JP2005255468A - COATING LIQUID FOR FORMING Bi-BASED DIELECTRIC THIN FILM WITH PARAELECTRIC OR FERROELECTRIC PROPERTY, AND Bi-BASED DIELECTRIC THIN FILM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for forming a Bi-based dielectric thin film showing paraelectric or ferroelectric property in compliance with applications of semiconductor memories. <P>SOLUTION: This coating liquid for forming a Bi-based dielectric thin film showing paraelectric or ferroelectric property contains a composite metal oxide expressed by the formula: äBi<SB>4-x</SB>, (La<SB>z</SB>, B<SB>1-z</SB>)<SB>x</SB>}<SB>n</SB>(Ti<SB>3-y</SB>, A<SB>y</SB>)O<SB>12+α</SB>(wherein A is a metal element such as Ge; B is a rare earth element except lanthanum or a metal element such as Ca or Sr; 0≤x<4, 0≤y≤0.3, 0<z≤1; n=0.7-1.4; α is a valence determined by the metal composition ratio) and contains a composite metal alkoxide formed from at least two metal alkoxides, i.e., oxides of Bi and Ti. The coating liquid is preferably a sol-gel liquid obtained by hydrolysis or partial condensation reaction treatment using water or water and a catalyst. Preferably, the coating liquid contains an alkanolamine. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating liquid for forming a paraelectric or ferroelectric Bi-based dielectric thin film, and a Bi-based dielectric thin film formed using the same. The coating liquid of the present invention can function as both a paraelectric material and a ferroelectric material, and can be widely applied to fields using pyroelectricity, high dielectric property, and ferroelectricity. In particular, the present invention can be widely applied according to the required characteristics of semiconductor devices such as a single capacitor (thin film capacitor), a DRAM, and a capacitor of a nonvolatile memory.

  Due to the need for increased memory capacity of semiconductor memory, DRAM (= Dynamic Random Access Memory) has a high dielectric constant (high dielectric), paraelectric or ferroelectric dielectric as a charge storage capacitor. The use of thin films has been studied. On the other hand, a ferroelectric dielectric thin film is used for a nonvolatile integrated memory because of its high remanent polarization, and research using the hysteresis, dielectric thin film material applicable to the memory element, and Development of a method for forming a thin film has been actively conducted.

  As described above, in the semiconductor memory element, a desirable material is properly used in each of the paraelectric to ferroelectric dielectric thin films depending on the application.

  Memory elements such as DRAM and SRAM (= Static Random Access Memory) are fields in which miniaturization is particularly advanced among semiconductor devices, and in order to ensure the reliability by keeping the soft error rate low. Therefore, it is necessary to secure a capacitor capacity per memory cell above a certain value.

Conventionally, to ensure capacitor area by adopting a three-dimensional structure, also by using the Si _x N _y film or SiO _x / Si _x N _y multilayer film as a capacitor, has solved this problem. Although the Si _x N _y film has high insulation resistance and can be thinned, the relative permittivity (ε) is as low as about 4 to 7, and a three-dimensional structure is indispensable for storing a sufficient charge. there were.

  However, the three-dimensional structure has a very heavy burden on the planarization of the interlayer insulating film. From the standpoint of reducing leakage current, capacitor thinning is approaching its limit, and 256M (mega) DRAM and 1G (giga) DRAM generations require new technological breakthroughs. ing.

  In addition to the memory, in many semiconductor elements such as logic elements, there are many elements having a capacitor. In these elements as well, technical breakthrough is required.

  Under such circumstances, a high dielectric constant film is considered promising as a constituent material of the capacitor.

As a high dielectric constant film, Ta ₂ O ₅ (tantalum oxide: ε = 20 to 35) or a complex oxide system exhibiting paraelectricity, piezoelectricity, pyroelectricity due to a perovskite type unit crystal lattice structure Ceramics are known. As the composite oxide ceramics, for example, BST (barium strontium titanate: ε = 400 or more) and PZT (lead zirconate titanate: ε = 1000 or more) are known. If these high dielectric constant films are used as the constituent material of the capacitor, it is possible to secure a sufficient capacity even in a planar capacitor structure, facilitating device manufacturing, and improving device reliability. be able to.

  Especially in the production of multilayer ceramic capacitors, it is generally necessary to make BTO (barium titanate oxide) powder into a slurry and fire it after film formation. In order to obtain a sufficient capacitor capacity, it is necessary to stack several hundred layers, but by using a high dielectric constant film, it is possible to obtain a high capacity without so much multilayering.

  The relationship between the capacitance (C) and the dielectric constant (ε) is expressed by the following equation.

C = ε · S / D (where ε = nE)
(Where C is the capacitance, ε is the dielectric constant, S is the electrode area, D is the film thickness, n is the vacuum dielectric constant (8.854187816E ^-12 ), and E is the relative dielectric constant.)

  As is clear from the above formula, by increasing D (film thickness) and increasing S (electrode area) to increase C (capacitance), increase ε (dielectric constant). There is a method of increasing C (capacitance). In order to avoid the problem of adopting a three-dimensional structure as described above, it is effective to use a method of increasing ε, that is, a high dielectric constant material.

  Among the above high dielectric materials, lead-based dielectrics such as PZT (lead zirconate titanate) have been used as ferroelectric materials because they have high remanent polarization. Therefore, there is a need for an alternative material that does not contain lead. Examples of ferroelectric materials other than lead-based ferroelectrics include bismuth strontium tantalate (SBT) (for example, see Patent Document 1), bismuth titanate (BIT) (for example, see Patent Document 2 and Patent Document 3), Bismuth (Bi) -based ferroelectric materials such as lanthanum bismuth titanate (BLT) (for example, see Patent Documents 4 to 7) in which a part of bismuth of BIT is replaced with La have been reported. BIT is a material having a remanent polarization value higher than that of SBT. However, BLT has been reported to have a remanent polarization value higher than that of BIT, and has attracted attention in recent years.

  Examples of methods for forming these Bi-based ferroelectric thin films include sputtering, CVD, and coating-type film forming methods. Bi-based ferroelectric thin films have an oxide component of a metal element constituting the thin film. Therefore, thin film formation methods such as sputtering and CVD require costly equipment and are expensive, and it is difficult to control and manage the desired dielectric film composition. Is considered difficult to apply. On the other hand, the coating-type film forming method is promising because it does not require an expensive apparatus, the film forming cost is relatively low, and the desired dielectric film composition control and management are easy.

  As a coating liquid for forming a Bi-based ferroelectric thin film used in this coating type film forming method, a salt of a carboxylic acid having a medium chain hydrocarbon group such as 2-ethylhexanoic acid and a constituent metal element of the thin film, An organic coating solution is known in which an organic metal compound such as a metal alkoxide compound composed of an alcohol such as ethanol, methoxyethanol, or methoxypropanol and a constituent metal element of the thin film is dissolved in an organic solvent.

  However, it is required to further stabilize the metal composition ratio in the coating solution and to suppress the phenomenon in which the metal composition ratio in the thin film changes due to the burning of highly sublimable metals (such as Bi) during the formation of the thin film. ing.

  Therefore, a coating-type material, which is a material for forming a BIT-based or BLT-based ferroelectric thin film in which the metal composition is stabilized and the phenomenon that the metal composition ratio in the thin film changes is suppressed. Realization is required.

  In addition, depending on the use of the semiconductor memory, there is a field where paraelectricity is desirable. Therefore, development of a material having a paraelectric property, a low leakage current, and a high dielectric constant is also desired.

  In Patent Document 8 and Patent Document 9, there is a description of attempts to stabilize the metal composition ratio and to suppress the phenomenon in which the metal composition ratio in the thin film is changed by combining metal alkoxides. The material described in is only related to the coating liquid for forming the SBT ferroelectric thin film, and there is no description about the coating liquid for forming the BIT or BLT ferroelectric thin film or the coating liquid for forming the paraelectric thin film. .

