JP2004339057A - COATING LIQUID FOR DEPOSITING Bi-BASED FERROELECTRIC THIN FILM, AND METHOD OF DEPOSITING Bi-BASED FERROELECTRIC THIN FILM USING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for depositing a BLTO (Bi-La-Ti-O) type Bi-based ferroelectric thin film in which the decomposing temperature of organic components is low, inorganization is possible in a short time, and also, the reduction ratio in weight after decomposition is low, and to provide a method of depositing a Bi-based ferroelectric thin film using the same. <P>SOLUTION: The coating liquid is used for depositing a thin film comprising a Bi layered compound expressed by the formula of La<SB>1-x</SB>Bi<SB>4-y</SB>Ti<SB>3</SB>O<SB>12+α</SB>(wherein, x, y and α are the number of 0 to <1). The coating liquid is (i) the one for depositing a Bi-based ferroelectric thin film comprising an organic metal compound(s) obtained in such a manner that a metal alkoxide corresponding to two or more kinds of metals selected from La, Bi and Ti forms compound metal alkoxide, or (ii) the one for depositing a Bi-based ferroelectric thin film comprising an organic metal compound containing La, Bi and Ti and a specified compound(s) represented by triglyme, tetraglyme, dipivaloyl methane, pinacol, pivalic acid, hexylene glycol or the like. The method of depositing a Bi-based ferroelectric thin film uses these coating liquids. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating solution for forming a BLTO-type Bi-based ferroelectric thin film and a method for forming a Bi-based ferroelectric thin film using the same. The present invention is suitably used particularly for nonvolatile ferroelectric memories.

In recent years, (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2- Na, K, and rare earth elements) and combinations of these ions; B represents 4, 5, or 6-valent ions (eg, metal elements such as Ti, Nb, Ta, W, Mo, Fe, Co, and Cr) And a combination of these ions; m = 1 to 5 is an integer). The Bi-based ferroelectric (BLSF) thin film having a layered structure represented by the following general formula has a small coercive electric field of PE hysteresis. Since it has characteristics such as less fatigue of a film due to polarization reversal, it has been spotlighted as a material for semiconductor memories and sensors (for example, see Non-Patent Documents 1 and 2). Among them, SBTO type using Sr as A metal element and Ta as B metal element; SBNO type using Sr as A metal element and Nb as B metal element; Bi-based ferroelectric thin films such as SBTNO type using Ta and Nb as metal elements; BLTO type using La as A metal element and Ti as B metal element are attracting attention as materials that exhibit the above characteristics well. In recent years, research has been actively conducted.

  Examples of the method of forming the Bi-based ferroelectric thin film include a sputtering method, a CVD method, and a coating type film forming method. The Bi-based ferroelectric thin film has a large amount of an oxide component of a metal element constituting the thin film. Therefore, the thin film forming method by the sputtering method or the CVD method requires an expensive apparatus and is expensive, and it is difficult to control the composition of a desired dielectric film and to manage the dielectric film. It is considered difficult to apply. On the other hand, the coating film forming method is promising because it does not require expensive equipment, the film forming cost is relatively low, and the control of the desired dielectric film composition and its management are easy.

  Examples of the coating liquid for forming a Bi-based ferroelectric thin film used in this coating film forming method include a salt of a carboxylic acid having a medium-chain hydrocarbon group such as 2-ethylhexanoic acid and a metal element constituting the thin film. There is known an organic coating solution obtained by dissolving an organic metal compound such as a metal alkoxide compound including an alcohol such as ethanol, methoxyethanol and methoxypropanol and a metal element constituting the thin film in an organic solvent.

  Among them, the coating liquid containing the metal alkoxide compound can stabilize the metal composition ratio in the coating liquid by complexing or hydrolyzing the metal alkoxide compound, and the metal (Bi) having a high sublimation property when forming a thin film. (See, for example, Patent Documents 1 and 2).

  By the way, in order to manufacture a device such as a Bi-based ferroelectric memory having a small film fatigue and excellent electric characteristics by using a Bi-based ferroelectric thin film, it is necessary to use a high temperature of about 800 ° C. for about 30 to 120 minutes. A step of performing a long-time heat treatment (crystallization treatment of a film) is required. However, such a long-time high-temperature heat treatment has a problem that an integrated circuit or a substrate is likely to be thermally damaged. With the rapid progress of high density and high integration of semiconductor devices in recent years, in the manufacture of ferroelectric elements used in these semiconductor devices, a manufacturing process which is not affected as much as possible by heat damage due to heat treatment. Is more strongly required than before. Therefore, development of a coating solution that can be crystallized at a low temperature or a coating solution that can be crystallized by heating for a short time is required.

