JP2000001368A - Ferroelectric thin film, stock solution for forming same and formation of same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ferroelectric thin film having enhanced uniformity of surface shape by preparing a soln. contg. a metallic compd. contg. one or more constituent metals, its partial hydrolyzate or its partial polycondensation product and allowing the metallic compd. to include an oxo complex of Ti and/or Zr, its partial hydrolyzate or its partial polycondensation product. SOLUTION: A metallic compd. contg. a constituent metal such as lead acetate or lanthanum acetate is dissolved in a solvent such as 2-methoxyethanol, oxo complexes of Ti and Zr such as TiOCl2 and ZrO(CH3COO)2 are also dissolved in such an amt. as to make the number of the metallic atoms >=0.001 time the number of all the metallic atoms in the resultant soln. and tetraisopropoxides of Ti and Zr are further added. Partial hydrolysis is carried out by heating to prepare a film forming soln. and this soln. is applied to a heat resistant substrate, dried and heated to 150-550 deg.C to convert the compds. into metal oxides by hydrolysis. Firing is then carried out at 500-800 deg.C to obtain the objective ferroelectric thin film represented by the formula (where 0<=x<1 and 0<=y<=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a raw material solution for forming a metal oxide-based ferroelectric thin film which can be expected to be applied to various dielectric devices due to its electrical and / or optical properties. And a method of forming a ferroelectric thin film using the same, and a formed ferroelectric thin film. The raw material solution for film formation of the present invention can form a ferroelectric thin film having a uniform surface morphology and excellent electric characteristics.

[0002]

BACKGROUND OF THE INVENTION In general _{formula: Pb 1-x La x (} Zr y Ti 1-y) 1-x / 4 O 3
(0 ≦ x <1, 0 ≦ y ≦ 1) Metal oxide having a composition represented by, for example, lead zirconate titanate (PZT) and lanthanum-doped lead zirconate titanate (PLZT)
Is a ferroelectric having a perovskite crystal structure,
Due to its high dielectric constant and excellent ferroelectric and optical properties, thin films of these compounds have already been used for capacitor films, optical sensors,
In addition to being used for optical circuit elements, it is expected to be applied to new dielectric devices such as nonvolatile memories.
Bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) is also a ferroelectric material having a layered perovskite structure (a crystal structure in which a perovskite structure and Bi ₂ O ₃ are stacked in layers), which is also used for the same applications as above. Application is expected.

The DRAM, which is the mainstream of the rewritable memory, is a volatile memory, and it is necessary to periodically supply a current for storing data, and large power consumption poses an environmental problem. Therefore, a ferroelectric memory which is nonvolatile and can hold data for a long time, consumes less power, and is compatible with a DRAM has been attracting attention. In addition to the above features, ferroelectric memories have the advantages of low writing voltage, high-speed writing, many rewritable times, bit rewritable, and random access. Is currently underway.

In a ferroelectric memory, a capacitor portion of a DRAM is replaced with a ferroelectric thin film, and the thin film has a storage function by utilizing a hysteresis phenomenon of spontaneous polarization of the ferroelectric. As a ferroelectric thin film material of this ferroelectric memory, a PZT-based material having a large spontaneous polarization is advantageous.

In general, a metal oxide type ferroelectric thin film can be formed using various physical vapor deposition methods, chemical vapor deposition methods, and wet film formation methods. Examples of a suitable film forming method include a sputtering method which is a physical vapor deposition method, an MOCVD method which is a chemical vapor deposition method, and a sol-gel method which is a wet film forming method. Among them, the sol-gel method is usually the most inexpensive and simple to form a ferroelectric thin film.

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,
After the coating film is dried, it is heated to, for example, about 400 ° C. in air to form a metal oxide film, and then fired at a temperature equal to or higher than the crystallization temperature of the metal oxide (eg, about 700 ° C.). Is a method of forming a ferroelectric thin film by crystallizing the compound. As a hydrolyzable metal compound as a raw material, an organic compound such as a metal alkoxide, a partial hydrolyzate or a partial polycondensate thereof is generally used.

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 (eg, metal acetylacetonate) or a carboxylate (eg, acetate) is applied to a substrate, and 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, only the types of the starting compounds are different,
The film forming operation is almost the same as the sol-gel method.

