JP3146961B2 - Composition for forming (Ba, Sr) TiO3 dielectric thin film and method for forming (Ba, Sr) TiO3 thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to (Ba, Sr) Ti
Composition for forming O ₃ dielectric thin film and (Ba, Sr) TiO
₃ relates to a method of forming a thin film, in particular, the composition for forming a useful Ba _1-x Sr _x TiO ₃ dielectric thin film as a capacitor insulating film of the thin film capacitor or a semiconductor integrated circuit device (capacitor DRAM) or the like and formed About the method.

[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] Japanese Patent Application Laid-Open No. 7-17713 discloses that
As a dielectric thin film having a high dielectric constant and good insulation properties, (B
(a, Sr) A material in which Mn, Pb, and a rare earth element are added to a TiO ₃ -based dielectric has been proposed.

[0006]

In the case of a substance having a perovskite structure having a high dielectric constant, carriers due to defects are likely to be generated. Particularly, a (Ba _{1 -x} Sr _x ) TiO ₃ -based material has a high relative dielectric constant. Since there is a tendency that the larger the leakage current is, the countermeasures are required.

In the sol-gel method using a lower carboxylate as a raw material as in the method described in Japanese Patent Application Laid-Open No. 1-1000024, high-temperature sintering of 800 ° C. or more is required at the time of crystallization. However, it has not been practically used due to the large leakage current. 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. In this sol-gel method, there is a method of forming a thin film using a raw material having a relatively low thermal decomposition temperature while keeping the heat treatment temperature as low as possible. However, this does not solve the problem of a decrease in the relative dielectric constant.

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, carriers are particularly likely to be generated due to defects, and the higher the relative dielectric constant, the larger the leak current tends to be. It is considered difficult to achieve both dielectric constant and high insulation.

In the dielectric thin film described in Japanese Patent Application Laid-Open No. 7-17713 to which Mn, Pb and rare earth elements are added, when these elements are added, an integrated circuit may cause a malfunction of a semiconductor (transistor). There is.

The present invention can solve the above-mentioned conventional problems, and can form a dielectric thin film having a high dielectric constant and a high insulation, which is effective as a capacitor material for various uses in electronic devices (Ba, Sr). and to provide a TiO ₃ thin film-forming composition and such (Ba, Sr) TiO ₃ using a thin film-forming composition (Ba, Sr) TiO ₃ thin film forming method.

[0012]

According to the first aspect of the present invention, (Ba, S
r) The composition for forming a TiO ₃ thin film has a molar ratio of Ba: S
r: Ti = (1-x): x: y (where 0 ≦ x ≦ 1.
(0, 0.9 ≦ y ≦ 1.1) and a Si component of 0.5 to 10 mol% as Si with respect to the main component.

In a molar ratio, Ba: Sr: Ti = (1-x):
x: y (however, 0 ≦ x ≦ 1.0, 0.9 ≦ y ≦ 1.
By blending a main component having the composition of 1) and a Si component of 0.5 to 10 mol% as Si with respect to the main component, the composition can be easily controlled, and a low-cost sol-gel method is used. , A high dielectric constant and a high insulating property (Ba, S
r) It becomes possible to form a TiO ₃ dielectric thin film.

Such a composition for forming a (Ba, Sr) TiO ₃ dielectric thin film can be easily prepared by mixing barium carboxylate, strontium carboxylate, titanium alkoxide and silicon alkoxide in an organic solvent. .

The method for forming a (Ba, Sr) TiO ₃ thin film of the present invention comprises applying the composition for forming a (Ba, Sr) TiO ₃ dielectric thin film of the present invention to a substrate by spin coating, followed by drying. Then, it is characterized by firing at 450 to 800 ° C. By this firing, the Si component becomes a Si oxide.

[0016]

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

The composition for forming a (Ba, Sr) TiO ₃ dielectric thin film of the present invention has a molar ratio of Ba: Sr: Ti = (1-
x): x: y (where 0 ≦ x ≦ 1.0, 0.9 ≦ y ≦
1.1) a main component having the composition of
It contains 0.5 to 10 mol% of a Si component as i. In the present invention, the content of the Si component is
If the content is less than 0.5 mol% with respect to the above main component, Si
A sufficient improvement effect cannot be obtained by adding the components,
The insulation is low. When the Si component exceeds 10 mol% as Si with respect to the above-mentioned main component, the insulation rate decreases.
Therefore, Si is 0.5 to 10 mol% based on the above main component.
And

The (Ba, Sr) TiO of the present invention as described above
₍₃ ) The composition for forming a dielectric thin film uses barium carboxylate as a Ba raw material, strontium carboxylate as a Sr raw material, titanium alkoxide as a Ti raw material, and silicon alkoxide as a Si raw material. Can be easily prepared by mixing and dissolving in an organic solvent.

Barium carboxylate and / or thin film raw material
Alternatively, as the acyloxy group forming strontium carboxylate, those represented by the general formula C _n H _{2n + 1} COO ⁻ (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, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentane It is preferable to use an acyloxy group derived from an acid, 2-ethylhexanoic acid, or 3-ethylhexanoic acid.

In the above general 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.

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

On the other hand, examples of the titanium alkoxide include titanium alkoxides of a linear or branched alcohol having 2 to 5 carbon atoms, such as titanium ethoxide, titanium isopropoxide, titanium butoxide, and titanium amiloxide. It is preferable to use titanium isopropoxide since the reaction rate is appropriate.

