JP2003054934A - Porous silicon oxide thin film and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a silicon oxide thin film which has a controlled porous structure. SOLUTION: A copolymer thin film is deposited by plasma polymerization of a gaseous mixture of a silicon-based monomer and a hydrocarbon-based monomer in a fixed ratio. After that, the copolymer thin film is further treated by an electric discharge with oxygen or an oxygen-containing gas as a plasma source, and the polymer component originated from the hydrocarbon-based monomer is removed by etching, and simultaneously, the silicon-based polymer part is oxidized and converted into silicon oxide to obtain the porous silicon oxide thin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for treating a silicon-containing polymer thin film obtained by plasma copolymerization with an oxidizing plasma to remove a hydrocarbon-based polymer portion as a copolymerization component and at the same time to oxidize the same. The present invention relates to a silicon oxide thin film having a porous structure at the molecular level by a method of converting into silicon, a manufacturing method for preparing the same, and a processed product thereof. The porous silicon oxide thin film having such a structure has a characteristic that the surface exhibits a characteristic morphology, a large surface area, and the like, and a light-scattering material, an immobilizing material for bio-related molecules such as an enzyme, It can be used as a molecular adsorbent or a separation membrane material.

[0002]

2. Description of the Related Art As a method for obtaining a silicon oxide-based substance, it is known to oxidize a silicon-based polymer by heating it at 800 to 1000 ° C. However,
Since this involves high temperature processing, there are restrictions on processing and processing. Further, it is not suitable for obtaining a porous thin film effectively, and it is virtually impossible to construct a porous structure at the molecular level.

On the other hand, as a method of providing a thin film layer made of silicon oxide, a method of subjecting a plasma-polymerized thin film made of a silicon-based monomer to an oxidative conversion treatment with an oxidizing plasma is known. Further, a method is known in which oxygen is simultaneously introduced into a monomer gas at the time of plasma polymerization of a silicon-based monomer to cause a reaction, and a silicon oxide layer is obtained by simultaneous oxidation.

The above two methods consisting of a plasma process do not form silicon oxide by thermal oxidation.
That is, these are all non-heating processes and are characterized in that they can be applied to a substrate such as a polymer to provide a silicon oxide thin film layer.

Each of the films obtained by the above methods is a thin film layer deposited by polymerization using a plasma-activated molecular species obtained from the gas phase as an intermediate, and is obtained by oxidative etching from the surface of this layer. A thin film having a uniform structure can be obtained.

[0006]

However, they do not have a porous structure with a controlled pore size. Therefore, there is a structural problem in order to exert the function related to the morphology of the surface of the silicon oxide thin film. That is, it has been difficult to immobilize an enzyme that can effectively work for the first time with a porous thin film having a certain pore size, to impart a light-shielding property due to diffused reflection of light, and to exert functions such as membrane permeation.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventor has previously introduced a certain proportion of a component which is easily decomposed and desorbed when a silicon-based polymer thin film layer is formed by plasma polymerization. Then, these can be desorbed by etching to form a pore structure in the film at the molecular level,
It has been found that the above problems can be solved by going through this process.

That is, a micro-sized portion which can be removed preferentially by oxidation etching is introduced into the silicon-based plasma polymer thin film, and this portion is desorbed by the oxidation etching treatment and at the same time the silicon-based polymer portion is oxidized. After this, a porous silicon oxide layer is formed.

The present invention provides a porous silicon oxide thin film thus obtained and a method for producing the same. The outline of the present invention will be described below.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the plasma polymerization in the method of the present invention, the radical species activated by plasma serve as a growth point to initiate the reaction. That is, the electrons generated under the discharge collide with a gaseous organic compound, which dissociates the chemical bond forming the compound to generate a radical, and the generated gas-phase radical is recombined. A polymer having a crosslinked structure is formed.