  In particular, a coating solution that can be crystallized by heating for a short time is desirable from the viewpoint of improving the throughput. Therefore, a coating solution suitable for a rapid heating treatment method called an RTA (= Rapid Thermal Annealing) method or an RTP (= Rapid Thermal Processing) method. Development of a liquid is desired. Since the Bi-based ferroelectric thin film is an inorganic metal oxide film, it is desirable that the coating liquid suitable for the RTA method has a low decomposition temperature of an organic component in the coating liquid and is inorganic in a short time. Further, it is desirable that the weight loss after decomposition of the organic component is small so that cracks do not occur and a porous film is not formed.

Tadashi Takenaka, “Bismuth Layered Structure Ferroelectrics and Particle Orientation”, Report of the Japan Society of Applied Physics, Applied Electronic Properties Subcommittee, November 22, 1994, pp. 1-8 "Ceramics" Vol. 30, no. 6, pp. 499-503 (1995) JP-A-10-258252 JP-A-10-259007

  The present invention has been made in view of the above circumstances, and is a coating liquid for forming a Bi-based ferroelectric thin film that has a low decomposition temperature of an organic component, can be mineralized in a short time, and has a small weight loss rate after decomposition. And a method of forming a Bi-based ferroelectric thin film using the same.

  The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a coating solution containing an organometallic compound containing a composite metal alkoxide has solved the above-mentioned problems, especially for forming a BLTO-type Bi-based ferroelectric thin film. The above problem can be solved by further blending a specific compound represented by triglyme, dipivaloylmethane, pinacol, pivalic acid, hexylene glycol and the like into the coating solution. This led to the completion of the present invention.

  That is, the present invention provides the following general formula (1)

La _1-x Bi _4-y Ti ₃ O _{12 + α} (1)

(In the formula, x, y, and α each independently represent a number from 0 to less than 1.)
A coating liquid for forming a thin film containing a Bi layered compound represented by the formula: wherein the coating liquid is a metal alkoxide corresponding to at least two metals of La, Bi, and Ti; Provided is a coating liquid for forming a Bi-based ferroelectric thin film, comprising a formed organometallic compound.

  Further, the present invention provides the following general formula (1)

La _1-x Bi _4-y Ti ₃ O _{12 + α} (1)

(In the formula, x, y, and α each independently represent a number from 0 to less than 1.)
A coating liquid for forming a thin film containing a Bi layered compound represented by the formula: wherein the coating liquid is an organic metal compound containing La, Bi, and Ti; and the following general formulas (2) to (6)

_{H 3 CO- (C 2 H 4} O) n -CH 3 (2)
(R ¹ ) ₃ C—CO—CH ₂ —CO—C (R ¹ ) ₃ (3)
_{^{(R 1) 2 C (OH}} ) -C (OH) (R 1) 2 (4)
(R ¹ ) ₃ C-COOH (5)
(R ¹ ) ₂ C (OH) —CH ₂ —CH (OH) R ¹ (6)

(Wherein, R ¹ represents an alkyl group having 1 to 3 carbon atoms, and n represents an integer of 2 to 5)
A coating liquid for forming a Bi-based ferroelectric thin film, comprising at least one compound selected from the compounds represented by the formula:

  Further, the present invention provides a method of forming a Bi-based ferroelectric thin film by applying a coating solution for forming a Bi-based ferroelectric thin film on a substrate, drying the applied solution, and then performing a rapid heating treatment at a temperature rising rate of 10 ° C./s or more. A method for forming a Bi-based ferroelectric thin film is provided.

  According to the present invention, a coating solution for forming a BLTO-type Bi-based ferroelectric thin film that has a low decomposition temperature of an organic component, can be mineralized in a short time, and has a small weight loss rate after decomposition, and And a method of forming a Bi-based ferroelectric thin film using the same. Therefore, according to the present invention, crystallization of a film can be performed without performing long-time heating at a high temperature of about 800 ° C. as in the related art. The resulting thin film has good crystallinity, fine crystal grains, high density, and excellent film quality with few voids. In addition, the Pr value (polarization value) is also improved.

  The coating liquid for forming a Bi-based ferroelectric thin film according to the present invention includes the following two embodiments.

  The first aspect is represented by the following general formula (1)

La _1-x Bi _4-y Ti ₃ O _{12 + α} (1)

(In the formula, x, y, and α each independently represent a number from 0 to less than 1.)
A coating liquid for forming a thin film containing a Bi layered compound represented by the formula: wherein the coating liquid is a metal alkoxide corresponding to at least two metals of La, Bi, and Ti; It is a coating liquid for forming a Bi-based ferroelectric thin film, which contains the formed organometallic compound.

