JP4943920B2 - Method for manufacturing ferroelectric memory device - Google Patents

Description

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

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 type 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 at the same time. 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 such as Ir (iridium) is generally used in consideration of thermal and chemical stability. However, in order to orient the PZT film in the (111) orientation, it is necessary to orient the Ir film in the (111) orientation. However, since the Ir film has a weak self-orientation property, the crystal orientation is on the underlayer having the (111) orientation. It is necessary to form an Ir film.
However, even if the Ir film is (111) oriented, it is difficult to make the crystal orientation of the PZT film formed on this surface (111) oriented.

Therefore, the surface of the Ir film constituting the lower electrode is oxidized to form an IrOx film that is an oxide of Ir, and PZT is formed on this surface by metal organic chemical vapor deposition (MOCVD). It has been proposed that the crystal orientation of PZT is changed to (111) orientation by forming (see, for example, Patent Document 1). Here, the IrOx film is formed by exposing the Ir film to an oxygen atmosphere at a high temperature.
However, since the IrOx film is formed by thermal oxidation, it is difficult to obtain desired film quality such as in-plane uniformity and film thickness. In addition, since the desired film quality cannot be obtained, there is a problem that the crystal orientation of the ferroelectric film formed on the IrOx film varies.
Therefore, it is conceivable that an IrOx film having a desired film quality is formed by forming an oxide film on the surface layer of the lower electrode by sputtering, thereby improving the crystal orientation of the ferroelectric film.
JP 2003-324101 A

  However, the following problems remain in the conventional method for manufacturing a ferroelectric memory device. That is, it is desired to further improve the surface morphology of the PZT film formed by the MOCVD method to increase the yield of the ferroelectric memory device.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a method for manufacturing a ferroelectric memory device that can improve the surface morphology of a ferroelectric film.

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, a step of forming the lower electrode, by reaction with an organic metal raw material gas and oxygen gas, and forming a first ferroelectric film made of Pb (Zr, Ti) O ₃ on the lower electrode, an organic metal by reaction of the raw material gas and oxygen gas, and forming a second ferroelectric layer consisting of Pb (Zr, Ti) O ₃ in the first ferroelectric film, the step of forming the lower electrode A step of forming an electrode film made of an iridium film , and a step of forming an electrode oxide film made of an iridium oxide film on the electrode film using a sputtering method, and forming the first ferroelectric film in the electrolytic oxide film The first film forming temperature lower than the recrystallization temperature of the electrolytic oxide film by temperature adjustment at a lower temperature range than the recrystallization temperature and a temperature higher than the crystallization temperature of the first ferroelectric film A Pb (Zr, Ti) O ₃ film having a perovskite structure is formed on the electrode film by a reaction between the organometallic source gas and the oxygen gas and oxygen atoms contained in the electrode oxide film ; In the ferroelectric film forming step, a Pb (Zr, Ti) O ₃ film having a perovskite structure is formed on the first ferroelectric film by a reaction between the organic source gas and the oxygen gas. .
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, A step of forming the lower electrode; a step of forming a first ferroelectric film on the lower electrode by a reaction of an organometallic source gas and an oxygen gas; and a reaction of an organometallic source gas and an oxygen gas. Forming a second ferroelectric film on the first ferroelectric film, wherein the lower electrode forming step includes forming an electrode film, and a constituent material of the electrode film on the electrode film. Forming an electrode oxide film composed of an oxide of the above, and in the step of forming the first ferroelectric film, the amount of oxygen necessary for the oxygen gas amount to react with the organometallic source gas With less and at least the first The film temperature is lower than the recrystallization temperature of the electrode oxide film, and in the step of forming the second ferroelectric film, the amount of oxygen gas is greater than or equal to the amount of oxygen necessary for reacting the organometallic source gas. It is characterized by that.