As described above, the sol-gel method and the MOD method have the same film forming operation, so that a method in which both are mixed 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 Becomes an oxide.

Hereinafter, the term including the sol-gel method, the MOD method, and a method in which these are mixed is referred to as “sol-gel method or the like”. The sol-gel method and the like are characterized in that, in addition to the advantages of being inexpensive, simple, and suitable for mass production, the composition of the film is easily controlled and 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.

[0010]

The titanic acid / zirconic acid based ferroelectric thin film formed by the conventional sol-gel method or the like has irregularities on the surface, and the formed particles have an uneven particle diameter.
For example, a PZT or PLZT thin film formed by this method generally has a non-uniform surface morphology divided into coarse perovskite crystal grains having a grain size of about 1000 nm or more and fine zirconia crystal grains. are doing.

If there are non-uniform portions in the surface morphology, it is expected that the electrical characteristics will also be non-uniform depending on the location. Therefore, when a fine capacitor film is cut out from this film, it may be electrically inferior depending on the cut-out location, and the reliability or yield of the product is greatly impaired. Is a major obstacle for ferroelectric thin films.

The present invention has been made to solve this problem, and when a ferroelectric thin film containing Ti and / or Zr is formed by a sol-gel method or the like, a ferroelectric thin film having a uniform surface morphology is obtained. It is an object to provide a raw material solution for film formation capable of forming a thin film, a method for forming a ferroelectric thin film using the raw material solution, and a formed ferroelectric thin film.

[0013]

Means for Solving the Problems As a result of repeated studies to solve the above-mentioned problems, the present inventors have found that a film-forming raw material solution used in a sol-gel method or the like has Ti and / or Zr as a raw material metal compound. The inclusion of an oxo complex (a complex in which an oxide ion O ^2- is coordinated with a metal) dramatically improves the uniformity of the surface morphology of the formed ferroelectric thin film and solves the above-mentioned problems. They have found that they can do so and have reached the present invention.

The present invention provides a solution for forming a ferroelectric thin film comprising a composite metal oxide containing Ti and / or Zr by a sol-gel method or the like, wherein each component metal or 2
A metal compound containing the above component metal, a partial hydrolyzate thereof, and / or a solution containing a partial polycondensate thereof in an organic solvent, and wherein the metal compound is an oxo complex of Ti and / or Zr; A raw material solution for forming a ferroelectric thin film, comprising a hydrolyzate and / or a partial polycondensate thereof.

The amount of the oxo complex of Ti and / or Zr is preferably such that the number of metal atoms of the oxo complex is at least 0.001 times the total number of metal atoms present in the raw material solution. Preferably it is 0.005 to 0.5 times.

The ferroelectric thin film has a general formula: Pb _{1-x
La x (Zr y Ti 1-} y) 1-x / 4 O 3 ( where, 0 ≦ x <1,0 ≦ y
≦ 1) or bismuth titanate is preferred.

According to the present invention, there is also provided a ferroelectric thin film formed by applying and heating the above-mentioned raw material solution. This film formation may be performed according to a conventional method. That is, this raw material solution is applied to a heat-resistant substrate, and a metal oxide film is formed by heating, and if necessary, coating and heating are repeated until the film has a desired thickness, and the heating or the coating is performed during the heating or the coating. By baking the film at a crystallization temperature or higher after repeated heating, a ferroelectric thin film can be formed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A ferroelectric thin film formed in the present invention is a thin film of a complex oxide type ferroelectric material containing one or both of Ti and Zr. Examples of such a ferroelectric material, the general _{formula: Pb 1-x La x (} Zr y Ti 1-y) 1-x / 4 O
₃ (where x is a decimal smaller than 0 or 1, y is 0, 1
Or a decimal number smaller than 1) and a composite oxide having a perovskite crystal structure and bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) having a layered perovskite structure.

The composite oxide of PT (lead titanate),
Examples include, but are not limited to, PZT (lead titanium zirconate) and PLZT (lanthanum-containing lead zirconate titanate). Also, this or other ferroelectric material can contain a trace amount of a doping element.
Examples of doping elements include Ca, Sr, Ba, Hf, Sn, Th,
Y, Sm, Dy, Ce, Bi, Sb, Nb, Ta, W, Mo, Cr, Co, N
i, Fe, Cu, Si, Ge, U, Sc and the like. Its content is 0.05% by atomic fraction of metal atoms in the above general formula.
It is as follows.

