JP2008053281A - High dielectric film and method for forming the same - Google Patents

Abstract

Disclosed is a dielectric film that is free from cracks, has a small film shrinkage, and has excellent dielectric characteristics in the formation of a high dielectric film made of a perovskite type dielectric material by the MOD method.
A multilayer dielectric thin film formed by laminating three or more layers is produced by repeatedly performing the following steps (1) and (2) on a substrate, and then the obtained multilayer dielectric thin film is formed. Main firing is performed.
Step (1): A coating solution comprising a coating composition containing an alkaline earth metal element and at least one metal element selected from the group consisting of titanium, tin, and zirconium in a mixed solvent on a substrate. A dielectric thin film formed by a single coating is applied in an amount sufficient for the film thickness to be 30 to 120 nm after pre-baking, and then dried.
Step (2): The dielectric thin film formed on the substrate is heated at a temperature of 550 to 800 ° C. in an oxygen atmosphere and temporarily fired.
[Selection figure] None

Description

  The present invention relates to a high dielectric film and a method for forming the same, and more specifically, formation of a high dielectric film made of a perovskite dielectric material by an organic acid salt pyrolysis method (hereinafter sometimes referred to as MOD method). The present invention relates to a dielectric film having no cracks, small film shrinkage, and excellent dielectric characteristics, and a method for forming the same. As a result, it is possible to obtain a high dielectric film excellent in dielectric characteristics, which is suitable for capacitor materials for various applications in electronic devices such as thin film capacitors, capacitive insulating films of semiconductor integrated circuit devices, and capacitor materials of DRAMs.

In recent years, with the miniaturization of capacitor elements and the high integration of semiconductor integrated circuits, capacitor insulating films used for capacitor insulating films of thin film capacitors and semiconductor integrated circuit devices, capacitor materials of DRAMs, etc. have a high dielectric constant. Substances are sought. As such a material having a high dielectric constant, a composite oxide having a perovskite crystal structure is known. For example, barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ), barium strontium titanate ((Ba, Sr) TiO ₃ ), or the like, or the composite oxide as a main component Further, perovskite type composite oxides in which magnesium is substituted at the Ba site and tin and zirconium are substituted at the Ti site are attracting attention.

  Further, as a method for forming a thin film of a substance having such a high dielectric constant, a sputtering method, a sol-gel method, a MOD method, a CVD method or the like is performed. However, both the sputtering method and the CVD method have a complicated apparatus and have a drawback that the film formation speed is slow, and the area on which the film can be formed is small, so that a film with a large area can be obtained. There is a problem that it is not possible. On the other hand, in a coating method such as a sol-gel method or a MOD method, a liquid material containing a compound that forms a perovskite-type composite oxide by thermal decomposition is applied onto a substrate and baked. There is an advantage that a thin film having a large area can be obtained with inexpensive equipment, and this is a promising method which is industrially excellent in mass productivity. Here, as a preparation procedure of the dielectric film by the coating method, for example, the perovskite type complex oxidation containing an alkaline earth metal element and at least one selected from titanium, tin, or zirconium, and thermally decomposing it is performed. A composite organic acid salt solution for forming a product is applied onto a substrate by a spin coating method, then dried at about 200 ° C., and then temporarily fired at 300 to 500 ° C. to form a thin film several times. After the film thickness is obtained, final firing is performed at 700 to 800 ° C. to obtain a dielectric film.

Conventionally, for example, the following (A) to (C) have been proposed for coating solutions for forming a thin film used in the sol-gel method or the MOD method.
(I) Use barium and titanium metal soap (for example, refer to Patent Document 1).
(B) A barium carboxylate salt such as barium acetate and a raw material of titanium isopropoxide are dissolved in an organic solvent containing ethylene glycol monomethyl ether and hydrolyzed to obtain a composition for forming a barium titanate thin film (for example, , See Patent Document 2).
(C) Barium strontium carboxylate, strontium carboxylate, and titanium isopropoxide are dissolved in an organic solvent as an ester to form a composition for forming a barium strontium titanate thin film (see, for example, Patent Document 3). .

  However, these proposals have many technical problems and practical problems. For example, in (i), barium and strontium carbonates are not produced during pyrolysis of metal soap during firing, but the weight change due to volatilization of organic components is large, so cracks occur in the formed thin film, There arises a problem that the shrinkage of the resin becomes large. In (b), since a carboxylate is used as a raw material, a high temperature exceeding 800 ° C. is required for crystallization during firing. As a result, deterioration of insulation is unavoidable, and since leakage current is large, it has not been put into practical use. The cause of this deterioration is considered to be that micro cracks or voids are generated in the thin film due to rapid shrinkage of the film due to high-temperature firing or reaction with the base electrode. In (c), by using an ester as the solvent, the change in weight due to the volatilization of the organic component is small, and cracking and film shrinkage are unlikely to occur. However, expensive barium carboxylate and strontium carboxylate must be used, when a metal film is used for the base electrode, the wettability is poor and it is difficult to obtain a uniform coating film, and the solvent is only an ester. When it is, there existed problems, such as that the preservability by external air will deteriorate.

  As described above, in the coating method used for the formation of a high dielectric film made of a perovskite type dielectric material, the problems such as the storage stability of the coating liquid, the occurrence of cracks in the formed film, and the shrinkage of the film must be cleared. Therefore, it has been difficult to satisfy all of these requirements and achieve high dielectric properties. By the way, in the bulk body manufactured by the method of sintering powder due to the instability factors of the prior art as described above, even when a material that can obtain a dielectric constant of several thousand to 10,000 is thinned, At present, the relative dielectric constant remains below about 500.

