JP2783158B2 - Manufacturing method of oxide thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film capacitor and an oxide thin film formed on a substrate using an organometallic compound and usable for a capacitor, a piezoelectric material, a pyroelectric material and the like.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing an oxide thin film,
A film is formed by a dry process such as a sputtering method or a vacuum evaporation method, and a film is formed by a wet process such as a sol-gel method. However, in the case of film formation by a dry process,
These devices are very expensive and have different vapor pressures for each element, making it impossible to stably produce thin films with excellent stoichiometry, poor crystallinity, and low productivity. It has the disadvantage of high cost and is far from practical. On the other hand, the sol-gel method using organometallic compounds has advantages in terms of precise chemical composition control, uniformity at the molecular level, low temperature of the process, large area, low equipment cost, etc., and research is being conducted in various fields. Have been done. For example,
In Japanese Patent Application Publication No. 2-27482, a solution containing an organometallic compound was applied on a glass substrate and dried in air at room temperature for 30 minutes and further dried in a thermostat at 110 ° C. for 30 minutes to terminate the hydrolysis. Thereafter, a method of producing an oxide thin film by firing at a temperature of 550 to 800 ° C. while forcibly supplying steam in an electric furnace has been proposed. However,
The process exemplified in this method has a problem that a high temperature is required for crystallization of a thin film because hydrolysis is not performed before coating. Japanese Patent Application Laid-Open No. 4-19911 discloses a method in which a metal-organic compound of lead, lanthanum, titanium, and zirconium is dissolved in an organic solvent, and then a stabilizer and a predetermined amount of water are added thereto to form a lead titanate. A method for forming a ferroelectric thin film of (PT), lead zirconate titanate (PZT), PZT with a third component added, and lead zirconate titanate with a lanthanum (PLZT) has been proposed. However,
Since the thin film produced by this method utilizes hydrolysis with only 0.1 to 1.5 mol of water per mol of metal atom, there is still a problem that crystallization of the thin film requires a high temperature. Also, Mat. Res. Soc. Symp. P
rc. , Vol. 1,200, pp. 173 to 178, based on an alkoxide, partially hydrolyze a solution by adding water and an acid or an alkali, apply it to a Si substrate, and heat-treat to prepare a Pb-containing composite oxide thin film Is described. However, there is a problem that crystallization requires a high temperature under the conditions specifically described therein.

[0003]

Many of the above-mentioned oxides that have been conventionally proposed can be used as a ferroelectric thin film, and the ferroelectric thin film is composed of a ferroelectric material and a piezoelectric material. It is used in many fields of electronics due to its many properties, such as electrical properties, pyroelectricity, and electro-optic effect. In recent years, application of DRAM (Dynamic RAM) to memory cells has attracted attention with the rapid development of integration. Therefore, improvement of the manufacturing method is required. The present invention has been made in view of the above situation. That is, an object of the present invention is to stabilize a uniform and highly stoichiometric oxide thin film which can be used for a thin film capacitor, a piezoelectric substance, a pyroelectric substance, etc. on a substrate using an organometallic compound at a low temperature. And to provide a method for manufacturing.

[0004]

As a result of the study, the present inventors have found that an organic solvent solution of a complex metal alkoxide compound was hydrolyzed in advance by adding a specific amount of water and an inorganic catalyst or acetic acid and heating. Thereafter, when the thin film is formed by coating on a substrate and then heat-treated, it has been found that a uniform and excellent stoichiometric oxide thin film can be formed at a low temperature, and the present invention has been completed. That is, the present invention provides a compound represented by the general formula:
In a method for producing an oxide thin film represented by ABO ₃ (A is an element selected from IA, IIA, IIIA, IVB and VB, and B is an element selected from IVA and VA), Elemental: In a solution of a complex metal alkoxide compound containing A and B in an organic solvent, water is used in an amount such that the molar ratio of the complex metal alkoxide compound and water is 1: 0.5 to 1: 3, and the complex metal alkoxide compound is Adding an inorganic catalyst or acetic acid in an amount such that the molar ratio of the inorganic catalyst or acetic acid is 1: 0.15 to 1: 0.5, hydrolyzing, applying the resultant on a substrate to form a thin film, and then performing heat treatment. It is characterized by.

