JP2008294345A - Manufacturing method of ferroelectric memory device, and ferroelectric memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a ferroelectric memory device capable of reducing a leak current at an interface between a lower electrode and a ferroelectric film, and the ferroelectric memory device. <P>SOLUTION: The manufacturing method of the ferroelectric memory device includes a stage of forming the lower electrode 23a, a stage of forming a ferroelectric film 24a having an ABO<SB>3</SB>type perovskite crystal structure on the lower electrode 23a, and a stage of forming an upper electrode 25a on the ferroelectric film 24a, where the stage of forming the lower electrode 23a includes a stage of forming a buffer film 33a aligning the ferroelectric film 24a in a (111) plane direction as a surface layer of the lower electrode 23, and the stage of forming the ferroelectric film 24a includes a stage of forming an amorphous initial film 34a having some of B elements of ABO<SB>3</SB>substituted for Nb on the lower electrode 23a, a stage of crystallizing the initial film 34a, and a stage of forming a core film 35a on the initial film 34a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a ferroelectric memory device having a ferroelectric capacitor and a ferroelectric memory device.

A ferroelectric memory device (FeRAM) is a nonvolatile memory capable of low voltage and high speed operation utilizing spontaneous polarization of a ferroelectric material, and a memory cell can be composed of one transistor / one capacitor (1T / 1C). . Therefore, since it can be integrated in the same manner as a DRAM, it is expected as a large-capacity nonvolatile memory.
Here, as the ferroelectric material, a perovskite oxide such as lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT) or a bismuth layer such as bismuth strontium tantalate (SrBi ₂ TaO ₉ : SBT) is used. Compound etc. are mentioned.

By the way, in order to maximize the ferroelectric properties of the ferroelectric material, the crystal orientation is extremely important. For example, when PZT is used as the ferroelectric material, there is a dominant orientation depending on the crystal system. In general, in the use of a memory device, a titanium-rich composition containing more Ti (titanium) than Zr (zirconium) is employed in order to obtain a larger amount of spontaneous polarization. In this composition range, PZT belongs to tetragonal crystal, and its spontaneous polarization axis is c-axis. In this case, ideally, the maximum amount of polarization can be obtained by orienting the c-axis, but in reality, it is very difficult and an a-axis orientation component orthogonal to the c-axis is present simultaneously. However, this a-axis orientation component does not contribute to polarization reversal, and thus the ferroelectric characteristics may be impaired.
Therefore, it is considered that the a-axis is oriented in a direction offset by a certain angle from the substrate normal by setting the crystal orientation of PZT to the (111) orientation. According to this, since the polarization axis has a component in the substrate normal direction, it is possible to contribute to polarization inversion. On the other hand, since the polarization axis of the c-axis orientation component is also at a certain offset angle with respect to the normal direction of the substrate, a certain amount of loss occurs in the surface charge amount induced by polarization reversal. However, since all crystal components can contribute to polarization reversal, the charge extraction efficiency is remarkably superior to the c-axis orientation.

Here, in order to orient (111) the PZT, the crystal orientation of the lower electrode on which the PZT film is formed on the upper surface is important. As a material constituting the lower electrode, a noble metal is generally used in consideration of thermal and chemical stability. Especially, since Pt (platinum) has a very strong self-orientation property, the PZT film can be easily (111) oriented.
However, Pt is rich in reactivity with Pb (lead) which is a constituent element of the PZT film. Therefore, when a PZT film is formed using a metal organic chemical vapor deposition (MOCVD) method, the activated Pb and Pt react to form a PbPt alloy, causing volume expansion. There is a problem that the surface morphology deteriorates.
Accordingly, a method of manufacturing a ferroelectric memory device in which a PZT film is formed in a (111) orientation by forming in advance a PbPt alloy film having a small lattice constant mismatch with the PZT film on the surface layer of the lower electrode. Has been proposed (see, for example, Patent Document 1).
Republished WO 2004/066388

  However, the following problems remain in the conventional method for manufacturing a ferroelectric memory device. That is, even when the PbPt alloy film is formed, there is a problem that a large leak current is generated because the matching at the interface between the lower electrode and the PZT film is insufficient.

