JP2000103693A - Ferroelectric thin film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a defect-free thin film having uniform surface and high quality in high efficiency at a low investment cost by coating a substrate with an organic solvent solution of an organometallic compound such as a metal alkoxide in an atmosphere having a specific humidity and heat-treating the coating film to effect epitaxial growth of the film. SOLUTION: A single crystal substrate such as Al2O3 is coated with an organic solvent solution of an organometallic compound in an atmosphere having a relative humidity controlled to 1-25%RH, preferably about 1-10%RH by introducing dry nitrogen gas, etc. The organometallic compound is a metal alkoxide, metal oxide, etc., of a reaction product of an organic compound with a metal having a boiling point of >=80 deg.C and its organic ligand is preferably expressed by formula R1OR2 (R1 is an aliphatic hydrocarbon group; R2 is a bivalent aliphatic hydrocarbon group which may contain ether bond). The organic solvent is preferably R1OR2OH. A ferroelectric thin film having uniform and smooth surface and free from defect such as crack can be produced by heat-treating the coating film in an oxygen-containing atmosphere at about 300-1200 deg.C to effect epitaxial growth of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial ferroelectric thin film manufactured using a metal organic compound as a raw material and usable for an optical modulation element, an optical switching element, an optical deflection element, a wavelength conversion element, and the like, and a method of manufacturing the same. About.

[0001]

2. Description of the Related Art Ferroelectric thin films can be applied to many optical waveguides, such as second harmonic devices, optical switches, and optical modulators, due to the properties of ferroelectric materials, such as excellent nonlinear optical effects and electro-optical effects. Are being considered. Conventionally, as a method of manufacturing a ferroelectric thin film, a vapor phase growth method such as an rf-magnetron sputtering method, an ion beam sputtering method, a laser ablation method, and an MOCVD method has been mainly used. However, the apparatus used for vapor phase growth is very expensive, and has problems of thin film surface properties, composition control, and uniformity, and a ferroelectric thin film of a practical level has not yet been obtained.

On the other hand, a ferroelectric thin film is obtained by applying an organometallic compound having advantages in terms of precise chemical composition control, lowering the temperature of a process, uniformity, low equipment cost, etc. to a substrate and then heating the substrate. A method generally called a sol-gel method is disclosed in Japanese Patent Publication No. 62-27482.
In this method, a ferroelectric thin film having a predetermined thickness can be generally obtained by laminating a ferroelectric thin film having a constant thickness of 50 nm to 200 nm. Because it was only possible to obtain a thin film with low
Light scattering due to crystal grain boundaries and pinholes was too large to be used as an optical waveguide or the like at all.

The present inventors have proposed Mater. Lett. ,
10, 348 (1991), a sol-gel method was used to prepare a complex alkoxide Li [Nb (OC ₂ H ₅ )] ₆ precursor solution using ethyl alcohol as a solvent without hydrolyzing it at all. It has been discovered that a ferroelectric LiNbO ₃ thin film grows epitaxially on a sapphire single crystal substrate by applying and heating it on a crystal substrate. Specifically, as water was added to the complex alkoxide LiNb (OC ₂ H ₅ ) ₆ precursor solution using ethyl alcohol as a solvent, the LiNbO ₃ thin film after firing changed from an oriented film to a polycrystalline film. However, when calcination is performed using a precursor that does not add water and does not undergo hydrolysis, the LiNbO ₃ thin film grows epitaxially at a temperature of only 400 ° C. When the polycrystalline film and the oriented film were fired at a high temperature, the density was greatly reduced by the crystal grain growth and the pore diameter growth. However, the epitaxial LiNbO ₃ film remained in the polycrystalline film and the oriented film even after the crystal grain growth. In comparison, it had a very large sub-grain (a structure having a crystal grain shape, but the orientation of each crystal grain was almost or completely aligned) and had a high density. The epitaxial film showed a higher refractive index than the polycrystalline film and the oriented film, and the other films became opaque after high-temperature crystal grain growth, but were almost transparent. However, a detailed study reveals that epitaxial LiN fired at a temperature of 400 ° C.
The bO ₃ ferroelectric thin film is single crystal and has a smooth surface,
It was found that pores having a diameter of several nanometers were included, so that the density was not sufficiently high and the refractive index was not as high as that of a single crystal. 70
The ferroelectric thin film fired at a temperature of 0 ° C. was a single crystal, had extremely large sub-grain compared to a polycrystalline film and an oriented film, had a high density, and had a refractive index relatively close to that of a single crystal. The film contained some pores, the surface was not optically smooth, and the film was not sufficiently transparent.