In plasma polymerization, a polymerized thin film can be formed directly from various organic monomer gases, and by applying a film, sheet, granular material, etc., the surface of these molded products can be coated. Moreover, the function of the film can be controlled by selecting the monomer species.
It is possible to form a uniform thin film that is extremely close to the surface of the substrate.

Silicon-based monomers such as siloxane, silane, and silazane used in the present invention are compounds that are easily plasma-polymerized, and efficiently give a polymerized thin film through a silicon-silicon crosslinking reaction. Silicon oxide can be formed by subjecting these silicon-based polymer thin films to oxidation treatment with an oxidizing plasma.

On the other hand, the hydrocarbon-based monomer is similarly polymerized under the irradiation of plasma to form a polymerized thin film composed of the constituent elements, which gives a dense structure by crosslinking. These are oxidatively etched by being treated with oxidative plasma, or are ash decomposed to be removed by desorption.

By plasma polymerization of a mixed gas composed of a silicon-based monomer and a hydrocarbon-based monomer, a copolymer thin film containing both polymer components can be formed according to the mixing ratio. Using this copolymer thin film, the introduced hydrocarbon polymer part is removed by oxidative etching or ash decomposition to form voids, and at the same time, the silicon component is oxidized to form a silicon oxide thin film having a desired porous structure. To form.

In the method of the present invention, the silicon-based monomer used as the raw material for plasma polymerization is not particularly limited as long as it can be vaporized at a temperature of up to about 50 ° C. under high vacuum and becomes a gas. For example, siloxane compounds such as hexamethyldisiloxane, tetramethyldisiloxamethylcyclosiloxane, tetramethyldisiloxane, silane compounds such as hexamethyldisilane, and silazane compounds such as hexamethyldisilazane are used.

The hydrocarbon-based monomer is not particularly limited, and is a commonly used straight-chain hydrocarbon such as methane, ethane and propane, an aromatic compound such as toluene and a hetero compound such as pyridine and pyrrole. Compound, acetic acid,
Carboxylic acid compounds such as acrylic acid and methacrylic acid, and ketone compounds such as acetone can be used. A portion formed by a carbonyl group or a carboxylic acid group in the copolymer thin film can be effectively removed by oxidative etching by oxidizing plasma treatment.

The silicon-based monomer is a substance which is easily polymerized under plasma, and even in the copolymerization reaction, any ratio of both monomers can be used as long as favorable conditions can be obtained for the partial pressure of the monomer in the system and the discharge by the discharge output. Polymerization is possible. In order to provide a suitable porous silicon oxide thin film in the method of the present invention, the ratio of the hydrocarbon-based monomer in the mixed gas of the silicon-based monomer and the hydrocarbon-based monomer to be copolymerized is 0.1 to 0. 8, more preferably 0.2 to
The range of 0.6 is desirable.

The formation of the copolymer thin film and the treatment of the thin film with oxygen plasma in the method of the present invention can be carried out using a known plasma polymerization apparatus. The generation of plasma discharge is generally due to a radio wave of 13.56 MHz.
However, it is not limited to this frequency. It suffices that the monomer be activated and polymerized under discharge, and for example, an audio wave on the order of kHz or a microwave having a larger wave number can be used.

The shape, size, and treatment mode of the reactor for plasma polymerization and treatment with an oxidizing plasma are not particularly limited. As long as polymer film formation and oxidative plasma treatment are possible, a tubular reactor or a bell jar type reactor can be used without any problem.

The state of thin film formation by plasma polymerization depends on the conditions of plasma discharge as well as the conditions of supplying the monomer gas.

The film formation rate is influenced by the monomer supply rate in the reaction system, that is, the gas pressure in addition to the discharge output. In order to carry out the plasma polymerization more effectively, the mixed gas containing the raw material compounds is introduced so that the total pressure is in the range of 1 to 10 Pascal, and electric power of sufficient strength is added to activate the gas into plasma. All that is necessary is to prepare the conditions that can be achieved.

