JP2002193616A - Coating fluid for forming ferroelectric thin film and its production method and ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating fluid for forming a ferroelectric thin film which contains effective components soluble in general organic solvent and has good preserving stability and reproductivity and which is also capable of forming the ferroelectric thin film by firing at a low temperature, and provide a method of producing the same, and also provide the ferroelectric thin film using the method. SOLUTION: The coating fluid for forming the ferroelectric thin film includes a first organic metal compound (A) in which carboxyl groups is substituted for at least a part of functional groups of hydrolyzed condensate that is obtained by hydrolysis and condensation of a metal alkoxide (a), and a second organic metal compound (B) which comprises at least one compound selected from among a metal alkoxide (b) having a metal different from that of the above metal alkoxide (a), a hydrolyzed condensaste (c) which is obtained by hydrolysis and condensation of the metal alkoxide (b), a compound (d) which is formed by substituting carboxyl groups for at least a part of the functional groups of the metal oxide (b), and a compound (e) which is formed by substituting carboxyl groups for at least a part of the functional groups of the hydrolyzed condensate (c).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating solution for forming a ferroelectric thin film, a method for producing the same, and a ferroelectric thin film.
More specifically, a coating liquid for forming a ferroelectric thin film, which contains an active ingredient soluble in a general-purpose organic solvent, has excellent storage stability and reproducibility, and can form a ferroelectric thin film even by firing at a low temperature, The present invention relates to a ferroelectric thin film manufactured by using the manufacturing method and the coating solution.

[0002]

_2. Description of the Related Art In recent years, the formula (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O
_{3m + 1} ) Bi-based ferroelectric (BL) having a layered structure shown in ^2-
(SF) thin films have attracted attention. In the above formula, A is 1,
Divalent or trivalent ions (for example, Bi, Pb, Ba, Sr,
Ca, Na, K, and rare earth elements) or a combination of these ions, and B is 4, 5, 6,
Charged ions (eg, Ti, Nb, Ta, W, Mo, F
e, ions of metal elements such as Co, Cr, etc.) or a combination of these ions, and m is an integer of 1 to 5.

A Bi-based ferroelectric (BLSF) thin film having such a layered structure has characteristics such as a small coercive electric field of PE hysteresis and little fatigue of the film due to polarization reversal. (Mr. Tadashi Takenaka, “Bismuth Layered Structure Ferroelectrics and Particle Orientation”, Research Report of the Japan Society of Applied Physics, Applied Electronic Properties Subcommittee, November 22, 1994, pp. 1-
8; “Ceramics” Vol. 30, no. 6, pp.
499-503 (1995)).

Above all, a SrBi ₂ Ta ₂ O ₉ -based, ie, (Bi ₂ O ₂ ) ²⁺ (SrTa ₂ O ₇ ) ^{2 −} BLSF thin film has attracted particular attention as a material that remarkably exhibits these characteristics. Examples of a method for forming these BLSF thin films include a sputtering method, a CVD method, and a coating film forming method.
Because it contains a large amount of metal oxide as a constituent of the thin film,
There are problems such as the need for expensive equipment and high cost, and the difficulty of controlling and managing the composition of the dielectric film.
In particular, there is a problem that application to a large-diameter substrate is difficult.

On the other hand, the coating type film forming method does not require an expensive apparatus, the film forming cost is relatively low, and
It is promising because the control and management of the composition of the dielectric film is easy. BLSF used in this coating type film forming method
As the system coating solution, a carboxylate of Sr or Bi (for example, 2-ethylhexanoate) and an alkoxide compound of Ta are dissolved in acetate to form a coating solution (the twelfth ferroelectric application). Conference proceedings; Mitsubishi Materials Corporation; 24-TP-11 (pp. 57-58); 1
995.5.24-27, "Jpn. J. Appl. P.
hys. "Vol. 34 (1995) pp. 5096-
5099) or 2- such as Sr, Bi, Ta, Nb, Ti, etc.
Ethyl hexanoate is dissolved in xylene and MOD (Me
tallo-Organic Decomposition
on) -type coating solution (the same proceedings; Olympus Optical Co., Ltd., Symmetrics Corporation; 26-
TC-10, pp. 139-140, 1995.5.2
4-27) has been reported.

However, when a thin film is formed using these coating liquids, baking must be performed twice at a high temperature of about 800 ° C. in an oxygen atmosphere in order to obtain appropriate electric characteristics. High-temperature heating in oxygen has a large thermal effect on the substrate, and Pt / SiO ₂ or Pt / Ta / SiO ₂ / Si substrates used for producing ferroelectric nonvolatile memories and the like have Pt Damage such as oxidation of the film occurs. In addition, there is also a problem that the thin film surface is roughened due to the growth of crystal grains, and as a result, electrical characteristics are deteriorated such as an increase in leak current. In addition, it was not always satisfactory from the viewpoint of the productivity of the semiconductor manufacturing process.

Japanese Patent Application Laid-Open No. Hei 10-259007 discloses a coating liquid for forming a Bi-based ferroelectric thin film, which contains Bi and A metal elements (where A is Bi, Pb, B
a, Sr, Ca, Na, K and at least one metal element selected from rare earth elements) and B metal element (B is Ti, Nb, Ta, W, Mo, F
e, at least one metal element selected from Co and Cr), and at least two of them form complex metal alkoxides. Water or an organometallic compound obtained by hydrolysis with water and a catalyst, and containing 1 to 1.1 mol times the theoretical value of Bi
Has been proposed.

