JP2000204476A - Manufacturing method of functionally graded material - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a functionally gradient material capable of forming a thin film at high speed by performing plasma discharge near atmospheric pressure without requiring a high degree of vacuum. SOLUTION: Under a pressure close to the atmospheric pressure, a base material is arranged between a pair of opposed electrodes, and a pulse-shaped voltage having a voltage rise time of 100 μs or less and an electric field intensity of 1 to 100 kV / cm is applied between the opposed electrodes. In performing the discharge plasma treatment by applying the voltage, the maximum value and the minimum value in one cycle of the applied voltage are continuously changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a functionally gradient material.

[0002]

2. Description of the Related Art A functionally graded material is a material based on a new concept. Functionally graded materials manufactured by using a gas phase synthesis method such as PVD or CVD include electric / magnetic, optical, chemical, biological / medical. Applications are desired in a wide range of fields such as aviation and space. It is known that the functionally graded material is effective as a means for preventing cracks and improving the adhesion to a substrate. Therefore, in recent years, applications to new optical materials by continuously changing the refractive index have been reported.

[0003] With the spread of color displays,
A high resolution is required, and a multi-layer deposited film utilizing light interference or a film coated with a CVD film and provided with an antireflection function has been put to practical use. However, antireflection coatings made of these multi-layer coatings are currently applied only to a limited number of high-grade products due to their high formation costs.
The challenge is to obtain a high-performance antireflection film at low cost.

[0004] For example, a plasma C
In forming the hard coat layer by the VD method, the refractive index of the portion in contact with the plastic substrate is substantially equal to the refractive index of the substrate, and the reflectance is reduced over a wide area by continuously decreasing in the thickness direction. Method (Japanese Unexamined Patent Publication No. 7-5)
No. 6002) has been proposed.

[0005]

However, the above method requires a high degree of vacuum when forming a hard coat layer by the plasma CVD method, which not only hinders mass production, but also reduces the length of the product. There is a drawback that it cannot be handled, and the processing speed is slow.

Further, when plasma discharge is performed near the atmospheric pressure, the substrate is greatly damaged, so that it cannot be applied to the formation of a thin film on a substrate having low heat resistance.

An object of the present invention is to provide a method for producing a functionally gradient material which can form a thin film at a high speed by performing a plasma discharge near atmospheric pressure without requiring a high degree of vacuum and solving the above problems. Aim.

[0008]

According to the method for producing a functionally gradient material of the present invention, a substrate is placed between a pair of opposed electrodes under a pressure near atmospheric pressure, and a voltage rise time between the opposed electrodes is 100 μs. Hereinafter, when performing a discharge plasma treatment by applying a pulsed voltage having an electric field intensity of 1 to 100 kV / cm, the maximum value and the minimum value in one cycle of the applied voltage are continuously changed. is there.

In the present invention, "under a pressure near the atmospheric pressure" means
Refers to a pressure of 100 to 800 Torr. In particular, the pressure can be easily adjusted and the device can be simplified.
The range of rr is preferred.

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

[0011] In the present invention, it is preferable to use an apparatus in which a solid dielectric is provided on at least one of the opposing surfaces of the electrodes. In this case, the portion where the plasma is generated is located between the solid dielectric and the electrode when a solid dielectric is provided on one of the electrodes, and between the solid dielectrics when the solid dielectric is provided on both of the electrodes. The space between them.

Examples of the material of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. And the like.

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

In the present invention, the electric field applied between the electrodes is pulsed, the voltage rise time is 100 μs or less, the electric field intensity is 1 to 100 kV / cm, and the maximum in one cycle of the applied voltage. The value and the minimum value change continuously.

FIG. 1 shows an example of a pulse voltage waveform used in the present invention. (A) is immediately after application (b) is after 30 seconds,
(C) shows the state after one minute, and changes continuously from (a) through (b) to (c).

