JP2002047011A - Method of forming compact perovskite metallic oxide thin film and compact perovskite metallic oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form perovskite metallic oxide thin film which can coat with thick film of 0.1 μm or more by once application, and is very compact and excellent in characteristics such as dielectric or conductive characteristics at comparatively low firing temperature of 1000 deg.C or lower. SOLUTION: A method of forming the perovskite metallic oxide thin film comprises the steps where liquid of raw material for forming metallic oxide thin film is applied to a substrate, the metallic oxide is crystallized and the perovskite metallic oxide film is formed by heating; the perovskite metallic oxide obtained from liquid phase part of applying liquid, forms low density film structured with granular crystal of mean grain size 200 nm or less, and compact perovskite metallic oxide thin film is obtained by sintering this low density film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a perovskite-type metal oxide thin film, which can be expected to be applied to various dielectric devices due to its electrical and / or optical properties, by a sol-gel method or the like. The present invention relates to a method for forming a very dense perovskite-type metal oxide thin film at a relatively low sintering temperature, and a dense perovskite-type metal oxide thin film formed by this method.

[0002]

BACKGROUND OF prior art metal oxide thin film, PLZT as specifically doped lanthanum lead zirconate (PZT) and its titanate _{(Pb x La 1-x (} Zr y T
i _1-y ) _{1-X / 4} O ₃ ) or SBT (SrBi
Metal oxide thin film such as ₂ Ta ₂ O ₉ ) has a high dielectric constant,
Due to its excellent ferroelectric properties, application to various dielectric devices is expected. Further, SRO (SrRuO ₃₎ thin film or _{LSCO (La X Sr 1-X} CoO 3) thin film, has attracted attention as an electrode material or the like to its excellent conductive properties, applications to various devices have been expected.

[0003] As a method of forming these metal oxide thin films, there are a sputtering method, an MOCVD method and the like. As a relatively inexpensive and simple method of forming a thin film, there is a sol-gel method of applying an organic metal solution to a substrate. is there.

In the sol-gel method, a raw material solution containing a hydrolyzable compound of each component metal as a raw material, a partial hydrolyzate thereof and / or a partial polycondensate thereof is applied to a substrate, and the coating film is dried. Thereafter, the ferroelectric thin film is formed, for example, by heating to about 400 ° C. in the air to form a metal oxide film, and further firing at a temperature higher than the crystallization temperature of the metal oxide to crystallize the film. How to

As a method similar to the sol-gel method, there is an organic metal decomposition (MOD) method. In the MOD method, a raw material solution containing a thermally decomposable organometallic compound, for example, a metal β-diketone complex (for example, metal acetylacetonate) or a carboxylate (for example, acetate) is applied to a substrate, Heating in air or an oxygen-containing atmosphere, etc., causes evaporation of the solvent in the coating film and thermal decomposition of the metal compound to form a metal oxide film, which is then fired at a crystallization temperature or higher to crystallize the film. To Therefore, the film forming operation is almost the same as that of the sol-gel method except for the type of the starting compound.

As described above, since the sol-gel method and the MOD method have the same film forming operation, a method using both of them is also possible. That is, the raw material solution may contain both a hydrolyzable metal compound and a thermally decomposable metal compound. In this case, hydrolysis and thermal decomposition of the raw material compound occur during heating of the coating film, and the metal Oxide forms.

Accordingly, the sol-gel method, MO
The D method and methods using these methods in combination are referred to as “sol-gel method”.

[0008] The sol-gel method and the like have the advantages of being inexpensive, simple, and suitable for mass production.
An excellent feature is that the film thickness is relatively uniform. Therefore, it can be said that this is the most advantageous film forming method for forming a ferroelectric thin film on a relatively flat substrate.

Metal alkoxides or organic acid salts are generally used as an organic metal raw material for the sol-gel method or the like. As the organic solvent for dissolving these organometallic raw materials, alcohols, ethylene glycol derivatives, xylene, toluene and the like can be used.
As an organic solvent for the raw material solution for forming a perovskite oxide thin film, an ethylene glycol derivative is considered to be good, and in particular, ethylene glycol monomethyl ether (2-methoxyethanol) has been widely used (for example, Jp.
nJAppl.Phys.Vol.33 (1994) pp.5196-5200, JP-A-9
-28415 publication).