[0008] This coating solution is free from precipitation of excessive metal element particles, has a small leak current, has excellent hydrogen heat treatment resistance and pressure resistance, and can form a dense film.
It is described as having excellent storage stability. However, in the specific example described in the above publication, in order to obtain appropriate electric characteristics, when forming a ferroelectric thin film, baking is performed twice at a high temperature of 800 ° C. in an oxygen atmosphere. High-temperature heating in oxygen has problems such as thermal effects on the substrate and roughening of the thin film surface due to the growth of crystal grains, and has not always been sufficiently satisfactory as a coating solution.

The present inventors have conducted intensive studies to solve the above problems, and as a result, have hydrolyzed and condensed the metal alkoxide (a) to at least a part of the functional groups of the hydrolyzed condensate obtained. A first organometallic compound (A) obtained by substitution with a carboxyl group, a metal alkoxide (b) composed of a metal element different from the metal alkoxide (a), and hydrolysis and condensation of the metal alkoxide (b) The compound (d) obtained by substituting at least a part of the functional group of the metal alkoxide (b) with a carboxyl group, and at least one of the functional groups of the hydrolytic condensate (c). A second organometallic compound (B) consisting of at least one compound selected from the compounds (d) in which the moieties are substituted with carboxyl groups
Is soluble in general-purpose organic solvents, has excellent storage stability and reproducibility during use, and is capable of forming a thin film even by firing at a low temperature, so that bismuth strontium tantalate (SBT) The present inventors have succeeded in developing a coating liquid for forming a ferroelectric thin film as described in (1) and have completed the present invention.

[0010]

An object of the present invention is to solve the above-mentioned problems of the prior art, and contains an active ingredient soluble in a general-purpose organic solvent, and has excellent storage stability and reproducibility during use. Moreover, it is an object of the present invention to provide a coating liquid for forming a ferroelectric substance capable of forming a thin film even by firing at a low temperature, a method for producing the same, and a ferroelectric thin film produced using the excellent coating liquid.

[0011]

SUMMARY OF THE INVENTION The coating liquid for forming a ferroelectric thin film of the present invention comprises:
A first organometallic compound (A) obtained by substituting at least a part of the functional groups of the hydrolysis condensate obtained by hydrolyzing and condensing the metal alkoxide (a) with a carboxyl group, and the metal alkoxide (a) Metal alkoxides of different metals
(b) a hydrolysis condensate (c) obtained by hydrolyzing and condensing the metal alkoxide (b), and the metal alkoxide
Compound (d) obtained by substituting at least a part of the functional group of (b) with a carboxyl group and compound (e) obtained by substituting at least a part of the functional group of the hydrolysis condensate (c) with a carboxyl group And a second organometallic compound (B) comprising at least one compound selected from the group consisting of:

The metal of the metal alkoxide (a) and the metal alkoxide (b) is Li, Na, K, Mg, Ca,
Sr, Ba, La, Ti, Zr, Hf, V, Nb, T
a, Cr, Mo, W, Mn, Fe, Co, Ni, Cu,
The metal is preferably selected from Zn, Pb and Bi. Further, the metal of the metal alkoxide (a) and the metal alkoxide (b) is a metal selected from Pb, Zr, Ti and La, and the metal species of the metal alkoxide (a) and the metal alkoxide (b) A total of 3 to 4 types, or Sr, Bi, Ti, Ta
And Nb, and the total of the metal species of the metal alkoxide (a) and the metal alkoxide (b) is preferably 3 to 4.

The method for producing a coating solution for forming a ferroelectric thin film according to the present invention is characterized in that at least a part of the functional groups of the hydrolysis condensate obtained by hydrolyzing and condensing the metal alkoxide (a) is substituted with a carboxyl group. First organometallic compound (A)
And a metal alkoxide (b) of a metal different from the metal alkoxide (a), a hydrolysis condensate (c) obtained by hydrolysis and condensation of the metal alkoxide (b), and a functional group of the metal alkoxide (b). At least one compound selected from a compound (d) obtained by substituting at least a part of the functional group of the carboxyl group and a compound (e) obtained by substituting at least a part of the functional group of the hydrolysis condensate (c) by a carboxyl group; And a second organic metal compound (B) consisting of

The metal of the alkoxide (a) and the metal alkoxide (b) in this production method is Li, Na, K,
Mg, Ca, Sr, Ba, La, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co,
It is preferably a metal selected from Ni, Cu, Zn, Pb and Bi. The metal of the metal alkoxide (a) and the metal alkoxide (b) in this production method is a metal selected from Pb, Zr, Ti and La, and the metal alkoxide (a) and the metal alkoxide (b) The total of the metal species is 3 to 4 or a metal selected from Sr, Bi, Ti, Ta and Nb, and the total of the metal species of the metal alkoxide (a) and the metal alkoxide (b) is It is preferable that there are three to four types.

The ferroelectric thin film of the present invention is characterized in that it is formed from the above-mentioned coating liquid for forming a ferroelectric thin film.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Next, the coating liquid for forming a ferroelectric thin film of the present invention, a method for producing the same, and a ferroelectric thin film will be specifically described. The coating liquid for forming a ferroelectric thin film of the present invention comprises a first organic metal obtained by substituting at least a part of the functional groups of a hydrolysis condensate obtained by hydrolyzing and condensing a metal alkoxide (a) with a carboxyl group. Compound (A),
The metal alkoxide (b) of a metal different from the metal alkoxide (a), a hydrolysis condensate (c) obtained by hydrolyzing and condensing the metal alkoxide, and at least a part of the functional groups of the metal alkoxide (b) A compound comprising at least one compound selected from a compound (e) obtained by substituting at least a part of the functional groups of the compound (d) substituted by a carboxyl group and the hydrolytic condensate (c) by a carboxyl group. And 2 organometallic compounds (B).