Such a ferroelectric thin film is typically prepared by using a raw material solution containing a hydrolyzable or thermally decomposable organometallic compound such as a component metal alkoxide, an organic acid salt or a β-diketone complex. A method of forming a film by a sol-gel method or the like is well known to those skilled in the art (for example,
236404). The present invention is characterized in that the raw material solution contains an organic or inorganic oxo complex of Ti and / or Zr as a metal compound.
The solution composition and the film forming method may be generally the same as the conventional sol-gel method.

Preferred metal compounds as raw materials are hydrolyzable or thermally decomposable organometallic compounds. For example,
Representative examples include alkoxides, organic acid salts, and β-diketone complexes, but various other complexes such as amine complexes can also be used for metal complexes. As β-diketone, acetylacetone (= 2,4-pentanedione),
Heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoylacetone and the like can be mentioned.

Specific examples of suitable organometallic compounds as raw materials include, as the lead compound and the lanthanum compound, organic acid salts such as acetates (lead acetate and lanthanum acetate) and alkoxides such as diisopropoxy lead. As the titanium compound, alkoxides such as tetraethoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetra-i-butoxytitanium, tetra-t-butoxytitanium, and dimethoxydiisopropoxytitanium are preferable, but organic acid salts or organic metal salts are preferred. Complexes can also be used. The zirconium compound is the same as the above-mentioned titanium compound.

The metal compound as a raw material may be a 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 and PbO ₂ [Zr (OC ₄ H ₉ ) ₃ ] ₂ .

A precursor of a composite metal oxide (oxide containing two or more metals) as a ferroelectric material is prepared by dissolving together a metal compound used as a raw material of each component metal in an appropriate organic solvent. A raw material solution containing is prepared.

The solvent to be used may be appropriately selected from those capable of dissolving the metal compound according to the starting metal compound. Generally, one or more solvents selected from alcohols, carboxylic acids, esters, ketones, ethers, cycloalkanes, aromatic solvents and the like can be used.

As the alcohol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-
Alkanols such as butanol, isobutyl alcohol, 1-pentanol, 2-pentanol and 2-methyl-2-pentanol, cycloalkanols such as cyclohexanol, and alkoxy alcohols such as 2-methoxyethanol can be used. When the metal compound contains an alkoxide, the solvent is preferably an alcohol or a mixed solvent containing an alcohol.

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-dimethylpentanoic acid, 2-ethyl Hexanoic acid, 3-ethylhexanoic acid and the like can be mentioned.

Examples of the ester solvent include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate,
Tert-butyl acetate, isobutyl acetate, n-amyl acetate,
Examples thereof include sec-amyl acetate, tert-amyl acetate, and isoamyl acetate.

Examples of ketone solvents are acetone, methyl ethyl ethone and methyl isobutyl ketone. Ether solvents include chain ethers such as dimethyl ether and diethyl ether, and cyclic ethers such as tetrahydrofuran and dioxane. Examples of cycloalkane solvents include cycloheptane, cyclohexane, and the like. Examples of the aromatic solvent include toluene, xylene, and the like.

The proportion of each metal compound (including the oxo complex of Ti and / or Zr described later) contained in the solution may be substantially the same as the composition ratio in the ferroelectric thin film to be formed. However, lead compounds generally have high volatility, and lead deficiency may occur due to evaporation during heating for changing to a metal oxide or during firing for crystallization. Therefore, in anticipation of this loss,
(Eg, 2-20% excess). The degree of lead deficiency varies depending on the type of lead compound and film formation conditions, and can be determined by experiment.

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

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 performed, the stability of the raw material solution is remarkably reduced, gelation is easily caused, and uniform film formation is difficult. Suitable heating conditions are a temperature of 80 to 200 ° C. and a time of about 0.5 to 50 hours. During the hydrolysis, the hydrolyzate becomes -MO-
Polycondensation may occur partially due to bonding (M = metal). If such polycondensation is partial, it is acceptable.

