JPS6335708B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a thin film of a novel conductive material, and in particular, the present invention relates to a method for manufacturing a thin film of a novel conductive material, and in particular, the present invention relates to a method of manufacturing a thin film of a novel conductive material, and in particular, the present invention relates to a method of manufacturing a thin film of a novel conductive material by depositing a condensed heat-resistant polymer imparted with conductivity by thermal decomposition onto a substrate by a physical vapor deposition method such as sputtering in a vacuum. The present invention relates to a method for forming a thin film on. Recently, many attempts have been made to impart electrical conductivity to organic polymers, which are originally electrically insulating, and to create unique properties that cannot be achieved with inorganic metals, semiconductors, and oxides. One important method in this effort is the formation of pyrolytic polymers. This is an attempt to obtain a polycondensed compound by thermal decomposition starting from a specific material. The product is mainly carbonaceous, but its electrical conductivity is controlled by the starting materials. Pyrolytic polymers have a long history and are a material that attracted attention in the early 1960s. For example, the thermal decomposition of polyacrylonitrile by the Russian school is famous;
An electrical conductivity of 2Scm ^-1 has been obtained. (AV
Airapetjanc et al. Dokl.Akad.Nauk SSSR magazine,
148, p. 605, 1963). Also in 1964, IBM
Mr. SDBruck of the company thermally decomposed polyimide (DuPont's Kapton H film) at 800℃, and 20Scm ^-1
It was discovered that an electrical conductor having a conductivity of . The conductivity of polyimide film is 10 ^-18 S at room temperature.
cm ^-1 , and the conductivity changes as much as 10 to ²⁰ due to thermal decomposition, so this method is considered to be an excellent method for imparting conductivity to organic polymer materials. Good fit. In this way, the types of materials that can be made highly conductive through thermal decomposition are limited, but as a result of research by the same applicant, some condensation polymers can similarly become highly conductive through thermal decomposition. It was discovered that. The polymer belongs to the class of heat-resistant polymers developed from recent advances in polymer chemistry, such as aromatic polyamide, polyamideimide, polyesteramide, polybenzimidazole, polyoxadiazole, polythiadiazole, and polybenzthiazole. It is. These materials can be heated in vacuum or in an inert gas stream to
When pyrolyzed at a temperature of 1000°C, it gives a conductivity of up to 500 Scm ^-1 . Based on these discoveries, the same applicant has proposed a method for producing new conductive materials and a conductive composition comprising these powders and a polymeric binder. The pyrolytic polymer applied by the same applicant is characterized by high conductivity and thermal and chemical stability, so in addition to being a conductive film for resistors and conductors, it can also be used as a heater and actuator. Applications can be considered in a wide variety of fields, including sensors for pressure, strain, and wind speed, oxidation-resistant and corrosion-resistant electrodes, and absorption films for solar heat collectors. However, in order to realize such various applications, it is necessary to manufacture the above-mentioned pyrolytic polymer film according to the purpose. First of all, all of the heat-resistant polymers listed above are obtained as cast films of 2 to 150 microns, and those with a thickness of 20 microns or more do not form pores or cracks even after thermal decomposition, and are free and flexible. This film is suitable for applications such as conductors and sensors. In addition, pyrolysis products are crushed into powders of several microns or less and dispersed in a polymer or glass binder, which is ideal for use as a conductive film, as described in the invention of the same applicant. . Furthermore, in order to expand the applications of this material, it is necessary to manufacture strong, highly heat-resistant, conductive thin films of several thousand angstroms or less. Therefore, an object of the present invention is to provide a method for producing a thin film of a heat-resistant polymer imparted with electrical conductivity by thermal decomposition. The present invention provides a novel method for producing a conductive thin film based on the fact that a film produced under certain thermal decomposition conditions can be made into a thin film by a physical vapor deposition method such as sputtering. The simplest physical vapor deposition method is vacuum thermal evaporation, but the pyrolytic polymer used in the present invention
This method was found to be unusable, as it was never deposited at a rate greater than 100 angstroms. Next, we considered a method (plasma CVD) in which the polymer is decomposed in RF plasma and precipitated on the substrate, but in this case, only a highly transparent and insulating film of 10 ^-10 Scm ^-1 or less could be deposited. I couldn't get it. After investigating various other physical vapor deposition methods, it was found that it is effective to deposit a thin film on a substrate by bombarding a pyrolytic polymer with high-energy particles. High-energy particles include discharged argon, nitrogen, and the like, and high-frequency sputtering or ion beam sputtering is optimal as a physical vapor deposition method using these. However, these methods do not allow the deposition of all polymers; for example, polymers that do not undergo thermal decomposition do not evaporate at all, or polymers that are pyrolyzed at temperatures below 750°C do not evaporate. Either there was no evaporation or the evaporation rate was extremely low. Examples and application examples will be described below to explain the effects of the present invention. Example 1 Polyoxadiazole (POD film, 50 microns) sold by Furukawa Electric Co., Ltd. was thermally decomposed in vacuum at 900°C for 1 hour to obtain a black film exhibiting an electrical conductivity of 300 Scm ^-1 . . This is the target portion 11 of the ion beam sputtering apparatus shown in FIG.
