JPH07315810A - Production of oxide thin film - Google Patents

Abstract

PURPOSE:To provide a method for stably producing an uniform oxide thin film, capable of utilizing for thin film condensers, capacitors, piezoelectric substances, pyroelectric substances, etc., and excellent in stoichiometric properties at a low temperature on a substrate using an organometallic compound. CONSTITUTION:In this method for producing an oxide thin film expressed by the general formula, ABO3 (A is an element selected from groups IA, IIA, IIIA, IVB and VB; B is an element selected from groups IVA and VA), water in such amount as to give (1:0.5) to (1:3) molar ratio of the complex metal alkoxide compound containing the elements A and B to water and an inorganic catalyst or acetic acid in such amount as to give (1:0.15) to (1:0.5) molar ratio of the composite metal alkoxide compound to the inorganic catalyst or acetic acid are added to an organic solvent solution of the complex metal alkoxide compound to hydrolyze the complex metal alkoxide compound and the hydrolyzed compound is applied onto a substrate to form a thin film and the thin film is heat-treated.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a method for producing an oxide thin film,
A film is formed by a dry process such as a sputtering method or a vacuum evaporation method, or a film is formed by a wet process such as a sol-gel method. However, in case of film formation by dry process,
Since these devices are very expensive and the vapor pressures differ for each element, it is not possible to stably produce thin films with excellent stoichiometry, crystallinity deteriorates, and productivity is low. It has a drawback of high cost and is far from practical use. On the other hand, the sol-gel method using an organometallic compound has advantages in precise chemical composition control, molecular level uniformity, low process temperature, large area, low equipment cost, etc. It is being appreciated. For example, Japanese Patent Publication 6
In JP-A 2-27482, a solution containing an organometallic compound is applied on a glass substrate and dried in air at room temperature for 30 minutes and further in a thermostat bath at 110 ° C. for 30 minutes to complete hydrolysis. Then, a method of producing an oxide thin film by firing at a temperature of 550 to 800 ° C. while forcibly introducing steam in an electric furnace has been proposed. However,
The process exemplified by this method has a problem that a high temperature is required for crystallization of a thin film because hydrolysis is not performed before coating. Further, in JP-A-4-19911, lead titanate is prepared by using a solution prepared by dissolving a metal organic compound of lead, lanthanum, titanium and zirconium in an organic solvent, and then adding a stabilizer and a predetermined amount of water. A method of forming a ferroelectric thin film of (PT), lead zirconate titanate (PZT), PZT added with a third component, and lead zirconate titanate titanate (PLZT) has been proposed. However,
Since the thin film produced by this method utilizes hydrolysis by only 0.1 to 1.5 mol of water per mol of metal atom, there is a problem that crystallization of the thin film requires high temperature. In addition, Mat. Res. Soc. Symp. P
roc. , Vol. 1,200, p173-178, water and an acid or an alkali are added to a solution based on an alkoxide to partially hydrolyze it, which is coated on a Si substrate and heat-treated to prepare a Pb-containing complex oxide thin film. It is described to do. However, under the conditions specifically described therein, there is a problem that crystallization requires a high temperature.

[0003]

Many of the above-mentioned oxides that have been proposed so far can be used as a ferroelectric thin film, and the ferroelectric thin film is a ferroelectric substance having a ferroelectric property and a piezoelectric property. It has been used in many fields of electronics due to its many properties such as electrical conductivity, pyroelectricity, and electro-optic effect. In recent years, the application of DRAM (Dynamic RAM) to memory cells has been attracting 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 circumstances. That is, the object of the present invention is to stabilize an oxide thin film, which is uniform and excellent in stoichiometry and which can be used for a thin film capacitor, a piezoelectric body, a pyroelectric body, etc., on a substrate using an organometallic compound at low temperature. To provide a manufacturing method.

