JPH0343282B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a thin film by plasma polymerization, which has a high polymerization rate and can form a dense polymer film. Thin films created by plasma polymerization using hydrocarbons as monomers have a polymer structure with high crosslink density and high mechanical strength, and typically have a specific gravity of 1 to 1.5 and a gas permeability of 10 ^-10 to 1.5. 10 ^-11 ( ^cm3
(STP)・cm・cm ^-2・S ^-1・cmHg ^-1 ). In particular, plasma polymerization using methane as a monomer is known to produce dense thin films, but the polymerization rate is slow, resulting in low productivity and the inability to obtain specific gravity of 2 or more, resulting in poor density. However, the drawback was that the scope of industrial application was narrow. The purpose of the present invention is to provide a method for forming a thin film by plasma polymerization that improves these drawbacks.
(A), (A) + (B) mixed monomer gas, (A) + (C) mixed monomer gas selected from hydrocarbon gas (B), hydrogen gas (C) and halogen gas (D) , (A) + (B) + (C) mixed monomer gas and (B) + (D) mixed monomer gas to perform a plasma polymerization reaction using one or more mixed monomer gases to create a thin film. In this method, the electron temperature at the location where plasma polymerization is performed is set to 30,000 to 90,000, and the ratio of the number of halogen atoms to hydrogen atoms in the mixed monomer gas is 1:
The purpose is to perform plasma polymerization at a ratio of 2 to 5:1, thereby producing a dense thin film with a high polymerization rate. The plasma polymerization apparatus used in the present invention has an electron temperature of 30,000 at the location where plasma polymerization is performed.
〓~90000〓, preferably 35000〓~80000〓. If it is less than 30,000〓, a dense film will not be formed.
If it exceeds 90,000〓, the polymerization rate will be extremely slow, which is not preferable. Measurement of electron temperature is carried out using, for example, a probe heated to a high temperature as disclosed in JP-A-54-135574. The ultimate degree of vacuum of the apparatus is 10 ^-5 Torr or more, and it is desirable that the degree of vacuum during plasma polymerization is in the range of 10 ^-3 to 1 Torr. Furthermore, the plasma discharge format may be any type, such as direct current discharge, low frequency discharge, high frequency discharge, or microwave discharge, and the shape of the electrodes and coils, and the structure of the cavity and antenna may also be arbitrary, and these may be used for polymerization. Does not affect results. The hydrocarbon gas may be of any type as long as it can be gasified in the vacuum described above. Saturated hydrocarbons are preferred, especially methane. Fluorine, chlorine, bromine, and iodine can be used as the halogen gas, and among these, fluorine and chlorine are particularly preferred. Halogenated hydrocarbons are hydrocarbons in which at least one hydrogen atom has been replaced with a halogen atom, and include trifluoromethane, tetrafluoromethane, hexafluoroethane, tetrafluoroethylene, or these hydrogen atoms. These include compounds in which elementary atoms are replaced with chlorine atoms. In the present invention, methane tetrafluoride, 6
Ethane fluoride is preferred, and methane tetrafluoride is particularly preferred. In the present invention, halogenated hydrocarbon gas (A) +
Hydrocarbon gas (B) mixed monomer gas, halogenated hydrocarbon gas (A) + hydrogen gas (C) mixed monomer gas, halogenated hydrocarbon gas (A) + hydrocarbon gas (B) + hydrogen gas (C) mixed Monomer gas and hydrocarbon gas (B)+
1 selected from halogen gas (D) mixed monomer gas