Hereinafter, the present invention will be described in detail. In the present invention, in the oxide represented by the general formula: ABO ₃ ,
Are groups IA, IIA, IIIA, IVB and V
Represents an element selected from Group B, specifically, Li,
K, Mg, Sr, Ba, La, Pb and Bi; and B represents an element selected from Group IVA and Group VA of the periodic table. Specifically, Ti, Zr, Nb and Ta Is raised.

The organic ligand of the composite metal alkoxide compound containing A and B has the formula: R ¹ O— or R ² O
R ³ O— (wherein, R ¹ and R ² represent an aliphatic hydrocarbon group, and R ³ represents a divalent aliphatic hydrocarbon group which may have an ether bond). Is preferred.
In particular, in R ² OR ³ O—, R ² represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, and R ³ represents an aliphatic hydrocarbon group having 2 to 4 carbon atoms. It is preferable from the viewpoint of. As a specific example of the organic ligand, R ¹ O—
_{2 H 5 O-, C 3 H} 7 O-, C 4 H 9 O- etc., also,
As R ² OR ³ O—, CH ₃ OC ₂ H ₄ O—, C _{2
H 5 OC 2 H 4 O-,} C 3 H 7 OC 2 H 4 O-, C 4 H
_{9 OC 2 H 4 O-, C} 2 H 5 OC 2 H 4 OC 2 H 4 O-
And the like.

In the present invention, the composite metal alkoxide compound is obtained by mixing a metal alkoxide compound containing A and a metal alkoxide compound containing B with a predetermined composition by a general formula:
R ¹ OH or R ² OR ³ OH (wherein R ¹ and R ²
Represents an aliphatic hydrocarbon group, and R ³ represents a divalent aliphatic hydrocarbon group which may have an ether bond. Can be synthesized by distillation and reflux in an organic solvent represented by the formula (1).

In the organic solvent represented by the above general formula,
The aliphatic hydrocarbon group for R ¹ and R ² has 1 carbon atom.
Preferably an alkyl group having to 4, the R ^3, carbon atoms 2
A divalent group having 4 to 8 carbon atoms in which an alkylene group having 4 to 4 carbon atoms and an alkylene group having 2 to 4 carbon atoms are bonded by an ether bond is preferable. Specific examples of the organic solvent, for example,
Alcohols such as methanol, ethanol, propanol, butanol, etc., monoalkyl ethers of ethylene glycol such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Monoalkyl ethers of diethylene glycol such as ether and diethylene glycol monopropyl ether; 1,2-propylene glycol monoalkyl ethers such as 1,2-propylene glycol monomethyl ether; 1,3-propylene glycol monomethyl ether; and 1,3-propylene Glycol monoethyl ether, 1,3-propylene glycol mono Monoalkyl ethers of 1,3-propylene glycol Ropirueteru the like, but not limited thereto. These may be used alone or in combination of two or more.

The composite metal alkoxide compound synthesized by the above method is obtained in a state of being dissolved in an organic solvent, but an organic solvent may be further added. Further, depending on the type of the metal alkoxide compound and the organic solvent to be used, a group represented by the formula: R ¹ O— or R ² OR ³ O—, which is an organic ligand of the formed composite metal alkoxide compound, is combined with the composite metal alkoxide. A group in a dissolving organic solvent: R
^In some cases, ¹ O— or R ² OR ³ O— may be the same, and as a result of transesterification, they may be different from each other. However, when the carbon number of R ³ of the organic ligand is 4 or more, it is preferable that R ³ of the organic solvent is different from that of the organic ligand in terms of application. The concentration of the composite metal alkoxide compound in the organic solvent solution is preferably in the range of 0.01 to 10M, and more preferably 0.05 to 2.0M.

[0010] The organic solvent solution of the composite metal alkoxide compound obtained as described above is hydrolyzed by adding water and an inorganic catalyst or acetic acid, and then the obtained partially hydrolyzed solution is coated on a substrate. To form a thin film. In the present invention, when performing this hydrolysis, the molar ratio of the composite metal alkoxide containing A and B to water is from 1: 0.5 to
The molar ratio of water and the composite metal alkoxide of A or B to the inorganic catalyst or acetic acid is 1: 3.
It is necessary to add an inorganic catalyst or acetic acid so that the ratio becomes 15 to 1: 0.5 (range (2) in FIG. 1), and carry out the hydrolysis reaction at a temperature of 50 ° C. to 150 ° C. When the hydrolysis reaction is performed under such conditions, the crystallization temperature of the thin film is low, and the coating solution does not gel. On the other hand, the conventional case where the amount of water is smaller than the above range (FIG. 1)
In the range (1)), the hydrolysis reaction does not easily proceed, the crystallization temperature is high, and when the amount of water is too large (range (3) in FIG. 1), gelation or precipitation occurs during the reaction. Things happen. When the amount of the inorganic catalyst or acetic acid is too small (range (1) in FIG. 1), the hydrolysis reaction does not easily proceed, and when it is too large, the hydrolysis reaction proceeds rapidly and gelation occurs. As the inorganic catalyst, ammonia, nitric acid and hydrochloric acid are used. Among them, it is particularly effective to use ammonia in order to obtain a dense thin film.