However, in general, when a film is formed by a sol-gel method using a sol-gel solution using 2-methoxyethanol as an organic solvent, the thickness of a crack-free thin film formed by one coating is at most 0. .About.1 μm (film thickness after annealing), which caused a reduction in production efficiency and an increase in film formation cost.

Accordingly, as a method of increasing the film formation throughput by increasing the film thickness that can be formed by one coating and lowering the film formation cost, 1,3-propanediol (Journal) is used as an organic solvent of the sol-gel liquid. of Materials Sci
ence 30 (1995) pp. 2507-2516), propylene glycol, triethylene glycol (Japanese Patent Application No. 11-24873).
No. 4), acetic acid (J. Appl. Phys. 64 (1988) 2717) and the like have been proposed. With a sol-gel liquid using these solvents, it is possible to form a film with a thickness of 0.1 μm or more by one application.

However, in these sol-gel solutions,
As the thickness of a single applied film is increased, voids tend to be formed and a film having a low density tends to be formed. Further, as the temperature during pre-baking after application is increased, voids are more easily generated. The reduction in the density of the formed thin film causes deterioration in characteristics when applied to electrical and optical devices and electrodes.

In particular, a sol-gel solution using propylene glycol or triethylene glycol as a solvent can provide a dense film even at a film thickness of 0.1 μm or more, but it varies depending on the type of a raw material solution for forming a metal oxide thin film. 0.
When the film thickness is about 5 to 1 μm, voids are generated, and the decrease in density cannot be ignored.

In order to further increase the film thickness that can be applied at one time, a solution obtained by adding fine particles of a perovskite-type metal oxide to a solution in which a metal oxide is dissolved in an organic solvent as a sol-gel liquid and uniformly mixing the solution is used. Although a method using the same has been proposed (Japanese Patent Application Laid-Open No. 6-119811), a thick film can be formed by this method, but voids are generated and a low-density film is obtained.

As another film forming method, there is a screen printing method. This method is a method in which perovskite-type metal oxide powder is mixed with an organic vehicle containing ethyl cellulose and α-terpineol as main components, and the mixture is squeegeeed to form a film on a substrate and fired. Then, it is difficult to obtain a dense film without voids by firing at 1000 ° C. or lower. For this reason, baking at 1000 ° C. or higher is generally required, and there is a disadvantage that a substrate having no heat resistance to a high temperature of 1000 ° C. or higher (for example, a silicon substrate) cannot be used.

[0016]

As described above, according to the conventional method, a thick film having a thickness of 0.1 μm or more is formed by one coating and a dense perovskite-type metal is formed at a relatively low firing temperature of 1000 ° C. or less. An oxide thin film could not be formed.

The present invention solves the above-mentioned conventional problems and can form a thick film having a thickness of 0.1 μm or more by one coating.
Moreover, a method for forming a perovskite-type metal oxide thin film which is extremely dense at a relatively low firing temperature of 1000 ° C. or less and has excellent properties such as dielectric properties or conductive properties, and a dense perovskite formed by this method It is an object to provide a type metal oxide thin film.

[0018]

According to the method of forming a dense perovskite-type metal oxide thin film of the present invention, a raw material coating solution for forming a metal oxide thin film is applied to a substrate, and the metal oxide is formed by heating. In the method for forming a perovskite-type metal oxide thin film by crystallization, the perovskite-type metal oxide obtained from the liquid phase portion of the coating solution has an average particle size of 2
The method is characterized by comprising a first step of forming a low-density film composed of granular crystals of 00 nm or less and a second step of sintering the low-density film.

That is, the present inventors have studied a method of increasing the film formation density in forming a perovskite-type metal oxide thin film by a sol-gel method or the like, and as a result, by crystallizing under a condition that a large amount of voids are formed, By forming a very low-density film composed of fine-grained crystals and sintering the fine-grained crystals of the low-density film at a relatively low temperature of 1000 ° C. or less, a very dense perovskite type It has been found that a metal oxide thin film can be formed.

The details of the mechanism of formation of a dense perovskite-type metal oxide thin film by this method are not clear, but by crystallizing under a condition in which a large amount of voids are formed, a large amount of voids are formed in the grain boundary. (Grain boundaries), a very low-density film composed of fine-grained crystals is formed. Since this low-density film is composed of very fine-grained crystals, the sintering temperature is low. It is considered that the densification can be easily performed.