JP-A-9-286619 JP-A-8-40965 JP-A-8-91841 JP 2003-192431 A JP 2003-82470 A JP 2002-265224 A JP 2002-255557 A Japanese Patent Laid-Open No. 10-258252 Japanese Patent Laid-Open No. 10-259007

  It is an object of the present invention to provide a coating liquid for forming a ferroelectric Bi-based dielectric thin film in which the metal composition ratio is stabilized and the phenomenon that the metal composition ratio in the thin film changes is suppressed. To do.

  In addition, since the present invention has a field in which paraelectricity is more desirable than ferroelectricity depending on the application, it is a paraelectric, low leakage current, and a paraelectric Bi-based dielectric having a high dielectric constant. An object is to provide a coating solution for forming a thin film.

  In order to achieve the above object, the present invention provides a coating solution for forming a ferroelectric Bi-based dielectric thin film containing a composite metal oxide represented by the following general formula (I), comprising at least Bi, Provided is the coating solution containing a composite metal alkoxide formed by two metal alkoxides of Ti.

{Bi _4-x , (La _z , B _1-z ) _x } _n (Ti _3-y , A _y ) O _{12 + α} (I)
(In the formula, A represents at least one metal element selected from V, Cr, Mn, Si, Ge, Zr, Nb, Ru, Sn, Ta, and W; B represents a rare earth element excluding lanthanum; Represents at least one metal element selected from Ca, Sr, and Ba; x, y, and z are represented by 0 ≦ x <4, 0 ≦ y ≦ 0.3, and 0 <z ≦ 1, respectively. N represents a number from 0.7 to 1.4; α represents a value determined by the metal composition ratio.)

  The present invention also provides a coating liquid for forming a paraelectric Bi-based dielectric thin film, which includes a composite metal alkoxide formed of at least two metal alkoxides of Bi and Ti, or at least a Bi alkoxide. The coating liquid containing a mixed metal alkoxide obtained by mixing Ti and a alkoxide is provided.

  Here, the coating solution includes a paraelectric material including a composite metal oxide represented by the above general formula (I) (wherein A, B, x, y, z, n, and α are as defined above). A coating liquid for forming a conductive Bi-based dielectric thin film is preferable.

  In the present invention, a coating solution for forming the above-mentioned paraelectric Bi-based dielectric thin film is applied on a substrate and subjected to a heat treatment (first heat treatment) at 500 to 700 ° C. without applying a heat drying treatment. To form a coating film, and if necessary, the steps from the application to the heat treatment (first heat treatment) are repeated a plurality of times to form a coating film laminate, and then a heat treatment at 600 to 700 ° C. A method for forming a paraelectric Bi-based dielectric thin film is provided.

  The present invention also provides a paraelectric Bi-based dielectric thin film obtained by applying a coating liquid for forming the above-mentioned paraelectric Bi-based dielectric thin film on an electrode provided on a substrate and baking the coating liquid. provide.

  The present invention provides a coating liquid for forming a ferroelectric Bi-based dielectric thin film in which the metal composition ratio is stabilized and the phenomenon that the metal composition ratio in the thin film changes is suppressed. The present invention also provides a coating liquid for forming a paraelectric Bi-based dielectric thin film having a low leakage current and a high dielectric constant.

  The coating solution of the present invention can function as a paraelectric material or a ferroelectric material by controlling the metal composition ratio in the coating solution or by controlling the thin film formation conditions. Therefore, the coating liquid of the present invention can be widely applied according to the required characteristics of semiconductor devices, such as DRAM in which a paraelectric material is preferably used, and a nonvolatile memory in which a ferroelectric material is preferably used. .

  I. Coating liquid for forming a ferroelectric Bi-based dielectric thin film (hereinafter also referred to as “Bi-based ferroelectric thin film forming coating liquid”).

  The coating liquid for forming a Bi-based ferroelectric thin film in the present invention is a coating liquid for forming a Bi-based ferroelectric thin film containing a composite metal oxide represented by the following general formula (I).

{Bi _4-x , (La _z , B _1-z ) _x } _n (Ti _3-y , A _y ) O _{12 + α} (I)

  In the above formula, A represents at least one metal element selected from V, Cr, Mn, Si, Ge, Zr, Nb, Ru, Sn, Ta, and W. In the coating liquid for forming a ferroelectric thin film, Ge is particularly preferably used as A.

  B represents at least one metal element selected from rare earth elements excluding lanthanum, Ca, Sr, and Ba. Of these, lanthanoids are preferable, and praseodymium (Pr), cerium (Ce), and neodymium (Nd) are particularly preferably used.

  x represents a number represented by 0 ≦ x <4. Preferably 0 <x <4.

  y represents a number represented by 0 ≦ y ≦ 0.3. Preferably 0 <y ≦ 0.3. When Ge is used as the A metal, y is preferably y = 0.05 to 0.20, particularly preferably y = 0.10 to 0.15.

  z represents a number represented by 0 <z ≦ 1. Preferably 0 <z <1.

  n shows the number of 0.7-1.4.

  α represents a value determined by the metal composition ratio. Preferably, −5 ≦ α ≦ 5, and more preferably −2 ≦ α ≦ 2.

  The coating solution contains a composite metal alkoxide formed of at least two metal alkoxides of Bi and Ti. Preferably, the coating solution is further hydrolyzed and partially condensed using water or water and a catalyst. A sol-gel solution.

  That is, in the production of the coating solution of the present invention, among the metal elements contained in the coating solution, both Bi and Ti use metal alkoxide as a starting material. As for La, A metal element, and B metal element (however, A metal element and B metal element may not be included), each metal alkoxide is preferably used as a starting material, but metal acetate (for example, lanthanum acetate) Etc.), β-diketone metal complexes and the like can also be used as starting materials. These are not limited to examples. In the present invention, it is preferable to use a metal acetate (lanthanum acetate) as the lanthanum from the viewpoints of availability, low cost, and excellent characteristics. As the A metal element and the B metal element, it is preferable to use respective metal alkoxides.

Specifically, the following modes (where A metal and B metal are included) are exemplified, but the invention is not limited to these examples.
(A) An embodiment containing BiTi composite metal alkoxide, La alkoxide (or acetate etc.), A metal alkoxide (or acetate etc.), B metal alkoxide (or acetate etc.).
(B) An embodiment containing BiTiLa composite metal alkoxide, A metal alkoxide (or acetate, etc.), B metal alkoxide (or acetate, etc.).
(C) An embodiment containing BiTiLaA metal composite alkoxide, B metal alkoxide (or acetate, etc.).
(D) An embodiment containing BiTiLaA metal B metal composite alkoxide.

  In the present invention, the embodiment (d) above in which all metal elements form a composite alkoxide is most preferred. In this way, by converting two or more kinds of different metals into a composite metal alkoxide, it is possible to more effectively suppress the phenomenon of precipitation (segregation) and burning of a single metal element.

The composite metal alkoxide as used in the present invention refers to Bi alkoxide, Ti alkoxide, alkoxide of other metal elements (La, A metal element, B metal element), acetate, β-diketone metal complex, etc. The compound obtained by making it recirculate | reflux for about 2 to 15 hours on 30-100 degreeC heating conditions in it. Since the end point of the reaction gradually changes in color and finally becomes a brownish brown liquid, the end point of the reaction is preferably set as the end point of the reaction. The composite metal alkoxide thus obtained is described in “Glass / ceramics production technology by sol-gel method and its application” (Applied Technology Publishing Co., Ltd., issued on June 4, 1989). Those defined in 46 to 47 are preferable examples. Specifically, TiBi (OR) ₄ (OR) ₃ , LaTiBi (OR) ₃ (OR) ₄ (OR) ₃ , LaTiBiA (OR) ₃ (OR) ₄ (OR) ₃ (OR) _m , LaTiBiB (OR) ) ₃ (OR) ₄ (OR) ₃ (OR) _n , LaTiBiAB (OR) ₃ (OR) ₄ (OR) ₃ (OR) _m (OR) _n (where A and B are as defined above) Yes; m is the valence of the A metal element; n is the valence of the B metal element; R is independently an alkyl group having 1 to 6 carbon atoms, etc.) However, it is not limited to these examples. In the present invention, Bi, which has high sublimation property, is combined with Ti, which is an essential metal element, so that a film having a composition ratio close to the raw material charge ratio can be formed.

