JP2002100626A - Embrocation for forming ferroelectric thin film and ferroelectric thin film produced by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an embrocation for forming a ferroelectric thin film producing a smooth ferroelectric thin film. SOLUTION: The embrocation for forming the ferroelectric thin film includes an organic compound expressed by a formula HOOC-R1-X and an organic metal compound. In the formula, R1 is a bivalent organic group; X is one of any functional groups selected from a group comprising -CONR, 2R3, -OR2,-NR2R3,- NR2COR3, or expressed by formula I, formula II, formula III, -C≡N, -N≡N, -N≡C,-CR2=N-R3, -COR2 and -COCH2COOR2. However, R2 and R3 are a hydrogen atom, or a saturated or an unsaturated carbon hydride group independently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating liquid for forming a ferroelectric thin film used for a semiconductor memory or the like.

[0002]

_2. Description of the Related Art In recent years, the formula (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O
_{2m + 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,
Indicate Ca, Na, K, and rare earth elements) or a combination of these ions; B represents 4, 5, 6-valent ions (eg, Ti, Nb, Ta, W, Mo, F
e, ions of metal elements such as Co and Cr), or a combination of these ions; 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, SrBi ² T
a ₂ O ₂ system, that is, (Bi ₂ O ₂ ) ²⁺ (SrTa ₂ O ₇ )
^{The 2-} BLSF thin film is particularly attracting attention as a material exhibiting these characteristics remarkably.

[0004] As a method of forming these BLSF thin films,
Examples of the method include a sputtering method, a CVD method, and a coating film forming method. However, a thin film forming method by a sputtering method or a CVD method requires an expensive apparatus because a large amount of metal oxide is contained as a constituent of the thin film. There are problems such as high cost and difficulty in controlling and managing the composition of the dielectric film. In particular, there is a problem in that application to a large-diameter substrate is difficult. On the other hand, the coating film forming method is promising because it does not require expensive equipment, the film forming cost is relatively low, and the control and management of the composition of the dielectric film are easy.

[0005] BL used in this coating type film forming method
As SF-based coating solution, MOD is obtained by dissolving 2-ethylhexanoate such as Sr, Bi, Ta, Nb, and Ti in xylene.
(Metallo-Organic Decomposition) type coating solution (Preprints; Olympus Optical Co., Ltd., Symmetrics Corporation; 26-TC-10, pp. 13)
9-140, 1995.5.524-27), Sr, B
Carboxylates of i (eg, 2-ethylhexanoate)
And an alkoxide compound of Ta dissolved in acetate to form a coating solution (Preliminary Proceedings of the 12th Ferroelectric Application Conference; Mitsubishi Materials Corporation; 24-TP-11 (p
p. 57-58); 1995.5.24-27, "Jpn.
J.Appl.Phys. "Vol.34 (1995) pp.5096-5099), Sr,
Bi, Ta alkoxy metals, β-diketone metal complexes, and metal acetates are reacted with alcohols, carboxylic anhydrides, glycols, β-diketones, and dicarboxylic acid monoesters to form a coating solution. (Japanese Patent Laid-Open No. 9
-286719).

However, these coating solutions contain a large amount of organic components in the entire coating solution, and have high film-reducing properties due to burning of the organic components during coating, baking, and crystallization treatments.
The obtained film was porous, and the surface shape (surface morphology) of the film was not good, and it was difficult to apply it to an VLSI device, and it was not always satisfactory. In addition, the surface of the thin film is roughened by the growth of crystal grains, and as a result, there is a problem that electrical characteristics are deteriorated such as an increase in leak current. It was not always satisfactory from the viewpoint of the productivity of the semiconductor manufacturing process.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of these problems of the prior art, and provides a coating liquid for forming a ferroelectric thin film capable of obtaining a smooth ferroelectric thin film. That is the task.

[0008]

The present invention for solving the above-mentioned problems has the following general formula (1): HOOC-R ¹ -X (1) wherein R ¹ is a divalent organic group, X is -CONR
^{2 R 3, -OR 2, -NR} 2 R 3, -NR 2 COR 3,

[0009]

Embedded image

-CR ² = NR ³ , -COR ² , -COC
Any functional group selected from the group consisting of H ₂ COOR ² (provided that R ² and R ³ are each independently a hydrogen atom,
Or a saturated or unsaturated hydrocarbon group. ), And a coating liquid for forming a ferroelectric thin film, which comprises an organic metal compound.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. I. Carboxylic acid group-containing organic compound The carboxylic acid group-containing organic compound used in the coating solution for forming a ferroelectric thin film of the present invention is represented by the following general formula (1): HOOC-R ¹ -X (1) .

In the general formula (1), R ¹ is a divalent organic group, preferably an alkylene group, more preferably an alkylene group having 1 to 6 carbon atoms. The general formula (1)
In, X is ^{-CONR 2 R 3, -OR 2,} -NR
^{2 R 3, -NR 2 COR 3} ,

[0013]

Embedded image

-CR ² = NR ³ , -COR ² , -COC
Any functional group selected from the group consisting of H ₂ COOR ² (provided that R ² and R ³ are each independently a hydrogen atom,
Or a saturated or unsaturated hydrocarbon group. ), And preferably, X is -CONR ² R ^3. Among the organic compounds represented by the general formula (1), particularly preferred are carboxylic acid monoamides represented by the general formula (2).

HOOC— (CH ₂ ) _n —CONR ² R ³ (2) In the general formula (2), n is a positive number of 1 to 5, and R ² and R ³ are each independently a hydrogen atom Alternatively, it is a saturated or unsaturated hydrocarbon group having 1 to 5 carbon atoms. More preferably, n is a positive number of 2 to 4, and R ² and R ³ are each independently preferably a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. Although not particularly limited, specifically, for example, succinic monodihydroamide, succinic monodimethylamide, succinic monodiethylamide, succinic monodipropylamide, glutaric monodimethylamide, glutaric monodiethylamide , 5- (dihydrocarbamoyl) -n-hexanoic acid, 5- (diethylcarbamoyl) -n-hexanoic acid, and the like.

II. Organometallic Compound The metal element used in the present invention is not particularly limited, but may be, for example, Li, Na, K, Mg, C
a, Sr, Ba, Sc, Y, La, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co,
Examples thereof include Ni, Cu, Zn, Ga, Pb, and Bi. Preferably, Pb, Ti, Zr, Nb,
Ta, Bi, Sr, more preferably B
A combination of i, Sr and Ta is preferred.

Examples of the organometallic compound include metal alkoxides, partial hydrolysis products thereof, metal oxides, metal carboxylate salts, inorganic metal salts, metal hydroxides, and the like, and reaction products of these metal compounds. it can. Preferably, metal carboxylate, metal alkoxide, metal hydroxide and a reaction product of these metal compounds can be mentioned.

II-1. Metal alkoxide A metal alkoxide is a compound in which a metal atom has reacted with an alcohol, and is represented by the following general formula (3). M ^a (OR ⁴ ) _a (3) (where, M represents a metal, a is a positive number of 1 to 7 according to the valence of the metal, and R ⁴ is a saturated or unsaturated metal. It is a hydrocarbon group or a hydrocarbon group further substituted with an alkoxyl group.) The alcohols forming the metal alkoxide are not particularly limited, and for example, those represented by the following formula (4) are preferred. be able to.

R ⁵ OH (4) wherein R ⁵ is 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. The alcohols in the case where R ⁵ is a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms are not particularly limited. For example, methanol, ethanol, 1-propanol, Examples thereof include 2-propanol, butanol, amyl alcohol, and cyclohexanol.

In the case where R ⁵ is a hydrocarbon group further substituted with an alkoxyl group having 1 to 6 carbon atoms, the alcohols are not particularly restricted but include, for example, methoxymethanol and methoxyethanol. , Ethoxymethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, propoxypropanol and the like.

II-2. Hydrolysis of Metal Alkoxide Hydrolysis of the metal alkoxide 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. The catalyst used for this hydrolysis is not particularly limited, and those known for hydrolysis reactions of metal alkoxides,
For example, inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid; acid catalysts such as acetic acid, propionic acid, and butyric acid; and organic catalysts such as sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide. And inorganic and organic alkali catalysts. However, inorganic alkalis such as sodium hydroxide and potassium hydroxide may cause metal ions such as sodium and potassium to remain in the coating solution and affect the electrical properties of the coating film. Nitrogen-containing alkali may form a nitrogen compound having a high boiling point after the hydrolysis reaction, and this may affect the densification of the coating film during the firing step. It is preferable to use a catalyst.

The above hydrolysis conditions 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.).

II-3. Metal carboxylate The metal carboxylate is a compound represented by the following general formula (5). M ^b (OCOR ⁶ ) _b (5) (where b represents the valence of the metal, x is a positive number of 1 to 7, and R ⁶ is a saturated or unsaturated hydrocarbon group.) Metal The carboxylic acids forming the carboxylate are not particularly limited, but for example, those represented by the following formula (6) can be mentioned as preferred examples.

R ⁷ COOH (6) (In the formula, R ⁷ represents a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms.) The carboxylic acids are not particularly limited. , 2-methylpropionic acid, pentanoic acid, 2,2-dimethylpropionic acid, butanoic acid, hexanoic acid, 2-ethylhexanoic acid, octylic acid, nonanoic acid, and decanoic acid.

The above carboxylate salts have poor reactivity with water and metal alkoxides, suppress the reaction in solution with other metal compounds, and improve the storage stability. II-4. Exchange of Functional Group of Metal Compound The metal compound used in the coating solution for forming a ferroelectric thin film of the present invention may be in a state where its functional group is substituted.

The substitution of the functional group of the metal compound includes
For example, one obtained by reacting a functional group (a hydroxyl group and / or an alkoxy group) of a hydrolyzate with a carboxyl group of a carboxylic acid can be mentioned as a preferred example.
The above carboxylic acids can substitute the functional groups of the compound in the coating solution of the present invention and improve the storage stability.

As such carboxylic acids, preferred examples include at least one selected from the group consisting of carboxylic acids. Preferred examples of the carboxylic acids include at least one selected from the group consisting of carboxylic acids represented by the following formula (7). R ⁸ COOH (7) (In the formula, R ⁸ represents a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms.) The carboxylic acids are not particularly limited,
For example, acetic acid, 2-methylpropionic acid, pentanoic acid,
Examples thereof include 2,2-dimethylpropionic acid, butanoic acid, hexanoic acid, 2-ethylhexanoic acid, octylic acid, nonanoic acid, and decanoic acid.

III. Preparation of Coating Solution for Forming Ferroelectric Thin Film In addition, a metal element component contained as an organometallic compound in the coating solution for forming a ferroelectric thin film of the present invention, preferably
Appropriate values for the contents of the Bi metal element component, the Sr metal element component, and the Ta metal element component cannot be uniformly determined depending on the application location, conditions, and the like of the coating solution of the present invention. Therefore, the optimal value of the content is determined by the type of the applicable device (for FRAM, DRAM, MFS, MF
IS, 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). Is preferred.

In the present invention, in order to form a film composed of three or more metal elements, a coating solution in which the metal compound is dissolved in a solvent (hereinafter referred to as “coating solution”) is applied to a substrate, It is preferable to form by drying. As a solvent for dissolving such a metal compound, for example, an alcohol solvent, a polyhydric alcohol solvent, an ether solvent, a ketone solvent, an ester solvent,
Lower carboxylic acid solvents and the like can be mentioned.

The alcohol solvent is not particularly restricted but includes, for example, methanol, ethanol, propanol, butanol, amyl alcohol, cyclohexanol, methylcyclohexanol and the like. Examples of the polyhydric alcohol solvent include, but are not limited to, ethylene glycol monomethyl ether, ethylene glycol monoacetoester, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monoethyl ether, propylene glycol monoacetate, and dipropylene. Glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, methoxybutanol and the like can be mentioned.

The ether solvent is not particularly restricted but includes, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane and the like. . Examples of the ketone solvent include, but are not particularly limited to, 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, Examples thereof include dimethyl oxide, holon, cyclohexanone, and diacetone alcohol.

The ester solvent is not particularly restricted but includes, for example, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, lactic acid Ethyl, methoxybutyl acetate,
Examples thereof include diethyl oxalate and diethyl malonate.