A mixture of more than one monomer gas is used. The amount of the gas flowing into the plasma polymerization apparatus must be such that the ratio of the number of halogen atoms to the number of hydrogen atoms contained in the gas is in the range of 1:2 to 5:1.
When the number of halogen atoms exceeds five times the number of hydrogen atoms,
The film growth rate is reduced and etching occurs at high electron temperatures. Conversely, when the number of halogen atoms is less than 1/2 of the number of hydrogen atoms, a sparse polymer film containing a large amount of halogen atoms is formed. Therefore, in order to make a dense polymer film, the content must be within the above range. For example, in the case of tetrafluoromethane and methane, and tetrafluoroethylene and methane gas, the volume ratio of inflow amounts under standard conditions is 1:2 to 5:1, and in the case of hexafluoroethane and methane, it is 1:3. ~
10:3 is appropriate. That is, it is sufficient that the ratio of the number of halogen atoms to the number of hydrogen atoms in the monomer gas flowing into the plasma polymerization reaction vessel is 1:2 to 5:1. As a result of plasma polymerization performed by the above method, the plasma polymerization rate or polymer film formation rate was more than three times that of when methane was the only monomer, the specific gravity of the polymer film was 2.0 or more, and there were no halogen atoms or hydrogen atoms. As a result, a dense film with an extremely low gas permeability coefficient was formed, and the hardness of the polymer film was 1 Kg/cm ² or more in terms of Vickers hardness. The dense and hard thin film obtained by the method of the present invention has the advantage of the plasma polymerization method that it can be adhered to any substrate with good adhesion, and the chemical property of the plasma polymerization film that it is resistant to acids, alkalis, and organic solvents. Combined with its stability, it has a wide range of applications. The thin film obtained by the method of the present invention is useful as a surface coating film for plastic vacuum vessels that require low gas permeability, and as an inner coating film for vacuum systems that avoid metals. Also, coatings on friction surfaces that require hardness, especially acids, alkalis, etc.
Rubber, plastic, etc. used in an organic solvent atmosphere.
It is useful as a coating film for friction surfaces of metals, etc. For example, it is useful as a surface protective film for magnetic tapes such as metal coating tapes or vapor-deposited tapes, or as a friction surface coating for recording heads. It is also useful for coating the cutting edge of tools, the cutting edge of knives for preparing specimens in electron microscopes, and the coating of plastic lenses. From an industrial perspective, their usefulness is realized by the productivity, ie, high film growth rate, and the possibility of mass production, ie, large-area processing. The former is one of the important elements of the present invention, and it has become possible to achieve productivity (film growth rate) that is, for example, 4 times or more compared to the conventional case where only methane is used as a monomer. (Example 1
and Comparative Example 1) The latter is one of the features of the plasma polymerization method. In other words, since the substrate is coated just by passing through the plasma, compared to directional film formation methods such as vapor deposition methods and beam methods using ions and molecules (ion beam method, molecular beam method), Large-area expansion and mass production are extremely easy. Another important point is that the plasma polymerization method is a dry process and requires no pre-treatment or post-treatment. Examples of the present invention are shown below, but the present