  Examples of the alcohol that forms the metal alkoxide and the composite metal alkoxide include the following general formula (II):

R ₁ OH (II)

(In the formula, R ₁ 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 alcohols include those in which R ₁ is further substituted with an alkoxyl group having 1 to 6 carbon atoms. Specifically, methoxymethanol, methoxyethanol, ethoxymethanol, ethoxyethanol, etc. Is exemplified.

  In these metal alkoxides and composite metal alkoxides, a part of the alkoxyl group may be substituted with alkanolamine, carboxylic anhydride, dicarboxylic acid monoester, β-diketone, glycol and the like described later.

  The coating solution of the present invention is preferably a sol-gel solution obtained by further subjecting the coating solution containing the composite metal alkoxide to hydrolysis or partial condensation treatment with water or water and a catalyst.

  The hydrolysis reaction is performed by adding water or water and a catalyst to the coating solution and stirring at 20 to 50 ° C. for several hours to several days. Examples of the catalyst include those known for hydrolysis reactions 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. Inorganic / organic alkali catalysts such as ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide. However, inorganic alkalis such as sodium hydroxide and potassium hydroxide are concerned that metal ions such as sodium and potassium may remain in the coating solution and affect the electrical properties of the film. In the present invention, the nitrogen-containing alkali of may form a nitrogen compound having a high boiling point after the hydrolysis reaction, which may affect the densification of the coating film during the firing step. It is particularly preferable to use an acid catalyst.

  The hydrolysis reaction can also be performed by applying the coating solution on the electrode and then exposing the coating surface to a humidified atmosphere. For example, the hydrolysis reaction is performed at 50 to 120 ° C. for about 10 to 60 minutes under a humidity of 50 to 100%. be able to.

  The above conditions can be appropriately selected according to the use of the film, and are not limited to the above.

  By hydrolyzing in this way, the content of organic components in the entire coating film after the drying step can be reduced, and metalloxane bonds of each metal are formed. Precipitation (segregation) and burning can be suppressed. The reason for this is that each organometallic compound has an organic group in its structure, but by hydrolyzing it, organic groups such as alkoxyl groups can be eliminated to form a more inorganic metalloxane bond. it can. The desorbed organic group becomes a low-boiling point alcohol, glycol or the like and remains in the coating solution or coating, but evaporates with the solvent in the drying process. Can be formed. In addition, due to compounding and metalloxane bond formation, the connection between metal elements is strengthened, precipitation (segregation) and burnout of metal elements such as Bi are suppressed, leakage current is small, hydrogen heat treatment resistance and pressure resistance are excellent. A film can be formed.

  Moreover, it is preferable that this invention coating liquid mix | blends alkanolamine. By using alkanolamine, the coating property can be improved particularly effectively.

  Examples of the alkanolamine include triethanolamine, diethanolamine, dibutylethanolamine, diethylethanolamine and the like. Of these, triethanolamine is most preferable from the viewpoint of improving coating properties.

  The compounding amount of the alkanolamine is, for example, 1 mol of a composite metal oxide represented by the above general formula (I) (wherein A, B, x, y, z, n and α are as defined above). The amount is preferably 0.5 to 20 mol, particularly 1 to 10 mol. If it is out of the above range, the effect of blending alkanolamine tends to be insufficient, which is not preferable.

  In addition, when performing the said hydrolysis process, it is preferable to mix | blend an alkanolamine after a hydrolysis process.

  In the present invention, a conventionally known stabilizer can also be added.

  The said stabilizer is for improving the storage stability of a coating liquid, For example, carboxylic anhydrides, dicarboxylic acid monoesters, (beta) -diketone, glycols etc. are used suitably.

  As carboxylic anhydrides, the following general formula (III)

R ₂ (CO) ₂ O (III)

(Wherein R ₂ represents a divalent saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
At least one selected from carboxylic anhydrides represented by the formula is preferably used. Specific examples of such carboxylic anhydrides include maleic anhydride, citraconic anhydride, itaconic anhydride, succinic anhydride, methyl succinic anhydride, glutaric anhydride, α-methylglutaric anhydride, α, α -Dimethyl glutaric acid, trimethyl succinic anhydride, etc. can be mentioned.

  As dicarboxylic acid monoesters, the following general formula (IV)

R ₃ OCOR ₄ COOH (IV)

(Wherein R ₃ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms; R ₄ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
Preferably, at least one selected from dicarboxylic acid monoesters represented by the formula:

  As such dicarboxylic acid monoesters, specifically, for example, those obtained by reacting a dibasic carboxylic acid with an alcohol to form a half ester, oxalic acid, malonic acid, succinic acid, 2 such as glutaric acid, adipic acid, pimelic acid, speric acid, azelic acid, sebacic acid, maleic acid, citraconic acid, itaconic acid, methyl succinic acid, α-methyl glutaric acid, α, α-dimethyl glutaric acid, trimethyl glutaric acid, etc. Establish at least one of carboxylic acids of basic acids and at least one of methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether and the like by a known method. Reaction It can be synthesized.

  As β-diketone, the following general formula (V)

R ₅ COCR ₆ HCOR ₇ (V)

(In the formula, R ₅ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms; R ₆ represents H or CH ₃ ; R ₇ represents an alkyl group or alkoxyl group having 1 to 6 carbon atoms; Represents
At least one selected from β-diketones containing a β-ketoester represented by the formula is preferably used.

  Specific examples of the β-diketone used in the present invention include acetylacetone, 3-methyl-2, 4-pentanedione, benzoylacetone and the like. Examples of β-ketoesters include ethyl acetoacetate and diethyl malonate. Other complex-forming agents are also applicable, but complex-forming agents such as dipivaloylmethane and its THF adduct, and hexafluoroacetylacetone, which forms a metal halide after firing, are sublimable or volatile. Since it forms a high metal complex, it is unsuitable for use in the coating solution of the present invention.

  As glycols, the following general formula (VI)

HOR ₈ OH (VI)

(In the formula, R ₈ represents a divalent saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms)
At least one selected from glycols represented by the formula is preferably used.

  Specific examples of glycols used in the present invention include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butane diol, pentane diol, hexylene glycol, 2-ethyl hexane diol, and glycerin glycol. Can be listed. These glycols are particularly effective when β-diketone is used as a stabilizer, and increases the stability of the liquid after the subsequent hydrolysis reaction.

  Any of the above stabilizers is preferably a short chain having 1 to 6 carbon atoms from the viewpoint of enhancing the inorganic properties of the coating after the drying step.

  In addition, substituted or unsubstituted lower monocarboxylic acids such as acetic acid, propionic acid, 2-ethylhexanoic acid, butyric acid, and valeric acid can also be suitably used as the stabilizer.

  As described above, the composite metal alkoxide is treated with carboxylic anhydrides, dicarboxylic acid monoesters, β-diketones, glycols, lower monocarboxylic acids, and the like for carboxylation, β-diketonization, chelation and the like. As a result, a product having polarity and excellent stability can be obtained, hydrolyzability is improved, and 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 the formation of an inorganic bond (metalloxane) bond composed of metal-oxygen atoms further precipitates a specific metal element such as Bi. The amount of segregation and the amount of burnout can be reduced, and the mineralization of the entire coating liquid can be increased.

  In addition, either the stabilization process by the said stabilizer and a hydrolysis process may be performed first, and you may use both together.

  By these hydrolysis treatment and stabilization treatment, it is possible to stabilize the storage of the coating solution, improve operability, lower temperature decomposition, increase the density, improve the coating property, and improve the solubility in a practical organic solvent.

