JPH1143328A - Thin film of ferroelectric substance, its production and production apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film of ferroelectric substance having a composition region most suitable for proving excellent residual polarization characteristics and a bismuth-based layer crystal structure high in reliability and to provide both a method for producing the ferroelectric substance and an apparatus for producing the same. SOLUTION: Liquid organometallic precursors housed in containers 11 to 13 in a liquid raw material feeding apparatus 10 are mixed in a fixed ratio by a liquid mixing valve 14 and vaporized in a vaporizing chamber 15 by heating at a temperature of 180-240 deg.C. The vaporized organometallic gas together with a carrier gas is sent to a gas mixing part 20 and mixed so as to adjust the ratio of the organometallic raw material gas containing the carrier gas to an oxygen gas to 30-80%. The reaction product is deposited on a substrate 31 in a reaction chamber 30. Then the deposit is heat-treated in an oxidizing atmosphere at a temperature of 600-800 deg.C. Consequently a thin film crystal comprising a ferroelectric substance of a bismuth-based layer structure, Srx Biy Ta2 O9 ±d (0.60<=x<1.00, 2.00<y<=2.50, 0<=d<=1.00) as a main phase is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric thin film having a bismuth-based layered crystal structure, a method of manufacturing the same, and a manufacturing apparatus therefor.
The present invention relates to a ferroelectric thin film suitable for use in a ferroelectric device such as a display, a method of manufacturing the same, and a manufacturing apparatus.

[0002]

2. Description of the Related Art In recent years, with the progress of film forming technology, application research on nonvolatile memory cells using ferroelectric thin films has been actively pursued. This non-volatile memory cell is a non-volatile random access memory (Ferroelectric Random Access Memories; FeRA) capable of high-speed rewriting by utilizing high-speed polarization inversion of a ferroelectric thin film and its residual polarization.
M) cell. As a material constituting such a memory, a bismuth-based layered crystal structure oxide can be given. The bismuth-based layered crystal structure oxide of the biggest disadvantages in which was fatigue phenomena conventionally used in have PZT (structural formula is PbZr _1-x Ti _x O ₃ compound) material, ie the residual due to repeated rewriting It attracts attention because no decrease in polarization is observed.

In order to apply such a ferroelectric material to an electronic device, it is essential to develop a thin film technology.
Further, it is required to achieve the bulk characteristics of the ferroelectric in a thin film form. Therefore, it is necessary to use a thin film deposition method capable of realizing various characteristics such as a desired stoichiometric ratio, crystallinity, crystal structure and crystal orientation in a thin film form. At present, ferroelectric thin films using these materials are obtained by spin coating methods such as MOD (Metal Organic Decomposition) method and sol-gel method, and exhibit good ferroelectric properties. The spin coating method has high throughput and excellent composition control,
In addition, there is an advantage that the cost of the manufacturing apparatus is low because a vacuum device is not required.

[0004] However, this method has problems such as generation of particles and contamination in the thin film manufacturing process, and also has a problem that it has poor compatibility with the current silicon device manufacturing process due to poor step coverage. .

Therefore, in order to apply these materials to memories of high integration in the future, chemical vapor deposition excellent in step coverage, film quality, uniformity, prevention of particle generation, processing speed and the like corresponding to miniaturization. Method, namely, CVD (Ch
The development of the emical vapor deposition method is strongly desired. At present, the bismuth-based layered crystal structure of ferroelectric thin film C
There are very few reports on fabrication methods using the VD method.
SrB, one of the ferroelectrics having a bismuth-based layered crystal structure
Regarding the formation of the i ₂ Ta ₂ O ₉ thin film by the CVD method,
S. B. Desu et al. (Applied Physics Letters Vol.6
8, (5) 1996, pp. 616) and T. Ami et al, MRS Symposi
um Proceedings Vol. 415 (1996) p. 195-200), but little else.

[0006]

However, the S.P.
B. According to the study of Desu et al., The remanent polarization value which is an index of the polarization state of the ferroelectric thin film is 2Pr = 8.3 μC /
cm ² , which is a value normally obtained for a thin film formed by a spin coating method (2Pr = 15 to 25 μC /
cm ² ). The deposition rate is 3
nm / min, which is a practical level (10 to 20 nm / m
in). Further, the method by nets has a film formation rate of 15 to 20 nm / min, which is a value that can withstand a practical level, but the remanent polarization value is 2 Pr = 10 to 1
It is 1 μC / cm ² , which is smaller than a value usually obtained in a thin film formed by spin coating.