The raw material solution may contain a small amount of a stabilizer. By adding the stabilizer, the hydrolysis rate of the raw material solution,
The polycondensation rate and the like are suppressed, and the storage stability is improved. Compounds useful as stabilizers include β-diketones (eg, acetylacetone, heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoylacetone, etc.), ketone acids (eg, acetoacetic acid) , Propionylacetic acid, benzoylacetic acid, etc.), lower alkyl esters of these ketone acids such as methyl, propyl, butyl, etc., oxy acids (eg, lactic acid, glycolic acid, α-oxybutyric acid, salicylic acid, etc.),
Lower alkyl esters of these oxyacids, oxyketones (eg, diacetone alcohol, acetoin, etc.),
α-amino acids (eg, glycine, alanine, etc.) and alkanolamines (eg, diethanolamine, triethanolamine, monoethanolamine, etc.).

The amount of the stabilizer added is 0.1 to 5 in terms of the number of stabilizer molecules based on the total number of metal elements present in the raw material solution.
The amount is preferably twice, more preferably 0.2 to 3 times.
The stabilizer may be added at any stage in the production process of the raw material solution. However, when azeotropic distillation described below is performed, it is preferable to add the stabilizer after the distillation. In the case where the above-mentioned partial hydrolysis of the metal alkoxide is performed, it is preferable to add a stabilizer before the partial hydrolysis because the hydrolysis rate can be easily controlled. When a stabilizer is added,
To promote hydrolysis after coating, a small amount of water may be added to the raw material solution.

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

The concentration of the raw material solution is not particularly limited and varies depending on the coating method to be used and the presence or absence of partial hydrolysis. In general, the total metal content in terms of metal oxide (including the metal derived from the oxo complex described later) Is preferably in the range of 0.1 to 20% by weight.

The raw material solution according to the present invention contains an oxo complex of Ti and / or Zr. An oxo complex is a complex to which an oxide ion O ²⁻ is coordinated. In the raw material solution
All of the Ti compound and the Zr compound may be converted to such an oxo complex of Ti and Zr. However, oxo complexes of Ti and Zr are more expensive than, for example, alkoxides of these metals, and if they are all oxo complexes, the cost of film formation will be high. Therefore, only a part of the Ti compound and / or Zr compound will be oxo complex. A complex is sufficient.

A typical example of an oxo complex of Ti and Zr is TiO.
It is a compound represented by L ₂ or ZrOL ₂ (wherein L represents a monovalent anionic ligand). The ligand L may be derived from any of an organic compound and an inorganic compound.

Examples of organic ligands are anions derived from alcohols, carboxylic acids, β-diketones, β-ketoesters, β-imino ketones and the like. That is, the organic ligand L may be an alkoxylate, carboxylate, β-diketonate (= β-ketoenolate), β-enol ester, β-iminoenol, or the like. Representative anions include alkoxylates (eg, ethylate, isopropylate, n-butyrate, t-butylate, methoxyethylate, ethoxyethylate, etc.) and β-diketonate [acetylacetonate (= 2,4-pentanedionato )
, Dipivaloylmethanate, etc.). Examples of the inorganic ligand include a halogen ion, a nitrate ion (NO ₃ ⁻ ), and a hydroxyl ion (OH ⁻ ). Further, part or all of the ligand may be an amine or ammonia.

As another oxo complex, there is a type called a μ-oxo complex in which O ²⁻ is a bridge between two metal ions. For example, L ₃ Ti-O-TiL ₃ or L ₃ Zr-O-ZrL ₃
And further, compounds having a structure represented by the following formula. The ligand L may be the same as described above.

[0041]

Embedded image

The oxo complex of Ti is synthesized by adding an oxidizing agent to a Ti alkoxide, a carboxylate, a β-diketone complex, a β-ketoester complex, a β-iminoketo complex, a hydroxy complex, and the like to oxidize. May be.
The oxo complex of Zr may be synthesized by a similar method. As the oxidizing agent, nitric acid, ozone, oxygen (air), perchloric acid, NO _x gas, peroxyacids, hydrogen peroxide, hydrogen peroxide and the like are preferable.