  Examples of the solvent for the coating liquid for forming the Bi-based ferroelectric thin film include saturated aliphatic solvents, aromatic solvents, alcohol solvents, glycol solvents, ether solvents, ketone solvents, ester solvents, and the like. Can do.

  Examples of alcohol solvents include methanol, ethanol, propanol, butanol, amyl alcohol, cyclohexanol, and methylcyclohexanol.

  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, propylene Examples include glycol dipropyl ether, dipropylene glycol monoethyl ether, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, 3,3′-dimethylbutanol and the like.

  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, trimethylnonanone, acetonitrile acetone, dimethyl oxide, phorone, 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.

  Further, in the present invention, sol-gelation by a hydrolysis treatment, stabilization treatment, etc. are performed, so that not only low-boiling alcohol solvents but also aromatic compounds (toluene, xylene, etc.) and high-boiling-points that have been conventionally avoided. Combinations such as diols can also be used.

  These solvents can be used alone or in the form of a mixture of two or more. In the present invention, a solvent other than an alcohol-based solvent is preferably used for reasons of applicability during thin film formation and stability of the coating solution. In particular, a glycol solvent is preferably used.

  In the Bi-based ferroelectric thin film forming coating solution, Bi, Ti, and A metal element (calculated as A = 0 when A metal element is not included), Bi: (Ti + A) = 1.07 to It is preferable to contain it in the ratio of 1.15: 1 (molar ratio). By adjusting the molar ratio of each component in the coating solution within the above range, a film having excellent ferroelectricity and high polarization (Pr) can be formed.

  Next, an example of a method for manufacturing a ferroelectric thin film and a ferroelectric memory (ferroelectric element) using the coating liquid for forming a Bi-based ferroelectric thin film of the present invention will be described. However, it is not limited to this.

  First, a substrate such as a Si wafer is oxidized to form a Si oxide film on the substrate, and a metal such as Pt, Ir, Ru, Re, Os, and a conductive metal oxide that is a metal oxide thereof are formed thereon. The lower electrode is formed by a known method such as sputtering or vapor deposition. Then, the coating solution of the present invention is applied onto the lower electrode by a known coating method such as a spinner method or a dip method, and the first heat treatment (drying) is performed at a temperature of 50 to 400 ° C., preferably 150 to 300 ° C. ) To form a coating film. Subsequently, the process from application to drying is repeated a plurality of times as desired to set a desired film thickness. Next, main baking is performed at a temperature of 600 to 750 ° C. in an oxygen atmosphere to form a ferroelectric thin film having a crystal structure. In the main baking step, a furnace method in which the temperature is increased from room temperature to the main baking temperature at a temperature increase rate of about 5 to 20 ° C./min, and then the main baking temperature is maintained and baking is performed for about 10 to 80 minutes. Various firing methods such as an RTP method in which the temperature is raised to the main firing temperature at a temperature rise rate of about 150 ° C./sec and then fired for about 0.5 to 3 minutes while maintaining the main firing temperature can be selected. By using the coating solution of the present invention, the temperature of the main baking (crystallization of the thin film composition) can be performed at a low temperature of 600 to 700 ° C.

  Next, an electrode (upper electrode) is formed on the ferroelectric thin film produced as described above. As the upper electrode, the metals, metal oxides, etc. mentioned as the material for the lower electrode can be used. These materials are formed on the ferroelectric thin film by a known method such as sputtering or vapor deposition, and in an oxygen atmosphere. And firing at 600 to 700 ° C. to produce a ferroelectric memory. At this time, as the upper electrode, a material different from that of the lower electrode may be used. For example, Ir may be used for the lower electrode and Ru may be used for the upper electrode.

  In addition, when performing a hydrolysis reaction in a humidified atmosphere, it can be carried out at a humidity of 50 to 100%, preferably 70 to 100%, a temperature of 50 to 120 ° C., for 10 to 60 minutes before the above-described preliminary baking. .

  In the present invention, it is possible to suppress the leakage current in the coating liquid production by strengthening the connection between the metal elements and suppressing the precipitation (segregation) and burnout of the metal elements, particularly by the combination and mineralization by hydrolysis. In addition, the characteristics as a ferroelectric memory such as crystallinity, resistance to hydrogen heat treatment and pressure resistance are improved.

In addition, after forming the upper electrode, protective film formation (passivation) such as SiO ₂ and aluminum wiring are performed. Particularly, since it has excellent resistance to hydrogen heat treatment, ferroelectric characteristics during passivation film formation and aluminum wiring forming Therefore, the ferroelectric memory using the BLSF film can be put into practical use.

  In addition, even if the coating solution is insufficiently mineralized by the sol-gel method (hydrolysis treatment) or is not subjected to any hydrolysis treatment, before the coating is fired at the time of forming the coating on the substrate. By exposing the coating film to a humidified atmosphere for a certain period of time, the coating film can be mineralized by hydrolytic condensation polymerization, and a dense film can be formed.

  If the hydrolysis treatment in the coating solution described above is performed excessively, the coating solution may become thickened / gelled or change with time. is there.

  II. Coating liquid for forming a paraelectric Bi-based dielectric thin film (hereinafter also referred to as “Bi-based paraelectric thin film forming liquid”).

  The coating liquid for forming a Bi-based paraelectric thin film in the present invention contains a mixed metal alkoxide formed by at least two metal alkoxides of Bi and Ti, or a mixed metal formed by mixing at least a Bi alkoxide and a Ti alkoxide. The said coating liquid containing an alkoxide.

  The mixed alkoxide can be produced by adding Bi alkoxide and Ti alkoxide to an alcohol solution and mixing them. The alcohol forming the metal alkoxide is the above-mentioned I. The alcohol described in the item can be preferably used.

  The composite metal alkoxide is the above-mentioned I. It can be manufactured in the same manner as described in the item.

  Thus, the Bi-based paraelectric thin film forming coating solution according to the present invention also includes a BIT-based coating solution. Even when a mixed alkoxide is contained, a high dielectric constant and a reduction in leakage current can be achieved. The use of the composite metal alkoxide is superior in the denseness of the thin film.

  The Bi-based paraelectric thin film-forming coating solution is preferably the above-mentioned I. A material for forming a paraelectric Bi-based dielectric thin film (that is, a BLT thin film) containing the composite metal oxide represented by the general formula (I) described in the item (1) is preferable. In the formula, A, B, x, y, z, n, and α are as defined and explained above. However, the paraelectric thin film may include a mode in which Bi alkoxide and Ti alkoxide are mixed to form a mixed alkoxide. It may be a composite metal alkoxide containing Bi and Ti.

  The difference between the formation of the paraelectric thin film and the ferroelectric thin film mainly includes the case where the compound represented by the above general formula (I) is derived from the difference in the composition and the difference in the thin film formation conditions. .

  Taking the thin film formation represented by the general formula (I) as an example, the coating liquid for forming a ferroelectric thin film is the above-mentioned I. As described in the above item, the ratio of the metal element in the coating solution is adjusted so that Bi, Ti and A metal elements are Bi: (Ti + A) = 1.07 to 1.15: 1 (molar ratio). preferable. Further, Ge is preferably used as the A metal element.

  On the other hand, in order to form a paraelectric thin film, the ratio of the metal element in the coating solution is as follows: Bi, Ti and A metal element are Bi: (Ti + A) = 0.90 to 1.06: 1 (molar ratio). It is preferable to adjust to. In the coating liquid for forming a paraelectric thin film, Ge is used as the A metal element, and Sr, Ba, Pr, erbium (Er), yttrium (Y), etc. are preferably used as the B element.

  Paraelectric thin film formation conditions are as follows.

  In the case where the coating solution has a composition adjusted to Bi: (Ti + A) = 0.90 to 1.06: 1 (molar ratio), the forming means is not particularly limited, and the paraelectric property is reduced by the conventional dielectric film forming means. A thin film can be formed.