As a substrate on which the partial hydrolysis solution obtained as described above is applied, any substrate can be used as long as it can be applied to a target device.
ITO / SiO ₂ glass, Pt / Ti / SiO ₂ / S
i, Al ₂ O _{3 and the} like can be used. As a method of applying the above partial hydrolysis solution on a substrate, a spin coating method,
A dipping method, a spray method, a screen printing method, an inkjet method, or the like can be used. The applied substrate is subjected to a heat treatment. That is, the substrate is heated at a heating rate of 0.1 to 500 ° C./sec, and the coating layer is thermally decomposed at a temperature of 100 to 500 ° C. where crystallization does not occur.
The oxide thin film is crystallized in a temperature range of 0 ° C to 800 ° C. When the application is repeated, after application,
The substrate is heated at a heating rate of 500 ° C./sec.
The coating layer is thermally decomposed in a temperature range of 00 ° C. where crystallization does not occur. After repeating this application and thermal decomposition a predetermined number of times, 2
The oxide thin film is crystallized in a temperature range of 00 ° C to 800 ° C. This heat treatment forms an oxide thin film.

[0012]

In the present invention, the precursor formed by forcibly partially hydrolyzing the mixture by adding a specific amount of water and an inorganic catalyst or acetic acid as described above, and heating the resultant mixture is converted into the oxidized compound formed in the final stage. It is considered that since the structure is close to the structure of the substance ABO ₃ , it is easily crystallized. Further, this partial hydrolysis solution is extremely stable against gelling, the structure of the precursor can be controlled, and a thin film can be formed stably.

[0013]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. Example 1 Ti (OiC ₃ H ₇ ) ₄ was dissolved in ethylene glycol monoethyl ether dehydrated with a molecular sieve to 0.6 M, and the solution was stirred at 135 ° C. for 2 hours.
Distilled for hours. The molar ratio of Sr to Ti is 1: 1 in this solution.
Sr (OC ₂ H ₅ ) ₂ was added to obtain a 0.6 M solution. Next, this solution was distilled at 135 ° C. for 2 hours with stirring, and further refluxed for 18 hours to obtain a composite metal alkoxide: SrTi (OC ₂ H ₄ OC ₂ H ₅ ) ₆ . This alcohol substitution reaction was confirmed by the ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. Further, to this solution were added water having a molar ratio to Ti of 1: 2 and ammonia having a molar ratio of 1: 0.2, followed by stirring at 100 ° C. for 3 hours to obtain a uniform partial hydrolysis solution. This solution was spin-coated on a Pt / Ti / SiO ₂ / Si substrate, then heated at a rate of 10 ° C./sec and held at 300 ° C. for 2 minutes and 425 ° C. for 30 minutes. The obtained SrTiO ₃ thin film was composed of a single perovskite phase, and its surface was optically smooth and transparent.
Further, Pt was vapor-deposited on the thin film as a counter electrode, and the relative dielectric constant of the thin film was measured.

Comparative Example 1 Ti (OiC ₃ H ₇ ) ₄ was dissolved in ethylene glycol monoethyl ether dehydrated with a molecular sieve to 0.6 M, and the solution was stirred at 135 ° C. for 2 hours.
Distilled for hours. The molar ratio of Sr to Ti is 1: 1 in this solution.
Sr (OC ₂ H ₅ ) ₂ was added to obtain a 0.6 M solution. Next, this solution was distilled at 135 ° C. for 2 hours with stirring, and further refluxed for 18 hours to obtain a composite metal alkoxide: SrTi (OC ₂ H ₄ OC ₂ H ₅ ) ₆ . This alcohol substitution reaction was confirmed by the ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. This solution was added to Pt / Ti / SiO ₂
/ Si substrate, followed by heating at a rate of 10 ° C / sec, 300 ° C for 2 minutes and 425 ° C for 30 minutes.
Hold for minutes. The surface of the obtained thin film was optically smooth and transparent, but was in an amorphous state as a result of X-ray diffraction.