After exhausting to 1.5×10 ^-6 Torr, argon was introduced from the gas inlet 14 to bring the pressure to 2×10 ^-4 Torr. The heater 13 in the discharge chamber 12 is heated to discharge argon, and approximately
A DC voltage of 1.5 KV was applied, and the target 11 was sputtered with an argon ion beam 17. In this case, the current of the lens 16 was adjusted so that the beam current was between 10 and 20 mA/cm ² . A 6000 angstrom thick film was deposited on the glass and glazed alumina substrate 15 by sputtering for 1 hour. The conductivity of the film is 190Scm ^-1 , the pencil strength is 9H or more, and it is 190Scm -1 even with concentrated sulfuric acid.
It remained uncorroded for more than several months. When we measured the temperature dependence of electrical conductivity, we found that the activation energy of the electrical conductivity of the thin film was less than 0.01 eV, which was almost the same as that of the film after thermal decomposition. POD film before pyrolysis and 750℃ using the same method.
Sputtering of POD films pyrolyzed at temperatures up to 100 mL was performed, but it was not possible to deposit conductive thin films. Example 2 A polyimide film (Kapton H film, 150 microns) sold by DuPont was thermally decomposed at a temperature of 800 to 1000°C in a nitrogen stream to produce a film of 20 to 100 Scm.
^-1 conductive film (thickness 120-90 microns) was obtained.
When this film was physically vapor deposited for 30 minutes in the same manner as in Example 1, a translucent black thin film of 600-900 angstroms was deposited on the glass substrate. The conductivity of the thin film was 20Scm ^-1 and had little dependence on the thermal decomposition temperature. When we measured the electronic spectrum of a 600 angstrom film, it showed an absorption characteristic that had a large peak at wavelengths of 3000 angstroms or less, but gradually decreased toward longer wavelengths, and the extinction coefficient at 10000 angstroms (1 micron) was 2. ×10 ⁵ cm ^-1 than ordinary metals
It showed an extremely high light transmittance. The absorption peak below 3000 angstroms is considered to be evidence that the deposited film retains its organic nature. Example 3 In this example, polybenzimidazole, which is another example of a condensed polymer having a nitrogen-containing heterocycle, will be described. The polybenzimidazole used here is

A polyamic acid of the form [formula] was obtained and used as an intermediate containing it in the molecule. This intermediate is a solution of dimethylacetamide or dimethylformamide, and this solution is cast onto Teflon or silicone rubber and cured at a temperature of about 250°C.
Thermal decomposition was carried out between 1000℃. Conductivity is 900℃
It was 200 Scm -1 in 1 hour, and 350 Scm ^-1 in 1 hour at 1000°C.
This product was processed using the ion beam sputtering device shown in Figure 1 at an acceleration voltage of 2KV and a current density of 30m.
It was sputtered at A/cm ² for 1 hour and deposited onto a 25 micron polyimide substrate. The film thickness was 3000 angstroms, and the electrical conductivity was 100 Scm ^-1 . The adhesion between the conductive thin film and the polyimide substrate was good, making it difficult to scratch even with a 9H pencil, and no peeling due to bending of the substrate was observed. Application Example 1 Here, an application of the conductive thin film obtained by the present invention to a heater will be shown. Polybenzthiazole, which had been pyrolyzed at 850 DEG C. for 5 hours, was precipitated by the method of Example 1 onto a sintered alumina substrate 23 provided with silver-palladium printed electrodes 22 in the configuration shown in FIG. 21 is a conductive film of precipitated polybenzthiazole. The precipitate 21 penetrates into the alumina sintered body 23,
It turned into a near-gray film. The resistance value of the film 21 was controlled by the sputtering time as shown below.