  The present invention has been made in view of the above-described conventional problems, and provides a method for manufacturing a ferroelectric memory device and a ferroelectric memory device capable of reducing leakage current at the interface between a lower electrode and a ferroelectric film. With the goal.

The present invention employs the following configuration in order to solve the above problems. That is, a method for manufacturing a ferroelectric memory device according to the present invention is a method for manufacturing a ferroelectric memory device including a ferroelectric capacitor having a ferroelectric film sandwiched between a lower electrode and an upper electrode, Forming the lower electrode; forming the ferroelectric film having an ABO ₃ type perovskite crystal structure on the lower electrode; and forming the upper electrode on the ferroelectric film. And the step of forming the lower electrode includes a step of forming a buffer film that provides an orientation in a (111) plane orientation with respect to the ferroelectric film on a surface layer of the lower electrode, The step of forming a film includes a step of forming an amorphous initial film in which a part of the B element of ABO ₃ is substituted with Nb on the lower electrode, a step of crystallizing the initial film, and a step of forming on the initial film A process of forming a core film. And wherein the Rukoto.

  In the present invention, the leakage current between the lower electrode and the core film can be reduced by forming the initial film partially substituted with Nb (niobium) on the lower electrode. That is, when an initial film in which part of the B element is substituted with Nb is formed between the core film and the lower electrode, the Schottky barrier at the interface between the lower electrode and the ferroelectric film is increased. Therefore, electron injection from the lower electrode to the ferroelectric film is suppressed. Thereby, the leakage current of the ferroelectric capacitor is greatly reduced. Here, in order to crystallize after forming the amorphous initial film, the initial film is crystallized while being oriented in the (111) plane orientation by the buffer film. Therefore, the lattice constant matching between the initial film and the buffer film can be easily obtained. The core film formed on the initial film also grows while being oriented in the (111) plane orientation with the initial film as a nucleus. Further, by forming the initial film, it is possible to prevent the constituent elements from reacting between the buffer film and the core film during the formation of the core film, and to suppress the deterioration of the surface morphology.

In the method of manufacturing a ferroelectric memory device according to the present invention, the initial film may be made of a material obtained by substituting a part of Zr or Ti of Pb (Zr, Ti) O ₃ with Nb. .
In the present invention, the initial film is formed using PZTN in which a part of the B element of PZT is substituted with Nb.

In the method for manufacturing a ferroelectric memory device according to the present invention, it is preferable that the core film is made of Pb (Zr, Ti) O ₃ .
In the present invention, the core film is made of PZT, so that the ferroelectric characteristics of the ferroelectric film can be sufficiently obtained.

In the method for manufacturing a ferroelectric memory device according to the present invention, it is preferable that a buffer film made of Pt is formed on the surface layer of the lower electrode.
In the present invention, by forming a buffer film made of Pt having high self-orientation on the surface layer of the lower electrode, the initial film can be crystal-grown while being more reliably oriented in the (111) plane orientation. Therefore, the ferroelectric film can be more reliably oriented in the (111) plane orientation.

In the method for manufacturing a ferroelectric memory device according to the present invention, the initial film may be formed by a sol-gel method.
In this invention, a solution (or dispersion liquid) in which an organic compound such as an alkoxide, which is a compound containing a constituent element constituting the initial film, is dissolved (or dispersed) in a solvent (or dispersion medium) is applied on the lower electrode. Then, this is heated, dried and crystallized to form an initial film.

In the method for manufacturing a ferroelectric memory device according to the present invention, the initial film is preferably crystallized under reduced pressure.
In the present invention, the organic components contained in the applied film can be released at a lower temperature than under atmospheric pressure. Thereby, the crystallization temperature of the initial film can be lowered to reduce the thermal influence on other elements.

In the method for manufacturing a ferroelectric memory device according to the present invention, the initial film is preferably crystallized while heating the back surface side of the lower electrode.
In the present invention, by crystal growth of the initial film from the surface layer side of the lower electrode, the crystal orientation of the (111) orientation in the surface layer of the lower electrode is easily reflected in the initial film, and the initial film is more reliably (111). Can be oriented.