  As a suitable forming means, a coating liquid is applied on the substrate, and then a first heating (drying) treatment at 50 to 400 ° C., preferably 150 to 300 ° C. is performed to form a coating film. Depending on the process, the process from coating to drying is repeated a plurality of times to form a laminate of coating films, and then the second heat treatment (firing process) is performed at 600 to 700 ° C., preferably 600 to 670 ° C. Thus, there is a means for forming a thin film.

  Thereby, a suitable paraelectric thin film having a high dielectric constant while being paraelectric can be formed.

  In addition, when the coating liquid is not a composition adjusted to Bi: (Ti + A) = 0.90 to 1.06: 1 (molar ratio), the following means are used to form a suitable paraelectric thin film. It is preferable.

  A coating solution is formed on a substrate by applying a coating solution and performing a first heat treatment (preliminary firing) at 500 to 700 ° C., preferably 550 to 650 ° C., without applying a drying treatment by heating. If desired, the process from coating to baking is repeated a plurality of times to form a laminate of coating films. Next, a thin film is formed by performing a second heat treatment (baking treatment) at 600 to 700 ° C., preferably 600 to 670 ° C. Thereby, a suitable paraelectric thin film having a high dielectric constant while being paraelectric can be formed.

  In addition, although the said drying process means the process which dries a coating film substantially without performing a heat processing, the heat processing of the grade which does not produce the decomposition | disassembly phenomenon of the organic component in a coating film substantially. (For example, a temperature close to room temperature) may be included.

  Regarding the components (for example, the combination of a solvent, a stabilizer, an alkanolamine, etc.) blended in the coating liquid for forming a paraelectric thin film, dielectric element formation, etc. As described in the item.

  The contents of Bi, Ti, La, A metal element component, and B metal element component in the Bi-based dielectric thin film forming coating solution vary depending on the application location and conditions of the coating solution of the present invention. Types (for FRAM, DRAM, MFS, MFIS, MFMIS, etc.), types of upper and lower electrodes used, thickness, combination, barrier layer type, thickness, and presence / absence of seed layer (orientation) The appropriate value can be selected according to the time.

The coating liquid of the present invention is used for the blending amount of each organometallic compound, the type and amount of residual alkoxy groups, the carbonyl group blending ratio, the degree of complexation, the hydrolysis rate, the degree of condensation polymerization, the degree of complex alkoxylation, and the like. Since it can be selected in various ways depending on the application, conditions (temperature during drying, firing, temperature, atmosphere, temperature raising method, etc.), the embodiments of the present invention shown in the following examples are suitable for these many application fields. It is only an example and this invention is not limited at all by these Examples.
[Example]

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.

[Bi-based ferroelectric thin film forming coating solution]
(Synthesis Example 1)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1.12: 1 showing n = 1.0250, x = 0.7317, y = 0, Z = 1, α = 0.1500) (Molar ratio)))
To 1-methoxy-2-propanol, 0.0750 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and these were put into an eggplant flask, and heated and stirred at 80 ° C. Bismuth tributoxide was added in an amount of 0.3350 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize a Bi—Ti—La triple metal alkoxide (BLT composite solution).

To the above BLT composite solution, 0.3000 mol of 2-ethylhexanoic acid as a stabilizer was added and stirred at room temperature. Further, 0.2000 mol of triethanolamine was added as a stabilizer and then heated to 60 ° C. Then, 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 2)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1.12: 1 showing n = 1.0250, x = 0.7317, y = 0, Z = 1, α = 0.1500) (Molar ratio)))
To 1-methoxy-2-propanol, 0.0750 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and this was put into an eggplant flask and heated and stirred at 80 ° C. Bismuth tributoxide was added in an amount of 0.3350 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize a Bi—Ti—La triple metal alkoxide (BLT composite solution).

To the BLT composite solution, 0.3000 mol of ethyl acetoacetate as a stabilizer was added and heated and stirred, and then 0.2000 mol of water was added and stirred at room temperature. Further, 0.1000 mol of propylene glycol as an additive was added as a stabilizer and stirred at room temperature to prepare a coating solution for forming a lanthanum bismuth titanate (BLT-based) thin film.
(Synthesis Example 3)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1.13 showing n = 1.0250, x = 0.60829, y = 0, z = 0.5714, α = 0.1500) : 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0400 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and these were put into an eggplant flask and heated and stirred at 80 ° C. To this, 0.3400 mol of bismuth tributoxide and 0.0300 mol of triisopropoxy praseodymium were added, and the mixture was again heated and stirred at 60 ° C. to synthesize a bimetallic compound alkoxide of Bi—Ti—La—Pr (BLT). System composite liquid).

To this BLT composite solution, 0.2000 mol of water was added and stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 4)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1.n = n = 0.9762, x = 0.6829, y = 0.1429, z = 1, α = −0.1429). 08: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0667 mol of lanthanum acetate, 0.2857 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are put into an eggplant flask and heated and stirred at 80 ° C. went. Bismuth tributoxide was added in an amount of 0.3238 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi—Ti—La—Ge four-component metal alkoxide (BLT-based composite solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 5)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = n = 0.99881, x = 0.080, y = 0.1429, z = 0.9435, α = −0.0714) 1.08: 1 (molar ratio))]
In 1-methoxy-2-propanol, 0.0660 mol of lanthanum acetate, 0.0040 mol of cerium trimethoxypropylate, 0.2857 mol of titanium tetrabutoxide and 0.0143 mol of germanium tetrabutoxide were added. The mixture was placed in an eggplant flask and heated and stirred at 80 ° C. Bismuth tributoxide was added in an amount of 0.3238 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi-Ti—La—Ce—Ge five-metal complex alkoxide (BLT composite solution).

  0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.

[Bi-based paraelectric thin film forming coating solution]
(Synthesis Example 6)

[In the above general formula (I), n = 0.830, x = 0.6747, y = 0, z = 1, α = −1.020 coating liquid (Bi: (Ti + A) = 0.92: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0560 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and this was put into an eggplant flask and heated and stirred at 80 ° C. Bismuth tributoxide was added thereto in an amount of 0.2760 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize a Bi—Ti—La three-component metal alkoxide (BLT-based composite solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 7)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1.04: n = 0.9338, x = 0.6747, y = 0, z = 1, α = −0.3975): 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0630 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and this was put into an eggplant flask and heated and stirred at 80 ° C. Bismuth tributoxide was added to them in an amount of 0.3105 mol, and the mixture was again heated and stirred at 60 ° C. to synthesize a Bi—Ti—La three-component metal alkoxide (BLT-based composite solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 8)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 0.92 showing n = 1.0375, x = 1.3398, y = 0, z = 0.4029, α = 0.2250) : 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0560 mol of lanthanum acetate and 0.3000 mol of titanium tetrabutoxide were added, and these were put into an eggplant flask, and heated and stirred at 80 ° C. Bismuth tributoxide (0.2760 mol) and triisopropoxy praseodymium (0.0830 mol) were added to them, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi-Ti-La-Pr four-metal complex alkoxide (BLT). System composite liquid).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 9)

[In the above general formula (I), n = 0.8893, x = 0.6747, y = 0.1429, z = 1, α = −0.6645 coating liquid (Bi: (Ti + A) = 0. 99: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0600 mol of lanthanum acetate, 0.2875 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are put into an eggplant flask and heated and stirred at 80 ° C. went. 0.2957 mol of bismuth tributoxide was added to them, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi—Ti—La—Ge four-component metal alkoxide (BLT-based composite solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C. and substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 10)

