JP2000256863A - Production of composite oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thin film even on a substrate inferior in heat resistance without executing high temp. heating treatment by coating the surface of a substrate with a precursory soln. dissolved into a mixed soln. of a monoalkyl ether and an alcohol to form a film and crystallizing this thin film. SOLUTION: A precursory coating soln. using respective alkoxydes of Ba, Sr and Ti as a starting material is prepd. This precursory coating soln. is applied on the surface of a substrate to form a film. The formed thin film is irradiated with light of <=360 nm wave length to crystallize the thin film, by which a thin film of a multiple oxide having a Perovskite type structure of a compsn. expressed by (Ba1-xSrx)TiO is formed. As a solvent dissolving the alkoxydes, a mixed soln. of either ethylene glycol-monoalkyl ether or propylene glycol monoalkyl ether and an alcohol selected from 1 to 4C primary alcohols is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite oxide of a plurality of types of elements, in particular, an oxide of Ba, an oxide of Sr and T
The present invention relates to a method for producing a composite oxide film for producing a composite oxide thin film composed of an oxide of i.

[0002]

2. Description of the Related Art There are many functional substances in a composite oxide of a plurality of types of elements, and one of them is a composite oxide of Ba, Sr and Ti, that is, a composition formula (Ba _1-x Sr
_x ) A composite oxide having a perovskite structure represented by TiO ₃ (hereinafter, referred to as “BST”) has a high dielectric property and is used as a thin film material such as a thin film capacitor, a capacitor, and a piezoelectric material. In the present invention, in the composite oxide having a perovskite structure represented by the composition formula (Ba _1-x Sr _x ) TiO ₃ , when x = 0 in the composition formula, that is, when BaTiO ₃ (titanium oxide Barium) or when x = 1 in the composition formula, that is, when S = 1
rTiO ₃ (strontium titanate) is also included, and in the following description, these are referred to as BST for convenience. This BST thin film is manufactured by various methods.

For example, JP-A-9-40683 discloses a method of forming a BST film by a CVD method, and JP-A-9-148538 discloses a method of manufacturing a BST thin film by a sputtering method. Is disclosed.

Japanese Patent Application Laid-Open Nos. Hei 7-2322961 and Hei 9-78249 disclose Ba, Sr and T
Each metal alkoxide or each organic metal salt of i is dissolved and mixed in a solvent, and the obtained solution is applied on a substrate to form a thin film, and 300 ° C. to 1,200 ° C. (650 ° C.).
C. to 850.degree. C.) to obtain a crystallized BST thin film by heat treatment. Further, JP-A-8-337421, JP-A-9-123
No. 54, etc., a composition obtained by mixing each carboxylate of Ba and Sr and an alkoxide of Ti in a solvent is applied to a substrate, dried, and then fired at a temperature of 450 ° C. to 800 ° C. Discloses a method for forming a BST thin film.

[0005]

However, the CVD method disclosed in Japanese Patent Application Laid-Open No.
There are problems that it is difficult to control the composition ratio of each oxide of a, Sr, and Ti, and a large-scale apparatus is required because the reaction is a gas phase reaction under vacuum. Further, C
In the VD method, there is a problem that the temperature of the substrate becomes as high as about 600 ° C. Also, Japanese Patent Application Laid-Open No. 9-14853
In the method of forming a thin film of BST on a substrate by a sputtering method disclosed in Japanese Patent Publication No. 8 (JP-A) No. 8 etc., a target which is a sintered body is required, and a heat treatment at a high temperature is required in the process of obtaining the target. . Further, the sputtering method also has a problem that a large-scale apparatus is required because the processing is performed in a vacuum process.

[0006] Japanese Patent Application Laid-Open No. 7-232961, Japanese Patent Application Laid-Open
As disclosed in JP-A-78249 and the like, a sol-gel method using each metal alkoxide of Ba, Sr and Ti (or an organic metal salt) as a starting material is used.
In the method of forming a BST thin film on a substrate, it is necessary to perform a heat treatment at a temperature of usually 600 ° C. to 900 ° C. in order to crystallize the thin film after applying a precursor solution on the substrate to form a film. . Further, even by a pyrolysis method as disclosed in JP-A-8-337421, JP-A-9-12354, etc., after the composition is applied to a substrate and dried, the thin film on the substrate is heated to 450 ° C. It is necessary to fire at a temperature of 800 ° C. As described above, in the conventional sol-gel method or thermal decomposition method using an alkoxide (or a metal salt), heat treatment at a high temperature is required to obtain a crystallized BST thin film. For this reason, these conventional methods cannot form a BST thin film on a substrate having low heat resistance such as plastics.

