JP2009302305A - Manufacturing method of ferroelectric memory element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an improved ferroelectric memory element by forming a ferroelectric film having an improved crystal orientation. <P>SOLUTION: The manufacturing method of a ferroelectric memory element includes processes of: forming a first electrode 33a in an upper portion of a substrate; forming a titanium film 341 on the first electrode 33a; depositing a product generated by allowing a first organic metal gas to react with a first oxygen gas on the titanium film 341, forming a solid solution composed of the product and the titanium film 341 to form a first ferroelectric film 34a on the first electrode 33a; and forming a second electrode 35a at an upper portion of the first ferroelectric film 34a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a ferroelectric memory device.

  A ferroelectric memory device using spontaneous polarization of a ferroelectric material is expected as a nonvolatile memory device capable of low voltage operation and high speed operation. In addition, since the ferroelectric memory device can be composed of one transistor / one capacitor, the memory cell can be integrated as high as a DRAM and is expected as a large-capacity memory device.

Ferroelectric materials include perovskite oxides such as lead zirconate titanate (Pb (Zr, Ti) O ₃ , hereinafter referred to as PZT), and bismuth such as bismuth strontium tantalate (SrBi ₂ Ta ₂ O ₉ ). Layered compounds are promising. In order to maximize the spontaneous polarization of the ferroelectric material, the crystal orientation is extremely important.

  When PZT is used, the amount of spontaneous polarization can be increased by using a composition containing more Ti (titanium) than Zr (zirconium). In this composition range, PZT belongs to a face-centered cubic crystal, and its spontaneous polarization axis is the c-axis. In this case, the maximum amount of polarization can be obtained by c-axis orientation, but in reality, an a-axis orientation component perpendicular to the c-axis is simultaneously generated. Since the a-axis orientation component does not contribute to polarization reversal, if the ratio increases, the amount of spontaneous polarization decreases.

  Therefore, a method is considered in which the crystal orientation of the PZT is changed to the (111) orientation so that all crystal components contribute to the polarization inversion, and the charge extraction efficiency is improved as compared with the case of the c-axis orientation. In order to align the crystal orientation of PZT to (111), the crystal orientation of the lower electrode serving as the base is important. As a material for the lower electrode, it is considered that noble metals such as iridium and platinum are preferable from the viewpoint of thermal and chemical stability.

  Examples of the PZT film forming method include a sol-gel method, a sputtering method, and an MOCVD method. According to the MOCVD method, a film having a high film density can be formed, and the amount of spontaneous polarization can be increased. In addition, the MOCVD method can be expected to lower the film forming temperature and improve the coverage, and is therefore advantageous for achieving high integration of ferroelectric memory elements.

As a method of forming a (111) oriented ferroelectric film on a lower electrode made of a noble metal by MOCVD, there is one disclosed in Patent Document 1. In Patent Document 1, a (111) -oriented lower electrode made of iridium is formed, its surface layer is thermally oxidized to form an iridium oxide layer, and a ferroelectric film made of PZT is formed thereon. At the time of forming the ferroelectric film, the MOCVD method is used in which the organic metal source gas of PZT and oxygen gas are chemically reacted to form a film by supplying less oxygen gas necessary for the chemical reaction. Later, an oxygen gas more than the amount necessary for the chemical reaction is supplied to form a thick film. Although the detailed mechanism has not yet been elucidated, the iridium oxide layer contributes to the determination of the growth orientation of PZT, and PZT can be mainly (111) oriented.
JP 2003-324101 A

However, even if the method of Patent Document 1 is used, there is a possibility that the surface morphology becomes rough on the lower electrode for the following reason, and the self-polarization amount of the ferroelectric film is reduced.
Since iridium has a very high melting point, a film having a polycrystalline structure is formed when the film is formed with orientation controlled. When the surface layer is oxidized by thermal oxidation or the like, oxygen gas easily permeates between crystal grains, so that the speed and degree of oxidation vary between the crystal grains and the crystal grain boundaries. Then, the volume expansion due to oxidation varies, and surface morphology roughness having protrusions and the like on the surface layer of the lower electrode is generated. It is difficult to form a ferroelectric film by controlling the orientation on the protrusions, and it is difficult to make this part contribute to polarization reversal.

  In addition, as a technique different from Patent Document 1, it is conceivable to form the lower electrode from platinum. However, when PZT is formed on the lower electrode made of platinum, lead contained in the PZT organometallic source gas is thermally diffused into the lower electrode. Thermal diffusion of lead causes surface roughness on the lower electrode, which decreases the orientation of the ferroelectric film, and does not improve the interface bonding between the lower electrode and the ferroelectric film. Inconveniences such as deterioration of characteristics occur.

  The present invention has been made in view of the above circumstances, and provides a manufacturing method in which a good ferroelectric memory element can be obtained by forming a ferroelectric film having a good crystal orientation by MOCVD. Is one of the purposes.

