JP2005079538A - Ferroelectric film, ferroelectric capacitive element, and manufacturing method of them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferroelectric, capable of preventing a polarization property of a ferroelectric capacitor to a crystal grain size difference of the ferroelectric from deteriorating and which will not produce deterioration, even if a capacitor size is reduced accompanying microfabrication of a device, a capacitive element using the ferroelectric, and to provide a method of manufacturing the ferroelectric and the capacitive element. <P>SOLUTION: The ferroelectric capacitive element is provided with an insulating film 13a formed on a substrate 1, a lower electrode 5 embedded in the insulating film 13a so that at least a part of a front surface of the lower electrode 5 is exposed, a ferroelectric film 12 formed so as to extend over the insulating film 13a and the lower electrode 5, and an upper electrode 7 formed on the ferroelectric film 12. A crystal grain size of the ferroelectric film 12 is formed almost uniformly on the insulating film 13a contacting with the ferroelectric and on the lower electrode 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ferroelectric film, a capacitive element using the same, and a manufacturing method thereof.

  In recent years, with the advancement of digital technology, electronic devices have become more sophisticated as the tendency to process and store large volumes of data has been promoted, and semiconductor devices used have been rapidly miniaturized. . Along with this, in order to realize high integration of dynamic RAM (Random Access Memory), instead of conventional silicon oxide or nitride, a dielectric having a high dielectric constant (hereinafter referred to as high dielectric) is used as a storage capacity. A technology used as a capacitor film of an element has been widely researched and developed.

  Furthermore, research and development on ferroelectrics having spontaneous polarization characteristics are being actively pursued with the aim of commercializing a non-volatile RAM capable of high-speed writing and reading that has never been achieved.

  As a ferroelectric thin film used for a nonvolatile RAM, a bismuth layered structure ferroelectric having excellent resistance to rewriting stored data and capable of operating at a low voltage is promising. In general, a bismuth layer structure is represented by the following chemical formula (1).

(Chemical formula 1)
(Bi ₂ O ₂ ) (A _m-1 B _m O _{3m + 1} ) (1)
m: integer from 1 to 5
A: 1 to 3 metal
B: Tetravalent to hexavalent metal This structure is a structure in which bismuth oxide layers Bi ₂ O ₂ and perovskite layers A _m-1 B _m O _{3m + 1} are alternately laminated.

  Among a group of materials having a bismuth layer structure, a material called SBT is often used for nonvolatile memory applications. SBT is represented by the following chemical formula (2) in which m = 2, A is divalent Sr, and B is pentavalent Ta in the chemical formula (1) (hereinafter referred to as a normal type).

(Chemical 2)
(Bi ₂ O ₂ ) (SrTa ₂ O ₇ ) (2)
In addition, as shown in the schematic cross-sectional view of FIG. 10, the laminated structure of the normal type SBT has a structure in which bismuth oxide layers 201 and m = 2 perovskite layers 202 are alternately laminated.

The bismuth oxide layer 201 (chemical formula Bi ₂ O ₂ ) has a structure in which quadrangular pyramids are connected and spread in a plane as shown in the schematic diagram of the crystal structure in FIG. Bismuth 203 exists at the apex of the quadrangular pyramid, and oxygen 204 exists at each apex of the bottom surface. FIG. 11 also illustrates atoms such as oxygen atoms that exist at the boundary between the bismuth oxide layer 201 and the perovskite layer 202 in FIG. The same applies to other crystal structure schematic views.

The m = 2 perovskite layer 202 (chemical formula SrTa ₂ O ₇ ) has a layered structure in which two oxygen octahedrons are two-dimensionally spread as shown in the schematic diagram of the crystal structure in FIG. is there. Tantalum 205 exists at the B site, which is the center of the oxygen octahedron, and oxygen 204 exists at each vertex of the octahedron. In addition, strontium 206 is present at the A site, which is a space surrounded by an oxygen octahedron. The A site and B site also correspond to A and B in the chemical formula (1).

  SBT has also been attempted to improve the spontaneous polarization amount and prevent the spontaneous polarization amount from decreasing as the capacitor size is reduced.

The following two crystal structures have been proposed as a method for improving the spontaneous polarization of SBT.
[1] Mixed laminated superlattice type (for example, see Patent Document 1 below)
In the present invention, the entire layered structure is described widely, but here, a case where it is specifically applied to SBT will be described in accordance with the gist of the present invention.

  As shown in the cross-sectional schematic diagram of the mixed laminated superlattice, either the m = 2 perovskite layer 202 or the m = 1 perovskite layer 207 is between the bismuth oxide layers 201 as follows: Exists with range existence probability. If the existence probability of the perovskite layer 207 with m = 1 is δ (0 <δ <1), the existence probability of the perovskite layer 202 with m = 2 is 1−δ.

The m = 1 perovskite layer 207 is represented by TaO ₄ and has a layered structure in which an oxygen octahedron monolayer centered on tantalum 205 is expanded two-dimensionally as shown in the schematic diagram of its crystal structure in FIG. is there. If the valence is strictly calculated, the chemical formula is TaO _7/2 , and the number of oxygen is insufficient to form the structure of FIG. The lack of oxygen becomes vacancies.

The characteristics of the mixed laminated superlattice are that the amount of bismuth having a low melting point is larger than that of the normal structure, so that the crystal grains can be grown easily and the spontaneous polarization characteristics can be improved (the spontaneous polarization amount can be increased, etc.). It can be done.
[2] A-site Bi substitution type (for example, see Patent Document 2 below)
It is SBT having a composition represented by the following chemical formula (3).

(Chemical formula 3)
(Bi ₂ O ₂ ) [(Sr _1-x Bi _x ) Ta ₂ O ₇ ] (3)
Here, 0 <x <1.

If the cross-sectional schematic diagram of FIG. 10 is used to explain the laminated structure, it has a structure in which bismuth oxide layers 201 and m = 2 perovskite layers 202 are alternately laminated. The bismuth oxide layer 201 is represented by the chemical formula Bi ₂ O ₂ and has the same crystal structure of FIG. The m = 2 perovskite layer 202 is represented by the chemical formula (Sr _1-x Bi _x ) Ta ₂ O ₇ (where 0 <x <1). The A site is occupied by Sr with probability 1-x and Bi with probability x. In the normal type, the A site is all occupied by Sr, but it is replaced by Bi for x.

  Recent studies have confirmed that holes are generated at the A site. The reason is that a part of the divalent Sr is substituted with trivalent Bi, so that vacancies are generated to satisfy the charge neutrality law. In this case, the formula (3) becomes the following chemical formula (4).

(Chemical formula 4)
(Bi ₂ O ₂ ) [(Sr _1-x Bi _{2x / 3} ) Ta ₂ O ₇ ] (4)
(However, 0 <x <1)
In this case, the m = 2 perovskite layer 202 is represented by the chemical formula (Sr _1-x Bi _{2x / 3} ) Ta ₂ O ₇ and the A site is Sr with probability 1−x, Bi with probability 2x / 3, probability x / 3 is occupied by holes.

The feature of the A-site Bi substitution type is that Bi ³⁺ having a small ionic radius is substituted for Sr ²⁺ occupying the A site, so that the lattice distortion increases and the amount of spontaneous polarization increases.