The present invention has been made in view of the above circumstances, the control of the manufacturing process is relatively easy, no large-scale equipment is required, and even if heat treatment at a high temperature is not performed. An object of the present invention is to provide a method for manufacturing a composite oxide film capable of obtaining a BST thin film.

[0008]

The invention according to claim 1 is
A precursor coating solution was prepared using each alkoxide of Ba and / or Sr and Ti as a starting material, and the precursor coating solution was applied to the surface of the object to form a film, and then formed on the surface of the object. In the method for producing a composite oxide film in which a thin film is crystallized to form a BST thin film, the solvent for preparing the precursor coating solution may be ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, or ethylene. Using a mixed solution of glycol monoalkyl ether or propylene glycol monoalkyl ether and one or two or more alcohols selected from primary alcohols having 1 to 4 carbon atoms, applying the precursor coating solution to the substrate After coating on the surface of the substrate to form a film, the wavelength of the thin film formed on the surface of the substrate is 360 nm or less. Wherein the crystallizing a thin film was irradiated with light is.

According to a second aspect of the present invention, in the manufacturing method of the first aspect, an ArF excimer laser is used as a light source for irradiating the thin film formed on the surface of the object with light.
KrF excimer laser, XeCl excimer laser, Xe
F excimer laser, third harmonic of YAG laser or YA
It is characterized by using fourth harmonic light of a G laser.

According to the manufacturing method of the first aspect of the present invention,
As a solvent for preparing the precursor coating solution, selected from ethylene glycol monoalkyl ether or propylene glycol monoalkyl ether, or ethylene glycol monoalkyl ether or propylene glycol monoalkyl ether and a primary alcohol having 1 to 4 carbon atoms. The use of a mixed solution with one or two or more alcohols eliminates the use of stabilizers such as β-diketones and alkanolamines commonly used for stabilizing alkoxides. Also, the alkoxide is stabilized, and a homogeneous precursor coating solution can be obtained. For this reason, even if a stabilizer is not used, the film forming property of the precursor coating solution is improved, and uniform film formation on the surface of the object to be coated becomes possible.

After the precursor coating solution is applied to the surface of the object to form a film, the wavelength of the light applied to the thin film on the object is 3 nm.
By irradiating light having a wavelength of 60 nm or less, the light is absorbed by the thin film, and BST is crystallized with the energy. Accordingly, since it is not necessary to perform a heat treatment at a high temperature for crystallization of BST, a BST thin film can be formed on a substrate having low heat resistance such as plastics. Further, since it is not necessary to use a stabilizer such as β-diketone or alkanolamine when preparing the precursor coating solution, the amount of organic substances remaining in the thin film after film formation is reduced, and therefore, Deterioration of the film quality due to rapid decomposition of organic matter when the thin film is irradiated with light can be suppressed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

In the present invention, the target BST thin film is formed by preparing a precursor coating solution from each of the alkoxides of Ba, Sr and Ti as a starting material, and coating the precursor coating solution on the surface of the substrate. Thereafter, the thin film formed on the substrate surface is irradiated with light having a wavelength of 360 nm or less to crystallize the thin film.

The type of each of the starting alkoxides of Ba, Sr and Ti is not particularly limited. To reduce residual organic substances, titanium alkoxides having an alkoxyl group having 1 to 4 carbon atoms are used. Preferably, it is used. The barium alkoxide and the strontium alkoxide also preferably have an alkoxyl group having 1 to 4 carbon atoms, respectively. In particular, from the viewpoint of solubility in a solvent described below, the barium alkoxide and the metal strontium have 1 carbon atom. Preferred is an alkoxide synthesized by reaction with a primary alcohol having 1 to 4 or an ethylene glycol monoalkyl ether having 1 to 4 carbon atoms. In addition, Ba as a starting material,
The use of the carboxylate of Sr and Ti is not preferable because it causes deterioration of the film quality due to rapid decomposition of organic matter when the thin film is irradiated with light after film formation.

As the solvent for dissolving the alkoxide,
Ethylene glycol monoalkyl ether or propylene
Lenglycol monoalkyl ether or ethyl
Lenglycol monoalkyl ether or propylene
Glycol monoalkyl ether and carbon number 1-4
One or more selected from certain primary alcohols
Use a mixed solution with alcohol. Ethylene glycol
Monoalkyl ether is
Also, the general formula ROCH₂CH₂OH
Wherein the alkyl group represented by R preferably has 1 to 4 carbon atoms.
Good. Also, propylene glycol monoalkyl ether
Ter is also called alkoxypropanol and has the general formula RO
CH₂CH (CH₃) OH or the general formula ROC (C
H₃) HCH ₂Which is represented by OH,
It is preferred that the kill group has 1 to 4 carbon atoms. First grade Al
Calls include methanol, ethanol or prop
It is preferred to use knol.