Example 2 A thin film was prepared in the same manner as in Example 1 except that nitric acid was used instead of ammonia as the inorganic catalyst. The obtained SrTiO ₃ thin film was composed of a single phase of perovskite. It was optically smooth and transparent. Example 3 Pb (OOCCH ₃ ) ₂ and Ti (OiC
₃ H ₇ ) ₄ was dissolved in ethylene glycol monomethyl ether dehydrated with a molecular sieve to 0.6 M,
This solution was distilled at 124 ° C. for 1 hour with stirring and refluxed for 18 hours to obtain a composite metal alkoxide: PbT
iO ₂ (OC ₂ H ₄ OCH ₃ ) ₂ was obtained. This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. Further, water having a molar ratio to Ti of 1: 2 and ammonia having a molar ratio of 1: 0.2 were added to the solution,
Stirring at 3 ° C. for 3 hours gave a uniform partial hydrolysis solution. This solution was spin-coated on a Pt / Ti / SiO ₂ / Si substrate and subsequently heated at a rate of 10 ° C./sec to 300 ° C.
For 2 minutes and 450 ° C. for 30 minutes. The obtained PbTiO ₃ thin film was composed of a single perovskite phase, and its surface was optically smooth and transparent. Furthermore, Pt was deposited as a counter electrode on the thin film, and the relationship between voltage and polarizability was measured. As a result, hysteresis was shown.

Comparative Example 2 Pb (OOCCH ₃ ) ₂ and Ti (OiC)
₃ H ₇ ) ₄ was dissolved in ethylene glycol monomethyl ether dehydrated with a molecular sieve to 0.6 M,
This solution was distilled at 124 ° C. for 1 hour with stirring and refluxed for 18 hours to obtain a composite metal alkoxide: PbT
iO ₂ (OC ₂ H ₄ OCH ₃ ) ₂ was obtained. This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. This solution was spin-coated on a Pt / Ti / SiO ₂ / Si substrate, subsequently heated at a rate of 10 ° C./sec and held at 300 ° C. for 2 minutes and 450 ° C. for 30 minutes. The surface of the obtained thin film was optically smooth and transparent, but was in an amorphous state as a result of X-ray diffraction.

Example 4 LiOC ₂ H ₅ and Nb (OC ₂ H ₅ ) ₅ were dissolved in ethanol dehydrated with a molecular sieve to give 0.5M
The solution was refluxed at 78 ° C. for 24 hours while stirring the solution to obtain a composite metal alkoxide: LiNb (OC ₂ H ₅ ) ₆
I got This solution was a uniform, pale yellow, transparent liquid without precipitates. Further, the molar ratio of this solution to Li is 1:
2 water and 1: 0.2 ammonia 7
The mixture was refluxed at 8 ° C. for 24 hours to obtain a uniform partial hydrolysis solution. This solution was spin-coated on an ITO / SiO ₂ glass substrate, and then heated at a rate of 10 ° C./sec.
C. for 2 minutes and 400.degree. C. for 30 minutes. The obtained thin film LiNbO ₃ had good crystallinity, and the surface was optically smooth and transparent.

Comparative Example 3 LiOC ₂ H ₅ and Nb (OC ₂ H ₅ ) ₅ were dissolved in ethanol dehydrated with a molecular sieve to 0.5 M, and the solution was refluxed at 78 ° C. for 24 hours with stirring. A composite metal alkoxide: LiNb (OC ₂ H ₅ ) ₆ was obtained. This solution was a uniform, pale yellow, transparent liquid without precipitates. This solution was spin-coated on an ITO / SiO ₂ glass substrate and subsequently heated at a rate of 10 ° C./sec.
Hold at 300 ° C. for 2 minutes and 400 ° C. for 30 minutes.
The surface of the obtained thin film was optically smooth and transparent, but was in an amorphous state as a result of X-ray diffraction.