[Table] Next, a lead wire was attached to the electrode 22 by soldering, and its performance as a heater was examined. When a resistance value of about 3.5KΩ was formed depending on the electrode shape and sputtering time, and an alternating current of 100V was applied, the alumina substrate 23 was heated to 450°C and became a heater with no change in characteristics for more than 1000 hours in air. When the voltage was further increased to 130V or higher, the heater operated stably up to a temperature at which the alumina substrate 23 cracked due to local heating. Although this example shows the good stability of the conductive thin film produced according to the present invention, this feature can be utilized to create other heating elements, such as thermal heads for heat-sensitive recording, which currently use silicon-deposited films. It can be used as such. Application Example 2 Next, the formation of a bond between a conductive thin film obtained by the present invention and a silicon single crystal will be described. The first film was made by thermally decomposing polyimide (Kapton H film) at 1000℃ for 1 hour.
A conductive thin film was deposited on a single crystal silicon substrate using the apparatus shown in the figure. Silicon is diffusion doped n/
Using an n ⁺ type wafer, silicon was first sputtered with an ion beam for 10 minutes to clean the surface, and then a pyrolytic polymer was precipitated thereon for 30 minutes at a heating voltage of 1 KV and a beam current of 10 mA/cm ² . The film was a uniform semi-transparent film with a thickness of 500 angstroms. Electrode lead wires were attached to the silicon substrate and the deposited film, and current-voltage characteristics were measured, and the results shown in FIG. 3 were obtained. The voltage is plotted so that the deposited film is positive, and from the results in this figure it can be seen that the deposited film is of P type. The forward current-voltage characteristics are matched to the formula J∝exp [-q/kT (V-V _b )], and the built-in potential V _b is the highest.
It was found that it reached 0.9V. This value is higher than that of the junction of gold, platinum, and n-silicon, and higher than that of polyacetylene-n-silicon (0.72 V), which has recently attracted attention for forming a high barrier. This indicates that the conductive thin film obtained by the present invention has high electronegativity and therefore a high work function, and forms a large barrier to n-type semiconductors. It goes without saying that the junction element with a semiconductor produced in this way can be used as a highly thermally stable rectifying element, solar cell, optical sensor, etc. As described above, the present invention provides an electrically conductive thin film in which either a bonded polymer having a nitrogen-containing heterocycle or an aromatic polyamide, which has been imparted with electrical conductivity by thermal decomposition, is deposited on a substrate by physical vapor deposition in a vacuum. As a physical vapor deposition method, sputtering with high-energy particles such as ion beam sputtering is optimal, but even ordinary high-frequency sputtering using argon may introduce impurities. A thin film can be precipitated in the same way, except that Further, the polymer raw materials used here are not limited to those listed in the examples, but include condensed polymers having a nitrogen-containing heterocycle that can be imparted with high conductivity by thermal decomposition, such as polyamideimide, Polyesterimide, polythiadiazole or aromatic polyamide can be used as well.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an ion beam sputtering apparatus used to carry out the method of the present invention, FIG. FIG. 3 is a diagram showing the current-voltage characteristics of the junction element with n-type silicon. 11...Target, 12...Discharge chamber, 13...
...Heater, 14...Gas inlet, 15...Substrate,
16...Lens, 17...Ion beam, 21...
... Conductive thin film, 22 ... Silver palladium electrode, 23
...Alumina substrate.

Claims (1)

[Claims] 1. 800 to 1000°C in vacuum or inert gas
Production of a conductive thin film, which is characterized by physical vapor deposition on another substrate in vacuum, targeting either a condensed polymer having a nitrogen-containing heterocycle or an aromatic polyamide that has been heat-treated in a temperature range of Method. 2 The condensed polymer having a nitrogen-containing heterocycle is polyimide, polyamideimide, polyesterimide, polybenzimide, polyoxadiazole,
The method for producing a conductive thin film according to claim 1, which is either polybenzthiazole or polythiadiazole. 3. The conductive thin film according to claim 1, wherein the aromatic polyamide is obtained by a condensation reaction of m-phenylenediamine and isophthalic acid, or p-phenylenediamine and terephthalic acid. manufacturing method. 3. The method for producing a conductive thin film according to claim 1, wherein the physical vapor deposition method is an ion beam sputtering method.