JP2003174028A - Manufacturing method for ferroelectric thin film, ferroelectric capacitor, and ferroelectric memory element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for directly manufacturing a bismuth-based ferroelectric thin film at a low crystallization temperature by an MOCVD method, and to provide a method for manufacturing a ferroelectric capacitor and a ferroelectric memory element. <P>SOLUTION: A ferroelectric thin film is formed by supplying an MOCVD feed gas with an alcohol gas used as a reaction-accelerating agent. When a bismuth laminar compound SrBi<SB>2</SB>Ta<SB>2</SB>O<SB>9</SB>or an SrBi<SB>2</SB>Nb<SB>2</SB>O<SB>9</SB>thin film is formed, metal alkoxide Bi(OR)<SB>3</SB>(R=alkyl), bimetal alkoxide Sr[Ta(OR)<SB>6</SB>]<SB>2</SB>, or bimetal alkoxide Sr[Nb(OR)<SB>6</SB>]<SB>2</SB>is used as a raw material. In this case, the bimetal alkoxide Sr[Ta(OR)<SB>6</SB>]<SB>2</SB>contains Ta and Sr so that the atom ratio is 2:1 in one molecule, and the bimetal alkoxide Sr[Nb(OR)<SB>6</SB>]<SB>2</SB>contains Nb and Sb in the atom ratio of 2:1 in one molecule. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric thin film, a ferroelectric capacitor and a ferroelectric memory device, and more particularly to a ferroelectric thin film capable of lowering the manufacturing process temperature, The present invention relates to a method for manufacturing a ferroelectric capacitor and a ferroelectric memory element.

[0002]

2. Description of the Related Art Ferroelectric materials have a spontaneous polarization, a high dielectric constant,
Since it has many functions such as electro-optical effect, piezoelectric effect, and pyroelectric effect, it has been applied to a wide range of device development. For example, it is used as an insulating film for a large-capacity capacitor of DRAM by utilizing the high dielectric constant of a ferroelectric substance, and is also used for a non-volatile memory utilizing the polarization reversal and remanent polarization characteristic of the ferroelectric substance, so to speak, hysteresis characteristic. ing.

There are roughly two types of memories that utilize the spontaneous polarization characteristics of ferroelectric substances. The first type is a normal DRAM type memory cell in which the memory capacitor material is replaced with a paraelectric material from a ferroelectric material. This is the difference in the current that flows through the ferroelectric capacitor when a voltage for writing and reading is applied by applying a voltage to the ferroelectric capacitor to set the polarization state, that is, the amount of charge stored in the ferroelectric capacitor. Is to detect the polarization state. The second type has a structure in which the gate insulating film of the MOS-FET is replaced with a ferroelectric material. This is to detect the polarization state by the difference in the current flowing through the channel portion between the source and drain corresponding to the polarization direction of the ferroelectric gate. The semiconductor device of the present invention belongs to the former.

As a first type ferroelectric memory cell, for example, a one-transistor + 1-capacitor structure (1T / 1 in which a selection transistor is added to a ferroelectric capacitor) is used.
Non-volatile memory cells having C) can be mentioned. This ferroelectric capacitor is composed of, for example, a lower electrode, an upper electrode, and a ferroelectric thin film sandwiched between them.

In order to realize a ferroelectric non-volatile memory by actually incorporating a ferroelectric substance into a semiconductor device, the ferroelectric substance is required to have the following characteristics. Large remanent polarization, small coercive electric field, high phase transition temperature (Curie temperature), low crystallization temperature, excellent environmental resistance (hydrogen and heat), and no fatigue phenomenon. Regarding the crystallization temperature of the ferroelectric substance, in order to obtain a crystal structure having ferroelectricity, it is necessary to perform heat treatment within a temperature range determined by the material. If this temperature is high, the underlying transistor layer may be adversely affected by reaction and mutual diffusion. Therefore, the lower crystallization temperature is preferable from the viewpoint of compatibility with the existing semiconductor manufacturing process.

As a ferroelectric material used for a capacitor or a semiconductor memory device, a large remanent polarization P can be obtained.
A lead-based oxide material having a perovskite structure represented by ZT (Pb (Zr _x , Ti _1-x ) O ₃ : lead zirconate titanate) was the mainstream. However, this type of ferroelectric material has a drawback that a fatigue phenomenon occurs in which the magnitude of spontaneous polarization decreases when polarization inversion is repeated. On the other hand, a bismuth layer structure compound, for example, SrBi ₂ Ta ₂ O ₉ (S
BT), SrBi ₂ Nb ₂ O ₉ (SBN) thin film is 10
^It has an excellent fatigue characteristic that the characteristic does not change even after ¹² or more polarization reversals, and in SBT, the electrolysis with which the polarization is saturated is small, which is advantageous for low voltage operation. Therefore, in recent years, bismuth compound materials have attracted attention and have been actively studied.

Regarding the method of forming a ferroelectric thin film such as a bismuth layered structure compound, at present, physical methods such as vacuum deposition method, sputtering method and laser ablation method, or organic metal compound as a starting material are used to heat these materials. Sol-gel method or MOD that decomposes and oxidizes to obtain an oxide ferroelectric
(Metal Organic Decomposit
Ion) method, LSMCD (Liquid Source)
Misted Chemical Depositi
on) method and MOCVD (Metal Organ)
ic Chemical Vapor Deposit
Ion) method and other chemical methods are used. The MOD method is easy to control the composition, has excellent reproducibility, enables large-area film formation under normal pressure, and has the advantages of being industrially low cost. Ferroelectric thin films exhibiting ferroelectric properties have been obtained. However, in order to apply it to a highly integrated memory, MOC with excellent step coverage, film quality, uniformity, suppression of particle generation, and processing speed.
There is a strong demand for development of the VD method.

In applying the MOCVD method, the selection of raw materials is an important point. The source material used for MOCVD has a sufficient vapor pressure at a low temperature, has a high decomposition temperature, does not decompose in the process of vaporization and transportation, maintains a stable vapor pressure for a long time, and has a stable vapor pressure in the vapor phase. It is required to have characteristics such as no reaction between source materials in the above. Also,
In order for the raw material gas to be constantly supplied at a saturated vapor pressure, it is also a condition that it is desirable that the liquid or gas is more preferable than the solid.

Regarding the formation of the bismuth layered compound thin film by using the MOCVD method, the inventor of the present application has already proposed the selection and production of the source raw material, and the transportation and treatment of the raw material, and obtained good results by this proposal. There is. For details, refer to Japanese Patent No. 3116768 (referred to as Document 1), "C.
Isobe et al., Integrated Ferroelectrics, p95-103,
1997 "(referred to as reference 2), and Japanese Patent No. 313700
No. 4 (referred to as Document 3).

Next, problems of the conventional method of manufacturing a ferroelectric thin film will be described with reference to FIGS. Figure 12
It is a schematic diagram of the conventional apparatus which produces | generates the thin film of a bismuth layered structure compound, for example using MOCVD method. FIG.
FIG. 3 is a flow chart showing a conventional process for producing a thin film of a bismuth layered structure compound by using the MOCVD method. Here, an example of forming a ferroelectric thin film made of SrBi ₂ Ta ₂ O ₉ by using a so-called flash MOCVD method in which a raw material is dissolved in a liquid, transported and mixed in a liquid phase, and vaporized by a vaporizer is used. And

The MOCVD apparatus of FIG. 12 comprises raw material containers 110 and 111 made of stainless steel, a liquid mixer 113 for mixing the raw material solutions in a liquid state from the respective raw material containers, and connecting the respective raw material containers and the liquid mixer 113. A pipe 114 made of stainless steel, an argon carrier gas is introduced, and a vaporizer 119 for vaporizing the mixed solution from the liquid mixer 113, the gas mixture from the vaporizer 119 and the oxygen gas introduced as an oxidant are mixed. Gas mixer 120,
A pipe 115 made of stainless steel connecting the vaporizer 119 and the gas mixer 120, a gas spraying head 121 for uniformly spraying the source gas from the gas mixer 120 onto the substrate surface, a substrate 122 on which a ferroelectric thin film is formed, It is composed of a substrate stage 123 supporting the substrate 122, a MOCVD reaction chamber 124 which is a place where a chemical reaction such as a source gas and an oxidant gas occurs, and a vacuum pump 125 for exhausting the MOCVD reaction chamber 124. The pipe 115
A heating means (not shown) such as a heater is arranged in the chamber to control the temperature so that the raw material gas flowing in the pipe does not aggregate. A heater (not shown) is incorporated in the substrate stage 123, and the substrate 122 can be heated to a desired temperature.