invention is not limited to the examples unless the gist of the invention is exceeded. FIG. 1 shows an example of the plasma polymerization apparatus used in this example, in which 1 is a reaction vessel, 2 is an electrode for plasma generation, 3 is a power source for plasma excitation, 4 is a pressure gauge, 5 and 6 are gas cylinders, 7 is a gas flow rate control valve, 8 is a vacuum exhaust port, and 9 is a substrate. Monomer gas is introduced into the reactor 1 from the gas cylinders 5 and 6 at an appropriate flow rate through the gas flow rate control valve 7, plasma is generated through the plasma generation electrode 2, a polymerization reaction is carried out, and the gap between the electrodes is A thin film was formed on the surface of the substrate 9 placed on the substrate. Pressure gauge 4
This is to confirm that the degree of vacuum in the reactor is at a predetermined value. Example 1 Methane (CH ₄ ) gas and tetrafluoromethane (CF ₄ )
The gases were mixed at a molecular mixing ratio of 1:1.5 to obtain a gas monomer, which was used to perform plasma polymerization. Gas flow rate is 100% methane gas
cm ³ /min, Freon gas is 150cm ³ /min, and the degree of vacuum is 50m by adjusting the exhaust volume from exhaust port 8.
I kept it to Torr. A 10KHz alternating current was applied between the two plasma generation electrodes, giving a power of 100W, and the electron temperature was set at 4.5×10 ⁴ near the center between the electrodes. A silicon wafer and a porous film (Millipore type VS) were used as the substrate 9, and a polymer film was formed on the surface thereof. Polymerization was carried out for 30 minutes. Also,
The ratio F/C of the number of fluorine and carbon atoms in the film measured by ESCA (electron spectroscopy using X-ray irradiation) is
It was 0.02. Comparative Example 1 Polymerization was carried out under the same conditions as in Example 1 except that only methane gas was used as the monomer gas and the flow rate was 250 cm ³ /min. Example 2 Using the apparatus shown in Figure 1, the flow rate of tetrafluoromethane was
100c.c. (STP)/min, hydrogen gas flow rate 100c.c.
(STP)/min, and the degree of vacuum was 30 mTorr.
A 10KHz alternating current was applied to the two electrodes for plasma generation, and 70W of power was supplied, making the electron temperature 3.5×10 ⁴ 〓. By polymerizing for 30 minutes, the thickness was 1800Å.
A specific gravity of 2.2 and an atomic ratio F/C in the film of 0.2 were obtained. Oxygen gas permeability is 1.2×10 ^-15 (cm ³ (STP)・cm・cm
^-2・S ^-1・cmHg ^-1 ). Example 3 Using the same apparatus shown in Figure 1, the flow rate of ethane gas was 70 c.c. (STP)/min, and the flow rate of fluorine gas was 280 c.c. (STP)/min.
cc (STP)/min, and the degree of vacuum was maintained at 100 mTorr. A 10KHz AC 80W was applied to the plasma excitation electrode, and the electron temperature was set to 4.2×10 ⁴ 〓. By carrying out polymerization for 30 minutes, a thickness of 2200 Å, a specific gravity of the film of 2.1, and an atomic ratio of F/C in the film of 0.2 were obtained. Oxygen gas permeability is 2.2×10 ^-15 (cm ³ (STP) cm cm ^-2 S ^-1 cm
Hg ^-1 ). Comparative Example 2 In Example 1, except that a mixed gas of methane gas with a flow rate of 300 cm ³ /min and tetrafluoride methane gas with a flow rate of 100 cm ³ /min was used as the monomer gas.
Other than that, polymerization was carried out under the same conditions. in this case,
The atomic ratio F/C in the film measured by ESCA is approximately
It was 0.7. The thickness, specific gravity, and oxygen gas permeability of each of the polymer films of Example 1, Example 2, Practical Example 3, Comparative Example 1, and Comparative Example 2 thus obtained were measured. The results are shown in Table-1.