The main reason why sufficient remanent polarization characteristics cannot be obtained in a ferroelectric thin film having a bismuth-based layered crystal structure manufactured by the CVD method is that the optimum composition of a thin film capable of sufficiently obtaining remanent polarization characteristics is obtained. Is not grasped. That is, for example, an oxide composed of strontium (Sr), bismuth (Bi), tantalum (Ta), and oxygen (O), which is one of the bismuth-based layered crystal structure ferroelectrics, provides good remanent polarization characteristics. The range of the film composition is limited, and the optimum composition is considered to be a composition range other than the stoichiometric composition (SrBi ₂ Ta ₂ O ₉ ).

Further, when the above-mentioned optimum composition is realized by the CVD method, a precise composition control technique for realizing the optimum composition is required. However, strontium,
It is extremely difficult to control the mixing of the three types of source gases, bismuth and tantalum, to freely change the composition ratio in the thin film. One of the factors that makes it difficult to control the composition is the low vapor pressure of the organometallic raw material that provides the element constituting the ferroelectric having the bismuth-based layered crystal structure. For example, strontium tetramethylheptanedione (Sr (C ₁₁ H ₂₀ O) ₂ ) and triphenylbismuth (Bi (C ₆ H) which are typical organometallic raw materials constituting SrBi ₂ Ta ₂ O ₉ having a stoichiometric composition. ₅ ) ₃ ) is solid at room temperature, and tantalum ethoxide (Ta (OC ₂ H ₅ ) ₅ ) is liquid at room temperature. Therefore, in order to evaporate these and send them to the reaction chamber, strontium tetramethylheptanedione can be 200 to 200 Torr even under a reduced pressure of 1 to 10 Torr.
It is necessary to heat at 250 ° C., a temperature in the range of 100-150 ° C. for triphenylbismuth and tantalum ethoxide. Exposure of organometallic raw materials to such high temperatures for a long period of time causes some decomposition and reaction, resulting in fluctuations in the gas supply to the reaction chamber, resulting in fluctuations in composition and reproducibility for each operation. Leads to a decline. Another factor that makes it difficult to control the composition is that when heat treatment is performed at a temperature of 700 to 800 ° C. in order to crystallize a thin film formed by a CVD method, bismuth oxide (Bi ₂ O) having high volatility is obtained.
₃ ) volatilization, or change in film composition due to diffusion of bismuth remaining in the film as a metal by heat treatment.

The present invention has been made in view of the above problems, and a first object of the present invention is to provide a bismuth-based layered crystal structure having an optimum composition range for obtaining good remanent polarization characteristics and a high reliability. An object of the present invention is to provide a ferroelectric thin film.

A second object of the present invention is to produce a ferroelectric thin film having a bismuth-based layered crystal structure with an optimum composition precisely and with good reproducibility even when a high-temperature heat treatment is performed in a vaporization step and a heat treatment step. It is an object of the present invention to provide a method and apparatus for manufacturing a ferroelectric thin film that can be used.

[0011]

The ferroelectric thin film according to the present invention contains strontium (Sr), bismuth (Bi), tantalum (Ta), and at least tantalum of niobium (Nb) and oxygen (O). A layered crystal structure,
The composition formula is represented by Sr _x Bi _y Ta ₂ O ₉ ± _d or Sr _x
Bi _y (Ta, Nb) ₂ O ₉ ± _d (where 0.60 ≦ x
<1.00, 2.00 <y ≦ 2.50, 0 ≦ d ≦ 1.0
0).