On the other hand, the present inventors have proposed an organic compound corresponding to an organic functional group of an organometallic compound as a precursor,
Alternatively, it is possible to rapidly heat the substrate at a temperature rising rate of 1 to 500 ° C./s using an organometallic compound in which the boiling point of the solvent of the precursor at normal pressure is at least 80 ° C. And found that it is very important for suppressing pores, and filed a patent application (Japanese Patent Application Laid-Open No. 07-785).
08). Further, they have found that an extremely smooth epitaxial thin film can be obtained using a buffer layer, and have applied for a patent (Japanese Patent Application Laid-Open No. 09-329722).

However, in these methods, it is necessary to perform application in a low moisture glove box in order to suppress hydrolysis of metal alkoxide and the like, and it is difficult to control the humidity (dew point) in the glove box. In addition, when an application is made in a glove box, there is a problem that the operability is difficult and the production efficiency is low.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances in the above prior art. That is, an object of the present invention is to provide a high-quality ferroelectric thin film having a uniform surface free from peeling, cracking, and dimple-like defects, which can be used for various electronic devices and electronic devices. An object of the present invention is to provide a method of manufacturing a ferroelectric thin film that can be efficiently manufactured at low equipment cost.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when an organic solvent solution of a metal organic compound is applied on a substrate, the relative humidity is not less than 1% RH and not more than 25% RH. By applying and then heat-treating, it is possible to epitaxially grow a ferroelectric thin film having a uniform surface and no defects without using a large-scale device such as a closed glove box, that is, moisture is also reduced. The inventors have found that it does not significantly affect the physical properties of the thin film up to a certain amount, and have achieved the present invention. That is,

<1> A solution of a metal organic compound in an organic solvent is
A ferroelectric thin film obtained by applying a film on a substrate in an atmosphere having a relative humidity of 1% RH or more and 25% RH or less, and then performing a heat treatment to epitaxially grow the film.

<2> A mixture of a plurality of organometallic compounds selected from metal alkoxides, which are reaction products of an organic compound having a boiling point of 80 ° C. or more with a metal, and metal salts, or a mixture thereof. The ferroelectric thin film according to <1>, which is a reaction product.

<3> When the organic ligand of the metal organic compound has the formula R ¹ OR ² O— (where R ¹ represents an aliphatic hydrocarbon group, and R ² may have an ether bond. The ferroelectric thin film according to <1> or <2>, wherein the ferroelectric thin film is a valent aliphatic hydrocarbon group.

<4> The organic solvent has a formula R ¹ OR ² OH (wherein R ¹ represents an aliphatic hydrocarbon group, and R ² represents a divalent aliphatic hydrocarbon group which may have an ether bond). The ferroelectric thin film according to any one of the above <1> to <3>.

<5> The ferroelectric thin film according to any one of <1> to <4>, wherein the surface roughness (Ra) is 5 nm or less.

<6> The ferroelectric thin film according to any one of <1> to <4>, wherein the surface roughness (Ry) is 50 nm or less.

<7> A solution of a metal organic compound in an organic solvent is
This is a method for producing a ferroelectric thin film, wherein a ferroelectric thin film is applied on a substrate in an atmosphere having a relative humidity of 1% RH or more and 25% RH or less, and then heat-treated to epitaxially grow the substrate.

<8> The metal organic compound is a mixture of a plurality of organic metal compounds selected from metal alkoxides and metal salts which are reaction products of an organic compound having a boiling point of 80 ° C. or higher with a metal, or a mixture thereof. <7> The method for producing a ferroelectric thin film according to <7>, wherein the method is a reaction product.

<9> The organic ligand of the metal organic compound is represented by the formula R ¹ OR ² O— (wherein R ¹ represents an aliphatic hydrocarbon group and R ² may have an ether bond. <7> or <8>, which represents a monovalent aliphatic hydrocarbon group.