  The method for manufacturing a ferroelectric memory device according to the present invention includes a step of forming a first electrode above a substrate, a step of forming a titanium film on the first electrode, a first organometallic gas, and a first oxygen. A product generated by reacting a gas is formed on the titanium film, and the product and the titanium film are dissolved to form a first ferroelectric film on the first electrode. And a step of forming a second electrode above the first ferroelectric film.

  In the step of forming the first ferroelectric film, since the first electrode is covered with the titanium film, the component derived from oxygen gas or organometallic gas is prevented from diffusing into the first electrode. Accordingly, surface roughness of the first electrode due to diffusion is prevented, and a flat first ferroelectric film can be formed on the flat first electrode. Therefore, a decrease in the amount of spontaneous polarization due to the unevenness can be avoided, and the first ferroelectric film having good characteristics can be obtained. As described above, according to the present invention, a ferroelectric film having good characteristics can be formed, and a good ferroelectric memory element can be manufactured.

Forming a second ferroelectric film by reacting a second organometallic gas and a second oxygen gas on the first ferroelectric film, and forming the first ferroelectric film; The ratio of titanium contained in the first organometallic gas is preferably smaller than the ratio of titanium contained in the second organometallic gas.
If an attempt is made to form the first ferroelectric film using the organometallic gas used in the second ferroelectric film forming step, a titanium-rich ferroelectric film is formed by the amount of the underlying titanium film, and leakage occurs. It becomes easy to produce.
If the ratio of titanium contained in the first organometallic gas is reduced as described above, the first ferroelectric film having a predetermined composition ratio can be formed, and leakage can be prevented.

Forming a second ferroelectric film by reacting a second organometallic gas and a second oxygen gas on the first ferroelectric film, and forming the first ferroelectric film; In the above, it is preferable that the first organometallic gas does not contain titanium.
When an organometallic gas containing titanium is reacted, a titanium-rich ferroelectric film is formed as much as the underlying titanium film, and leakage is likely to occur.
If the first organometallic gas not containing titanium is used as described above, the first ferroelectric film having a predetermined composition ratio can be formed, and leakage can be prevented.

In the step of forming the first ferroelectric film, the amount of the first oxygen gas is preferably equal to or less than an amount necessary for burning the organic component of the first organometallic gas.
In this way, a small amount of the first oxygen gas is consumed in the combustion of the first organometallic gas, and the underlying titanium film is not oxidized. Therefore, the crystal structure of the titanium film is prevented from being changed by oxidation, and the first ferroelectric film having a good crystal orientation can be formed. In addition, it is possible to prevent the solid solution of the titanium film from being hindered by the oxidation, and it is possible to form a good first ferroelectric film.

In the step of forming the first electrode, it is preferable to form the first electrode including a (111) -oriented surface layer belonging to a face-centered cubic crystal.
In this way, the titanium film can be formed reflecting the crystal structure of the surface layer of the first electrode, and the crystal orientation of the titanium film can be improved.

In the step of forming the first electrode, a first electrode including a surface layer made of iridium can be formed.
Since iridium is thermally and chemically stable, a highly reliable ferroelectric memory element can be obtained. Further, when the first electrode made of iridium is oxidized due to its polycrystalline structure, the surface morphology becomes rough. According to the present invention, since the diffusion of oxygen to the first electrode can be prevented, the oxidation of the first electrode can be prevented. Therefore, surface morphology roughness can be prevented, and a good first ferroelectric film can be formed on a good first electrode.

Further, in the step of forming the first electrode, the first electrode including a surface layer made of platinum can be formed.
Since platinum is thermally and chemically stable, a highly reliable ferroelectric memory element can be obtained. In the first electrode made of platinum, a component derived from an organometallic gas (for example, lead) is easily diffused, and if the diffusion occurs, the surface becomes rough and the characteristics are deteriorated. According to the present invention, since the diffusion of the component derived from the organometallic gas can be prevented, the surface roughness of the first electrode can be prevented, and a good first ferroelectric film can be formed on the good first electrode. Can be formed.

The titanium film preferably has a (001) close-packed structure belonging to hexagonal crystals.
Since titanium is a metal particularly excellent in self-orientation, a (001) close-packed titanium film belonging to hexagonal crystal can be formed. Therefore, a (111) -oriented first ferroelectric film belonging to tetragonal crystal can be formed on the titanium film. Since the (111) -oriented first ferroelectric film has good charge extraction efficiency, a ferroelectric capacitor including the first ferroelectric film can have good characteristics.