In the present invention, the firing temperature in the first step is preferably 300 to 1000 ° C., and the firing temperature in the second step is preferably 600 to 1000 ° C.
The step and the second step are preferably performed in one continuous process.

Further, the raw material coating solution for forming a metal oxide thin film may contain perovskite-type metal oxide fine particles, whereby the film thickness which can be formed by one coating can be further increased. .

The dense perovskite-type metal oxide thin film of the present invention is formed by the method of forming a dense perovskite-type metal oxide thin film of the present invention.
It is a perovskite type metal oxide thin film of 0% or less, and realizes various devices with high characteristics at low cost by firing at low temperature.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

As the perovskite-type metal oxide thin film formed in the present invention, a perovskite-type oxide thin film composed of Pb and Zr and / or Ti, in particular, lead zirconate titanate: PZT thin film, PLZT thin film, Ba and / or Or Sr
And a perovskite oxide thin film composed of Ti, such as a BST thin film, an SBT thin film containing Bi, Sr and Ta, an SRO thin film containing Sr and Ru, and an LSCO thin film containing La, Sr and Co.

This oxide material can contain a trace amount of a doping element. Examples of doping elements include C
a, Sr, Ba, Hf, Sn, Th, Y, Sm, Dy,
Ce, Bi, Sb, Nb, Ta, W, Mo, Cr, C
o, Ni, Fe, Cu, Si, Ge, U, Sc, V, P
r, Nd, Eu, Gd, Tb, Ho, Er, Tm, Y
b, Lu, La, and the like, and the content thereof is preferably 0.1 or less in terms of the atomic fraction of metal atoms in the thin film.

The raw material coating liquid for forming a metal oxide thin film used in the present invention is obtained by dissolving a raw material metal compound in an organic solvent.
Carboxylic acids, esters, ketones, ethers, cycloalkanes, aromatic solvents and the like can be mentioned.In particular, when propylene glycol or triethylene glycol is used, it differs depending on the type of the metal compound forming the thin film, A thick film having a thickness of about 0.5 to 1 μm
Crystallization by forming at a high calcining temperature of about ° C or higher is preferable in that a very low-density film composed of fine granular crystals can be formed. It is considered that this is because a large amount of voids are generated during calcination and crystallization. By firing such a low-density film at a temperature of 1000 ° C. or less and sintering the fine granular crystals, a very dense perovskite-type metal oxide thin film is formed.

In this case, as the organic solvent, a single solvent of propylene glycol, a single solvent of triethylene glycol, a mixed catalyst of propylene glycol and triethylene glycol, a mixed solvent of propylene glycol and another organic solvent, triethylene glycol And a mixed solvent of propylene glycol, triethylene glycol and another organic solvent.
When a mixed solvent of propylene glycol and / or triethylene glycol and another organic solvent is used, propylene glycol and / or
Or the proportion of triethylene glycol is 20% by weight or more,
It is particularly preferable that the content be 30% by weight or more.

Other organic solvents that can be used in combination include:
Alcohols other than propylene glycol and / or triethylene glycol, carboxylic acids, esters, ketones,
Examples include ethers, cycloalkanes, and aromatic solvents. Among them, alcohols include ethanol, 1-
Propanol, 2-propanol, 1-butanol, 2
-Alkanols such as butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol and 2-methyl-2-pentanol, cycloalkanols such as cyclohexanol, and Alkoxy alcohols such as 2-methoxyethanol and 1-ethoxy-2-propanol can be used.

Examples of the carboxylic acid solvent include n-
Butyric acid, α-methylbutyric acid, i-valeric acid, 2-ethylbutyric acid,
2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3
-Dimethylbutyric acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentane Acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid and the like.

Examples of the ester solvents include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, and isoamyl acetate. And the like.

The ketone solvents include acetone, methyl ethyl ethone, and methyl isobutyl ketone. The ether solvents include chain ethers such as dimethyl ether and diethyl ether, and cyclic ethers such as tetrahydrofuran and dioxane. As the cycloalkane-based solvent, cycloheptane,
Cyclohexane and the like, and aromatic solvents include toluene, xylene and the like.