In the present invention, the surface morphology of the ferroelectric film can be improved by preventing recrystallization of the electrode oxide film at least at the beginning of the process of forming the first ferroelectric film. That is, the first ferroelectric film is formed without recrystallization of the electrode oxide film by lowering the film formation temperature at the beginning of the first ferroelectric film formation process to be lower than the recrystallization temperature of the electrode oxide film. The first film to be constructed is formed. At this time, since the amount of oxygen gas is less than the amount of oxygen necessary for reacting the organometallic source gas, the organometallic source gas deprives oxygen in the electrode oxide film and decomposes and oxidizes, thereby causing the first strong gas. The first film of the dielectric film is formed. Thereby, since the electrode oxide film is reduced, recrystallization of the electrode oxide film is suppressed. Therefore, the regrowth of the electrode oxide film can be prevented even if the film forming temperature is set to the recrystallization temperature of the electrode oxide film after the first film of the first ferroelectric film is formed on the electrode oxide film. Therefore, the surface morphology of the ferroelectric film is improved, and the defect of the ferroelectric capacitor characteristics can be prevented and the yield can be improved.
Here, it is possible to easily make the film quality of the electrode oxide film in-plane uniform as compared with forming the oxide film by oxidizing the surface of the lower electrode by oxidizing the lower electrode. Thereby, the crystal orientation of the ferroelectric film formed on the electrode oxide film is made uniform.
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.

In the method for manufacturing a ferroelectric memory device according to the present invention, it is preferable that a film formation temperature in the step of forming the second ferroelectric film is higher than a recrystallization temperature of the electrode oxide film.
In the present invention, the second ferroelectric film with good crystallinity can be formed by setting the film forming temperature higher than the recrystallization temperature. Therefore, the crystallinity of the ferroelectric film is improved.

In the method for manufacturing a ferroelectric memory device according to the present invention, the ferroelectric film may be composed of Pb (Zr, Ti) O ₃ .
In the present invention, the ferroelectric film is formed of PZT, which is a ferroelectric material having a perovskite crystal structure.

In the method for manufacturing a ferroelectric memory device according to the present invention, the electrode oxide film is preferably formed by sputtering.
In the present invention, an electrode oxide film having a uniform film quality is formed at a low temperature using a sputtering method.

In the method for manufacturing a ferroelectric memory device according to the present invention, the partial pressure of oxygen gas in the atmospheric gas during sputtering is preferably 20% or more and 40% or less.
In the present invention, the first ferroelectric film formed on the electrode oxide film can be more reliably set to a desired crystal orientation. That is, by setting the partial pressure of the oxygen gas to 20% or more, it is possible to prevent the formed electrode oxide film from being sufficiently oxidized and becoming close to a metallic state. Further, by setting the partial pressure of oxygen gas to 40% or less, the formed electrode oxide film becomes too stable due to oxidation and is difficult to be reduced, and the surface structure (orientation) of the electrode film is the first ferroelectric. Prevents transmission to the membrane. Therefore, it becomes easy to make the first ferroelectric film have a desired crystal orientation.

In the method for manufacturing a ferroelectric memory device according to the present invention, the electrode oxide film preferably has a thickness of 30 nm or less.
In the present invention, by setting the thickness of the electrode oxide film to be greater than 0 nm and 30 nm or less, the electrode oxide film becomes too thick and the surface structure (orientation) of the electrode film is not transmitted to the first ferroelectric film. To prevent that. As a result, the first ferroelectric film can be more reliably set to a desired crystal orientation.

In the method for manufacturing a ferroelectric memory device according to the present invention, the oxygen amount of the oxygen gas at the time of forming the first ferroelectric film is smaller than an oxygen amount necessary for reacting the organometallic source gas. Thus, it may be 0.1 times or more and less than 1.0 times.
In the present invention, the oxygen amount of the oxygen gas at the time of forming the first ferroelectric film is 0.1 times or more and less than 1.0 times the oxygen amount necessary for reacting the organometallic source gas. Thus, a reducing atmosphere is formed in which the organic metal source gas takes oxygen in the electrode oxide film and decomposes and oxidizes.