  In the above, it is preferable that the organometallic compound contains at least a BiTi composite metal alkoxide formed by a Bi alkoxide and a Ti alkoxide.

  A second aspect is to form a Bi-based ferroelectric thin film containing a Bi layered compound represented by the general formula (1) (where x, y, and α are as defined above). Wherein the coating liquid comprises an organometallic compound containing Bi, La, and Ti, and the following general formulas (2) to (6):

_{H 3 CO- (C 2 H 4} O) n -CH 3 (2)
(R ¹ ) ₃ C—CO—CH ₂ —CO—C (R ¹ ) ₃ (3)
_{^{(R 1) 2 C (OH}} ) -C (OH) (R 1) 2 (4)
(R ¹ ) ₃ C-COOH (5)
(R ¹ ) ₂ C (OH) —CH ₂ —CH (OH) R ¹ (6)

(Wherein, R ¹ represents an alkyl group having 1 to 3 carbon atoms, and n represents an integer of 2 to 5)
A coating liquid for forming a Bi-based ferroelectric thin film, comprising at least one selected from the compounds represented by

  In the second aspect, the organometallic compound preferably contains a composite metal alkoxide formed by a metal alkoxide corresponding to at least two metals of La, Bi, and Ti. Further, it is preferable that the organometallic compound contains at least a BiTi composite metal alkoxide formed by a Bi alkoxide and a Ti alkoxide.

  Hereinafter, the coating liquid for forming a Bi-based ferroelectric thin film according to the first and second embodiments will be described in detail.

  In the coating liquid for forming a Bi-based ferroelectric thin film of the present invention, the organic metal compound containing La, Bi, and Ti (that is, the metal element constituting the BLTO-type Bi-based ferroelectric thin film) is 2-ethylhexanoic acid. Such as a salt of a carboxylic acid having a medium chain hydrocarbon group with La, Bi, and Ti; a metal alkoxide compound composed of La, Bi, and Ti; and an alcohol such as ethanol, methoxyethanol, and methoxypropanol; and a metal acetate. Organometallic compounds are mentioned. In the present invention, the metal alkoxide compound to which at least one alkoxyl group is bonded is generally used in the coating liquid of the second embodiment because of the stabilization of the metal composition ratio, and particularly, in the coating liquid of the second embodiment, due to alkoxide exchange and the like. It is preferably used from the viewpoint that the reaction with the compounds represented by the formulas (2) to (6) is easier.

  Preferred examples of such a metal alkoxide compound include those containing a Bi alkoxide, a La alkoxide, and a Ti alkoxide.

  In the metal alkoxide compound, a plurality of different groups other than the alkoxyl group may be bonded to the metal element, for example, a carboxyl group or the like may be bonded.

  In the present invention, it is particularly preferable that at least two different metal alkoxides among the La alkoxide, Ti alkoxide, and Bi alkoxide form a composite metal alkoxide. By thus forming a composite of two or more different metal alkoxides, the precipitation (segregation) and burning out of a single metal element can be suppressed, and thus the generation of leak current can be more effectively suppressed. .

  Specific examples of the metal alkoxide contained in the coating liquid for forming a Bi-based ferroelectric thin film include the following (a) to (e).

(A) LaBi composite metal alkoxide and Ti alkoxide.
(B) BiTi composite metal alkoxide and La alkoxide.
(C) LaTi composite metal alkoxide and Bi alkoxide.
(D) LaBiTi composite metal alkoxide.
(E) La alkoxide, Ti alkoxide, and Bi alkoxide.

The composite metal alkoxide referred to in the present invention refers to a compound obtained by reacting different metal alkoxides in a solvent at a temperature of 20 to 100 ° C. for about 2 to 15 hours. At the end point of the reaction, the color of the liquid gradually changes and eventually turns into a brownish liquid. Therefore, the point at which the liquid completely changes color is preferably set as the end point of the reaction. The composite metal alkoxide obtained in this manner is described in “Plasma Ceramics Production Technology by Sol-Gel Method and Its Application” (Applied Technology Publishing Co., Ltd., published on June 4, 1989), pp. 147-181. 46-47, and specifically, LaBi (OR ² ) ₃ (OR ³ ) ₃ , TiBi (OR ⁴ ) ₄ (OR ³ ) ₃ , LaTi (OR ² ) ₃ (OR ⁴ ) ₄ , LaTiBi (OR ² ) ₃ (OR ⁴ ) ₄ (OR ³ ) ₃ (where R ² , R ³ and R ⁴ each independently represent an alkyl group having 1 to 6 carbon atoms) It is considered to be represented by Above all, LaBi (OR ² ) ₃ (OR ³ ) ₃ , TiBi (OR ⁴ ) ₄ (OR ³ ) ₃ , LaTiBi (OR ² ) ₃ (OR ⁴ ) ₄ (OR ³ ) ₃ , that is, it is preferable to use (a), (b), and (d) among the above exemplified embodiments.