The pulse voltage waveform in the present invention is not limited to the above-mentioned waveform, but the shorter the rise time of the pulse, the more efficient the ionization of the processing gas during plasma generation. If the rise time of the pulse (the time until it reaches Vp ⁺ ) exceeds 100 μs, the discharge state tends to shift to an arc and becomes unstable, so that a high-density plasma state due to the pulse electric field cannot be expected. Further, it is better that the rise time is fast. However, there is a limit to a device that has an electric field intensity large enough to generate plasma at normal pressure and generates an electric field with a fast rise time. It is difficult to achieve a pulsed electric field with a rise time of less than. More preferably, the rise time is 50 ns to 5 μs. Here, the rise time refers to a time during which the voltage change is continuously positive.

It is preferable that the fall time of the pulse electric field is also steep.
It is preferable that the time scale is less than μs. For example, in the power supply device used in the embodiment of the present invention, the rise time and the fall time can be set to the same time, although it differs depending on the pulse electric field generation technique.

Further, modulation may be performed using pulses having different pulse waveforms, rise times, and frequencies.

The frequency of the pulse electric field is 0.5 kHz to 1
Preferably, it is 00 kHz. If the frequency is less than 0.5 kHz, the plasma density is low, so that it takes too much time for the treatment. If the frequency exceeds 100 kHz, arc discharge is likely to occur. More preferably, the frequency is 1 kHz or more. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

The pulse duration in the above-mentioned pulse electric field is preferably 1 to 1000 μs. 1μ
s, the discharge becomes unstable, and
If it exceeds s, it is easy to shift to arc discharge. More preferably, it is 3 μs to 200 μs. Here, one pulse duration is an example shown in FIG.
It refers to the time during which a pulse is continuous in a pulse electric field composed of N and OFF repetitions. In the case of the intermittent pulse as shown in FIG. 2A, the pulse duration is equal to the pulse width time, but in the case of the pulse having the waveform as shown in FIG. Means time including

Further, in order to stabilize the discharge, it is preferable to have an OFF time lasting at least 1 μs within 1 ms of the discharge time.

In the present invention, when applying the discharge voltage, the maximum value and the minimum value in one cycle of the applied voltage are changed continuously. In applying the pulse voltage, a direct current may be superimposed.

FIG. 3 shows a block diagram of a power supply when such a pulsed electric field is applied. FIG. 4 shows an equivalent circuit diagram of the power supply. In FIG. 4, SW is a semiconductor element functioning as a switch. By using a semiconductor element having a turn-on time and a turn-off time of 500 ns or less as the switch, the electric field strength as described above is 1 to 100 kV / cm, and the rise time and fall time of the pulse are 100 μs or less. Such a high voltage and high speed pulsed electric field can be realized.

Hereinafter, the principle of the power supply will be briefly described with reference to the equivalent circuit diagram of FIG. + E is a positive DC voltage supply unit, and -E is a negative DC voltage supply unit. SW1
Reference numerals 4 to 4 denote switch elements composed of the high-speed semiconductor elements as described above. D1 to D4 indicate diodes. I _{1 to} I ₄ indicate the direction of current flow.

[0025] First, when turned ON SW1, load of the positive polarity is charged in the flow direction current I _1. Then, the SW1 is turned OFF, by turning ON the SW2 instantaneously, the electric charge charged is charged in the direction of I ₃ through SW2 and D4. Next, when the switch SW3 is turned on after the switch SW2 is turned off, the load having the negative polarity causes the current I ₂
Charge in the direction of flow. Next, the SW3 is turned OFF, by turning ON the SW4 instantaneously, the electric charge charged is charged in the direction of I ₄ through SW4 and D2.

At this time, by providing variable resistors R ₁ and R ₂ in parallel with the power supplies + E and −E, the peak voltage can be changed continuously. By repeating the above series of operations, the output pulses shown in FIGS. 1A, 1B, and 1C can be obtained. The advantage of this circuit is that even if the load impedance is high, the charged electric charge can be reliably discharged by operating SW2 and D4 or SW4 and D2, and the switch of high-speed turn-on. High-speed charging can be performed by using the elements SW1 and SW3, so that a pulse signal having a very fast rise time and fall time as shown in FIG. 1 can be obtained.