Coating solution for forming ferroelectric thin film and production thereof
Method The coating liquid for forming a ferroelectric thin film of the present invention comprises a first organometallic compound (A) and a second organometallic compound (B) containing a metal different from (A). This first organometallic compound (A)
A compound obtained by substituting at least a part of a hydroxyl group and an alkoxyl group, which are functional groups of a hydrolyzed condensate obtained by hydrolyzing and condensing a metal alkoxide (a), with a carboxyl group.

Further, the second organometallic compound (B) is a metal alkoxide (b) different from the above-mentioned metal alkoxide (a), and a hydrolysis condensate (hydrolysis condensate obtained by hydrolyzing and condensing the metal alkoxide (b)). c), a compound obtained by substituting a functional group such as an alkoxyl group of the metal alkoxide (b) with a carboxyl group and at least a part of the functional group of the hydrolysis condensate (c) are substituted with a carboxyl group. Compound
It consists of at least one compound selected from (e).

(Metal element) The first organometallic compound (A)
And the metal of the metal alkoxides (a) and (b) in the second organometallic compound (B) is Li, Na, K, Mg, Ca, S
r, Ba, La, Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Z
Each of them can be selected from n, Pb, Bi and the like.

Furthermore, these metals include Na, C
a, Sr, Ba, La, Ti, Zr, Hf, Nb, T
A metal selected from a, Mo, W, Pb, Bi and the like is preferable. The metal alkoxide (a) and the metal alkoxide (b) may each be composed of two or more metal alkoxides, or (a) or (b) may be composed of one type of metal alkoxide. Is also good.

The type of the metal may be appropriately selected according to the intended ferroelectric thin film, and is usually expressed as the sum of the metal types of the first organometallic compound (A) and the second organometallic compound (B). 3 or more, preferably 3 to 5, more preferably 3 to
There are four types. Particularly preferably, 3 to 4 types selected from Pb, Zr, Ti and La, and Sr, Bi,
It is 3 to 4 kinds selected from Ti, Ta and Nb.

(Metal alkoxide) The metal alkoxides (a) and (b) used in the present invention are compounds obtained by reacting a metal atom with an alcohol, and are represented by the following general formula (1). M ^a (OR ¹ ) _a (1) In the formula (1), M represents a metal, and a is a positive number of 1 to 7 according to the valence of the metal. R ¹ is the alcohol O
It is a residue excluding the H group.

The alcohol forming the metal alkoxide is not particularly limited, but may be, for example, the following formula (2)
The following can be mentioned as preferable examples. R ¹ OH (2) In the formula (2), R ¹ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms or a hydrocarbon group further substituted with an alkoxyl group having 1 to 6 carbon atoms. Show.

When R ¹ is a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms, the alcohol may be, for example,
Examples thereof include methanol, ethanol, 1-propanol, 2-propanol, butanol, amyl alcohol, and cyclohexanol. When R ¹ is a hydrocarbon group further substituted with an alkoxy group having 1 to 6 carbon atoms, examples of the alcohol include methoxymethanol, methoxyethanol, ethoxymethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, and the like. And propoxypropanol.

The metal alkoxides (a) and (b) in the present invention
May be any of a mixture of only one kind, a state in which two or more kinds of metal alkoxides are mixed, and a composite metal alkoxide containing two or more kinds of metals in one molecule. As the composite metal alkoxide, for example,
Two or more metal alkoxides in a solvent at 30 to 100 ° C
At a temperature of about 2 to 15 hours.

Thus, a composite metal alkoxide containing two or more metals in one molecule is prepared in advance,
Alternatively, a mixed solution of different types of metal alkoxides may be introduced into the hydrolysis-condensation step and treated under the hydrolysis-condensation conditions. This is preferable because the steps are simplified.

(Hydrolytic condensation of metal alkoxide (a))
In the present invention, the metal alkoxide (a) is hydrolyzed and condensed. This hydrolysis can be performed by adding water or water and a catalyst to the metal alkoxide and stirring the mixture at 20 to 100 ° C. for several hours to several days. Water is usually 100 mol% or less, preferably 50 to 100 mol%, based on 100 mol% of the alkoxyl group of the metal alkoxide (a).
Used in an amount of 5 mol%.

Under the above conditions, condensation is carried out together with hydrolysis to produce a hydrolyzed condensate. There is no particular limitation on the catalyst, and those known for hydrolysis / condensation reactions of metal alkoxides (a), for example, hydrochloric acid, sulfuric acid,
Inorganic acids such as nitric acid; acid catalysts such as organic acids such as acetic acid, propionic acid, butyric acid, and maleic acid; and inorganic catalysts such as sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide. Organic alkali catalysts and the like can be mentioned.

However, with inorganic alkalis such as sodium hydroxide and potassium hydroxide, metal ions such as sodium and potassium may remain in the coating solution and affect the electrical properties of the coating. Nitrogen-containing alkalis such as amines may form a nitrogen compound having a high boiling point after the hydrolysis reaction, which may affect the densification of the coating film during the firing step. It is preferred to use an acid catalyst.