  As the metal compound corresponding to La, Ti, and Bi, not only metal alkoxide but also metal acetate and the like can be used as described above. In the present invention, metal acetate (lanthanum acetate) is preferably used as lanthanum in terms of easy availability, low cost, and excellent characteristics. It is preferable that Ti and Bi use respective metal alkoxides. When lanthanum acetate is used, the aspect (b) of the composite metal alkoxide is “BiTi composite metal alkoxide and La acetate”.

  Examples of the metal alkoxide and the alcohol forming the composite metal alkoxide include the following general formula (7)

R ⁵ OH (7)

(Wherein, R ⁵ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
Is preferably used. Specific examples of these alcohols include methanol, ethanol, propanol, butanol, amyl alcohol, and cyclohexanol.

Examples of alcohols other than the above-mentioned alcohols include those in which R ⁵ is further substituted with an alkoxyl group having 1 to 6 carbon atoms, and specifically, methoxymethanol, methoxyethanol, ethoxymethanol, ethoxyethanol , Methoxypropanol, ethoxypropanol and the like.

  In the coating liquid of the present invention, in addition to the organometallic compound, at least one selected from compounds represented by the following general formulas (2) to (6) (hereinafter, also referred to as “specific compounds”) is preferable. It is blended in.

_{H 3 CO- (C 2 H 4} O) n -CH 3 (2)
(R ¹ ) ₃ C—CO—CH ₂ —CO—C (R ¹ ) ₃ (3)
_{^{(R 1) 2 C (OH}} ) -C (OH) (R 1) 2 (4)
(R ¹ ) ₃ C-COOH (5)
(R ¹ ) ₂ C (OH) —CH ₂ —CH (OH) R ¹ (6)

(In the formula, R ¹ represents an alkyl group having 1 to 3 carbon atoms, and n represents an integer of 2 to 5.)
Among the above specific compounds, examples of the compound represented by the general formula (2) include triglyme and tetraglyme. Among them, tetraglyme is preferable because the decomposition temperature is extremely low and the decomposition characteristics are good.

  As the compound represented by the general formula (3), dipivaloylmethane is particularly preferred because of its good decomposition characteristics.

  As the compound represented by the general formula (4), pinacol is particularly preferred because of its good decomposition properties.

  As the compound represented by the general formula (5), pivalic acid is particularly preferable since it easily forms an adduct and has good decomposition characteristics. The compound represented by the general formula (IV) may form an acid anhydride.

  As the compound represented by the general formula (6), 2-methyl-2,4-pentanediol (= hexylene glycol) is particularly preferred because of its good decomposition characteristics.

  In the coating liquid according to the second aspect of the present invention, the specific compound and the organometallic compound are contained as a reaction product obtained by reacting the two, and the decomposition efficiency of the organic component is very high, This is preferable because the weight loss rate after decomposition is small.

  The reaction product is obtained, for example, by adding one or more kinds of organometallic compounds to an organic solvent, adding one or more kinds of the above-mentioned specific compounds, and then adding a temperature of about 10 to 80 ° C. Under the conditions, it can be synthesized by heat treatment for about 0.5 to 10 hours, but the reaction conditions are not limited to the above temperature, reaction time, and the like.

  The coating liquid of the second aspect of the present invention can be obtained by adding and mixing the reaction product of each of the thus synthesized organometallic compounds and the specific compound to an organic solvent. Alternatively, a specific compound to be used is added to a mixed solution in which an organometallic compound to be used in advance is added to an organic solvent and mixed, and heating is performed for about 0.5 to 3 hours under a temperature condition of about 10 to 80 ° C., particularly, Can be obtained by performing a heat treatment for about 1.5 to 2.5 hours under a temperature condition of about 50 to 60 ° C., but the preparation of the coating solution of the present invention is limited to the above examples. Not.

  The amount of the specific compound to be used is expressed by the following formula 1 with respect to the total valence of the metal element having a stoichiometric composition ratio in the coating solution (hereinafter simply referred to as “total valence”).