In the method for manufacturing a ferroelectric memory device according to the present invention, the oxygen amount of the oxygen gas at the time of forming the second ferroelectric film is smaller than an oxygen amount necessary for reacting the organometallic source gas. It may be 1.0 times or more.
In the present invention, the amount of oxygen in the oxygen gas at the time of forming the second ferroelectric film is set to 1.0 times or more than the amount of oxygen necessary for reacting the organometallic raw material gas, thereby providing the second ferroelectric film. A sufficient amount of oxygen is supplied during the formation of the body film to form a second ferroelectric film free from oxygen vacancies.

  Hereinafter, an embodiment of a method for manufacturing a ferroelectric memory device according to the present invention will be described 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, a ferroelectric memory device manufactured by the method for manufacturing a 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 32 (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 is made of Ir, for example. The lower electrode 23 is made of Ir, at least one of Pt, Ru (ruthenium), Rh (rhodium), Pd (palladium), and Os (osmium), or an alloy selected from those containing Ir. It may be constituted by. Further, the lower electrode 23 may be a single layer film or a laminated multilayer film.

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.
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). As the ferroelectric material constituting the ferroelectric film 24, a known material such as SBT or (Bi, La) ₄ Ti ₃ O ₁₂ (bismuth lanthanum titanate: BLT) is used in addition to PZT. Also good.

  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 31, the drain region 32 and the channel region (not shown) formed on the surface layer of the semiconductor substrate 2, the gate insulating film 33 formed on the channel region, and the gate insulating film 33. The gate electrode 34 is provided. The transistor 4 is electrically connected to the plug 17 formed on the drain region 32.
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 35 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, an electrode film 41a and an electrode oxide film 42a constituting the lower electrode 23a shown in FIG. 2F are formed on the oxygen barrier film 22a.
First, the electrode film 41a is formed on the oxygen barrier film 22a (FIG. 2D). Here, an electrode film 41a 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 41a on the crystalline oxygen barrier film 22a, the crystallinity of the electrode film 41a is remarkably improved, and the crystal orientation of the oxygen barrier film 22a is reflected in the electrode film 41a. Thereby, the electrode film 41a is oriented in the (111) plane orientation similar to that of the oxygen barrier film 22a.

Then, an electrode oxide film 42a is formed on the electrode film 41a (FIG. 2E). Here, an Ir oxide film 42a made of IrOx is formed on the electrode film 41a by forming Ir on the electrode film 41a by sputtering while supplying oxygen gas. Thus, the electrode oxide film 42a is formed with a uniform film thickness by using the sputtering method. In addition, since the electrode oxide film 42a 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, the ratio of oxygen gas supplied into the chamber at the time of sputtering film formation is 30% in terms of a molar ratio in a mixed gas with another gas such as an inert gas supplied together with the oxygen gas. As a result, a sufficiently oxidized electrode oxide film 42a is formed. Note that the ratio of oxygen gas at the time of sputtering film formation may be 20% or more and 40% or less.

  Next, a ferroelectric film 24a shown in FIG. 2G is formed on the electrode oxide film 42a. Here, the ferroelectric film 24a is formed by MOCVD using an MOCVD apparatus 50 as shown in FIG. Here, FIG. 3 is a schematic view showing an MOCVD apparatus. Further, FIG. 4 shows changes over time in the temperature of the semiconductor substrate 2 and the flow rate of oxygen gas by the MOCVD method.

  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.