  Also, like the mixed superlattice type, the amount of Bi having a low melting point is larger than that of the normal type, so it is easy to grow crystal grains and improve the spontaneous polarization characteristics (e.g., increase the amount of spontaneous polarization). be able to.

  The above two conventional methods show a method for increasing the spontaneous polarization.

On the other hand, the following two proposals have been made as a method for preventing the spontaneous polarization amount from decreasing with the miniaturization of the capacitor size.
[3] Seed crystallization (see, for example, Patent Document 3 below)
A large ferroelectric crystal is generated on the surface of the lower electrode using the seed provided on the surface of the lower electrode as a starting point for crystallization, and a thin film capacitor with very few crystal grain boundaries is realized by forming an upper electrode smaller than this crystal. Yes.
[4] Crystallization after processing (for example, see Patent Document 4 below)
A method is shown in which a dielectric film is formed by depositing an upper electrode on a precursor film made of an amorphous phase or a fluorite phase and then processing it into a capacitor shape by etching, followed by heat treatment to change the phase to perovskite. According to this method, the capacitor area is reduced due to metal deposition on the capacitor side wall and conductive oxide generation that occurs when a capacitor is processed by depositing an upper electrode on a dielectric film crystallized in advance in perovskite. The problem that accompanies is solved.

These conventional examples were effective in suppressing leakage current and breakdown voltage reduction, and it was expected that the amount of spontaneous polarization could be prevented from decreasing with capacitor size miniaturization.
Japanese National Patent Publication No. 11-509683 JP-A-9-213905 Japanese Patent Laid-Open No. 2001-6864 JP-A-11-121696

  However, in the above-described conventional example, it has been clarified through experiments by the present inventors that the ferroelectric polarization characteristics are deteriorated such as a decrease in the polarization amount as the capacitor area is miniaturized.

  The reason for this is that in these structures, the invention has been made paying attention to the improvement of the ferroelectric crystal when forming the ferroelectric on the lower electrode. On the insulating film and on the lower electrode, each electrode is formed separately, each individual lower electrode is embedded in the insulating film, and at least a part of the surface of the lower electrode is exposed. In the case where the ferroelectric is formed so as to straddle, the base of the ferroelectric is composed of a different film of the lower electrode and the insulating film. Since the ferroelectric crystal nuclei are mainly generated on the electrode surface, large ferroelectric crystal grains can be formed on the electrode as compared with the insulating film, and it has been found that the above-mentioned problem occurs.

  For this reason, even if the spontaneous polarization can be increased with a relatively large capacitor, the proportion of the influence of relatively small ferroelectric crystal grains around the electrode increases as the capacitor area becomes finer, resulting in a decrease in ferroelectric polarization characteristics. I found out that

  As described above, the conventional example has a problem that it is impossible to obtain a capacitive element having the reliability necessary for miniaturization of the capacitor.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and is a ferroelectric in which the ferroelectric polarization characteristics are prevented from being deteriorated due to the miniaturization of the area of the ferroelectric capacitor, the capacitive element using the ferroelectric, and the manufacturing process. An object of the present invention is to provide a ferroelectric film in which deterioration of ferroelectric polarization characteristics is prevented by adding a paraelectric precursor to the dielectric precursor, and a method of manufacturing a capacitive element using the same.

  That is, the present inventors added a paraelectric precursor to the ferroelectric precursor, and crystallized this to form a ferroelectric film. As a result, crystal nucleation occurs, and the crystallization of the ferroelectric material, which is independent of the underlayer, occurs, and a ferroelectric material in which the difference in crystal grain size on the surface of the buried electrode and the surrounding insulating film is suppressed is obtained. Therefore, it has been found that the crystal grain size of the ferroelectric film is formed almost uniformly on the insulating film and the conductor in contact with the ferroelectric substance. Therefore, the present invention can prevent a failure due to an increase in leakage current of a capacitive element or a decrease in breakdown voltage, or a decrease in polarization characteristics such as a decrease in polarization amount, and can prevent a deterioration in ferroelectric polarization characteristics. The present invention provides a dielectric film, a ferroelectric memory that can be highly integrated, a capacitive element that can realize a high dielectric memory, and a method of manufacturing the same.

  In order to achieve the above object, the ferroelectric film of the present invention includes an insulating film formed on a substrate and a conductor embedded in the insulating film so that at least a part of its surface is exposed. A ferroelectric film formed over the insulating film, wherein a crystal grain size of the ferroelectric film is formed substantially uniformly on the insulating film and the conductor in contact with the ferroelectric substance. To do.

  The ferroelectric capacitor of the present invention includes an insulating film formed on a substrate, a lower electrode embedded in the insulating film so that at least a part of the surface thereof is exposed, the insulating film and A ferroelectric film formed over the lower electrode; and an upper electrode formed on the ferroelectric film, wherein the insulating film has a crystal grain size in contact with the ferroelectric. It is characterized by being formed substantially uniformly on the upper and lower electrodes.

  In the ferroelectric capacitor according to the present invention, it is preferable that the crystal grain size of the lower electrode in a portion in contact with the ferroelectric is formed to be substantially uniform.

  In the ferroelectric capacitor of the present invention, it is preferable that the crystal grain size of the upper electrode in a portion in contact with the ferroelectric is formed to be substantially uniform.

In the ferroelectric capacitor of the present invention, the thickness of the ferroelectric film is 100 nm or less, and the size of the capacitance defining port defined by the lower electrode is 50 × 50 μm ² or less. Is preferred.

In the ferroelectric capacitor according to the present invention, the ferroelectric capacitor is preferably a ferroelectric capacitor that generates a residual polarization amount of at least 15 μC / cm ² by 1.8 V pulse wave switching.

  The method for manufacturing a ferroelectric film according to the present invention extends over an insulating film formed on a substrate and a conductor embedded in the insulating film so that at least a part of the surface is exposed. A method for manufacturing a ferroelectric film for forming a ferroelectric film, comprising: forming a conductor patterned in a predetermined shape on the substrate; and insulating the conductor to cover the conductor Forming a film; removing a predetermined region of the insulating film to expose at least part of the surface of the conductive film; and forming a ferroelectric precursor on the insulating film and the exposed conductor. And a paraelectric precursor containing at least a part of the constituent metal elements of the ferroelectric film to form a precursor film, and crystallizing the precursor film to form the ferroelectric film And a step of forming a film.

  The method for manufacturing a ferroelectric capacitor according to the present invention extends over an insulating film formed on a substrate and a lower electrode embedded in the insulating film so that at least a part of the surface is exposed. A method of manufacturing a capacitive element having a formed ferroelectric film, comprising: forming a lower electrode on the substrate; and forming a first insulating film on the substrate so as to cover the lower electrode A step of removing a predetermined region of the first insulating film to expose at least a part of the surface of the lower electrode, and a ferroelectric layer on the first insulating film and the exposed lower electrode. Forming a precursor film by mixing a conductive precursor and a paraelectric precursor containing at least a part of the constituent metal elements of the ferroelectric film, and forming an upper electrode on the precursor film. And forming a second insulating film on the upper electrode. And a step of crystallizing the precursor film to form the ferroelectric film.

  In the method for manufacturing a ferroelectric capacitor according to the present invention, it is preferable that after forming the upper electrode on the precursor film, the precursor film is crystallized to form the ferroelectric film.