Next, please refer to the flow chart of FIG.
Gara, using the above equipment, the bismuth compound SrBi_TwoT
a_TwoO₉The process of forming the thin film of will be described. First,
For example, tantalum Ta and Sr are added in a ratio of 2: 1 in one molecule.
Bimetallic alkoxide raw material contained in a child ratio,
And bismuth source, eg triphenylbis
A mass is prepared, and for example, tetrahydrofuran (T
HF) and the like, and the raw material containers 110 and 111 are dissolved.
(Step S41). And of the above ingredients
The THF solution is independently liquid-mixed via a pipe 114.
It is conveyed to 113 and mixed at a determined ratio (step
S42). Next, add the above raw material mixture to an argon carrier.
It is introduced into the vaporizer 119 together with the agus and vaporized (step
S43). Next, the vaporized raw material mixture is
Mixed with gas and oxygen gas in the gas mixer 120,
Introduced into the reaction chamber 124, platinum (Pt) is formed into a film,
Spray on the substrate 122 held at about 400 ° C.,
Target bismuth compound SrBi _TwoTa_TwoO₉Same configuration as
Forming amorphous bismuth compound thin films containing elements
Yes (step S44). Then, the substrate 122 is set to about 70
Heat to 0-800 ° C and perform post-annealing (step
S47). As a result, the substrate 122 on which platinum is formed
Above, the desired SrBi_TwoTa_TwoO₉Crystal film can be formed
It

[0013]

As described above, the MOCV
Ferroelectrics such as SrBi using the D method_TwoTa_TwoO₉
In the conventional manufacturing method, first, at low temperature
(About 400 ℃) Amorphous structure (or Fluorite)
A thin film of high temperature processing (700
(C-800 ℃) (Bost annealing)
i-layered structure ferroelectric SrBi_TwoTa_TwoO₉Can get
it can. Using this two-step film formation process, 700 ° C
In the following, SrBi_TwoTa_TwoO ₉Can be fully crystallized
The crystal structure with remanent polarization required for ferroelectric memory.
Not obtained, but 700 ° C-800 ° C anneal temperature
A crystalline film having good electrical characteristics is obtained. That
Therefore, this method is widely used.

However, a temperature as high as 700 ° C. to 800 ° C. is not preferable because it is not compatible with the existing semiconductor manufacturing process. In such a high-temperature oxygen atmosphere, contact defects and characteristics due to mutual diffusion between the ferroelectric thin film and the lower electrode interface, oxidation of the contact plug material, and mutual diffusion between the contact plug material and the lower electrode and ferroelectric thin film. There are problems such as deterioration.

In particular, the ferroelectric memory has a capacity of 64-256 Mb.
In the case of high integration up to the it class, a ferroelectric capacitor is formed on the same plane as the select transistor of the memory cell used in the low capacity device. , Converted to a stack cell structure in which a ferroelectric capacitor connected via a contact plug is formed,
It is necessary to reduce the chip area. In the process of manufacturing such a compact structure, the influence of the above reaction and diffusion becomes larger. For example, the 70 required for crystallization of a bismuth compound film of a ferroelectric capacitor.
At a temperature of 0 ° C. or higher, diffusion and reaction occur between polysilicon or tungsten used for the plug and platinum Pt or iridium Ir used for the lower electrode of the ferroelectric capacitor,
The characteristics of the ferroelectric capacitor are greatly deteriorated.

In order to prevent this, an attempt to provide a diffusion prevention layer between the lower electrode and the plug is effective, but TiN which is widely used as a diffusion prevention layer is generally 600 to 650.
C is the upper limit temperature of the diffusion preventing function, and a material that sufficiently functions as a diffusion preventing layer at 700 ° C. or higher has not been found yet. Therefore, in order to apply a ferroelectric substance such as a bismuth layered structure compound to a highly integrated semiconductor memory device,
It is indispensable to develop a thin film manufacturing technology including thin film compactness and flattening, especially to lower the film forming temperature.

Up to now, various methods have been developed to lower the crystallization temperature of the bismuth layer structure compound. By improving the two-step process described above, sufficient electrical characteristics have not been obtained at post-annealing temperatures lower than 700 ° C. Further, for example, in Japanese Patent No. 2967189 (referred to as Document 4), a complex alkoxide (triple alkoxide) containing Sr, Bi, and Ta3 metals in one molecule.
Is synthesized, and the complex alkoxide is hydrolyzed to obtain a target SBT precursor. The molecular structure of the precursor is S
Since it is the same as the sublattice of the crystal structure of BT, the precursor was crystallized at a low temperature of 550 ° C. by a coating method such as spin coating to form a thin film of SBT.

Further, in Japanese Patent Laid-Open No. 11-97630 (referred to as reference 5), a thin titanium oxide film and a bismuth oxide film are sequentially formed at 450 ° C. or lower by MOCVD, and the same is formed on the bismuth oxide thin film. 450 ° C or less, MOC
A bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) layered compound could be formed by the VD method. According to Document 5, the bismuth oxide thin film having a low crystallization temperature becomes a buffer layer of bismuth titanate and acts as an initial nucleus of crystal. Since the crystal nucleation density is low on the Pt substrate, dense crystals cannot be grown.

Further, Japanese Laid-Open Patent Publication No. 10-223847 (referred to as Document 6) improves a spin coating process and uses a bismuth layer structure compound SrBi ₂ T by a 650 ° C. method.
It was possible to crystallize a ₂ O ₉ . In addition, in JP-A-9-69614 (referred to as reference 7) and JP-A-8-340084 (referred to as reference 8), the spin coating process is improved to improve the bismuth layer structure compound S.
An attempt was made to lower the crystallization temperature of BT.

However, Document 4 shows only the result of the spin coating method, and does not have the result of the MOCVD method required for manufacturing a highly integrated ferroelectric memory. Document 5 mainly shows the results of crystallization of a bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) layered compound at a low temperature, and it is claimed that it is effective for crystallization of Y1-based materials such as SBT. Not performed. References 6, 7, and 8 are improvements in the spin coating process, and there is no essential improvement.

In view of the above background, an object of the present invention is to produce a ferroelectric thin film directly by MOCVD without post-annealing and at a low temperature, and to produce a ferroelectric capacitor. A method and a method of manufacturing a ferroelectric memory device are provided.

[0022]

In order to achieve the above object, a method for producing a ferroelectric thin film according to the present invention is a method for producing a ferroelectric thin film by a chemical vapor deposition method, wherein: A raw material gas of a plurality of kinds of organometallic compounds containing a metal element that constitutes the ferroelectric thin film is supplied together with at least an alcohol gas as a reaction accelerator to form the ferroelectric thin film. By adding the alcoholic reaction accelerator, the crystallization temperature of the ferroelectric thin film is lowered.

When producing a bismuth layered compound, B
Metal alkoxide Bi (OR) ₃ containing i (R =
The composition of bismuth in the bismuth layered compound can be controlled by using, for example, alkyl) as a raw material and controlling the amount of the oxygen gas supplied as the oxidizing agent. Furthermore, in the case of producing a bismuth layered compound composed of SrBi ₂ Ta ₂ O ₉ , a bimetal alkoxide Sr containing Ta and Sr in the molecule at an atomic ratio of 2: 1.
[Ta (OR) ₆ ] ₂ is used as a raw material. Or Sr
When a bismuth layered compound composed of Bi ₂ Nb ₂ O ₉ is produced, a bimetal alkoxide Sr [Nb (Ob) containing Nb and Sb in a molecule at an atomic ratio of 2: 1 is produced.
R) ₆ ] ₂ (R = alkyl) is used as a raw material.

In order to achieve the above object, a method of manufacturing a ferroelectric capacitor according to the present invention comprises a step of forming a first electrode layer, and a chemical vapor deposition method on the first electrode layer. And a step of forming a second electrode layer on the ferroelectric thin film.
In the step of forming the ferroelectric thin film on the electrode layer by chemical vapor deposition, the raw material gases of a plurality of kinds of organometallic compounds containing a metal element forming the ferroelectric thin film are reacted at least with each other. It is supplied onto the first electrode layer together with an alcohol gas as a promoter to form the ferroelectric thin film. By adding the alcoholic reaction accelerator, the crystallization temperature of the ferroelectric thin film is lowered. Ferroelectric film bismuth layer compound of the ferroelectric capacitor, for _example, SrBi 2 _Ta 2 _{O 9,} or, SrBi ₂
When a bismuth layered compound made of Nb ₂ O ₉ is used, the raw material selection and the composition control when forming the film by the chemical vapor deposition method are the same as in the method for manufacturing the ferroelectric thin film.

In order to achieve the above object, a method of manufacturing a ferroelectric memory device according to the present invention includes a ferroelectric capacitor including a select transistor and a ferroelectric capacitor connected to one impurity diffusion region of the select transistor. A method of manufacturing a dielectric memory device, comprising: forming the select transistor in a predetermined region of a semiconductor substrate; forming an insulating film on a semiconductor substrate including the select transistor; Forming a conductive contact plug reaching one of the impurity diffusion regions of the transistor; forming a lower electrode layer of the ferroelectric capacitor connected to the conductive contact plug; and forming a lower electrode layer on the lower electrode layer. Forming a ferroelectric thin film of the ferroelectric capacitor by a chemical vapor deposition method, and forming the ferroelectric thin film on the ferroelectric thin film. And a step of forming an upper electrode layer of a capacitor, wherein in the step of forming the ferroelectric thin film on the lower electrode layer by a chemical vapor deposition method, a metal element forming the ferroelectric thin film is added. Supplying a plurality of kinds of organometallic compound raw material gas, and at least an alcohol gas as a reaction accelerator on the lower electrode layer,
The crystallization temperature of the ferroelectric thin film is lowered by adding the alcoholic reaction promoter that forms the ferroelectric thin film at a predetermined film forming temperature, and the film forming temperature is the lower electrode. The temperature is lowered below the temperature that causes a diffusion or chemical reaction in the vicinity of.