[In the above general formula (I), coating solution (Bi: (Ti + A) = n = 0.9881, x = 0.8210, y = 0.1429, z = 0.7622, α = −0.0714) 1.05: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0633 mol of lanthanum acetate, 0.2875 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are put into an eggplant flask and heated and stirred at 80 ° C. went. Bismuth tributoxide (0.3121 mol) and erbium isopropoxide (0.0198 mol) were added to them, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi-Ti-La-Er-Ge five-metal complex alkoxide. (BLT complex solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 11)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = n = 0.9881, x = 0.8210, y = 0.1429, z = 0.7622, α = −0.0716) 1.05: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0633 mol of lanthanum acetate, 0.2875 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are put into an eggplant flask and heated and stirred at 80 ° C. went. Bismuth tributoxide 0.3121 mol and yttrium trimethoxypropylate 0.0198 mol were added to them, and the mixture was again heated and stirred at 60 ° C. to synthesize a bimetallic compound alkoxide of Bi—Ti—La—Y—Ge. (BLT complex solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 12)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1 indicating n = 1.0128, x = 0.9180, y = 0.1429, z = 0.6812, α = 0.0768) .04: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0633 mol of lanthanum acetate, 0.2875 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are put into an eggplant flask and heated and stirred at 80 ° C. went. Bismuth tributoxide (0.3121 mol) and barium diisopropoxide (0.0296 mol) were added thereto, and the mixture was again heated and stirred at 60 ° C. to synthesize a bimetallic compound alkoxide of Bi—Ti—La—Ba—Ge. (BLT complex solution).

0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C., and 1-methoxy-2-propanol was substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.
(Synthesis Example 13)

[In the above general formula (I), a coating solution (Bi: (Ti + A) = 1 indicating n = 1.0128, x = 0.9180, y = 0.1429, z = 0.6812, α = 0.0768) .04: 1 (molar ratio))]
To 1-methoxy-2-propanol, 0.0633 mol of lanthanum acetate, 0.2875 mol of titanium tetrabutoxide, and 0.0143 mol of germanium tetrabutoxide are added, and these are placed in an eggplant flask and heated and stirred at 80 ° C. It was. Bismuth tributoxide (0.3121 mol) and strontium diisopropoxide (0.0296 mol) were added to them, and the mixture was again heated and stirred at 60 ° C. to synthesize Bi-Ti-La-Sr-Ge 5-type complex metal alkoxide. (BLT complex solution).

  0.2000 mol of water was added to this BLT composite solution, and the mixture was stirred at room temperature. To these, 0.3000 mol of 2-ethylhexanoic acid was added as a stabilizer and stirred at room temperature. They were concentrated by heating at 60 ° C. and substituted with 1,2-dimethoxy-propane to prepare a coating solution for forming a lanthanum bismuth titanate (BLT system) thin film.

  Using the coating liquid for forming a Bi-based ferroelectric thin film prepared in Synthesis Examples 1 and 2, the applicability and density were evaluated as follows.

[Applicability]
A 60 nm Pt lower electrode was formed by sputtering on a 6 inch silicon wafer on which a 100 nm thick thermal oxide film SiO ₂ was formed.

At the stage where the coating liquid for forming a Bi-based ferroelectric thin film prepared in Synthesis Examples 1 and 2 was spin-coated on the substrate at 500 rpm for 1 second and then at 2000 rpm for 30 seconds, the state of the coating film surface was visually observed. Thereafter, a heat treatment was performed at 700 ° C. for 30 minutes, and the state of the thin film surface was similarly observed visually. The results are shown in Table 1.
(The state of the coating film after application and before heat treatment)
A: Uniform coating was possible (state of thin film after heat treatment)
A: A uniform thin film was formed.

[density]
The Bi-based ferroelectric thin film forming coating solution prepared in Synthesis Examples 1 and ₂ was spin-coated on a 3-inch silicon wafer on which a thermal oxide film SiO ₂ of 100 nm was formed for 1 second at 500 rpm and then for 30 seconds at 2000 rpm. Thereafter, a heat treatment was performed at 700 ° C. for 30 minutes to form a thin film. The film thickness and refractive index were calculated using an ellipsometer, and the density was measured. When the film thickness was the same, it was determined that the density was high if the refractive index was high, and the density was low if the refractive index was low. The results are shown in Table 1.

  From the results of coating properties shown in Table 1, no striation occurred in the coating solution of Synthesis Example 1, and the fired thin film did not become cloudy. This is thought to be due to the effect of adding alkanolamines effectively leading to improved coatability. In Synthesis Example 2, a uniform thin film could be produced without any problem. This is considered to be a hydrolysis effect. From the density results shown in Table 1, it can be seen that the thin films prepared from the coating solutions of Synthesis Examples 1 and 2 have a high refractive index and a high density.

[Evaluation of relationship between heating temperature and thin film crystallization using coating solutions prepared in Synthesis Examples 1 and 2]
Using the coating solutions prepared in Synthesis Examples 1 and 2, a heat treatment was performed at a heating temperature of 650 ° C. or 700 ° C. to form a thin film, and the relationship between the heating temperature and crystallization of the thin film was evaluated.

Specifically, a 60 nm Pt lower electrode was first formed by sputtering on a 6 inch silicon wafer on which a 100 nm thick thermal oxide film SiO ₂ was formed.

  On the substrate having the lower electrode, the coating solution prepared in Synthesis Examples 1 and 2 is spin-coated at 500 rpm for 1 second and then at 2000 rpm for 30 seconds using a spin coater, and dried at 250 ° C. for 5 minutes. It was. This coating-drying process is repeated four times in total, and finally, a heat treatment (first heat treatment) at 650 ° C. for 60 minutes or 700 ° C. for 60 minutes is performed in an oxygen atmosphere to form a BLT dielectric having a film thickness of 150 nm. A body thin film was formed.

  The thin film was subjected to X-ray diffraction (XRD) measurement to obtain an XRD curve. FIG. 1 shows the XRD curve of the thin film prepared by Synthesis Example 1, and FIG. 2 shows the XRD curve of the thin film prepared by Synthesis Example 2.

  As can be seen from FIGS. 1 and 2, in any of the coating solutions of Synthesis Examples 1 and 2, the thin film forms the crystal structure of the target lanthanum bismuth titanate (BLT) under both low temperature firing conditions of 650 ° C. and 700 ° C. I found out.

[Hysteresis Characteristics of Dielectric Element Formed Using Dielectric Thin Film Formed in Example 2]
For each thin film formed in Example 2, a Pt upper electrode having a diameter of 200 μm and a thickness of 300 nm was formed by RF magnetron sputtering through a metal mask.

  Next, recovery annealing (second heat treatment) at 650 ° C. for 30 minutes or 700 ° C. for 30 minutes was performed in an oxygen atmosphere at the same temperature as that processed in Example 2 to form a dielectric element. The hysteresis curves of this dielectric element are shown in FIGS. 3-1 and 3-2.

  As shown in FIGS. 3A and 3B, the BLT ferroelectric thin film having a large polarization value (Pr) under the low temperature firing conditions of 650 ° C. and 700 ° C. in the thin films prepared from the coating liquids of Synthesis Examples 1 and 2. It was found that it can be formed.

[Hysteresis characteristics of dielectric element formed using coating solution prepared in Synthesis Example 3]
In the same manner as in Example 2, the coating solution prepared in Synthesis Example 3 was spin-coated at 500 rpm for 1 second, then 2000 rpm for 30 seconds, dried at 250 ° C. for 5 minutes, and these coating-drying steps were performed. Repeated 4 times, and finally, heat treatment (first heat treatment) at 650 ° C. for 30 minutes in an oxygen atmosphere, followed by heat treatment (second heat treatment) at 700 ° C. for 60 minutes, and a BLT dielectric of 150 nm A body thin film was formed.

  Next, a Pt upper electrode was formed in the same manner as in Example 3, and recovery annealing (third heat treatment) at 700 ° C. was performed to produce an element. The hysteresis curve of this element is shown in FIG.

  FIG. 4 shows that a BLT ferroelectric thin film having a large polarization amount (Pr) can be formed even under low-temperature firing conditions of 700.degree.