The method for producing a ferroelectric thin film according to the present invention comprises:
At least strontium (Sr), bismuth (Bi)
Vaporizing step of vaporizing a liquid organometallic precursor containing each component of tantalum (Ta) and tantalum (Ta) in a vaporization chamber, and gas mixing for mixing a carrier gas containing the vaporized organometallic precursor and oxygen gas at a predetermined ratio. Process, a carrier gas containing a mixed organometallic precursor and an oxygen gas are reacted in a reaction chamber within a predetermined pressure range to decompose and deposit on a substrate heated at a predetermined temperature range to form an oxide. A thin film forming step of forming a thin film, and a ferroelectric thin film having a desired bismuth layer structure is formed by subjecting an oxide thin film formed on a substrate to heat treatment in a predetermined temperature range and performing crystallization including composition control. And a heat treatment step. Preferred conditions in each step of this method are as follows: in the vaporization step, the temperature of the vaporization chamber is in the range of 180 to 240 ° C.
In the gas mixing step, at least one of argon (Ar) and dry nitrogen (N ₂ ) is used as a carrier gas, and a mixing ratio of oxygen gas (oxygen / oxygen) to a carrier gas containing a vaporized organometallic precursor is used. Carrier gas) in the range of 30 to 70%. In the thin film forming step, the temperature of the substrate is set in a range of 400 to 700 ° C., and the pressure in the reaction chamber is set in a range of 5 to 12 Torr, more preferably, 7 to 10 Torr. Further, in the heat treatment step, it is desirable to heat-treat the oxide thin film at a temperature in the range of 600 to 800 ° C.

An apparatus for producing a ferroelectric thin film according to the present invention comprises:
The mixed region of the carrier gas containing the organometallic precursor gas and the oxygen gas is set to a predetermined range on the substrate according to the film composition, preferably a region of 13 to 33 cm on the substrate.

The ferroelectric thin film according to the present invention has better remanent polarization characteristics than the conventional ferroelectric thin film by setting the film composition in the above range.

In the method for producing a ferroelectric thin film according to the present invention, it is possible to precisely control the mixing ratio of at least three source gases of strontium, bismuth and tantalum, and to obtain an optimum composition exhibiting excellent ferroelectricity. Is produced with good reproducibility.

In the apparatus for manufacturing a ferroelectric thin film according to the present invention, the mixed region of the organometallic precursor gas and the oxygen gas is set to a predetermined range on the substrate according to the film composition, particularly 13 to 3 on the substrate.
By setting the area in the range of 3 cm, a ferroelectric thin film having an optimum composition can be manufactured.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The ferroelectric thin film according to the present embodiment is a layered crystal structure oxide containing strontium, bismuth, tantalum and oxygen, and the composition formula of this ferroelectric thin film is Sr
_x Bi _y Ta ₂ O ₉ ± _d Note that a part of the tantalum site may be replaced by niobium. In this case, the composition formula is Sr _x Bi _y (Ta, Nb) ₂ O ₉ ± _d.
It is represented by This ferroelectric thin film includes a layer composed of [Bi ₂ O ₂ ] ²⁺ and [SrTa ₂ O ₇ ] ²⁻ or [Sr (Tr
a, Nb) ₂ O ₇ ] ^2- layers.

Here, in the present embodiment, the values of x and y in the present embodiment are in the following ranges for the reasons described later (see FIG. 8). 0.60 ≦ x <1.00, 2.00 <y ≦ 2.50, 0
≦ d ≦ 1.00

More preferably, the respective ranges are as follows. 0.70 ≦ x ≦ 0.90, 2.10 ≦ y ≦ 2.40

The ferroelectric thin film of the present embodiment does not have a stoichiometric composition, is in a state where strontium is insufficient and bismuth is excessive, and as a result, has a good remanent polarization characteristic. ing. This is considered to be affected by the crystal structure obtained by partial substitution of strontium and bismuth.

Hereinafter, a method of manufacturing a ferroelectric thin film having such a composition will be described.

Here, as a substrate for forming a thin film, for example, a titanium (Ti) film and a platinum (Pt) film are sequentially formed on a silicon substrate (Si / SiO ₂ ) used as a lower electrode of FeRAM by a sputtering method. A method of forming a dielectric thin film having the above composition on this substrate will be described.

First, prior to the description of a specific method, a flash-MOCVD (Metal Organic Chemical Vapor Depo) for producing a ferroelectric thin film having a bismuth-based layered structure will be described.
sition) The device will be described.

FIG. 1 shows a schematic configuration of the flash-MOCVD apparatus. The MOCVD apparatus includes a liquid source supply device 10 for supplying a liquid organometallic precursor (organic metal source) as a gas, a carrier gas containing an organometallic precursor gas supplied from the liquid source supply device 10, A gas mixing section 20 for mixing oxygen gas (O ₂ ) with a gas mixed by the gas mixing section 20 to react and thermally decompose to form an oxide thin film on the substrate 31 30 and a vacuum exhaust device 40 for evacuating the inside of the reaction chamber 30 by a pump 41.