In the step of forming the titanium film, it is preferable to form the titanium film having a thickness of 2 nm to 5 nm.
If the thickness of the titanium film is 2 nm or more, the first electrode can be satisfactorily covered with the titanium film. Therefore, it is possible to prevent the first electrode from being partially exposed, and to reliably prevent the component derived from oxygen gas or organometallic gas from diffusing into the first electrode.
Further, it is preferable that the titanium film does not remain after the step of forming the first ferroelectric film. Further, it is preferable that the first electrode and the first ferroelectric film are in contact with each other after the step of forming the first ferroelectric film.
By eliminating the titanium film, it is possible to prevent deterioration of the characteristics of the ferroelectric memory element due to the remaining titanium film.

The first ferroelectric film is preferably PZT.
Since PZT has a track record as a ferroelectric material, it can be made highly reliable by using it.

  Hereinafter, although embodiment of this invention is described, the technical scope of this invention is not limited to the following embodiment. In the following description, various structures are illustrated using drawings, but in order to show the characteristic parts of the structures in an easy-to-understand manner, the structures in the drawings are shown in different sizes and scales from the actual structures. There is. First, the configuration of an example of a ferroelectric memory element obtained by the manufacturing method of the present invention will be described.

  FIG. 1 is a cross-sectional side view showing the main part of a ferroelectric memory device provided with a ferroelectric memory element (ferroelectric capacitor) of this example. As shown in FIG. 1, the ferroelectric memory device 1 has a stack type structure, and includes a base 2 having a transistor 22 and a ferroelectric capacitor 3 provided on the base 2.

The base 2 includes a transistor 22 provided on a silicon substrate (substrate) 21 made of, for example, single crystal silicon, and a base insulating film 23 made of SiO ₂ provided so as to cover the transistor 22. . An element isolation region 24 is provided on the surface layer of the silicon substrate 21, and the space between the element isolation regions 24 corresponds to one memory cell. The memory cell has a ferroelectric capacitor 3 and a transistor 22 for switching an electric signal to the ferroelectric capacitor 3. The ferroelectric memory device 1 includes a large number of memory cells, one of which is enlarged in FIG.

  The transistor 22 includes a gate insulating film 221 provided on the silicon substrate 21, a gate electrode 222 provided on the gate insulating film 221, source regions 223 provided on both sides of the gate electrode 222 on the surface of the silicon substrate 21, and The drain region 224 and sidewalls 225 provided on the side surfaces of the gate electrode 222 are configured. In this example, a first plug 25 that is electrically connected to the source region 223 is provided, and a second plug 26 that is electrically connected to the source region 223 is provided to the drain region 224.

  The first plug 25 and the second plug 26 are made of a conductive material such as W (tungsten), Mo (molybdenum), Ta (tantalum), Ti (titanium), or Ni (nickel). In this example, the first plug 25 is electrically connected to a bit line (not shown), and the source region 223 and the bit line are electrically connected through the first plug 25.

  The ferroelectric capacitor 3 of this example is formed on the conductive film 31 and the oxygen barrier film 32 that are sequentially formed on the base insulating film 23 and the second plug 26. The ferroelectric capacitor 3 has a configuration in which a lower electrode (first electrode) 33, a ferroelectric film 34, and an upper electrode (second electrode) 35 are stacked in order from the lower layer. The lower electrode 33 is electrically connected to the second plug 26 through the oxygen barrier film 32 and the conductive film 31. That is, the lower electrode 33 and the drain region 224 are electrically connected.

  The conductive film 31 is made of a conductive material such as TiN, and the oxygen barrier film 32 is made of a conductive material having an oxygen barrier property such as TiAlN, TiAl, TiSiN, TiN, TaN, and TaSiN. The conductive film 31 and the oxygen barrier film 32 are preferably made of a material containing Ti that is particularly excellent in self-orientation. In this way, the crystal orientation of the lower electrode 33 and the ferroelectric film 34 is improved. be able to.

  The lower electrode 33 is a single layer film or a multilayer film in which a plurality of layers are laminated. As the film constituting the lower electrode, at least one of Ir (iridium), Pt (platinum), Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium) or an alloy thereof or these A film made of these oxides can be used. In view of thermal and chemical stability, those made of noble metals such as iridium and platinum are preferred. Further, as will be described later in the first embodiment, a titanium film is formed on the lower electrode 33 in the manufacturing process of the ferroelectric capacitor. In order to control the orientation of the titanium film, the crystal structure of the lower electrode 33 is preferably a (111) orientation belonging to a face-centered cubic crystal or a (001) orientation belonging to a hexagonal crystal. In this example, the lower electrode 33 made of a single-layer iridium film is employed, and the crystal orientation is (111) orientation belonging to the face-centered cubic crystal.

The ferroelectric film 34 has a perovskite structure whose composition is represented by the general formula of ABO ₃ . A typical material is PZT containing lead at the A site and titanium and zirconium at the B site. A substance obtained by substituting a part of Pb at the A site with La (lanthanum), Ca (calcium), or Sr (strontium) may be used. In addition to Ti and Zr (zirconium) as B site, V (vanadium), Nb (niobium), Ta, Cr (chromium), Mo (molybdenum), W (tungsten), and Mg (magnesium) One or more may be added. Specific examples of the ferroelectric material other than PZT include SBT, (Bi, La) ₄ Ti ₃ O ₁₂ (bismuth lanthanum titanate: BLT), and the like.