The lower carboxylic acid solvent is not particularly restricted but includes, for example, acetic acid, propionic acid, butyric acid, valeric acid and the like. The above solvents can be used alone or in combination of two or more. As the various solvents described above, the most preferable one 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 concentration of the organometallic compound in the coating solution in terms of metal oxide is preferably 1 to 20 solids.
% By weight, preferably 5 to 15% by weight. IV. Ferroelectric thin film formation In the present invention, the substrate on which the coating solution is applied
For example, a silicon wafer may be used.

Even if a silicon oxide film, a metal such as Pt, Ir, Ru and the like, and an electrode made of a metal oxide such as a conductive metal oxide, and other structural layers are formed on the silicon wafer. Good. Then, the above coating liquid is applied onto the substrate by a known coating method such as a spinner method or a dipping method, and dried at a temperature of usually 50 to 250 ° C.

Next, calcination is performed at a temperature of 250 to 500 ° C. It is preferable that the operation from coating to calcination is repeated several times to set a desired film thickness. The ferroelectric thin film preferably has a thickness of 10 to 200 nm. Next, main firing is performed at a high temperature of 700 to 900 ° C., typically 750 ° C., to form a ferroelectric thin film having a crystal structure. Room temperature (25 ± 2 ° C) in the main firing step
The furnace method in which the temperature is raised to the main firing temperature at a heating rate of about 5 to 20 ° C./min, and then the main firing temperature is maintained for about 30 to 80 minutes, from room temperature to 30 to 250 ° C./s
RTP which raises the temperature to the main firing temperature at a temperature raising rate of about ec, and then fires for about 0.5 to 3 minutes while maintaining the main firing temperature
Various firing methods such as a method can be selected.

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

Here, as the upper electrode, the metals, metal oxides, and the like mentioned as materials for the lower electrode can be used. 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.

[0039]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited by these Examples.

[0040]

EXAMPLE 1 Preparation of Coating Solution _{Sr (O i C 3 H 7} ) 2 3.70g, Ta (OC 2 H 5) 5 1
After mixing 6.25 g and 355.0 g of propylene glycol monopropyl ether, and stirring at 25 ° C. for 1 hour,
373.1 g of a mixed solution of Sr metal alkoxide and Ta metal alkoxide was obtained.

0.9 g of water and 88.56 g of propylene glycol monopropyl ether were mixed, and a mixed solution of the above Sr metal alkoxide and Ta metal alkoxide was added.
After adding to 1 g, the temperature was raised to 60 ° C., and the mixture was heated and stirred for 4 hours. After the completion of the reaction, the mixture was cooled to room temperature to obtain a solution of an organometallic compound in which SrTa metal alkoxides were hydrolyzed.

26.82 g of 2-ethylhexanoic acid was added to the obtained solution of the organometallic compound, and the mixture was stirred at 25 ° C. for 30 minutes to exchange the functional group of the organometallic compound. C. and stirred under reduced pressure for 30 minutes to obtain 36.0 g of a solution from which low-boiling alcohol was removed. After cooling to room temperature, the mixture was diluted 4-fold with propylene glycol monopropyl ether to prepare a coating solution A.

On the other hand, Bi (OtC ₅ H ₁₁ ) ₃ 18.82
g, propylene glycol monopropyl ether 35
After mixing 5.0 g and stirring at 25 ° C. for 1 hour, 373.82 g of a solution of Bi metal alkoxide was obtained. 22.47 g of 5- (diethylcarbamoyl) pentanoic acid was added to 373.82 g of the obtained Bi metal alkoxide solution,
After stirring at 25 ° C for 2 hours to exchange the functional group of the organometallic compound, the solution was heated to 40 to 50 ° C and stirred under reduced pressure for 30 minutes to remove the low boiling alcohol from the solution. 0 g was obtained. After cooling to room temperature, the mixture was diluted 4 times with propylene glycol monopropyl ether.
Was prepared. The coating solution A and the coating solution B are mixed in equal amounts, and the solid content concentration is 10% by weight in terms of SrBiTa oxide.
(Sr: Bi: Ta = 0.9: 2: 2 (molar ratio)) was obtained.