As the starting metal compound, a metal compound containing each component metal or two or more component metals, a partial hydrolyzate thereof and a partial polycondensate thereof can be used, and a particularly preferred metal compound is a hydrolyzable metal compound. Alternatively, it is a thermally decomposable organometallic compound. For example, alkoxides, organic acid salts, β-diketone complexes and the like are typical examples, but various other complexes such as amine complexes can be used for metal complexes. Here, examples of the β-diketone include acetylacetone (= 2,4-pentanedione), heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, and benzoylacetone.

Specific examples of the organometallic compound suitable as a raw material are as follows. As the lead compound and the lanthanum compound, organic acid salts such as acetate (lead acetate, lanthanum acetate), diisopropoxy lead, and lanthanum-2-methoxyethoxy are used. And alkoxides such as alkoxide. As a titanium compound,
Titanium tetraethoxy, titanium tetraisopropoxy,
Alkoxides such as tetra-n-butoxytitanium, tetra-i-butoxytitanium, tetra-t-butoxytitanium and dimethoxydiisopropoxytitanium are preferred, but organic acid salts or organometallic complexes can also be used. The zirconium compound is the same as the above-mentioned titanium compound. Examples of the strontium compound include organic acid salts such as strontium 2-ethylhexanoate and alkoxides such as strontium diisopropoxide. As the barium compound and the bismuth compound, the same organic acid salt and alkoxide as the strontium compound can be used. Examples of the tantalum compound include alkoxides such as tantalum pentaethoxide. Examples of the ruthenium compound include organic acid salts such as ruthenium octylate. Examples of the cobalt compound include organic acid salts such as cobalt octylate.

The starting metal compound may be a complex metal compound containing two or more component metals, in addition to the compound containing one kind of metal as described above. Examples of such composite metal compounds include PbO
₂ [Ti (OC ₃ H ₇ ) ₃ ] ₂ , PbO ₂ [Zr (OC
₄ H _{9) 3] 2} and the like.

In the present invention, in the first step, in order to positively generate voids in the film, organic substances which decompose or evaporate during calcination and crystallization or binders used in screen printing (polyvinylpyrrolidone, ethylcellulose, α -Terpineol, polyvinyl alcohol, etc.) may be added to the raw material coating liquid for forming a metal oxide thin film.

Further, in order to further increase the film thickness applied at a time, perovskite-type metal oxide fine particles are added to a solution in which a metal compound is dissolved in an organic solvent as a raw material coating solution for forming a metal oxide thin film. Raw material liquids mixed uniformly may be used. In this case, the average particle diameter of the perovskite-type metal oxide fine particles used is preferably about 0.01 to 10 μm.

Further, in the present invention, β-diketones may be blended as a stabilizer in the raw material coating liquid, and the compounding of the stabilizer suppresses the accelerated decomposition rate and the polycondensation rate of the raw material coating liquid. And its storage stability is improved. In this case, the amount of β-diketones added as a stabilizer is β-diketone relative to the total number of metal elements present in the raw material coating solution.
The amount is preferably 0.1 to 5 times, more preferably 0.2 to 3 times, the number of molecules of the diketones. If the amount of the β-diketone is too large, the stability may be reduced. If the amount is too small, the effect of the β-diketone cannot be sufficiently obtained. As the β-diketones to be used, acetylacetone, benzoylacetone, dibenzoylacetone, diisobutylmethane, dipivaloylmethane, 3-methylpentane-2,4
-Dione, 2,2-dimethylpentane-3,5-dione, heptafluorobutanoylpivaloylmethane, trifluoroacetylacetone and the like, among which economicalness, denseness of the film, and halides are included. Acetylacetone is desirable from the viewpoint that there is no acetylacetone.

The β-diketones as a stabilizer may be added at any stage in the production process of the raw material coating solution, but when azeotropic distillation described below is performed, it is preferable to add it after this distillation. . In the case where the metal alkoxide is partially hydrolyzed, it is preferable to add β-diketones before the partial hydrolysis because the hydrolysis rate can be easily controlled. When β-diketones are added, a small amount of water may be added to the raw material coating liquid in order to promote hydrolysis after coating.

In the present invention, a metal compound used as a raw material of each of the above-mentioned component metals is dissolved in the above-mentioned organic solvent, and, if necessary, a stabilizer, an organic substance or a binder for forming voids, a perovskite, etc. A raw material coating solution containing a precursor of a composite metal oxide (an oxide containing two or more metals) of a perovskite-type metal oxide thin film to be formed is prepared by adding fine metal oxide particles.