  In the method for manufacturing a ferroelectric capacitor according to the present invention, the second insulating film is formed on the upper electrode, and then the precursor film is crystallized to form the ferroelectric film. Is preferred.

  According to the present invention, it is possible to prevent the deterioration of the polarization characteristics of the ferroelectric capacitor with respect to the difference in the crystal grain size of the ferroelectric, and the ferroelectric film that does not deteriorate even when the capacitor size is reduced as the device is miniaturized Capacitance elements using the same and methods for manufacturing these can be provided. Therefore, the present invention is useful for the downsizing of electronic devices and the manufacture of electronic devices that can process or store a larger amount of data.

  The ferroelectric film of the present invention is a ferroelectric film formed over an insulating film formed on a substrate and a conductor embedded so as to be partially exposed in the insulating film. Thus, the crystal grain size of the ferroelectric film is formed substantially uniformly on the insulating film and the conductor. Accordingly, it is possible to provide a ferroelectric that prevents the polarization characteristics of the ferroelectric capacitor from being deteriorated.

  In the ferroelectric film of the present invention, it is preferable that the ferroelectric film has a bismuth layer structure in which bismuth oxide layers and perovskite layers are alternately stacked. By using the ferroelectric film having such a structure, a highly reliable ferroelectric capacitor can be provided.

In the ferroelectric film of the present invention, the bismuth oxide layer has a Bi ₂ O ₂ structure, and the perovskite layer has (A _1−x Bi _{2x / 3} ) _m−1 B _m O _{3m + 1} (0 < x <1) structure, and in the (A _1-x Bi _{2x / 3} ) _m-1 B _m O _{3m + 1} structure, A is composed of a divalent metal, B is composed of a pentavalent metal, m Is preferably m = 1 with probability δ (0 <δ <1) and m = 2 with probability 1−δ.
According to this configuration, it is possible to obtain a bismuth layer-structure ferroelectric single-phase ferroelectric in which no precipitate is generated, the remanent polarization 2Pr is large, and a defect due to an increase in leakage current or a decrease in breakdown voltage of the capacitive element. It is preferable that a ferroelectric film can be prevented.
When manufacturing a ferroelectric film having the above composition, the ratio of each metal component calculated by determining the target existence probability δ and substituting the probability δ into the above chemical formula If a precursor film is formed using a raw material composition (a raw material composition corresponding to the ratio of each metal component in the total composition including the usage ratio of the paraelectric precursor and the ferroelectric precursor) and heat-treated, Thus, a ferroelectric material having a perovskite layer with a target existence probability of m = 1 and a perovskite layer with m = 2 can be formed. The same applies to other cases.

In the ferroelectric film of the present invention, the A is Sr, it is preferable that the B is a _{Ta 1-y Nb y (0} ≦ y ≦ 1).
According to this configuration, since the ferroelectric film having excellent fatigue characteristics can be obtained, a capacitive element having excellent rewrite resistance can be realized.

  In the ferroelectric film of the present invention, it is preferable that the δ is in a range of 0.01 <δ <0.3 and the x is in a range of 0.01 <x <0.3.

  According to this configuration, a ferroelectric film having a larger remanent polarization 2Pr can be obtained, which is preferable.

  The ferroelectric capacitor of the present invention includes an insulating film formed on a substrate, a lower electrode embedded so as to be partially exposed in the insulating film, and the insulating film and the lower electrode. A ferroelectric film formed over the ferroelectric film and an upper electrode formed on the ferroelectric film, wherein the crystal grain size of the ferroelectric film is formed substantially uniformly on the insulating film and the lower electrode Has been.

  Accordingly, it is possible to provide a ferroelectric capacitor element in which the polarization characteristics are prevented from being deteriorated, and it is possible to contribute to the downsizing of the electronic device and the manufacture of an electronic device capable of processing or storing a larger amount of data.

  Further, in the ferroelectric capacitor of the present invention, it is confirmed that the crystal grain size of the lower electrode in the portion in contact with the ferroelectric is formed almost uniformly. The crystal grain size can be made more uniform, which is preferable.

  Further, in the ferroelectric capacitor according to the present invention, the fact that the crystal grain size of the upper electrode in the portion in contact with the ferroelectric is formed almost uniformly means that the ferroelectric formed on the lower side of the upper electrode The crystal grain size of the film can be made more uniform, which is preferable.

Further, in the ferroelectric capacitor of the present invention, the thickness of the ferroelectric film is 100 nm or less, the size of the capacitance defining port defined by the lower electrode is 50 × 50 μm ² or less, This is preferable because it can be applied to the manufacture of electronic devices which can prevent or reduce polarization characteristics and have high reliability and can process or store data with a larger size and a larger capacity.

In the ferroelectric capacitor of the present invention, it is highly reliable that the ferroelectric capacitor is a ferroelectric capacitor that generates a residual polarization amount of at least 15 μC / cm ² by 1.8 V pulse wave switching. It is preferable to be a capacitive element.

  The method for manufacturing a ferroelectric film according to the present invention extends over an insulating film formed on a substrate and a conductor embedded in the insulating film so that at least a part of the surface is exposed. A method for manufacturing a ferroelectric film for forming a ferroelectric film, comprising: forming a conductor patterned in a predetermined shape on the substrate; and insulating the conductor to cover the conductor Forming a film; removing a predetermined region of the insulating film to expose at least part of the surface of the conductive film; and forming a ferroelectric precursor on the insulating film and the exposed conductor. And a paraelectric precursor containing at least a part of the constituent metal elements of the ferroelectric film to form a precursor film, and crystallizing the precursor film to form the ferroelectric film Forming a film.

  Paraelectric precursors begin to crystallize at a lower temperature than ferroelectric precursors. As a result, the paraelectric precursors form fine crystals in the ferroelectric precursor film mixed with the paraelectric precursors during the crystallization process, and these become crystal nuclei resulting in the crystallization of the ferroelectric precursors. The ferroelectric can be crystallized without being affected by the underlayer. Therefore, the crystal grain size of the ferroelectric film formed by this method can be formed almost uniformly on the insulating film and the conductor such as the lower electrode in contact with the ferroelectric substance.

  As the paraelectric precursor used as the raw material, it is preferable to use a paraelectric precursor containing at least a part of the metal elements constituting the ferroelectric film having the final target composition.

  In the manufacturing method of the ferroelectric film of the present invention, the usage ratio of the paraelectric precursor and the ferroelectric precursor is a paraelectric property with respect to the total amount of the paraelectric precursor and the ferroelectric precursor. The proportion of the precursor is preferably about 0.01 to 30 mol%, more preferably 10 to 20 mol%.

  In the method for manufacturing a ferroelectric film according to the present invention, a step of applying a solution of a ferroelectric precursor to which the paraelectric precursor is added on the insulating film and the conductor, and a heat treatment on the substrate. In addition, the method preferably includes a step of crystallizing the ferroelectric film.