The conditions for the hydrolytic condensation are not limited to those described above, and can be appropriately selected according to the use of the film. By performing the hydrolysis treatment in this manner, the content of the organic component in the entire coating film after the drying step can be reduced, and the metalloxane bond (Bi-O-Bi, Bi-O- Ta, Bi-O
—Sr, Ta—O—Bi—O—Sr, etc.).

(Functional Substitution of Hydrolytic Condensate) The first organometallic compound (A) in the present invention is obtained by hydrolyzing and condensing the above metal alkoxide (a). It is obtained by reacting with a carboxylic acid and substituting a hydroxyl group and an alkoxyl group or any one of these functional groups of the hydrolyzed condensate with a carboxyl group.

This functional group substitution is carried out by adding a predetermined amount of a carboxylic acid to a solution of the hydrolyzed condensate, and adding the carboxylic acid to the solution at 20 to 100 ° C. for 0.1 minute.
The mixture is stirred for 5 to 5 hours, and a low-boiling alcohol or the like is removed from the solution of the hydrolyzed condensate, whereby a desired first organometallic compound (A) solution can be obtained. For example, the low-boiling alcohol may be removed by heating the solution of the hydrolyzed condensate to 40 to 60 ° C. and stirring under reduced pressure for 10 minutes to 2 hours.

As described above, the storage stability of the coating liquid for forming a ferroelectric thin film according to the present invention can be improved by substituting the functional group of the hydrolysis condensate with a carboxyl group. Preferred examples of the carboxylic acid include at least one selected from carboxylic acids represented by the following formula (3).

R ³ COOH (3) [In the formula (3), R ³ represents a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms. Specific carboxylic acids include, for example, acetic acid, 2-methylpropionic acid, pentanoic acid, 2,2-dimethylpropionic acid, butanoic acid, hexanoic acid, 2-ethylhexanoic acid, octylic acid, nonanoic acid, and decanoic acid And the like.

The amount of the carboxylic acid used is based on 100 mol% of the alkoxyl group of the metal alkoxide.
Usually, it is 100 mol% or less, preferably 5 to 95 mol%. (Hydrolytic condensation of metal alkoxide (b)) In the present invention, the metal alkoxide (b) can be used as the second organometallic compound (B), and the metal alkoxide (b)
Is hydrolyzed and condensed to obtain a hydrolyzed condensate (c)
Can also be used as the second organometallic compound.

This hydrolysis is carried out by adding water,
Alternatively, the reaction can be carried out by adding water and a catalyst and stirring at 20 to 100 ° C. for several hours to several days. Water is
100 mol% or less, preferably 50 to 100 mol%, based on 100 mol% of the alkoxyl group of the metal alkoxide (b).
Used in an amount of 5 mol%. Under the above conditions, condensation is performed together with hydrolysis to produce a hydrolyzed condensate (c).

The catalyst is not particularly limited, and any known catalyst for hydrolysis and condensation of the metal alkoxide (b) can be used. Examples of such a catalyst include acid catalysts such as inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid; organic acids such as acetic acid, propionic acid, butyric acid, and maleic acid;
Examples thereof include inorganic and organic alkali catalysts such as sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide.

Among these, it is more preferable to use an acid catalyst. In the case of inorganic alkalis such as sodium hydroxide and potassium hydroxide, metal ions such as sodium and potassium may remain in the coating solution and affect the electrical properties of the coating film. This is because a nitrogen-based alkali may form a nitrogen compound having a high boiling point after the hydrolysis reaction, which may affect the densification of the coating film during the firing step.

The conditions for the hydrolysis-condensation are not limited to those described above, and can be appropriately selected according to the use of the film. By performing the hydrolysis treatment in this manner, the content of the organic component in the entire coating film after the drying step can be reduced, and the metalloxane bond (Bi-O-Bi, Bi-O- Ta, Bi-O
—Sr, Ta—O—Bi—O—Sr, etc.).

(Functional Group Substitution of Metal Alkoxide (b) and Hydrolysis Condensate (c)) As described above, the second organometallic compound (B) differs from the first organometallic compound (A) in the present invention. A metal alkoxide (b) composed of a different metal element, a hydrolysis condensate (c) obtained by hydrolyzing and condensing the metal alkoxide (b), and an alkoxyl group which is a functional group of the metal alkoxide (b) is carboxyl. And at least one compound selected from the group consisting of a compound (d) obtained by substituting a carboxyl group and a compound obtained by substituting an alkoxyl group, which is a functional group of the hydrolytic condensate (c), with a carboxyl group.

In particular, the substitution of the functional group of the metal alkoxide (b) or the functional group of the hydrolysis condensate (c) with a carboxyl group improves the storage stability of the coating liquid for forming a ferroelectric thin film in the present invention. It is preferable because it can be used. This functional group substitution is carried out in a metal alkoxide (b) solution or a hydrolysis condensate (c) solution by adding a predetermined amount of a carboxylic acid as shown in the functional group substitution of the hydrolysis condensate derived from the metal alkoxide (a). Addition and stirring at 20 to 100 ° C. for 0.5 to 5 hours.

The amount of the carboxylic acid used is based on 100 mol% of the alkoxyl group of the metal alkoxide.
Usually, it is 100 mol% or less, preferably 5 to 100 mol%. After completion of the functional group substitution, the functional group-substituted compound obtained by removing the low-boiling alcohol from the metal alkoxide (b) solution or the hydrolyzed condensate (c) after the functional group substitution.
(d) or a desired second organometallic compound (B) solution containing the compound (e) can be obtained.