  Since PZT has a track record as a ferroelectric material, it can be made highly reliable by using it. In the case of using PZT, it is preferable to make the Ti content larger than the Zr content from the viewpoint of increasing the spontaneous polarization amount. In this case, from the viewpoint of improving the hysteresis characteristics, the crystal structure of PZT is preferably (111) orientation belonging to tetragonal crystal.

  In this example, the upper electrode 35 is electrically connected to a ground line (not shown) and is made of a single layer film or a multilayer film. As the film constituting the upper electrode, a film made of Al (aluminum), Ag (silver), Ni (nickel), or the like can be used in addition to the film applicable to the lower electrode described above. In this example, a multilayer film in which a platinum film, an iridium oxide film, and an iridium film (not shown) are sequentially laminated from the lower layer side.

  With the above structure, when a voltage is applied to the gate electrode 222 of the transistor 22, an electric field is applied between the source region 223 and the drain region 224 to turn on the channel, and a current flows therethrough. It becomes possible. When the channel is turned on, an electric signal from the bit line electrically connected to the source region 223 is transmitted to the drain region 224 and further to the ferroelectric capacitor 3 electrically connected to the drain region 224. Is transmitted to the lower electrode 33. A voltage can be applied between the upper electrode 35 and the lower electrode 33 of the ferroelectric capacitor 3, and charges (data) can be accumulated in the ferroelectric film 34. As described above, the ferroelectric memory device 1 can read or write data (electric charge) by switching the electric signal to the ferroelectric capacitor 3 by the transistor 22.

  Next, an embodiment of a method for manufacturing a ferroelectric memory device according to the present invention will be described based on a method for manufacturing the ferroelectric memory device 1.

[First Embodiment]
2A to 2C, 3A to 3C, and 4A to 4C are cross-sectional process diagrams illustrating a method for manufacturing the ferroelectric memory device 1 of the present embodiment. is there. In FIG. 2B and subsequent figures, the lower layer structure of the base 2 such as the transistor 22 is omitted.

  First, as shown in FIG. 2A, the base 2 is formed using a known method or the like. Specifically, for example, the element isolation region 24 is formed on the silicon substrate 21 by the LOCOS method, the STI method, or the like, and the gate insulating film 221 is formed on the silicon substrate 21 between the element isolation regions 24 by the thermal oxidation method or the like. . Then, a gate electrode 222 made of polycrystalline silicon or the like is formed on the gate electrode 222. Then, impurities are implanted into the surface layer of the silicon substrate 21 between the element isolation region 24 and the gate electrode 222 to form doped regions 223 and 224. Then, a sidewall 225 is formed using an etch back method or the like. Then, impurities are further implanted into the doped regions 223 and 224 outside the sidewall 225 to form high-concentration impurity regions. Here, the doped region 223 is a source region, and the doped region 224 is a drain region.

Then, a base insulating film 23 is formed on the silicon substrate 21 on which the transistor 22 is formed by depositing SiO ₂ by, for example, a CVD method. Then, the base insulating film 23 on the source region 223 and the drain region 224 is etched to form a through hole that exposes the source region 223 and a through hole that exposes the drain region 224. Then, in each of these through holes, for example, Ti and TiN are sequentially formed by sputtering to form an adhesion layer (not shown).

  Then, tungsten is formed on the entire surface of the base insulating film 23 including the inside of the through hole by, for example, a CVD method, and the tungsten is embedded in the through hole. Then, the tungsten on the base insulating film 23 is removed by polishing the base insulating film 23 by a CMP method or the like. In this way, the first plug 25 is embedded in the through hole on the source region 223, and the second plug 26 is embedded in the through hole on the drain region 224. The base 2 is obtained as described above.

  Next, as shown in FIG. 2B, a conductive film 31a and an oxygen barrier film 32a are sequentially formed on the base insulating film 23. Specifically, Ti is formed on the base insulating film 23 by using, for example, a CVD method or a sputtering method. Since Ti has a high self-orientation property, a (001) -oriented close-packed film belonging to hexagonal crystals can be obtained. Then, a conductive film 31a made of TiN is formed by nitridation 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. If the temperature of the heat treatment is less than 650 ° C., the thermal effect on the transistor 22 can be reduced, and if the temperature is 500 ° C. or higher, the nitriding treatment can be shortened. The formed conductive film 31a has a (111) orientation belonging to the face-centered cubic crystal, reflecting the orientation of Ti in the original metal state.