The oxo complex of Ti and / or Zr can be added to the raw material solution at any time. When the oxo complex is a compound having water of crystallization, as described above, the water of crystallization of the oxo complex is added before the water of crystallization derived from the metal organic acid salt is removed by azeotropic distillation. Removal is preferred. On the other hand, when the oxo complex is a compound having no water of crystallization, it is preferable to add the oxo complex after removing water by azeotropic distillation.

When heating is carried out to partially hydrolyze or partially polycondense the hydrolyzable metal compound, particularly metal alkoxides, the oxo complex may be added before or after this heating. If added before heating, the oxo complex may undergo partial hydrolysis or partial polycondensation during heating. Therefore, in this case, a partial hydrolyzate and / or a partial polycondensate of the oxo complex is contained in the raw material solution. However, since the oxo ligand (O ²⁻ ) of the oxo complex is stable, it is considered that this ligand remains in the complex even after heating.

When the oxo complex of Ti and / or Zr is present in the raw material solution, the surface morphology of the ferroelectric thin film formed from the raw material solution is remarkably improved. More specifically, the crystal grains become finer, the particle diameter becomes substantially uniform throughout the film, there is no variation, and no phase other than perovskite or layered perovskite such as a zirconia phase is observed. This is because the crystallization temperature of the oxo complex of Ti or Zr is low, so that the film can be calcined and / or crystallized.
During (firing), first, a large number of TiO ₂ or ZrO ₂ crystals are uniformly formed on the substrate, and these are used as initial nuclei for crystal growth, so that a ferroelectric thin film composed of uniform and fine crystal grains is formed. It is presumed that it is.

As described above, since the crystal grains are fine and uniform, and no phase other than perovskite (or lamellar perovskite) is generated, the electrical characteristics are uniform throughout the film.
Even if a device is manufactured from any part of the ferroelectric thin film, a product of almost the same quality can be obtained, and the reliability of the product is improved.

To obtain this effect, the number of metal atoms of the oxo complex of Ti and / or Zr is preferably at least 0.001 times the total number of metal elements present in the raw material solution. Preferably it is 0.005 times to 0.5 times.

As described above, a ferroelectric thin film can be formed from this raw material solution in the same manner as in the conventional sol-gel method. First, a raw material solution is applied on a substrate. The coating is usually 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.
For example, the temperature may be in the range of 100 to 180 ° C. However, since the solvent is removed during the heating for the conversion to the next metal oxide, the drying step of the coating film is not necessarily required.

Thereafter, as a calcining step, the coated substrate is heated to completely hydrolyze or thermally decompose the organometallic compound to convert it into a metal oxide, thereby forming a film made of the metal oxide. This heating is performed in an atmosphere containing steam in the sol-gel method requiring hydrolysis, for example, in an air or steam-containing atmosphere (eg, a nitrogen atmosphere containing steam), and in the MOD method for thermal decomposition, an oxygen-containing atmosphere is used. Generally done in The heating temperature varies depending on the type of metal oxide, but is usually in the range of 150 to 550 ° C.
00-450 ° C. The heating time is selected so that hydrolysis and thermal decomposition proceed completely, but is usually about 1 minute to 2 hours.

In the case of the sol-gel method or the like, it is often difficult to obtain a film thickness necessary for the ferroelectric thin film by one application, so that the above application and (drying) heating are performed as necessary. By repeating this, a metal oxide film having a desired thickness is obtained. 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 higher than the crystallization temperature of the metal oxide to obtain a crystalline metal oxide thin film having a perovskite type (layered perovskite type) crystal structure. . The firing for crystallization may not be performed once at the end, but may be performed following the above-described calcination for each applied coating, but it is necessary to repeat firing at a high temperature many times. Therefore, it is economically advantageous to perform the operation at the end.

The firing temperature for this crystallization is usually 500
It is in the range of -800 ° C, for example, 600-750 ° C. Therefore, a substrate having heat resistance enough to withstand this firing temperature is used. The firing (annealing) time for crystallization is usually about 1 minute to 2 hours, and the firing atmosphere is not particularly limited, but is usually air or oxygen.