For example, metal alkoxide after functional group substitution
(b) heating the solution to 40-60 ° C and under reduced pressure for 10 minutes to 2 hours;
The low-boiling alcohol may be removed by stirring for an hour. Further, the metal alkoxide (b), a hydrolysis condensate (c) obtained by hydrolyzing the metal alkoxide (b),
A compound (d) obtained by substituting at least a part of the functional group of the metal alkoxide (b) with a carboxyl group, and a compound obtained by substituting at least a part of the functional group of the hydrolysis condensate (c) with a carboxyl group For (e), for example, these can be separately prepared, and these can be used alone or in combination of two or more.

(Coating solution for forming a ferroelectric thin film) The solution of the second organometallic compound (B) thus obtained and the first organometallic compound (A) are mixed to obtain the ferroelectric thin film of the present invention. A coating liquid for forming a dielectric thin film is obtained. In mixing (B) and (A), a desired coating solution can be obtained by appropriately diluting with a solvent.

An appropriate value for the content of each metal element component in the coating liquid for forming a ferroelectric thin film, for example, the content of the Bi metal element component, the Sr metal element component, and the Ta metal element component is as follows. It cannot be determined uniformly because it differs depending on the location, conditions, etc. where the coating liquid for forming a ferroelectric thin film of the invention is applied. Therefore, the above-mentioned content depends on the type of the applicable device (for FRAM, for DRAM, for MFS,
MFIS, MFMIS, etc.), the type and thickness of the upper and lower electrodes to be used, the type and thickness of the barrier layer, and the presence / absence of a seed layer (alignment film) as appropriate. do it.

The coating liquid for forming a ferroelectric thin film of the present invention and
The method for producing this coating solution is based on the formation of any ferroelectric thin film.
Also applicable to Particularly, it is suitable for forming a Bi-based ferroelectric thin film.
Applicable well. For example, the expression (Bi_TwoO_Two)²⁺(A_m-1
B_mO_{3m + 1})^2-[Wherein A is a mono-, di- or trivalent ion (eg,
For example, Bi, Pb, Ba, Sr, Ca, Na, K, and
And rare earth element ions) or a combination of these ions
B denotes a 4, 5, 6-valent ion (for example,
Gold such as Ti, Nb, Ta, W, Mo, Fe, Co, Cr
) Or a combination of these ions
And m is an integer of 1 to 5. ]
Ferroelectric thin film, specifically, SrBi_TwoTa_TwoO₉system;
(Bi_TwoO_Two)²⁺(SrTa_TwoO₇)^2-Based ferroelectric thin film
Doya, formula (Bi_TwoO_Three) (M¹ _lM^Two _mO_x) [Where M¹Is
Divalent metal ion, M^TwoIs a pentavalent metal ion
Where l and m are positive numbers from 0.5 to 5, x is M ¹
And M^TwoIs a positive number calculated from the valence of ]
And a ferroelectric thin film having a structure.

Ferroelectric Thin Film and Method for Producing the Same In the present invention, in order to form a ferroelectric thin film composed of a plurality of, preferably three or more metal elements, the first organometallic compound (A) and the second It is preferable to form the coating solution by dissolving the organometallic compound (B) in a solvent (hereinafter, referred to as “coating solution”), apply the coating solution to a substrate, and dry as necessary. Such an organometallic compound (A),
Examples of the solvent for dissolving (B) include alcohol solvents, polyhydric alcohol solvents, ether solvents, ketone solvents, ester solvents, and lower carboxylic acid solvents.

As the alcohol solvent, methanol,
Ethanol, propanol, butanol, amyl alcohol, cyclohexanol, methylcyclohexanol and the like can be mentioned. Examples of polyhydric alcohol solvents include ethylene glycol monomethyl ether, ethylene glycol monoacetoester, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monoethyl ether, propylene glycol monoacetate, dipropylene glycol monoethyl ether, propylene glycol monomethyl ether, Propylene glycol monopropyl ether, methoxybutanol and the like can be mentioned.

Examples of the ether solvent include methylal, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane and the like. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethyl nonanone, acetonitrile acetone, dimethyl oxide, holon, cyclohexanone, Acetone alcohol and the like can be mentioned.

Examples of the ester solvents include ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate, And diethyl malonate. Examples of lower carboxylic acid solvents include acetic acid, propionic acid, butyric acid, valeric acid and the like.

One of the above solvents may be used,
A combination of more than one species can be used. As the above-mentioned various solvents, the most preferable ones can be used as appropriate according to the difference in application conditions such as the open spin coating method, the closed spin coating method, the mist-forming LSM-CVD method, and the dipping method.

In the present invention, the total concentration of the organometallic compounds (A) and (B) in the coating solution is 1 to 20% by weight, preferably 5 to 15% by weight in terms of metal oxide. is there. Examples of the substrate on which the coating solution is applied include a silicon wafer. On this silicon wafer, a silicon oxide film, an electrode made of a metal such as Pt, Ir, Ru and the like, and a metal oxide such as a conductive metal oxide may be formed.

Then, the above coating solution is applied onto the substrate by a known coating method such as a spinner method or a dipping method.
Drying is usually performed at a temperature of 50 to 400 ° C, preferably 150 to 250 ° C. Next, calcination is performed at a temperature of 250 to 500C. It is preferable that a series of operations from the application of the coating solution, drying and calcination are repeated several times to set a desired film thickness.