Is preferably in the range of the amount of use (the number of moles). In Formula 1, the range of (total valence) / 6 ≦ used amount (mol number) ≦ (total valence) / 2 is particularly preferable. When the amount (mol number) used is less than (total valence) / 30, the effect of lowering the decomposition temperature of the organic component is not sufficiently exerted. The upper limit of the amount of the specific compound used is not particularly limited. However, if added in an excessively large amount, the coating characteristics of the coating solution may be degraded or may affect the densification of the formed film. Is preferably about (total valence) / 2 mol or less with respect to the total valence of

  The total valence is calculated by the following equation (2).

Is the value represented by For example, in the case of a coating solution having a stoichiometric composition ratio containing 0.75 mol of a La compound, 3.25 mol of a Bi compound, and 3.0 mol of a Ti compound, ｛[3 (valence of La) × 0. 75 (mol)] + [3 (valence of Bi) × 3.25 (mol)] + [4 (valence of Ti) × 3 (mol)]｝ = 24 (total valence).

  Examples of the solvent of the coating liquid for forming a Bi-based ferroelectric thin film according to the first embodiment and the second embodiment include a saturated aliphatic solvent, an aromatic solvent, an alcohol solvent, a glycol solvent, an ether solvent, Ketone solvents, ester solvents and the like can be mentioned. Among them, alcohol-based solvents, glycol-based solvents, ether-based solvents, ketone-based solvents, ester-based solvents and the like having an oxygen atom in the molecule are suitably used when preparing a hydrolysis-type sol-gel solution.

  Examples of the alcohol solvent include methanol, ethanol, propanol, butanol, amyl alcohol, cyclohexanol, methylcyclohexanol and the like.

  Examples of glycol solvents include ethylene glycol monomethyl ether, ethylene glycol monoacetate, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monoacetate, propylene glycol dimethyl ether, propylene glycol diethyl ether, and propylene. Examples thereof include glycol dipropyl ether, dipropylene glycol monoethyl ether, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, and 3,3′-dimethylbutanol.

  Examples of ether solvents include methylal, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane, and the like.

  Ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethyl nonanone, acetonitrile acetone, dimethyl oxide, holon, cyclohexanone, diacetone alcohol Etc. are exemplified.

  Ester solvents include ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate, diethyl malonate , Triethyl citrate, tributyl citrate and the like.

  These solvents can be used alone or in a mixture of two or more.

  In the present invention, the coating liquid for forming a Bi-based ferroelectric thin film according to the first or second embodiment is water or a sol-gel liquid which has been subjected to hydrolysis and partial polycondensation treatment using water and a catalyst. Some are also preferably used.

  In addition, those in which the above-mentioned coating liquid for forming a Bi-based ferroelectric thin film has been subjected to a stabilization treatment with a stabilizer such as carboxylic anhydrides, dicarboxylic monoesters, β-diketones, and glycols are also preferably used.

  Further, both the above-mentioned hydrolysis / partial polycondensation treatment and the above-mentioned stabilization treatment may be used in combination.

  That is, in the present invention, (i) the coating liquid is subjected to hydrolysis or partial polycondensation treatment using water or water and a catalyst to form a sol-gel liquid. (Ii) The coating liquid is water or A hydrolysis and partial polycondensation treatment using water and a catalyst to form a sol-gel liquid, and then a stabilizing treatment by adding a stabilizing agent; (iii) a stabilizing treatment of the coating solution; (iv) Preferred examples include stabilizing the coating solution and then subjecting it to hydrolysis or partial polycondensation using water or water and a catalyst to form a sol-gel solution.

  The stabilizer is for improving the storage stability of the coating solution, and particularly for suppressing the thickening and gelling of the coating solution after hydrolysis.

  In the above stabilizer, the carboxylic anhydrides include the following general formula (8)

R ⁶ (CO) ₂ O (8)

(Wherein, R ⁶ represents a divalent saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
At least one selected from the carboxylic anhydrides represented by

  Specific examples of such carboxylic anhydrides include, for example, maleic anhydride, citraconic anhydride, itaconic anhydride, succinic anhydride, methylsuccinic anhydride, glutaric anhydride, α-methylglutaric anhydride, α, α -Dimethylglutaric acid, trimethylsuccinic anhydride and the like.

  Further, as the dicarboxylic acid monoesters, the following general formula (9)

R ⁷ OCOR ⁸ COOH (9)

(Wherein, R ⁷ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms; R ⁸ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
At least one selected from dicarboxylic acid monoesters represented by

  As such a dicarboxylic acid monoester, specifically, for example, a half-esterified product obtained by reacting a carboxylic acid of a dibasic acid with an alcohol can be used, and oxalic acid, malonic acid, succinic acid, Glutaric acid, adipic acid, pimelic acid, speric acid, azelic acid, sebacic acid, maleic acid, citraconic acid, itaconic acid, methylsuccinic acid, α-methylglutaric acid, α, α-dimethylglutaric acid, trimethylglutaric acid, etc. An ester of at least one carboxylic acid of a basic acid and at least one kind of methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, etc. by a known method. Reaction It can be synthesized.