The ratio of each metal compound contained in the raw material coating solution may be substantially the same as the metal atomic ratio of the perovskite-type metal oxide thin film to be formed. However, a volatile substance such as a lead compound may have a defect due to evaporation during heating for changing to a metal oxide or during firing for crystallization. Therefore, in anticipation of this deficiency, a volatile substance such as a lead compound may be present in a slight excess (for example, a 2 to 30% excess). The degree of this defect varies depending on the type of the compound and the film forming conditions, and can be determined in advance by an experiment.

The concentration of the metal compound in the raw material coating solution is not particularly limited, and varies depending on the coating method used and the presence or absence of partial hydrolysis. Generally, the total metal content in terms of metal oxide is 0.1 to 40% by weight. % Is preferred.

When the above-mentioned perovskite-type metal oxide fine particles are mixed, if the mixing ratio of the metal oxide fine particles is too small, there is no effect of addition, and if the mixing ratio is too large, the metal oxide particles cannot be uniformly dispersed. 90% by weight or less, particularly 1 to 80% by weight in the coating solution, and a total of 5 to 90% with the total concentration of the above metal compound in terms of metal oxide.
It is preferable to set the mixing ratio so as to be% by weight.

When the above-mentioned organic substance or binder for forming voids is mixed, the concentration of the mixture is not particularly limited.
It is preferably 0% by weight. If the concentration is lower than this range, the effect of addition cannot be obtained, and if the concentration is higher, the viscosity increases,
Filtration and film formation are difficult.

A solution in which a metal compound or the like is dissolved in an organic solvent can be used as it is as a raw material coating solution for film formation by a sol-gel method or the like. Alternatively, in order to promote film formation, the solution may be heated to partially hydrolyze or partially polycondense a hydrolyzable metal compound (eg, alkoxide) and use the film for film formation. That is, in this case, the raw material coating liquid contains, for at least a part of the metal compound, a partial hydrolyzate and / or a partial polycondensate.

The heating for the partial hydrolysis is controlled by controlling the temperature and time so that the hydrolysis does not proceed completely.
When the hydrolysis is completely carried out, the stability of the raw material coating liquid is remarkably reduced, gelation is easily caused, and uniform film formation becomes difficult.
The heating conditions are a temperature of 80 to 200 ° C. and a temperature of 0.5 to 5
About 0 hours is appropriate. During hydrolysis, the hydrolyzate may be partially polycondensed by -MO- bonds (M = metal), but such polycondensation is acceptable if it is partially.

When the raw material coating solution contains both a metal alkoxide and a metal carboxylate, it is preferable to remove crystallization water accompanying the metal carboxylate before mixing with the metal alkoxide. This removal of water of crystallization
It can be carried out by first dissolving only the metal carboxylic acid in a solvent, and distilling and dehydrating the solution. Therefore, it is preferable to use a solvent which can be azeotropically distilled with water in this case. If mixed with the metal alkoxide without removing the water of crystallization of the metal carboxylate, the hydrolysis of the metal alkoxide may progress too much or its control may be difficult,
Precipitation may occur after partial hydrolysis.

In the present invention, a perovskite-type metal oxide thin film is formed by the sol-gel method using the thus prepared raw material coating solution for forming a metal oxide thin film according to the following procedure.

First, a raw material coating solution for forming a metal oxide thin film is applied on a substrate. The coating is generally performed by spin coating, but other coating methods such as roll coating, spraying, dipping, curtain flow coating, and doctor blade can also be applied. After application, the coating is dried and the solvent is removed. The drying temperature varies depending on the type of the solvent, but is usually about 80 to 200 ° C., preferably 10 to 200 ° C.
The temperature may be in the range of 0 to 180 ° C. However, since the solvent is removed during the heating in the next step for converting the metal compound in the raw material coating liquid into the metal oxide, the drying step of the coating film is not necessarily required.

Thereafter, as a calcining step, the applied substrate is heated to completely hydrolyze or thermally decompose the organometallic compound and convert it to a metal oxide, thereby forming a film made of the metal oxide. This heating is generally performed in an atmosphere containing water vapor in a sol-gel method requiring hydrolysis, for example, air or an atmosphere containing water vapor (for example, a nitrogen atmosphere containing water vapor).
The MOD method for thermal decomposition is performed in an oxygen-containing atmosphere. The heating temperature varies depending on the type of the metal oxide, but is usually in the range of 150 to 550 ° C, preferably 300 to 450 ° C. The heating time is selected so that the hydrolysis and thermal decomposition proceed completely, but is usually about 1 minute to 2 hours.