JP-A-1-308801 (first page) Japanese Patent Laid-Open No. 1-100024 (first page) JP-A-8-337421 (first page, second page)

  In view of the above-mentioned problems of the prior art, the object of the present invention is to form a high dielectric film made of a perovskite-type dielectric material by the MOD method, with no cracks, small film shrinkage, and excellent dielectric properties. Another object of the present invention is to provide a dielectric film and a method for forming the dielectric film.

  In order to achieve the above object, the present inventors have conducted extensive research on a method for forming a high dielectric film made of a perovskite-type dielectric material. Using a specific coating composition as a coating liquid, repeatedly performing a process of obtaining a dielectric coating film having a specific thickness on a substrate and a process of obtaining a dielectric thin film by pre-baking it on specific conditions After the multilayer dielectric thin film is formed by laminating three or more layers, the multilayer dielectric thin film is subjected to main firing. In addition, the inventors have found that a dielectric film excellent in dielectric characteristics can be obtained, and completed the present invention.

That is, according to the first invention of the present invention, after the multilayer dielectric thin film formed by laminating three or more layers on the substrate by repeating the following steps (1) and (2), The present invention provides a method for producing a high dielectric film, comprising subjecting the obtained multilayer dielectric thin film to main firing.
Step (1): At least selected from the group consisting of barium, strontium, magnesium, and calcium in a mixed solvent consisting of an ether solvent and / or an alcohol solvent, a carboxylic acid solvent, and an ester solvent on the substrate. A dielectric formed by a single coating of a coating solution comprising a coating composition containing one alkaline earth metal element and at least one metal element selected from the group consisting of titanium, tin, and zirconium. The body thin film is applied in an amount sufficient to be 30 to 120 nm after calcination and then dried.
Step (2): The dielectric thin film formed on the substrate is heated at a temperature of 550 to 800 ° C. in an oxygen atmosphere and temporarily fired.

According to a second aspect of the present invention, there is provided the method for forming a dielectric film according to the first aspect, wherein the substrate is a Pt film / TiO ₂ film / SiO ₂ layer / Si substrate. Provided.

  According to a third aspect of the present invention, there is provided the method for forming a dielectric film according to the second aspect, wherein the substrate is pretreated.

  According to a fourth aspect of the present invention, in the fourth aspect, the pretreatment is performed by heat-treating the substrate at a temperature of 700 to 900 ° C. in an oxygen atmosphere while the film is formed. After coating the coating solution used in the organic acid salt pyrolysis method on the Pt film of the uppermost layer of the heat-treated substrate, the film is baked at a temperature of 700 to 900 ° C. in an oxygen atmosphere to have a film thickness of 30 to There is provided a method for forming a high dielectric film, comprising forming a reaction suppression layer comprising a dielectric thin film of 80 nm.

  According to a fifth aspect of the present invention, in the first aspect, the ether solvent is methyl cellosolve, the alcohol solvent is 2-propanol or 1-butanol, the carboxylic acid solvent is 2-ethylhexanoic acid, There is provided a method for forming a high dielectric film, wherein the ester solvent is butyl acetate or isopentyl acetate.

  According to the sixth aspect of the present invention, in the first aspect, the content ratio of the metal component in the coating solution used in the step (1) is 0.2 to 0.4 mol / in terms of metal element concentration. A method of forming a high dielectric film characterized by being L is provided.

  According to a seventh aspect of the present invention, there is provided the method for forming a high dielectric film according to the first aspect, wherein the main firing is performed at a temperature of 700 to 900 ° C. in an oxygen atmosphere. Is done.

  According to an eighth aspect of the present invention, there is provided a high dielectric film made of a perovskite type dielectric material obtained by the formation method of any one of the first to seventh aspects of the invention.

  According to the ninth aspect of the present invention, in the eighth aspect, the average crystal grain size of the composite oxide in the dielectric thin film layer is 20 to 50 nm. Is provided.

  The high dielectric film and the method for forming the same according to the present invention are free from cracks when forming a high dielectric film made of a perovskite-type dielectric material by the MOD method, have small film shrinkage, and have excellent dielectric properties. Since the dielectric film can be formed efficiently, its industrial value is extremely large.

Hereinafter, the high dielectric film of the present invention and the method for forming the same will be described in detail.
1. High Dielectric Film Forming Method The high dielectric film forming method of the present invention is a multilayer dielectric thin film formed by laminating three or more layers on a substrate by repeating the following steps (1) and (2). Then, the obtained multilayer dielectric thin film is subjected to main firing.
Step (1): At least selected from the group consisting of barium, strontium, magnesium, and calcium in a mixed solvent consisting of an ether solvent and / or an alcohol solvent, a carboxylic acid solvent, and an ester solvent on the substrate. A dielectric formed by a single coating of a coating solution comprising a coating composition containing one alkaline earth metal element and at least one metal element selected from the group consisting of titanium, tin, and zirconium. The body thin film is applied in an amount sufficient to be 30 to 120 nm after calcination and then dried.
Step (2): The dielectric thin film formed on the substrate is heated at a temperature of 550 to 800 ° C. in an oxygen atmosphere and pre-baked. Thereby, there is no generation of cracks, and the film shrinkage is small. A dielectric film having excellent characteristics can be obtained.

  In the present invention, when applying the coating liquid in the step (1), the coating is performed so that the film thickness per dielectric thin film after temporary baking is 30 to 120 nm, and oxygen is formed when forming the dielectric thin film. It is important that heating is performed at a temperature of 550 to 800 ° C. in the atmosphere to perform preliminary firing, and the number of repetitions of steps (1) and (2) is three or more. As a result, the obtained dielectric film has a cross-section having a structure in which three or more dielectric thin film layers having a thickness of 30 to 120 nm are laminated, and is obtained by laminating such dielectric thin films. The dielectric film exhibits particularly excellent dielectric characteristics because each of the dielectric thin film layers constituting the dielectric film has excellent dielectric characteristics.

  That is, the preliminary baking is performed to eliminate the solvent in the coating film, but the dielectric thin film is completely crystallized by increasing the temperature of the temporary baking from the normal 300 to 500 ° C. to 550 to 800 ° C. And crystal grain growth is also promoted. As a result, the formed dielectric thin film itself sufficiently functions as a dielectric, and the dielectric characteristics per layer are increased.

  In the above method, the coating liquid is a solvent comprising an ether solvent and / or an alcohol solvent, a carboxylic acid solvent, and an ester solvent, and the metal component is selected from the group consisting of barium, strontium, magnesium and calcium. It is important to use a coating composition containing at least one selected alkaline earth metal element and at least one metal element selected from the group consisting of titanium, tin and zirconium. Thereby, in each dielectric thin film layer made of a perovskite type dielectric material constituting the dielectric, it is possible to form a dielectric having no cracks, small film shrinkage, and excellent dielectric characteristics. That is, by selecting a solvent that constitutes the coating composition, a coating solution that satisfies the solubility, coating properties, storage stability, and film crystallinity of the metal component can be obtained.

(1) Coating composition and production method thereof The production method of the coating composition is not particularly limited, and includes the following steps (a) to (d).
(A) a metal of at least one alkaline earth metal element selected from the group consisting of barium, strontium, magnesium and calcium, an alkoxide or a carboxylate thereof, an ether solvent and / or an alcohol solvent, and a carboxylic acid After being added to a mixed solution comprising a solvent or an ester solvent containing the same, heat treatment is performed at a temperature of 80 to 110 ° C. in a nitrogen or inert gas atmosphere, so that the metal element concentration is 0.2 to 0.8 mol / A step of preparing an organic acid salt solution (A) of L,
(B) An alkoxide or carboxylate of at least one element selected from the group consisting of titanium, tin and zirconium is added to an ester solvent, and the metal element concentration is 0.2 to 0.8 mol / L. A step of preparing an alkoxide liquid (B),
(C) The organic acid salt solution (A) and the alkoxide solution (B) are mixed in such a proportion that the total amount of metal elements contained in the former and the total amount of metal elements contained in the latter are equal in molar ratio. A step of synthesizing a complex organic acid salt solution (C) by mixing at a temperature of 80 to 110 ° C. in a nitrogen or inert gas atmosphere after mixing,
(D) The obtained complex organic acid salt solution (C) is heat-treated at a temperature of 80 to 125 ° C. in a nitrogen or inert gas atmosphere, thereby promoting the complex alkoxidation reaction, while the metal element concentration is increased. Step of diluting the metal element concentration to 0.2 to 0.4 mol / L by adding an alcohol solvent and an ester solvent after concentrating to 1.0 to 1.6 mol / L ,

  In the manufacturing method, it is important to carry out according to the procedure of the above steps. If this procedure is different, the stability of the resulting coating solution may be inferior, or the constituent metal may volatilize during baking during film formation, causing the film composition to deviate from the liquid composition.

  The step (a) of the above production method comprises at least one alkaline earth metal element metal selected from the group consisting of barium, strontium, magnesium and calcium, an alkoxide or carboxylate thereof, an ether solvent (hereinafter, And / or an alcohol solvent (hereinafter sometimes abbreviated as alcohol) and a carboxylic acid solvent (hereinafter sometimes abbreviated as carboxylic acid) or a mixture thereof. After adding to a mixed solution composed of an ester solvent (hereinafter sometimes abbreviated as an ester), heat treatment is performed at a temperature of 80 to 110 ° C. in a nitrogen or inert gas atmosphere, and the metal element concentration is 0.1. This is a step of preparing a 2-0.8 mol / L organic acid salt solution (A).

In the step (a), by selecting the raw material form, the organic solvent, and the blending ratio thereof, the solubility and storage stability of the metal in the organic acid salt solution (A), and the coating composition for forming a high dielectric thin film The effect which satisfies the volatility or decomposability etc. which cause the coating-film property of a thing and a film defect is acquired.
For example, the stability of the liquid is improved by adding an ester and an ether. In particular, the ester has the effect of improving the coating properties by being added to the liquid.

  Here, when a metal is used as a raw material for alkaline earth metal elements such as barium, strontium, magnesium and calcium, and is dissolved in 2-propanol or methyl cellosolve, the carboxylic acid or ester having high solubility and low water miscibility If an appropriate amount of is mixed, a part of it will undergo substitution reaction with the alkyl group of the metal alkoxide to prepare a stable organic acid salt solution.

  Further, the carboxylate is not particularly limited, but a lower carboxylate such as barium acetate, calcium acetate, calcium ethylhexanoate is preferable. When these are used as raw materials, many of them are difficult to dissolve in lower alcohols, so they are dissolved in carboxylic acid or ester and carboxylic acid and then diluted with alcohol.

  Further, the alkoxide is not particularly limited, and examples thereof include methoxide, ethoxide, isopropoxide, butoxide and the like, but it is particularly preferable to use isopropoxide or butoxide because of an appropriate reaction rate. . When these are used as raw materials, higher alcohols, carboxylic acids, esters, or mixed solvents thereof can be suitably used. In addition, since lower alcohol contains water | moisture content and becomes unstable, it is not preferable.

  In the step (a), the blending ratio of the ether and / or alcohol, the carboxylic acid and the ester in the mixed solution is not particularly limited, and the volume ratio is 2: 3 to 3: 2. It is preferable. That is, if the blending ratio is outside this range, dissolution is insufficient and undissolved substances are likely to be generated, which is not preferable because precipitation occurs and the liquid becomes unstable. As a result, the stability of the liquid is increased, and even if it is not immediately mixed with the alkoxide liquid (B) to synthesize the perovskite type dielectric material, it can be obtained in a sealed container without any change for 3 months. . However, when no carboxylic acid is added, for example, a mixed solvent of alcohol and ester, the solubility of the metal is low and the storage stability of the liquid is poor.

On the other hand, when an organic solvent such as ether, alcohol, carboxylic acid or ester is used alone or in any combination other than the conditions of the present invention, the above effects cannot be obtained.
For example, when metals are used as raw materials for alkaline earth metal elements such as barium, strontium, magnesium, calcium, etc., they are easily dissolved in alcohol or ether, but the resulting alkoxide solution lacks stability against water and is therefore exposed to the open air. There is a problem that it cannot be stored and storage stability is poor. Generally, diketone acetylacetone, ethyl acetoacetate, and the like are added to the metal alkoxide in an equimolar amount to improve the stability of the liquid, but the metal film that is the base electrode of the dielectric thin film There is a problem that the wettability of the film is poor, and cracks are generated during film baking, resulting in a decrease in film density.

  In addition, when a lower carboxylate is used as a raw material, as described above, many of them are difficult to dissolve in a lower alcohol, so that they are generally dissolved using an ester or a carboxylic acid. However, when only an ester is used, particles are precipitated during storage because of the low solubility of the carboxylate. Furthermore, there is a problem that the wettability with the metal film as the base electrode of the dielectric thin film is poor and a uniform film cannot be obtained. On the other hand, carboxylic acid is a useful organic solvent that stabilizes storage stability because it has high solubility and low water miscibility, but it is difficult to volatilize and remove by heating. Therefore, when a large amount of carboxylic acid is used, an organic component remains during film formation. The same applies to a mixed solution of an ester and a carboxylic acid.

  In addition, the ether, alcohol, carboxylic acid or ester used in the step (a) is not particularly limited, but the solubility of the raw material, the stability of the organic acid salt solution, the coating property during film formation, If the volatilization or decomposability at the time of film heat treatment is not good, the dielectric properties of the film will deteriorate, so it can be selected to optimize them.

  As the ether used in the step (a), methyl cellosolve or ethyl cellosolve having a boiling point of 200 ° C. or less is preferable, and methyl cellosolve is more preferable.

  The alcohol used in the step (a) is preferably at least one selected from the group consisting of 1-propanol, 2-propanol, 1-butanol, 2-butanol and methanol, more preferably 2-propanol and 1-butanol. preferable. That is, the boiling point of the alcohol used is preferably from 80 to 160 ° C, more preferably from 80 to 130 ° C. That is, by mixing those having a boiling point of 160 ° C. or less, volatilization or decomposability at the time of heat treatment of the formed film is improved, and a film with less shrinkage and cracks can be obtained. However, when an alcohol solvent having a boiling point of less than 80 ° C. is used, when the metal alkoxide solution is mixed and heated to synthesize a composite organic acid salt solution, the concentration of the solution fluctuates and the synthesis becomes unstable.

  The carboxylic acid used in the step (a) has a boiling point of 200 ° C. or lower and is excellent in handleability, solubility and stability, from 2-ethylhexanoic acid, 3-ethylhexanoic acid, and 3-methylpentanoic acid. At least one ethylhexanoic acid selected from the group consisting of the above is preferred, and 2-ethylhexanoic acid is more preferred.

  The ester used in the step (a) is preferably at least one selected from the group consisting of ethyl acetate, butyl acetate, isobutyl acetate, and isopentyl acetate having a boiling point of 200 ° C. or less, more preferably butyl acetate or isopentyl acetate. preferable.

  The heating and melting conditions used in the step (a) are performed at a temperature of 80 to 110 ° C. That is, when the heating temperature is less than 80 ° C., the formation of the organic acid salt is insufficient. On the other hand, when the heating temperature exceeds 110 ° C., volatilization of the organic solvent becomes active. Moreover, it does not specifically limit as heating time, 2 to 10 hours are preferable, and the time for the production | generation of organic acid salt is fully chosen is selected.

  The concentration of the metal element in the organic acid salt solution (A) obtained in the step (a) is 0.2 to 0.8 mol / L. That is, when the metal element concentration is less than 0.2 mol / L, the productivity is low because the concentration is dilute. On the other hand, when the metal element concentration exceeds 0.8 mol / L, the solution becomes insufficient and the solution is not stable. There is.

The step (b) of the above production method comprises adding an alkoxide or carboxylate of at least one element selected from the group consisting of titanium, tin and zirconium in an ester solvent, and then in a nitrogen or inert gas atmosphere. In which the alkoxide liquid (B) having a metal element concentration of 0.2 to 0.8 mol / L is prepared by heating at a temperature of 20 to 60 ° C. for dissolution. The metal alkoxide is represented by the general formula: M (OR) _n (wherein R represents a linear or branched alkyl group, M represents a metal element, and n is 2 or 4) For example, the chemical formula of titanium alkoxide is Ti (OR 3) ₄ .

The alkoxide used in the step (b) is not particularly limited, and examples thereof include methoxide, ethoxide, isopropoxide, butoxide, and the like. In particular, since the reaction rate is appropriate, isopropoxide or It is preferable to use butoxide.
In addition, the carboxylate used in the step (2) is not particularly limited, and acetate or ethylhexanoate can be used.

  As the organic solvent used in the step (b), an ester solvent, particularly an acetate ester is used. That is, when the mixed solution is added with alcohol, it may gradually become cloudy and precipitate.

  The ester is preferably at least one selected from the group consisting of ethyl acetate, butyl acetate, isobutyl acetate, and isopentyl acetate having a boiling point of 200 ° C. or less, and more preferably butyl acetate or isopentyl acetate.

  The heating and melting conditions used in the step (b) are performed at a temperature of 20 to 60 ° C. That is, when the heating temperature is less than 20 ° C., the formation of the metal alkoxide is insufficient. On the other hand, when heating temperature exceeds 60 degreeC, volatilization of the organic solvent will become active. Moreover, it does not specifically limit as heating time, 10 minutes-2 hours are preferable, and time for formation of metal alkoxide fully is chosen.

  The metal element concentration of the alkoxide liquid (B) obtained in the step (b) is 0.2 to 0.8 mol / L. That is, when the metal element concentration is less than 0.2 mol / L, the productivity decreases when the concentration is dilute. On the other hand, when the metal element concentration exceeds 0.8 mol / L, dissolution is insufficient and the liquid is not stable.

  In the step (c) of the above production method, the organic acid salt solution (A) and the alkoxide solution (B) are obtained by adding a molar ratio of the total amount of metal elements contained in the former and the total amount of metal elements contained in the latter. In the step of mixing the mixed organic acid salt liquid (C) by mixing at a blending ratio so as to be equal to each other and then heat-treating at a temperature of 80 to 125 ° C. in a nitrogen or inert gas atmosphere. Here, the organic acid salt liquid (A) and the metal alkoxide contained in the alkoxide liquid (B) react to synthesize a complex organic acid salt that forms the perovskite complex oxide by thermal decomposition.

  The heating condition used in the step (c) is 80 to 125 ° C. That is, when the heating temperature is less than 80 ° C., the synthesis reaction is insufficient, the constituent elements exist alone, the difference in hydrolysis rate occurs, and the uniformity of the film composition is inferior. On the other hand, when the heating temperature exceeds 125 ° C., not only the volatilization of the organic solvent is activated, but also the metal alkoxide is volatilized at the same time, resulting in a composition shift. Moreover, it does not specifically limit as heating time, 2-10 hours are preferable and the time for which synthesis | combination is fully performed is selected.

  In the step (d) of the production method, the obtained complex organic acid salt solution (C) is heat-treated at a temperature of 80 to 125 ° C. in a nitrogen or inert gas atmosphere, whereby the complex organic acidification reaction is performed. After concentrating the metal element concentration to 1.0 to 1.6 mol / L, further adding an alcohol solvent and an ester solvent to reduce the metal element concentration to 0.2 to 0. This is a step of diluting to 4 mol / L. As a result, the coating composition for forming a high dielectric thin film that satisfies the coating properties and storage stability, does not generate cracks, has a small film shrinkage, and has excellent dielectric properties. Things are obtained.

  Here, first, the complex organic acid salt solution (C) is heated in an inert gas atmosphere at 80 to 125 ° C. to volatilize a part of the solvent, and once the metal element concentration is 1.0 to 1.6 mol. A high concentration solution of / L is prepared. The organic solvent is volatilized by introducing the inert gas while heating. At this time, most of the volatile organic solvent is a low boiling point, particularly an alcohol or an ester. Thereby, the synthesis reaction is further promoted by increasing the concentration. However, since precipitation occurs when the concentration is too high, 1.6 mol / L is the upper limit. On the other hand, if it is less than 1.0 mol / L, the synthesis effect cannot be expected. As the heating temperature at this time, 80 to 125 ° C. at which the synthesis reaction proceeds is used. In addition, when temperature exceeds 125 degreeC, volatilization of a metal alkoxide will occur.

  Next, an ester and alcohol are added to the high concentration liquid as a diluent at room temperature and mixed to adjust the metal element concentration to 0.2 to 0.4 mol / L. Here, as a diluent, the main component is alcohol which does not easily break the structure of the synthesized liquid. However, since the ester is reduced by increasing the concentration, the coating properties are inferior as it is. Therefore, it is necessary to add ester.

  The ester is not particularly limited, and butyl acetate or isobutyl acetate is preferable, and 2-propanol and / or 1-butanol is preferable as the alcohol. As the blending ratio, alcohol: ester = 4: 1 to 2: 1 is preferable.

  High dielectric thin film formation that can form a dielectric thin film that satisfies the coating properties and storability by the above manufacturing method, and that is free from cracks, has a small film shrinkage, and has excellent dielectric properties. A coating composition is obtained. Various additives for improving the performance as a coating solution such as coating properties, storage stability, and crystallinity can be added to the coating composition. The additive is added in the step (d) or thereafter.

(2) Substrate and its pretreatment method The substrate used in the above-mentioned forming method is not particularly limited. For example, Si, Pt / Ti / SiO ₂ / Si, Pt / Ta / SiO ₂ / Si, Pt / SiO ₂ / Si, Ru / RuO ₂ / SiO ₂ / Si, RuO ₂ / Si, RuO ₂ / Ru / SiO ₂ / Si, Ir / IrO ₂ / Si, Pt / Ir / IrO ₂ / Si, Pt / IrO ₂ / Si, Pt / TiO ₂ / SiO ₂ / Si, and the like are mentioned. Among them, Pt film / TiO ₂ film / SiO ₂ layer / Si substrate is preferable, and the substrate subjected to the following pretreatment (hereinafter, Particularly preferred is a pre-treated substrate).

The Pt film / TiO ₂ film / SiO ₂ layer / Si substrate is not particularly limited, and the TiO ₂ film and the Pt film are still formed on the SiO ₂ layer / Si substrate. A film having a Pt film thickness of 100 to 300 nm and a TiO ₂ film thickness of 80 to 150 nm is used. As a method for producing the Pt film, for example, a Ti film is formed on a commercially available SiO ₂ / Si substrate by sputtering. After being formed into a film having a thickness of 100 nm, the film was once taken out and oxidized at 600 to 700 ° C. in the atmosphere for 1 to 2 hours, and a Pt film was formed on the TiO ₂ film of the obtained substrate by sputtering to 200 nm. The film is formed with a film thickness.