  As β-diketones, the following general formula (10)

R ⁹ COCR ¹⁰ HCOR ¹¹ (10)

(Wherein, R ⁹ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms; R ¹⁰ represents H or CH ₃ ; R ¹¹ represents an alkyl group or an alkoxyl group having 1 to 6 carbon atoms) Represents)
At least one selected from β-diketones containing β-ketoesters represented by the following formulas is preferably used.

  Specific examples of the β-diketones used in the present invention include, for example, acetylacetone, 3-methyl-2,4-pentanedione, benzoylacetone and the like. Examples of the β-ketoester include ethyl acetoacetate and diethyl malonate. Although other complexing agents are also applicable, complexing agents such as hexafluoroacetylacetone, which form a metal halide after firing, form a highly sublimable or highly volatile metal complex. Use in liquids is unsuitable.

  As glycols, the following general formula (11)

HOR ¹² OH (11)

(Wherein, R ¹² represents a saturated or unsaturated divalent hydrocarbon group having 1 to 6 carbon atoms)
At least one selected from glycols represented by formula (1) is preferably used.

  As the glycols used in the present invention, specifically, 1,2-ethanediol, 1,3-propanediol, 1,2-propanediol, 2,3-butanediol, diethylene glycol, 1,5-pentane Diol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanediol, dipropylene glycol, 2,2-diethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexane Diol, 2-ethyl-1,3-hexanediol, tetraethylene glycol and the like can be exemplified.

  Any of the above stabilizers is preferably a short-chain one having 1 to 6 carbon atoms from the viewpoint of increasing the polarity of the metal compound and the inorganicity after coating.

  In addition, lower monocarboxylic acids such as acetic acid, propionic acid, butyric acid, and valeric acid can be used as a stabilizer if desired.

  When the Bi-based ferroelectric coating solution is subjected to hydrolysis / partial polycondensation, the hydrolysis / partial polycondensation reaction is carried out by adding water, or water and a catalyst to the coating solution, and treating the solution at 20 to 50 ° C. For several hours to several days. As the catalyst, those known for hydrolysis reaction of metal alkoxides, for example, acid catalysts such as inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, organic acids such as acetic acid, propionic acid and butyric acid, sodium hydroxide and potassium hydroxide Examples thereof include inorganic and organic alkali catalysts such as ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide. In the present invention, it is particularly preferable to use an acid catalyst from the viewpoint of film properties.

  By reacting the composite metal alkoxide with the stabilizer as described above and performing a treatment such as carboxylation, β-diketonation, or chelation, a product having polarity and excellent stability can be obtained. As a result, the hydrolysis property is improved, and the solubility in a practical polar solvent is also improved. As a result, the condensation polymerization reaction by the sol-gel method can sufficiently proceed in the coating solution, and Bi-O-Bi, Bi-OT1, Bi-O-La, Ti-O-Bi-O- Generation of an inorganic bond (metalloxane) bond such as La can further reduce the amount of precipitation (segregation) and burnout of a specific metal element such as Bi, and can increase the mineralization of the entire coating liquid.

  In the method of forming a thin film of the present invention, the Bi-based ferroelectric thin film is subjected to a rapid heating treatment at a rate of 10 ° C./s or more, preferably 50 ° C./s or more, after the above-mentioned coating solution of the present invention is applied on a substrate and dried. To form

  The substrate to be used is not particularly limited, and examples thereof include a semiconductor substrate such as silicon and a glass substrate.

  Further, a substrate on which an electrode material of a ferroelectric memory is formed may be used.For example, an upper portion of a substrate such as a silicon wafer is oxidized to form a Si oxide film or the like, and a substrate on which an electrode material is formed, A substrate in which an electrode material is formed on a substrate on which an insulating layer, a lower wiring, an interlayer insulating layer, and the like are formed may be used. When an electrode material is provided, the electrode material can be formed by a known method such as sputtering or vapor deposition, and its film thickness is not particularly limited. The electrode material is not particularly limited as long as it is a material exhibiting conductivity, and examples thereof include metals such as Pt, Ir, Ru, Re, and Os, and conductive metal oxides that are metal oxides thereof. Can be used.

  As a method of applying the coating liquid for forming a Bi-based ferroelectric thin film, a known application method such as a mist deposition method (LSMCD), a spinner method, or a dip method can be used.

