JPH0248563B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for sequentially plasma polymerizing different monomers to form a multilayer thin polymer film. Conventionally, stretching methods, vapor deposition methods, casting methods, and the like are known as methods for forming polymer multilayer thin films each having a thickness of 1000 Å or less. However, in the stretching method, a multi-layered thick film is stretched to form a thin film of about 1000 Å, but because the physical properties of each layer, such as the glass transition point, are different, stress concentration occurs only in a specific film during stretching. In addition, the bonds between the layers are broken, resulting in peeling and the desired thin film cannot be obtained. In addition, although it is possible to create a thin multilayer film using the polymer vapor deposition method, each layer is only physically attached, so it is very brittle and can be peeled off with a small amount of force. Furthermore, in the casting method, a multilayer film is obtained by repeatedly applying a polymer solution onto a solid surface and evaporating the solvent to form a thin polymer film.
If a large amount of solvent is used, if the solvent is selected incorrectly, the thin film that has already been formed will be redissolved and a multilayer structure will not be obtained. Since it is small in number, it has drawbacks such as low strength. The purpose of the present invention is to use plasma polymerization method,
The object of the present invention is to provide a method for forming a multilayer thin polymer film in which each layer is strongly bonded by chemical bonds even when the thickness is less than Å. According to the present invention, a first plasma polymerizable monomer is introduced into a plasma reactor equipped with plasma excitation means, and the plasma is excited to form a first film of a desired thickness on a solid surface provided in the reaction chamber. forming a plasma-polymerized thin film, then stopping the introduction of the first monomer;
Next, a second plasma polymerizable monomer is introduced, and the electron temperature Te and electron density n _e at the surface of the film forming body are such that 4000K≦Te≦80000K, and 10 ⁶ pieces/cm ³ ≦n _e ≦10 ⁹ pieces. A second plasma-polymerized thin film having a desired thickness is formed on the first thin film under conditions of /cm ³ , and the above operations are repeated as necessary to sequentially form a multilayer structure film. A method for forming a multilayer thin polymer film is provided. Although the type of plasma polymerization reactor used in the present invention is not limited, for example, a reactor as shown in FIG. 1 can be used. Monomer and rare gas are introduced into the reactor main body 12 from the monomer inlet 1 and the rare gas inlet 2, and the plasma excitation coil 4
By exciting plasma, a plasma polymerized film is formed on the film forming body 5. The inside of the reactor is preferably kept under reduced pressure of 10 ^-3 to ^{10 2} torr during plasma excitation by adjusting the exhaust volume control valve 6 . In order to avoid the formed thin film from being affected by severe heat during plasma excitation, high electron temperature, and plasma with electron density, for example, in the case of a high frequency induction plasma reactor, the plasma excitation coil 4 (position B in Fig. 1) is used. Keep the film forming body (position A in Figure 1) on which the plasma polymerized film is formed away from the (distance x)
is preferred. The wall of the reactor near the coil is extremely hot, so if a film is formed near position B, the film will be at a high temperature due to heat conduction and will be susceptible to thermal deterioration. It becomes more susceptible to deterioration due to collisions with particles and ions. Therefore, when creating a multilayer film by sequentially introducing different monomers and sequentially forming plasma polymerized films,
When forming the second and subsequent films by plasma polymerization, it is preferable to keep the film forming body separated from the excitation coil by a distance x so as not to deteriorate the already formed film below. This distance is influenced by the electron temperature and electron density of the plasma and cannot be determined unconditionally.If the electron temperature Te and the electron density n _e are at position A on the surface of the film forming body, 4000≦Te≦80000K, 10 ⁶
It is preferable to separate them so that 9 pieces/cm ³ ≦n _e ≦10 ⁹ pieces/cm ³ . When the electron temperature Te exceeds 80,000 K and/or when the electron density n _e exceeds 10 ⁹ /cm ³ , the film is degraded by collisions with electrons and ions as described above, resulting in peeling of the film and pinholes. etc. will occur. Also, the electron temperature Te
If the temperature is less than 4000K and/or the electron density n _e is 10 ⁶
When the number of particles/cm ³ is less, the adhesion to the film forming body becomes weak. Here, the measurement of Te and n _e can be done, for example, in Japanese Patent Application No. 53-33226.