The liquid raw material supply device 10 vaporizes the organometallic precursor dissolved in a predetermined solvent and kept in a liquid state by a flash vaporization method. That is, the liquid material supply device 10 includes a container 11 containing a liquid organometallic precursor containing bismuth (Bi) and a container 1 containing a liquid organometallic precursor containing strontium (Sr).
2 and containers 13 each containing a liquid organometallic precursor containing tantalum (Ta). Container 11-
13 contains an organometallic precursor containing strontium (Sr), bismuth (Bi) and tantalum (Ta) components, respectively.

Examples of the organometallic precursor include, for example, strontium (Sr) component and tetraglyme (CH ₃ OCH ₂ CH ₂ OCH ₃ ) in Sr-tetramethylheptanedione (Sr (C ₁₁ H ₂₀ O) ₂ ). ) Of the adduct
on product (addition product), using triphenylbismuth (Bi (C ₆ H ₅ ) ₃ ) for the bismuth (Bi) component and Ta-based for the tantalum (Ta) component. some alkoxy groups isopropoxide compound substituted by tetramethylheptanedione _{(Ta (O-iC 3 H} 7) 4 (C 11 H 20 O) 2)
Is used. The liquid organometallic precursors contained in these containers 11 to 13 are pumped together with a carrier gas (for example, argon (Ar)) by a liquid pump (not shown), and are electrically and precisely controlled by a liquid mixing valve (mixing). The mixture is mixed at a predetermined ratio by the manifold (14). The liquid raw material supply device 10 includes a flash vaporization type vaporization chamber 15, in which the liquid organometallic precursor mixed by the liquid mixing valve 14 is heated at a predetermined temperature (180 to 240 ° C.). (Flash vaporization) on a high quality metal frit (not shown).

The gas mixing section 20 is provided at a stage before the reaction chamber 30, that is, above the reaction chamber 30. The gas mixing section 20 is formed in a cylindrical shape having a diameter of 3 cm, and an organic metal inflow port 21 through which a carrier gas containing a vaporized organometallic precursor flows in as shown in FIG. An oxygen inlet 22 for supplying oxygen (O ₂ ) gas is provided on the side surface. The lower end of the gas mixing section 20 communicates with the ceiling of the reaction chamber 30. Reaction chamber 3
A shower nozzle 32 is installed inside the chamber 0 so as to face the gas mixing section 20. A substrate 31 is disposed below the shower nozzle 32 in the reaction chamber 30, and the substrate 31 is heated to a predetermined temperature (400 to 700
° C).

The mixing process in the gas mixing section 20 is important for achieving a desired film composition and a uniform and uniform film formation, and particularly the relationship between the substrate 31 and the gas mixing region thereon. Assuming that a distance from the position where the two types of gases collide, that is, a point where the extension line of the organometallic inlet 21 and the extension line of the oxygen gas inlet 22 are orthogonal to the substrate 31 is the mixing distance L, the mixing distance L is It is desirable to be in the range of 13 to 33 cm. In the present embodiment, the substrate 3
The distance between 1 and the shower nozzle 32 is, for example, 3 cm. When the mixing distance L is less than 13 cm, the gas phase reaction of the mixed gas does not sufficiently proceed, and the bismuth concentration in the film becomes lower than a desired value. On the other hand, when the mixing distance between the organometallic precursor gas and the oxygen gas in the gas mixing section 20 exceeds 33 cm, the gas phase reaction proceeds excessively, causing a gas phase nucleation reaction and, as a result, generating particles. .

Next, a method of manufacturing a ferroelectric thin film having a bismuth-based layered structure according to the present embodiment will be specifically described.
The ferroelectric thin film is formed by vaporizing a liquid organometallic precursor containing strontium (Sr), bismuth (Bi) and tantalum (Ta) in a vaporization chamber (A).
A gas mixing step (B) of mixing a carrier gas containing a vaporized organometallic precursor and oxygen gas; and a reaction chamber having a predetermined pressure by mixing the carrier gas containing the mixed organometallic precursor and oxygen gas. A thin film forming step of forming an oxide thin film by reacting and decomposing in step (1) and depositing it on a substrate (C)
And a heat treatment step (D) of forming a desired ferroelectric thin film having a bismuth layered structure by subjecting the oxide thin film formed on the substrate to heat treatment to control the composition.

