JP2007314366A - Thin film-forming composition and dielectric thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a thin film having excellent storage stability and film quality. <P>SOLUTION: The thin film-forming composition contains barium carboxylate such as barium ethylhexanoate, strontium carboxylate such as strontium ethylhexanoate and titanium carboxylate such as titanium 2-ethylhexanoate and if need be, calcium carboxylate such as calcium ethylhexanoate, wherein the molar ratio x, y, z and w in the respective content of the barium component, the strontium component, the calcium component and the titanium component satisfies x+y+z=1 and 0.85≤w≤1.2. A dense dielectric thin film is obtained by spin coating using the thin film-forming composition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film forming composition and a dielectric thin film, and more particularly to a thin film forming composition suitable for a dielectric thin film material of a thin film capacitor, and a dielectric thin film using the same.

Since the (Ba, Sr) TiO ₃ ceramic material has a high dielectric constant, it has recently attracted attention as a dielectric thin film material for thin film capacitors.

  Thin film formation methods include CVD, sputtering, and the like. These methods are complicated in apparatus, have a low film formation speed, and have a small film formation area, so that a film with a large area is obtained. There is a drawback that you can not.

Therefore, in recent years, research and development of a spin coating method using a liquid raw material has been actively conducted. Patent Document 1 discloses barium carboxylate, strontium carboxylate, and titanium alkoxide in a molar ratio of Ba: Sr. : Ti = (1-x): x: y (where 0 ≦ x ≦ 1.0, 0.9 ≦ y ≦ 1.1) Ba _1-x Sr mixed in an organic solvent _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 content of the carboxylic acid in the composition is 2 to 11 with respect to titanium of the titanium alkoxide. A composition for forming a Ba _1-x Sr _x Ti _y O ₃ thin film having a double mole has been proposed.

JP-A-9-12354

  However, in patent document 1, since chemically unstable titanium alkoxide is used as a titanium source, there existed a problem that it was inferior in preservability.

  That is, titanium alkoxide is chemically unstable and is hydrolyzed by moisture in the air to produce titanium oxide and alcohol. As a result, there is a problem in that the liquid characteristics are deteriorated, the long-term storage is difficult, and the storage stability is poor.

  For this reason, since titanium alkoxide is industrially inexpensive, it has been dealt with by using it all at once so that it can be stored for as long as possible.

  In addition, when forming a dielectric thin film using the thin film forming composition of Patent Document 1, after applying the thin film forming composition on a substrate by spin coating or the like, the organic solvent is evaporated by heating and drying. Need to be removed. For example, when 2-ethylhexanoic acid is used as the organic solvent, since the boiling point of 2-ethylhexanoic acid is 235 ° C., after applying the thin film forming composition on the substrate, the temperature is 235 ° C. or higher. It is necessary to carry out a drying treatment and evaporate and remove 2-ethylhexanoic acid, which is an organic solvent.

  However, since titanium alkoxide is chemically unstable as described above, it is easily hydrolyzed by water vapor in the air at a high temperature of 235 ° C. or more to produce titanium oxide and alcohol. As a result, since this titanium oxide is mixed in the film as an impurity, there is a problem that a short circuit or the like is liable to occur and the electrical characteristics are deteriorated.

  The present invention has been made in view of such circumstances, a composition for forming a thin film capable of forming a thin film having good storage quality and good film quality, and a dielectric manufactured using the same. An object is to provide a thin body film.

  The present inventor has intensively studied to achieve the above object, and as a titanium source, by using titanium carboxylate instead of the titanium alkoxide described in Patent Document 1, good storage without deterioration over time can be achieved. A barium titanate-based thin film-forming composition having good properties can be obtained, and by using the thin-film forming composition, a dielectric thin film having good film quality can be obtained without deterioration of film characteristics. I got the knowledge that I can do it.