This is done using a probe heated to a high temperature as disclosed in . Furthermore, when forming a multilayer film, if monomers or oligomers used in the formation of the previous film remain on the reactor wall when introducing monomers for the formation of the subsequent film, the formation of the subsequent film may be affected. It is preferable to remove the monomers and oligomers from the previous stage because they are mixed as impurities in the process. Therefore, before introducing the next monomer, the introduction of the previous monomer is stopped, the reactor is evacuated with a pump, then only the rare gas is introduced, and the inside of the reactor is cleaned with rare gas plasma. Perform exhaust. By this operation, most of the monomers and oligomers adsorbed on the vessel wall are removed. The rare gas plasma excitation power at this time is preferably about the same as the excitation power during formation of the plasma polymerized film. then the first
A second monomer is introduced in the same manner as the monomer introduction. Further, monomers are introduced in the same manner as necessary and a multilayer thin polymer film is obtained by plasma polymerization. Monomers used in the present invention include most gasifiable organic compounds, such as styrene, acetylene, ethylene, allylamine, benzene, aniline, pyridine, etc., and silicone-based inorganic compounds, such as silane, organosilane, etc. , there are no particular limitations as long as the compound is plasma polymerizable. Further, the film-forming body is not particularly limited as long as it is a solid that does not undergo decomposition or other changes in quality in plasma.
For example, not only polymer films such as polycarbonate films, cellulose acetate films, polypropylene films, and polyethylene films, but also inorganic materials such as glass and metals can be used as the film forming body. During plasma polymerization, it is desirable to introduce a rare gas at the same time as monomer introduction in order to prevent pressure fluctuations in the reactor and stabilize the reaction system. When the plasma polymerized film formed on the surface of the film forming body reaches a desired thickness, the introduction of the monomer and rare gas is stopped. The film thickness can be calculated, for example, from the plasma reaction time and the weight change before and after the reaction of the film forming material, taking into account the surface area and density, or when using a smooth surface as the film forming material, it can be determined by optical interferometry. can. It can also be measured by the method described in the method for measuring the production rate and manufacturing method of plasma polymerized film, which was previously filed by some of the inventors of the present invention (Japanese Patent Application No. 1988-88031). In this method, in a plasma polymerization reaction using a probe for measuring plasma characteristics that has a heating means, the surface temperature Tc of the probe is set at the time when a film produced by the plasma polymerization reaction starts to adhere to the surface of the probe. , the relationship between this surface temperature Tc and the plasma polymerized film production rate kr calculated from the measured value of the weight of the plasma polymerized film produced for a certain period of time at that temperature is created in advance as a kr-Tc diagram, and the plasma polymerization This is a method for measuring the plasma polymerization film formation rate, which is characterized in that kr is calculated by measuring Tc during the test. In this method, when the plasma polymerized film starts to adhere,
Tc is detected from the fact that the current-voltage characteristic curve in the electric circuit of the probe changes from its normal shape and position as the plasma polymerized film begins to adhere to the probe surface, and the temperature of the probe surface at that time is measured. It can be determined by This method: (1) The plasma polymerization film formation rate can be measured much more easily than conventional methods. In other words,
The plasma polymerization film formation rate can be measured simply by electrically operating the reactor from outside without opening or closing the reactor. (2) It is possible to measure the plasma polymerization film formation rate while the reaction is in progress, so even if some trouble occurs during the reaction and the polymerization film formation rate changes, the change can be detected immediately. Therefore, there is no need to waste subsequent reactions. The troubles referred to here are troubles that cannot be detected by vacuum gauges, wattmeters, etc., such as the incorporation of trace amounts of impurities, fluctuations in partial pressure due to some cause, and disturbances in plasma. (3) Since it utilizes the electrical insulation properties of polymer films, it can be applied to measure the plasma polymer film formation rate of almost all monomers that can be plasma polymerized. It has the following characteristics and is preferable as a