As the ferroelectric thin film, 10 to 200 nm
It is preferable that the film thickness is as follows. Next, 700-900
Main firing is performed at a temperature of about 700C, preferably about 700 to 750C, to form a ferroelectric thin film having a crystal structure. In the firing step, the temperature is changed from room temperature (25 ± 2 ° C.) to 5-20 ° C.
The furnace method in which the temperature is raised to the main firing temperature at a temperature raising rate of about / min, and then the main firing temperature is maintained and firing is performed for about 30 to 80 minutes, and the main firing is performed at a temperature rising rate of about 30 to 300 ° C / sec from room temperature. Various firing methods can be selected, such as an RTP method in which the temperature is raised to the temperature, and then the main firing temperature is maintained, and firing is performed for about 0.5 to 3 minutes.

In the present invention, a substrate formed by forming an electrode (lower electrode) made of a metal such as Pt, Ir, Ru or the like and a conductive metal oxide as a metal oxide on a silicon wafer is used as the substrate. After a ferroelectric thin film is formed thereon by the method of the present invention, an electrode (upper electrode) is formed on the ferroelectric thin film, whereby a ferroelectric memory can be manufactured.

Here, as the upper electrode, the metals and metal oxides listed as the material for the lower electrode can be used, and these materials are formed on the ferroelectric thin film by a known method such as a sputtering method or a vapor deposition method. The ferroelectric memory is formed and annealed under the same conditions as or less than the firing conditions to produce a ferroelectric memory.

[0057]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. 1. Preparation of coating liquid

[0058]

Example 1 (Preparation of coating liquid 1) Sr (OiC ₃ H ₇ )
₂ 3.70 g, Ta (OC ₂ H ₅ ) ₅ 16.25 g and propylene glycol monopropyl ether 355.0 g
And stirred at 25 ° C. for 1 hour, and then a mixed solution 373.1 of an Sr metal alkoxide and a Ta metal alkoxide was used.
g was obtained.

0.9 g of water and 88.56 g of propylene glycol monopropyl ether were mixed, and this was added to 373.1 g of the above mixed solution of the Sr metal alkoxide and the Ta metal alkoxide. , 4
Heating and stirring were performed for hours. After the reaction is completed, cool to room temperature,
A solution of a hydrolyzed condensate in which SrTa metal alkoxides were hydrolyzed and condensed was obtained.

26.82 g of 2-ethylhexanoic acid was added to the obtained solution of the hydrolyzed condensate, and the mixture was stirred at 25 ° C. for 30 minutes to exchange the functional groups of the hydrolyzed condensate. Heated to ５０50 ° C. and stirred under reduced pressure for 30 minutes to obtain 50 g of a solution from which low-boiling alcohol was removed,
This was used as a coating liquid 1 (a solution of the first organometallic compound (A)).

(Preparation of Coating Liquid 2) Bi (OtC ₅ H ₁₁ ) ₃
After 18.82 g and 355.0 g of propylene glycol monopropyl ether were mixed and stirred at 25 ° C. for 1 hour, 373.82 g of a Bi metal alkoxide solution was obtained. The obtained Bi metal alkoxide solution 373.82
17.31 g of 2-ethylhexanoic acid was added to the resulting mixture at 25 ° C.
After the functional group exchange of the Bi metal alkoxide was performed, the solution was heated to 40 to 50 ° C. and stirred under reduced pressure for 60 minutes to remove the low-boiling alcohol.
0 g was obtained, and this was applied to coating solution 2 (second organometallic compound (B)).
Solution).

The coating liquid 1 and the coating liquid 2 were mixed with Sr: Bi: T
a = 0.9: 2: 2, diluted with propylene glycol monopropyl ether to a concentration of 10% by weight in terms of metal oxide, and coated with a coating solution 3 (a coating solution for forming a ferroelectric thin film). ) Got.

[0063]

Example 2 (Preparation of coating liquid 4) Bi (OtC ₅ H ₁₁ ) ₃
After 18.82 g and 355.0 g of propylene glycol monopropyl ether were mixed and stirred at 25 ° C. for 1 hour, 373.82 g of a Bi metal alkoxide solution was obtained. The obtained Bi metal alkoxide solution 373.82
A 20% aqueous solution of maleic acid was added to g, and the mixture was heated to 60 ° C. and heated and stirred for 4 hours. This solution is kept at 40-50 ° C.
And stirred under reduced pressure for 60 minutes to obtain 50 g of a solution from which low-boiling alcohol was removed.
Solution of organometallic compound (B)).

The coating liquid 1 and the coating liquid 4 were mixed with Sr: Bi: T
a = 0.9: 2: 2, diluted with propylene glycol monopropyl ether to a concentration of 10% by weight in terms of metal oxide, and coated with coating solution 5 (coating solution for forming a ferroelectric thin film). ) Got.

[0065]

Comparative Example 1 3.70 g of Sr (OiC ₃ H ₇ ) ₂ , Bi (O
_{tC 5 H 11) 3 18.82g,} Ta (OC 2 H 5) 5 16.
After mixing 25 g and 355.0 g of propylene glycol monopropyl ether and stirring at 25 ° C. for 1 hour,
Sr metal alkoxide, Bi metal alkoxide and T
393.7 g of a mixed solution of a metal alkoxide was obtained.

9.0 g of water and 885.6 g of propylene glycol monopropyl ether were mixed, and mixed with the above Sr metal alkoxide, Bi metal alkoxide and T
After adding 393.7 g of the mixed solution of the metal alkoxide a, the temperature was raised to 60 ° C., and the mixture was heated and stirred for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, and the SrBiTa metal alkoxide was hydrolyzed and condensed. A solution of the condensate was obtained.