  Then, a TiAlN film is formed on the conductive film 31a by using, for example, a sputtering method or a CVD method to form an oxygen barrier film 32a. The oxygen barrier film 32a can be formed epitaxially by matching the crystal orientation with the conductive film 31a serving as the base. That is, the (111) -oriented oxygen barrier film 32a belonging to the face-centered cubic crystal can be formed by reflecting the crystal orientation of the conductive film 31a.

Next, in this embodiment, a ferroelectric capacitor (ferroelectric memory element) is formed (manufactured) on the oxygen barrier film 32a.
First, as shown in FIG. 2C, the lower electrode 33a is formed on the oxygen barrier film 32a. Similar to the oxygen barrier film 32a, the lower electrode 33a can be formed by reflecting the crystal orientation of the base, and can be formed in the (111) orientation. Here, the lower electrode 33a having a thickness of about 100 nm is formed. Since iridium has an extremely high melting point, the lower electrode 33a has a polycrystalline structure having a large number of (111) -oriented crystal grains 331 and crystal grain boundaries (interfaces) 332 between the crystal grains 331.

  Next, as shown in FIG. 3A, a titanium film 341 is formed on the lower electrode 33a. As described above, titanium is a metal excellent in self-orientation, and a (001) -oriented titanium film 341 belonging to hexagonal crystal is obtained. Further, the lower electrode 33a has a (111) orientation belonging to the face-centered cubic crystal, and the crystal structure of the (001) orientation belonging to the hexagonal crystal is well lattice-matched, so that the titanium film 341 having a good crystal orientation is formed. Can be formed. The thickness of the titanium film is preferably 2 nm or more so that it covers the lower electrode 33a without exposing it, and is preferably 5 nm or less in order to satisfactorily dissolve the titanium film in a subsequent step. In the present embodiment, a titanium film is formed on the lower electrode 33a by sputtering to a thickness of about 5 nm to form a titanium film 341.

  Next, a ferroelectric film is formed on the lower electrode 33a using the MOCVD method. Here, a ferroelectric layer is formed by chemically reacting the first organometallic gas containing the metal component of the ferroelectric film and the first oxygen gas using the MOCVD apparatus 50 as shown in FIG. In this embodiment, a ferroelectric layer is formed and used as a ferroelectric film. Hereinafter, the configuration of the MOCVD apparatus will be described.

  FIG. 5 is a diagram schematically showing the MOCVD apparatus 50. As shown in FIG. 5, the MOCVD apparatus 50 includes a chamber 51 that houses the substrate 2, a susceptor 52 that is disposed in the chamber 51 and places the substrate 2, and a shower head 53 that supplies gas into the chamber 51. And a heating lamp 54 for heating the mounted substrate 2.

  The shower head 53 is provided with supply pipes 55 and 56 for supplying the raw material gas, oxygen gas, and the like of the ferroelectric film 34 into the chamber 51. The MOCVD apparatus 50 is configured to supply source gas into the chamber 51 from the supply pipe 55 and supply oxygen gas into the chamber 51 from the supply pipe 56 by supply means (not shown) provided outside the chamber 51. It has become. The supply pipes 55 and 56 are provided independently of each other, and are not encountered until the source gas and the oxygen gas are supplied to the chamber 51. The chamber 51 is appropriately provided with an exhaust port (not shown). The susceptor 52 is provided with a heater (not shown) separately from the heating lamp 54.

  In order to form a ferroelectric layer using the MOCVD apparatus 50, first, the substrate 2 on which the titanium film 341 is formed is placed on the susceptor 52. Then, a first organometallic gas, which is a mixed gas of a lead-containing first source gas, a titanium-containing second source gas, and a zirconium-containing third source gas, and a first oxygen are supplied from a supply pipe 56 into the chamber 51. Supply gas. Here, the mixing ratio of the first organometallic gas is adjusted so that the zirconium / titanium composition ratio is about 45/55 to 20/80.

Specific examples of the first source gas include Pb (DIBM) [Pb (C ₉ H ₁₅ O ₂ ) ₂ : lead bis (diisobutyrylmethanato)] and Pb (DPM) ₂ [Pb (C ₁₁ H ₁₉ O ₂ ) ₂ : Lead (dipivaloylmethanato)] and the like.
As a specific example of the second source gas, Ti (OiPr) ₂ (DPM) ₂ [Ti (Oi-C ₃ H ₇ ) ₂ (C ₁₁ H ₁₉ O ₂ ) ₂ : titanium (diisopropoxy) (diisobutene) Tyrylmethanato)], Ti (OiPr) ₂ (DPM) _{2 and the} like.
Specific examples of the third source gas include Zr (DIBM) [Zr (C ₉ H ₁₅ O ₂ ) ₂ : zirconium (diisobutyrylmethanato)] and Zr (IBPM) ₄ [Zr (C ₁₀ H ₁₇ O ₂ ) ₂ : zirconium tetrakis (isobutyryl pivaloylmethanato)] and the like.