  The method for manufacturing a ferroelectric capacitor element according to the present invention extends over an insulating film formed on a substrate and a lower electrode embedded in the insulating film so that at least a part of its surface is exposed. A method of manufacturing a capacitive element having a ferroelectric film formed by the method comprising: forming a lower electrode on the substrate; and forming a first insulating film on the substrate so as to cover the lower electrode. Forming a step of removing a predetermined region of the first insulating film to expose at least a part of the surface of the lower electrode; and forming a strong force on the first insulating film and the exposed lower electrode. Forming a precursor film by mixing a dielectric precursor and a paraelectric precursor containing at least a part of the constituent metal elements of the ferroelectric film; and an upper electrode on the precursor film. And forming a second insulating film on the upper electrode And a step of crystallizing the precursor film to form the ferroelectric film. Therefore, as described above, the crystal grain size of the ferroelectric film formed by this method can be formed almost uniformly on the insulating film and the conductor such as the lower electrode in contact with the ferroelectric, A highly reliable ferroelectric capacitor in which deterioration of characteristics is prevented can be manufactured.

  In the method for manufacturing a ferroelectric capacitor of the present invention, it is preferable that after forming an upper electrode on the precursor film, the precursor film is crystallized to form the ferroelectric film. When the dielectric film is crystallized, the upper electrode is also formed on the upper side thereof, thereby suppressing the roughness on the surface side when the ferroelectric film is crystallized and preventing the surface from becoming rough, A highly reliable ferroelectric capacitor element in which the polarization characteristic is prevented from being deteriorated is preferable.

  In the method for manufacturing a ferroelectric capacitor of the present invention, the second insulating film is formed on the upper electrode, and then the precursor film is crystallized to form the ferroelectric film. Preferably, the heat treatment acts uniformly, and the uniformization of the crystal grain size of the ferroelectric film further proceeds. That is, if heat treatment is performed with the upper electrode exposed without the second insulating film, the upper electrode reflects the heat because it is a metal, but if it is covered with the second insulating film, it corresponds to the upper electrode. The part also absorbs heat easily, the heat treatment acts uniformly, the uniformity of the crystal grain size further progresses, and a more reliable ferroelectric capacitor element in which the polarization characteristic is prevented from being manufactured is manufactured. Can be preferable.

  In the method for manufacturing a ferroelectric film of the present invention, it is highly reliable that the ferroelectric film is formed from a bismuth layered structure in which bismuth oxide layers and perovskite layers are alternately stacked. This is preferable because a body capacitor can be provided.

In the method for producing a ferroelectric film of the present invention, the bismuth oxide layer has a Bi ₂ O ₂ structure, and the perovskite layer has (A _1-x Bi _{2x / 3} ) _m-1 B _m O _{3m + 1} (0 <x <1) structure, wherein (A _1-x Bi _{2x / 3} ) _m-1 B _m O _{3m + 1} structure, A is a divalent metal and B is a pentavalent metal The value of m is m = 1 with probability δ (0 <δ <1), and m = 2 with probability 1-δ. It is possible to obtain a body, and since it is possible to obtain a ferroelectric film that has a large remanent polarization 2Pr and can prevent a defect due to an increase in leakage current and a decrease in breakdown voltage of the capacitive element, it is preferable.

In the method of manufacturing the ferroelectric film of the present invention, the A is Sr, ferroelectric said B is _{Ta 1-y Nb y (0} ≦ y ≦ 1) is excellent in fatigue properties Since it can be set as a body film, the capacitive element excellent in rewriting tolerance is realizable, and it is preferable.

In the method of manufacturing a ferroelectric film according to the present invention, it is preferable that the δ is in the range of 0.01 <δ <0.3 and the x is in the range of 0.01 <x <0.3. This is preferable.
As described above, according to the present invention, the ferroelectric area dependency of the ferroelectric polarization can be suppressed almost completely, and the defect due to miniaturization of the capacitive element, the capacitive element using the same, and the manufacturing method thereof Can be provided.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a structural cross-sectional view of the capacitive element of this embodiment. A transistor 104 including source and drain regions 102 and a gate 103 is formed on a substrate 101 such as a semiconductor such as silicon. An insulating film 105 made of an oxide film (commonly referred to as BPSG: boron phosphorous glass) such as SiO ₂ to which B (boron) and P (phosphorus) are added is formed so as to cover the transistor 104. A contact plug 106 made of tungsten is formed on the insulating film 105. A lower electrode 108 is formed on the insulating film 105 so as to cover the contact plug 106. The lower electrode 108 is electrically connected to the source and drain regions 102 of the transistor 104 through the contact plug 106. The structure of the lower electrode 108 is Pt / IrO ₂ / Ir / TiAlN from the upper layer, and the film thicknesses are 100 nm / 50 nm / 50 nm / 100 nm, respectively. In this example, the area of the square lower electrode 108 was set to 0.4 × 0.4 μm ² (design value). A buried insulating film 107 made of an oxide film such as SiO ₂ is formed in a region on the insulating film 105 other than where the lower electrode 108 exists. The buried insulating film is not particularly limited, and an SiO ₂ film manufactured by a plasma CVD method using ozone and TEOS (tetraethylorthosilicate) is used. A ferroelectric film 109 having a film thickness of 100 nm is formed on the entire surface of the lower electrode 108 and a part on the surrounding buried insulating film 107. An upper electrode 110 made of Pt and having a thickness of 50 nm is formed on the ferroelectric film 109. The area of the square upper electrode 110 was 0.44 × 0.44 μm ^{2 in} this example. A capacitive element 111 is composed of the lower electrode 108, the ferroelectric film 109, and the upper electrode 110. The nonvolatile memory is formed by the transistor 104 being an access transistor and the capacitor 111 being a data storage capacitor. In this illustrated example, the size of the surface of the lower electrode is the size of the capacity defining port.

  The ferroelectric film 109 has a laminated structure shown in the schematic cross-sectional view of FIG. That is, either the m = 2 perovskite layer 122 or the m = 1 perovskite layer 127 exists between the bismuth oxide layers 121. If the existence probability of the perovskite layer 127 with m = 1 is δ (0 <δ <1), the existence probability of the perovskite layer 122 with m = 2 is 1−δ. δ is preferably 0.01 <δ <0.3. Once the target existence probability value is determined, the raw material composition (paraelectric precursor and ferroelectric precursor content) corresponding to the ratio of each metal component calculated by substituting the probability value into the chemical formula is calculated. If the heat treatment is performed using the raw material composition according to the ratio of each metal component in the total composition including the use ratio, the target existence probability of m = 1 perovskite layer 127 and m = 2 perovskite layer 122 is obtained. A ferroelectric can be formed. The same applies to other cases.

The perovskite layer 127 of m = 1 is represented by the chemical formula TaO ₄ when B in the formula (1) is Ta, and a schematic diagram of the crystal structure thereof is an oxygen octahedron centered on tantalum 125 as shown in FIG. It is a layered structure in which a single layer spreads two-dimensionally. In FIG. 3, 124 indicates oxygen.

The perovskite layer 122 with m = 2 is represented by the chemical formula (Sr _1-x Bi _{2x / 3} ) Ta ₂ O ₇ (where 0 <x <1), as in the case of formula (4). As shown in FIG. 4, it is a layered structure in which two oxygen octahedrons centered on tantalum 125 are vertically overlapped and spread two-dimensionally. Tantalum 125 exists at the B site, which is the center of the oxygen octahedron, and oxygen 124 exists at each vertex of the octahedron. The A site 128, which is the space surrounded by the oxygen octahedron, is occupied by Sr with probability 1−x, Bi with probability 2x / 3, and vacancy with probability x / 3. x is preferably 0.01 <x <0.3.