First, an initial film (first ferroelectric film) 43a is formed on the electrode oxide film 42a (FIG. 2F). Here, the semiconductor substrate 2 on which the electrode oxide film 42a is formed is placed on the susceptor 52, and the semiconductor is heated by the heating lamp 54 while supplying the organic metal source gas and the oxygen gas into the chamber 51 from the supply pipes 55 and 56, respectively. The substrate 2 is heated from the lower surface side.
At this time, as a combination of each organic metal source gas supplied into the chamber 51, for example, a combination of Pb (DIBM), Zr (DIBM), Ti (OiPr) ₂ (DPM) ₂ , Pb (DPM) ₂ , Zr A combination of (IBPM) ₄ and Ti (OiPr) ₂ (DPM) ₂ can be given. DIBM is C ₉ H ₁₅ O ₂ (diisobutyryl methanato), IBPM is C ₁₀ H ₁₇ O ₂ (isobutyryl pivaloylmethanato), DPM is C ₁₁ H ₁₉ O ₂ (dipivaloylmethanato), OiPr represents Oi-C ₃ H ₇ respectively.

Here, as shown in FIG. 4, the heating temperature of the semiconductor substrate 2 is lower than 450 ° C. which is the recrystallization temperature of the electrode oxide film 42a and is 430 ° C. which is higher than the crystallization temperature of the initial film 43a. . Further, the flow rate of the oxygen gas is, for example, 600 sccm as shown in FIG. 4, and the oxygen amount is 0.1 times or more and less than 1.0 times the oxygen amount necessary for reacting the organic metal source gas. ing. That is, the amount of oxygen necessary for reacting the supplied organic metal source gas is not sufficiently supplied. The initial film 43a is formed for about 100 seconds, for example.
In this embodiment, the amount of oxygen necessary for reacting the organometallic source gas is necessary for burning carbon and hydrogen originating from the source of the organometallic source gas and discharging them as CO ₂ and H ₂ O. The sum of the amount of oxygen and the amount of oxygen necessary for crystallization of the PZT constituting the ferroelectric film 24a is shown.

The supplied organic metal source gas reacts with oxygen gas to be decomposed and oxidized to become crystallized PZT, which is deposited on the electrode oxide film 42a as the initial film 43a. At this time, since the oxygen gas is not sufficiently supplied, the organic metal source gas is separated and oxidized by taking oxygen in the IrOx constituting the electrode oxide film 42a. Further, since the heating temperature of the semiconductor substrate 2 is set lower than the recrystallization temperature of the electrode oxide film 42a, the initial film 43a is formed without the electrode oxide film 42a being recrystallized.
On the other hand, the electrode oxide film 42a has the same configuration as that of the electrode film 41a partially composed of Ir, because a part of oxygen in IrOx constituting the electrode oxide film 42a is deprived and reduced. At this time, since the deposition temperature of the initial film 43a is lower than the recrystallization temperature of the electrode oxide film 42a, the electrode oxide film 42a is not recrystallized. Further, even if the electrode oxide film 42a is reduced during the formation of the initial film 43a, recrystallization of the electrode oxide film 42a does not occur.
At this time, since the crystal orientation of the electrode film 41a is the (111) orientation, a part of the reduced electrode oxide film 42a exhibits the (111) orientation reflecting the crystal orientation of the electrode film 41a. Therefore, the initial film 43a exhibits a (111) orientation that reflects the crystal orientation of the reduced electrode oxide film 42a.

Here, by setting the film thickness of the electrode oxide film 42a to, for example, 20 nm or more and 30 nm or less, the electrode oxide film 42a reliably transmits the (111) orientation which is the surface structure of the lower electrode 23a to the initial film 43a.
Further, by setting the ratio of oxygen gas at the time of forming the electrode oxide film 42a to 20% or more and 40% or less, it is possible to prevent the electrode oxide film 42a from being sufficiently oxidized and close to a metallic state, and excessively. This prevents the orientation, which is the surface structure of the lower electrode 23a disposed in the lower layer, from being transmitted to the initial film 43a by oxidation.