The first organometallic gas and the first oxygen gas are supplied, and the base 2 is heated from the lower surface side to about 550 to 650 ° C. (here, 620 ° C.) by the heating lamp 54, and the The first organometallic gas and the first oxygen gas are chemically reacted. As the amount of the first oxygen gas to be supplied. The range is about 2000 to 5000 sccm. Thereby, carbon or hydrogen, which is an organic component contained in the first organometallic gas, can be burned, and lead, titanium, and zirconium, which are metallic components contained in the first organometallic gas, can be separated. The separated metal components are active, are bonded to each other, and are oxidized by the first oxygen gas to form a product film. The product here refers to, for example, PbOx, ZrOx, TiOx, PZT and the like. The production process of these products is as follows. Organic molecules CxHyOz coordinated to the organometallic raw materials (Pb- (CxHyOz), Zr- (CxHyOz), Ti- (CxHyOz) react with oxygen supplied to the chamber and burn, that is, such as CO ₂ or H ₂ O The metal atoms begin to oxidize and form oxides such as PbOx, TiOx, ZrOx, etc. These collide with each other and react, and partly Pb (Zr, Ti) Ox (PZT). PbOx, TiOx, ZrOx, and PZT are referred to as products, and some organic molecules are not completely detached and remain partially bonded, for example, (CxHyOz) -MO (M: Pb, Zr, Ti) and the like are also included in the product.

  Further, titanium contained in the titanium film 341 diffuses in the product film, and lead, zirconium, and oxygen diffuse in the titanium film 341. Since the lower electrode 33a is covered with the titanium film 341, the metal component and oxygen are prevented from diffusing here. Therefore, the lower electrode 33a made of iridium is prevented from being unevenly oxidized due to its polycrystalline structure and causing surface roughness. In this way, the titanium film 341 and the film made of the product of the chemical reaction are solid-solved and integrated to obtain a ferroelectric layer having a uniform composition. Here, the thickness of the ferroelectric layer is set to about 100 nm, and this is used as the ferroelectric film 34a as shown in FIG. The ferroelectric film 34a can be made to have a (111) orientation belonging to the face-centered cubic crystal, reflecting the crystal orientation of the titanium film 341.

Next, as shown in FIG. 3C, an upper electrode 35a made of a metal material such as platinum, iridium oxide, or iridium is formed on the ferroelectric film 34a by using, for example, a sputtering method or a CVD method.
Next, the conductive film 31a, the oxygen barrier film 32a, the lower electrode 33a, the ferroelectric film 34a, and the upper electrode 35a are patterned by using a known resist technique and photolithography technique to form the ferroelectric capacitor 3. To do. In this way, the ferroelectric memory device 1 shown in FIG. 1 is obtained.

  In the manufacturing method of this embodiment, since the (001) -oriented titanium film 341 is formed, oxidation of the lower electrode 33a is prevented, and surface roughness of the lower electrode 33a is prevented. Therefore, a flat ferroelectric film 34a can be formed above the flat lower electrode 33a. Further, the (111) -oriented ferroelectric film 34a belonging to the face-centered cubic crystal can be formed reflecting the orientation of the titanium film 341. Thus, a good ferroelectric film 34a can be formed, and a good ferroelectric memory element 3 can be manufactured.

In the first embodiment, the lower electrode 33a is formed of iridium, but it may be formed of platinum. In this case, the metal component contained in the first organometallic gas, such as lead, is prevented from diffusing into the lower electrode, and surface roughness of the lower electrode is prevented. Further, the surface layer of the lower electrode may have a (001 orientation) belonging to a hexagonal crystal in addition to the (111) orientation belonging to the face-centered cubic crystal. In addition, other crystal orientations may be used. In this case, by making it amorphous, the self-orientation of titanium can be expressed well, and the orientation of the titanium film can be improved. Specific examples of the amorphous surface layer include iridium oxide.
Although the stack type ferroelectric memory device has been described in the first embodiment, the present invention can also be applied to a planar type, and the effect of the present invention can also be obtained in this case.

[Second Embodiment]
Next, a second embodiment of the method for manufacturing a ferroelectric memory element according to the present invention will be described. This embodiment is different from the first embodiment in that a ferroelectric layer is formed by performing a low titanium process, and a ferroelectric layer (first ferroelectric film) and a core layer (second ferroelectric). A ferroelectric film composed of a body film) is formed.

  4A to 4C are cross-sectional process diagrams illustrating a method for manufacturing a ferroelectric memory element according to the second embodiment. First, as shown in FIG. 4A, as in the first embodiment, a conductive film 31a, an oxygen barrier film 32a, a lower electrode 33a, and a titanium film are formed on the base 2 shown in FIG. 2A. 341 are formed in order.