[0004]

Means for Solving the Problems As a result of investigations, the present inventors have previously hydrolyzed a solution of a complex metal alkoxide compound in an organic solvent by adding a specific amount of water and an inorganic catalyst or acetic acid and heating the solution. After that, it was found that when a thin film was formed by coating on a substrate and then heat-treated, a uniform oxide film having excellent stoichiometry could be produced at low temperature, and the present invention was completed. That is, the present invention has the general formula:
In the method for producing an oxide thin film represented by ABO ₃ (A is an element selected from Group IA, Group IIA, Group IIIA, Group IVB and Group VB, and B is an element selected from Group IVA and Group VA), In an organic solvent solution of a complex metal alkoxide compound containing the elements A and B, an amount of water such that the molar ratio of the complex metal alkoxide compound to water is 1: 0.5 to 1: 3, and the complex metal alkoxide compound. Inorganic catalyst or acetic acid in a molar ratio of 1: 0.15 to 1: 0.5 is added, and after being hydrolyzed, it is applied on a substrate to form a thin film, and then heat treated. Is characterized by.

The present invention will be described in detail below. In the present invention, in the oxide represented by the general formula: ABO ₃ ,
Is IA, IIA, IIIA, IVB and V of the Periodic Table
It represents an element selected from Group B, and specifically, Li,
K, Mg, Sr, Ba, La, Pb and Bi are mentioned, and B represents an element selected from Group IVA and Group VA of the Periodic Table, specifically, Ti, Zr, Nb and Ta. Can be given.

The organic ligand of the complex metal alkoxide compound containing A and B has the formula: R ¹ O- or R ² O
(In the formula, R ¹ and R ² represents an aliphatic hydrocarbon group, R ³ represents. A divalent aliphatic hydrocarbon group which may have an ether bond) R ³ O-is selected from 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, From the point of, it is preferable. Specific examples of the organic ligand include C as R ¹ O-.
₂ H ₅ O-, C ₃ H ₇ O-, C ₄ H ₉ O-, etc.
The _{^{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-
Etc.

In the present invention, the composite metal alkoxide compound is a metal alkoxide compound containing A and a metal alkoxide compound containing B in a predetermined composition, represented by the 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. ) In an organic solvent represented by), it can be synthesized by distillation and reflux.

In the organic solvent represented by the above general formula,
The aliphatic hydrocarbon group for R ¹ and R ² has 1 carbon atom
~ 4 alkyl groups are preferred, and R ³ has 2 carbon atoms.
A alkylene group having 4 to 4 carbon atoms and a divalent group having 4 to 8 carbon atoms in which an alkylene group having 2 to 4 carbon atoms is bonded by an ether bond are preferable. Specific examples of the organic solvent include, for example,
Alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether and other ethylene glycol monoalkyl ethers, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether Ether, diethylene glycol monoalkyl ethers such as diethylene glycol monopropyl ether, 1,2-propylene glycol monoalkyl ethers such as 1,2-propylene glycol monomethyl ether, 1,3-propylene glycol monomethyl ether, 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 kind of the metal alkoxide compound used and the organic solvent, a group of the formula: R ¹ O— or R ² OR ³ O—, which is an organic ligand of the formed complex metal alkoxide compound, and a complex metal alkoxide are used. Group in Dissolving Organic Solvent: R
¹ O- or R ² OR ³ O- may be the same or different as a result of a transesterification reaction, but they may be either case. However, when the number of carbon atoms of the R ³ in the organic ligand is 4 or more, R ³ of the organic solvent, different person from that of the organic ligand preferably on the coating. The concentration of the composite metal alkoxide compound in the organic solvent solution is preferably 0.01 to 10 M, and more preferably 0.05 to 2.0 M.

An 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 applied onto a substrate. To form a thin film. In the present invention, when this hydrolysis is carried out, the molar ratio of the composite metal alkoxide containing A and B to water is 1: 0.5 to.
The molar ratio of water and the mixed metal alkoxide of A or B to the inorganic catalyst or acetic acid is 1: 0.
It is necessary to add an inorganic catalyst or acetic acid having a ratio of 15 to 1: 0.5 (range (2) in FIG. 1) and carry out the hydrolysis reaction at a temperature of 50 to 150 ° C. When the hydrolysis reaction is carried out under such conditions, the crystallization temperature of the thin film is low and gelling of the coating solution does not occur. On the other hand, in the conventional case where the amount of water is smaller than the above range (see FIG.
In the range (1)), the hydrolysis reaction is difficult to 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. A thing arises. Further, when the amount of the inorganic catalyst or acetic acid is too small (range (1) in FIG. 1), the hydrolysis reaction is difficult to proceed, and when the amount is too large, the hydrolysis reaction rapidly proceeds and gelation occurs. Ammonia, nitric acid, and hydrochloric acid are used as the inorganic catalyst. Of these, it is particularly effective to use ammonia in order to obtain a dense thin film.