  The drying treatment can be performed in a nitrogen atmosphere, an air atmosphere, an oxygen atmosphere, or the like. The drying time varies depending on the drying temperature, and is not particularly limited. However, it is preferable that the drying time is such that the coating film on the substrate does not flow and the film thickness does not change or flow down when the substrate is transported. The drying means is not particularly limited, and can be performed by, for example, a method of placing a substrate on which a coating film is formed on a hot plate at a set temperature.

  Subsequently, a heat treatment is performed. By the heat treatment, the organic components in the coating film are baked and removed, and a metal oxide film is formed. Although there is no particular limitation on the heating means, the coating liquid of the present invention is a material that has a low decomposition temperature of organic components, can be mineralized in a short time, and has a small weight loss rate after decomposition. It is suitable for a rapid heating (RTA) method using a plate or an annealing lamp. By using the coating liquid of the present invention, the decomposition of organic components does not become insufficient even in a short heat treatment such as the RTA method, and a film having excellent crystallinity can be formed. That is, in the present invention, a film excellent in crystallization from a fluorite structure to a perovskite structure is formed by using the above-mentioned coating solution of the present invention. This means that, for example, in the XRD measurement, there is almost no broad peak around 2θ = 33 ° and around 48 ° derived from the fluorite structure, and further, a sharp peak around 2θ = 29 ° derived from the perovskite structure is large. It is shown from what is seen.

  Note that the heat treatment can be performed in an inert gas such as nitrogen, in the air, or in an oxygen atmosphere, and can be appropriately selected depending on the purpose.

  Further, a low-speed heat treatment method using a furnace (furnace) with a low temperature rising rate can also be applied. When this low-speed heating treatment method is used, it is preferable to use a coating solution that has been subjected to the above-mentioned hydrolysis treatment and stabilizer addition treatment from the viewpoint of improving the surface morphology of the formed film. In particular, those subjected to the stabilizer addition treatment are excellent in the denseness and electrical properties of the coating.

  The thickness of the ferroelectric thin film is not particularly limited, but is laminated at about 20 to 100 nm per layer, and applied several times (usually about 2 to 5 times) until the final film thickness becomes about 80 to 300 nm. It is preferable to repeat the drying → heating treatment in order to obtain good electric characteristics.

  According to the present invention, crystallization of a film can be performed without performing long-time heating at a high temperature of about 800 ° C. as in the related art. The resulting thin film has good crystallinity, fine crystal grains, high density, and excellent film quality with few voids. In addition, the Pr value (polarization value) is also improved.

[Example]
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Preparation of coating liquid 1] (composite → hydrolysis)
At room temperature (25 ° C.), while stirring 700 g of 2-methoxypropanol, 0.075 mol of La acetate, 0.30 mol of Ti isopropoxide, and 0.325 mol of Bibutoxide are added in this order, and the mixture is stirred until it is uniformly dissolved. Continued.

  Then, the mixture was heated until the liquid temperature reached 80 ° C., and stirred for 2 hours while maintaining this temperature.

  Thereafter, the heating was stopped, and stirring was continued until the liquid temperature reached room temperature. Then, 0.2 mol of water was added little by little. After the addition was completed, stirring was performed for 2 hours, and the composite metal alkoxide solution (solution B) was added. Obtained.

  Subsequently, the mixture was diluted with 2-methoxypropanol to prepare a coating solution 1 having a concentration of 10% by weight in terms of lanthanum bismuth titanium oxide.

[Preparation of coating liquid 2] (composite → hydrolysis → addition of specific compound)
A composite metal alkoxide solution (solution B) was obtained in the same manner as described in Preparation of Coating Liquid 1.

  Then, while stirring the solution B vigorously, 0.45 mol of tetraglyme (corresponding to 4.5 mol equivalents when the total valence of metal elements is converted into 24 valences) is added, and then the liquid temperature becomes 50 ° C. The mixture was stirred for 3 hours while maintaining the same temperature.

  Subsequently, the mixture was diluted with 2-methoxypropanol to prepare a coating liquid 2 having a concentration of 10% by weight in terms of lanthanum bismuth titanium oxide.

[Evaluation of TG curve]
The coating solution 1 and the coating solution 2 were subjected to a heat treatment at 20 ° C./min to remove the solvent, and then cooled once to 20 ° C., and again subjected to a heat treatment at a heating rate of 20 ° C./min to obtain TG ( = Thermogravimetry) curves were determined. The TG curve of the coating solution 1 is shown in FIG. 1, and the TG curve of the coating solution 2 is shown in FIG. In FIGS. 1 and 2, the “TEMP” curve indicates the coating temperature (° C.).