[Hysteresis characteristics and leak characteristics of dielectric elements formed using the coating solution prepared in Synthesis Example 4]
In the same manner as in Example 2, the coating solution prepared in Synthesis Example 4 was spin-coated at 500 rpm for 1 second and then at 2000 rpm for 30 seconds, and dried at 250 ° C. for 5 minutes. After repeating the above, a heat treatment (first heat treatment) is performed at 650 ° C. for 30 minutes in an oxygen atmosphere, followed by a heat treatment (second heat treatment) at 700 ° C. for 60 minutes, and a BLT system having a film thickness of 190 nm A dielectric thin film was formed.

  Next, a Pt upper electrode was formed by the same method as in Example 3, and recovery annealing (third heat treatment) at 700 ° C. was performed to produce a dielectric element. FIG. 5 shows a hysteresis curve of the dielectric element, and FIG. 6 shows a leak characteristic.

  As is apparent from FIG. 5, it was found that a BLT ferroelectric thin film having a large polarization (Pr) can be formed even under low temperature firing conditions of 700 ° C. Moreover, it was found from FIG. 6 that the leak characteristics are also excellent.

[Hysteresis characteristics and leak characteristics of dielectric elements formed using the coating solution prepared in Synthesis Example 5]
In the same manner as in Example 2, the coating solution prepared in Synthesis Example 5 was spin-coated at 500 rpm for 1 second and then at 2000 rpm for 30 seconds, and dried at 250 ° C. for 5 minutes. After repeating the above, a heat treatment (first heat treatment) at 650 ° C. for 30 minutes is performed in an oxygen atmosphere, followed by a heat treatment (second heat treatment) at 700 ° C. for 60 minutes, and a BLT system having a film thickness of 150 nm A dielectric thin film was formed.

  Next, a Pt upper electrode was formed by the same method as in Example 3, and recovery annealing (third heat treatment) at 700 ° C. was performed to produce a dielectric element. FIG. 7 shows a hysteresis curve of the dielectric element, and FIG. 8 shows a leak characteristic.

  From FIG. 7, it was found that a BLT ferroelectric thin film having a large polarization amount (Pr) can be formed even under a low temperature firing condition of 700 ° C. Moreover, it was found from FIG. 8 that the leak characteristics are very excellent.

  It will be shown below that a paraelectric thin film can be formed by changing the film forming conditions (heating conditions) using the same coating liquid as that used to form a ferroelectric thin film.

  The coating solution prepared in Synthesis Example 2 was used. In Examples 2 and 3, it was confirmed that the thin film obtained using the coating solution was a BLT crystal thin film exhibiting ferroelectricity.

Specifically, a 60 nm Pt lower electrode was first formed by sputtering on a 6 inch silicon wafer on which a 100 nm thick thermal oxide film SiO ₂ was formed.

  On the substrate having the lower electrode, the coating solution prepared in Synthesis Example 2 is spin-coated at 500 rpm for 1 second and then at 2000 rpm for 30 seconds using a spin coater, and in an oxygen atmosphere at 600 ° C. for 60 minutes, or A heat treatment (first heat treatment) at 650 ° C. for 60 minutes was performed. After repeating these coating-heat treatment processes four times, a heat treatment (second heat treatment) at 650 ° C. for 60 minutes was performed in an oxygen atmosphere to form a BLT dielectric thin film having a thickness of 150 nm. The thin film was subjected to X-ray diffraction (XRD) measurement to obtain an XRD curve. The results are shown in FIG.

  As is apparent from FIG. 9, in Examples 2 and 3, the coating solution of Synthesis Example 2 that formed the crystal structure of the target lanthanum bismuth titanate was used. In Example 7, the crystallinity of lanthanum bismuth titanate was increased. It became low and confirmed that there were many amorphous states.

[Hysteresis Characteristics and Leakage Characteristics of Dielectric Element Formed Using Dielectric Thin Film Formed in Example 7]
A Pt upper electrode having a diameter of 200 μm and a thickness of 300 nm was formed on the thin film formed in Example 7 through a metal mask by an RF magnetron sputtering method.

  Next, recovery annealing (third heat treatment) at 650 ° C. was performed in an oxygen atmosphere. FIG. 10 shows a hysteresis curve after recovery annealing of the dielectric element.

  As is clear from FIG. 10, in Examples 2 and 3, the coating liquid of Synthesis Example 2 in which the dielectric thin film exhibiting ferroelectricity was formed under a 650 ° C. low temperature firing condition by changing the heating (firing) method. It was found that a dielectric thin film exhibiting a paraelectric property can be formed, and from FIG. 11, it was found that a dielectric element produced using the thin film has excellent leakage characteristics.

[Example of metal composition exhibiting paraelectric properties]
A 60 nm Pt lower electrode was formed by sputtering on a 6 inch silicon wafer on which a 100 nm thick thermal oxide film SiO ₂ was formed.

  On the substrate having the lower electrode, using a spin coater, the coating solution prepared in Synthesis Examples 6 to 13 is spin-coated at 500 rpm for 1 second, then 2000 rpm for 30 seconds, and dried at 250 ° C. for 5 minutes. It was. After repeating these coating-drying steps four times, a heat treatment (first heat treatment) is performed at 650 ° C. for 30 minutes in an oxygen atmosphere, and then a heat treatment (second heat treatment) is performed at 650 ° C. for 60 minutes. A BLT-based dielectric thin film having a thickness of 140 nm was formed. The thin film was subjected to X-ray diffraction (XRD) measurement to obtain an XRD curve. The results are shown in FIG.

  From FIG. 12, it was confirmed that, when any of the coating liquids of Synthesis Examples 6 to 13 was used, the crystallinity of lanthanum bismuth titanate in the thin film was low and the amorphous state was large under the low-temperature firing conditions at 650 ° C. .

[Hysteresis Characteristics and Leakage Characteristics of Dielectric Element Formed Using Dielectric Thin Film Formed in Example 9]
Among the dielectric thin films formed in Example 9, a Pt upper electrode having a diameter of 200 μm and a film thickness of 300 nm is formed through a metal mask on the dielectric thin film formed using the coating liquid prepared in Synthesis Examples 9-11. The RF magnetron sputtering method was used.

  Next, recovery annealing (third heat treatment) at 650 ° C. at the same temperature as that processed in Example 9 was performed in an oxygen atmosphere. The hysteresis curves and leakage characteristics of each dielectric thin film after recovery annealing are shown in the following figures. Table 2 shows the dielectric constants of the coating liquids of Synthesis Examples 9 to 11.

FIG. 13: Dielectric thin film hysteresis curve formed from the coating liquid of Synthesis Example 9 FIG. 14: Dielectric thin film leakage characteristics formed from the coating liquid of Synthesis Example 9 FIG. 15: Dielectric thin film hysteresis formed from the coating liquid of Synthesis Example 10 Curve FIG. 16: Leakage characteristic of dielectric thin film formed from the coating liquid of Synthesis Example 10 FIG. 17: Hysteresis curve of dielectric thin film formed from the coating liquid of Synthesis Example 11 FIG. 18: Dielectric thin film formed from the coating liquid of Synthesis Example 11 Leakage characteristics

  13-18, it was found that a dielectric thin film exhibiting paraelectricity can be formed under low temperature firing conditions at 650 ° C. It was also found that the leakage characteristics of these BLT dielectric thin films are very excellent and have a high dielectric constant.

  For the coating solutions of Synthesis Examples 6-8 and 12-13 other than those described above, dielectric elements were prepared, and these BLT-based dielectric thin films similarly have paraelectric properties, excellent leakage characteristics, and high It was also confirmed to have a dielectric constant.

  As described above in detail, it has been found that a coating solution using a specific metal alkoxide raw material becomes a paraelectric material exhibiting good high dielectric properties (low leakage current and high dielectric constant). Also, by making this a composite metal alkoxide, the coating property is good, a dense film can be formed, the metal composition ratio is stabilized, and the phenomenon of changing the metal composition ratio in the thin film is suppressed, and the operability is also improved. The coating solution was excellent in stability (such as aging) (not easily affected by the environment such as humidity).