In the discharge obtained by the above method,
The discharge current density between the counter electrodes is 0.2 to 300 mA / c.
m ² is preferred.

The discharge current density is a value obtained by dividing a value of a current flowing between electrodes by discharge by an area of a discharge space in a direction orthogonal to a direction of current flow, and a parallel plate type electrode is used. In this case, it corresponds to a value obtained by dividing the current value by the facing area. In the present invention, a pulse-like current flows to form a pulse electric field between the electrodes. In this case, the maximum value of the pulse current, that is, Vp ^{+ in} FIG.
～Vp ^- value of refers to a value obtained by dividing the above area.

In a glow discharge under a pressure near the atmospheric pressure,
As shown below, it has been revealed by the present inventors that the discharge current density reflects the plasma density and is a value that affects the surface treatment effect, and the discharge current density between the electrodes has been described above. When the content is in the range of 0.2 to 300 mA / cm ² , uniform surface discharge plasma can be generated and good surface treatment can be performed.

The substrate used in the present invention includes
Examples thereof include plastics such as polyethylene, polypropylene, polystyrene, polycarbonate, polyethylene terephthalate, polytetrafluoroethylene, and acrylic resin, glass, ceramic, and metal. Examples of the shape of the substrate include a plate shape and a film shape, but are not particularly limited thereto. ADVANTAGE OF THE INVENTION According to this invention, it can respond | correspond easily to the process of the base material which has various shapes.

In the present invention, when performing the discharge plasma processing, a processing gas is supplied to the substrate during the processing time.

The above-mentioned processing gas is not particularly limited as long as it excites and decomposes in the discharge plasma generation space to form a thin film on the base material.

As the processing gas, a metal-containing gas can be suitably used. As the metal, for example, Al, As,
Bi, B, Ca, Cd, Cr, Co, Cu, Ga, G
e, Au, In, Ir, Hf, Fe, Pb, Li, N
a, Mg, Mn, Hg, Mo, Ni, P, Pt, Po,
Rh, Sb, Se, Si, Sn, Ta, Te, Ti,
Metals such as V, W, Y, Zn, Zr and the like can be mentioned, and as a processing gas containing the metal, a metal organic compound, a metal-
Processing gases such as a halogen compound, a metal-hydrogen compound, a metal-halogen compound, and a metal alkoxide are exemplified.
These may be used alone or in combination of two or more.

When the metal is Si, for example, tetramethylsilane [Si (CH ₃ ) ₄ ], dimethylsilane [S
i (CH ₃ ) ₂ H ₂ ], tetraethylsilane [Si (C ₂ H ₅ )
₄ ] and the like; metal halide compounds such as silicon tetrafluoride (SiF ₄ ), silicon chloride (SiCl ₄ ) and silicon chloride (SiH ₂ Cl ₂ ); monosilane (SiH ₄ ), disilane (SiH ₃ ) SiH ₃ ), trisilane (SiH ₃ SiH ₂ Si)
H ₃ ) and other metal hydrogen compounds; tetramethoxysilane [Si
(OCH ₃ ) ₄ ], tetraethoxysilane [Si (OC
₂ H ₅ ) ₄ ], triethoxymethylsilane [SiCH ₃ (OC ₂
H ₅ )] and the like. These may be used alone or in combination of two or more.

When the metal is Ti, for example, tetramethyl titanium [Ti (CH ₃ ) ₄ ], dimethyl titanium [T
i (CH ₃ ) ₂ H ₂ ], tetraethyl titanium [Ti (C ₂ H ₅ )
_4] an organometallic compound such as; 4 silicon fluoride (TiF _4), 4 silicon tetrachloride (TiCl _4), metal halide compounds such as 2 silicon tetrachloride (TiH ₂ Cl _2); Mono titanium (TiH _4), Jichitan (TiH ₃ TiH ₃ ), trititanium (TiH ₃ TiH ₂ Ti)
H ₃₎ metal hydride such as; tetramethoxy titanium [Ti
(OCH ₃ ) ₄ ], tetraisopropoxy titanium [Ti (O
CH ₃ CHCH ₃ ) ₄ ]. These may be used alone or in combination of two or more. Among the above-mentioned metal-containing gases, in consideration of safety, it is preferable that there is no danger of ignition or explosion in the atmosphere, such as metal alkoxides and metal halides, at normal temperature and in the air. Thus, metal alkoxides are preferably used.