The mixing ratio when a mixed solution of ethylene glycol monoalkyl ether or propylene glycol monoalkyl ether and a primary alcohol is used as a solvent is not particularly limited, since it is determined appropriately depending on the solubility and concentration of the alkoxide used. Considering the film-forming properties of the precursor coating solution, the proportion of ethylene glycol monoalkyl ether or propylene glycol monoalkyl ether is preferably 50% or more. Incidentally, by using a mixed solution of ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether or ethylene glycol monoalkyl ether or propylene glycol monoalkyl ether and a primary alcohol as a solvent,
Since the alkoxide is stabilized to obtain a homogeneous precursor coating solution, it is not necessary to use a stabilizer such as β-diketone or alkanolamine.

The method for preparing the precursor coating solution is not particularly limited, but each alkoxide of Ba, Sr and Ti is added to a solvent, and the mixture is reacted while heating to cause hydrolysis and polymerization of each alkoxide. And, by using the above-mentioned solvent, a homogeneous precursor coating liquid can be obtained. For the hydrolysis, an acid catalyst and / or a base catalyst may be used. Preferably, a mineral acid such as hydrochloric acid or an organic acid such as acetic acid is used.

The obtained precursor coating solution can be applied on the surface of a substrate by a usual method to form a film on the substrate. In this case, since the coating liquid has excellent stability, it can be formed by various coating methods such as spin coating, dip coating, spray coating, flow coating, and bar coating.

When a thin film is formed on a substrate, the thin film is irradiated with light having a wavelength of 360 nm or less. Any type of light source can be used as long as it can emit light having a wavelength of 360 nm or less. For example, an ArF excimer laser, a KrF excimer laser, a XeCl excimer laser, a XeF excimer laser, a third harmonic of a YAG laser, or For example, fourth harmonic light of a YAG laser is used. It is also possible to use two or more of these light sources in combination. When irradiating this thin film with light, depending on the purpose, the substrate may be heated,
It is also possible to place the substrate under reduced pressure or to control the atmosphere (oxidizing atmosphere or non-oxidizing atmosphere). By irradiating the thin film with light, the thin film is crystallized, and a target BST thin film is formed on the surface of the substrate.

[0020]

[Examples 1 to 13]

Diisopropoxybarium, diisopropoxystrontium and tetraisopropoxytitanium were added to a solvent (alcohol), and the mixed solution was heated and reacted in a 90 ° C. oil bath. To the obtained reaction solution, a dilute solution of an alcohol (alcohol of the same kind as the solvent) of 0.1 M hydrochloric acid in an equimolar amount to the total alkoxide was added, and the mixed solution was hydrolyzed. The concentration of the coating solution was adjusted so that the final oxide concentration was 5% by weight.

The obtained coating solution is applied on a silicon substrate provided with a Pt electrode using a spin coater,
Treated at a rotation speed of 00 rpm for 20 seconds (45% humidity)
After forming the film, the coating film formed on the substrate was dried at a temperature of 100 ° C. for 15 minutes. As a result, a film thickness of about 200
A coating film having a thickness of nm was obtained.

Irradiating the obtained coating film with ultraviolet light;
The characteristics of the obtained thin film were evaluated. That is,
The crystal phase was identified by an X-ray diffraction method, and the film thickness was measured by a step meter. Table 1 summarizes the composition of the coating solution, the synthesis conditions, the irradiation conditions of ultraviolet light, and the evaluation results of the obtained thin films. In the column of "solvent" in Table 1, "ME" indicates 2-methoxyethanol, "EE" indicates 2-ethoxyethanol, and "MP" indicates 1-methoxy-2-propanol.

[0024]

[Table 1]

In each of Examples 1 to 13, a perovskite single-phase film was obtained regardless of the composition. FIG. 1 shows an X-ray diffraction pattern of the thin film obtained in Example 2.

Example 14 Diisopropoxybarium, diisopropoxystrontium and tetraisopropoxytitanium were converted to (Ba _0.25 Sr _0.75 ) TiO.
Each was weighed so as to have a composition of ₃ and the final coating solution had an oxide concentration of 5% by weight, and added to a solvent (alcohol). The mixed solution was heated in a 90 ° C. oil bath. The reaction was performed to prepare a coating solution.

The obtained coating solution was applied on a silicon substrate provided with a Pt electrode using a spin coater,
Treated at a rotation speed of 00 rpm for 20 seconds (45% humidity)
After forming the film, the coating film formed on the substrate was dried at a temperature of 100 ° C. for 15 minutes to obtain a coating film.

The obtained coating film was irradiated with KrF excimer laser light (energy density: 50 mJ / cm ² , number of shots: 100 times). As a result, a BST thin film having the target crystal phase was obtained. Table 1 shows the evaluation results.