In the ferroelectric described above, the mixed superlattice type m = 2 perovskite layer of [1] is replaced with the perovskite layer represented by the formula (4) shown in the A-site Bi substitution type of [2]. It has been replaced and has both the features [1] and [2]. Ca and Ba may be used instead of Sr, and Sr, Ca and Ba may be mixed at an arbitrary ratio. Further, Nb and V may be used instead of Ta, and Ta, Nb and V may be mixed and used at an arbitrary ratio. Usually, Ta _1-y Nb _y (0 ≦ y ≦ 1) is often used.

  The first characteristic of the ferroelectric having this structure is that the Bi ratio of the low melting point is larger than that of the ferroelectric having the normal structure described above. The crystal grain size is increased, and the amount of spontaneous polarization can be increased.

Hereinafter, a ferroelectric precursor film in which, for example, a precursor corresponding to a raw material of paraelectric BiTaO ₄ is mixed with a precursor used as a raw material when forming the ferroelectric as described above is used on a substrate. A method for making the crystal grain size of the ferroelectric film formed on the insulating film in which the lower electrode is embedded substantially uniform regardless of the underlying lower electrode or the insulating film will be described.

  Paraelectric precursors begin to crystallize at a lower temperature than ferroelectric precursors. As a result, the paraelectric precursors form fine crystals in the ferroelectric precursor film mixed with the paraelectric precursors during the crystallization process, and these become crystal nuclei resulting in the crystallization of the ferroelectric precursors. The ferroelectric can be crystallized without being affected by the underlayer. An example of the ferroelectric crystal grain size formed by this method is shown in FIG. 5 in comparison with the conventional example. In crystal grain size measurement, after removing a part of the upper electrode of the ferroelectric capacitor element so that the formed ferroelectric film is exposed, an image obtained by observing the surface with an SEM (scanning electron microscope) is used. The Grain Analysis function of the Scanning Probe Image Processor (hereinafter referred to as SPIP) program of Image Metrology ApS (Germany) was used. The crystal grain size of the conventional ferroelectric film observed in the SEM photograph was observed to be 50 nm to 150 nm on the lower electrode 108 and 40 nm to 110 nm on the buried insulating film 107. That is, the crystal grain size is smaller on the buried insulating film 107 than on the lower electrode 108, and the variation in crystal grain size is larger on both the lower electrode 108 and the buried insulating film 107.

  On the other hand, the crystal grain size observed in the SEM photograph of the ferroelectric film formed according to the embodiment of the present invention is 100 nm to 160 nm on the lower electrode 108, and 100 nm to 160 nm on the buried insulating film 107. It was found that the film was almost uniform regardless of the insulating film 107.

  FIG. 5 shows a distribution diagram of the result of analyzing the grain size variation of the ferroelectric film crystal by the grain analysis function of the SPIP program when formed according to the conventional example described above and the embodiment of the present invention. It was. About 240 crystal grain sizes analyzed in the conventional example and about 120 crystal grain sizes observed in the embodiment of the present invention are compared in FIG. As in the embodiment of the present invention, it is preferable that the crystal grain size is mainly 100 nm or more and the width of variation is 100 nm or less.

  The crystal structure of the ferroelectric film according to the present embodiment has a large tolerance to the composition shift, so that the paraelectric does not precipitate even when the paraelectric precursor is added. Further, the upper electrode formed on the ferroelectric film having a substantially uniform crystal grain size also has a substantially uniform crystal grain size, and can be highly reliable against stress migration.

The ferroelectric film was formed as follows. 2-ethylhexanoate of each component element was used as a raw material. That is, 2-ethylhexanoic acid Sr, 2-ethylhexanoic acid Bi, and 2-ethylhexanoic acid Ta were used in a ratio of the number of elements of each metal component of 1: (1.99 / 0.81) :( 1.9 / 0. 81), and the whole was diluted to 0.08 mol / l on the basis of Sr of 2-ethylhexanoic acid using n-octane as a solvent, and a ferroelectric film was formed by an organometallic thermal decomposition method. The use ratio of the above raw material composition is a composition ratio including a paraelectric precursor when it is assumed that 10 mol% of Bi ₂ TaO _11/4 is used as the paraelectric.

As described above, a ferroelectric precursor mixed solution containing a paraelectric precursor was used to form a ferroelectric film. Then, by a method similar to that described in the third embodiment to be described later, a buried insulating film [here, ozone and TEOS] is formed on the lower electrode (surface side is Pt) made of Pt and an oxygen barrier layer (IrO / Ir / TiAlN). SiO ₂ film formed by SA-CVD method (low pressure chemical vapor deposition method) using (tetraethylorthosilicate)] is formed to a thickness of 450 nm and the surface Pt of the lower electrode using CMP (chemical / mechanical polishing method) Is exposed to a thickness of 300 nm, and a mixed solution of a paraelectric precursor and a ferroelectric precursor having the above composition is applied by spin coating over the lower electrode (Pt on the surface side) and the buried insulating film. Then (see FIG. 8C), the wafer is baked at about the temperature at which the solvent volatilizes (150 to 300 ° C.) to form a ferroelectric precursor film having a thickness of 150 nm. Thereafter, pre-sintering is performed using RTP (rapid thermal processing) for forming nuclei that serve as a base point for crystal growth. The temperature at which the nucleus is formed differs depending on the type of the ferroelectric material, but the SBT material is about 650 ° C. for about 1 minute. On top of this, a conductive film made of Pt serving as an upper electrode is formed to the above thickness by sputtering. The precursor film is heat-treated at a high temperature and crystallized to form a capacitive insulating film made of a ferroelectric film. The SBT material is approximately 650 ° C to 800 ° C, but here it is heat treated at approximately 800 ° C for 1 minute. A ferroelectric film having a thickness of 100 nm was formed.

The obtained ferroelectric film is composed of a Bi ₂ O ₂ bismuth oxide layer and a perovskite layer (m = 1 TaO ₄ and m = 2 (Sr _1-x Bi _{2x / 3} ) Ta ₂ O ₇ ) Are alternately laminated, and the probability of existence of a perovskite layer with m = 1 is δ = 0.1, so the probability of existence of a perovskite layer with m = 2 is 0.9, and The value of x of the perovskite layer with m = 2 was 0.1.

Note that the ferroelectric film of the conventional example described in FIG. 5 is SrBi ₂ Ta ₂ O ₇ , and no paraelectric precursor is added. That is, in terms of the raw material composition, 2-ethylhexanoic acid Sr, 2-ethylhexanoic acid Bi, and 2-ethylhexanoic acid Ta were mixed and used at a ratio of the number of elements of each metal component of 1: 2: 2. Is. Also in this case, the whole was diluted to 0.08 mol / l based on 2-ethylhexanoic acid Sr using n-octane as a solvent. Other points are the same as above.