Next, a core film (second ferroelectric film) 44a is formed on the initial film 43a (FIG. 2G). Here, similarly to the initial film 43a described above, the core film 44a is formed by the MOCVD method using the MOCVD apparatus 50.
At this time, the flow rate of the oxygen gas is, for example, 2000 sccm as shown in FIG. 4, and for example, the amount of oxygen in the oxygen gas is more than the amount of oxygen necessary for reacting the organometallic source gas. That is, the amount of oxygen necessary for reacting organic components in the supplied organometallic raw material gas is sufficiently supplied. Further, the heating temperature of the semiconductor substrate 2 is, for example, 650 ° C. which is equal to or higher than the recrystallization temperature of the electrode oxide film 42a. The formation time of the core film 44a is about 600 seconds, for example.

The supplied organic metal source gas reacts with oxygen gas in the same manner as described above, decomposes and oxidizes to form crystallized PZT, which is deposited on the initial film 43a as the core film 44a. At this time, by forming the core film 44a in an atmosphere sufficiently supplied with oxygen gas, a high-quality core film 44a with few oxygen vacancies is formed. Even if the electrode oxide film 42a that has not been reduced remains in the lower electrode 23a, the initial film 43a is formed on the lower electrode 23a. The regrowth of the electrode oxide film 42a is prevented even when the temperature is higher than the recrystallization temperature of the oxide film 42a.
As described above, the ferroelectric film 24a including the initial film 43a and the core film 44a is formed. The semiconductor substrate 2 may be heated using a heater provided on the susceptor 52.

Subsequently, an upper electrode 25a is formed on the ferroelectric film 24a (FIG. 2 (h)). 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.

Here, the PZT film (ferroelectric film 24) formed by the manufacturing method of the ferroelectric memory device 1 in the present embodiment, the PZT film formed by the conventional manufacturing method, and the oxide film by the conventional manufacturing method FIGS. 5 to 7 show surface morphologies with the PZT film when the film is formed by sputtering. Here, FIG. 5 to FIG. 7 are SEM images showing the surface morphology of the PZT film in each manufacturing method.
As shown in FIGS. 5 to 7, the PZT film formed by the manufacturing method in this embodiment is compared with the PZT film in the conventional manufacturing method or the manufacturing method in which the oxide film is formed by the sputtering method in the conventional manufacturing method. It can be seen that the surface of the PZT film is flattened and the surface morphology is improved.

As described above, according to the method for manufacturing the ferroelectric memory device 1 in the present embodiment, the initial film 43a is formed at a temperature lower than the recrystallization temperature of the electrode oxide film 42a to prevent recrystallization of the electrode oxide film 42a. As a result, the surface morphology of the ferroelectric film 24a can be improved, the defect of the capacitor characteristics of the ferroelectric capacitor 3 can be prevented, and the yield can be improved.
In addition, by setting the partial pressure of the oxygen gas during the sputter deposition of the electrode oxide film 42a to 20% or more and 40% or less, the electrode oxide film 42a can be sufficiently oxidized and the electrode oxide film 42a is oxidized. This prevents the orientation of the electrode film 41a from being transmitted to the initial film 43a without being reduced when the initial film 43a is formed due to being too stable.
The degree of crystal orientation of the ferroelectric film 24a can be further increased by setting the thickness of the electrode oxide film 42a to 30 nm or less.

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 film formation temperature is set lower than the recrystallization temperature of the electrode oxide film throughout the initial film formation process, but the film formation temperature must be lower than the recrystallization temperature at the stage of forming the bottom layer of the initial film. That's fine. That is, by covering the electrode oxide film with the lowermost layer of the initial film, significant regrowth of the electrode oxide film is suppressed even when the electrode oxide film is heated to a recrystallization temperature or higher. Further, the reduction of the electrode oxide film also suppresses the recrystallization of the electrode oxide film when the electrode oxide film is heated to the recrystallization temperature or higher. Therefore, the film formation temperature may be equal to or higher than the recrystallization temperature after the lowermost layer of the initial film is formed in the initial film formation process.
As long as the electrode oxide film can be formed at a low temperature as compared with oxidizing the surface layer of the lower electrode by thermal oxidation, other methods such as a CVD method may be used instead of the sputtering method.
Furthermore, the partial pressure of oxygen gas in the atmospheric gas during sputtering is set to 20% or more and 40% or less. If a sufficiently oxidized electrode oxide film can be formed and the initial film can have a desired crystal orientation, Other values may be used.
Further, although the film thickness of the electrode oxide film is set to 20 nm or more and 30 nm or less, other values may be used as long as the ferroelectric film can be formed with a desired crystal orientation.