  In addition, a coating liquid using a specific composite metal alkoxide raw material is a ferroelectric thin film that exhibits good high dielectric properties (low leakage current and high dielectric constant) and ferroelectricity (such as a large remanent polarization value). Can be formed under low temperature conditions (700 ° C or lower), and the coating property is good, a dense film can be formed, the metal composition ratio is stabilized, and the phenomenon that the metal composition ratio in the thin film changes is suppressed. In addition, the coating liquid was excellent in operability (not easily influenced by the environment such as humidity) and stability (such as aging).

  Further, by using the hydrolysis product, it was possible to further stabilize the metal composition ratio and further suppress the phenomenon in which the metal composition ratio in the thin film changes.

  Furthermore, application | coating property improved by mix | blending alkanolamine.

It is a graph which shows the XRD curve of the dielectric material thin film formed using the coating liquid of the synthesis example 1. FIG. It is a graph which shows the XRD curve of the dielectric material thin film formed using the coating liquid of the synthesis example 2. 6 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 1. It is a graph which shows the hysteresis characteristic of the dielectric material element formed using the coating liquid of the synthesis example 2. FIG. 10 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 3. 10 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 4. 10 is a graph showing the leakage characteristics of a dielectric element formed using the coating liquid of Synthesis Example 4. 10 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 5. 10 is a graph showing the leakage characteristics of a dielectric element formed using the coating liquid of Synthesis Example 5. It is a graph which shows the XRD curve of the dielectric material thin film (paraelectricity) formed using the coating liquid of the synthesis example 2. It is a graph which shows the hysteresis characteristic of the dielectric material element (paraelectricity) formed using the coating liquid of the synthesis example 2. It is a graph which shows the leak characteristic of the dielectric material element (paraelectricity) formed using the coating liquid of the synthesis example 2. It is a graph which shows the XRD curve of the dielectric thin film formed using the coating liquid of the synthesis examples 6-13. 14 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 9. 10 is a graph showing leakage characteristics of a dielectric element formed using the coating liquid of Synthesis Example 9. 14 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 10. 10 is a graph showing leakage characteristics of a dielectric element formed using the coating liquid of Synthesis Example 10. 14 is a graph showing hysteresis characteristics of a dielectric element formed using the coating liquid of Synthesis Example 11. 14 is a graph showing leakage characteristics of a dielectric element formed using the coating liquid of Synthesis Example 11.

Claims (20)

A coating solution for forming a ferroelectric Bi-based dielectric thin film containing a composite metal oxide represented by the following general formula (I), which is formed of at least two metal alkoxides of Bi and Ti The coating solution comprising a composite metal alkoxide.
{Bi _4-x , (La _z , B _1-z ) _x } _n (Ti _3-y , A _y ) O _{12 + α} (I)
(In the formula, A represents at least one metal element selected from V, Cr, Mn, Si, Ge, Zr, Nb, Ru, Sn, Ta, and W; B represents a rare earth element excluding lanthanum; Represents at least one metal element selected from Ca, Sr, and Ba; x, y, and z are represented by 0 ≦ x <4, 0 ≦ y ≦ 0.3, and 0 <z ≦ 1, respectively. N represents a number from 0.7 to 1.4; α represents a value determined by the metal composition ratio.)   A sol-gel solution in which the coating solution contains a composite metal alkoxide formed of at least two metal alkoxides of Bi and Ti, and is further hydrolyzed and partially condensed using water or water and a catalyst. The coating solution according to claim 1, wherein The coating solution according to claim 1 or 2, wherein alkanolamine is blended in the coating solution.   The coating liquid of any one of Claims 1-3 in which x shows the number represented by 0 <x <4 in the said general formula (I).   The coating liquid of any one of Claims 1-4 in which z shows the number represented by 0 <z <1 in the said general formula (I).   The coating liquid according to claim 1, wherein in the general formula (I), y represents a number represented by 0 <y ≦ 0.3.   The coating liquid according to claim 1, wherein, in the general formula (I), the A metal element is Ge, and y = 0.05 to 0.20.   The Bi, Ti, and A metal element (however, the A metal element may not be included) are contained in a ratio of Bi: (Ti + A) = 1.07 to 1.15: 1 (molar ratio). The coating liquid according to any one of? 7.   A coating solution for forming a paraelectric Bi-based dielectric thin film containing at least a composite metal alkoxide formed of two metal alkoxides of Bi and Ti, or a mixture of at least Bi alkoxide and Ti alkoxide The said coating liquid containing the mixed metal alkoxide formed. The coating solution according to claim 9, which is a coating solution for forming a paraelectric Bi-based dielectric thin film containing a composite metal oxide represented by the following general formula (I).
{Bi _4-x , (La _z , B _1-z ) _x } _n (Ti _3-y , A _y ) O _{12 + α} (I)
(In the formula, A represents at least one metal element selected from V, Cr, Mn, Si, Ge, Zr, Nb, Ru, Sn, Ta, and W; B represents a rare earth element excluding lanthanum; Represents at least one metal element selected from Ca, Sr, and Ba; x, y, and z are represented by 0 ≦ x <4, 0 ≦ y ≦ 0.3, and 0 <z ≦ 1, respectively. N represents a number from 0.7 to 1.4; α represents a value determined by the metal composition ratio.)   The coating solution contains a composite metal alkoxide formed of at least two metal alkoxides of Bi and Ti, or a mixed metal alkoxide formed by mixing at least a Bi alkoxide and a Ti alkoxide, and further contains water, or The coating solution according to claim 9 or 10, which is a sol-gel solution obtained by hydrolysis and partial condensation treatment using water and a catalyst.   The coating solution according to any one of claims 9 to 11, wherein alkanolamine is blended in the coating solution.   The coating liquid according to any one of claims 10 to 12, wherein in the general formula (I), x represents a number represented by 0 <x <4.   The coating liquid according to any one of claims 10 to 13, wherein in the general formula (I), z represents a number represented by 0 <z <1.   The coating liquid according to any one of claims 10 to 14, wherein in the general formula (I), y represents a number represented by 0 <y ≦ 0.3.   The Bi, Ti, and A metal element (however, the A metal element may not be included) are contained at a ratio of Bi: (Ti + A) = 0.90 to 1.06: 1 (molar ratio). The coating liquid according to any one of -15.   The coating liquid according to any one of claims 9 to 16 is applied onto a substrate, and a coating film is formed by performing a heat treatment (first heat treatment) at 500 to 700 ° C without performing a heat drying treatment. If desired, the steps from the application to the heat treatment (first heat treatment) are repeated a plurality of times to form a laminate of the coating film, and then heat treatment at 600 to 700 ° C. (second heat treatment) is performed. A method of forming a paraelectric Bi-based dielectric thin film. A paraelectric Bi-based dielectric thin film containing a composite metal oxide represented by the following general formula (I).
{Bi _4-x , (La _z , B _1-z ) _x } _n (Ti _3-y , A _y ) O _{12 + α} (I)
(In the formula, A represents at least one metal element selected from V, Cr, Mn, Si, Ge, Zr, Nb, Ru, Sn, Ta, and W; B represents a rare earth element excluding lanthanum; Represents at least one metal element selected from Ca, Sr, and Ba; x, y, and z are represented by 0 ≦ x <4, 0 ≦ y ≦ 0.3, and 0 <z ≦ 1, respectively. N represents a number from 0.7 to 1.4; α represents a value determined by the metal composition ratio.)   The Bi, Ti, and A metal elements (however, the A metal element may not be included) are contained at a ratio of Bi: (Ti + A) = 0.90 to 1.06: 1 (molar ratio). The thin film described. The thin film of Claim 18 or 19 formed by apply | coating the coating liquid of any one of Claims 9-16 on the electrode provided on the board | substrate, and baking.

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