First, in the vaporization step (A), the liquid organometallic precursors contained in the containers 11 to 13 in the liquid raw material supply device 10 are each pressure-fed together with a carrier gas by a liquid pump (not shown). On the way, each organometallic precursor is a liquid mixing valve 14 which is electrically controlled precisely.
Is mixed at a predetermined ratio. After that, the mixed solution is sent to the vaporization chamber 15 and has a predetermined temperature (180 to 24).
(0 ° C.) to vaporize (flash vaporize) on the porous metal frit.

The vaporized organometallic gas proceeds to the gas mixing step (B). That is, the organometallic gas is supplied to the gas mixing section 2 through the organometallic inlet 21 together with the carrier gas.
It is sent to 0. An oxygen inlet 22 is provided in the gas mixing section 20.
The oxygen gas is supplied through the, and the oxygen gas and the carrier gas containing the organic metal gas are mixed. As described above, the mixing process in the gas mixing section 20 is very important. That is, among the three kinds of organometallic materials, particularly, triphenylbismuth containing bismuth generates a bismuth oxide on the substrate surface through a reaction with oxygen in a gas phase.
In order to obtain a thin film having a desired uniform and uniform film composition, it is important to precisely control the rate of a gas phase reaction between oxygen and a carrier gas containing an organometallic raw material gas in the gas mixing section 20. is there. Specifically, the ratio of the organic metal source gas including the carrier gas to the oxygen gas is 30 to 80%,
Preferably, it is 40 to 60%. Here, for example, both the flow rate of the organic metal source gas including the carrier gas and the flow rate of the oxygen gas are set to 500 cc / min.

As for the mixing ratio of each organometallic raw material, EPMA (Electron Probe Micro Analysis), XRF (X-ray Fluorescence Analysis) and the like are performed on the composition of the thin film produced as a trial, and the mixing ratio is compared with the target composition. Thus, a desired composition can be obtained by adjusting the mixing ratio based on this.

The mixed organometallic raw material gas and oxygen gas are sent together with the carrier gas from the gas mixing section 20 through the shower nozzle 32 to the evacuated reaction chamber 30,
The process proceeds to the thin film forming step (C). In the thin film forming step (C), the organometallic raw material gas and the oxygen gas react with each other, and the reactant deposits on the substrate 31 to form an oxide thin film.

Further, this oxide thin film is subjected to a heat treatment step (D).
Move to. That is, in the reaction chamber 30 or a heating chamber (not shown), in an oxidizing atmosphere,
Heat treated at a temperature in the range of 0 ° C., ferroelectric resulting bismuth-based layered structure _{Sr x Bi y Ta 2 O 9} ± d (0.
60 ≦ x <1.00, 2.00 <y ≦ 2.50, 0 ≦ d
≦ 1.00) as the main phase. In addition,
The heat treatment is preferably performed at 800 ° C. for 1 hour in a normal pressure oxygen stream.

Thereafter, the thus obtained Sr _x
Identification analysis by X-ray diffraction was performed on the thin film crystal having Bi _y Ta ₂ O ₉ ± _d as a main phase. In addition, in order to compare with the X-ray diffraction pattern of the obtained thin film crystal, the thin film immediately after the film formation and before the heat treatment was also subjected to identification analysis by X-ray diffraction. FIG. 3 shows the X-ray diffraction pattern before the heat treatment, and FIG. 4 shows the X-ray diffraction pattern after the heat treatment.
3 and 4 show that crystallization occurred by the heat treatment in the oxidizing atmosphere, and a ferroelectric having a bismuth-based layered crystal structure was generated.

Next, a bismuth layered crystal structure ferroelectric Sr _x Bi _y T formed on a substrate 31 as a lower electrode
a ₂ O ₉ ± _d on a thin film having a main phase of 200 n
An upper electrode made of a platinum (Pt) thin film of about m was formed by a sputtering method, the hysteresis characteristics of the ferroelectric thin film were measured, the remanent polarization value and the coercive electric field were obtained, and the thin film characteristics were evaluated. FIG. 5 is a characteristic diagram showing the ferroelectric hysteresis when the applied voltage is changed from 2 to 10 V and the hysteresis is observed. Applied voltage is 3-4
At V, the hysteresis curve is already saturated,
The remanent polarization value and coercive electric field were 2Pr = 21.3 μ, respectively.
C / cm ² and Ec = about 47.2 KV / cm. These values are almost the same as those of the ferroelectric film produced by the spin coating method, and have sufficiently reached the practical level.

As described above, in this embodiment, a thin film oxide is formed by the flash MOCVD method, and is subjected to a heat treatment at a predetermined temperature, whereby the ferroelectric Sr _x Bi having a bismuth layered crystal structure exhibiting good characteristics is obtained. _y Ta ₂ O ₉ ±
_d thin film can be formed. In the flash MOCVD method, the composition ratio of each element can be changed by adjusting the substrate temperature, reaction pressure, and oxygen partial pressure during film formation.

FIG. 6 is a characteristic diagram showing, as an example, the effect of the reaction pressure in the reaction chamber 30 on the film composition. In FIG. 6, the horizontal axis represents the pressure, and the vertical axis represents the film composition after the heat treatment. The bismuth composition is 2 × Bi /
The composition of Ta and strontium is represented by 2 × Sr / Ta. The film composition was measured using an EPMA (Electron Probe Microanalyzer), and Sr _1.0 Bi
_{Using 2.4} Ta _2.0 O _9.0 as a standard sample, the characteristic X of each element at any five points on the sample surface by the constant clock method
Lines, SrLα, BiMα, TaMα and OK
The intensity of α was measured and determined from the average value. Also, EP
CAMBAX SX-50 was used for MA, and the measurement conditions for the electron beam acceleration voltage, the primary electron beam current, and the electron beam irradiation area were 5 kV, 60 nA, and 100 μm × 100 μm, respectively. From FIG. 6, when the reaction pressure is a value within the range of 0.5 to 12 Torr,
It can be seen that the higher the reaction pressure, the higher the mixing ratio of bismuth, especially at 5 Torr or higher. It is also found that the film composition of strontium also depends on the reaction pressure.

FIG. 7 shows the remanent polarization value (2) in each thin film composition when various thin films were produced by adjusting film forming conditions such as substrate temperature, reaction pressure and oxygen partial pressure during film formation.
Pr). As can be seen from FIG. 7, there is a clear correlation between the thin film composition and the remanent polarization value. That is, to obtain a larger remanent polarization value,
It is necessary that the film composition after the heat treatment satisfies a certain range, and the remanent polarization value tends to gradually decrease as the film composition deviates from the range. That is, from FIG.
In order to satisfy r> 10 μC / cm ² , it is a necessary condition that the thin film composition after the heat treatment satisfies 0.60 ≦ x <1.00 and 2.00 <y ≦ 2.50 as described above. You can see that. Further, in order to satisfy 2Pr> 15 μC / cm ² , the composition of the thin film after the heat treatment must be 0.70 ≦ x ≦ 0.
It can also be seen that the requirement is that 90 and 2.10 ≦ y ≦ 2.40.

As described above, in the method of manufacturing a ferroelectric thin film according to the present embodiment, the film forming conditions (substrate temperature, reaction pressure and oxygen partial pressure) are adjusted, so that the composition range can be freely controlled. Thus, a highly reliable ferroelectric thin film having a bismuth-based layered crystal structure having a desired remanent polarization characteristic and a composition formula of Sr _x Bi _y Ta ₂ O ₉ ± _d can be produced with good reproducibility. Therefore, by using the ferroelectric thin film having the bismuth layered crystal structure, a highly reliable semiconductor memory cell having stable characteristics can be manufactured.

In the above embodiment, as the organometallic precursor, strontium (Sr) component is
A compound in which a tetraglyme adduct is added to tetramethylheptanedione is used, triphenylbismuth is used for a bismuth (Bi) component, and a part of the alkoxy group of Ta-isopropoxide is used for a tantalum (Ta) component. A compound substituted by tetramethylheptanedione was used. In addition, for a strontium (Sr) component, a compound in which an adduct of tetrahydrofuran was added to Sr-tetramethylheptanedione was used, and bismuth (Bi) was used. A) a compound in which at least one member selected from the group consisting of an alkyl group, a fluorine-substituted alkyl group and an alkoxy group is introduced on the phenyl group of triphenylbismuth, Bi-tetramethylheptanedione, Bi-alkoxide, and Bi -Consisting of acetyl acetate Using at least one of,
And, with respect to the tantalum (Ta) component, at least one alkoxy group selected from the group consisting of Ta-ethoxide, Ta-tert-butoxide and Ta-ethoxide, Ta-isopropoxide and Ta-tert-butoxide alkoxy group. At least one member of the group consisting of compounds partially substituted by tetramethylheptanedione may be used.