[0044]

Comparative Example 1 Preparation of Comparative Coating Liquid The coating liquid composed of Sr and Ta was the same as the coating liquid A in Example 1. On the other hand, Bi (OtC
_After mixing 18.82 g of ₅ H ₁₁ ) _{3 and} 355.0 g of propylene glycol monopropyl ether, stirring the mixture at 25 ° C. for 1 hour, 373.82 g of a Bi metal alkoxide solution was obtained.
I got

The obtained Bi metal alkoxide solution 37
To 3.82 g, 17.31 g of 2-ethylhexanoic acid was added, and the mixture was stirred at 25 ° C. for 2 hours to exchange the functional group of the organometallic compound. Then, the solution was heated to 40 to 50 ° C. After stirring for 3 minutes, 36.0 g of a solution from which low-boiling alcohol was removed was obtained. After cooling to room temperature, the mixture was diluted 4-fold with propylene glycol monopropyl ether to prepare Comparative Coating Liquid B. The coating solution A and the comparative coating solution B were mixed in equal amounts, and the solid content concentration was 1 in terms of SrBiTa oxide.
0 wt% (Sr: Bi: Ta = 0.9: 10: 10 (molar ratio)) Comparative coating solution 1 was obtained.

[0046]

Example 2 and Comparative Example 2 Formation of Ferroelectric Thin Film A 100 nm thick Pt lower electrode was formed by a sputtering method on a silicon wafer having a diameter of 6 inches on which a thermally oxidized SiO ₂ film of 1000 nm was formed. . Next, Example 1 and Comparative Example 1 were formed on the Pt lower electrode.
The coating solution 3 or the comparative coating solution 2 obtained in the above was used at 500 rpm for 5 seconds using a spin coater, and then at 3000 rpm.
m for 20 seconds, dried at 250 ° C. for 5 minutes, and then heated from 25 ° C. to 1.25 ° C./sec.
The temperature was raised to 0 ° C., and calcination was performed for 5 minutes. The operation from the above coating to calcination was repeated three times, and then from 25 ° C. to 25 ° C.
/ Sec at a heating rate of 750 ° C.
By baking at 50 ° C. for 0.5 minutes, 150 nm
A thick ferroelectric thin film was formed.

The surfaces of the ferroelectric thin films produced in Example 2 and Comparative Example 2 were observed by AFM. The result is shown in FIG.
As shown in FIG. Further, the surface roughness of the ferroelectric thin films produced in Example 2 and Comparative Example 2 was measured by AFM. Measurement is J
In the manner defined by the IS standard B0601, the measurement conditions (actual range) l _c 666.67, and Ra obtained as L 1990, Rmax, measured at any 10 points in the ferroelectric thin film Rz and the mean value . Table 1 shows the results.

[0048]

[Table 1]

[0049]

As described above, according to the present invention,
It is possible to provide a coating liquid for a ferroelectric thin film from which a smooth ferroelectric thin film can be obtained.

[Brief description of the drawings]

FIG. 1 is an AFM photograph of a surface of a ferroelectric thin film produced in an example of the present invention.

FIG. 2 shows an AFM of the surface of a ferroelectric thin film produced in a comparative example.
It is a photograph.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Miyawaki 2--11-24 Tsukiji, Chuo-ku, Tokyo Inside JSR Corporation (72) Inventor Kinji Yamada 2-11 Tsukiji, Chuo-ku, Tokyo No. 24 FSR in JSR Co., Ltd. (reference) 5F058 BA20 BC03 BF46 BH01

Claims (3)

[Claims] 1. The HOOC-R of the general formula (1)¹−X (1) (where R¹Is a divalent organic group, and X is -CONR^Two
R^Three, -OR^Two, -NR^TwoR ^Three, -NR^TwoCOR^Three, Embedded image-CR^Two= N-R^Three, -COR^Two, -COCH_TwoCOOR^Two
Any functional group selected from the group consisting of^Two
And R^ThreeAre each independently a hydrogen atom or a saturated
Or an unsaturated hydrocarbon group. )
Compound, and an organometallic compound.
Coating solution for forming dielectric thin film. 2. The organic compound represented by the general formula (1) is represented by the following general formula (2): HOOC- (CH ₂ ) _n -CONR ² R ³ (2) (wherein n is 1 to 5) Wherein R ² and R ³ are each independently a hydrogen atom or a saturated or unsaturated hydrocarbon group having 1 to 5 carbon atoms.) Coating solution for forming ferroelectric thin film. 3. A ferroelectric thin film produced by using the coating solution according to claim 1.