In the case of a sol-gel method or the like, it is often difficult to obtain a film thickness required for a perovskite-type metal oxide thin film by a single application. The calcination is repeated to obtain a metal oxide film having a desired film thickness. The film obtained in this way is amorphous or crystalline and has insufficient crystallinity, so that it has low polarizability and cannot be used as a ferroelectric thin film. Therefore, finally, as a crystallization annealing step, firing is performed at a temperature equal to or higher than the crystallization temperature of the metal oxide to obtain a crystalline metal oxide thin film having a perovskite crystal structure. The firing for crystallization is not performed once at the end, but may be performed after the above-mentioned calcination for each applied coating film,
Since firing at a high temperature needs to be repeated many times, it is economically advantageous to perform the final batch.

In the present invention, in this crystallization step, the perovskite-type metal oxide obtained from the liquid phase of the coating solution forms a low-density film composed of granular crystals having an average particle size of 200 nm or less. One step and a second step of sintering the low density film are performed.

The firing temperature in the first step is preferably 300 to 1000 ° C., more preferably 550 to 750 ° C.
It is. If the firing temperature is lower than the above range, a sufficient crystal film cannot be obtained. Even if the firing temperature is high, there is almost no effect of promoting crystallization, which is disadvantageous in practical use. The firing time varies depending on the firing temperature, but is usually about 1 minute to 2 hours.

The low-density film formed in the first step is a film in which the porosity of the perovskite-type metal oxide obtained from the liquid phase portion of the coating solution is about 20 to 60%. Crystal particles of the perovskite-type metal oxide obtained from the liquid phase portion of the coating solution constituting
It is preferably about 00 nm.

The firing temperature in the second step for sintering such a low-density film is preferably from 600 to 1000 ° C., more preferably from 750 to 950 ° C. If the sintering temperature is lower than the above range, sufficient densification by sintering cannot be achieved, and even if the sintering temperature is high, there is almost no effect of improving sinterability, which is disadvantageous in practical use. The firing time varies depending on the firing temperature.
It takes about 10 minutes to 10 minutes.

The firing atmosphere in the first and second steps is usually air or oxygen.

The first step and the second step may be performed separately from each other, but after the first step, it is efficient to raise the firing temperature and continuously perform the second step. In addition, it is preferable that the firing temperature of the second step of sintering is higher by about 100 to 500 ° C. than the firing temperature of the first step for forming the low-density film. By doing
The low-density film having a porosity as described above is 10% or less, particularly 0 to 10%.
Densify to 5% porosity.

The heat-resistant substrate material used for forming such a perovskite-type metal oxide thin film includes metals such as silicon (single crystal or polycrystal), platinum, stainless steel, nickel, ruthenium oxide, iridium oxide, and the like. strontium ruthenate (SrRuO ₃₎ or lanthanum cobaltate strontium _{((La X Sr 1-X} ) C
and inorganic compounds such as alumina, magnesia, quartz, aluminum nitride, and titanium oxide, such as perovskite conductive oxides such as oO ₃ ). In the case of a capacitor film, the substrate is a lower electrode, and as the lower electrode,
For example, Pt, Pt / Ti, Pt / Ta, Ru, RuO
₂ , Ru / RuO ₂ , RuO ₂ / Ru, Ir, Ir
O ₂ , Ir / IrO ₂ , Pt / Ir, Pt / IrO ₂ ,
A perovskite-type conductive oxide such as SrRuO ₃ or (La _X Sr _1-X ) CoO ₃ can be used (note that a two-layer structure using “/” indicates “upper layer / lower layer”). It is.).

The thickness of the perovskite-type metal oxide thin film thus formed varies depending on the use of the derivative device, but is usually preferably about 500 to 10 μm. It is useful for derivative devices and the like.

[0060]

The present invention will be described more specifically below with reference to examples and comparative examples.