  The present invention has been made based on such knowledge, and the thin film forming composition according to the present invention is a thin film forming composition in which a plurality of types of carboxylates are contained in an organic solvent. The plurality of types of carboxylate salts include barium carboxylate, strontium carboxylate, and titanium carboxylate, and the molar ratios x, y, and w of the barium component, strontium component, and titanium component are as follows: It is characterized by satisfying x + y = 1 and 0.85 ≦ w ≦ 1.2.

  In the composition for forming a thin film of the present invention, the carboxylate has a carbon number n of 1 to 17.

  The thin film-forming composition of the present invention is characterized in that the titanium carboxylate is titanium 2-ethylhexanoate, the barium carboxylate is barium ethylhexanoate, The strontium acid is characterized by being strontium ethylhexanoate.

  The thin film-forming composition of the present invention is characterized in that the organic solvent contains a carboxylic acid and a carboxylic acid ester.

  Furthermore, in the composition for forming a thin film of the present invention, the plurality of types of carboxylates include calcium carboxylate, and the molar ratios x, y, and z of the barium component, the strontium component, and the calcium component are x + y + z = 1, wherein the calcium carboxylate is calcium ethylhexanoate.

  In addition, the dielectric thin film according to the present invention is characterized in that the above-described thin film forming composition is applied on a base material, dried, and then heat-treated.

  According to the thin film-forming composition of the present invention, a thin film-forming composition comprising a plurality of types of carboxylates contained in an organic solvent such as carboxylic acid or ester, , Barium carboxylate such as barium ethylhexanoate, strontium carboxylate such as strontium ethylhexanoate, and titanium carboxylate such as titanium 2-ethylhexanoate, and each content of barium component, strontium component, and titanium component Since the molar ratios x, y, and w satisfy x + y = 1, 0.85 ≦ w ≦ 1.2, instead of titanium alkoxide, a chemically stable carboxylic acid such as titanium 2-ethylhexanoate Titanium is contained in the composition for forming a thin film, and the composition for forming a thin film is capable of forming a thin film having good storage quality and good film quality. It is possible to obtain.

  In addition, even when the carboxylate contains calcium carboxylate such as calcium ethylhexanoate, the thin film forming composition contains titanium carboxylate instead of titanium alkoxide. As described above, a composition for forming a thin film can be obtained that has good storage stability and can form a thin film having good film quality.

  In addition, according to the dielectric thin film of the present invention, the thin film-forming composition described above is applied onto a substrate, dried, and then heat treated. No titanium oxide is generated during the heat treatment, and therefore no titanium oxide is mixed in the film, which does not cause deterioration of electrical characteristics due to a short circuit or the like. It is possible to obtain a barium titanate-based high dielectric constant thin film having excellent film characteristics.

  Next, an embodiment of the present invention will be described in detail.

  A composition for forming a thin film according to an embodiment of the present invention is a composition for forming a thin film in which a plurality of types of carboxylates are contained in an organic solvent, and the plurality of types of carboxylates are Including barium acid, strontium carboxylate, and titanium carboxylate, the molar ratios x, y, and w of the barium component, strontium component, and titanium component are x + y = 1, 0.85 ≦ w ≦ 1. 2 is satisfied.

  And the composition for thin film formation which can form the thin film which has favorable storability and favorable film quality by this can be obtained.

In other words, the general formula: to form by _{(Ba x Sr y) Ti w} O spin coating a dielectric thin film of perovskite structure expressed using liquid raw materials _3, the thin film-forming composition of the liquid It is necessary to prepare.

  And this kind of composition for thin film formation has conventionally used titanium alkoxide as a titanium source so that patent document 1 may also describe.

  However, as described in the section of [Problems to be Solved by the Invention], titanium alkoxide lacks chemical stability and has a disadvantage of poor storage stability because it reacts with moisture in the air to cause hydrolysis. There is. In addition, titanium alkoxide reacts easily with water vapor in the air even after heat drying after spin coating and hydrolyzes to produce titanium oxide and the titanium oxide is mixed in the film. Such a problem is likely to occur, and the electrical characteristics may be deteriorated.