If the metal-containing gas is a gas, it can be introduced into the discharge space as it is. If it is liquid or solid, it can be introduced into the discharge space via a vaporizer.
By using such a processing gas, SiO ₂ , T
By forming a metal oxide thin film such as iO ₂ or SnO ₂ , electrical and optical functions can be given to the substrate surface.

From the viewpoint of economy and safety, it is preferable to perform the treatment in an atmosphere diluted with a diluent gas, rather than in the atmosphere of the treatment gas alone. Examples of the diluting gas include rare gases such as helium, neon, argon, and xenon, and nitrogen gas. These may be used alone or in combination of two or more. When the processing gas is a liquid and has a high boiling point, it is preferable to use it after heating or vaporizing it with a vaporizer using ultrasonic waves and diluting it with a large amount of diluting gas.

As a diluent gas, a compound having more electrons is more advantageous in increasing the plasma density and performing high-speed processing. However, argon or nitrogen is preferred in that it is easily available and inexpensive. When a diluent gas is used, the concentration of the processing gas is preferably 0.01 to 10% by volume. When a metal alkoxide is used as a processing gas, an oxygen gas may be added in order to form a dense metal oxide thin film having a small amount of organic components.

Further, by using a fluorine-containing compound gas as the above-mentioned processing gas, a fluorine-containing polymer film can be formed on the surface of the substrate to lower the surface energy and obtain a water-repellent surface.

Further, by performing the treatment in an atmosphere of a monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule, a hydrophilic polymer film can be deposited.

When the functionally graded material obtained in the present invention is used for optical applications, a gas for forming a high-refractive-index film such as TiO _{2 or} ZrO ₂ may be used as the above-mentioned processing gas. A processing gas for forming a low-refractive-index film such as SiO _2, Al ₂ O _{3, or a} fluorine-based thin film may be appropriately selected from the above-mentioned processing gases.

(Function) In the method for producing a functionally gradient material according to the present invention, a substrate is placed between a pair of opposed electrodes under a pressure near atmospheric pressure, and a voltage rise time between the opposed electrodes is 100 μm.
Since a discharge plasma treatment is performed by applying a pulse-like voltage having an electric field intensity of 1 to 100 kV / cm or less, discharge before transition to arc discharge is performed by applying a pulsed electric field. It is considered that the cycle of stopping the discharge and restarting the discharge has been realized, and in an atmosphere that does not contain a component that has a long time from the plasma discharge state such as helium to the arc discharge state, the gas existing in the plasma generation space is not included. Regardless of the type, it is possible to stably generate discharge plasma. The reaction gas can be efficiently decomposed by the steep voltage application.

Further, according to the present invention, since the maximum value and the minimum value in one cycle of the applied voltage are continuously changed, for example, the base material is arranged on the installed lower electrode, When a processing gas for forming a film such as TiO _{2 and} SiO ₂ is selectively used as a processing gas, if the polarity of the upper electrode is biased positively, metal oxide ions concentrate on the anode (upper electrode) side. Therefore, the film formation rate on the base material is slowed down, the resulting film has low density, a porous film is easily formed, and when the polarity of the upper electrode is negatively biased, the metal oxide ions are deposited on the lower electrode. Since the film is concentrated on the side, the film forming speed on the base material is increased, and the denseness of the obtained film is increased. Therefore, it is possible to obtain a functionally graded material in which the film quality changes continuously and gradiently in the thickness direction and a film having no clear interface is formed on the substrate.