A bismuth layer compound such as Sr is formed on the ferroelectric film of the ferroelectric capacitor of the ferroelectric memory device.
Bi ₂ Ta ₂ O ₉ (SBT) or SrBi ₂ N
When a bismuth layered compound composed of b ₂ O ₉ (SBN) is used, the selection of raw materials and the control of the composition at the time of forming the film by chemical vapor deposition are controlled by the ferroelectric thin film and the ferroelectric thin film. This is the same as the method for manufacturing a capacitor.

The above-mentioned ferroelectric thin film and ferroelectric capacitor
According to the method of manufacturing a ferroelectric semiconductor device,
The crystallization temperature of the body thin film can be lowered. For example, SrBi_Two
Ta _TwoO₉The Bi layered compound consisting of
A crystal is formed at around 600 ° C, which is lower by about 100 ° C.
It becomes possible. The low temperature process brought about by this
Lowers the upper limit of heat resistance required for various barrier metals.
Can be used as a barrier metal
More choices for materials. As a result, directly above the transistor
It is easy to fabricate a stack structure cell in which a ferroelectric substance is placed in
It is possible to increase the integration density of ferroelectric non-volatile memory.
Can be converted. Also, the MOCVD method is used.
Since it forms a film, it is a thin film with high density and good surface coverage.
Can be formed. In addition, the cleanliness of the thin film is improved and productivity is improved.
Can be increased.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The ferroelectric thin film of the present invention is described below.
An embodiment of a method of manufacturing a ferroelectric capacitor and a ferroelectric semiconductor memory device will be described with reference to the accompanying drawings. In the present invention, alcohols (alcohol (R-OH), methanol (C
H ₃ -OH), ethanol _{(C 2} H 5 -OH), propanol _{(C 3} H 7 -OH), butanol _{(C 4} H 9 -O
H) or the like) as a reaction promoter to accelerate the reaction between the source gases, and thus the growth process of the thin film crystals, directly and at low temperature without heat treatment such as post-annealing. Grow thin film crystals from gas. The reason will be described below.

As is well known, the MOCVD method uses III-V.
This is a method that enables direct crystal growth without post-annealing, as typified by crystal growth of group compound semiconductors, and at the same time a clean and highly productive method required for semiconductor processes. The MOCVD method is widely used. MOCVD directly on ferroelectrics such as Bi layered compounds such as SBT without post annealing.
It is basically possible to grow crystals by the method, and it is considered that the crystallization temperature required for the direct crystal growth process is lower than the post-annealing temperature.

In the MOCVD method, the process of growing a crystal from the supplied raw material is a decomposition reaction of the raw material molecules,
And the progress of the oxidation reaction of the products of the decomposition reaction. It is considered that if the decomposition reaction and the oxidation reaction are efficiently performed at a low temperature, the product of the oxidation reaction can be crystallized at that temperature. In the MOCVD method, thermal energy is used as the decomposition energy of the decomposition reaction and oxygen is used as the oxidation energy of the oxidation reaction. Further, in order to efficiently carry out the decomposition reaction and the oxidation reaction, it is possible to add another energy source. Generally, energy additions such as plasma and light are widely used, but it is customary that the apparatus becomes complicated and the setting of film forming conditions becomes more difficult.

Therefore, as a simpler method, it is effective to add a reaction accelerator utilizing a chemical reaction. In the MOCVD method described above, alcohols (alcohols (R-OH), methanol _(CH 3 -OH), ethanol _{(C 2} H 5 -OH), propanol _{(C 3} H 7 -O
H), butanol _{(C 4} H 9 -OH) or the like)
Is introduced into the raw material gas, the decomposition reaction of the molecules of the raw material is promoted. This is because alcohols act as a nucleophile in the gas phase or on the surface of the substrate to accelerate the decomposition reaction through attack on the alkoxy group of the alkoxide raw material. Therefore, a lower substrate heating enables the same crystal growth.

[0032]First embodiment In this embodiment, as an example of generation of a ferroelectric thin film,
Wool Y1-based material such as SrBi_TwoTa_TwoO₉(S
BT) bismuth layered compound thin film is formed by MOCVD
A method of forming at a low film forming temperature will be described below. I mentioned above
As described above, when the MOCVD method is used, the raw material should be selected.
It becomes an event. As the source material used for MOCVD,
Must have sufficient vapor pressure at low temperature, have high decomposition temperature, and
Do not disassemble in the process of liquefaction and transportation, for a long time
Maintaining a stable vapor pressure, between source materials in the vapor phase
Characteristics such as no reaction of are required. Also, always tired
In order to supply the raw material gas at the state of Japanese vapor pressure,
It is also required that it should be liquid or gas rather than
Conditions. Traditional source material, even if
Sr (THD)_Two, Bi (C₆H ₅)_Three, Ta (O
C_TwoH₅)_FourDesired depending on the combination of (THD)
It is extremely difficult to control the composition. This is this
This is because the reactivity of these raw materials is sensitive to the substrate temperature.
In addition, the reactivity of each raw material has different temperature dependence.
This is because it is important. As mentioned above, the applicant of the present invention is
When the method D is used, selection and production of the source material,
We have already made good proposals regarding the transport and processing of raw materials
I'm getting results. The details are Japanese Patent No. 3116768
Report (Reference 1), “C. Isobe et al., Integrated Ferroel
ectrics, p95-103, 1997 ”(Reference 2) and Patent No. 3
No. 137004 (reference 3)
It In the present invention, selection of raw materials, production, transportation, and other
For processing, the method disclosed in the above publications is used.

FIG. 1 is a schematic view of an apparatus for producing a ferroelectric thin film according to the first embodiment of the present invention. The apparatus shown in FIG. 1 is an apparatus used in the MOCVD method, that is, a raw material is dissolved in a solvent, the raw material is transported and mixed in a liquid phase, and vaporized by a vaporizer. FIG. 2 is a flow chart showing a process of forming a ferroelectric thin film using the apparatus shown in FIG.

The MOCVD apparatus of FIG. 1 comprises a stainless steel source container (cylinder) 10, 11, and 1.
2, a liquid mixer 13 for mixing the raw material solution in a liquid state from each raw material container, a stainless steel pipe 14 connecting the raw material container and the liquid mixer 13, and a liquid mixer 13 A vaporizer (Vaporizer, Flash Vap) that vaporizes the mixed solution.
orizing zone) 19, a gas mixer (Gas Mixer) 20 for mixing oxygen gas as an oxidant, the vaporized mixed solution, and a carrier gas, a vaporizer 19
Pipe made of stainless steel that connects the gas mixer 20 with
5, a gas spraying head 21 for uniformly spraying the mixed raw material gas onto the surface of the substrate, a substrate 22 on which a ferroelectric thin film is deposited, a substrate stage 23 supporting the substrate 22, a chemical reaction of the raw material gas, an oxidant gas, etc. M where it happens
It comprises an OCVD reactor 24 and a vacuum pump 25 for exhausting the MOCVD reaction chamber 24.

In the MOCVD apparatus of FIG. 1, the vaporizer 1
A heating means (not shown) such as a heater is provided in the pipe 15 connecting the gas mixer 9 and the gas mixer 20, and the temperature is controlled so that the raw material gas flowing in the pipe does not aggregate. The raw material gas introduced into the MOCVD reaction chamber 24 is passed through the gas blowing head 21 and the substrate 2 placed on the substrate stage 23.
Sprayed on 2. A heater (not shown) is incorporated in the substrate stage 23 to heat the substrate 22 to a desired temperature. In the MOCVD reaction chamber 24,
It is exhausted by the vacuum pump 25. By producing an organometallic raw material containing a metal element that constitutes the desired ferroelectric substance,
It is possible to introduce the above-mentioned device, vaporize and react these raw materials in the device, and form a ferroelectric thin film.

Next, referring to FIG. 2, the above MOC
A specific example of the method of manufacturing the ferroelectric thin film of the present embodiment using the VD device will be described. This specific example is an example in the case of manufacturing a ferroelectric thin film having a composition of SrBi ₂ Ta ₂ O ₉ (SBT). Step S1: First, the raw materials necessary for forming the SBT thin film are prepared. In this embodiment, as a raw material of Sr and Ta, the alkaline earth metal Sr and Ta are 1: 2 in one molecule.
Alkoxide raw material contained at an atomic ratio of, so-called bimetallic alkoxide Sr [Ta (OC
₂ H ₅ ) ₆ ] ₂ is used as a source material. As already shown in Reference 1, the bimetallic alkoxide raw material is effective in producing a bismuth layered compound.