<10> The organic solvent has the formula R ¹ OR ² OH
(Wherein, R ¹ represents an aliphatic hydrocarbon group, and R ² represents a divalent aliphatic hydrocarbon group optionally having an ether bond). Or a method for producing a ferroelectric thin film described in

<11> By sending dry nitrogen around the coating apparatus, the relative humidity is 1% RH or more and 25% RH.
<7> to above, wherein the atmosphere is controlled to the following.
<10> The method for producing a ferroelectric thin film according to any one of <10>.

According to the method of manufacturing a ferroelectric thin film of the present invention, rapid hydrolysis and dew condensation can be suppressed by performing coating in an atmosphere in which the relative humidity is controlled at 1 to 25% RH. Ferroelectric thin film with industrial quality and production stability because it is possible to efficiently and reproducibly produce a uniform epitaxial thin film free of thin film exfoliation, cracks and dimple defects at low equipment cost. Can be obtained.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The ferroelectric thin film of the present invention is obtained by applying an organic solvent solution of a metal organic compound on a substrate in an atmosphere having a relative humidity of 1% RH or more and 25% RH or less, and then performing a heat treatment to epitaxially grow the substrate. Things.

Surface roughness (Ra) of the ferroelectric thin film of the present invention
Is preferably 5 nm or less, more preferably 3 nm or less, and still more preferably 1 nm or less. Surface roughness (Ra)
However, if it exceeds 5 nm, scattering of light on the surface is large,
There is a possibility that use as an optical waveguide becomes difficult. The surface roughness (Ry) of the ferroelectric thin film of the present invention is preferably 50 nm or less, more preferably 30 nm or less, and more preferably 10 nm or less.
The following are more preferred. Surface roughness (Ry) of 50 nm
When it exceeds, light scattering on the surface is large, and it may be difficult to use it as an optical waveguide.

In the present invention, the surface roughness (Ra) and the surface roughness (Ry) are determined by observing surface irregularities with an atomic force microscope (AFM) according to the method described in JIS-B0601-1994. , You can ask.

Hereinafter, the ferroelectric thin film of the present invention will be described through a manufacturing method. In the method for producing a ferroelectric thin film of the present invention, an organic solvent solution of a metal organic compound is applied to a substrate in an atmosphere having a relative humidity of 1% RH to 25% RH and then heat treated. This is a manufacturing method for epitaxially growing a thin film.

The organic solvent solution of the metal organic compound can be used in any case where a mixture of a plurality of metal organic compounds selected from metal alkoxides and metal salts, or a reaction product thereof is dissolved in an organic solvent. However, it is preferable to use a metal alkoxide that is a reaction product of an organic compound having a boiling point of 80 ° C. or higher and a metal, and a mixture of a plurality of metal organic compounds selected from metal salts, or a reaction product thereof. .

An organic compound having a boiling point of 80 ° C. or higher;
Metal alkoxide, which is a reaction product with metal, and metal
A mixture of a plurality of metal organic compounds selected from salts, or
Such reaction products include, for example, LiOCH_Three,
LiOC_TwoH_Five, LiOC_ThreeH₇, LiOC_FourH₉, K
OCH_Three, KOC_TwoH_Five, KOC_ThreeH₇, KOC
_FourH ₉, Mg (OCH_Three)_Two, Mg (OC_TwoH_Five)_Two,
Mg (OC_ThreeH₇)_Two, Mg (OC_FourH₉)_Two, Sr
(OCH_Three)_Two, Sr (OC_TwoH_Five)_Two, Sr (OC_Three
H₇)_Two, Sr (OC_FourH₉)_Two, Ba (OC
H_Three)_Two, Ba (OC_TwoH_Five)_Two, Ba (OC_ThreeH₇)
_Two, Ba (OC_FourH₉)_Two, Ba (C_TwoH_ThreeO_Two)_Two,
La (OCH_Three)_Three, La (OC_TwoH_Five)_Three, La (O
C_ThreeH₇)_Three, PbOCH _Three)_Two, Pb (OC
_TwoH_Five), Bi (OC_ThreeH₇)_Three, TaOCH_Three)_Five,
Ta (OC_TwoH_Five)_Five, Ta (OC_ThreeH₇)_Five, Ti
(OCH_Three)_Four, Ti (OC_TwoH_Five)_Four, Ti (OC_Three
H₇)_Four, Ti (OC_FourH₉)_Four, Zr (OC
H_Three)_Four, Zr (OC_TwoH_Five)_Four, Zr (OC_ThreeH₇)
_Four, Zr (OC_FourH₉)_Four, Nb (OCH_Three)_Five, Nb
(OC_TwoH_Five)_Five, Nb (OC_ThreeH₇)_Five, Nb (OC
_FourH₉)_FiveMetal alkoxides, such as lead acetate,
Organic coordination such as sumasu, bismuth acetate oxide, lanthanum acetate
Child is CH_ThreeOCO- metal salts having a boiling point of 80 ° C. or lower
Distillation or reflux, or distillation and reflux in the organic compound above
But are not limited to
Not necessarily.

Examples of the organic compound having a temperature of 80 ° C. or higher include an organic solvent represented by R ¹ OH or R ¹ OR ² OH, and an organic solvent represented by R ¹ OR ² OH is preferable. Specific examples of the organic solvent at 80 ° C. or higher include, for example, alcohols such as propanol and butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether such as ethylene glycol monobutyl ether. Monoalkyl ethers of diethylene glycol such as alkyl ethers, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 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, - Although 1,3-propylene glycol monoalkyl ethers such as propylene glycol monopropyl ether and the like, but is not limited thereto. These may be used alone or in combination of two or more.

The organic solvent solution of the metal organic compound is a mixture or a reaction product dissolved in an organic solvent, but a second organic solvent may be further added. Further, depending on the type of the metal organic compound and the organic solvent used, the group represented by R ¹ O— or R ¹ OR ² O— which is an organic ligand of the formed metal organic compound and the metal organic compound are dissolved. The group represented by R ¹ O— or R ¹ OR ² O— in the organic solvent to be formed may be the same or different due to transesterification, but either case may be used.

As the second organic solvent, the same organic solvents as those described above as the organic compound having a temperature of 80 ° C. or higher can be used.

It is preferable that the metal organic compound has R ¹ O— or R ¹ OR ² O— as an organic ligand, and the stability of the metal alkoxide compound solution and the uniformity and denseness of the prepared thin film. In view of the above, it is more preferable to have R ¹ OR ² O—. Specifically, 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—.

As the metal organic compound, specifically,
LiNb (OC_TwoH_Five)₆, LiNb (OC_TwoH_FourOC
H_Three)₆, LiNb (OC_TwoH_FourOC_TwoH_Five)₆, Sr
Ti (OC_TwoH_Five)₆, SrTi (OC_TwoH_FourOC
H_Three)₆, SrTi (OC_TwoH_FourOC_TwoH_Five)₆, (B
a, Sr) Ti (OC_TwoH_Five)₆, (Ba, Sr) Ti
(OC_TwoH_FourOCH_Three)₆, (Ba, Sr) Ti (OC
_TwoH_FourOC_TwoH_Five)₆, PbTiO_Two(C_TwoH_FourOCH
_Three)_Two, PbTiO_Two(C_TwoH_FourOC_TwoH_Five)_Two, Pb
(Zr, Ti) O_Two(C_TwoH_FourOCH_Three)_Two, Pb (Z
r, Ti) O_Two(C _TwoH_FourOC_TwoH_Five)_Two, (Pb, L
a) (Zr, Ti) O_Two(C_TwoH_FourOCH_Three)_Two, (P
b, La) (Zr, Ti) O_Two(C_TwoH_FourOC_TwoH_Five)
_TwoAnd the like.

R ¹ O— and R ¹ O representing the above organic ligands
R ² O— and R ¹ OH and R ¹ representing the organic solvent
In OR ² OH, in the formula, R ¹ represents an aliphatic hydrocarbon group, and R ² represents a divalent aliphatic hydrocarbon group which may have an ether bond. As the aliphatic hydrocarbon group for R ¹ ,
An alkyl group having 1 to 4 carbon atoms is preferred. As R ² ,
An alkylene group having 2 to 4 carbon atoms, a total of 4 to 4 carbon atoms in which the alkylene group having 2 to 4 carbon atoms is bonded by an ether bond;
A divalent group of 8 is preferred.

The concentration of the organic solvent solution of the metal organic compound is preferably about 0.01 to 10 M, more preferably 0.05 to 2.0 M.

According to the method for producing a ferroelectric thin film of the present invention, good epitaxial growth can be achieved by applying the organic solvent solution of the metal organic compound in a state in which hydrolysis is not performed. In some cases, it is effective to apply after hydrolysis.

In the method for producing a ferroelectric thin film according to the present invention, the organic solvent solution of the metal organic compound is mixed with a relative humidity of 1% RH.
In an environment of not less than 25% RH, preferably the relative humidity is 1
Coating on a substrate in an environment of not less than% RH and not more than 10% RH is effective in controlling the environment and in producing a uniform thin film without defects. The relative humidity is 25%
When it is higher than RH, dimple-like defects occur on the surface of the prepared thin film, and a uniform thin film cannot be prepared. Further, when the relative humidity is lower than 1% RH, such a simple device cannot achieve the above, and requires a large-scale device such as a glove box, for example, which increases equipment costs and deteriorates operability. Would.

In the present invention, the relative humidity can be measured by a capacitance type humidity sensor, a polymer sensor, an alumina-based ceramic sensor or the like which is usually commercially available.

The environment where the relative humidity is 1% RH or more and 25% RH or less is preferably controlled by feeding dry air, a gas such as nitrogen or argon to the periphery of the coating apparatus. It is also effective to use a simple device that surrounds the periphery of the coating device with a container as shown in FIG.

The gas such as dried air, nitrogen, argon and the like refers to a gas such as air, nitrogen and argon dried at a dew point of about −50 ° C. or less.

FIG. 1 is a schematic view of an example of a coating apparatus used in the method for producing a ferroelectric thin film of the present invention. The container 3 surrounding the coating apparatus provided with a substrate outlet 5 and a dry gas inlet 4 is provided. This is an apparatus in which a coating apparatus 2 and a substrate 1 are arranged on the coating apparatus 2.

In order to control the relative humidity within the above-mentioned range, it is only necessary to feed dry gas, nitrogen, argon or the like from the dry gas inlet 4, and to control the gas flow rate. Accordingly, it is possible to control the relative humidity within the above range even when the substrate outlet 5 is left open. Since the substrate outlet 5 is thus open, the substrate 1 can be easily taken in and out, and there is no need to attach and detach gloves as in the case of using a glove box. Becomes

As the substrate, any substrate can be used as long as it can be applied to a target element.
For epitaxial growth, for example, Al ₂ O ₃ ,
LiTaO ₃ , MgO, MgAl ₂ O ₄ , ZnO, Sr
Single crystals such as TiO ₃ can be used.

The coating method includes spin coating, dipping, spraying, screen printing, and the like.
An ink jet method and the like can be mentioned. The coating device is not particularly limited, and a known device may be used.

In the method for producing a ferroelectric thin film of the present invention, a ferroelectric thin film can be formed by applying an organic solvent solution of the metal organic compound on a substrate in the above environment and then performing a heat treatment.

The heat treatment is carried out in an atmosphere containing oxygen, preferably in oxygen, at a rate of 0.1 to 1000 ° C./sec.
The amorphous thin film is obtained by heating the substrate at a heating rate of preferably 1 to 100 ° C./sec and thermally decomposing the coating layer in a temperature range of 100 to 500 ° C., preferably 200 to 400 ° C. where crystallization does not occur. To form Furthermore, in an atmosphere containing oxygen, preferably in oxygen, 0.1 to 100
Heat at a heating rate of 0 ° C./sec, preferably 1-100 ° C./sec, and heat at 300-1200 ° C., preferably 40
The ferroelectric thin film is crystallized in a temperature range of 0 to 900 ° C. As these oxygen atmospheres, it is preferable to use an atmosphere dried for at least a certain period of time from the viewpoint of the quality of the obtained thin film, but it is also possible to humidify as necessary. After this crystallization, it is preferable to perform cooling at a cooling rate of 0.01 to 100 ° C./sec. This heat treatment forms a ferroelectric thin film.

[0044]

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) Pb (OOCCH ₃ ) ₂ , L
a (OC ₃ H ₇ (i)) ₃ , Zr (OC ₃ H ₇ (i))
₄ , Ti (OC ₃ H ₇ (i)) ₄ as a starting material and Pb
Is dissolved in 2-methoxyethanol at a ratio of Pb / La / Zr / Ti = 106/9/65/35, which is 15% in excess of the stoichiometric composition with respect to other elements, and is dissolved at 124.5 ° C. for 6 hours. After performing the distillation, reflux was performed for 18 hours,
Finally, a 0.6 M PLZT precursor solution having a Zr + Ti concentration was obtained.

After the obtained precursor solution was passed through a 0.2 μm filter, spin coating was performed on an SrTiO ₃ substrate under an atmosphere controlled at a relative humidity of 25% RH. Next, the substrate was placed in a humidified oxygen atmosphere at 10 ° C /
s, and kept at 350 ° C. for 2 minutes, then 40 ° C.
The temperature was raised at 750 ° C./s and maintained at 750 ° C. for 2 minutes to obtain a PLZT thin film of Example 1 having a thickness of about 100 nm.

The obtained PLZT thin film of Example 1 was evaluated by X-ray diffraction.
01) Only the diffraction peak was shown. Further analysis by an X-ray diffraction pole figure confirmed that the crystal orientations of SrTiO ₃ and PLZT in the substrate plane were the same, and that the thin film was epitaxially grown and had no misoriented plane. When the surface of this thin film was observed with a high-resolution SEM, the surface was extremely uniform and smooth. Further, when the Ra surface roughness was measured with an atomic force microscope (AFM), the Ra roughness was It was only 1 nm or less.

Comparative Example 1 The PLZT of Comparative Example 1 was manufactured in the same manner as in Example 1 except that spin coating was performed on the SrTiO ₃ substrate in the atmosphere (normal laboratory environment) at a relative humidity of 46% RH. A thin film was obtained.

The obtained PLZT thin film of Comparative Example 1 was evaluated by an X-ray diffraction θ-2θ pattern.
Although the T thin film was a thin film preferentially oriented to the (001) plane,
A misoriented plane of the (110) plane was also observed. When the surface of this thin film was observed by AFM, it was found that about 1.
Numerous dimple-shaped defects having a diameter of 3 μm were present.

Comparative Example 2 A PLZT thin film of Comparative Example 2 was obtained in the same manner as in Example 1 except that spin coating was performed on an SrTiO ₃ substrate under an atmosphere in which the relative humidity was controlled to 40% RH.

The obtained thin film of Comparative Example 2 was subjected to X-ray diffraction θ-2.
When evaluated by the θ pattern, this PLZT thin film was a thin film preferentially oriented to the (001) plane.
A misoriented plane of the 0) plane was also observed. When the surface of the thin film was observed by AFM, the surface was found to have a thickness of about 0.9 μm.
Numerous dimple-like defects of diameter existed.

Example 2 A PLZT thin film of Example 2 was obtained in the same manner as in Example 1 except that spin coating was performed on a SrTiO ₃ substrate under a nitrogen atmosphere in which the relative humidity was controlled at 10% RH. .

When the obtained thin film of Example 2 was evaluated by X-ray diffraction, this PLZT thin film showed only a (001) diffraction peak. Further analysis by an X-ray diffraction pole figure confirmed that the crystal orientations of SrTiO ₃ and PLZT in the substrate plane were the same, and that the thin film was epitaxially grown and had no misoriented plane. When the surface of the thin film was observed with a high-resolution SEM, the surface was extremely uniform and smooth. Furthermore, when the Ry surface roughness was measured by an atomic force microscope (AFM), the Ry roughness was It was only 10 nm or less.

(Example 3) In Example 2, the flow rate of the dry nitrogen gas fed into the coating apparatus was further increased, so that the relative humidity around the coating apparatus was controlled to 1% RH in a nitrogen atmosphere, and SrTiO _{3 was used.} Except that spin coating was performed on the substrate, the P
An LZT thin film was obtained.

When the obtained thin film of Example 3 was evaluated by X-ray diffraction, this PLZT thin film showed only a (001) diffraction peak. Further analysis by an X-ray diffraction pole figure confirmed that the crystal orientations of SrTiO ₃ and PLZT in the substrate plane were the same, and that the thin film was epitaxially grown and had no misoriented plane. When the surface of this thin film was observed with a high-resolution SEM, the surface was extremely uniform and smooth. Further, when the Ra surface roughness was measured with an atomic force microscope (AFM), the Ra roughness was It was only 1 nm or less.

Comparative Example 3 A PLZT thin film of Comparative Example 3 was obtained in the same manner as in Example 1, except that spin coating was performed on a SrTiO ₃ substrate under a nitrogen atmosphere in which the relative humidity was controlled at 30% RH. .

When the obtained thin film of Comparative Example 3 was evaluated by X-ray diffraction, this PLZT thin film showed only a (001) diffraction peak. Further analysis by an X-ray diffraction pole figure confirmed that the crystal orientations of SrTiO ₃ and PLZT in the substrate plane were the same, and that the thin film was epitaxially grown and had no misoriented plane. However, when the surface of this thin film was observed by AFM, numerous dimple-like defects having a diameter of about 0.4 μm were found on the surface.

FIG. 2 shows the relationship between the relative humidity (% RH) at the time of coating on the surfaces of the PLZT thin films obtained in Examples 1 to 3 and Comparative Examples 1 to 3 and the diameter of dimple-like defects (μm). Show. 2, the surface of the thin film obtained by performing the spin coating in an atmosphere having a relative humidity of 25% RH or less was uniform, smooth, and free from defects. On the other hand, defects were present on the surface of the thin film obtained by performing spin coating in an atmosphere having a relative humidity of 30% RH or more, and the size (diameter) of the thin film increased with an increase in the relative humidity.

Example 4 Equimolar amounts of LiOC ₂ H ₅ and Nb (OC ₂ H ₅ ) ₅ were dissolved in 2-methoxyethanol dehydrated by molecular sieve to obtain a 0.6 M solution. This solution was distilled at 124.5 ° C. for 2 hours with stirring, and refluxed for 22 hours to obtain a double alkoxide Li [Nb (OC ₂ H ₄ OCH ₃ )] ₆ . This alcohol substitution reaction was confirmed by a ¹ H-NMR spectrum. Thereafter, this solution was passed through a 0.2 μm filter in an atmosphere where the relative humidity was controlled at 5% RH, and the sapphire (0001) single crystal substrate (α-Al ₂ O ₃ (00
01)) was spin-coated at 2000 rpm. The spin-coated substrate was heated at 20 ° C./s in a dry oxygen atmosphere and held at 300 ° C.
The temperature was kept at 00 ° C. for 90 minutes, and finally, the electric furnace was turned off and cooled. Thereby, the Li of Example 4 having a thickness of about 100 nm
An NbO ₃ thin film was obtained.

The obtained LiNbO ₃ thin film of Example 4 was
Evaluation by line diffraction showed only a (0006) diffraction peak due to the (0001) plane. Further analysis by X-ray diffraction pole figure shows that sapphire and LiNbO
The crystal orientation in the substrate plane of No. ₃ was consistent. When the obtained thin film was observed with a high-resolution SEM, the surface was extremely smooth, had no grain boundaries or pores, and was a mirror-like surface such that no contrast could be obtained. Further, when this thin film was observed by AFM, the Ra surface roughness was only 1 nm or less, and no dimple-like defect was observed. FIG. 2 shows the relationship between the relative humidity (% RH) at the time of coating on the surface of the LiNbO ₃ thin film and the diameter (μm) of the dimple-like defect.

Example 5 Equimolar amounts of LiOC ₂ H ₅ and Ta (OC ₂ H ₅ ) ₅ were dissolved in 2-methoxyethanol dehydrated by molecular sieve to obtain a 0.6 M solution. This solution was distilled at 124.5 ° C. for 2 hours with stirring, and further refluxed for 22 hours to obtain a double alkoxide Li [Ta (OC ₂ H ₄ OCH ₃ ) ₆ ]. This alcohol substitution reaction was confirmed by a ¹ H-NMR spectrum. This solution was spin-coated at 2000 rpm on a sapphire (0001) single crystal substrate through a 0.2 μm filter under a nitrogen atmosphere controlled at a relative humidity of 20% RH. The spin-coated substrate is heated at 20 ° C./s in a dry oxygen atmosphere to 300
After holding at 700C, the temperature was held at 700C for 30 minutes, and finally, the electric furnace was turned off and cooled. Thereby, the film thickness is about 100 n.
m of the LiTaO ₃ thin film of Example 5 was obtained.

The obtained LiTaO ₃ thin film of Example 5 was
Evaluation by line diffraction showed only a diffraction peak due to the (0001) plane. Further analysis by the X-ray diffraction pole figure showed that the crystal orientations of sapphire and LiTaO _{3 in} the substrate plane were the same. When the obtained thin film was observed with a high-resolution SEM, it was found that the surface was extremely smooth and had no grain boundaries or pores. Further, when this thin film was observed by AFM, the Ra surface roughness was only 1 nm or less, and no dimple-like defect was observed. FIG. 2 shows the relationship between the relative humidity (% RH) at the time of coating on the surface of the LiTaO ₃ thin film and the diameter (μm) of the dimple-like defect.

As described above, the present invention provides a high-quality ferroelectric thin film having a uniform surface free of thin film peeling, cracks, and dimple-like defects, which can be used for various electronic devices and electronic devices. In addition, it is possible to provide a method of manufacturing a ferroelectric thin film that can efficiently manufacture the ferroelectric thin film at low equipment cost.

[Brief description of the drawings]

FIG. 1 is a schematic view of an entire example of a coating apparatus used in a method for producing a ferroelectric thin film of the present invention.

FIG. 2 is a diagram showing the relationship between the relative humidity during coating and the diameter of dimple-shaped defects on the thin film surfaces of Examples 1 to 5 and Comparative Examples 1 to 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Coating device 3 Container 4 Dry gas inlet 5 Substrate outlet

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomo Takeda 430 Nakaicho Sakai, Ashigara-gun, Kanagawa Green Tech Nakai Inside Fuji Xerox Co., Ltd. Inside

Claims (11)

[Claims] An organic solvent solution of a metal organic compound is applied on a substrate in an atmosphere having a relative humidity of 1% RH or more and 25% RH or less, and then heat treated to obtain an epitaxial growth. Dielectric thin film. 2. A mixture of a plurality of organic metal compounds selected from metal alkoxides, which are reaction products of an organic compound having a boiling point of 80 ° C. or higher with a metal, and metal salts, or a reaction thereof. The ferroelectric thin film according to claim 1, which is a product. 3. An organic ligand of a metal organic compound having the formula R ¹
OR ² O— (wherein, R ¹ represents an aliphatic hydrocarbon group;
² represents a divalent aliphatic hydrocarbon group which may have an ether bond. The ferroelectric thin film according to claim 1 or 2, wherein 4. An organic solvent having the formula R ¹ OR ² OH (wherein
R ¹ represents an aliphatic hydrocarbon group, and R ² represents a divalent aliphatic hydrocarbon group which may have an ether bond. The ferroelectric thin film according to claim 1, wherein 5. The ferroelectric thin film according to claim 1, wherein the surface roughness (Ra) is 5 nm or less. 6. The ferroelectric thin film according to claim 1, which has a surface roughness (Ry) of 50 nm or less. 7. A ferroelectric material characterized in that an organic solvent solution of a metal organic compound is applied on a substrate in an atmosphere having a relative humidity of 1% RH to 25% RH and then heat treated for epitaxial growth. Manufacturing method of thin film. 8. A mixture of a plurality of organometallic compounds selected from metal alkoxides, which are reaction products of an organic compound having a boiling point of 80 ° C. or higher with a metal, and a metal salt, or a reaction thereof. The method for producing a ferroelectric thin film according to claim 7, which is a product. 9. The organic ligand of the metal organic compound is represented by the formula R ¹
OR ² O— (wherein, R ¹ represents an aliphatic hydrocarbon group;
² represents a divalent aliphatic hydrocarbon group which may have an ether bond. The method for producing a ferroelectric thin film according to claim 7 or 8, wherein 10. An organic solvent represented by the formula R ¹ OR ² OH (wherein R ¹ represents an aliphatic hydrocarbon group, and R ² represents a divalent aliphatic hydrocarbon group which may have an ether bond). The method for producing a ferroelectric thin film according to claim 7. 11. An atmosphere having a relative humidity of 1% RH or more and 25% RH or less by sending dry nitrogen around the coating apparatus. Production method of a ferroelectric thin film. [0001]