method for measuring film thickness in the present invention. The probe having a heating means used in this method can be heated to 1000㎓ or more by heating with an internal heater or infrared heating, for example, as disclosed in the above-mentioned Japanese Patent Application No. 53-33226. A probe whose heating temperature can be freely adjusted is preferable. Hereinafter, the present invention will be explained by taking as an example the case where a high frequency induction type plasma reactor is used (FIG. 1), but it goes without saying that the present invention is not limited thereto. The plasma excitation coil may be a normal high-frequency plasma coil, and may be of an inductive type or a capacitive type. The monomer supply section is as shown in FIG. 2, and the monomers from monomer containers 101 to 104 are turned into gases and introduced into the reactor through valves 109 to 112 and a flow meter 114. In addition, the valve 113
is a line exhaust valve. The monomer container is
The temperature control devices 105 to 108 freely control the temperature up to about 400° C. above the liquid nitrogen temperature. The rare gas supply section includes a rare gas cylinder 11, an inlet 2, and a rare gas flow meter 9. A porous glass filter, for example, is held on a support and fixed at position A as a film forming body for forming a multilayer thin polymer film. Repeat evacuation and introduction of rare gas into the reactor, and after sufficiently evacuation, energize the plasma excitation coil to turn the rare gas into plasma, cleaning the inside of the reactor with rare gas plasma, then stop introducing rare gas and fully evacuate the reactor. do. The first monomer is supplied at a constant flow rate from the inlet port 1,
At the same time, a rare gas is introduced from the inlet 2 at a constant flow rate. Plasma is excited to form a first layer of plasma polymerized film. In this case, optimal values for the plasma conditions, such as the pressure inside the reactor and the plasma excitation power, are determined in advance for the monomer. When a plasma-polymerized film of a predetermined thickness is formed, the excitation coil is turned off, the introduction of monomer and rare gas is stopped, and it is sufficiently evacuated, and cleaning with rare gas is performed as described above, followed by evacuation again. Next, a second monomer and rare gas are introduced to form a second layer of plasma polymerized film. Thereafter, by repeating these operations, a multilayer thin film is obtained. Note that the electron temperature Te and electron density n _e at the position A, as well as the film thickness of each layer can be measured by using the probe 13 having a heating means. The multilayer thin film obtained by the present invention is a structurally stable film that is difficult to peel off because each layer is strongly bonded to each other by chemical bonds. Furthermore, since all layers are formed in a closed system, it is superior in terms of pollution and safety, and is extremely easy to operate. Further, the thickness of each layer can be easily controlled by changing the plasma polymerization time and plasma conditions. The properties of the film obtained by plasma polymerization vary depending on the monomer and reaction conditions, so by stacking these multiple layers, extremely high-performance films can be obtained. It can be used as a protective film for semiconductors. The present invention will be further explained by examples. Example 1 Using the plasma reactor shown in FIGS. 1 and 2,
Example of creating a two-layer thin film in which argon is used as the rare gas, and the first layer is a benzene plasma polymerized film using benzene as a monomer, and the second layer is an allylamine plasma polymerized film using allylamine as a monomer. state. A polycarbonate film was used as the film forming body, and the distance between position A of the film forming body and position B of one end of the coil was 20 cm. The plasma conditions when creating the first layer were benzene inflow rate of 500STPc.c./min and argon inflow rate of 150STPc.c./min.
min, pressure 0.5 torr, and plasma excitation power 40 W. The plasma conditions when creating the second layer were allylamine inflow rate 400 STPc.c./min, argon inflow rate 100 STP.
cc/min, pressure 0.5 torr, and plasma excitation power 30W. Also, Te at position A of the film forming body
(K) and n _e were as follows. For benzene plasma: Te = 40,000 K n _e = 5 x 10 ⁷ pieces/cm ³ For allylamine plasma, Te = 53,000 K n _e = 2 x 10 ⁸ pieces/cm ³ Under these conditions, benzene plasma polymerization is performed for 2 minutes. As a result, a benzene plasma polymerized film with a thickness of about 300 Å was obtained. Next, after evacuating and cleaning the inside of the reactor as described above, allylamine plasma polymerization was performed for 2.5 minutes to obtain a film with a thickness of about 200 Å. We were able to create a thick allylamine plasma polymerized film. The thickness of each film is the diameter/mmφ that can be heated by the inserted sheath heater, and the length is 10 mm.