【table】

[Table] The thickness was measured optically, and the specific gravity was obtained by calculating the weight film thickness from the increase in the weight of the substrate, and dividing the weight film thickness by the optical film thickness. Example 4 The plasma polymerization of Example 1, Comparative Example 1, and Comparative Example 2 was continued until the film thickness reached approximately 1 μm, and then the Vickers hardness of the polymerized film was measured. The results are shown in Table-2.

[Table] Example 5 Methane (CH ₄ ) gas and tetrafluoromethane (CF ₄ )
Gas and hydrogen (H ₂ ) gas at a molecular number mixing ratio of 0.5:
Mix it in a ratio of 1.5:1 to make a gas monomer,
Plasma polymerization was performed using this. The gas flow rate is 50cm ³ /min for methane gas and 50cm 3 /min for freon gas.
150cm ³ /min, hydrogen gas 100cm ³ /min, and the degree of vacuum was 50mTorr by adjusting the exhaust volume from exhaust port 8.
I kept it. A 10 KHz alternating current was applied between the two plasma generation electrodes, giving a power of 150 W, and the electron temperature was set to 7×10 ⁴ 〓 near the center between the electrodes. A silicon wafer and a porous film (Millipore type VS) were used as the substrate 9, and a polymer film was formed on the surface thereof. Polymerization was carried out for 30 minutes. Also,
The ratio F/C of the number of fluorine and carbon atoms in the film measured by ESCA (electron spectroscopy using X-ray irradiation) is
It was 0.08. Comparative Example 3 In Example 1, as plasma excitation power
Add 40W to increase the electron temperature near the center between the electrodes to 2.1
×10 ⁴ 〓, and other conditions were kept the same. ESCA the ratio F/C of the number of fluorine and carbon atoms in the polymer film
When measured, it was 0.9. Comparative Example 4 In Example 1, as plasma excitation power
Apply 300W and increase the electron temperature near the center between the electrodes to 95
×10 ⁴ 〓. Other conditions are the same. In this case, almost no polymer film was deposited, and the optical thickness was less than 50 Å. Comparative Example 5 In Example 2, as plasma excitation power
Add 30W to increase the electron temperature near the center between the electrodes to 1.9
×10 ⁴ 〓. Other conditions are the same. The thickness of the film deposited on the substrate was 200 Å, and the atomic ratio F/C in the film was 1.8. Because the membrane was thin, specific gravity values could not be obtained. Comparative Example 6 In Example 2, the plasma excitation power was
300W, and the electron temperature near the center between the electrodes is 9.7×
10 ⁴ 〓. Other conditions were the same. In this case, a silicon wafer substrate was etched. The thickness, specific gravity, and oxygen gas permeability of each of the polymer films of Example 5 and Comparative Examples 3 to 6 were measured and shown in Table 1. Comparative Example 7 The following experiment was conducted using the apparatus shown in FIG. 2, which is similar to the plasma polymerization apparatus described in JP-A-56-60447. Here, a quartz tube with a diameter of 3 cm was used as the reaction tube, and argon or hydrogen was flowed from the upstream portion, and methane and tetrafluoromethane were flowed from the downstream portion. The microwave used was 2.25GHz. A porous substrate (Millipore VS) was used, and it was installed at each point A, B, and C in Figure 2. Point A is 5 cm from the end surface of the microwave cavity, and point B is 10 cm from the end surface of the microwave cavity.
cm, point C is 15 cm. A film was prepared under the plasma conditions shown in Table 3, and the atomic ratio F/C and oxygen gas permeability in the film were measured. Table 4 shows the results. Further, the electron temperature during the reaction was measured at each point A, B, and C.

[Table] 〓−〓 means that the ion density is too low to measure the electron temperature.

【table】 [Brief explanation of drawings]

FIG. 1 is a conceptual elevational view of a plasma polymerization apparatus used in Examples of the present invention. Figure 2 shows comparative example 7.
1 is a conceptual elevational cross-sectional view of a plasma polymerization apparatus used in FIG. 1... Reaction container, 2... Plasma generation electrode, 3...
Plasma excitation power source, 4...pressure gauge, 5, 6...gas cylinder, 7...gas flow rate adjustment valve, 8...vacuum exhaust port, 9...substrate, 10...microwave cavity,
DESCRIPTION OF SYMBOLS 11... Quartz reaction tube, 12... Waveguide, 13... Microwave power supply, 14... Plasma region, 15... Pressure gauge,
16...Adjustment valve, 17...Flow rate adjustment valve, 18
...Argon gas, 19...Hydrogen gas, 20...Methane gas, 21...Tetrafluoromethane gas.

Claims (1)

[Claims] 1 Halogenated hydrocarbon gas (A), hydrocarbon gas
(B), (A) + (B) mixed monomer gas selected from hydrogen gas (C) and halogen gas (D), (A) + (C) mixed monomer gas, (A) + (B) ) Mixed monomer gas, (A)+
A mixed monomer gas selected from (B) + (C) mixed monomer gas and (B) + (D) mixed monomer gas, and in which the ratio of the number of halogen atoms to the number of hydrogen atoms is 1:2 to 5:1. Plasma polymerization is performed by converting into plasma, and the electron temperature at the location where plasma polymerization is being performed is set to 30,000 to 90,000, and the degree of vacuum at the location is set to 10 ^-3 Torr or more and less than 1 Torr. A thin film production method characterized by: