JP3152135B2 - Composition for forming Ba1-xSrxTiyO3 thin film and method for forming Ba1-xSrxTiyO3 thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to Ba _1-x Sr _x Ti
_y O ₃ thin film forming composition and Ba _1-x Sr _x Ti _y O ₃
Relates to a method of forming the thin film, in particular, the capacitor insulating _{film, Ba 1-x Sr x Ti} y O 3 dielectric thin film-forming composition to be effectively used like in the capacitor material of the DRAM in the thin-film capacitor and a semiconductor integrated circuit device, and Ba _{The present} invention relates to a method for forming a _1-x Sr _x Ti _y O ₃ thin film.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of capacitor elements and the high integration of semiconductor integrated circuits, a material having a high dielectric constant is required for a capacitor insulating film applied thereto. Examples of the material having a high dielectric constant include BaTiO ₃ , SrTiO ₃ , and (Ba _1-x Sr) having a perovskite crystal structure.
_x ) Barium titanate-based dielectric materials such as TiO ₃ have been attracting attention.
There are a sol-gel method and a CVD method. Specifically, the following has been proposed.

(I) A composition for forming a barium titanate thin film by dissolving barium lower carboxylate (preferably barium acetate) and titanium isopropoxide in an organic solvent containing ethylene glycol monomethyl ether and contacting water with this (JP-A-1-1000024).

(Ii) BaCO ₃ , SrCO ₃ and TiO
₍₂ ) A method of forming a (Ba _1-x Sr _x ) TiO ₃ thin film by a sputtering method at a substrate temperature of 400 to 600 ° C. by calcining the mixed powder at 800 to 1000 ° C. as a target.

[0005]

In forming a barium titanate-based thin film by a conventional sol-gel method, Japanese Patent Laid-Open No.
In order to use a lower carboxylate as a raw material as in the method described in JP-A-100024, a temperature as high as 800 ° C. or more is required for crystallization, and deterioration of insulating properties due to this high-temperature sintering is inevitable. Has not been put to practical use due to its large size. It is considered that the deterioration of the insulating property is caused by generation of minute cracks and voids in the thin film due to abrupt shrinkage of the film due to high-temperature baking and deterioration of the underlying electrode.

JP-A-3-257020 discloses that even when a BST thin film is formed by a sputtering method, the leak characteristics deteriorate when the substrate temperature exceeds 600 ° C.

As described above, in a substance having a perovskite structure having a high dielectric constant, particularly, carriers due to defects tend to be easily generated, and the higher the relative dielectric constant, the larger the leak current tends to be. It is said that it is difficult to achieve both high insulation and high insulation.

The present invention solves the above conventional problems, effective capacitor material for various applications in electronic devices, Ba _1-x capable of forming a dielectric thin film having a high dielectric constant and high insulating properties providing Sr _x Ti _y O ₃ thin film-forming composition and such _{Ba 1-x Sr x Ti y} O 3 Ba using a thin film forming composition _{1-x Sr x Ti y O} 3 thin film forming method The purpose is to:

[0009]

A Ba _1-x Sr according to claim 1
_The composition for forming a thin film of _x Ti _y O ₃ is obtained by mixing barium carboxylate, strontium carboxylate and titanium alkoxide in a molar ratio of Ba: Sr: Ti = (1-x): x: y
(Provided that 0 ≦ x ≦ 1.0, 0.9 ≦ y ≦ 1.1) and Ba _1-x Sr _x Ti _y O ₃ obtained by dissolving a calcium compound in an organic solvent. A composition for forming a thin film, wherein the organic solvent is a mixed solvent containing a carboxylic acid and an ester, and the content of the carboxylic acid in the composition is 2 to 11 moles relative to the titanium alkoxide, and When the content of the calcium compound is Sr in the composition
It is characterized by being 0.5 to 10 mol% in terms of Ca with respect to the content.

As an organic solvent for dissolving barium carboxylate, strontium carboxylate and titanium alkoxide as a raw material for a thin film, a carboxylic acid, in particular, a carboxylic acid forming barium carboxylate and / or strontium carboxylate is used together with ordinary esters and alcohols. By mixing and using the same carboxylic acid in an appropriate amount, the stability of the composition for forming a thin film can be enhanced, and a uniform thin film can be formed. For this reason, when forming a thin film, low-temperature baking can be performed, and therefore, good Ba _1-x Sr _x can be obtained without causing problems such as deterioration of a substrate and deterioration of electric characteristics such as a dielectric constant.
A Ti _y O ₃ thin film can be formed.

Further, by dissolving a predetermined amount of a calcium compound, it becomes possible to form an ideal dielectric thin film having a large relative dielectric constant and a high insulating property.

[0012] In the present invention, in particular, an acyloxy group constituting the barium carboxylic acid and carboxylic acid strontium general formula _{C n H 2n + 1 COOO -} ( where, n is 3
The carboxylic acid of the organic solvent is preferably the same carboxylic acid as the carboxylic acid forming barium carboxylate and / or strontium carboxylate.

With such a composition for forming a Ba _1-x Sr _x Ti _y O ₃ thin film, it is applied to a substrate and dried,
By baking at 450 to 800 ° C., a Ba _{1 -x} Sr _x Ti _y O ₃ thin film having a high dielectric constant and a high insulating property can be easily formed.

[0014]

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

The composition for forming a Ba _1-x Sr _x Ti _y O ₃ thin film of the present invention contains a carboxylic acid and an ester as an organic solvent for dissolving barium carboxylate, strontium carboxylate and titanium alkoxide as thin film raw materials. A mixed solvent, for example, a mixed solvent of a carboxylic acid and an ester, a mixed solvent of a carboxylic acid, an ester and an alcohol, preferably a mixed solvent of a carboxylic acid and an ester is used.

In the mixed solvent according to the present invention, the carboxylic acid includes barium carboxylate and / or
Alternatively, it is preferable to use the same carboxylic acid as the carboxylic acid forming strontium carboxylate. Therefore, as the carboxylic acid, a carboxylic acid represented by the general formula C _n H _{2n + 1} COOH (where n is an integer of 3 to 7), specifically, n-butyric acid, α-methylbutyric acid, i -Valeric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3-dimethylbutyric acid, 3-methylpentanoic acid,
-Methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-
Dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 2
It is preferable to use -ethylhexanoic acid and 3-ethylhexanoic acid.

Examples of the ester include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, and isoamyl acetate. It is preferable to use 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol, 1-propanol.
It is preferred to use pentanol, 2-pentanol, 2-methyl-2-pentanol, iso-amyl alcohol.

In the present invention, the ratio of the carboxylic acid used as the solvent is 2 to 11 times the molar amount of the titanium alkoxide used as the raw material for the thin film. If the ratio of the carboxylic acid is less than twice the molar amount of the titanium alkoxide, the effects of using the carboxylic acid to improve the solubility, stability and uniform thin film formation cannot be sufficiently obtained. When the ratio of the carboxylic acid exceeds 11 times the molar amount of the titanium alkoxide, the viscosity of the solution becomes too high, and it is difficult to apply the solution uniformly.

In the case of a mixed solvent of a carboxylic acid and an ester, the composition of the mixed solvent is preferably 3 to 40% by weight of the carboxylic acid and 20 to 90% by weight of the ester.
In the case of a mixed solvent of a carboxylic acid, an ester and an alcohol, the ester 1 is contained with respect to 3 to 40% by weight of the carboxylic acid.
Preferably, the content is 4 to 60% by weight and the alcohol is 7 to 30% by weight.

The composition for forming a thin film of Ba _1-x Sr _x Ti _y O _{3 according to the} present invention is obtained by converting barium carboxylate, strontium carboxylate and titanium alkoxide, which are raw materials for a thin film, into such a mixed solvent in terms of oxide. Total concentration of 4-1
0% by weight, and the calcium compound has a Ca conversion ratio of 0.5 to 1 with respect to the Sr content.
It is prepared by dissolving so as to be 0 mol%.

Here, the calcium compound is not particularly limited as long as it can be dissolved in the above-mentioned mixed solvent, and is usually calcium 2-ethylhexanoate,
Calcium 2-ethylbutyrate, calcium propionate,
Calcium salts of organic acids such as calcium acetate, organic calcium compounds such as calcium acetylacetonate and calcium alkoxide, and calcium salts of inorganic acids such as calcium chloride and calcium nitrate can be used.

In the present invention, if the content of the calcium compound is less than 0.5 mol% in terms of Ca with respect to the Sr content in the composition, the effect of improving the dielectric constant and insulating properties by adding the calcium compound is sufficient. 10 mol%
If it exceeds, the dielectric constant decreases.

In the present invention, of the thin film raw materials,
Examples of the titanium alkoxide include titanium alkoxides of linear or branched alcohols having 2 to 5 carbon atoms, for example, titanium ethoxide, titanium isopropoxide, titanium butoxide, and titanium amiloxide. Therefore, it is preferable to use titanium isopropoxide.

The acyloxy group constituting barium carboxylate and strontium carboxylate has the general formula C
_n H _{2n + 1} COO ⁻ (where n is an integer of 3 to 7) is preferable.

In the above formula, when n is 2 or less, a carbonate is easily formed at the time of thermal decomposition. Conversely, when n is 8 or more,
The change in weight due to evaporation of the organic components is large, and a homogeneous film without cracks cannot be formed.

Specific examples of barium carboxylate and strontium carboxylate include the aforementioned barium salts and strontium salts of carboxylic acids as specific examples of the carboxylic acid in the mixed solvent.

The acyloxy groups of barium carboxylate and strontium carboxylate may be the same or different.

The barium carboxylate, strontium carboxylate and titanium alkoxide as the raw materials for the thin film are mixed in the above-mentioned mixed solvent so that a desired composition of Ba _1-x Sr _x Ti _y O ₃ is obtained.

The Ba _1-x Sr _x Ti _{y of the} present invention as described above
Depending on the composition for forming the O ₃ thin film, Ba _1-x Sr _x Ti _y O ₃
To form a thin film, Si, Pt / Ti / SiO ₂ / Si,
Pt / Ta / SiO ₂ / Si, Pt / SiO ₂ / Si,
Ru / RuO ₂ / SiO ₂ / Si, RuO ₂ / Si, R
uO ₂ / Ru / SiO ₂ / Si, Ir / IrO ₂ / S
i, Pt / Ir / IrO ₂ / Si, Pt / IrO ₂ / S
The composition of the present invention is applied onto a substrate such as i, and dried (temporary firing) and main firing. If a desired film thickness cannot be obtained by one application, the application and drying steps are repeated a plurality of times, and then the main firing is performed. Here, the drying (temporary firing) is performed at 150 to 400 ° C., and the main firing is performed at 450 to 400 ° C.
This is performed at 800 ° C. for about 30 minutes to 2 hours.

[0030]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Examples 1 to 4 and Comparative Examples 1 to 3 Barium 2-ethylhexanoate, strontium 2-ethylhexanoate and titanium isopropoxide were used as thin film raw materials, and the composition ratio was Ba _0.7 Sr _0.3 TiO _3.
Was dissolved in a mixed solvent of 2-ethylhexanoic acid and isoamyl acetate so that the total concentration in terms of oxide of the composition was 7% by weight. The amount of 2-ethylhexanoic acid in this mixed solvent was twice as much as that of titanium isopropoxide.

To this solution, calcium 2-ethylhexanoate was further added at the ratio shown in Table 1 (however, no calcium compound was added in Comparative Example 1), and the mixture was refluxed for 1 hour to sufficiently homogenize. A composition for forming a thin film of the present invention was prepared.

This composition for forming a thin film is applied on a titanium platinum substrate by spin coating and dried at 300 ° C. for 10 minutes. The coating and drying steps are repeated three times, and finally 550 ° C.
For 1 hour to form a Ba _0.7 Sr _0.3 TiO ₃ thin film. An upper electrode is deposited on this thin film with gold, and the relative dielectric constant,
The leakage current density and the dielectric loss were measured, and the results are shown in Table 1.

[0034]

[Table 1]

Examples 5 to 8 and Comparative Examples 4 and 6 The same as Examples 1 to 4 and Comparative Examples 1 to 3, except that the thin film raw materials were dissolved so as to have a composition ratio of Ba _0.5 Sr _0.5 TiO _3. The relative dielectric constant, the leakage current density and the dielectric loss were measured, and the results are shown in Table 2.

[0036]

[Table 2]

Examples 9 to 12 and Comparative Examples 7 to 9 The same as Examples 1 to 4 and Comparative Examples 1 to 3, except that the thin film raw materials were dissolved so as to have a composition ratio of Ba _0.3 Sr _0.7 TiO _3. The relative dielectric constant, the leak current density and the dielectric loss were measured, and the results are shown in Table 3.

[0038]

[Table 3]

Examples 13 to 18 The same procedures as in Example 2 were carried out except that the calcium compounds shown in Table 4 were used, and the relative dielectric constant, leak current density and dielectric loss were measured. The results are shown in FIG.

[0040]

[Table 4]

Examples 19 to 21, Comparative Examples 10 to 12 The same procedures as in Example 2 were carried out except that the amount of 2-ethylhexanoic acid relative to titanium isopropoxide in the mixed solvent was set to the ratio shown in Table 5, The relative dielectric constant, leak current density and dielectric loss were measured, and the results are shown in Table 4.

[0042]

[Table 5]

[0043]

As described in detail above, the Ba _1-x S of the present invention is used.
r _x Ti _y O ₃ thin film forming composition and Ba _1-x Sr _x T
According to the method for forming an i _y O ₃ thin film, a composition for forming a thin film having excellent stability, uniformity and coatability can be used in an amount of 450 to 800.
Forming a Ba _1-x Sr _x Ti _y O ₃ thin film that is homogeneous and has remarkably good electric properties such as dielectric constant and insulation without causing problems such as deterioration of the base material by firing at a relatively low temperature of ℃ can do.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-39313 (JP, A) JP-A-7-252664 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 23/00 C04B 35/46 H01B 3/12 303 CA (STN)

Claims (3)

(57) [Claims] 1. A barium carboxylate, strontium carboxylate and titanium alkoxide are used in a molar ratio of Ba: S
r: Ti = (1-x): x: y (where 0 ≦ x ≦ 1.
0, 0.9 ≦ y ≦ 1.1) Ba mixed with an organic solvent and a calcium compound dissolved therein.
_1-x Sr _x Ti _y O ₃ thin film forming composition, wherein the organic solvent is a mixed solvent containing a carboxylic acid and an ester, and the carboxylic acid content in the composition is 2 to the titanium alkoxide. Ba _1-x , wherein the content of the calcium compound is 0.5 to 10 mol% in terms of Ca with respect to the Sr content in the composition.
A composition for forming a Sr _x Ti _y O ₃ thin film. 2. The composition according to claim 1, wherein the acyloxy group constituting barium carboxylate and strontium carboxylate is represented by the general formula C _n H _{2n + 1} COO ⁻ (where n is an integer of 3 to 7). , the carboxylic acid of the organic _{solvent, Ba 1-x Sr x Ti} y O 3 thin film-forming composition, wherein the at least one of a carboxylic acid and a carboxylic acid to form a barium carboxylic acid and / or carboxylic acid strontium. 3. The Ba _1-x Sr _x Ti _{y according to} claim 1 or 2.
The composition for forming an O ₃ thin film is applied to a substrate, dried, and dried at 450 ° C.
Ba _1-x Sr _x characterized in that it is fired at up to 800 ° C.
A method for forming a Ti _y O ₃ thin film.