In the method for manufacturing a ferroelectric memory device according to the present invention, the core film may be formed by a reaction between an organic metal source gas and an oxygen gas.
In this invention, the core film is formed using the MOCVD method in which the organometallic source gas and oxygen are reacted. Here, even if the constituent element of the organometallic source gas is activated, the reaction of the activated constituent element with the buffer film is suppressed because the initial film is formed on the buffer film.

The ferroelectric memory device according to the present invention is a ferroelectric memory device comprising a ferroelectric capacitor having a ferroelectric film sandwiched between a lower electrode and an upper electrode, wherein Pt is formed on the surface layer of the lower electrode. The ferroelectric film is made of a material formed on the buffer film and having a part of Zr or Ti of Pb (Zr, Ti) O ₃ replaced with Nb. And a core film made of Pb (Zr, Ti) O ₃ .
In the present invention, as described above, the leakage current between the lower electrode and the core film can be reduced by forming the initial film partially substituted with Nb on the lower electrode.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS A ferroelectric memory device manufacturing method and a ferroelectric memory device according to an embodiment of the present invention will be described below with reference to the drawings. In each drawing used in the following description, the scale is appropriately changed to make each member a recognizable size.

[Ferroelectric memory device]
First, the ferroelectric memory device in this embodiment will be described with reference to FIG. Here, FIG. 1 is an enlarged cross-sectional view schematically showing a ferroelectric memory device.
The ferroelectric memory device 1 is a stack type having a 1-transistor / 1-capacitor (1T / 1C) type memory cell structure, and is formed on a semiconductor substrate 2 and a semiconductor substrate 2 as shown in FIG. The ferroelectric capacitor 3 and the transistor 4 are provided.

The semiconductor substrate 2 is made of, for example, Si (silicon), and an interlayer insulating film 11 stacked in order on the upper surface is formed.
The interlayer insulating film 11 is made of, for example, SiO ₂ (silicon oxide) and covers the transistor 4 formed on the semiconductor substrate 2. A through hole 16 is formed on a drain region 42 described later of the interlayer insulating film 11 and is filled with a plug 17.
The plug 17 is made of a conductive material filled in the through hole 16, and is made of, for example, W (tungsten), Mo (molybdenum), Ta (tantalum), Ti, Ni (nickel), or the like.

The ferroelectric capacitor 3 is formed on the interlayer insulating film 11 and the plug 17, and a conductive film 21, an oxygen barrier film 22, a lower electrode 23, a ferroelectric film 24, and an upper electrode 25 are laminated in order from the lower layer. It has a configuration.
The conductive film 21 is made of a conductive material such as TiN, for example, and is intended to connect the plug 17 and the ferroelectric capacitor 3.
The oxygen barrier film 22 is made of a material having an oxygen barrier property, such as TiAlN, TiAl, TiSiN, TiN, TaN, or TaSiN.

The lower electrode 23 has a structure in which an electrode film 31, an electrode oxide film 32, and a buffer film 33 are stacked in order from the lower layer.
The electrode film 31 is made of, for example, Ir (iridium).
The electrode oxide film 32 is made of IrOx, which is an Ir oxide constituting the electrode film 31, and has a film thickness of, for example, 20 nm to 30 nm.
The buffer film 33 is made of a metal material with high self-orientation, such as Pt, and has a thickness of 10 nm to 50 nm, for example.
Here, in addition to Ir, the electrode film 31 is selected from at least one of Pt, Ru (ruthenium), Rh (rhodium), Pd (palladium), and Os (osmium) or including Ir in these. You may comprise an alloy. The electrode film 31 may be a single layer film or a laminated multilayer film. The electrode oxide film 32 may be an oxide of these metal materials constituting the electrode film 31.

The ferroelectric film 24 is made of a ferroelectric material having a perovskite crystal structure represented by the general formula of ABO ₃ . Here, A in the above general formula consists of Pb, and B consists of at least one of Zr and Ti. The ferroelectric film 24 has a configuration in which an initial film 34 and a core film 35 are laminated in order from the lower layer.
The initial film 34 is composed of PZTN in which part of Zr or Ti, which is a B element of PZT represented by Pb (Zr, Ti) O ₃ , is substituted with Nb, and the film thickness thereof is, for example, 10 nm or more and 30 nm or less. It is about.
Further, the substitution amount of Nb for the B element constituting the initial film 34 is 10% or more and 50% or less. By setting the Nb substitution amount to 10% or more, the Schottky barrier between the lower electrode 23 and the ferroelectric film 24 can be made sufficiently high to suppress the occurrence of leakage current. Further, by setting the Nb substitution amount to 50% or less, the ferroelectric characteristics of the ferroelectric film 24 can be reliably obtained.