The bimetallic alkoxide raw material is prepared as follows. First, a tantalum alkoxide compound, for example, Ta (OC ₂ H ₅ ) ₅ is selected and dissolved in an alcohol, preferably absolute ethanol, to give 0.5M.
A solution having a concentration of about 1 / l is prepared. Next, the alkaline earth metal Sr is weighed so as to have an atomic composition of Ta: Sr = 2: 1 and dispersed in the above alcohol solution. Then, the alcohol solution is refluxed for several days to synthesize an alcohol solution of a bimetallic alkoxide compound having a desired composition. These operations are preferably carried out in a stream of dry nitrogen or argon gas. At this time, hydrogen gas is generated as shown in the following chemical reaction. 2Ta (OC ₂ H ₅ ) ₅ + Sr + 2C ₂ H ₅ OH → SrTa ₂ (OC ₂ H ₅ ) ₁₂ + H ₂ ↑ The raw material solution prepared here is dissolved in an organic solvent THF as described later, Fill the raw material containers 10 and 11, respectively.

Alkoxy bismuths such as Bi (O- ^t C ₄ H ₉ ) ₃ are used as a raw material of Bi.
(Bi (C ₆ H ₅ ) ₃ , DPM which has been used conventionally
Combinations such as Bi (DPM) ₃ which is a complex are also possible. )

In the present embodiment, as a reaction accelerator of the above-mentioned raw material bimetallic alkoxide Sr [Ta (OC ₂ H ₅ ) ₆ ] ₂ and alkoxybismuth Bi (O- ^t C ₄ H ₉ ) ₃ , alcohol (R- OH), methanol (C
H ₃ -OH), ethanol _{(C 2} H 5 -OH), propanol _{(C 3} H 7 -OH), butanol _{(C 4} H 9 -O
The raw material container 12 is filled with a solution of any alcohol such as H), for example, ethanol. The addition amount of ethanol is, for example, 0.1 to 5% with respect to the lower two types of organic metal raw materials.

Step S2: Subsequently, the liquid raw material produced above is conveyed. The bimetallic alkoxide material (Sr [Ta (OC ₂ H ₅ ) ₆ ] ₂ ) is a solid at room temperature, and heating at 150 ° C. to 200 ° C. is necessary to gasify it as a source material for MOCVD. is there.
Generally, it is not easy to gasify such a low vapor pressure material, and it is necessary to devise a gas supply method in order to perform stable gas supply and form a film by the MOCVD method. As one method, the MOCV adopted in this embodiment is used.
Method D. That is, the solid source material is dissolved, dissolved in an organic solvent, conveyed, mixed, and flash vaporized.
Specifically, the bimetallic alkoxide Sr [Ta (O
C ₂ H _{5) 6] 2} and alkoxy bismuth Bi ^(O-t C
₄ H ₉ ) ₃ is, for example, tetrahydrofuran (T
HF) Dissolved in an organic solvent, the solutions are filled in the raw material containers 10 and 11, respectively, and the raw material solutions of both kinds and the ethanol solution filled in the raw material container 12 are independently conveyed in a liquid state.

The three kinds of solutions are conveyed to the liquid mixer 13 through the pipe 14, and are mixed at a predetermined ratio (for example, Sr [T
_{a (OC 2 H 5) 6} ] 2): Bi (O- t C 4 H 9) 3
= 4: 6) Mix with the liquid mixer 13. Raw material container 10
The transport amount of the organometallic raw materials filled in Nos. 11 and 11 is, for example, 0.1 to 0.5 ml / min, while the transport amount of the ethanol liquid filled in the raw material container 12 is 0.01 to 0.5 ml / min. It is 0.05 ml / min.

Step S3: Next, the raw material mixture from the liquid mixer 13 is vaporized with the argon carrier gas in the vaporizer 19.
It is introduced and vaporized. For example, if the inside of the vaporizer 19 is 0.
Reduce pressure to 1-10 Torr and heat to 140 ° C. The flow rate of the argon carrier gas is 200 cc, and the mixed solution introduced under heating and reduced pressure is diffused and vaporized on the porous metal plate arranged in the vaporization chamber. Sr [Ta
_{(OC 2 H 5) 6]} 2 and ^{_{Bi (O- t C 4 H 9}} ) 3
It is also possible to use a compound obtained by substituting a part of these compounds with different substituents, using as a basic raw material structure. By the replacement, it is possible to increase vaporization characteristics and thermal stability. As an example, Sr [Ta (OC ₂ H ₅ )
₅ (OC ₂ H ₄ OCH ₃ )] ₂ , Sr [Ta (OC ₂ H
₅ ) ₆ (OC ₂ H ₄ N (CH ₃ ) ₂ )] _{2 and the} like.

Step S4: Subsequently, a mixture of the raw material gas from the vaporizer 19, the alcohol gas, and the argon carrier gas is introduced into the gas mixer 20 together with the oxygen gas as the oxygen agent through the pipe 15. Mix it.
As described above, the pipe 15 is provided with a heating means (not shown) such as a heater, and the source gas flowing in the pipe is
The temperature of the raw material is kept at 0 ° C to 200 ° C. It is important that oxygen is uniformly mixed in the gas mixer 20 that mixes the source gas, the alcohol gas, and the argon carrier gas with the oxygen gas. Therefore, a shielding plate that promotes mixing is installed in the gas mixer.

The mixture of the raw material gas, the alcohol gas, the oxygen gas, and the argon carrier gas from the gas mixer 20 is introduced into the reaction chamber 24 through the heated pipe and is conveyed to the surface of the substrate 22. The mixed gas is uniformly supplied to the surface of the substrate 22 by the spraying head 21 to form a film on the substrate 22. The substrate 22 has Ti, T
An adhesive layer made of iO2, TiN, IrHf, or the like, having the outermost surface formed of Pt or Ir, is used. Reaction chamber 24
The internal pressure is 1 Torr, and the temperature of the substrate 22 is about 600.
It is about ℃. As a result, for example, a bismuth-based ferroelectric thin film made of Bi, Sr, and Ta is formed on a platinum (Pt) substrate.

SrBi ₂ Ta produced as described above
The thin film ₂ O _9, X-ray diffraction (X-Ray Dif
Fraction: XRD) measurement was performed to determine the crystallographic orientation of the crystal phase and the thin film. FIG. 3 shows a diffraction pattern (XRD pattern) obtained by X-ray diffraction measurement. In FIG. 3, the vertical axis represents the relative intensity of the measured X-rays, for example,
It represents the number of counts, and the horizontal axis is the angle with respect to the incident X-rays that the X-rays diffracted by a certain crystal plane in the thin film to be measured have passed through the crystal plane. It becomes twice the incident angle θ with respect to the crystal plane (2θ). Figure 3
Then, SrBi ₂ Ta ₂ O _{9 having} a perovskite crystal structure is used.
The peak corresponding to the (115) crystal plane peculiar to the is clearly shown. Then, Sr of the perovskite crystal structure
Diffraction peaks corresponding to crystal planes such as (200) and (006) peculiar to Bi ₂ Ta ₂ O ₉ also appear. This means that the formed SrBi ₂ Ta ₂ O ₉ thin film is a crystal thin film having a desired perovskite structure. Therefore, the crystal structure of the bismuth-based ferroelectric thin film made of Bi, Sr, and Ta can be directly (in one step) formed on a platinum (Pt) substrate, and heat treatment (post-annealing) is required. Disappears.

In the MOCVD method, the introduction of alcohols into the raw material gas promotes the decomposition reaction of the raw material molecules, and the growth of the ferroelectric thin film crystal on the Pt film on the substrate at a relatively low temperature. Made possible.

[0047] SrBi ₂ Ta ₂ to derive the ferroelectric properties of O ₉ as _sufficient, SrBi 2 _Ta 2 _{O 9} ratio of each element constituting the, i.e. desired composition and the composition ratio (Bi /
It is important to precisely control so that Sr / Ta = 2/1/2). Bimetallic source Sr [Ta
By using (OC ₂ H ₅ ) ₆ ] ₂ , Sr: Ta
Is always kept constant and does not change significantly depending on the film forming conditions. On the other hand, when a ^{_{Bi (O- t C 4 H 9}} ) 3 to Bi source, Bi quantity introduced into the film can be controlled by various film forming conditions. For example, the desired composition (Bi /
Sr / Ta = 2/1/2) so that the flow rate of oxygen gas as an oxidant, the pressure in the reaction chamber 24, and the liquid mixer 13
The mixing ratio of the raw material solution in step 1 is adjusted.

FIG. 4 shows an example of such control. Figure 4
Then, the horizontal axis represents the flow rate of oxygen. The vertical axis on the left side is the atomic ratio of Bi and Ta in one molecule (Bi / Ta) in the bismuth layered compound SrBi ₂ Ta ₂ O ₉ obtained above, and the composition of Bi in the thin film is It represents. The vertical axis on the right side is the bismuth layered compound SrBi ₂ Ta ₂ O obtained above.
_{In 9} , the atomic ratio of Sr and Ta in one molecule (Sr / T
It is a), and represents the composition of Sr in the thin film. Therefore, FIG. 4 shows that in the formed crystalline thin film of SrBi ₂ Ta ₂ O ₉ with respect to Ta, the composition of Bi and Sr (Bi / T
a and Sr / Ta) show the dependence on the flow rate of oxygen.
As can be seen from FIG. 4, the bimetallic source Sr [Ta
Since (OC ₂ H ₅ ) ₆ ] ₂ is used, Sr: Ta is always kept constant (about 1: 2) and is independent of the oxygen flow rate. On the other hand, the in-film Bi can be set to a desired amount by changing the oxygen flow rate. For example, since Bi / Ta becomes 1, the flow rate of oxygen should be around 50%.