In the first embodiment of the present invention, the crystal grain size of the lower electrode in contact with the ferroelectric film and the crystal grain size of the upper electrode in contact with the ferroelectric film are both 100 to 200 nm. There was almost uniform. Further, the residual polarization 2Pr by 1.8V pulse wave switching is 16μC / cm ^2, 2Pr conventional example of comparison was 10 [mu] C / cm ^2.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  In order to confirm the effect of the present embodiment from the viewpoint of the composition conditions, a capacitor element was actually fabricated and evaluated. As in the first embodiment, the ferroelectric film was formed using an organometallic pyrolysis method. The composition condition was changed by changing the amount of constituent metals charged into the solution. The capacitive element was similarly created by the method shown in the first embodiment.

Fig. 6 shows the composition dependence of ferroelectrics. In FIG. 6, the tantalum element ratio is fixed at 2, and the strontium / bismuth element ratio is changed. The straight line a represents the stoichiometric composition of the mixed laminated superlattice type, and the straight line b represents the A-site Bi substituted type. The crystal structure of the embodiment of the present invention is formed in region B in this example. Note that the region A is a composition region determined above the straight line a, and the region C is a composition region determined below the straight line b. As described above, the ferroelectrics having these compositions can be manufactured by using raw materials containing respective metal components at a ratio corresponding to the stoichiometric ratio of the metal components. As an example, in order to make a ferroelectric material having a composition at the right end position on the straight line a in FIG. 6, that is, Bi of 2.4, Sr of 0.8, and Ta of 2 elements, 2-ethylhexanoic acid is used. For example, using 2-ethylhexanoic acid Sr at a ratio of 0.8 and 2-ethylhexanoic acid Bi at a ratio of 2 to the ratio of Ta (the ratio of the number of metal elements, the same shall apply hereinafter) Sr _0.8 Bi _2.4 Ta ₂ O _y can be obtained by the decomposition method. Here, y is the amount of oxygen in a chemical equivalent ratio (the same applies hereinafter, where y = 9.4). Similarly, in order to obtain a ferroelectric at the lower end position on the straight line b, that is, an element ratio of Bi of 2.2, Sr of 0.7, and Ta of 2, 2-ethylhexanoic acid Ta is a ratio of 2. In contrast, for example, Sr _0.7 Bi _2.2 Ta ₂ O _y can be obtained by organometallic pyrolysis using 2-ethylhexanoic acid Sr in a ratio of _{0.7 and 2} -ethylhexanoic acid Bi in a ratio of _2.2. Yes (here y = 9). Further, in order to form a ferroelectric having the composition in the lower right corner of the region B, 2-ethylhexanoic acid Ta is in a ratio of 2, for example, 2-ethylhexanoic acid Sr is 0.7, 2-ethylhexanoic acid. By using Bi at a ratio of 2.4, Sr _0.7 Bi _2.4 Ta ₂ O _y can be obtained by the organometallic pyrolysis method (here, y = 9.3). In addition, in order to obtain various ranges of ferroelectric compositions in the region B, it is preferable to set the raw material composition ratio within the above-mentioned range where δ is 0.01 <δ <0.3 and x is 0.01 <x <0.3.

Next, in order to confirm the effect of this embodiment from the viewpoint of the area of the capacitive element, the prototype was evaluated by changing the area of the capacitive element. It should be noted that the ferroelectric film was formed by using the organometallic pyrolysis method, except that the composition of the metal elements constituting the obtained ferroelectric film was slightly changed, as described in the first embodiment. Almost the same method was adopted. That is, a method substantially similar to that described in the first embodiment was adopted except that Nb was further used instead of Ta at a ratio of the number of elements of Ta of 0.96 and Nb of 0.04. As a raw material, 2-ethylhexanoate of each component element (metal element) was used as in the first embodiment. Specifically, 2-ethylhexanoic acid Sr, 2-ethylhexanoic acid Bi, 2-ethylhexanoic acid Ta, and 2-ethylhexanoic acid Nb are 1: (1.99 / 0.81) in terms of the number of elements of each metal component. ): [(1.9 × 0.96) /0.81]: [(1.9 × 0.04) /0.81] in a mixed ratio and using n-octane as a solvent based on 2-ethylhexanoic acid Sr as a whole. The film was diluted to 0.08 mol / l and a ferroelectric film was formed by organometallic pyrolysis. The use ratio of the above raw material composition is a composition ratio including the paraelectric precursor when it is assumed that 10 mol% of Bi ₂ Ta _0.96 Nb _0.04 O ₄ is used as the paraelectric.

Sample TA24-16 was prepared using a mixed solution with a ferroelectric precursor containing the paraelectric precursor as described above. The obtained ferroelectric film is composed of a Bi ₂ O ₂ structure bismuth oxide layer and a perovskite layer (Ta _0.96 Nb _0.04 O ₄ with m = ₁ and (Sr _1-x Bi _{2x / 3} ) with m = 2). Ta _1.92 Nb _0.08 O ₇ ) is formed from a bismuth layered structure consisting of alternating layers, and the probability of existence of a perovskite layer with m = 1 is probability δ = 14/57, and therefore there is a perovskite layer with m = 2 The probability was 43/57, and the value of x in the perovskite layer with m = 2 was 3/43.

Fig. 7 shows the electrode size dependence of the residual polarization 2Pr (μC / cm ² ). The lower electrode and the upper electrode were square electrodes. The length (μm) of one side of the capacitor lower electrode on the horizontal axis in FIG. 7 indicates the length of one side of the square electrode. The length of one side of the upper electrode was 10% longer than the length of one side of the lower electrode. Sample TA24-04 Bi prepared using SrBi ₂ Ta _1.92 Nb _0.08 O ₉ as the ferroelectric composition of the conventional example (paraelectric precursor raw material corresponding to Ta _0.96 Nb _0.04 O ₄ corresponding to paraelectric) Compared to those not added), the crystal grain size is uniformly formed around the periphery of the electrode, so that even a fine capacitor of 0.4 × 0.4 μm ² shows a characteristic without deterioration. If it is formed so as to have a size larger than the crystal grain size of the ferroelectric formed in this embodiment, desired characteristics can be obtained even with a fine capacitor of 1.6 × 1.6 μm ² or less, and the area becomes small. It is suitable for miniaturization of a capacitor element.

  The crystal grain size of the ferroelectric film of sample TA24-16 in the second embodiment of the present invention is 100 nm to 160 nm on the lower electrode, and 100 nm to 160 nm on the buried insulating film, and on the lower electrode and the buried insulating film. It was almost uniform regardless of the above. It was observed that the crystal grain size of the ferroelectric film of the sample TA24-04 in the conventional example was 50 nm to 150 nm on the lower electrode and 40 nm to 110 nm on the buried insulating film. That is, the crystal grain size was smaller on the buried insulating film than on the lower electrode, and the variation in crystal grain size was larger on both the lower electrode and the buried insulating film.