However, in a normal Pt film / TiO ₂ film / SiO ₂ layer / Si substrate, a dielectric thin film made of a perovskite type complex oxide is formed on the Pt film in this state as it is for crystallization. When firing at a high temperature of 600 to 900 ° C., a reaction occurs at the interface between the dielectric thin film and the Pt film, resulting in a problem that the dielectric constant of the dielectric decreases.

As a countermeasure for this, as a pretreatment of the substrate, the substrate is heat-treated in an oxygen atmosphere at a temperature of 700 to 900 ° C. with the film being formed, and is then applied to the uppermost Pt film of the heat-treated substrate. After applying the coating solution used in the organic acid salt pyrolysis method, firing in an oxygen atmosphere at a temperature of 700 to 900 ° C. to form a reaction suppression layer made of a dielectric thin film having a thickness of 30 to 80 nm Is preferred. As a result, a decrease in the dielectric constant of the dielectric can be prevented.
In other words, the Ti component in the TiO ₂ film is completely oxidized in advance by heat-treating the substrate as it is in a state of 700 to 900 ° C. in an oxygen atmosphere. Further, it is possible to suppress the Ti component that further diffuses into the Pt film during high-temperature firing.

The temperature for the heat treatment is 700 to 900 ° C., and the heat treatment is preferably performed within 2 hours at this temperature, and more preferably 20 minutes to 2 hours. That is, when the temperature is lower than 700 ° C., the suppression of the diffusion of the Ti component is insufficient. On the other hand, when the temperature exceeds 900 ° C., the crystallization of the Pt film itself is promoted, the surface unevenness becomes severe, and the flatness of the film becomes a problem. If the heating time exceeds 2 hours, crystallization of the Pt film itself is promoted. At this time, no separation occurs between the Pt film and the TiO ₂ film.

Further, the reaction suppression layer can be obtained by forming a dielectric thin film on the heat-treated substrate. Thereby, if a dielectric film is further formed thereon, a dielectric having a high dielectric constant can be obtained. That is, since TiO ₂ due to a partially diffused Ti component is generated on the surface of the Pt film of the substrate after the heat treatment, a reaction occurs when the dielectric thin film is fired at this temperature. In order to avoid this, a dielectric thin film is formed as the reaction suppression layer so that the progress of the reaction is completed inside the dielectric thin film.

  As the coating solution, it is not necessary to use a component having the same composition as that of the coating solution used in forming the dielectric thin film constituting the subsequent dielectric, and a solution having a desired composition is selected.

When the thickness of the reaction suppression layer composed of the dielectric thin film after firing is less than 30 nm, the effect of suppressing the reaction with TiO ₂ is low. On the other hand, when the thickness exceeds 80 nm, no further suppression effect is observed. This affects the dielectric characteristics of the film and lowers the dielectric constant.

As temperature at the time of the said baking, it is 700-900 degreeC, and it is preferable to heat-process at this temperature for 20 minutes-2 hours. That is, when the temperature is lower than 700 ° C., the effect of suppressing the reaction with TiO ₂ is insufficient. On the other hand, when the temperature exceeds 900 ° C., crystallization of the Pt film itself is promoted, which causes a problem. The oxygen atmosphere at the time of firing is not particularly limited, and is preferably, for example, in an oxygen gas stream of 1 to 3 L / min.

(3) Coating, drying, pre-baking and main baking In the above forming method, the coating, drying, pre-baking and main baking methods include, for example, the above-mentioned coating composition for forming a high dielectric thin film on the substrate. The coating liquid is dropped so that the film thickness per dielectric thin film after temporary baking becomes 30 to 120 nm, coated by spin coating, dip coating, etc., dried at a temperature of 200 ° C., and then in an oxygen atmosphere. A series of steps including a step of performing preliminary firing at a temperature of 550 to 800 ° C. to form a dielectric thin film is repeated three or more times, the dielectric thin film is laminated, and finally the final firing is performed. Thereby, a dielectric film having the multilayer structure is obtained.

  The pre-baking conditions are preferably 550 to 800 ° C., preferably 600 to 650 ° C. for 20 minutes to 1 hour. That is, when the temperature is lower than 550 ° C., the crystallization of the complex oxide in the dielectric thin film layer is not performed, and no lamination occurs in the obtained dielectric film. Therefore, division of each layer is not observed in the TEM observation of the cross section. On the other hand, when the temperature exceeds 800 ° C., on the contrary, the growth of crystal grains is excessively promoted, and a large crack is generated at the laminated interface, which affects the dielectric constant. In these temperature ranges, the complex oxide in the dielectric thin film layer is completely crystallized and the crystal grain size grows. Here, the average crystal grain size of the complex oxide in the dielectric thin film layer is 20 to 50 nm, desirably 40 to 50 nm. These crystallinity and average crystal grain size can be determined from XRD and TEM observation. In addition, the atmosphere is an air atmosphere, but an oxygen atmosphere in which the solvent is easily removed is preferable.

  In the above forming method, it is required to repeat the above series of steps until the thickness of the obtained dielectric after firing reaches a desired thickness, for example, 350 to 450 nm. The effective thickness of one layer of the dielectric thin film after calcination is 30 to 120 nm, preferably 40 to 110 nm, more preferably 70 to 100 nm. That is, when the film thickness is less than 30 nm, the number of coating films is very large, which causes a problem in productivity. On the other hand, when the film thickness exceeds 120 nm, the volatility of the solvent is inferior even if the calcining temperature is increased, and defects are increased in the layer.