The core film 35 is made of PZT and has a film thickness of, for example, about 70 nm to 90 nm. That is, the thickness of the initial film 34 in the ferroelectric film 24 is, for example, 10% or more and 30% or less. Thus, by setting the thickness of the initial film 34 with respect to the ferroelectric film 24 to 10% or more, generation of a leak current between the ferroelectric film 24 and the lower electrode 23 can be reliably suppressed. Further, by setting the thickness of the initial film 34 to the ferroelectric film 24 to 30% or less, the ferroelectric characteristics of the ferroelectric film 24 can be maintained.
In the ferroelectric film 24, a part of Pb constituting A in the above general formula may be replaced with La (lanthanum), and a part of Zr and Ti constituting B may be replaced with V (vanadium), It may be substituted with at least one of Ta, Cr (chromium), Mo, W, Ca (calcium), Sr (strontium), and Mg (magnesium).

  The upper electrode 25 is made of, for example, a multilayer film of Pt or IrOx and Ir. The upper electrode 25 may be the same material as the lower electrode 23 described above, a single layer film made of Al (aluminum), Ag (silver), Ni, or the like, or a multilayer film in which these are stacked.

The transistor 4 is formed on the source region 41, the drain region 42 and the channel region (not shown) formed on the surface layer of the semiconductor substrate 2, the gate insulating film 43 formed on the channel region, and the gate insulating film 43. The gate electrode 44 is provided. The transistor 4 is electrically connected to the plug 17 formed on the drain region 42.
In addition, a plurality of transistors 4 are formed at intervals in the semiconductor substrate 2 and are insulated from each other by an element isolation region 45 provided between the other adjacent transistors 4.

[Manufacturing Method of Ferroelectric Memory Device]
Next, a manufacturing method of the above-described ferroelectric memory device 1 will be described with reference to FIG. Here, FIG. 2 is an explanatory view showing a manufacturing process of the ferroelectric memory device.
First, the transistor 4 is formed on the semiconductor substrate 2 and the interlayer insulating film 11 covering the transistor 4 is formed. Then, a through hole 16 penetrating the interlayer insulating film 11 is formed, and the through hole 16 is filled with a plug 17 (FIG. 2A).

Next, the ferroelectric capacitor 3 is formed on the interlayer insulating film 11. Here, the conductive film 21a, the oxygen barrier film 22a, the lower electrode 23a, the ferroelectric film 24a, and the upper electrode 25a are formed on the interlayer insulating film 11 in order from the lower layer.
First, a conductive film 21a is formed on the interlayer insulating film 11 (FIG. 2B). Here, a film made of Ti is formed on the interlayer insulating film 11 by using, for example, a CVD method or a sputtering method. At this time, since Ti generally has a high self-orientation property, a hexagonal close-packed film having a (001) orientation is formed by CVD or sputtering. Therefore, a film made of Ti exhibits (001) orientation due to self-orientation. Then, the conductive film 21a is formed by nitriding treatment in which this film is subjected to heat treatment (for example, 500 ° C. or more and 650 ° C. or less) in a nitrogen atmosphere. At this time, by setting the heat treatment temperature to less than 650 ° C., the influence on the characteristics of the transistor 4 is suppressed, and by setting the heat treatment temperature to 500 ° C. or higher, the nitriding treatment can be shortened. The formed conductive film 21a becomes (111) -oriented TiN, reflecting the orientation of Ti in the original metal state.