  Therefore, in this embodiment, instead of titanium alkoxide, a chemically stable titanium carboxylate is used as a titanium source, so that it is possible to form a thin film having good storage properties and good film quality. A thin film forming composition is realized.

Here, Ba component and Sr the molar ratio x of component, y is, was set to be 1 (x + y = 1) in total, the general _formula: consisting of _{(Ba x Sr y) Ti w} O 3 perovskite This is because the Ba site composition is stoichiometric in the mold structure.

Moreover, the content molar ratio w of the titanium component is set to 0.85 ≦ w ≦ 1.2 when the dielectric thin film is formed when the content molar ratio w is less than 0.85 or exceeds 1.2. This is because, in addition to the perovskite complex oxide composed of Ba _x Sr _y ) Ti _w O ₃ , other phases such as TiO ₂ and BaCO ₃ may be mixed in the film, which may lead to deterioration of electrical characteristics.

As the carboxylate, a chain monocarboxylate represented by the general formula: (C _n H _{2n + 1} COO) _m M (n, m is a positive integer, M is a metal) is preferably used, and formic acid (HCOOH), acetic acid _(CH 3 COOH), propionic acid _{(C 2} H 5 COOH), butanoic acid _{(C 3} H 7 COOH), hexanoic acid _(C 5 H ₁₁ COOH), ethylhexanoic acid _(C 7 H ₁₅ COOH ), Various carboxylates such as a salt of n-octadecanoic acid (C ₁₇ H ₃₅ COOH) can be used, and the carbon number n is preferably 17 or less. This is because when the carbon number n exceeds 17, it becomes difficult to produce a solution, which is not preferable as a thin film forming composition for spin coating.

  The organic solvent is not particularly limited, and for example, a mixed solvent of carboxylic acid and carboxylic acid ester or a mixed solvent of carboxylic acid, carboxylic acid ester, and alcohol can be used. A mixed solvent of an acid and a carboxylic acid ester is preferably used.

  In addition, this thin film-forming composition has a barium carboxylate so that the molar ratios x, y, and w of the barium component, the strontium component, and the titanium component satisfy x + y = 1 and 0.85 ≦ w ≦ 1.2. , Strontium carboxylate, and titanium carboxylate are weighed in predetermined amounts, and then these weighed products are put into a predetermined amount of an organic solvent and sufficiently stirred, whereby they can be easily produced.

FIG. 1 is a cross-sectional view schematically showing an embodiment of a thin film capacitor manufactured using the above thin film forming composition. This thin film capacitor is formed on a substrate 1 made of Si or the like with Pt or the like. together with the lower electrode 2 made of metal is formed, the formula is on the lower electrode _{2: (Ba x Sr y)} Ti w O 3 in the dielectric thin film represented (BST film) 3 is formed, further An upper electrode 4 made of a metal such as Pt is formed on the surface of the dielectric thin film 3.

  The thin film capacitor is manufactured as follows.

  First, the lower electrode 2 is formed on the surface of the substrate 1 using a thin film forming method such as a sputtering method or a vacuum deposition method. Next, spin coating is performed using the above-described thin film forming composition, followed by heat drying treatment, followed by heat treatment, whereby the dielectric thin film 3 is formed on the lower electrode 2. That is, while rotating the substrate 1 at a high speed, the thin film forming composition is dropped on the lower electrode 21, and the thin film forming composition is uniformly spread on the lower electrode 2 using centrifugal force. A heat drying process is performed at a temperature of 235 ° C. or higher to evaporate and remove the organic solvent, and then a heat treatment is performed in a high temperature / high oxygen atmosphere of 500 ° C. or higher to form the dielectric thin film 3. The dielectric thin film 3 having a desired high dielectric constant can be formed by performing a heat treatment in a high-temperature, high-oxygen atmosphere after spin coating and drying as described above. After that, the upper electrode 4 is formed on the dielectric thin film 3 again using the above-described thin film forming method, whereby a thin film capacitor is manufactured.