According to the method of manufacturing the ferroelectric thin film of the present embodiment, the bismuth layer compound composed of SrBi ₂ Ta ₂ O _{9 is} lower than the conventional film forming temperature by about 100 ° C. 60
A crystal thin film can be formed at around 0 ° C. The resulting low temperature process can lower the upper limit of heat resistance required for various barrier metals, increasing the choice of materials that can be used as barrier metals. As a result, it becomes possible to easily manufacture a stack structure cell in which the ferroelectric substance is arranged directly above the transistor. Further, in the present embodiment, the bismuth layered compound is formed by MOCVD.
Since the film is formed by the method, a thin film having high density and good surface coverage can be formed, and the cleanliness of the thin film can be increased and the productivity can be increased.

[0050]Second embodiment The aforementioned SrBi_TwoTa_TwoO₉Changed the Ta site to Nb
Curie point and dielectric properties
Is known to change. For example, 25% of Ta
When is replaced by Nb (SrBi_Two(Ta_0.75
Nb_0.25) _TwoO₉), Which is an index of ferroelectric properties
While the polarization value increases, the hysteresis loop is rectangular
It is known that the sex improves. Therefore, this embodiment
At SrBi_TwoNb_TwoO₉Bi consisting of (SBN)
Method for forming thin film of smuth layered compound by MOCVD method
Will be explained. FIG. 5 shows a ferroelectric thin film according to this embodiment.
It is a schematic diagram of the apparatus which produces | generates. The device is basically as shown in FIG.
The same as the MOCVD apparatus shown, except that in FIG.
In the apparatus, the raw material liquid filled in the raw material container 30 is Sr [Ta
(OC_TwoH₅)₆]_TwoAnd Sr [Nb (OC_TwoH₅)₆]
_TwoIt is a mixture with.

The apparatus of FIG. 5 is as shown in the flow chart of FIG.
To produce a ferroelectric thin film crystal. First, SrB
i_TwoTa_TwoO₉(75%) + SrBi_TwoNb_TwoO₉(2
(5%) to prepare the raw materials necessary to form a thin film. Real
In the embodiment, as a raw material of Sr and Ta, the
Contains the alkaline earth metals Sr and Ta in an atomic ratio of 1: 2
Alkoxide raw material, so-called bimetallic alcohol
Xide Sr [Ta (OC_TwoH₅)₆]_TwoThe source material and
To use. In addition, as a raw material for Sr and Nb,
Alkaline earth metal Sr and Nb in an atomic ratio of 1: 2
Alkoxide raw material contained, so-called bimetallic
Alkoxide Sr [Nb (OC_TwoH₅)₆]_TwoThe source
Used as a raw material. The atomic ratio of Ta and Nb is 3: 1
So that Sr [Nb (OC_TwoH₅)₆] _TwoIs 1 mole pair
Sr [Ta (OC_TwoH₅)₆]_TwoBoth at a ratio of 3 moles
The mixed raw material obtained by mixing is, for example, tetrahydrofuran.
(THF) Dissolve in organic solvent and fill raw material container 30
It

Alkoxy bismuths such as Bi (O- ^t C ₄ H ₉ ) ₃ are used as a raw material of Bi. Combinations of Bi (C ₆ H ₅ ) ₃ , which has been used conventionally, and Bi (DPM) _3, which is a DPM complex, are also possible. The raw material is, for example, tetrahydrofuran (THF)
It is dissolved in an organic solvent and filled in the raw material container 11.

In this embodiment, the mixed bimetallic alkoxide [(Sr [Ta (OC ₂ H ₅ ) ₆ ]] is used.
_{2) (75%) + (} Sr [Nb (OC 2 H 5) 6] 2)
(25%)] and alkoxy bismuth Bi ^(O- _{t C} 4 H
₉ ) As the reaction accelerator of _3, the raw material container 12 is filled with any solution of alcohols, for example, ethanol.

Then, the three kinds of solutions are conveyed to the liquid mixer 13 through the pipe 14, and at a predetermined ratio (for example,
_{Sr [Ta (OC 2 H 5} ) 6] 2): Bi (O- t C 4
_{H 9) 3 - 1: 2} ) mixed in a liquid mixer 13. The carry amounts of the three types of solutions are the same as in the first embodiment.

Subsequently, the above raw material mixture was charged with argon gas.
It is introduced into the vaporizer 19 together with the rear gas and vaporized. Sr
[Nb (OC_TwoH₅)₆]_TwoVaporization characteristics of Sr [Ta
(OC_TwoH₅)₆] _TwoIs very similar to
Therefore, under the same vaporization conditions as in the first embodiment,
For example, depressurize the inside of the vaporizer 19 to 0.1 to 10 Torr.
And heat to 140 ° C. Argon carrier gas flow
Amount of 200cc, mixed solution introduced under heating and reduced pressure
Diffuse liquid on porous metal plate placed in vaporization chamber
Vaporize with.

Subsequently, a mixture of the vaporized raw material, ethanol, and an argon carrier gas is mixed with oxygen gas as an oxygen agent in the gas mixer 20 through the pipe 15 and introduced into the reaction chamber 24. , Ti, TiO2, Ti
The substrate 22 is formed by spraying Pt (or Ir) on the outermost surface with N, IrHf, etc. as an adhesive layer.
A film is formed on top. The pressure in the reaction chamber 24 is 1 Torr,
The temperature of the substrate 22 is about 600 ° C. As a result, on the substrate of the platinum (Pt), Bi, Sr, Ta, consisting _{Nb (Sr [Ta (OC 2} H 5) 6] 2) (75%) + (S
A ferroelectric thin film having a crystal structure of r [Nb (OC ₂ H ₅ ) ₆ ] ₂ ) (25%) is formed.

In order to sufficiently bring out the ferroelectric characteristics of the ferroelectric thin film, the ratio of each element constituting the ferroelectric substance,
That is, it is important to precisely control the composition ratio so as to obtain a desired composition. (Sr [Ta (OC ₂ H ₅ ) ₆ ]
_{2) (75%) + (} Sr [Nb (OC 2 H 5) 6] 2)
In (25%), Sr: Ta, Sr: Nb, Ta:
Since Nb is always kept constant, only the amount of Bi needs to be controlled. The amount of Bi introduced can be controlled by various film forming conditions such as the flow rate of oxygen gas as an oxidant, the pressure in the reaction chamber 24, and the mixing ratio of the raw material solution in the liquid mixer 13.

The method for producing a ferroelectric thin film crystal according to this embodiment has the same effect as that of the first embodiment.

Third Embodiment Although the source material vaporization method described above is a so-called liquid supply method, a so-called bubbling method in which a carrier gas is introduced into a source material filled in a stainless steel material container and vaporized is also used. It can also be adopted. In this embodiment, a film forming method by a bubbling method will be described.

FIG. 6 is a schematic view of an MOCVD apparatus relating to the method of manufacturing a ferroelectric thin film of this embodiment. In FIG. 6, the same reference numerals are used for the same constituents as in FIG. FIG. 7 is a flow chart showing a process of forming a ferroelectric thin film using the above apparatus. MOCV shown in FIG.
Device D is a stainless steel raw material container 70, 7
1, 72, constant temperature baths 76, 77, 78, a gas spray head 21 for uniformly spraying the source gas onto the substrate surface,
From the substrate 22 on which the ferroelectric thin film is deposited, the substrate stage 23 supporting the substrate 22, the MOCVD reaction chamber 24, the stainless steel pipe 74 connecting the raw material container and the MOCVD reaction chamber 24, and the vacuum pump 25 for discharging the used gas. It is configured. The constant temperature baths 76, 77, 78 are the raw material containers 7
The structure is such that the raw materials in 0, 71 and 72 are maintained at a desired temperature. A heating means (not shown) such as a heater is arranged in the pipe 74, and the raw material gas flowing in the pipe can be maintained at a desired temperature. The raw material gas introduced into the MOCVD reaction chamber 24 is blown onto the substrate 22 placed on the substrate stage 23 via the gas blowing head 21.
As a result, a thin film is formed on the surface of the substrate 22. A heater (not shown) is incorporated in the substrate stage 23 to heat the substrate 22 to a desired temperature. The inside of the MOCVD reaction chamber 24 is evacuated by the vacuum pump 25.