In the above-mentioned flash-MOCVD method, an example of manufacturing a ferroelectric thin film having a bismuth-based layered crystal structure with a composition formula of Sr _x Bi _y Ta ₂ O ₉ ± _d has been described. Replaced Sr _x Bi
_{When a} ferroelectric thin film having a composition of (Ta, Nb) ₂ O ₉ ± _d is manufactured, a container for an organometallic precursor containing a niobium (Nb) component is added to the liquid source supply device 10 of FIG. do it. As an organometallic precursor containing a niobium component, N
b-Ethoxide, Nb-isopropoxide, Nb-tert-butoxide and a part of at least one alkoxy group selected from the group consisting of Nb-ethoxide, Nb-isopropoxide and Nb-tert-butoxide are tetramethylheptane At least one selected from the group consisting of compounds substituted by dione may be used.

[0044]

As described above, according to the ferroelectric thin film of the present invention, the composition formula is changed to the bismuth-based layered crystal structure of S
r _x Bi _y Ta ₂ O ₉ ± _d or Sr _x Bi _y (T
a, Nd) ₂ O ₉ ± _d, and x,
y is 0.60 ≦ x <1.00, 2.00 <y
≦ 2.50, good remanent polarization characteristics are obtained,
This has the effect of improving reliability.

According to the method of manufacturing a ferroelectric thin film according to the present invention, since the film forming conditions such as the substrate temperature, the reaction pressure and the oxygen partial pressure are adjusted, the composition range can be freely controlled. As a result, there is an effect that the ferroelectric thin film of the present invention having a bismuth-based layered crystal structure can be manufactured accurately and with good reproducibility.

Further, according to the apparatus for manufacturing a ferroelectric thin film according to the present invention, the mixed region of the organometallic precursor gas and the oxygen gas is set within a predetermined range on the substrate according to the film composition. This has the effect that the ferroelectric thin film of the present invention can be manufactured with good reproducibility.

[Brief description of the drawings]

FIG. 1 shows a flash-MOCVD method for growing a bismuth-based layered structure ferroelectric according to an embodiment of the present invention.
It is a block diagram showing the outline of an apparatus.

FIG. 2 is a cross-sectional view illustrating a configuration near a gas mixing section of the MOCVD apparatus of FIG.

FIG. 3 is a characteristic diagram showing an X-ray diffraction pattern of a thin film formed by the MOCVD apparatus of FIG. 1 before heat treatment.

FIG. 4 is a characteristic diagram showing an X-ray diffraction pattern of a ferroelectric thin film formed by the MOCVD apparatus of FIG. 1 after heat treatment.

FIG. 5 is a diagram showing a hysteresis characteristic of a ferroelectric thin film formed by the MOCVD apparatus of FIG. 1;

FIG. 6 is a characteristic diagram showing a relationship between a film composition and a reaction pressure after film formation and heat treatment by the MOCVD apparatus in FIG. 1;

7 shows bismuth (Bi) and strontium (S) in the ferroelectric thin film formed by the MOCVD apparatus of FIG.
It is a characteristic view showing the relationship between the composition of r), and a remanent polarization value.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Liquid raw material supply apparatus, 11-13 ... Container, 14 ... Liquid mixing valve, 15 ... Vaporization chamber, 20 ... Gas mixing part, 21
... organic metal inlet, 22 ... oxygen inlet, 30 ... reaction chamber,
31: substrate, 32: shower nozzle, 33: heater, 4
0: vacuum pumping device, 41: pump

Claims (14)