  Furthermore, as the number of repetitions of a series of steps consisting of coating, drying and pre-baking, the above series of steps is repeated three times or more. That is, in the case of two layers, the dielectric constant becomes low because the thickness of the dielectric is reduced due to the limitation of the thickness of one dielectric thin film, so it is necessary to be laminated in three or more layers. Note that the number of layers is limited by the thickness of the dielectric.

  The conditions for the main firing are not particularly limited, and the firing is performed in an oxygen atmosphere at a temperature of 700 to 900 ° C. for 20 minutes to 2 hours. Thereby, a high dielectric film is obtained. That is, when the temperature is less than 700 ° C., shrinkage due to sintering is insufficient, and there are many voids in the film. Also, since the crystal is imperfect, the dielectric properties are not good. On the other hand, when the temperature exceeds 900 ° C., crystal grain growth is promoted too much, and a large crack is generated, which affects the dielectric constant.

2. High dielectric film The high dielectric film of the present invention comprises at least one alkaline earth metal element selected from the group consisting of barium, strontium, magnesium and calcium as a metal component obtained by the above forming method, titanium, tin And a dielectric film made of a perovskite type dielectric material containing at least one metal element selected from the group consisting of zirconium, and three or more dielectric thin film layers having a thickness of 30 to 120 nm are laminated. It is a dielectric film having a structure with no cracks, small film shrinkage and excellent dielectric characteristics.

  That is, the average crystal grain size of the complex oxide in the dielectric thin film layer constituting the dielectric film grows to 20 to 50 nm, and each of the dielectric thin film layers has excellent dielectric properties. The dielectric property of the dielectric film having the structure is improved. As a result, it is possible to obtain a high dielectric film excellent in dielectric characteristics suitable for capacitor materials for various uses in electronic devices, such as thin film capacitors, capacitive insulating films for semiconductor integrated circuit devices, and capacitor materials for DRAMs.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. The metal analysis and film evaluation methods used in Examples and Comparative Examples are as follows.
(1) Metal analysis: ICP emission analysis was performed.
(2) Evaluation method of film: The occurrence of cracks and shrinkage was evaluated by AFM observation of the film surface. The cross section was observed with a TEM to evaluate the thickness of the dielectric film, the number of dielectric thin film layers, and the average crystal grain size. The average layer thickness of each dielectric thin film layer is obtained by averaging the thickness of the dielectric film by the number of dielectric thin film layers. Further, a platinum upper electrode having a diameter of 0.3 mm was vapor-deposited on the thin film, and the relative dielectric constant and dielectric loss at an AC voltage of 1.0 V and a frequency of 1 MHz were measured in a room kept at 25 ° C.

Moreover, the coating liquid used by the Example and the comparative example followed the following preparation methods.
[Preparation method of coating solution]
Metal barium was added to 80 mL of a mixed solvent containing methyl cellosolve: 2-ethylhexanoic acid: butyl acetate = 2: 1: 1 in a volume ratio, and stirred and mixed at 80 ° C. for 2 hours in a nitrogen stream. An 8 mol / L barium organic acid salt solution (A) was prepared. Further, titanium isopropoxide was added to 20 mL of n-butyl acetate, and the mixture was stirred and mixed at room temperature in the atmosphere for 10 minutes to prepare a titanium alkoxide liquid (B) having a Ti concentration of 0.8 mol / L.
Next, the titanium alkoxide liquid (B1) is dropped into the barium organic acid salt solution (A1) so that the molar ratio is barium: titanium = 1: 1, and the mixture is stirred and mixed at 110 ° C. for 2 hours in a nitrogen stream. A complex organic acid salt solution (C) having a metal element concentration of 0.8 mol / L was obtained.
Next, the complex organic acid salt solution (C) was heated in a nitrogen stream at 125 ° C. for 1 hour to volatilize and concentrate a part of the organic solvent to obtain a high concentration solution having a metal element concentration of 1.2 mol / L. Finally, a diluent obtained by adding 2-propanol and butyl acetate at a volume ratio of 2: 1 was added to the high-concentration solution, and the metal element concentration was adjusted to 0.4 mol / L to obtain a coating solution.

(Example 1)
(1) Preparation of pretreatment substrate After a Ti film was formed to a thickness of 100 nm on a commercially available SiO ₂ / Si substrate by sputtering, it was once taken out and heated at 700 ° C. in the atmosphere for 2 hours for oxidation treatment. Using a Pt film / TiO ₂ film / SiO ₂ layer / Si substrate obtained by forming a Pt film with a film thickness of 200 nm on a TiO ₂ film of the obtained substrate by sputtering, first, oxygen of 2 L / min. Heat treatment was performed at 800 ° C. for 1 hour in a gas stream. Next, the coating solution obtained according to the above [Method for preparing coating solution] is thinly applied on the Pt film by spin coating, dried at 200 ° C., and then at 800 ° C. for 1 hour in a 2 L / min oxygen gas stream. A pretreatment substrate was obtained by firing and forming a reaction suppression layer comprising a dielectric thin film. The thickness of the dielectric thin film obtained here was 60 nm.
(2) Formation of dielectric film Subsequently, the coating liquid obtained according to the above [Method for preparing coating liquid] is applied onto the dielectric thin film of the substrate by spin coating, dried at 200 ° C., and 600 ° C. And calcination was performed for 10 minutes. Here, coating, drying, and pre-baking were repeated seven times, followed by main baking at 800 ° C. for 1 hour in an oxygen gas stream to form a dielectric film made of a BaTiO ₃ film. The coating amount of the coating solution was adjusted so that the thickness of the dielectric thin film formed by a single coating was 30 to 120 nm after temporary firing.
Thereafter, the obtained dielectric film was evaluated by the above-described film evaluation method. The results are shown in Tables 1 and 2.

(Example 2)
The formation of the dielectric film was performed in the same manner as in Example 1 except that the pre-firing condition was 800 minutes for 5 minutes and the pre-firing was repeated 5 times. It evaluated by the evaluation method. The results are shown in Tables 1 and 2.