Examples of heat-resistant substrate materials include silicon (single crystal or polycrystal), metals such as platinum and nickel, ruthenium oxide, iridium oxide, strontium ruthenate (SrRuO ₃ ), quartz, aluminum nitride, titanium oxide and the like. Inorganic compounds. In the case of a capacitor film, the substrate is the lower electrode. The lower electrode is, for example, P
t, Pt / Ti, Pt / Ta, Ru, RuO ₂ , Ru / RuO ₂ , RuO ₂ / Ru, I
r, IrO ₂ , Ir / IrO ₂ , Pt / Ir, Pt / IrO ₂ etc.
Before the upper layer).

The thickness of the ferroelectric thin film thus formed varies depending on the use of the dielectric device, but is usually preferably about 500 to 4000 °. The obtained ferroelectric thin film is useful for various dielectric devices as described above.

[0055]

EXAMPLES The starting metal compounds other than the oxo complex used in the examples are as follows. Pb: lead acetate trihydrate La: lanthanum acetate 1.5 hydrate Ti: titanium tetraisopropoxide Zr: zirconium tetra n-butoxide (Examples 1 to 9) Lead acetate trihydrate and acetic acid were placed in a suitable reaction vessel. Lanthanum 1.5 hydrate, 2-methoxyethanol as a solvent and an oxo complex of Ti or Zr shown in Table 1 (in the case of a compound having water of crystallization) were charged, and water was removed from the resulting solution by azeotropic distillation. . The solution thus dehydrated was mixed with titanium tetraisopropoxide and zirconium tetra-n-butoxide and an oxo complex of Ti or Zr shown in Table 1.
(Without water of crystallization) was added and dissolved. In addition,
The starting metal compound, including the metal component of the oxo complex, is Pb:
La: Zr: Ti was used in an atomic ratio of 110: 1: 52: 48.

Acetyacetone was added to this solution as a stabilizer.
(= 2,4-pentanedione) was added and dissolved in such an amount that the number of molecules became 1 times the total number of atoms of the metal elements present in the raw material solution. Then, water is added in an amount to give 1.5 times the number of molecules with respect to the total number of metal elements present in the raw material solution, and 2-methoxyethanol as a solvent is further added to the raw material compound in terms of oxide. Total content of 10wt%
The concentration was adjusted so that The solution was refluxed and heated under a nitrogen atmosphere for 3 hours to partially hydrolyze (or further partially polycondensate) the alkoxides of the raw material compound to obtain a raw material solution.

(Examples 10 to 12) Lead acetate 3 was placed in a suitable reaction vessel.
The hydrate, lanthanum acetate 1.5 hydrate and the solvent 2-methoxyethanol were charged, and water was removed from the resulting solution by azeotropic distillation. To the solution thus dehydrated, titanium tetraisopropoxide and zirconium tetra n-butoxide were added and dissolved. Next, acetylacetone as a stabilizer is added to this solution in an amount that gives a molecule number that is one-times the total number of metal elements present in the raw material solution (including the amount of the oxo complex added later). Dissolved.

Thereafter, water was added in an amount of 1.5 times the total number of atoms of the metal elements present in the raw material solution (as described above), and 2-methoxyethanol as a solvent was added. The concentration was adjusted so that the total content of the raw material compounds in terms of oxide (including the amount of the oxo complex added later) was 10 wt%. This solution was heated under reflux for 3 hours under a nitrogen atmosphere to partially hydrolyze the alkoxides of the starting compound.
(Or further partial polycondensation). Finally, an oxo complex of Ti or Zr having no water of crystallization described in Table 1 was added to obtain a raw material solution. Also in this example, the raw material metal compound including the metal component of the oxo complex was used in a ratio where the atomic ratio of Pb: La: Zr: Ti was 110: 1: 52: 48. The concentration was adjusted with a small amount of 2-methoxyethanol so that the total content of the starting compounds was 10 wt%.

Comparative Example 1 The procedure of Examples 10 to 12 was repeated, except that the oxo complex of Ti or Zr was not added at the end.
A raw material solution was prepared.

A PLZT-based ferroelectric thin film was formed on a substrate using the raw material solutions of these Examples and Comparative Examples. The substrate was Si (100) wafer / SiO ₂ (5000Å) / Pt (2000Å). Raw material solution is spin-coated (3000 rpm × 15 seconds)
And heated in air at 350 to 400 ° C. for 10 minutes to obtain a metal oxide film. This coating and heating were repeated a total of five times, and finally baked in oxygen at 700 ° C. for 5 minutes for crystallization to obtain a PLZT ferroelectric thin film having a perovskite crystal structure with a thickness of about 200 nm. .