  Next, an oxygen barrier film 22a is formed on the conductive film 21a (FIG. 2C). Here, the oxygen barrier film 22a made of TiAlN is formed on the conductive film 21a by using, for example, sputtering or CVD. Here, the oxygen barrier film 22a is formed epitaxially by matching the lattice structure of the conductive film 21a and the lattice structure of the oxygen barrier film 22a at the interface between the conductive film 21a and the oxygen barrier film 22a. Thereby, the oxygen barrier film 22a having the (111) orientation reflecting the (111) orientation of the conductive film 21a is formed. Further, since the oxygen barrier film 22a is made of crystalline TiAlN as described above, the oxygen barrier film 22a can be oriented in the (111) plane orientation.

Subsequently, a lower electrode 23a shown in FIG. 2F is formed on the oxygen barrier film 22a.
First, the electrode film 31a is formed on the oxygen barrier film 22a (FIG. 2D). Here, the electrode film 31a made of Ir is formed on the oxygen barrier film 22a by using, for example, a sputtering method or a CVD method. At this time, by forming the electrode film 31a on the crystalline oxygen barrier film 22a, the crystallinity of the electrode film 31a is remarkably improved, and the crystal orientation of the oxygen barrier film 22a is reflected in the electrode film 31a. Thereby, the electrode film 31a is oriented in the (111) plane orientation similar to that of the oxygen barrier film 22a.

  Then, an electrode oxide film 32a is formed on the electrode film 31a (FIG. 2E). Here, Ir is formed on the electrode film 31a by sputtering while supplying oxygen gas, thereby forming the electrode oxide film 32a made of IrOx on the electrode film 31a. At this time, the electrode oxide film 32 is formed with a uniform film thickness by using a sputtering method. In addition, since the electrode oxide film 32a is formed at a lower temperature than thermal oxidation, the thermal influence on other elements such as the transistor 4 formed in advance is reduced.

  Further, a buffer film 33a is formed on the electrode oxide film 32a (FIG. 2F). Here, a buffer film 33a made of Pt is formed on the electrode oxide film 32a by using, for example, a sputtering method or a CVD method. As described above, the lower electrode 23a is formed.

Next, a ferroelectric film 24a shown in FIG. 2 (h) is formed on the lower electrode 23a.
First, the initial film 34a is formed on the buffer film 33a (FIG. 2G). Here, a compound containing PbTN, Zr, Ti, Nb and the like, which are constituent elements of PZTN constituting the initial film 34a, for example, an organic compound such as alkoxide is dissolved in a solvent (or dispersion medium) on the buffer film 33a ( Alternatively, a solution (or dispersion) obtained by dispersion) is applied by a spin coating method or the like and dried. Thereby, an amorphous initial film 34a is formed.

Then, the semiconductor substrate 2 on which the amorphous initial film 34a is formed is introduced into the MOCVD apparatus 50 as shown in FIG. Here, FIG. 3 is a schematic view showing an MOCVD apparatus.
As shown in FIG. 3, the MOCVD apparatus 50 includes a chamber 51 that houses the semiconductor substrate 2, a susceptor 52 that is disposed in the chamber 51 and places the semiconductor substrate 2, and a shower head that supplies gas into the chamber 51. 53 and a heating lamp 54 for heating the semiconductor substrate 2 placed thereon. The shower head 53 is provided with supply pipes 55 and 56 for supplying an organic metal source gas or oxygen gas, which is a PZT source, into the chamber 51. The MOCVD apparatus 50 supplies an organic metal source gas into the chamber 51 from the supply pipe 55 and supplies oxygen gas into the chamber 51 from the supply pipe 56 by a supply means (not shown) provided outside the chamber 51. It is the composition to do. The supply pipes 55 and 56 are provided independently of each other, and are configured so as not to be encountered until the organic metal source gas and the oxygen gas are supplied to the chamber 51. Further, the chamber 51 is appropriately formed with an exhaust port (not shown). The susceptor 52 is provided with a heater (not shown) separately from the heating lamp 54.