The starting metal compounds used in the examples and comparative examples are as follows. Pb raw material compound: lead acetate trihydrate Zr raw material compound: zirconium tetra n-butoxide Ba raw material compound: barium 2-ethylhexanoate Sr raw material compound: strontium 2-ethylhexanoate (for a BST thin film) strontium-2-methoxy Ethoxide (for SRO thin film and LSCO thin film) Ti raw material compound: titanium tetraisopropoxide La raw material compound: lanthanum-2-methoxyethoxide Co raw material compound: cobalt 2-ethylhexanoate Ru raw material compound: 2-ethylhexanoic acid ruthenium

Example 1 (PZT thin film) A Pb raw material compound was dissolved in propylene glycol and dehydrated under reduced pressure. A Ti raw material compound, a Zr raw material compound and acetylacetone were added thereto, and the mixture was refluxed. did. Note that acetylacetone was added in an amount of 2 mol times the total of the Zr raw material compound and the Ti raw material compound.

Thereafter, the mixture is diluted with propylene glycol so that the total concentration of the starting compounds becomes 30% by weight in terms of oxides, and then refluxed, and further diluted with ethanol until the total concentration of the starting compounds becomes 25% by weight in terms of oxides. After dilution, a sol-gel solution was obtained. The metal atom ratio of this sol-gel solution is Pb / Zr
/ Ti = 125/52/48.

This sol-gel solution was treated with lead titanate (20 °) /
Pt (2000 °) / Ti (200 °) / SiO ₂ (5
000Å) / Si (100) wafer is applied by a spin coating method on a substrate, and is kept at a low temperature of 200 ° C. or less for 5 minutes.
After drying in the air (hot plate), at 450 ° C 5
It was calcined in the air (hot plate) for minutes. Then 7
After baking in oxygen at 00 ° C. for 1 minute for crystallization, 85
Sintered in oxygen at 0 ° C. for 1 hour.

For the obtained PZT thin film, a cross-sectional SEM
The film thickness and the porosity were examined by observing the image, and the results are shown in Table 1.

Comparative Example 1 A PZT thin film was formed in the same manner as in Example 1 except that the sintering step at 850 ° C. was not performed.
Observation of a cross-sectional SEM image of the T thin film reveals the film structure,
The film thickness and porosity were examined, and the results are shown in Table 1.

[0067]

[Table 1]

Example 2 (PZT thin film) In Example 1, the obtained sol-gel liquid had an average particle size of 0.3.
2 μm PZT fine particles (Pb / Zr / Ti = 125/5
2/48) was added to obtain a homogeneous dispersion by ultrasonic irradiation, and a PZT thin film was formed in the same manner except that this dispersion was applied, dried, calcined, crystallized, and sintered. However, the firing time for crystallization was 5 minutes, and the firing temperature for sintering was 900 ° C.

The cross section SEM of the obtained PZT thin film
The film thickness and the porosity were examined by observing the image, and the results are shown in Table 2.

Comparative Example 2 A PZT thin film was formed in the same manner as in Example 2 except that the sintering step at 900 ° C. was not performed.
Observation of a cross-sectional SEM image of the T thin film reveals the film structure,
The film thickness and porosity were examined, and the results are shown in Table 2.

[0071]

[Table 2]

Example 3 (BST thin film) Ti raw material compound, Ba raw material compound, Sr raw material compound and acetylacetone were dissolved in propylene glycol and refluxed. In addition, acetylacetone was added in a molar amount of 2 times the Ti raw material compound.

Thereafter, the mixture was diluted with propylene glycol so that the total concentration of the starting compounds was 15% by weight in terms of oxide to obtain a sol-gel solution. The metal atom ratio of this sol-gel liquid was Ba / Sr / Ti = 50/50/100.

This sol-gel solution was converted to Pt (2000 °) / T
i (200 °) / SiO ₂ (5000 °) / Si (10
0) First, it was applied on a wafer substrate by spin coating, dried at a low temperature of 200 ° C. or less for 5 minutes in the air (hot plate), and calcined at 450 ° C. for 5 minutes in the air (hot plate). . Then, after sintering in oxygen at 700 ° C. for 5 minutes for crystallization, sintering was performed at 900 ° C. for 1 hour in oxygen.

The cross section SEM of the obtained BST thin film
By observing the image, the film thickness and the porosity were examined, and the results are shown in Table 3.