  In the thin film capacitor thus obtained, since the dielectric thin film 3 is formed using the above-mentioned thin film forming composition, hydrolysis does not occur in the drying process after spin coating. Therefore, it is possible to avoid mixing of titanium oxide into the film, and it is possible to obtain a thin film capacitor having a dielectric thin film with good film quality without causing deterioration of electrical characteristics.

The present invention is not limited to the above embodiment. In the above embodiment, the composition for forming a thin film made of the general formula: (Ba _x Sr _y ) Ti _w O ₃ has been described in detail, but the general formula in which a part of Ba is replaced with Ca as well as Sr: _x Sr _y Ca _z) in a composition for _Ti w _{O 3} represented by a thin film formation can be applied. That is, also in this case, the same effect as described above can be obtained by using titanium carboxylate as the titanium source. However, the total of the molar ratios x, y, and z of the Ba component, Sr component, and Ca component must satisfy 1 (x + y + z = 1) so that the Ba site composition becomes a stoichiometric composition.

  Next, examples of the present invention will be specifically described.

Barium ethylhexanoate as a barium carboxylate so that each molar ratio of Ba, Sr, Ca, Ti is Ba: Sr: Ca: Ti = 0.70: 0.25: 0.05: 1.0 0.2960 g of ((C ₇ H ₁₅ COO) ₂ Ba: molecular weight = 423), 0.0935 g of strontium ethylhexanoate ((C ₇ H ₁₅ COO) ₂ Sr: molecular weight = 374) as strontium carboxylate, 0.0163 g of calcium ethylhexanoate ((C ₇ H ₁₅ COO) ₂ Ca: molecular weight = 326) as calcium acid acid, titanium 2-ethylhexanoate ((C ₇ H ₁₅ COO) ₄ Ti as titanium carboxylate: 0.6198 g of molecular weight = 620) was weighed.

Next, among these carboxylates, barium ethylhexanoate, strontium ethylhexanoate, and calcium ethylhexanoate were dissolved in 5 mL of 2-ethylhexanoic acid (C ₇ H ₁₅ COOH) as an organic solvent, and about 24 Stir for hours to make a mixed solution. Next, titanium 2-ethylhexanoate was added to the mixed solution, and the mixture was stirred for about 6 hours, and then 5 mL of isoamyl acetate (CH ₃ COOCH ₂ CH ₂ CH (CH ₃ ) ₂ ) was added and stirred for about 2 hours. A composition for forming a (Ba _0.70 Sr _0.25 Ca _0.05 ) Ti _1.0 O ₃ thin film having a molar concentration of 0.1 mol / L was obtained.

  Next, sputtering treatment was performed on a Si substrate having a diameter of 100 mm and a thickness of 0.5 mm, using Pt as a target, to produce a lower electrode (Pt film) having a thickness of 200 nm. Next, the Si substrate was rotated for 3 seconds at a rotation speed of 600 rpm and further for 30 seconds at a rotation speed of 4000 rpm, and the composition was dropped onto the lower electrode and spin-coated, and then on a hot plate adjusted to a temperature of 280 ° C. A drying treatment was performed for 10 minutes. After that, heat treatment was performed at a high temperature of 750 ° C. in a high oxygen atmosphere of 200 mL / min of oxygen to produce a 120 nm-thick dielectric thin film (BSCT film).

  Then, after that, sputtering treatment was performed again using Pt as a target to produce an upper electrode (Pt film) having a thickness of 200 nm on the dielectric thin film, thereby obtaining a thin film capacitor.

  Next, the cross section of the thin film capacitor was observed with an FE-SEM (Field Emission-Scanning Electron Microscopy).

  FIG. 2 is an SEM photograph of a cross section of the thin film capacitor.