Further, in the initial film formation step, the entire electrode oxide film is reduced, but it is sufficient that at least a part of the electrode oxide film including at least the outermost layer is reduced.
Furthermore, although the semiconductor substrate is heated from the lower surface side of the semiconductor substrate in the formation process of the ferroelectric film, it may be heated by other methods such as heating from the upper surface side.

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. It is a graph which shows a semiconductor substrate temperature and the time change of the flow volume of oxygen gas. It is a figure which shows the surface structure of the PZT film | membrane by the manufacturing method of this embodiment. It is a figure which shows the surface structure of the PZT film | membrane by the conventional manufacturing method. It is a figure which shows the surface structure of the PZT film | membrane which used the sputtering method by the conventional manufacturing method.

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, 41a Electrode film, 42a Electrode oxide film, 43a Initial film (1st ferroelectric) Body film), 44a Core film (second ferroelectric film)

Claims (6)

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;
By reaction with an organic metal raw material gas and oxygen gas, and forming a first ferroelectric film made of Pb (Zr, Ti) O ₃ on the lower electrode,
By reaction with an organic metal source gas and an oxygen gas, and forming a second ferroelectric layer consisting of Pb (Zr, Ti) O ₃ in the first ferroelectric film,
The lower electrode forming step includes a step of forming an electrode film made of an iridium film , and a step of forming an electrode oxide film made of an iridium oxide film on the electrode film by a sputtering method ,
In the step of forming the first ferroelectric film, the initial film formation temperature is made lower than the recrystallization temperature of the electrode oxide film by adjusting the temperature in a temperature range lower than the recrystallization temperature of the electrode oxide film. And a perovskite structure on the electrode film by a reaction between the organometallic source gas and the oxygen gas and oxygen atoms contained in the electrode oxide film, the temperature being higher than the crystallization temperature of the first ferroelectric film. A Pb (Zr, Ti) O ₃ film of
Forming a Pb (Zr, Ti) O ₃ film having a perovskite structure on the first ferroelectric film by a reaction between the organometallic source gas and the oxygen gas in the step of forming the second ferroelectric film; And a method of manufacturing a ferroelectric memory device. In the step of forming the first ferroelectric film, the film forming temperature is set to be equal to or higher than the recrystallization temperature after the lowermost layer of the first ferroelectric film is formed. Item 2. A method for manufacturing a ferroelectric memory device according to Item 1. 3. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the partial pressure of oxygen gas in the atmospheric gas during sputtering is 20% or more and 40% or less. The thickness of the electrolytic oxide film, method of manufacturing a ferroelectric memory device according to any one of claims 1 to 3, characterized in that at 30nm or less. The oxygen amount of the oxygen gas at the time of forming the first ferroelectric film is necessary for forming Pb (Zr, Ti) O ₃ having a perovskite structure by the reaction between the organometallic source gas and the oxygen gas. relative oxygen content, method of manufacturing a ferroelectric memory device according to claim 1, any one of 4, which is less than 1.0 times 0.1 times or more. The oxygen amount of the oxygen gas at the time of forming the second ferroelectric film is necessary for forming Pb (Zr, Ti) O ₃ having a perovskite structure by the reaction between the organometallic source gas and the oxygen gas. relative oxygen content, method of manufacturing a ferroelectric memory device according to any one of claims 1-5, characterized in that 1.0 times or more.

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