Comparative Example 3 A BST thin film was formed in the same manner as in Example 3 except that the sintering step at 900 ° C. was not performed.
Observation of a cross-sectional SEM image of the T thin film reveals the film structure,
The film thickness and porosity were checked, and the results are shown in Table 3.

[0077]

[Table 3]

Example 4 (LSCO thin film) Sr raw material compound, La raw material compound and Co raw material compound were dissolved in propylene glycol and refluxed.

Thereafter, the mixture was diluted with propylene glycol so that the total concentration of the raw material compounds became 15% by weight in terms of oxide to obtain a sol-gel liquid. The metal atom ratio of this sol-gel liquid was La / Sr / Co = 50/50/100.

Using this sol-gel solution, coating, drying, calcination, crystallization and sintering were performed in the same manner as in Example 3 to obtain LSCO
A thin film was formed.

For the obtained LSCO thin film, the section SE
By observing the M image, the film thickness and the porosity were examined.
It was shown to.

Comparative Example 4 An LSCO thin film was formed in the same manner as in Example 4 except that the sintering step at 900 ° C. was not performed.
For the SCO thin film, the film structure, film thickness, and porosity were examined by observing a cross-sectional SEM image, and the results are shown in Table 4.

[0083]

[Table 4]

Example 5 (SRO thin film) A Sr raw material compound and a Ru raw material compound were dissolved in propylene glycol and refluxed.

Thereafter, the mixture was diluted with propylene glycol so that the total concentration of the starting compounds was 15% by weight in terms of oxide, to obtain a sol-gel solution. The metal atom ratio of this sol-gel liquid was Sr / Ru = 100/100.

Using this sol-gel solution, coating, drying, calcination, crystallization, and sintering were performed in the same manner as in Example 3 to form an SRO thin film.

The SRO thin film thus obtained was subjected to a cross-sectional SEM
The film thickness and the porosity were examined by observing the image, and the results are shown in Table 5.

Comparative Example 5 An SRO thin film was formed in the same manner as in Example 5 except that the sintering step at 900 ° C. was not performed.
Observation of a cross-sectional SEM image of the O thin film shows the film structure,
The film thickness and porosity were examined, and the results are shown in Table 5.

[0089]

[Table 5]

[0090]

As described above in detail, according to the present invention, a very low-density film composed of fine granular crystals is formed, and this low-density film is sintered to form one film. A perovskite-type metal oxide that can form a thick film of 0.1 μm or more by coating and is extremely dense at a relatively low firing temperature of 1000 ° C. or less and is excellent in various properties such as dielectric properties or conductive properties. An object thin film can be formed.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/49 C04B 35/49 Z H01L 27/105 H01L 27/10 444C (72) Inventor Satoshi Fujita Hyogo 12-6 Mita City Techno Park Mitsubishi Materials Corporation Mita Plant F term (reference) 4G031 AA05 AA06 AA09 AA11 AA12 AA22 AA32 BA02 BA09 BA10 BA15 CA01 CA04 CA08 GA02 GA07 4G047 CA07 CB05 CB06 CC02 CD02 CD08 4G048 AA05 AB02 AC02 AD08 AE08 5F083 GA21 JA14 JA15 JA38 JA39 JA43 PR33

Claims (5)

[Claims] 1. A method for forming a perovskite-type metal oxide thin film by applying a raw material coating solution for forming a metal oxide thin film on a substrate and then heating to crystallize the metal oxide, thereby forming a perovskite-type metal oxide thin film. A first step of forming a low-density film composed of granular crystals having an average particle size of 200 nm or less, and a second step of sintering the low-density film. A method for forming a dense perovskite-type metal oxide thin film, comprising: 2. The dense perovskite-type metal oxide according to claim 1, wherein the sintering temperature in the first step is 300 to 1000 ° C. and the sintering temperature in the second step is 600 to 1000 ° C. Method of forming a thin film. 3. The method for forming a dense perovskite-type metal oxide thin film according to claim 1, wherein the first step and the second step are performed in one continuous process. 4. The dense perovskite-type metal oxide thin film according to claim 1, wherein the raw material coating solution for forming a metal oxide thin film contains perovskite-type metal oxide fine particles. Formation method. 5. A perovskite-type metal oxide thin film formed by the method for forming a dense perovskite-type metal oxide thin film according to claim 1, wherein the porosity is 10% or less. A dense perovskite-type metal oxide thin film characterized by the following.