  In the MOCVD apparatus 50 having such a configuration, the semiconductor substrate 2 on which the initial film 34a is formed is placed on the susceptor 52, and only the oxygen gas is supplied from the supply pipe 56 into the chamber 51 by the heating lamp 54. 2 is heated from the lower surface side. Here, the inside of the chamber 51 is in a reduced pressure state. Further, the heating temperature of the semiconductor substrate 2 is set to 650 ° C., for example. As described above, when the initial film 34a is heated, the buffer film 33a is (111) oriented, so that the initial film 34a grows while being oriented in the (111) plane orientation reflecting the crystallinity of the buffer film 33a. . At this time, since the semiconductor substrate 2 is heated from the lower surface side, the initial film 34a is crystallized in order from the buffer film 33a side. Further, since the initial film 34a is crystallized in the chamber 51 under reduced pressure, the solvent (or dispersion medium) contained in the amorphous initial film 34a is lower than that in the case of heating under atmospheric pressure. Evaporates at heating temperature. Therefore, the thermal influence on other elements such as the transistor 4 formed in advance is reduced. The semiconductor substrate 2 may be heated using a heater provided on the susceptor 52.

Further, the core film 35a is formed on the crystallized initial film 34a (FIG. 2 (h)). Here, the core film 35a is formed on the initial film 34a by the MOCVD method in which the organic metal source gas and the oxygen gas are respectively supplied from the supply pipes 55 and 56 into the chamber 51. At this time, examples of the organic metal source gas include a combination of Pb (DIBM), Zr (DIBM), and Ti (DIBM). DIBM represents C ₉ H ₁₅ O ₂ (diisobutyrylmethanato). Moreover, you may use another material as organometallic source gas.
Further, the flow rate of the oxygen gas is equal to or higher than the amount of oxygen necessary for reacting with the organometallic source gas. Therefore, the oxygen amount necessary for the reaction of the organic components in the supplied organometallic raw material gas is sufficiently supplied. In the present invention, the amount of oxygen necessary for reacting the organometallic raw material gas refers to CO ₂ (carbon dioxide) and H ₂ O (water) by burning carbon and hydrogen originating from the raw material of the organometallic raw material gas. Represents the sum of the amount of oxygen necessary for discharging and the amount of oxygen necessary for crystallization of the ferroelectric material constituting the ferroelectric film.
As described above, when the semiconductor substrate 2 is heated while supplying the mixed gas, the organic raw material gas takes oxygen in the oxygen gas and decomposes and oxidizes to form PZT crystallized on the initial film 34a. As deposited.

At this time, since the buffer film 33a made of Pt is covered with the initial film 34a made of PZTN, the reaction between Pb activated by the MOCVD method and the buffer film 33a is avoided. Therefore, a PbPt alloy is not formed.
In addition, the crystal orientation of the core film 35a is controlled to the (111) orientation with the initial film 34a having the (111) orientation as the nucleus. Then, by forming the core film 35a in an atmosphere supplied with a sufficient amount of oxygen, a high-quality core film 35a with few oxygen vacancies is formed.
As described above, the ferroelectric film 24a including the initial film 34a and the core film 35a is formed.

Subsequently, the upper electrode 25a is formed on the ferroelectric film 24a (FIG. 2 (i)). Here, the upper electrode 25a made of a metal material constituting the upper electrode 25 is formed on the ferroelectric film 24a by using, for example, a sputtering method or a CVD method.
Thereafter, the conductive film 21a, the oxygen barrier film 22a, the lower electrode 23a, the ferroelectric film 24a, and the upper electrode 25a formed by lamination are patterned by a photolithography technique or the like to form the ferroelectric capacitor 3. As described above, the ferroelectric memory device 1 shown in FIG. 1 is manufactured.

As described above, according to the method for manufacturing the ferroelectric memory device 1 and the ferroelectric memory device 1 in the present embodiment, the initial film 34 made of PZTN in which a part of PZT is replaced with Nb on the buffer film 33. Since it is provided, the occurrence of leakage current between the lower electrode 23 and the core film 35 can be suppressed.
In addition, since the amorphous initial film 34a is formed and then crystallized, the initial film 34a is crystallized by the buffer film 33a in the (111) plane orientation. At this time, since the initial film 34a is crystallized from the surface layer side of the lower electrode 23a, crystals grow while being more reliably oriented in the (111) plane orientation by the buffer film 33a. Then, lattice matching between the initial film 34a and the buffer film 33a can be easily obtained. Further, since the initial film 34a is formed, it is possible to prevent the activated Pt and Pb from reacting between the buffer film 33a and the core film 35a when the core film 35a is formed by the MOCVD method. Deterioration of is suppressed.
Then, by crystallizing the initial film 34a under reduced pressure, the heating temperature can be lowered and thermal influence on the transistor 4 and the like can be reduced as compared with crystallizing under atmospheric pressure.
Furthermore, by configuring the core film 35 with PZT, sufficient ferroelectric characteristics can be obtained in the ferroelectric film 24.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, the core film is composed of PZT in which a part of the B element is not substituted with Nb. However, if the ferroelectric film can maintain the ferroelectric characteristics, the core film is composed of PZTN substituted with Nb. May be.
The ferroelectric material constituting the ferroelectric film is not limited to PZT as long as it has an ABO ₃ type perovskite crystal structure.
The buffer film is made of Pt, but may be made of other materials as long as the ferroelectric film can be oriented in the (111) plane orientation.