  Further, the crystal grain size on the side of the lower electrode in contact with the ferroelectric film and the crystal grain size on the side of the upper electrode in contact with the ferroelectric film were both 100 to 200 nm and substantially uniform.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 8 (a), an insulating film 2 (specifically, SiO ₂ to which B (boron), P (phosphorus), etc. are added, commonly called BPSG: boron phosphorous glass) is applied to the substrate 1 by SA-CVD. A first contact that electrically connects the substrate and the lower electrode of the ferroelectric capacitor in the insulating film 2 with a thickness of 500 nm formed by a sub-atmospheric chemical deposition method (Sub-Atomospheric Chemical Deposition Method) Plug 3 [W (tungsten), PolySi (polysilicon), etc. Here, W was used]. Furthermore, a conductive film composed of a film (Pt) that promotes crystal growth of the ferroelectric film and an oxygen barrier layer (IrO / Ir / TiAlN) is formed on the Pt layer in order of the Pt layer by DC sputtering. The layers are stacked to a thickness of 100 nm / 50 nm / 50 nm / 100 nm, respectively, and patterned so as to cover the first contact plug 3 using a desired mask to form a square lower electrode 5 (area 0.5 × 0.5 μm ² : Design value) was formed.

Next, as shown in FIG. 8B, a buried insulating film 13a (specifically, a SiO ₂ film formed by the SA-CVD method using ozone and TEOS) is formed on the lower electrode 5, The surface of the lower electrode 5 was exposed using CMP (chemical / mechanical polishing method). At this time, the thickness of the lower electrode 5 and the buried insulating film 13a was set to 300 nm.

  Next, as shown in FIG. 8 (c), the raw material precursor composition having the same composition as the second embodiment, that is, 2-ethylhexanoic acid Sr, 2-ethylhexanoic acid Bi, 2-ethylhexanoic acid Ta , 2-ethylhexanoic acid Nb in terms of the number ratio of each metal component 1: (1.99 / 0.81): [(1.9 × 0.96) /0.81]: [(1.9 × 0.04) /0.81 The mixture was diluted to 0.08 mol / l based on 2-ethylhexanoic acid Sr using n-octane as a solvent. Thus, the ferroelectric precursor solution to which the paraelectric precursor has been added is applied by spin coating, the wafer is baked at a temperature at which the solvent volatilizes (150 to 300 ° C.), and the ferroelectric precursor film has a thickness of 150 nm. 12a was formed. Thereafter, pre-sintering was performed using RTP (Rapid Thermal Processing) for forming nuclei as a base point for crystal growth. The temperature at which the nucleus is formed differs depending on the type of the ferroelectric material, but the SBT material is about 650 ° C. for about 1 minute. A conductive film 7a made of Pt was formed thereon with a thickness of 50 nm by sputtering.

Next, as shown in FIG. 8 (d), the precursor film 12a and the square upper electrode 7 (area 0.6 × 0.6 μm ² ) are formed by patterning to cover the lower electrode 5 using a desired mask. did. Here, the ferroelectric film and the upper electrode are patterned using the same mask, but they may be formed using different masks. The crystal grains on the side of the lower electrode 5 and the upper electrode 7 that are in contact with the ferroelectric film were 100 nm to 200 nm, respectively. That is, when the ferroelectric film is crystallized, it is influenced by the lower electrode and the upper electrode, which are the base and upper layers. Therefore, if the crystal grain size of the lower electrode and the upper electrode is uniform, the ferroelectric film is formed between them. This is preferable because the crystal grain size of the ferroelectric material becomes even more uniform. If necessary, at least the lower electrode having a uniform crystal grain size may be used.

  Finally, as shown in FIG. 8 (e), the precursor film was heat-treated at a high temperature and crystallized to form a capacitive insulating film 12 made of a ferroelectric film. The SBT material is about 650 ° C. to 800 ° C. for 1 minute. In this embodiment, the heat treatment is performed immediately after the ferroelectric film is applied and after the capacitive element patterning. However, after the formation of the ferroelectric film, for example, after the second insulating film is formed on the upper electrode, It does not matter if there is at least one heat treatment step in the process. Incidentally, it is preferable that the crystal grain size of the upper electrode 7 on the side in contact with the ferroelectric film is substantially uniform as 100 nm to 200 nm as described above. That is, when the ferroelectric film is crystallized, it is affected by the upper electrode that is the upper layer, so if the crystal grain size of the upper electrode is uniform, the crystal grain size of the ferroelectric film below it is It becomes even more uniform and preferable.

In addition, the obtained ferroelectric film has a Bi ₂ O ₂ structure bismuth oxide layer and a perovskite layer (Ta _0.96 Nb _0.04 O ₄ with m = ₁ and m = 2 (Sr _1-x Bi _{2x / 3} )) Ta _1.92 Nb _0.08 O ₇ ) is formed from a bismuth layered structure consisting of alternating layers, and the probability of existence of a perovskite layer with m = 1 is probability δ = 14/57, and therefore there is a perovskite layer with m = 2 The probability was 43/57, and the value of x in the perovskite layer with m = 2 was 3/43.

As described above, the ferroelectric crystal grain sizes on the lower electrode embedded in the insulating film and the outer peripheral insulating film are 100 nm to 160 nm and 100 nm to 160 nm, respectively. Capacitance element can be formed, and the residual polarization amount 2Pr of the obtained capacitance element is 18.8 μC / cm ² , which prevents the deterioration of the polarization characteristics of the ferroelectric material even if the capacitor area is miniaturized. it can.

In this embodiment, an example in which a paraelectric precursor corresponding to paraelectric Bi ₂ Ta _0.96 Nb _0.04 O ₄ is used as a paraelectric precursor to be added has been described. For example, a paraelectric precursor corresponding to Bi ₂ TaO ₄ , Bi ₂ O _3, or Bi ₂ NbO ₄ may be used.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 9 (a), an insulating film 2 (specifically B (boron), P (phosphorus), etc.) is added on a substrate 1 (here, a silicon semiconductor substrate having a substrate diameter of 8 inches). SiO ₂ , commonly called BPSG (Boron Phosphorus Glass) is formed with a thickness of 450 nm by the SA-CVD method, and the first contact plug 3 that electrically connects the substrate and the lower electrode of the ferroelectric capacitor in the insulating film 2 [W (tungsten), PolySi (polysilicon), etc. Here, W was used]. Furthermore, a conductive film composed of a film (Pt) that promotes crystal growth of the ferroelectric film and an oxygen barrier layer (IrO / Ir / TiAlN) is formed on the Pt layer in order of the Pt layer by DC sputtering. Each of the layers is laminated to a thickness of 100 nm / 50 nm / 50 nm / 100 nm, and is patterned so as to cover the first contact plug 3 using a desired mask, and a square lower electrode 5 (area 0.4 × 0.4 μm ² : Design value) was formed.

Next, as shown in FIG. 9B, a buried insulating film 13a (specifically, a SiO ₂ film formed by the SA-CVD method using ozone and TEOS) is formed on the lower electrode 5, The surface of the lower electrode 5 was exposed using CMP (chemical / mechanical polishing method). At this time, the thickness of the lower electrode 5 and the buried insulating film 13a was set to 300 nm.

  Next, as shown in FIG. 9 (c), the raw material precursor composition having the same composition as the first embodiment, that is, 2-ethylhexanoic acid Sr, 2-ethylhexanoic acid Bi, 2-ethylhexanoic acid Ta Are mixed in the ratio of the number of elements of each metal component in a ratio of 1: (1.99 / 0.81) :( 1.9 / 0.81), and the whole is 2-ethyl with n-octane as a solvent. It was diluted to 0.08 mol / l based on hexanoic acid Sr. Thus, the ferroelectric precursor solution to which the paraelectric precursor has been added is applied by spin coating, the wafer is baked at a temperature at which the solvent volatilizes (150 to 300 ° C.), and the ferroelectric precursor film having a thickness of 150 nm. 12a was formed. Thereafter, pre-sintering was performed using RTP (Rapid Thermal Processing) for forming nuclei as a base point for crystal growth. The temperature at which the nucleus is formed differs depending on the type of the ferroelectric material, but the SBT material is about 650 ° C. for about 1 minute. A conductive film 7a made of Pt was formed thereon with a thickness of 50 nm by sputtering.