Next, an example of the ferroelectric thin film manufacturing method of the present embodiment will be described using the MOCVD apparatus described above with reference to the flowchart of FIG. This specific example is an example in the case of manufacturing a ferroelectric thin film made of SrBi ₂ Ta ₂ O ₉ (SBT). First, SrBi ₂ Ta
₂ O ₉ (SBT) is a raw material necessary for forming a thin film (step S71). In this embodiment, the same raw material as in the first embodiment is used. That is, as a raw material for Sr and Ta, the alkaline earth metal Sr and Ta are in a ratio of 1: 2 in one molecule.
Raw material containing so-called bimetallic alkoxide Sr [Ta (OC ₂ H ₅ ) ₆ ]
₂ is used as a source material. As Bi raw material, alkoxy bismuth compound, ^{_{e.g., Bi (O- t C 4 H}} 9)
₃ is used. Bi (C ₆ H ₅ ) which has been conventionally used
₃ and a combination of Bi (DPM) ₃ which is a DPM complex and the like. As a reaction accelerator in the raw material bimetallic alkoxide _{Sr [Ta (OC 2 H 5} ) 6] 2 and alkoxy bismuth ^{_{Bi (O- t C 4 H 9}} ) 3, either a solution of alcohols, such as ethanol also prepared To do. The method for producing the above raw materials is the same as in the first embodiment. The prepared raw material solution bimetallic alkoxide S
r [Ta (OC ₂ H ₅ ) ₆ ] ₂ and alkoxybismuth B
^{_{i (O- t C 4 H 9}} ) 3, and an ethanol solution of reaction accelerator respectively in the raw material containers 70, 71 and 72.

Subsequently, the melt in the raw material containers 70, 71, 72 is melted.
The liquid is conveyed to the gas mixer 20 (step S72). M
When performing the OCVD method, the raw material container 70 is filled with
Bimetallic alkoxide Sr [Ta (OC
_TwoH₅)₆]_TwoHeating the solution to, for example, 140 ° C.,
Alkoxybismuth Bi (O
−^tC_FourH₉)_ThreeIs heated to, for example, 120 ° C.
Add the ethanol solution filled in the chemical container 72 to 150 ° C.
Heat and heat each raw material container at a flow rate of 100-300 cc / min
Introduce argon gas and heat under reduced pressure to produce a bimetallic alloy.
Lucoxide Sr [Ta (OC_TwoH₅) ₆]_Two, Arcoki
Sibismuth Bi (O-^tC_FourH₉)_Three, And Ethan
Vaporize the solution. Then, the vaporized raw material and gas
Introducing the knoll into the pipe 74 kept at about 150 ° C.,
Send to gas mixer 20. The transfer amount of the three kinds of solutions is the first
Is the same as the embodiment of.

The flow rate of the mixed gas of the raw material gas and the gaseous ethanol from the gas mixer 20 is 100 cc / min.
Together with the oxygen gas and the diluting argon gas are uniformly placed on the substrate stage 22 by the spraying head 21 and sprayed onto the substrate 22, and then onto the substrate 22 with SrBi.
₂ Ta ₂ O ₉ grows. The substrate temperature is maintained at about 600 ° C.

In the above thin film formation process by MOCVD,
Also, the gaseous ethanol is MOCVD in the reaction chamber 24.
Bimetallic alkoxide Sr [Ta
(OC _TwoH₅)₆]_TwoAnd alkoxy bismuth Bi (O-
^tC_FourH₉)_ThreeIt promotes the decomposition reaction of
SrBi at high substrate temperature_TwoTa_TwoO₉Crystal growth of
Become.

As in the first and second embodiments, Sr
In order to sufficiently bring out the ferroelectric characteristics of Bi ₂ Ta ₂ O ₉ , the ratio of each element constituting SrBi ₂ Ta ₂ O ₉
That is, the composition ratio is set to the desired composition (Bi / Sr / Ta = 2 /
It is necessary to control precisely so that it becomes 1/2). By using bimetallic Sr [Ta (OC ₂ H ₅ ) ₆ ] ₂ as a raw material, Sr: Ta is always kept constant and does not fluctuate significantly depending on film forming conditions. On the other hand, Bi
When using ^{_{Bi (O- t C 4 H 9}} ) 3 to the source, Bi quantity introduced into the film, for example, the oxygen gas flow rate, the reaction chamber 2
It is possible to control by various film forming conditions such as the pressure inside 4.

According to the method of manufacturing a ferroelectric thin film of the present embodiment, SrBi ₂ Ta ₂ O ₉ which is a representative of bismuth layered compound ferroelectrics, which is important in manufacturing a ferroelectric memory,
At around 600 ° C, which is about 100 ° C lower than the conventional film formation temperature,
It is possible to form a crystalline thin film. The resulting low temperature process can lower the upper limit of heat resistance required for various barrier metals, increasing the choice of materials that can be used as barrier metals. as a result,
It becomes possible to easily manufacture a stack structure cell in which the ferroelectric substance is arranged directly above the transistor. Further, in the present embodiment, since the bismuth layered compound is formed by MOCVD, a thin film having a high density and good surface coverage can be formed, the cleanliness of the thin film can be improved, and the productivity can be improved. You can

Fourth Embodiment The present embodiment relates to a ferroelectric capacitor having a ferroelectric thin film by MOCVD method and a method for manufacturing a semiconductor memory device including the ferroelectric capacitor. The semiconductor memory device according to the present embodiment is composed of a cell of the ferroelectric non-volatile memory cell FeRAM having the above-mentioned 1-transistor + 1-capacitor (1T / 1C) structure.

FIG. 8A is a schematic partial cross-sectional view of a FeRAM memory cell manufactured based on the capacitor manufacturing method of this embodiment, and FIG. 8B is an equivalent circuit of the memory cell. Indicates. The memory cell shown in FIG. 8 has a capacitor structure in which a lower electrode layer 52, a ferroelectric thin film 53 and an upper electrode layer 54 are laminated, and a silicon semiconductor substrate 40.
A source / drain region 44, a channel region 45, and a gate electrode 43 formed above the channel region 45, that is, a so-called select transistor, that is, a 1T / 1C configuration. The ferroelectric thin film 53 is composed of, for example, SrBi ₂ Ta ₂ O ₉ . The memory cell further has an element isolation region 41 having a LOCOS structure and a gate oxide film 42 formed under a gate electrode 43.

The gate electrode 43 also serves as a word line, and is made of, for example, polysilicon, polycide, or metal silicide. The source / drain region 44 and the gate electrode 43 are covered with the insulating layer 50. The insulating layer 50 is, for example, BPSG.
Consists of.

In the capacitor structure of this memory cell, the lower electrode layer 52 made of Pt (platinum) is BPSG.
Is formed on the insulating layer 50. Further, a ferroelectric thin film 53 made of SrBi ₂ Ta ₂ O ₉ which is a bismuth layered ferroelectric thin film is formed on the lower electrode layer 52. Further, an upper electrode layer 54 made of Pt is formed on the ferroelectric thin film 53.

An upper insulating layer 60 made of, for example, BPSG is formed on the insulating layer 50, the lower electrode layer 52 and the upper electrode layer 54.
Are formed. A contact plug 65 is formed in the insulating layer 50 and the upper insulating layer 60 above one of the source / drain regions 44 (for example, the source region), and the contact plug 65 has one source at the bottom thereof. -Electrically connected to the drain region 44. Also on the upper insulating layer 60 above the lower electrode layer 52,
A contact plug 66 is formed. The lower electrode layer 52 is electrically connected to one of the source / drain regions 44 via the contact plug 66, the first wiring layer 68, and the contact plug 65. In addition, the upper electrode layer 54 is connected to the second wiring layer 69 through the contact plug 67 formed above the upper electrode layer 54.
Is electrically connected to. The second wiring layer 69 corresponds to a plate line.

The other source / drain region 44 (eg drain region) is electrically connected to a bit line (not shown) via a bit contact portion (not shown).

The method of manufacturing the semiconductor device according to this embodiment will be described below with reference to FIGS. First, as shown in FIG. 9A, a silicon semiconductor substrate 40
Then, the element isolation region 41 having a LOCOS structure is formed by a known method. Next, the surface of the semiconductor substrate 40 is oxidized to form the gate oxide film 42. Then, after depositing a polysilicon layer on the entire surface by, for example, a CVD method, the polysilicon layer is patterned by a photolithography technique and an etching technique to form a gate electrode 43 made of polysilicon. Then, ion implantation of impurity ions and activation of the implanted impurities are performed to form the source / drain regions 44 and the channel region 45. The gate electrode 43 also serves as a word line.

Next, on the semiconductor substrate 40, for example, BPS
The insulating layer 50 made of G is formed by the CVD method. Thus, the structure shown in FIG. 9A can be obtained. In addition,
After forming the insulating layer 50 made of BPSG, it is preferable to reflow the insulating layer 50 in a nitrogen gas atmosphere at 900 ° C. for 20 minutes, for example. Furthermore, if necessary, the top surface of the insulating layer 50 is chemically and mechanically polished by, for example, a chemical mechanical polishing method (CMP method) to planarize the insulating layer 50, and the insulating layer 50 is insulated by an etch back method. It is desirable to planarize layer 50. The film forming temperature of the insulating film 50 is 400 ° C.

Next, as shown in FIG. 9B, the insulating layer 5
The lower electrode layer 52 is formed on the upper surface of the substrate 0. That is, the lower electrode layer 52 made of Pt is deposited on the insulating layer 50 by the RF magnetron sputtering method. The thickness of the lower electrode layer 52 was set to 0.1 to 0.2 μm. After that, the lower electrode layer 52 is patterned into a desired shape by using, for example, an ion milling technique. The film forming temperature in the RF magnetron sputtering method is 600 to 750 ° C.