The appropriate discharge output depends not only on the conditions such as the pressure of the supplied monomer gas, but also on the shape of the polymerization apparatus and the installation state of the substrate. Generally, plasma polymerization is possible in the range of 10 to 200W. The polymerized film prepared under a low output gives a product film having a low degree of crosslinking and a high degree of organicity, and conversely gives a film having a high degree of crosslinking when the output is high. When the degree of crosslinking is extremely increased, an inorganic structure is considered.

As described above, the thin film produced by plasma polymerization of the silicon-based monomer has a crosslinkable structure, and the formed film is applied as a gas separation film such as oxygen and an organic solvent separation film such as ethanol. , Effective as a permselective membrane. Further, the produced film has excellent mechanical properties such as scratch strength and hardness. Furthermore, it is chemically stable and durable.

In the film material, the film thickness is also an important factor, but in the plasma polymerization, the film thickness can be controlled by appropriately selecting the length of the polymerization time under certain constant polymerization conditions. In the present invention, the thickness of the copolymer thin film is in the range of about 0.01 to 10 microns,
More preferably, 0.02-2.0 micron is desirable.

In the present invention, the thin film obtained by the copolymerization of the silicon-based monomer is treated with oxidizing plasma. As the oxidizing plasma gas, oxygen itself,
Alternatively, a gas containing oxygen such as air is used. The conditions of the oxidative plasma treatment in this case are not particularly limited, and it suffices that discharge occurs and oxidative etching occurs. That is, conditions such as gas pressure and discharge processing output are not particularly limited. The degree of oxidation depends on the supply amount and output of oxygen. For example, the oxygen partial pressure is 10 to 50.
By generating electric discharge at a power of 10 W to 100 W in Pascal, the desorption of carbon components and the formation of silicon oxide by oxidative etching can be efficiently promoted.

The porous silicon oxide thin film obtained by the present invention can be used in various applications depending on the chemical function and structure of the film. In particular, since the silicon oxide is randomly introduced into the polymer film, the porous light scattering material,
It can be used as an immobilizing material for bio-related molecules such as enzymes, a molecular adsorbing material, and a separation membrane material.

[0027]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A slide glass (1. cm) was placed in a cylindrical reaction tube made of Pyrex (registered trademark) glass having an inner diameter of 4.4 cm and a length of 40 cm.
8 cm × 4.0 cm), this system was vacuum degassed beforehand, and then acrylic acid (hereinafter referred to as A
A mixed gas of hexamethyldisiloxane (HMSO) having a ratio of A) of 0.33 was introduced at a total pressure of 3.0 Pascal. 1 after gas flow reaches steady state
A plasma processing apparatus of an inductive coupling type using a radio wave of 3.56 MHz was used to generate a plasma discharge with a power of 50 watts for reaction. After carrying out the polymerization reaction for 10 minutes, the discharge was stopped, the supply of the monomer gas was stopped, and then the vacuum deaeration was performed, and then the plasma oxidation treatment was further performed for 10 minutes at 20 W under the introduction condition of oxygen gas of 20 Pascal. . This step produced a porous silicon oxide layer corresponding to a thickness of about 0.93 micron.

Example 2 In the same manner as in Example 1, a mixed gas with HMSO having a toluene ratio of 0.33 was introduced, and copolymerization was carried out at 50 W under a monomer gas pressure of 3.0 Pascal. . After the polymerization treatment for 10 minutes, this was irradiated with oxygen plasma for 10 minutes at 50 Pascal and 100 W to obtain a porous silicon oxide thin film having a thickness of about 0.60 micron.

Example 3 In the same manner as in Example 1, a mixed gas with HMSO having a pyridine ratio of 0.33 was introduced, and copolymerization was carried out at 50 W under a monomer gas pressure of 3.0 Pascal. . After the polymerization treatment for 10 minutes, under the condition of 50 Pascal and 100 W,
Irradiation with oxygen plasma for 10 minutes gave a porous silicon oxide thin film with a thickness of about 0.54 micron.