(Example 3)
In the formation of the dielectric film, a coating solution having a metal element concentration of 0.3 mol / L obtained by changing the dilution degree of the coating solution obtained according to the above [Method for preparing coating solution] is used as the coating solution. The dielectric film obtained was evaluated by the above-described film evaluation method, except that it was used and coating, drying, and pre-baking were repeated 10 times in the same manner as in Example 1. The results are shown in Tables 1 and 2.

Example 4
The formation of the dielectric film was performed in the same manner as in Example 1 except that the main baking temperature was 700 ° C. Then, the obtained dielectric film was evaluated by the above-described film evaluation method. The results are shown in Tables 1 and 2.

(Example 5)
In the preparation of the pretreated substrate, the substrate was first heat-treated at 900 ° C. for 30 minutes, and then baking after coating was performed by heat-treating at 900 ° C. for 20 minutes, and the pretreated substrate obtained here The dielectric thin film was formed in the same manner as in Example 1 except that the film thickness of the dielectric thin film was set to 50 nm and that the condition of the main firing was 900 ° C. for 30 minutes in the formation of the dielectric film. The dielectric film was evaluated by the film evaluation method. The results are shown in Tables 1 and 2.

(Comparative Example 1)
The formation of the dielectric film was performed in the same manner as in Example 1 except that the pre-baking temperature was 300 ° C., and then the obtained dielectric film was evaluated by the film evaluation method. The results are shown in Tables 1 and 2.

(Comparative Example 2)
The formation of the dielectric film was performed in the same manner as in Example 1 except that the pre-baking temperature was 900 ° C., and then the obtained dielectric film was evaluated by the film evaluation method. The results are shown in Tables 1 and 2.

  As is clear from Tables 1 and 2, in Examples 1 to 5, the coating liquid was prepared using an ether solvent and / or an alcohol solvent, a carboxylic acid, and an ester solvent as solvent components. High dielectric constant containing at least one alkaline earth metal element selected from the group consisting of barium, strontium, magnesium and calcium and at least one metal element selected from the group consisting of titanium, tin and zirconium as the metal component The coating composition for forming a body thin film, and the coating liquid is applied so as to have a film thickness of 30 to 120 nm per dielectric thin film after pre-baking and dried, and then at a temperature of 550 to 800 ° C. in an oxygen atmosphere. 3 or more layers are laminated by repeating a series of calcination processes, and since it was performed by the forming method of the present invention, cracks were not generated. , Small shrinkage of the film, and it can be seen that excellent dielectric film dielectric characteristics can be obtained.

  On the other hand, in the comparative example 1 or 2, the temperature of the temporary firing does not meet these conditions, so that no lamination is observed in the cross-sectional structure of the obtained dielectric film, or a large crack occurs. Thus, it can be seen that satisfactory results cannot be obtained in the dielectric characteristics.

  As is clear from the above, the high dielectric film and the method of forming the same according to the present invention can obtain a dielectric film having excellent dielectric characteristics. Therefore, the thin film capacitor, the capacitive insulating film of the semiconductor integrated circuit device, and the DRAM capacitor It is suitable as a high dielectric film excellent in dielectric characteristics used for capacitor materials for various uses in electronic devices such as materials and a method for forming the same.

Claims (9)

After the multilayer dielectric thin film formed by laminating three or more layers is produced by repeating the following steps (1) and (2) on the substrate, the resultant multilayer dielectric thin film is then baked. A method for producing a high dielectric film.
Step (1): At least selected from the group consisting of barium, strontium, magnesium, and calcium in a mixed solvent consisting of an ether solvent and / or an alcohol solvent, a carboxylic acid solvent, and an ester solvent on the substrate. A dielectric formed by a single coating of a coating solution comprising a coating composition containing one alkaline earth metal element and at least one metal element selected from the group consisting of titanium, tin, and zirconium. The body thin film is applied in an amount sufficient to be 30 to 120 nm after calcination and then dried.
Step (2): The dielectric thin film formed on the substrate is heated at a temperature of 550 to 800 ° C. in an oxygen atmosphere and temporarily fired. The method of forming a dielectric film according to claim 1, wherein the substrate is a Pt film / TiO ₂ film / SiO ₂ layer / Si substrate.   The method for forming a dielectric film according to claim 2, wherein the substrate is pretreated.   In the pretreatment, the substrate is formed as it is, and heat treatment is performed at a temperature of 700 to 900 ° C. in an oxygen atmosphere, and then the organic acid salt heat is formed on the uppermost Pt film of the heat-treated substrate. After coating the coating solution used in the decomposition method, firing is performed at a temperature of 700 to 900 ° C. in an oxygen atmosphere to form a reaction suppression layer made of a dielectric thin film having a thickness of 30 to 80 nm. 4. The method for forming a high dielectric film according to claim 3, wherein   The ether solvent is methyl cellosolve, the alcohol solvent is 2-propanol or 1-butanol, the carboxylic acid solvent is 2-ethylhexanoic acid, and the ester solvent is butyl acetate or isopentyl acetate. 2. A method for forming a high dielectric film according to 1.   2. The high dielectric film according to claim 1, wherein the content ratio of the metal component in the coating liquid used in the step (1) is 0.2 to 0.4 mol / L in terms of metal element concentration. Forming method.   The method of forming a high dielectric film according to claim 1, wherein the main baking is performed at a temperature of 700 to 900 ° C. in an oxygen atmosphere.   A high dielectric film made of a perovskite dielectric material, which is obtained by the formation method according to claim 1.   9. The high dielectric film according to claim 8, wherein an average crystal grain size of the composite oxide in the dielectric thin film layer is 20 to 50 nm.