[0044]

EXAMPLES The present invention will be described in more detail with reference to Examples. In the following examples, a power supply (a semiconductor device: manufactured by Heiden Laboratories, a semiconductor device: manufactured by IXYS, model number TO-247AD) according to the equivalent circuit diagram of FIG. 3 was used.

FIG. 6 is a schematic sectional view showing an example of an apparatus for producing a functionally gradient material according to the present invention.

As shown in FIG. 6, the apparatus for producing a functionally graded material according to the present invention is provided with a pair of counter electrodes 3 and 4 in a container 2. It is electrically connected, the lower electrode 4 is grounded, and a pulse voltage is applied between the upper electrode 3 and the lower electrode 4. The substrate 5 is placed on the lower electrode 4 so that plasma is generated by the pulse voltage.

A processing gas introduction unit 6 is provided on the upper electrode 3 and the surface of the base material 5. The processing gas supply unit 7, the dilution gas supply unit 72, and the gas mixing ratio are controlled by the flow control unit 8. Is set to a predetermined value.

In the apparatus shown in FIG. 6, an upper electrode 3 and a lower electrode 4 (made of SUS304, diameter 80 mm, thickness 10
mm), a sprayed film of zirconium containing 8% by weight of yttrium oxide (relative dielectric constant: 16, film thickness: 500 μm) was used as a solid dielectric in close contact with each other. The distance between the upper electrode 3 and the lower electrode 4 is 3 mm, and the thickness of the 80 μm-thick film on which a film made of a 5 μm polyfunctional acrylic hard coat agent (manufactured by Dainichi Seika Co., Ltd .; Triacetyl cellulose was placed on the lower electrode 4.

Next, the inside of the container 2 was evacuated with an oil rotary pump (not shown) until the pressure reached 1 Torr, and argon gas was introduced until the pressure reached 760 Torr. Next, tetraisopropoxy titanium was supplied from the processing gas supply unit
The mixture is diluted with 3 SLM of argon gas so that the volume ratio becomes 3%, and introduced between the upper electrode 3 and the base material 5 from the processing gas introduction unit 6, and between the upper electrode 3 and the lower electrode 4 as shown in FIG. 2), a pulse voltage having a rising speed of 1 μs and a frequency of 2 kHz was applied from the pulse power supply 1 to generate discharge plasma.

Thereafter, while adjusting the variable resistors R _{1 and} R ₂ shown in FIG. 4, Vp ⁺ -Vp is obtained as shown in FIG. ^A voltage was applied while maintaining ⁻ = 4 kV.

As a result, a functionally graded material having a 3000 ° film formed on a polyfunctional acrylic hard coat film was obtained. As a result of measuring the refractive index of the surface of the obtained functionally graded material with an ellipsometer (manufactured by Mizojiri Optical Co., Ltd.), it was 1.98. Further, the thickness of the formed thin film was measured in the thickness direction by Auger electron spectroscopy while being etched by performing plasma treatment in an argon gas atmosphere at 1000 ° each. The results were 1.95 and 1.92, respectively.

[0052]

The method for producing a functionally graded material of the present invention is constructed as described above, so that a thin film can be formed at a high speed by performing a plasma discharge near the atmospheric pressure without requiring a high degree of vacuum. it can.

[Brief description of the drawings]

FIG. 1 is a graph showing a pulse voltage applied in an example, in which (a) is immediately after application, (b) is after 30 seconds, and (c).
Indicates a state after one minute.

FIG. 2 is an explanatory diagram of a pulse duration time.

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

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

FIG. 5 is a schematic sectional view showing an example of an apparatus for producing a functionally gradient material according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 pulse power supply 2 container 3 upper electrode 4 lower electrode 5 base material 6 processing gas introduction part

Claims (1)

[Claims] 1. A pulse-like voltage having a voltage rising time of 100 μs or less and an electric field intensity of 1 to 100 kV / cm between a pair of opposed electrodes under a pressure near atmospheric pressure. Wherein the maximum value and the minimum value of the applied voltage in one cycle are continuously changed in performing the discharge plasma treatment.