Examples of the silicon alkoxide include silicon alkoxides of linear or branched alcohols having 1 to 15 carbon atoms, for example, silicon tetramethoxide, silicon tetraethoxide, silicon tetraisopropoxide, silicon tetrabutoxide, silicon tetraalkoxide. Tetraamyloxide and the like can be mentioned, and it is particularly preferable to use silicon tetraethoxide because of an appropriate reaction rate.

As the organic solvent for dissolving these thin film materials, an ester and / or an alcohol, or a mixed solvent obtained by further mixing a carboxylic acid with the ester and / or an alcohol can be used.

Examples of the ester of the organic solvent include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, and n-acetate.
Amyl, sec-amyl acetate, tert-amyl acetate,
It is preferable to use isoamyl acetate, and as the alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol,
-Pentanol, 2-pentanol, 2-methyl-2-
Pentanol and iso-amyl alcohol are preferably used. Further, as the carboxylic acid, it is preferable to use a carboxylic acid containing an acyloxy group constituting the barium carboxylate and / or strontium carboxylate.

In the composition for forming a (Ba, Sr) TiO ₃ dielectric thin film of the present invention, barium carboxylate, strontium carboxylate and titanium alkoxide, which are thin film materials, are mixed in a predetermined composition ratio with respect to such an organic solvent. And a mixture is added and mixed with a predetermined amount of silicon alkoxide while dissolving so that the total concentration in terms of oxide becomes 4 to 10% by weight.

The (Ba, Sr) TiO of the present invention as described above
₃ ) (Ba, Sr) TiO
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, RuO ₂ / Ru / SiO ₂
/ Si, Ir / IrO ₂ / Si, Pt / Ir / IrO ₂
/ Si, Pt / IrO ₂ / Si, etc., the composition of the present invention is applied on a substrate, and dried (preliminary 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 is performed at 150 to 400 ° C., and the main baking is performed at 450 to 800 ° C. for about 30 minutes to 2 hours.

[0028]

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 3 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.
And dissolved in an organic solvent of isoamyl acetate so that the total concentration in terms of oxide of the composition was 7% by weight.

After further adding silicon tetraethoxide to the solution at a ratio shown in Table 1 (however, no silicon tetraethoxide was added in Comparative Example 1), the mixture was sufficiently homogenized by refluxing for 1 hour. A composition for forming a thin film of the present invention was prepared.

The composition for forming a thin film is applied on a titanium platinum substrate by a spin coating method and dried at 300 ° C. for 10 minutes. The coating and drying steps are repeated three times.
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.

[0032]

[Table 1]

Examples 4 to 6, Comparative Examples 4 to 6 The same as Examples 1 to 3 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.

[0034]

[Table 2]

[0035] Examples 7-9, except that dissolved in the solvent such that the composition ratio Ba _0.3 Sr _0.7 TiO ₃ Comparative Example 7-9 thin material, similar to the respective Examples 1-3 and Comparative Examples 1-3 The relative dielectric constant, the leak current density and the dielectric loss were measured, and the results are shown in Table 3.

[0036]

[Table 3]

Examples 10 to 12 and Comparative Examples 10 to 12 The same procedures as in Examples 1 to 3 and Comparative Examples 1 to 3 were carried out except that the thin film raw materials were dissolved so as to have a composition ratio of BaTiO ₃ . The relative dielectric constant, leak current density and dielectric loss were measured, and the results are shown in Table 4.

[0038]

[Table 4]

Examples 13 to 15 and Comparative Examples 13 to 15 The same procedures as in Examples 1 to 3 and Comparative Examples 1 to 3 were carried out except that the thin film material was dissolved so as to have a composition ratio of SrTiO ₃ . The relative dielectric constant, leak current density and dielectric loss were measured, and the results are shown in Table 5.

[0040]

[Table 5]

As is clear from Tables 1 to 5, according to the present invention, it is possible to obtain a (Ba, Sr) TiO ₃ dielectric thin film having a high dielectric constant and a high insulating property by adding a predetermined amount of Si. it can.

[0042]

As described in detail above, (Ba, S) of the present invention
r) a composition for forming a TiO ₃ dielectric thin film and (Ba, S
r) According to the method of forming a TiO ₃ thin film, a high dielectric constant and high insulating (Ba,
An Sr) TiO ₃ dielectric thin film is provided.

────────────────────────────────────────────────── (5) References JP-A-5-47213 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/46 C01G 23/00 CA (STN )

Claims (3)

(57) [Claims] 1. The molar ratio of Ba: Sr: Ti = (1-
x): x: y (where 0 ≦ x ≦ 1.0, 0.9 ≦ y ≦
1.1) a main component having the composition of
characterized in that it comprises a 0.5 to 10 mol% of Si component as i (Ba, Sr) TiO ₃ dielectric thin film-forming composition. 2. The method according to claim 1, wherein barium carboxylate, strontium carboxylate, titanium alkoxide and silicon alkoxide are mixed in an organic solvent.
_{3. The} composition for forming a (Ba, Sr) TiO ₃ dielectric thin film according to item 1. 3. (Ba, Sr) according to claim 1 or 2
The composition for forming a TiO ₃ dielectric thin film is applied to a substrate by a spin coating method, dried, and then dried at 450 to 800 ° C.
A method of forming a (Ba, Sr) TiO ₃ thin film, characterized by firing.