  As apparent from FIG. 2, it was found that a dense dielectric thin film (BSCT film) can be obtained.

  The capacitance C and dielectric loss tan δ of the thin film capacitor were measured with an impedance analyzer. The capacitance was 27 nF and the dielectric loss tan δ was 1.5%. The relative dielectric constant εr was determined to be 440 from the measured value of the capacitance C and the sample dimensions.

  Next, using an LCR meter, the relationship between the applied voltage V and the capacitance C was examined at each frequency of 1 kHz, 10 kHz, 100 kHz, and 1 MHz.

  FIG. 3 shows the measurement results.

  As is apparent from FIG. 3, the capacitance C is changed by 30% or more in the range of ± 3 V at any frequency, and a thin film capacitor having a large capacitance change rate such as a variable capacitance element is obtained. I understood that I can do it.

  This composition was sealed with nitrogen, and a similar thin film was prepared after 6 months. It was confirmed that a dielectric thin film having the same film characteristics as described above was obtained.

  Barium ethylhexanoate as barium carboxylate so that each molar ratio of Ba, Sr, Ca, Ti is Ba: Sr: Ca: Ti = 0.5: 0.4: 0.1: 1.2 0.2110 g, 0.1496 g of strontium ethylhexanoate as strontium carboxylate, 0.0326 g of calcium ethylhexanoate as calcium carboxylate, and 0.7437 g of titanium 2-ethylhexanoate as titanium carboxylate, respectively did.

Next, among these carboxylates, barium ethylhexanoate, strontium ethylhexanoate and calcium ethylhexanoate were dissolved in 6 mL of 2-ethylhexanoic acid as an organic solvent, and the mixed solution was stirred for about 24 hours. Produced. Next, titanium 2-ethylhexanoate was added to this mixed solution and stirred for about 6 hours, and then 4 mL of isoamyl acetate was added and stirred for about 2 hours, so that the molar concentration was adjusted to 0.1 mol / L (Ba A composition for forming a _0.50 Sr _0.40 Ca _0.10 ) Ti _1.2 O ₃ thin film was obtained.

  Thereafter, the lower electrode (Pt film), the dielectric thin film (BSCT film) and the upper electrode (Pt film) are sequentially formed on the Si substrate by the same method and procedure as in [Example 1]. A capacitor was produced.

  Next, when the electrostatic capacitance C and dielectric loss tan δ of the thin film capacitor were measured by the same method as in [Example 1], the electrostatic capacitance C was 15 nF and the dielectric loss was 1.1%. The relative dielectric constant εr was determined to be 244 from the measured value of the capacitance C and the sample dimensions.

  Furthermore, when the relationship between the applied voltage V and the capacitance C was examined at each frequency of 1 kHz, 10 kHz, 100 kHz, and 1 MHz, the capacitance C changed by 35% or more in the range of ± 3 V, and the variable capacitance It has been found that a thin film capacitor in which a large capacitance change rate is desired like an element can be obtained.

  This composition was sealed with nitrogen, and a similar thin film was prepared after 6 months. It was confirmed that a dielectric thin film having the same film characteristics as described above was obtained as in [Example 1].

Barium propionate as the barium carboxylate (Ba, Sr, Ca, Ti, so that each molar ratio of Ba: Sr: Ca: Ti = 0.6: 0.3: 0.1: 0.85) 0.5061 g of (C ₂ H ₅ COO) ₂ Ba: molecular weight = 283), 0.2082 g of strontium propionate ((C ₂ H ₅ COO) ₂ Sr: molecular weight = 234) as strontium carboxylate, calcium carboxylate 0.0552 g of calcium propionate ((C ₂ H ₅ COO) ₂ Ca: molecular weight = 186) as titanium, titanium 2-ethylhexanoate ((C ₇ H ₁₅ COO) ₄ Ti: molecular weight = 620 as titanium carboxylate ) Was weighed 1.5805 g each.