  Further, although the electrode oxide film made of IrOx is formed by sputtering, the electrode oxide film may be formed by forming an oxide film on the surface of the electrode film by thermal oxidation. Then, an electrode oxide film made of amorphous IrOx may be formed. At this time, although the surface of the electrode oxide film does not have a crystal structure, the initial film can be (111) oriented by forming a buffer film made of Pt having high self-orientation.

Further, although the initial film is crystallized under reduced pressure, it may be crystallized under atmospheric pressure as long as the thermal influence on other elements such as a transistor is suppressed. At this time, the heating temperature of the semiconductor substrate is about 700 ° C., for example.
The initial film is formed using the sol-gel method, but the initial film may be formed by other methods as long as the amorphous initial film is formed on the buffer film and then crystallized. .
Furthermore, when the initial film is crystallized, the semiconductor substrate is heated from the lower surface side of the semiconductor substrate, but if the initial film can be (111) oriented, it is heated by other methods such as heating from the upper surface side. May be.

1 is a schematic cross-sectional view showing a ferroelectric memory device in one embodiment. FIG. 7 is an explanatory diagram showing a manufacturing process of the ferroelectric memory device of FIG. 1. It is a schematic diagram which shows a MOCVD apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ferroelectric memory device, 3 Ferroelectric capacitor, 23, 23a Lower electrode, 24, 24a Ferroelectric film, 25, 25a Upper electrode, 33, 33a Buffer film, 34, 34a Initial film, 35, 35a Core film

Claims (9)

A method of manufacturing a ferroelectric memory device comprising a ferroelectric capacitor having a ferroelectric film sandwiched between a lower electrode and an upper electrode,
Forming the lower electrode;
Forming the ferroelectric film having an ABO ₃ type perovskite crystal structure on the lower electrode;
Forming the upper electrode on the ferroelectric film,
The step of forming the lower electrode includes a step of forming a buffer film that gives orientation in a (111) plane orientation with respect to the ferroelectric film on a surface layer of the lower electrode;
Forming the ferroelectric film includes: forming an amorphous initial film in which a part of the B element of ABO ₃ is substituted with Nb on the lower electrode; crystallizing the initial film; And a step of forming a core film on the initial film. 2. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the initial film is made of a material obtained by substituting a part of Zr or Ti of Pb (Zr, Ti) O ₃ with Nb. . _{3. The} method of manufacturing a ferroelectric memory device according to claim 1, wherein the core film is made of Pb (Zr, Ti) O ₃ .   4. The method for manufacturing a ferroelectric memory device according to claim 1, wherein the buffer film is made of Pt.   5. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the initial film is formed by a sol-gel method.   6. The method of manufacturing a ferroelectric memory device according to claim 5, wherein the initial film is crystallized under reduced pressure.   7. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the initial film is crystallized while heating a back surface side of the lower electrode.   8. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the core film is formed by a reaction between an organic metal source gas and an oxygen gas. A ferroelectric memory device comprising a ferroelectric capacitor having a ferroelectric film sandwiched between a lower electrode and an upper electrode,
A buffer film made of Pt is provided on the surface layer of the lower electrode,
The ferroelectric film is formed on the buffer film and is made of a material obtained by substituting a part of Zr or Ti of Pb (Zr, Ti) O ₃ with Nb; and Pb (Zr, Ti) A ferroelectric memory device comprising a core film made of O ₃ .

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