As the substrate to which the partially hydrolyzed 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 or the like can be used. As a method of applying the above partial hydrolysis solution onto the 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 coated substrate is heat-treated. That is, the substrate is heated at a heating rate of 0.1 to 500 ° C./sec, the coating layer is thermally decomposed in a temperature range of 100 to 500 ° C. where crystallization does not occur, and then 20
The oxide thin film is crystallized in the temperature range of 0 ° C to 800 ° C. When applying repeatedly, after applying,
The substrate is heated at a temperature rising rate of 500 ° C./sec to 100 ° C. to 5 ° C.
The coating layer is thermally decomposed in a temperature range of 00 ° C. where crystallization does not occur. After repeating this coating and thermal decomposition a predetermined number of times, 2
The oxide thin film is crystallized in the 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 partial hydrolysis by adding and heating the specific amount of water and the inorganic catalyst or acetic acid as described above is oxidized by the final step. Since it has a structure close to that of the product ABO ₃ , it is considered that the product is easily crystallized. Further, this partially hydrolyzed solution is extremely stable against gelation, the structure of the precursor can be controlled, and a thin film can be stably formed.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 Ti (O-i-C 3 H 7) 4 and was dissolved in ethylene glycol monoethyl ether which had been dehydrated by molecular sieve 0.6M, and the solution, at stirring 135 ° C. 2
Distilled for hours. The solution has a molar ratio of Sr to Ti of 1: 1.
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 ¹ H NMR spectrum. This solution was a transparent liquid which was uniform and light brown with no precipitate. Further, water having a molar ratio with Ti of 1: 2 and ammonia having a molar ratio of 1: 0.2 were added to this solution, and the mixture was stirred at 100 ° C. for 3 hours to obtain a uniform partially hydrolyzed solution. This solution was spin-coated on a Pt / Ti / SiO ₂ / Si substrate and subsequently 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 consisted of a perovskite single phase, and its surface was optically smooth and transparent.
Further, Pt was vapor-deposited on the upper portion of the thin film as a counter electrode, and the relative permittivity of the thin film was measured to obtain 100.

[0014] was dissolved Comparative Example 1 Ti (O-i-C 3 H 7) 4 ethylene glycol monoethyl ether which had been dehydrated by molecular sieve and 0.6M, and the solution, at stirring 135 ° C. 2
Distilled for hours. The solution has a molar ratio of Sr to Ti of 1: 1.
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 while 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 ¹ H NMR spectrum. This solution was a transparent liquid which was uniform and light brown with no precipitate. This solution is Pt / Ti / SiO ₂
/ Si substrate is spin-coated and then heated at a rate of 10 ° C / sec for 2 minutes at 300 ° C and 30 at 425 ° C.
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 consisted of a perovskite single phase, and its surface was It was optically smooth and transparent. Example ₃ Pb (OOCCH 3) ₂ and Ti (O-i-C
₃ H ₇ ) ₄ was dissolved in ethylene glycol monomethyl ether dehydrated with molecular sieves to make 0.6M,
This solution was distilled at 124 ° C. for 1 hour with stirring, and refluxed for 18 hours to obtain a mixed 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 transparent liquid which was uniform and light brown with no precipitate. Furthermore, water having a molar ratio with Ti of 1: 2 and ammonia having a molar ratio of 1: 0.2 were added to the solution, and 60
The mixture was stirred at 0 ° C. for 3 hours to obtain 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.
2 minutes and 450 ° C. for 30 minutes. The obtained PbTiO ₃ thin film consisted of a perovskite single phase, and its surface was optically smooth and transparent. Furthermore, when Pt was vapor-deposited as a counter electrode on the thin film and the relationship between the voltage and the polarizability was measured, 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 molecular sieves to make 0.6M,
This solution was distilled at 124 ° C. for 1 hour with stirring, and refluxed for 18 hours to obtain a mixed 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 transparent liquid which was uniform and light brown with no precipitate. 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 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 molecular sieves to give 0.5M.
Then, the solution was refluxed at 78 ° C. for 24 hours with stirring, and the mixed metal alkoxide: LiNb (OC ₂ H ₅ ) ₆
Got This solution was a uniform, light yellow transparent liquid without any precipitate. Furthermore, the molar ratio of Li to this solution is 1:
Add 2 parts water and 1: 0.2 ammonia to add 7
The mixture was refluxed at 8 ° C. for 24 hours to obtain a uniform partially hydrolyzed solution. This solution was spin-coated on an ITO / SiO ₂ glass substrate and subsequently heated at a rate of 10 ° C./sec to give 300
Hold at 2 ° C for 2 minutes and 400 ° C for 30 minutes. The obtained thin film LiNbO ₃ had good crystallinity, and its 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 molecular sieves to make 0.5 M, and this solution was refluxed at 78 ° C. for 24 hours while stirring. A composite metal alkoxide: LiNb (OC ₂ H ₅ ) ₆ was obtained. This solution was a uniform, light yellow transparent liquid without any precipitate. This solution was spin-coated on an ITO / SiO ₂ glass substrate and subsequently heated at a rate of 10 ° C./second,
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.