Next, among these carboxylates, barium propionate, strontium propionate, and calcium propionate are dissolved in 3 mL of propionic acid (C ₂ H ₅ COOH) as an organic solvent, and 2-ethylhexane is used. Titanium acid was dissolved in 2 mL of 2-ethylhexanoic acid (C ₇ H ₁₅ COOH) as an organic solvent, and each was stirred for about 24 hours to prepare two types of mixed solutions.

Next, the two mixed solutions are mixed with each other and stirred for about 6 hours, and then 5 mL of isoamyl acetate (CH ₃ COOCH ₂ CH ₂ CH (CH ₃ ) ₂ ) is added and stirred for about 2 hours. A composition for forming (Ba _0.60 Sr _0.30 Ca _0.10 ) Ti _0.85 O ₃ thin film prepared to 0.3 mol / L was obtained.

  Thereafter, a thin film capacitor was produced by the same method and procedure as in [Example 1] except that the heat treatment temperature after the drying treatment was 775 ° C. In the fabricated thin film capacitor, the film thickness of the upper electrode and the lower electrode was 200 nm, and the film thickness of the dielectric thin film was 200 nm, as in [Example 1] and [Example 2].

  Subsequently, when the electrostatic capacitance C and dielectric loss tan δ of the thin film capacitor were measured by the same method as in [Example 1], the electrostatic capacitance C was 22 nF and the dielectric loss tan δ was 2.3%. Further, the relative dielectric constant εr was determined from the measured value of the capacitance C and the sample size to be 331.

  Furthermore, when the relationship between the applied voltage V and the capacitance C was examined at each frequency of 1 kHz, 10 kHz, 100 kHz, and 1 MHz, the capacitance C changed by 28% or more in the range of ± 3 V, and the variable capacitance It has been found that a thin film capacitor in which a large capacitance change rate is desired like an element can be obtained.

  This composition was sealed with nitrogen, and a similar thin film was prepared after 6 months. It was confirmed that a dielectric thin film having the same film characteristics as described above was obtained.

It is sectional drawing which showed typically one Embodiment of the thin film capacitor containing the dielectric material thin film concerning this invention. It is a SEM photograph of the thin film capacitor manufactured in [Example 1]. It is a figure which shows the relationship between the applied voltage V and the electrostatic capacitance C in each frequency of 1 kHz, 10 kHz, 100 kHz, and 1 MHz.

Explanation of symbols

3 Dielectric thin film

Claims (9)

A thin film-forming composition comprising a plurality of types of carboxylates contained in an organic solvent,
The plurality of carboxylates include barium carboxylate, strontium carboxylate, and titanium carboxylate,
And each content molar ratio x, y, and w of a barium component, a strontium component, and a titanium component satisfy | fills x + y = 1 and 0.85 <= w <= 1.2, The composition for thin film formation characterized by the above-mentioned.   The composition for forming a thin film according to claim 1, wherein the carboxylate has 1 to 17 carbon atoms.   3. The thin film forming composition according to claim 1, wherein the titanium carboxylate is titanium 2-ethylhexanoate.   The composition for forming a thin film according to any one of claims 1 to 3, wherein the barium carboxylate is barium ethylhexanoate.   5. The thin film forming composition according to claim 1, wherein the strontium carboxylate is strontium ethylhexanoate.   The said organic solvent contains carboxylic acid and carboxylic acid ester, The composition for thin film formation in any one of Claim 1 thru | or 5 characterized by the above-mentioned.   The plurality of types of carboxylate salts include calcium carboxylate, and the molar ratios x, y, and z of the barium component, the strontium component, and the calcium component satisfy x + y + z = 1. The composition for thin film formation in any one of Claim 6.   8. The thin film forming composition according to claim 7, wherein the calcium carboxylate is calcium ethylhexanoate.   A dielectric thin film obtained by applying the thin film-forming composition according to any one of claims 1 to 8 onto a substrate, subjecting it to a drying treatment, and then performing a heat treatment.