[Claims] 1. Strontium (Sr) and bismuth (B)
i), a ferroelectric thin film having a layered crystal structure containing at least tantalum and oxygen (O) of tantalum (Ta) and niobium (Nb), and having a composition formula of Sr _x Bi _y Ta ₂ O ₉ ± _d or Sr _x Bi _y (T
a, Nb) ₂ O ₉ ± _d (where 0.60 ≦ x <1.0
0, 2.00 <y ≦ 2.50, 0 ≦ d ≦ 1.00). 2. The strength according to claim 1, wherein x and y in the composition formula are values in a range of 0.70 ≦ x ≦ 0.90 and 2.10 ≦ y ≦ 2.40, respectively. Dielectric thin film. 3. A vaporizing step of vaporizing a liquid organometallic precursor containing at least components of strontium (Sr), bismuth (Bi) and tantalum (Ta) in a vaporization chamber, comprising a vaporized organometallic precursor. A gas mixing step of mixing a carrier gas and an oxygen gas at a predetermined ratio; and reacting and decomposing a carrier gas and an oxygen gas containing the mixed organometallic precursor in a reaction chamber within a predetermined pressure range, A thin film forming step of forming an oxide thin film by depositing on a substrate heated in a temperature range, and performing a heat treatment in a predetermined temperature range on the oxide thin film formed on the substrate to perform crystallization including composition control. A heat treatment step of forming a ferroelectric thin film having a desired bismuth layered structure. 4. In the vaporizing step, the temperature of the vaporizing chamber is set to 1
4. The temperature range of 80 to 240 [deg.] C.
The method for producing a ferroelectric thin film according to the above. 5. The method according to claim 1, wherein the carrier gas is argon (A).
r) and dry nitrogen (N ₂₎ method of manufacturing a ferroelectric thin film according to claim 3, characterized by using at least one of. 6. The ferroelectric substance according to claim 5, wherein the mixing ratio of oxygen gas to the carrier gas containing the vaporized organometallic precursor (oxygen / carrier gas) is in the range of 30 to 70%. Manufacturing method of thin film. 7. The method according to claim 3, wherein the temperature of the substrate is set in a range of 400 to 700 ° C. in the thin film forming step. 8. The method according to claim 3, wherein the pressure in the reaction chamber is in a range of 5 to 12 Torr in the thin film forming step. 9. The method for producing a ferroelectric thin film according to claim 8, wherein the pressure in the reaction chamber is in a range of 7 to 10 Torr in the thin film forming step. 10. The method for producing a ferroelectric thin film according to claim 3, wherein the ferroelectric thin film is formed by heat-treating the oxide thin film at a temperature in the range of 600 to 800 ° C. in the heat treatment step. . 11. An adduct of at least one of tetrahydrofuran and tetraglyme is added to Sr-tetramethylheptanedione and Sr-tetramethylheptanedione as the organometallic precursor to a strontium (Sr) component. A compound obtained by introducing at least one member selected from the group consisting of an alkyl group, a fluorine-substituted alkyl group, and an alkoxy group on a phenyl group of triphenylbismuth, At least one member of the group consisting of Bi-tetramethylheptanedione, Bi-alkoxide and Bi-acetylacetate is used, and for tantalum (Ta) component, Ta-ethoxide, Ta-isopropoxide, Ta- Tert-butoxide and At least one selected from the group consisting of Ta-ethoxide, Ta-isopropoxide and Ta-tert-butoxide alkoxy groups, wherein at least one of the alkoxy groups is partially substituted with tetramethylheptanedione 4. The method for producing a ferroelectric thin film according to claim 3, wherein: 12. The organometallic precursor further contains a niobium (Nb) component, and the niobium (Nb) component is mixed with Nb-ethoxide, Nb-isopropoxide, and Nb.
Tert-butoxide and Nb-ethoxide, N
At least one selected from the group consisting of compounds in which a part of at least one alkoxy group in the group consisting of b-isopropoxide and Nb-tert-butoxide is substituted by tetramethylheptanedione is used. The method for producing a ferroelectric thin film according to claim 11, wherein 13. at least strontium (Sr);
After mixing a carrier gas containing an organometallic precursor gas containing each component of bismuth (Bi) and tantalum (Ta) with an oxygen gas, the mixed gas is decomposed in a reaction chamber, deposited on a substrate, and oxidized. In the apparatus for manufacturing a ferroelectric thin film for forming an object thin film, a mixed region of a carrier gas containing the organometallic precursor gas and an oxygen gas is set in a predetermined range on the substrate according to a film composition. Manufacturing apparatus for a ferroelectric thin film. 14. A mixed region of a carrier gas containing an organometallic precursor gas and an oxygen gas is formed on the substrate by a range of 13 to 3
14. An area within a range of 3 cm.
An apparatus for manufacturing the ferroelectric thin film according to the above.