The surface of the PLZT thin film thus formed was observed with a SEM to measure the average grain size of the crystal grains.
Variations in grain size and phases other than the perovskite phase
(Eg, zirconia phase) was determined. The average particle size is
This is the average intercept length of the particles calculated from the SEM photograph of the thin film surface. These results are summarized in Table 1 below together with the type and amount of the oxo complex.

[0062]

[Table 1]

As can be seen from Table 1, according to the present invention,
When the raw material solution contains an oxo complex of Ti or Zr,
Fine crystal grains (500 nm or less,
A ferroelectric thin film having a uniform surface morphology, having no variation in particle size and having no phase other than the perovskite phase (eg, zirconia phase), was formed. On the other hand, the ferroelectric thin film formed from the raw material solution of the comparative example that does not contain the oxo complex of Ti or Zr has crystal grains.
It was coarse at 1400 nm, with variations in particle size observed, and phases other than perovskite such as a zirconia phase were observed, and the surface morphology was uneven.

[0064]

According to the present invention, the non-uniformity of the surface morphology of the ferroelectric thin film formed by the sol-gel method or the like can be remarkably reduced, the crystal grains are fine, and the crystal grain size varies. In addition, a ferroelectric thin film having no phase other than the perovskite or layered perovskite phase can be formed. Therefore, since the electrical characteristics are uniform throughout the film without variation from place to place, when a dielectric device is manufactured from this ferroelectric thin film, a highly reliable product can be manufactured with high yield.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 21/8242 H01L 29/78 371 21/8247 29/788 29/792 (72) Inventor Akira Mori Hyogo 12-6 Mita City Techno Park Mita Plant, Mitsubishi Materials Corporation (72) Inventor Kensuke Kageyama 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Research Institute (72) Inventor Masaya Matsuura Omiya City, Saitama Prefecture 1-297 Kitabukurocho, Mitsubishi Materials Corporation Research Laboratory (72) Inventor Katsumi Ogi 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Research Laboratory F-term (reference) 4G031 AA09 AA11 AA12 AA32 AA35 BA09 CA08 GA01 GA07 5F001 AA17 AD12 AD33 AD41 AD51 AE20 AG01 AG30 5F083 AD11 FR01 GA21 GA27 GA30 JA15 JA17 PR23 PR33 5G3 03 AA10 AB20 BA03 BA12 CA01 CA09 CB05 CB15 CB25 CB35 CB39 DA02

Claims (6)

[Claims] 1. A raw material solution for forming a ferroelectric thin film made of a composite metal oxide containing Ti and / or Zr, wherein the metal compound contains each component metal or two or more component metals. The metal compound is an oxo complex of Ti and / or Zr, a partial hydrolyzate thereof, and / or a partial hydrolyzate thereof, and / or a solution containing a partial hydrolyzate and / or a partial polycondensate thereof in an organic solvent. A raw material solution for forming a ferroelectric thin film, comprising a condensate. 2. The ferroelectric thin film according to claim 1, wherein the number of metal atoms of the oxo complex of Ti and / or Zr is at least 0.001 times the total number of metal atoms present in the raw material solution. Raw material solution for film formation. 3. The ferroelectric thin film has a general formula: Pb _1-x La _x (Zr
The composition of the ferroelectric thin film according to claim 1, wherein the composition is represented by _y Ti _1-y ) _{1-x / 4} O ₃ (where 0 ≦ x <1, 0 ≦ y ≦ 1). Raw material solution for membrane. 4. The raw material solution for forming a ferroelectric thin film according to claim 1, wherein the ferroelectric thin film is bismuth titanate. 5. The material solution according to claim 1, which is applied to a heat-resistant substrate and heated to form a metal oxide film, and if necessary, the film has a desired thickness. A method of forming a ferroelectric thin film, which comprises sintering a film at a crystallization temperature or higher during or after the above-mentioned heating or after repeating the application and heating. 6. A ferroelectric thin film formed by the method according to claim 5.