Then, MOCVD is performed on the lower electrode layer 52.
A ferroelectric thin film 53 made of SrBi ₂ Ta ₂ O ₉ (SBT) is formed by the method. Specifically, under the same conditions as the method for forming the ferroelectric thin film described in the first and third embodiments, the organometallic compound bimetallic alkoxide Sr is used.
[Ta (OC ₂ H ₅ ) ₆ ] ₂ and alkoxybismuth Bi
The ^{_{(O- t C 4 H 9)}} 3 as a source gas, alcohols, for example, a gaseous ethanol as a reaction accelerator, 6
FIG. 9C shows the MOCVD method at a film forming temperature of 00 ° C.
As described above, the ferroelectric thin film 53 made of the bismuth layered ferroelectric thin film SrBi ₂ Ta ₂ O ₉ is formed on the lower electrode layer 52.
To form a film.

After that, the upper electrode layer 54 is formed on the ferroelectric thin film 53. The upper electrode layer 54 is made of Pt and can be formed by the same method as the lower electrode layer 52.

Next, the upper electrode layer 54 made of Pt is patterned into a desired shape by using, for example, the ion milling technique, and further, the ferroelectric thin film 53 is patterned by the RIE method. Thus, the capacitor structure shown in FIG. 10A can be obtained.

Next, as shown in FIG. 10B, an upper insulating layer 60 made of, for example, BPSG is formed on the insulating layer 50, the lower electrode layer 52 and the upper electrode layer 54. In addition,
After forming the upper insulating layer 60, the upper insulating layer 60 is preferably flattened. Then, the opening 61 is formed in the insulating layer 50 and the upper insulating layer 60 above the one source / drain region 44 by using the photolithography technique and the etching technique. In addition, the openings 6 are formed in the upper insulating layer 60 above the lower electrode layer 52 and above the upper electrode layer 54.
2, 63 are formed.

Then, as shown in FIG. 11, each opening 6
On the upper insulating layer 60 including the inside of 1, 62, 63, for example,
After forming the Ti layer and the TiN layer by the sputtering method,
Aluminum alloy on the N layer (eg Al-1% Si)
The wiring material layer 64 made of is formed by the so-called high temperature aluminum sputtering method. The film forming conditions for the Ti layer, the TiN layer, and the wiring material layer made of an aluminum alloy are illustrated below. The reason for forming the Ti layer and the TiN layer is to obtain a low ohmic contact resistance, to prevent the semiconductor substrate 40 from being damaged by the wiring material layer made of an aluminum alloy, and to improve the wettability of the aluminum alloy. is there.

Thus, the openings 61, 62, 63 have
An aluminum alloy is embedded to form contact plugs 65, 66, 67. Note that the TiN layer and the Ti layer are not shown in FIGS. 8A and 11. After that, the wiring material layer 64, T on the upper insulating layer 60,
The iN layer and the Ti layer are patterned to form a first wiring layer 68 and a second wiring layer 69 as shown in FIG.

The wiring material layer made of an aluminum-based alloy was formed by the so-called high temperature aluminum sputtering method, but the present invention is not limited to such a film forming method, and the so-called high temperature reflow method or high pressure reflow method is used. You can also do it. In the high temperature reflow method, a wiring material layer made of an aluminum alloy is deposited on the upper insulating layer 60 under the conditions exemplified below. The substrate heating temperature at this time is 150
° C.

After that, the semiconductor substrate 40 is heated to about 500 ° C. As a result, the wiring material layer made of an aluminum-based alloy deposited on the upper insulating layer 60 is brought into a fluid state, flows into the openings 61, 62, 63, and the opening 6 is formed.
1, 62 and 63 are securely filled with an aluminum alloy to form contact plugs 65, 66 and 67. On the other hand, a wiring material layer made of an aluminum alloy is left on the upper insulating layer 60. Heating temperature is 500 ° C
Is.

Here, a heating method called a substrate backside gas heating method is used, that is, the heater block arranged on the backside of the semiconductor substrate 40 is heated to a predetermined temperature (heating temperature),
This is a method of heating the semiconductor substrate 40 by introducing a process gas between the heater block and the back surface of the semiconductor substrate 40. As the heating method, other than this method, a lamp heating method or the like can be used.

In this embodiment, the lower electrode layer is Pt.
Instead of being composed of, for example, La-Sr-Co-O (LSCO) having a perovskite structure may be used alone or may be composed of two layers of LSCO / Pt from the bottom.

According to the method of manufacturing the ferroelectric memory element according to the present embodiment, the crystallization temperature of the bismuth layer compound thin film of the ferroelectric capacitor is 100 ° C. higher than the conventional film forming temperature.
The temperature is about 600 ° C. which is low to some extent, whereby the upper limit of heat resistance required for various barrier metals can be lowered, and the choice of materials that can be used as the barrier metal increases. As a result, it becomes possible to easily manufacture a stack structure cell in which the ferroelectric substance is arranged directly above the transistor. Further, in this embodiment, the bismuth layered compound is M
Since the film is formed by the OCVD method, it is possible to form a thin film having a high density and good surface coverage, and to improve the cleanliness of the thin film and the productivity.

The present invention has been described above based on the preferred embodiments, but the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist of the present invention. Is. In addition, Bi ₂ AB ₂ O ₉
(Here, A is one of alkaline earth metals Sr, Ba and Ca, and B is one of Ta and Nb)
A bismuth layered compound composed of a Y1-based material can be formed on a substrate by MOCVD.
Not only Sr / Ta but also Sr / Nb, Ba / Ta, Ba / Nb, Ca / T can be used as the combination of the elements A / B.
a and Ca / Nb can be mentioned. Further, the crystal growth promoting effect due to the promoting effect in the decomposition reaction of alcohols is not particularly limited to the bismuth compound. Further, the structure of the semiconductor element described in the manufacturing method of the capacitor structure of the semiconductor element of the present invention is an example, and the design can be appropriately changed. For example, a stack structure may be adopted and the ferroelectric capacitor may be arranged directly above the contact plug in contact with the transistor. Further, between the contact plug and the lower electrode of the ferroelectric capacitor, T
A diffusion barrier layer made of an oxide of i, Ta, or W may be formed. Further, a hydrogen barrier layer made of an appropriate material may be formed on the upper electrode of the ferroelectric capacitor.

[0088]

According to the present invention, a bismuth layered compound, which is important in manufacturing a ferroelectric memory, is added to SrBi ₂ Ta at about 600 ° C., which is about 100 ° C. lower than the conventional film forming temperature.
It is possible to form a crystal thin film of a Bi layered ferroelectric material typified by ₂ O ₉ . The resulting low temperature process can lower the upper limit of heat resistance required for various barrier metals, increasing the choice of materials that can be used as barrier metals. As a result, it becomes possible to easily manufacture a stack structure cell in which the ferroelectric substance is arranged directly above the transistor. Further, in the present embodiment, since the bismuth layered compound is formed by MOCVD, a thin film having a high density and good surface coverage can be formed, the cleanliness of the thin film can be improved, and the productivity can be improved. You can

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for producing a ferroelectric thin film according to a first embodiment of the present invention.

FIG. 2 is a flow chart showing a process of forming a ferroelectric thin film using the apparatus shown in FIG.

FIG. 3 is a diffraction diagram (XRD pattern) obtained by X-ray diffraction measurement of a bismuth layered compound obtained by the film forming method of the first embodiment of the present invention.

FIG. 4 shows an example in which the composition of the constituents of the formed thin film is controlled by the film forming conditions in the first embodiment of the present invention.

FIG. 5 is a schematic diagram of an apparatus for producing a ferroelectric thin film according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram of an apparatus for producing a ferroelectric thin film according to a third embodiment of the present invention.

FIG. 7 is a flow chart showing a process of forming a ferroelectric thin film using the apparatus shown in FIG.

FIG. 8 is a schematic sectional view (A) and an equivalent circuit diagram (B) of a semiconductor element manufactured by a method for manufacturing a capacitor structure of a semiconductor element according to a fourth embodiment of the present invention.

FIG. 9 is a partial cross-sectional view of a semiconductor substrate or the like for explaining a method for manufacturing a semiconductor element including a method for manufacturing a capacitor structure for a semiconductor element according to a fourth embodiment of the present invention.

FIG. 10 is a partial cross-sectional view of a semiconductor substrate or the like for explaining a method of manufacturing a semiconductor device including a method of manufacturing a capacitor structure of a semiconductor device according to a fourth embodiment of the present invention, following FIG.

11 is a partial cross-sectional view of a semiconductor substrate or the like for explaining a method for manufacturing a semiconductor element including a method for manufacturing a capacitor structure for a semiconductor element according to a fourth exemplary embodiment of the present invention, following FIG. 10;

FIG. 12 is a schematic view of a conventional apparatus for producing a thin film of a bismuth layered structure compound by using the MOCVD method.

FIG. 13 is a flow chart showing a conventional process for producing a thin film of a bismuth layered structure compound by using the MOCVD method.