Using two Ni probes (double probe method),
Calculated from the probe surface temperature Tc at which a film produced by plasma polymerization reaction begins to adhere to the surface of the probe prepared in advance and the weight of the plasma polymerized film produced in a certain period of time at this surface temperature Tc. It was determined by using a relationship diagram with the plasma polymerized film formation rate kr. When the surface of the two-layer thin film obtained in this example was observed with a scanning electron microscope, no pinholes, peeling, etc. were observed, and the film was uniform. The two-layer thin film obtained in this example is useful as a membrane for separating a mixed solvent of methanol and toluene. Example 2 A three-layer thin film consisting of a pyridine plasma-polymerized film, an acetylene plasma-polymerized film, and an aniline plasma-polymerized film was prepared on a silicon crystal film-forming body with a flat surface. The plasma reactor used was the same as in Example 1, and the distance x was 30 cm. The plasma polymerization conditions were plasma excitation power of 40W and pressure of 0.5torr for all three layers, argon gas was used as the rare gas, and 200STP was used during plasma polymerization for all three layers.
cc/min flowed. Monomer gas inflow rate is 300STPc.c./min for pyridine and 500STPc.c./min for acetylene.
min, aniline was 300 STPc.c./min.
Te and n _e at position A in each case were as follows.

[Table] Each film was created by plasma polymerization for 5 minutes, and the inside of the reactor was evacuated and cleaned when switching the type of monomer. When the thickness of each film was measured using various methods, they were: pyridine plasma polymerized film: 300 Å, acetylene: 500 Å, aniline: 120 Å. After carrying out a peeling test using Scotch tape on the three-layer thin film obtained in this example, the state of peeling of the film was observed using a scanning electron microscope, and no peeling was observed. The three-layer thin film obtained in this example is useful as a protective film for semiconductors. Comparative Example 1 A two-layer thin film of a benzene plasma polymerized film and an allylamine plasma polymerized film was prepared in the same manner as in Example 1, except that the distance between position A of the film forming body and position B of one end of the coil was 5 cm. In this case, Te and n _e at position A of the film forming body were as follows: For benzene plasma, Te = 85,000 K, n _e = 2 x 10 ⁹ pieces/cm ³ For allylamine plasma, Te = 91,000 K , n _e =4×10 ⁹ pieces/cm ³ . Under these conditions, benzene plasma polymerization is carried out by 2
By carrying out the polymerization for 2.5 minutes, a benzene plasma polymerized film with a thickness of about 200 Å is obtained. Next, after evacuating and cleaning the inside of the reactor as described above, allylamine plasma polymerization is carried out for 2.5 minutes to obtain a benzene plasma polymerized film with a thickness of about 120 Å. An allylamine plasma polymerized film with a thickness of
Wrinkles occurred due to peeling and heat shrinkage. Comparative Example 2 A three-layer thin film consisting of a pyridine plasma polymerized film, an acetylene plasma polymerized film, and an aniline plasma polymerized film was prepared in the same manner as in Example 2, except that the distance x was 45 cm and each film was plasma polymerized for 8 minutes. Created. Te and n _e at position A in each case were as follows:

[Table] When the thickness of each film was measured by various methods, it was 250 Å for pyridine plasma polymerized film, 500 Å for acetylene plasma polymerized film, and 150 Å for aniline plasma polymerized film. After carrying out a peeling test using Scotch tape on the three-layer thin film obtained in this comparative example, the state of peeling of the film was observed using a scanning electron microscope, and peeling was observed.

[Brief explanation of drawings]

FIG. 1 shows an example of a plasma reactor for implementing the present invention, and FIG. 2 shows an example of a monomer supply section in the reactor. 1... Monomer inlet, 2... Rare gas inlet,
3... High frequency power supply, 4... Coil for plasma excitation, 5... Film forming body, 6... Exhaust volume adjustment valve, 7... Exhaust port, 8... Monomer flow meter 9...
...Rare gas flow meter, 10...Monomer cylinder, 11
...Rare gas cylinder, 12...Reactor main body, 13...
... Probe, 101-104 ... Monomer cylinder, 10
5-108...Temperature control device, 109-
113...Valve, 114...Flowmeter, 115...
...Line to the reactor.

Claims (1)

[Claims] 1. A first plasma polymerizable monomer is introduced into a plasma reactor equipped with plasma excitation means, and the plasma is excited to form a first film of a desired thickness on a solid surface provided in the reaction chamber. After forming a plasma _- polymerized thin film of A second plasma-polymerized thin film of a desired thickness is formed on the first thin film under the conditions of ≦80000K and 10 ⁶ pieces/cm ³ ≦n _e ≦10 ⁹ pieces/cm ³ , and as necessary. A method for forming a multilayer thin polymer film, the method comprising: repeating the above operations to sequentially form a multilayer structure film.