  Next, as shown in FIG. 4B, the first organometallic gas and the first oxygen gas are chemically reacted to form a product on the titanium film 341, and this film and the titanium film 341 are formed. The ferroelectric layer 342 is formed by solid solution. Specifically, the substrate 2 on which the titanium film 341 is formed is placed on the susceptor 52 of the MOCVD apparatus 50. Then, the first organometallic gas and the first oxygen gas are supplied from the supply pipe 56 into the chamber 51. In the present embodiment, the first organometallic gas is supplied in which the composition ratio of titanium in the metal component is smaller than that of the ferroelectric film. Here, the first organometallic gas composed of the first source gas and the third source gas is supplied without supplying the second source gas containing titanium.

  The first organometallic gas and the first oxygen gas are supplied, and the base 2 is heated from the lower surface side to about 550 to 650 ° C. (here, 620 ° C.) by the heating lamp 54, and the The first organometallic gas and the first oxygen gas are chemically reacted. As the amount of the first oxygen gas to be supplied. The range is about 2000 to 5000 sccm. Thereby, lead and zirconium, which are metal components contained in the first organometallic gas, can be separated. The separated metal components are active, are bonded to each other, and are oxidized by the first oxygen gas to form a film.

  In addition, titanium contained in the titanium film 341 diffuses in the film, and lead, zirconium, and oxygen diffuse in the titanium film 341. The titanium film 341 and the film made of the product of the chemical reaction are solid-dissolved and integrated, and a portion consisting essentially of titanium is eliminated. As a result, a ferroelectric layer 342 is obtained as shown in FIG. Here, the thickness of the ferroelectric layer is about 5 nm. The ferroelectric layer 342 can have a (111) orientation belonging to a tetragonal crystal reflecting the crystal orientation of the titanium film 341.

By the way, when the ferroelectric layer has a titanium-rich composition, leakage easily occurs here, and it becomes difficult to secure the height of the Schottky barrier between the lower electrode and the ferroelectric layer. Therefore, the ferroelectric film is liable to leak.
In this embodiment, since the ferroelectric layer 342 is formed by reducing the supply amount of titanium by the amount corresponding to the titanium film 341, it is possible to prevent this from becoming a titanium-rich composition.

Next, as shown in FIG. 4C, a ferroelectric material is formed on the ferroelectric layer 342 to form the core layer 343, and the ferroelectric composed of the ferroelectric layer 342 and the core layer 343 is formed. The body film 34a is formed. As a method for forming the core layer, a sol-gel method, a sputtering method, or the like can be used in addition to the MOCVD method. In this embodiment, after the ferroelectric layer 342 is formed, the base is left on the susceptor 52 of the MOCVD apparatus 50, and the core layer 343 is formed by the MOCVD method. The core layer 343 can be formed in the same manner as the ferroelectric layer in the first embodiment. Here, the second organometallic gas, which is a mixed gas of the first to second source gases similar to the first embodiment, and the second oxygen gas are supplied to form the core layer 343 having a thickness of about 95 nm. To do. The core layer 343 can be formed by reflecting the crystal orientation of the ferroelectric layer 342, and can have a (111) orientation belonging to a face-centered cubic crystal.
Then, the ferroelectric memory device 1 shown in FIG. 1 is obtained by forming the upper electrode 35a, patterning, and the like as in the first embodiment.

  In the method for manufacturing a ferroelectric memory element according to the present embodiment, the ferroelectric layer 342 is formed by a low titanium process, so that the ferroelectric layer 342 has a titanium-rich composition due to the titanium film 341. It is prevented. Therefore, the ferroelectric film 34a that hardly causes leakage can be obtained. In addition, since the titanium composition ratio in the ferroelectric layer 342 and the titanium composition ratio in the core layer 343 can be made substantially the same, the characteristics of the ferroelectric film 34a can be stabilized. Further, since the ferroelectric layer 342 and the core layer 343 are formed in the (111) orientation, the ferroelectric film 34a made of these layers has good characteristics, and good ferroelectric with the same is provided. A body memory device can be manufactured.

[Third Embodiment]
Next, a third embodiment of the method for manufacturing a ferroelectric memory device will be described. This embodiment is different from the second embodiment in that a ferroelectric layer is formed by performing a low oxygen process. Specifically, the substrate 2 on which the titanium film 341 is formed is placed on the susceptor 52 of the MOCVD apparatus 50. Then, the first organometallic gas and the first oxygen gas are supplied from the supply pipe 56 into the chamber 51. The amount of the first oxygen gas to be supplied is not more than the amount necessary for burning the organic component of the first organometallic gas to be supplied. The amount of oxygen gas required to burn organic components can be calculated based on stoichiometry.