Example 4 In the same manner as in Example 1, a mixed gas with HMSO having an acetone ratio of 0.33 was introduced, and copolymerization was carried out at 50 W under a monomer gas pressure of 3.0 Pascal. . After the polymerization treatment for 10 minutes, it was irradiated with oxygen plasma for 10 minutes under the condition of 20 Pascal and 50 W to obtain a porous silicon oxide thin film having a thickness of about 0.4 micron.

Example 5 In the same manner as in Example 1, a mixed gas with hexamethyldisilazane (HMSZ) having an AA ratio of 0.5 was introduced to obtain a monomer gas pressure condition of 4.0 Pascal. Copolymerization was performed at 50W. After the polymerization treatment for 10 minutes, 20 Pascal oxygen gas was added, and the discharge irradiation was further performed at 20 W for 10 minutes,
The thin film layer was oxidized. Oxidation proceeded from the surface layer by this step, and a porous silicon oxide thin film having a thickness of about 0.8 μm was formed as a whole.

Example 6 In the same manner as in Example 5, a mixed gas with HMSZ in which the proportion of toluene was 0.2 was introduced, and the gas pressure was 4.0 Pascal at 13.56 MHz and 100 W at 20 W. After reacting for a minute to obtain a copolymer film, an oxygen gas of 50 Pascal was further introduced, and plasma treatment was performed at 100 W for 10 minutes. This step formed a layer of silicon oxide corresponding to a thickness of about 2.0 microns.

[0034]

EFFECTS OF THE INVENTION A porous silicon oxide thin film is obtained by treating a copolymer thin film obtained by plasma polymerization from a mixed gas of a silicon-based monomer and a hydrocarbon-based monomer in a fixed ratio with an oxidizing plasma. These thin films are used for immobilizing bio-related molecules such as enzymes, light-shielding materials,
It can be used as a molecular adsorption material.

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Claims (5)

[Claims] 1. A copolymer thin film is formed by plasma polymerization of a mixed gas of a certain proportion of a silicon-based monomer and a hydrocarbon-based monomer, and then the copolymerized thin film is further subjected to discharge using oxygen or an oxygen-containing gas as a plasma source. A porous silicon oxide thin film, which is obtained by performing treatment to remove a hydrocarbon-based monomer-derived polymer component by etching and at the same time oxidizing a silicon-based polymer portion to convert it into silicon oxide. 2. The hydrocarbon-based monomer is a linear compound such as methane, ethane or propane, an aromatic compound such as toluene, a hetero compound such as pyridine or pyrrole, a carboxylic acid such as acetic acid, acrylic acid, methacrylic acid or propionic acid. The porous silicon oxide thin film according to claim 1, which is at least one kind or two or more kinds selected from the group consisting of acid compounds and ketone compounds such as acetone. 3. The ratio of the hydrocarbon monomer gas in the mixed gas of the silicon-based monomer and the hydrocarbon-based monomer, which is introduced at the time of reaction for producing the copolymer thin film, is 0.1 in molar ratio.
To 0.8, and more preferably 0.2 to 0.6. 3. The porous silicon oxide thin film according to claim 1, wherein the porous silicon oxide thin film is in the range of 0.2 to 0.6. 4. The thin film layer made of silicon oxide has a thickness of 0.
01 micron to 10 micron, more preferably 0.0
4. The porous silicon oxide thin film according to claim 1, wherein the thickness is in the range of 2 microns to 2 microns. 5. A copolymer thin film is formed by plasma polymerization of a mixed gas of a certain proportion of a silicon-based monomer and a hydrocarbon-based monomer, and then the copolymerized thin film is further subjected to discharge using oxygen or an oxygen-containing gas as a plasma source. A method for producing a porous silicon oxide thin film, which is obtained by subjecting a hydrocarbon-based monomer-derived polymer component to etching removal to simultaneously oxidize a silicon-based polymer portion to convert it into silicon oxide.