JPH0776090B2 - Method for manufacturing zirconia thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a zirconia thin film.

[Prior Art and Problems] As is well known, zirconia has a high melting point and is used as a high temperature material. However, pure zirconia causes a transition from a low temperature type monoclinic crystal to a tetragonal crystal at about 1000 ° C. Destruction occurs due to the change in volume. Therefore, it is used as stabilized zirconia or partially stabilized zirconia in which yttrium (Y), calcium (Ca), etc. are added to stabilize the cubic crystal of the high temperature phase in a wide temperature range.

By the way, even in the case of forming a thin film of zirconia, a stabilizer is added to an object for use at high temperature. When making a zirconia thin film by vapor phase chemical reaction (CVD), which is one of the thinning techniques, a reaction using zirconium and a halide of a stabilizer as a raw material is generally used. Then, a high temperature of about 1000 ° C is required as the reaction temperature. Further, there is a problem that corrosive gas is generated as a reaction by-product and corrodes the apparatus and the substrate.

Under these circumstances, CVD using an organic zirconium compound that can be decomposed at a low temperature and does not generate a corrosive gas and an organic compound that is a stabilizer has been attempted. As such an organic compound, a group of compounds called β-diketone complex represented by acetylacetone complex is used. In addition, zirconium alkoxides are used as other organic compounds (Journal of Cry
stal Crows 74 vol. 409 p. 1986).

However, although studies using such zirconia organic compounds have been conducted, these studies are aimed at a stabilized zirconia film to which all stabilizers are added.
However, there are few organic compounds such as Y and Ca having a high vapor pressure, which are raw materials for the stabilizer, and a special device is required to vaporize them when they are used for vapor phase chemical vapor deposition.

Further, in vapor phase chemical deposition of oxide thin films including zirconia, a single crystal such as silicon or quartz as a substrate is used. When a metal substrate is used, the difference in thermal expansion coefficient between the metal and the oxide is large, and therefore the film may peel off due to internal stress of the formed film.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zirconia thin film which is stable in a wide temperature range and can be formed on a metal substrate with good adhesion, and a method for producing the same.

[Means for Solving the Problems] The present invention is a method for producing a zirconia thin film, which comprises producing a monoclinic zirconia by heat-treating a cubic zirconia thin film to which a stabilizer is not added at 500 ° C. or higher. is there.

In this invention, the heat treatment temperature of 500 ° C or higher is 500 ° C.
If it is less than 1, the dislocation to monoclinic crystal does not occur, or even if the dislocation occurs, the speed is very slow and not practical.

Further, a zirconia thin film can be produced by decomposing the alkoxide of zirconium as a raw material at a temperature of 500 ° C. or lower in a chemical vapor deposition method.

Examples of the zirconium alkoxide include zirconium ethoxide, zirconium isoproxide, and zirconium tert-butoxide. When used in the chemical vapor deposition method, zirconium tert-butoxide having a high vapor pressure is preferable. When zirconium tertiary oxide is used here, the decomposition reaction occurs from about 250 ° C., but at temperatures of 500 ° C. or higher, stable phase monoclinic or tetragonal zirconia is formed, which is not preferable.

Regarding the decomposition reaction of the alkoxide of zirconium tert-butoxide, the thermal decomposition reaction of this compound alone,
Alternatively, oxidative decomposition reaction under the condition that an oxidizing agent such as oxygen is added to this raw material, or hydrolysis by adding steam is included.

As a gas mixed when the alkoxide of zirconium is used as a raw material by the chemical vapor deposition method, nitrogen, argon, an inert gas such as helium, a reducing gas such as hydrogen,
Oxygen, carbon dioxide, an oxidizing gas such as steam, or a mixed gas is used.

As the pressure when the above reaction is performed by the chemical vapor deposition method, normal pressure or reduced pressure conditions are used.

Examples of the substrate for forming the zirconia thin film by the chemical vapor deposition method include a ceramic sintered body, a single crystal such as silicon, an amorphous material such as glass, and a metal such as stainless steel.