COMPARATIVE EXAMPLE 4 Ti (OiC ₃ H ₇ ) ₄ was dissolved in ethylene glycol monomethyl ether dehydrated with a molecular sieve to 0.6 M, and this solution was stirred at 135 ° C. for 2 hours. Distilled. To this solution was added Sr (OC ₂ H ₅ ) ₂ so that the molar ratio of Sr to Ti was 1: 1.
A 6M solution was obtained. Next, the solution was stirred for 135 minutes.
Distilled at 2 ° C. for 2 hours and refluxed for 18 hours to obtain a composite metal alkoxide: SrTi (OC ₂ H ₄ OC ₂ H ₅ ) ₆
I got This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. Further, to this solution, water having a molar ratio with Ti of 1: 1 and ammonia having a molar ratio of 1: 0.1 were added, and the mixture was stirred at 100 ° C. for 3 hours to obtain a uniform partial hydrolysis solution. This solution was converted to Pt / Ti / SiO ₂ /
The substrate was spin-coated on a Si substrate, subsequently heated at a rate of 10 ° C./sec, and kept at 300 ° C. for 2 minutes and at 400 ° C. for 30 minutes. The obtained SrTiO ₃ thin film was in an amorphous state. Further, when the heating temperature was examined, a high temperature of 550 ° C. or higher was required to obtain a perovskite single phase.

Comparative Example 5 Ti (OiC ₃ H ₇ ) ₄ was dissolved in ethylene glycol monomethyl ether dehydrated with a molecular sieve to 0.6 M, and this solution was stirred at 135 ° C. for 2 hours. Distilled. To this solution was added Sr (OC ₂ H ₅ ) ₂ so that the molar ratio of Sr to Ti was 1: 1.
A 6M solution was obtained. Next, the solution was stirred for 135 minutes.
Distilled at 2 ° C. for 2 hours and refluxed for 18 hours to obtain a composite metal alkoxide: SrTi (OC ₂ H ₄ OC ₂ H ₅ ) ₆
I got This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a uniform, light brown, transparent liquid without any precipitate. Further, to this solution, water having a molar ratio to Ti of 1: 5 and ammonia having a molar ratio of 1: 0.4 were added, and the mixture was stirred at 100 ° C. for 3 hours. Could not be obtained.
Therefore, subsequent experiments were stopped.

[0021]

According to the present invention, as described above, the general formula: AB
In producing an oxide thin film represented by O ₃ (where A and B have the same meanings as described above), a specific amount of water and an inorganic catalyst are added to an organic solvent solution of a composite metal alkoxide compound containing A and B. Alternatively, since an oxide thin film which has been subjected to a hydrolysis reaction by adding acetic acid in advance is used, a uniform and excellent stoichiometric oxide thin film can be formed at a low temperature. Therefore, the perovskite oxide thin film produced by the present invention can be used as a thin film capacitor and an oxide thin film that can be used for capacitors, piezoelectrics, pyroelectrics, and the like.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the relationship between the molar ratio of water and an inorganic catalyst or acetic acid to A and B for hydrolysis reaction added to a metal alkoxide for preparing an ABO ₃ type oxide thin film.

[Explanation of symbols]

(1) A range generally used for producing an ABO ₃ type oxide thin film by a conventional sol-gel method, (2)
... range in the present invention, (3) ... general range in which gelation occurs.

Claims (5)

(57) [Claims] 1. A general formula: ABO ₃ (A is IA group, IIA
, An element selected from group IIIA, group IVB and group VB, and B is an element selected from group IVA and group VA), the composite metal containing the elements: A and B In the organic solvent solution of the alkoxide compound, the molar ratio of the composite metal alkoxide compound and water is 1:
Water in an amount of 0.5 to 1: 3 and a molar ratio of the composite metal alkoxide compound to the inorganic catalyst or acetic acid of 1:
A method for producing an oxide thin film, comprising adding an inorganic catalyst or acetic acid in an amount of 0.15 to 1: 0.5, hydrolyzing, applying the resultant onto a substrate to form a thin film, and then performing heat treatment. . 2. The method according to claim 1, wherein the hydrolysis is performed at a temperature of 50 ° C. to 150 ° C. The organic ligand wherein the composite metal alkoxide compound has the formula: in R ¹ O-or R ² OR ³ O- (wherein, R ¹
And R ² represent an aliphatic hydrocarbon group, and R ³ represents a divalent aliphatic hydrocarbon group which may have an ether bond. 2. The method for producing an oxide thin film according to claim 1, wherein: 4. The organic solvent has the formula: R ¹ OH or R ² O.
R ³ OH (wherein R ¹ and R ² represent an aliphatic hydrocarbon group, and R ³ represents a divalent aliphatic hydrocarbon group which may have an ether bond). The method for producing an oxide thin film according to claim 1, wherein: 5. The method according to claim 1, wherein ammonia is used as the inorganic catalyst.