  In the present embodiment, the amount of the first oxygen gas to be supplied is about 625 to 1000 sccm. Further, as in the second embodiment, the first organometallic gas composed of the first source gas and the third source gas is supplied without supplying the titanium-containing second source gas. In this way, the supplied first oxygen gas is consumed for the combustion of the organic component of the first organometallic gas, which is prevented from oxidizing the titanium film 341. When the titanium film is oxidized, the crystal orientation becomes a rutile type, and it becomes difficult to form a tetragonal ferroelectric layer thereon. In this embodiment, the titanium film 341 is prevented from being oxidized. Therefore, the ferroelectric layer 342 having a favorable crystal orientation can be formed.

Then, by forming the core layer 343 on the ferroelectric layer 342 in the same manner as in the second embodiment, the ferroelectric film 34a is obtained. Here, the amount is larger than the amount necessary for burning the organic component of the second organometallic gas that supplies the second oxygen gas that is supplied when the core layer 343 is formed. Thereby, when the oxygen defect is produced in the ferroelectric layer 342 by the low oxygen process, this can be repaired.
Then, the ferroelectric memory device 1 shown in FIG. 1 is obtained by forming the upper electrode 35a, patterning, and the like as in the first embodiment.

  In the method for manufacturing a ferroelectric memory element of this embodiment, since the ferroelectric layer 342 is formed by a low oxygen process, oxidation of the titanium film 341 is prevented. Therefore, it is possible to prevent a change in crystal structure due to oxidation in the titanium film 341 and to form a ferroelectric layer having a good crystal orientation. Therefore, a good ferroelectric film 34a can be formed, and a good ferroelectric memory element can be manufactured.

1 is a side cross-sectional configuration diagram illustrating an example of a ferroelectric memory device according to a method of the present invention. (A)-(c) is sectional process drawing which shows the manufacturing method of 1st Embodiment. (A)-(c) is sectional process drawing which continues from FIG.2 (c). (A)-(c) is sectional process drawing which shows the manufacturing method of 2nd Embodiment. It is a schematic diagram which shows the structure of a MOCVD apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ferroelectric memory device, 2 ... Base | substrate, 3 ... Ferroelectric memory element, 21 ... Silicon substrate (substrate | substrate), 22 ... Transistor, 33, 33a ... Lower electrode , 34, 34a ... ferroelectric film, 35, 35a ... upper electrode, 332, 332a ... platinum film (surface layer), 341 ... titanium film, 342 ... ferroelectric layer (first layer) 1 ferroelectric film), 343... Core layer (second ferroelectric film)

Claims (12)

Forming a first electrode above the substrate;
Forming a titanium film on the first electrode;
A product generated by reacting the first organometallic gas and the first oxygen gas is formed on the titanium film, and the product and the titanium film are dissolved to form a solution on the first electrode. Forming a first ferroelectric film on the substrate;
Forming a second electrode above the first ferroelectric film, and a method for manufacturing a ferroelectric memory device. Forming a second ferroelectric film by reacting a second organometallic gas and a second oxygen gas on the first ferroelectric film;
The ratio of titanium contained in the first organometallic gas in the step of forming the first ferroelectric film is smaller than the proportion of titanium contained in the second organometallic gas. A method for manufacturing a ferroelectric memory device according to claim 1. Forming a second ferroelectric film by reacting a second organometallic gas and a second oxygen gas on the first ferroelectric film;
2. The method of manufacturing a ferroelectric memory device according to claim 1, wherein, in the step of forming the first ferroelectric film, the first organometallic gas does not contain titanium.   3. The step of forming the first ferroelectric film, wherein an amount of the first oxygen gas is equal to or less than an amount necessary for burning an organic component of the first organometallic gas. Or a method for producing a ferroelectric memory device according to 3 above.   5. The strong electrode according to claim 1, wherein in the step of forming the first electrode, a first electrode including a (111) -oriented surface layer belonging to a face-centered cubic crystal is formed. A method of manufacturing a dielectric memory device.   6. The method of manufacturing a ferroelectric memory element according to claim 1, wherein, in the step of forming the first electrode, a first electrode including a surface layer made of iridium is formed.   6. The method of manufacturing a ferroelectric memory element according to claim 1, wherein in the step of forming the first electrode, a first electrode including a surface layer made of platinum is formed.   The method for manufacturing a ferroelectric memory element according to claim 1, wherein the titanium film has a (001) close-packed structure belonging to a hexagonal crystal.   9. The method of manufacturing a ferroelectric memory element according to claim 1, wherein in the step of forming the titanium film, the titanium film having a thickness of 2 nm to 5 nm is formed.   10. The method of manufacturing a ferroelectric memory element according to claim 9, wherein the titanium film does not remain after the step of forming the first ferroelectric film.   11. The method of manufacturing a ferroelectric memory device according to claim 9, wherein the first electrode and the first ferroelectric film are in contact with each other after the step of forming the first ferroelectric film. Method. The method for manufacturing a ferroelectric memory element according to claim 1, wherein the first ferroelectric film is PZT.

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