44.71 g of 2-ethylhexanoic acid was added to the obtained solution of the hydrolyzed condensate, and the mixture was stirred at 25 ° C. for 30 minutes to exchange the functional groups of the hydrolyzed condensate. The mixture was heated to ５０50 ° C. and stirred under reduced pressure for 30 minutes to obtain 100 g of a solution from which low-boiling alcohol was removed. Next, the solution from which the low-boiling alcohol was removed,
After cooling to room temperature, the mixture was diluted with propylene glycol monopropyl ether to a concentration of 10% by weight in terms of metal oxide to prepare a coating liquid for forming an SBT dielectric thin film (Comparative coating liquid 5).

2. Formation of a ferroelectric thin film On a silicon wafer having a diameter of 6 inches on which thermally oxidized SiO _{2 of} 1000 nm was formed, 10 μm was formed by sputtering.
A Pt lower electrode having a thickness of 0 nm was formed. Next, the above Pt
On the lower electrode, the coating liquid 3 obtained in Example 1 was applied using a spin coater at 500 rpm for 5 seconds, and then 3000
After spin coating at 20 rpm for 20 seconds and drying at 250 ° C. for 5 minutes, the temperature is raised from 25 ° C. to 400 ° C. at a rate of 1.25 ° C./sec, and a heat treatment is performed for 5 minutes to form a coating film. Formed.

Next, the coating liquid 3 was applied to the coating film in the same manner as described above, dried, heated, and heat-treated. These operations were repeated three times in total. The temperature was increased from 25 ° C. to 750 ° C. at a rate of 40 ° C./sec, and then baked in a nitrogen atmosphere at 750 ° C. for 0.5 minute to form a 150 nm thick ferroelectric thin film.

Also, in the same manner as described above, using the coating liquid 4 obtained in Example 2 instead of the coating liquid 3 obtained in Example 1, a 150 nm thick film was formed on the Pt lower electrode. A dielectric thin film was formed. Further, a 150 nm-thick ferroelectric substance was formed on the Pt lower electrode in the same manner as above using the comparative coating liquid 5 obtained in Comparative Example 1 instead of the coating liquid 3 obtained in Example 1. A thin film was formed.

Then, a 0.2 mm diameter was formed on the ferroelectric thin film by a sputtering method via a metal mask.
Was formed and baked at 750 ° C. for 0.5 minute in a nitrogen atmosphere to produce a ferroelectric element. FIG. 1 schematically shows a sectional view of the obtained ferroelectric element. The hysteresis characteristics and the saturation characteristics of the ferroelectric element manufactured using the coating liquid 3 of Example 1 are shown in FIGS. 2 and 3, respectively, of the ferroelectric element manufactured using the coating liquid 4 of Example 2. The hysteresis characteristics and the saturation characteristics are shown in FIGS. 4 and 5, respectively. FIGS. 6 and 7 show the hysteresis characteristics and the saturation characteristics of the ferroelectric element manufactured using the coating liquid 5 of Comparative Example 1, respectively.

In FIG. 3, FIG. 5, and FIG.
Reverse polarization amount Pnv (μC / cm^Two) And ◆ are the remanent polarization 2
Pr (μC / cm^Two). 2 and 3
As shown, the strength obtained using the coating solution 3 of Example 1 was
The hysteresis characteristic of the dielectric element is closed on the high voltage side.
Good. The applied voltage is about 2 V for the non-inversion polarization amount Pnv
8 ~ 9μC / cm^TwoAnd shows a good saturation characteristic curve.
The residual polarization amount 2Pr is 11 μC at an applied voltage of 3V.
/ Cm ^TwoAnd shows a characteristic curve that is almost saturated.
I understand.

FIGS. 4 and 5 show the hysteresis characteristics and the saturation characteristics of the ferroelectric element manufactured using the coating liquid 4 of Example 2. FIG. As is clear from FIGS. 4 and 5, the hysteresis characteristic of the ferroelectric element obtained by using the coating liquid 4 of Example 2 is good because the high voltage side is closed. The non-inversion polarization amount Pnv is 9- at the applied voltage of about 2V.
10 μC / cm ² , showing a good saturation characteristic curve. The residual polarization amount 2 Pr is 13 μC / c at an applied voltage of 3 V.
m ² , which indicates that the characteristic curve is almost close to saturation.

On the other hand, as is clear from FIGS. 6 and 7, the hysteresis characteristic of the ferroelectric element obtained by using the comparative coating liquid 5 of Comparative Example 1 is the characteristic of the leak tendency in which the high voltage side is widened. In addition, it can be seen that the non-inversion polarization amount Pnv and the remanent polarization amount 2Pr do not reach saturation or do not reach saturation unless the voltage is on the high voltage side. As described above, by using the coating liquid for forming a ferroelectric thin film comprising the first organometallic compound (A) and the second organometallic compound (B) in the present invention (Examples 1 and 2),
A ferroelectric thin film can be formed at a low temperature such as 750 ° C., and a ferroelectric element having good hysteresis characteristics and saturation characteristics can be obtained. On the other hand, it can be understood that the effect as in the present invention cannot be obtained with the coating liquid as in Comparative Example 1.

[0075]

According to the present invention, the first organometallic compound is used.
The coating liquid for forming a ferroelectric thin film comprising (A) and the second organometallic compound (B) contains an active ingredient soluble in a general-purpose organic solvent, and has storage stability and reproducibility during use. It is practical because it is excellent. Further, by the production method of the present invention, such an excellent coating solution for forming a ferroelectric thin film can be obtained. In addition, the ferroelectric thin film forming coating liquid can favorably form a ferroelectric thin film even by firing at a low temperature.