  From the comparison between FIG. 1 and FIG. 2, in each case, the decomposition temperature of the organic component is low and the mineralization is performed in a short period of time. It was found that the temperature was low and the mineralization was performed in a short time. In addition, it turned out that the weight reduction rate after decomposition | disassembly of both the coating liquid 1 and the coating liquid 2 is small about 25-45%.

3 is a graph showing a TG curve of a coating solution 1. 6 is a graph showing a TG curve of a coating solution 2.

Claims (12)

The following general formula (1)
La _1-x Bi _4-y Ti ₃ O _{12 + α} (1)
(In the formula, x, y, and α each independently represent a number from 0 to less than 1.)
A coating liquid for forming a thin film containing a Bi layered compound represented by the formula: wherein the coating liquid is a metal alkoxide corresponding to at least two metals of La, Bi, and Ti; A coating liquid for forming a Bi-based ferroelectric thin film, comprising a formed organometallic compound.   The coating liquid for forming a Bi-based ferroelectric thin film according to claim 1, wherein the organometallic compound contains at least a BiTi composite metal alkoxide formed by a Bi alkoxide and a Ti alkoxide.   3. The Bi-based ferroelectric substance according to claim 1, wherein the Bi-based ferroelectric thin film forming coating liquid is water or a sol-gel liquid that has been hydrolyzed and partially polycondensed using water and a catalyst. Coating liquid for thin film formation.   The coating liquid for forming a Bi-based ferroelectric thin film is stabilized using at least one stabilizer selected from carboxylic anhydrides, dicarboxylic monoesters, β-diketones, and glycols. The coating liquid for forming a Bi-based ferroelectric thin film according to any one of claims 1 to 3.   A Bi-based ferroelectric thin film is formed by applying the coating liquid for forming a Bi-based ferroelectric thin film according to any one of claims 1 to 4 onto a substrate, drying the coated liquid, and then performing a rapid heating treatment at a temperature rising rate of 10 ° C./s or more. A method for forming a Bi-based ferroelectric thin film, comprising forming a body thin film. The following general formula (1)
La _1-x Bi _4-y Ti ₃ O _{12 + α} (1)
(In the formula, x, y, and α each independently represent a number from 0 to less than 1.)
A coating liquid for forming a thin film containing a Bi layered compound represented by the formula: wherein the coating liquid is an organic metal compound containing La, Bi, and Ti; and the following general formulas (2) to (6)
_{H 3 CO- (C 2 H 4} O) n -CH 3 (2)
(R ¹ ) ₃ C—CO—CH ₂ —CO—C (R ¹ ) ₃ (3)
_{^{(R 1) 2 C (OH}} ) -C (OH) (R 1) 2 (4)
(R ¹ ) ₃ C-COOH (5)
(R ¹ ) ₂ C (OH) —CH ₂ —CH (OH) R ¹ (6)
(Wherein, R ¹ represents an alkyl group having 1 to 3 carbon atoms, and n represents an integer of 2 to 5)
A coating liquid for forming a Bi-based ferroelectric thin film, comprising at least one compound selected from the compounds represented by the formula:   7. The Bi-based ferroelectric thin film according to claim 6, wherein the organometallic compound and at least one selected from the compounds represented by the general formulas (2) to (6) form a reaction product. Coating liquid.   8. The Bi-based ferroelectric thin film according to claim 6, wherein the organometallic compound contains a composite metal alkoxide formed by metal alkoxides corresponding to at least two kinds of metals among La, Bi, and Ti. Coating liquid.   The coating liquid for forming a Bi-based ferroelectric thin film according to any one of claims 6 to 8, wherein the organometallic compound contains at least a BiTi composite metal alkoxide formed by a Bi alkoxide and a Ti alkoxide.   The coating liquid for forming a Bi-based ferroelectric thin film according to any one of claims 6 to 9, wherein the coating liquid is water or a sol-gel liquid that has been hydrolyzed and partially polycondensed using water and a catalyst. Coating liquid for forming a Bi-based ferroelectric thin film.   The coating liquid for forming a Bi-based ferroelectric thin film is stabilized using at least one stabilizer selected from carboxylic anhydrides, dicarboxylic monoesters, β-diketones, and glycols. The coating liquid for forming a Bi-based ferroelectric thin film according to claim 1 or any one of claims 6 to 10.   A coating liquid for forming a Bi-based ferroelectric thin film according to any one of claims 6 to 11, which is applied to a substrate and dried, and then subjected to a rapid heating treatment at a temperature-raising rate of 10 ° C / s or more. A method for forming a Bi-based ferroelectric thin film, comprising forming a body thin film.

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