[Explanation of symbols]

10, 11, 12 ... Raw material container, 13 ... Liquid mixer, 1
4, 15 ... Piping, 19 ... Vaporizer, 20 ... Gas mixer, 2
DESCRIPTION OF SYMBOLS 1 ... Spraying head, 22 ... Substrate, 23 ... Substrate stage, 24 ... MOCVD reaction chamber, 25 ... Vacuum pump, 30
... raw material container, 40 ... semiconductor substrate, 41 ... element isolation region,
42 ... Gate oxide film, 43 ... Gate electrode, 44 ... Source / drain region, 45 ... Channel region, 50 ... Insulating layer,
52 ... Lower electrode layer, 53 ... Ferroelectric layer, 54 ... Upper electrode layer, 60 ... Upper insulating layer, 61, 62, 63 ... Opening part, 6
4 ... Wiring material layer, 65, 66, 67 ... Contact plug, 68 ... First wiring layer, 69 ... Second wiring layer, 70,
71, 72 ... Raw material container, 74 ... Piping, 76, 77, 78
... Constant temperature bath, 110, 111 ... Raw material container, 113 ... Liquid mixer, 114, 115 ... Piping, 119 ... Vaporizer, 120
... Gas mixer, 121 ... Spraying head, 122 ... Substrate, 123 ... Substrate stage, 124 ... MOCVD reaction chamber, 125 ... Vacuum pump.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4K030 AA11 AA14 AA24 BA01 BA17                       BA42 DA09 FA10 JA05 JA10                       LA02                 5F058 BA11 BC03 BF06 BF27 BJ04                 5F083 FR02 GA29 JA17 JA36 JA38                       JA39 JA40 JA45 MA05 MA06                       MA18 PR21 PR33

Claims (25)

[Claims] 1. A method for producing a ferroelectric thin film by a chemical vapor deposition method, comprising: reacting at least a source gas of a plurality of kinds of organometallic compounds containing a metal element constituting the ferroelectric thin film with at least a reaction. A method for producing a ferroelectric thin film, which comprises supplying the same with an alcohol gas as a promoter to form the ferroelectric thin film. 2. The ferroelectric thin film according to claim 1, wherein the ferroelectric thin film is formed at a film forming temperature lower than a crystallization temperature of the ferroelectric material when the alcoholic reaction accelerator is not added. Manufacturing method. 3. The ferroelectric thin film contains a bismuth layered compound, and the raw material is a metal alkoxide Bi containing Bi.
The method for producing a ferroelectric thin film according to claim 1, which contains (OR) ₃ (R = alkyl). 4. When supplying the raw material gas and the alcoholic reaction promoter, oxygen gas as an oxidant is also supplied, and the amount of the oxygen gas supplied is controlled.
The method for manufacturing a ferroelectric thin film according to claim 3, wherein the composition of bismuth in the ferroelectric thin film is controlled. 5. The ferroelectric thin film is SrBi ₂ Ta ₂ O ₉
4. The method for producing a ferroelectric thin film according to claim 3, wherein the raw material contains a bismuth layered compound of, and the raw material contains a bimetal alkoxide containing atoms of Ta and Sr in one molecule. 6. The bimetal alkoxide comprises Ta and S.
The method for producing a ferroelectric thin film according to claim 5, wherein r is contained in one molecule in an atomic ratio of 2: 1. 7. The ferroelectric thin film is SrBi ₂ Nb ₂ O ₉
4. The method for producing a ferroelectric thin film according to claim 3, wherein the raw material contains a bismuth layered compound of, and the raw material contains a bimetal alkoxide containing Nb and Sr atoms in one molecule. 8. The bimetal alkoxide is Nb and S.
The method for producing a ferroelectric thin film according to claim 7, wherein r is contained in one molecule in an atomic ratio of 2: 1. 9. A step of forming a first electrode layer, a step of forming a ferroelectric thin film on the first electrode layer by chemical vapor deposition, and a step of forming a ferroelectric thin film on the ferroelectric thin film. A step of forming a second electrode layer, the step of forming the ferroelectric thin film on the first electrode layer by a chemical vapor deposition method, the metal forming the ferroelectric thin film. Manufacture of a ferroelectric capacitor for forming a ferroelectric thin film by supplying a source gas of a plurality of kinds of organic metal compounds containing an element together with at least an alcohol gas as a reaction accelerator onto the first electrode layer. Method. 10. The ferroelectric capacitor according to claim 9, wherein the ferroelectric thin film is formed at a film forming temperature lower than a crystallization temperature of the ferroelectric material when the alcohol reaction accelerator is not added. Manufacturing method. 11. The ferroelectric thin film contains a bismuth layered compound, and the raw material is a metal alkoxide Bi containing Bi.
The method of manufacturing a ferroelectric capacitor according to claim 9, wherein (OR) ₃ (R = alkyl) is contained. 12. An oxygen gas as an oxidant is also supplied and supplied onto the first electrode layer when the source gas and the alcoholic reaction accelerator are supplied onto the first electrode layer. By controlling the amount of oxygen gas,
The method of manufacturing a ferroelectric capacitor according to claim 11, wherein the composition of bismuth in the ferroelectric thin film is controlled. 13. The ferroelectric thin film is SrBi ₂ Ta ₂ O.
_The method of manufacturing a ferroelectric capacitor according to claim 11, further comprising a bismuth layered compound of No. ₉ , wherein the raw material contains a bimetal alkoxide containing atoms of Ta and Sr in one molecule. 14. The method for manufacturing a ferroelectric capacitor according to claim 13, wherein the bimetal alkoxide contains Ta and Sr in a molecule in an atomic ratio of 2: 1. 15. The ferroelectric thin film is SrBi ₂ Nb ₂ O.
_The method for manufacturing a ferroelectric capacitor according to claim 11, further comprising a bismuth layered compound of No. ₉ , wherein the raw material contains a bimetal alkoxide containing atoms of Nb and Sr in one molecule. 16. The method of manufacturing a ferroelectric capacitor according to claim 15, wherein the bimetal alkoxide contains Nb and Sr in an atomic ratio of 2: 1 in one molecule. 17. A method of manufacturing a ferroelectric memory device including a select transistor and a ferroelectric capacitor connected to one impurity diffusion region of the select transistor, wherein the select is performed in a predetermined region of a semiconductor substrate. Forming a transistor, forming an insulating film on a semiconductor substrate including the select transistor, forming a conductive contact plug reaching the one impurity diffusion region of the select transistor in the insulating film, Forming a lower electrode layer of the ferroelectric capacitor connected to the conductive contact plug; and forming a ferroelectric thin film of the ferroelectric capacitor on the lower electrode layer by chemical vapor deposition. A step of forming, and a step of forming an upper electrode layer of the ferroelectric capacitor on the ferroelectric thin film, on the lower electrode layer In the step of forming the ferroelectric thin film by a chemical vapor deposition method, a raw material gas of a plurality of kinds of organometallic compounds containing a metal element forming the ferroelectric thin film, and at least alcohol as a reaction accelerator A method of manufacturing a ferroelectric memory device, wherein a similar gas is supplied onto the lower electrode layer to form the ferroelectric thin film at a predetermined film forming temperature. 18. The method of manufacturing a ferroelectric memory element according to claim 17, wherein the film forming temperature is lower than the crystallization temperature of the ferroelectric thin film when the alcohol reaction accelerator is not added. 19. The film forming temperature is lower than a temperature at which a diffusion or a chemical reaction occurs near the lower electrode.
7. A method for manufacturing a ferroelectric memory device according to 7. 20. The ferroelectric thin film contains a bismuth layered compound, and the raw material is a metal alkoxide Bi containing Bi.
The method of manufacturing a ferroelectric memory element according to claim 17, wherein (OR) ₃ (R = alkyl) is contained. 21. When the source gas and the alcoholic reaction accelerator are supplied onto the lower electrode layer, oxygen gas as an oxidant is also supplied onto the lower electrode layer, and the oxygen gas of the supplied oxygen gas is supplied. By controlling the quantity
21. The method of manufacturing a ferroelectric memory device according to claim 20, wherein the composition of bismuth in the ferroelectric thin film is controlled. 22. The ferroelectric thin film is SrBi ₂ Ta ₂ O.
21. The method of manufacturing a ferroelectric memory device according to claim 20, further comprising a bismuth layered compound of No. ₉ , wherein the raw material contains a bimetal alkoxide containing Ta and Sr atoms in one molecule. 23. The method of manufacturing a ferroelectric memory element according to claim 22, wherein the bimetal alkoxide contains Ta and Sr in an atomic ratio of 2: 1 in one molecule. 24. The ferroelectric thin film is SrBi ₂ Nb ₂ O.
21. The method of manufacturing a ferroelectric memory device according to claim 20, further comprising a bismuth layered compound of No. ₉ , wherein the raw material contains a bimetal alkoxide containing atoms of Nb and Sr in one molecule. 25. The method of manufacturing a ferroelectric memory device according to claim 24, wherein the bimetal alkoxide contains Nb and Sr in an atomic ratio of 2: 1 in one molecule.