[0019] Comparative Example 4 Ti (O-i-C 3 H 7) 4 was dissolved in ethylene glycol monomethyl ether which had been dehydrated by molecular sieve and 0.6M, and the solution, 2 hours at 135 ° C. with stirring Distilled. To this solution, Sr (OC ₂ H ₅ ) ₂ was added so that the molar ratio of Sr and Ti was 1: 1, and
A 6M solution was obtained. Then, while stirring this solution, 135
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
Got This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a transparent liquid which was uniform and light brown with no precipitate. Further, water having a molar ratio with Ti of 1: 1 and ammonia having a molar ratio of 1: 0.1 were added to this solution, and the mixture was stirred at 100 ° C. for 3 hours to obtain a uniform partially hydrolyzed solution. This solution is Pt / Ti / SiO ₂ /
It was spin-coated on a Si substrate, subsequently heated at a rate of 10 ° C./sec, and held at 300 ° C. for 2 minutes and 400 ° C. for 30 minutes. The obtained SrTiO ₃ thin film was in an amorphous state. Furthermore, when the heating temperature was examined, a high temperature of 550 ° C. or higher was required to obtain the perovskite single phase.

[0020] Comparative Example 5 Ti and _{(O-i-C 3 H} 7) 4 was dissolved in ethylene glycol monomethyl ether which had been dehydrated by molecular sieve 0.6M, 2 h the solution, while stirring 135 ° C. Distilled. To this solution, Sr (OC ₂ H ₅ ) ₂ was added so that the molar ratio of Sr and Ti was 1: 1, and
A 6M solution was obtained. Then, while stirring this solution, 135
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
Got This alcohol substitution reaction was confirmed by ¹ H NMR spectrum. This solution was a transparent liquid which was uniform and light brown with no precipitate. Further, water having a molar ratio with Ti of 1: 5 and ammonia having a ratio of 1: 0.4 were added to this solution, and the mixture was stirred at 100 ° C. for 3 hours. As a result, the solution became cloudy and a uniform solution was obtained. I couldn't get it.
Therefore, the subsequent experiments were stopped.

[0021]

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

[Brief description of drawings]

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

[Explanation of symbols]

(1) ... A range generally used in manufacturing 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)

[Claims] 1. A general formula: ABO ₃ (A is a group IA, IIA
Group A, an element selected from the group IIIA, the group IVB and the group VB, and B is an element selected from the group IVA and the group VA), in the method for producing an oxide thin film, a composite metal containing elements A and B. In the organic solvent solution of the alkoxide compound, the mixed metal alkoxide compound and water have a molar ratio of 1:
The amount of water is 0.5 to 1: 3, and the molar ratio of the complex metal alkoxide compound to the inorganic catalyst or acetic acid is 1 :.
A method for producing an oxide thin film, which comprises adding an inorganic catalyst or acetic acid in an amount of 0.15 to 1: 0.5, hydrolyzing the same, coating the same on a substrate to form a thin film, and then performing heat treatment. . 2. The method for producing an oxide thin film according to claim 1, wherein the hydrolysis is carried out 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. ) Are shown, The manufacturing method of the oxide thin film of Claim 1 characterized by the above-mentioned. 4. The organic solvent is of 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, which is characterized in that. 5. The method for producing an oxide thin film according to claim 1, wherein ammonia is used as the inorganic catalyst.