Therefore, a ferroelectric thin film having excellent electric characteristics and an excellent ferroelectric element using the same can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a cross-sectional view of a ferroelectric element evaluated in the present invention.

FIG. 2 is a graph showing a hysteresis characteristic of a ferroelectric element obtained by using the coating liquid 3 of Example 1.

FIG. 3 is a graph showing a saturation characteristic of a ferroelectric element obtained by using the coating liquid 3 of Example 1.

FIG. 4 is a graph showing a hysteresis characteristic of a ferroelectric element obtained by using the coating liquid 4 of Example 2.

FIG. 5 is a graph showing a saturation characteristic of a ferroelectric element obtained by using the coating liquid 4 of Example 2.

FIG. 6 is a graph showing a hysteresis characteristic of a ferroelectric element obtained by using the comparative coating solution 5 of Comparative Example 1.

FIG. 7 is a graph showing the saturation characteristics of a ferroelectric element obtained using the comparative coating solution 5 of Comparative Example 1.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/8247 C01B 13/18 5G303 29/788 H01L 29/78 371 29/792 27/10 444C // C01B 13/18 H01L 27/105 (72) Inventor Kinji Yamada 2-11-24 Tsukiji, Chuo-ku, Tokyo JSR Corporation F-term (reference) 4G042 DA01 DB11 DC03 DD02 DE09 DE14 4G048 AA05 AB02 AB05 AC02 AD02 AE08 5F058 BA11 BC03 BF46 BJ02 5F083 AD11 FR00 FR01 FR05 FR06 FR07 JA17 JA38 PR16 PR23 5F101 BA62 5G303 AA10 AB15 AB20 BA03 BA12 CA01 CB03 CB06 CB09 CB10 CB11 CB13 CB14 CB15 CB16 CB17 CB18 CB20 40

Claims (9)

[Claims] 1. A first organometallic compound (A) obtained by substituting at least a part of functional groups of a hydrolysis condensate obtained by hydrolyzing and condensing a metal alkoxide (a) with a carboxyl group; A metal alkoxide (b) of a metal different from the alkoxide (a), a hydrolysis condensate (c) obtained by hydrolyzing and condensing the metal alkoxide (b), at least a part of the functional groups of the metal alkoxide (b) Consists of at least one compound selected from a compound (d) obtained by substituting a carboxyl group for the compound (d) and a compound (e) obtained by substituting at least a part of the functional groups of the hydrolysis condensate (c) with a carboxyl group. A coating liquid for forming a ferroelectric thin film, comprising a second organic metal compound (B). 2. The method according to claim 1, wherein the metal of the metal alkoxide (a) and the metal of the metal alkoxide (b) are Li, Na, K, Mg,
Ca, Sr, Ba, La, Ti, Zr, Hf, V, N
b, Ta, Cr, Mo, W, Mn, Fe, Co, Ni,
The coating liquid for forming a ferroelectric thin film according to claim 1, wherein the coating liquid is a metal selected from Cu, Zn, Pb, and Bi. 3. The metal alkoxide (a) and the metal alkoxide (b) are metals selected from Pb, Zr, Ti and La, and the metal alkoxide (a) and the metal alkoxide (b) 2. The coating liquid for forming a ferroelectric thin film according to claim 1, wherein the total of the metal species of b) is 3 to 4. 4. The metal of the metal alkoxide (a) and the metal alkoxide (b) is Sr, Bi, Ti, Ta
2. The ferroelectric material according to claim 1, wherein the metal alkoxide (a) and the metal alkoxide (b) are 3 to 4 metals in total. Coating liquid for body thin film formation. 5. A first organometallic compound (A) obtained by substituting at least a part of functional groups of a hydrolysis condensate obtained by hydrolyzing and condensing a metal alkoxide (a) with a carboxyl group; A metal alkoxide (b) of a metal different from the alkoxide (a), a hydrolyzed condensate (c) obtained by hydrolyzing and condensing the metal alkoxide (b), at least a part of functional groups of the metal alkoxide (b) At least one compound selected from a compound (d) obtained by substituting a carboxyl group with a compound (d) and a compound (e) obtained by substituting at least a part of the functional groups of the hydrolysis condensate (c) with a carboxyl group. A method for producing a coating liquid for forming a ferroelectric thin film, comprising mixing a second organometallic compound (B). 6. The metal of the metal alkoxide (a) and the metal alkoxide (b) is Li, Na, K, Mg,
Ca, Sr, Ba, La, Ti, Zr, Hf, V, N
b, Ta, Cr, Mo, W, Mn, Fe, Co, Ni,
The method for producing a coating liquid for forming a ferroelectric thin film according to claim 5, wherein the coating liquid is a metal selected from Cu, Zn, Pb, and Bi. 7. The metal of the metal alkoxide (a) and the metal alkoxide (b) is a metal selected from Pb, Zr, Ti and La, and the metal alkoxide (a) and the metal alkoxide ( The method for producing a coating liquid for forming a ferroelectric thin film according to claim 5, wherein the total of the metal species of b) is 3 to 4. 8. The metal of the metal alkoxide (a) and the metal alkoxide (b) is Sr, Bi, Ti, Ta
6. The ferroelectric substance according to claim 5, wherein said metal alkoxide (a) and said metal alkoxide (b) have a total of 3 to 4 kinds of metals selected from N and Nb. A method for producing a coating liquid for forming a body thin film. 9. A ferroelectric thin film formed from the coating liquid for forming a ferroelectric thin film according to claim 1.