[Function] In the zirconia thin film according to the present invention, the cubic zirconia thin film serving as a base does not contain a stabilizer, and therefore, a monoclinic crystal, a tetragonal crystal, and a dislocation to a cubic crystal occur due to an increase in temperature. The film does not break due to changes. This is considered to be because the structure of the film formed by the chemical vapor deposition method is different from that of the sintered body, and the stress at the phase transition does not work inside the film. This means that the film is not peeled off even when a metal whose coefficient of thermal expansion is largely different from that of zirconia is used as the substrate, and has great practical value as a surface modification of the metal material.

[Example] An example of the present invention will be described below.

First, the film forming apparatus used in the method of the present invention will be described with reference to FIG.

In the figure, 1 is a reaction vessel. A susceptor 3 including a heater 2 is arranged in the reaction container 1. The susceptor 3 is adapted to rotate as indicated by an arrow X in the figure. A plurality of substrates 4 are placed on the susceptor 3 directly below nozzles described later. The substrate 4 is heated to a predetermined temperature.

A nozzle 4 is attached to the upper part of the reaction vessel 1, and a mass flow controller 6a is attached to the nozzle 4.
The pipe 7a, the mass flow controller 6b, and the second pipe 7b to which the valve 8a is attached are connected via the third pipe 7c. The bypass pipe 9 of the second pipe 7b on the downstream side of the mass flow controller 6b is provided with a carburetor 10 containing zirconium tert-butoxide through valves 8b and 8c. The vaporizer 10 is kept at, for example, 90 ° C. by the constant temperature bath 11.

A vacuum pump 14 communicates with the exhaust hole 12 of the reaction container 1 through an exhaust line 13. The reaction gas is exhausted by this vacuum pump 14. By mixing nitrogen with the exhaust gas in the middle of the exhaust line 13, the exhaust speed is adjusted and the pressure in the reaction vessel 1 is kept constant.

Next, the method of the present invention using the above film forming apparatus will be described. That is, first, the valve 8a of the second pipe 7b is "closed" and the vibrators 8b and 8c of the bypass line 9 are "opened". Next, Ar gas as carrier gas is 100cc per minute by the mass controller 6b.
And supply to the vaporizer 10. On the other hand, the mass flow controller 6a of the first pipe 7a adjusts the Ar gas to 5 per minute. As a result, the mixed gas of zirconium tert-butoxide vapor and argon was adjusted to 5 per minute.
It is further diluted with Ar gas and introduced into the reaction vessel 1 through the third pipe 7c and the nozzle 5. The substrate 4 in the reaction container 1 is
For example, heat to 350 ° C. Here, as the substrate 4, for example, Corning 7059 glass having a size of 20 mm × 20 mm × 2 mm, SUS304, Mo and mirror-polished SUS304 were used. The pressure inside the reaction vessel 1 was maintained at 75 Torr.

When a film was formed under these conditions for 1 hour, a white film of 10 to 20 mg was deposited on each substrate, but a transparent film was obtained especially on mirror-polished SUS304. As a result of X-ray diffraction, it was confirmed that all the films on the respective substrates were cubic zirconia.

Further, for a sample using Mo as a substrate, a similar coating was further formed on the back surface to cover the entire surface, and then heat treatment was performed in an annular furnace at 1300 ° C. for 3 hours in the air. No peeling was observed in the sample after the heat treatment. As a result of X-ray diffraction, it was confirmed to be monoclinic zirconia. The sample was further cycled in a ring furnace at 1400 ° C. for 1 hour and 900 ° C. for 1 hour five times to return to room temperature, but no peeling of the film was observed.

[Effects of the Invention] As described in detail above, according to the present invention, a zirconia thin film that is stable in a wide temperature range and can be formed on a metal substrate with good adhesion and that can be used as a heat-resistant protective film of metal or an optical film is provided. A method of manufacturing can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a film forming apparatus used in the present invention. 1 ... Reaction container, 2 ... Heater, 3 ... Susceptor, 4 ...
… Substrate, 5 …… Nozzle, 6a, 6b …… Mass flow controller, 7a, 7b, 7c …… Piping, 8a, 8b, 8c …… Valve, 10 ……
Vaporizer, 11 ... constant temperature bath, 12 ... exhaust hole, 14 ... vacuum pump.

Claims (1)

[Claims] 1. A method for producing a zirconia thin film, which comprises producing a monoclinic zirconia by heat-treating a cubic zirconia thin film containing no stabilizer at 500 ° C. or higher.