methanol, ethanol, and acetone, water, and mixtures thereof.

  Furthermore, a metal oxide thin film such as SiO2, TiO2 or SnO2 is formed using a processing gas such as metal metal-hydrogen compound, metal-halogen compound, metal alcoholate such as Si, Ti, Sn, etc. Can be provided with electrical and optical functions.

  It is preferable to perform the treatment in an atmosphere diluted with a diluent gas as described below. Examples of the diluent gas include noble gases such as helium, neon, argon, and xenon, nitrogen gas, and the like. These may be used alone or in admixture of two or more. Moreover, when using dilution gas, it is preferable that the ratio of the gas for processing is 1-10 volume%.

  According to the method of the present invention, stable treatment in argon and nitrogen gas is possible. In particular, the present invention is epoch-making in that various types of remote plasma processing using an atmosphere containing 70% or more of nitrogen as a processing gas is possible.

  The pressure of the processing gas is not less than atmospheric pressure, but is preferably 0.2 MPa or more, more preferably 0.4 MPa or more.

  Using the apparatus schematically shown in FIG. 1, the organic contaminants were cleaned by remote plasma on the surface of the glass substrate.

  Specifically, alumina plates (purity 95%) having a length of 90 mm, a width of 50 mm, and a thickness of 1 mm were prepared as the dielectric plates 5 and 7. The thicknesses of the dielectric layers 5 and 7 in which the electrodes 6A and 6B made of molybdenum metal are embedded in the central portion in the thickness direction of the alumina plate are 0.5 mm, respectively.

  The gap interval d of the discharge space was changed as shown in Tables 1 and 2. The distance d was adjusted with a spacer.

  As a power source, an inductive accumulation type pulse power source having a circuit configuration as shown in FIG. 3 was used. The pulse waveform of the pulse voltage is shown in FIG. The pulse width of the pulse voltage was 2 or 5 μm, the frequency was 16 kHz, and the output was 400 W.

  The capacity storage type pulse power supply of the circuit shown in FIG. 5 was also used. The pulse waveform is shown in FIG. The pulse duration was 10 μm or 20 μm. The pulse frequency was 16 kHz and the output was 400 W. The peak value and electric field strength are shown in Tables 1 and 2.

  High purity nitrogen gas (purity 99.999%) was used as the processing gas, the gas pressure was 0.5 MPa, and the flow rate was changed as shown in Tables 1 and 2.

  A disk-shaped substrate made of borosilicate glass was used as the object to be processed (diameter 30 mm, thickness 3 mm). The processed surface 11a of the disk-shaped substrate was mirror-polished. The initial water contact angle was 50 to 53 degrees. The conveyance speed of the substrate was 5 cm / second. The water contact angle on the treated substrate surface was measured by Elma sales company "G-1 type" (using ultrapure water). The measurement results are shown in Tables 1 and 2.

  Thus, according to the remote plasma processing method of the present invention, the water contact angle on the substrate surface could be remarkably reduced.

It is a figure which shows typically the remote plasma processing apparatus which can be used by the method of this invention. (A), (b), (c), and (d) are graphs showing the relationship between the waveform and the pulse width, respectively. It is a circuit diagram of an induction storage type pulse power supply. It is a graph which shows the pulse waveform of the pulse voltage of an induction storage type pulse power supply. It is a circuit diagram of a capacity storage type pulse power supply. It is a graph which shows the pulse waveform of a capacity | capacitance accumulation type pulse power supply.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Power supply 2 Gas pipe 3 Chamber 4A, 4B Electrode apparatus 5, 6, 12, 13 Dielectric layer 8 Discharge space 9 Process gas 10 Plasma-processed process gas 11 Non-processed object d Discharge space gap space | interval X Electrode space | interval

Claims (4)

Using a plasma processing apparatus comprising a pair of electrodes facing each other, and a solid dielectric layer placed on the facing surface of at least one of the pair of electrodes,
A processing gas having a pressure higher than atmospheric pressure is introduced into a discharge space provided between the pair of electrodes, and the processing gas is activated and activated by using a discharge generated by applying a pulse voltage to the pair of electrodes. When the processed gas is brought into contact with the object to be processed, the gap interval of the discharge space is 0.3 mm or less, the average electric field strength between the electrodes is 10 kV / cm or more, and the pulse width of the pulse voltage is 5 A remote plasma processing method, characterized in that the time is less than microseconds.   2. The plasma processing method according to claim 1, wherein an induction storage type pulse power source is used as the pulse power source for applying the pulse voltage.   3. The plasma processing method according to claim 1, wherein an electrostatic induction thyristor element is used as a switching element of a pulse power source for applying the pulse voltage.   The plasma processing method according to claim 1, wherein a nitrogen gas concentration in the processing gas is 70% by volume or more.

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