Comparative Example 1 Diisopropoxybarium, diisopropoxystrontium and tetraisopropoxytitanium were prepared by mixing (Ba _0.25 Sr _0.75 ) TiO ₃
And weighed so that the final coating solution had an oxide concentration of 5% by weight, added to a solvent (alcohol), and heated the mixed solution in a 90 ° C. oil bath to carry out the reaction. I let it. To the obtained reaction solution, acetylacetone in an equimolar amount to Ti was added to prepare a coating solution.

The obtained coating solution was applied on a silicon substrate provided with a Pt electrode using a spin coater,
Treated at a rotation speed of 00 rpm for 20 seconds (45% humidity)
After forming the film, the coating film formed on the substrate was dried at a temperature of 100 ° C. for 15 minutes to obtain a coating film.

The obtained coating film is more stable to humidity than the coating film obtained in each of the above-mentioned examples, and has a humidity of 7%.
Film formation was possible even at 0%. However, when the coating film was irradiated with KrF excimer laser light, the film was clouded at lower energy than the thin film obtained in the example, and a clean oxide film could not be obtained.

From these results, it was found that selection of a solvent used for preparing a coating solution is very important in order to obtain a BST thin film having a uniform crystallinity.

[Comparative Example 2] The coating film obtained in Example 2 was subjected to a heat treatment and the crystallization temperature was confirmed.
A single-phase film of a perovskite phase was obtained by a heat treatment at a temperature of 00 ° C. for 30 minutes.

As described above, it has been found that in order to obtain a crystallized BST thin film, it is necessary to perform a heat treatment at a temperature of at least about 600 ° C. in a normal heat treatment.

[Comparative Example 3] (Ba) was obtained in the same manner as in Example 14 by using diisopropoxybarium, diisopropoxystrontium and tetraisopropoxytitanium as starting materials, and using ethanol alone as a solvent.
A precursor coating liquid having a composition of _0.25 Sr _0.75 ) TiO ₃ was prepared. However, a complex salt was formed between Ba and Sr and the alkoxide of Ti, and a coating solution having a concentration higher than 1% could not be prepared.

An attempt was made to form a film using the obtained coating solution. However, in an environment with a humidity of 40%, the film became cloudy and a uniform thin film could not be obtained.

[0037]

According to the manufacturing method of the first aspect of the present invention, a BST thin film can be obtained without performing heat treatment at a high temperature. Therefore, it is possible to form a BST thin film on a substrate having poor heat resistance such as plastics. Further, even without using a stabilizer, the film-forming property of the precursor coating solution is improved, and a uniform film can be formed on the surface of the object to be coated, so that it remains in the thin film after film formation. The amount of the organic substance is reduced, and therefore, deterioration of the film quality due to rapid decomposition of the organic substance when the thin film is irradiated with light can be suppressed.

According to the manufacturing method of the second aspect of the present invention, the BST thin film can be crystallized by the energy of light without performing the heat treatment at a high temperature.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction pattern of a thin film obtained in Example 2 of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D075 BB48Z DB31 DC21 EB01 EC01 EC02 EC30 4G042 DA02 DB03 DB15 DD02 DD10 DE09 4G047 CA02 CA07 CB06 CC03 CD02 CD08 4G075 AA24 AA30 BB02 CA02 CA32 CA33 CA36 CA51 4K022 AA05 BA33A DA08 DB01

Claims (2)

[Claims] 1. The method of claim 1 wherein Ba and / or Sr and Ti
Prepare a precursor coating solution using each alkoxide as a starting material
And apply the precursor coating solution to the surface of the object to be coated to form a film.
And then crystallize the thin film formed on the surface of the object to be coated.
And the composition formula (Ba _1-xSr_x) TiO₃The pen represented by
Formation of composite oxide thin film with lobskite structure
In the method for producing a composite oxide film, ethylene is used as a solvent when preparing the precursor coating solution.
Glycol monoalkyl ether, propylene glycol
Lumonoalkyl ether or ethylene glycol
Monoalkyl ether or propylene glycol
Noalkyl ether and primary alcohol having 1 to 4 carbon atoms
With one or more alcohols selected from
Using the mixed solution of the above, the precursor coating liquid was applied to the surface of the object to be coated to form a film.
After that, the wavelength of the thin film formed on the surface of the object is 360
to crystallize a thin film by irradiating it with light
A method for producing a composite oxide film. 2. A light source for irradiating light to a thin film formed on the surface of an object to be coated is an ArF excimer laser or KrF.
The method for producing a composite oxide film according to claim 1, wherein the method is a third harmonic light of an excimer laser, a XeCl excimer laser, a XeF excimer laser, a YAG laser, or a fourth harmonic of a YAG laser.