Next, as shown in FIG. 9 (d), the precursor film 12a and the square upper electrode 7 (area 0.45 × 0.45 μm ² ) are formed by patterning so as to cover the lower electrode 5 using a desired mask. did. Here, the precursor film and the upper electrode are patterned using the same mask, but they may be formed using different masks. The crystal grain sizes of the lower electrode 5 and the upper electrode 7 on the side in contact with the ferroelectric film were 100 nm to 200 nm, both of which were almost uniform.

Next, as shown in FIG. 9 (e), the upper electrode 7 is covered with a second insulating film 14a (specifically, a SiO ₂ film formed by the SA-CVD method using ozone and TEOS). Thus, it was formed with a thickness of about 150 nm.

  Next, as shown in FIG. 9F, the second insulating film 14 and the buried insulating film 13 are formed in a predetermined pattern by patterning so as to cover the second insulating film 14a using a desired mask. did. Although the second insulating film and the buried insulating film are patterned using the same mask here, they may be formed using different masks.

  Finally, as shown in FIG. 9 (e), the precursor film was heat-treated at a high temperature and crystallized to form a capacitive insulating film 12 made of a ferroelectric film. The heat treatment of the SBT material is about 650 ° C. to 800 ° C. for about 1 minute. In this embodiment, since the heat treatment is performed after the ferroelectric capacitor element is covered with the second insulating film, the heat treatment acts uniformly and the crystal grain size is further uniformized. That is, when the heat treatment is performed with the upper electrode without the second insulating film exposed, the upper electrode reflects the heat because it is a metal, but if it is covered with the second insulating film, it corresponds to the upper electrode. The part is also preferable because it easily absorbs heat, the heat treatment acts uniformly, and the uniformity of the crystal grain size further proceeds.

The obtained ferroelectric film is composed of a Bi ₂ O ₂ bismuth oxide layer and a perovskite layer (M = 1 TaO ₄ and m = 2 (Sr _1−x Bi _{2x / 3} ) Ta ₂ O _7. ) Are alternately laminated, and the probability of existence of a perovskite layer with m = 1 is δ = 0.1, so the probability of existence of a perovskite layer with m = 2 is 0.9, and The value of x of the perovskite layer with m = 2 was 0.1.

As described above, the ferroelectric crystal grains of the lower electrode embedded in the insulating film and the outer peripheral insulating film have a crystal grain size of 100 nm to 160 nm and 100 nm to 160 nm, respectively, and the crystal grain size is substantially uniform. The residual polarization amount 2Pr of the obtained capacitive element is 16 μC / cm ² , and it is possible to prevent the deterioration of the polarization characteristics of the ferroelectric material even if the capacitor area is miniaturized. .

In this embodiment, the paraelectric precursor corresponding to the paraelectric BiTaO ₄ is used as the paraelectric precursor to be added. However, other Bi-containing paraelectrics such as Bi ₂ O _{3 are used.} Alternatively, a paraelectric precursor corresponding to BiNbO ₄ may be used.

  According to the present invention, it is possible to prevent the deterioration of the polarization characteristics of the ferroelectric capacitor with respect to the difference in the crystal grain size of the ferroelectric, and the ferroelectric film that does not deteriorate even if the capacitor size is reduced with the miniaturization of the device, Capacitance elements using the same and methods for manufacturing these can be provided. Therefore, the present invention is useful for the downsizing of electronic devices and the manufacture of electronic devices that can process or store a larger amount of data.

Cross-sectional view of the structure of the capacitive element according to the first embodiment of the present invention Sectional schematic diagram showing the structure of the perovskite layer in the first embodiment of the present invention Schematic diagram showing the crystal structure of the m = 1 perovskite layer in the bismuth layered ferroelectric in the first embodiment of the present invention Schematic diagram showing the crystal structure of an m = 2 perovskite layer in a bismuth layer-structured ferroelectric in the first embodiment of the present invention The figure which shows the crystal grain size of the bismuth layered crystal structure in the 1st Embodiment of this invention, and the crystal grain size of the bismuth layered crystal structure of a prior art example (comparison with the crystal grain size of the conventional bismuth layered crystal structure) The figure which shows the composition dependence of the bismuth layered crystal structure in the 2nd Embodiment of this invention The figure which shows the ferroelectric capacitor characteristic of the capacitive element in the 2nd Embodiment of this invention Process sectional drawing which shows the manufacturing method of the capacitive element in the 3rd Embodiment of this invention Process sectional drawing which shows the manufacturing method of the capacitive element in the 4th Embodiment of this invention Schematic diagram showing the bismuth layer structure in a conventional ferroelectric with a normal bismuth layer structure Schematic diagram showing the crystal structure of a bismuth oxide layer in a conventional ferroelectric with a normal bismuth layer structure Schematic diagram showing the crystal structure of an m = 2 perovskite layer in a conventional ferroelectric with a normal bismuth layer structure Cross-sectional schematic diagram showing a bismuth layered structure in a conventional ferroelectric layered superlattice bismuth layered structure Schematic diagram showing the crystal structure of the m = 1 perovskite layer in a conventional ferroelectric layered superlattice bismuth layer structure

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Insulating film 3 Contact plug 5 Lower electrode 7 Upper electrode 7a Conductive film 12 Capacitor insulating film made of ferroelectric film 12a Precursor film 13 Embedded insulating film 13a Embedded insulating film 14 Second insulating film 14a Second insulating film Film 101 semiconductor substrate 102 source and drain region 103 gate 104 transistor 105 insulating film 106 contact plug 107 buried insulating film 108 lower electrode 109 ferroelectric film 110 upper electrode 121 bismuth oxide layer 122 m = 2 2 perovskite layer 127 m = 1 Perovskite layer 124 oxygen 125 tantalum 128 A site 201 bismuth oxide layer 202 m = 2 perovskite layer 203 bismuth 204 oxygen 205 tantalum 206 strontium 207 m = 1 perovskite layer

Claims (10)

A ferroelectric film formed over an insulating film formed on a substrate and a conductor embedded in the insulating film so that at least a part of the surface thereof is exposed, the ferroelectric film A ferroelectric film characterized in that a crystal grain size of the body film is formed substantially uniformly on the insulating film and the conductor in contact with the ferroelectric substance. An insulating film formed on the substrate; a lower electrode embedded in the insulating film so that at least a part of the surface thereof is exposed; and a ferroelectric formed over the insulating film and the lower electrode A film and an upper electrode formed on the ferroelectric film, and the crystal grain size of the ferroelectric film is formed substantially uniformly on the insulating film and the lower electrode in contact with the ferroelectric A ferroelectric capacitive element characterized by comprising: 3. The ferroelectric capacitor element according to claim 2, wherein a crystal grain size of the lower electrode in a portion in contact with the ferroelectric is formed to be substantially uniform. 4. The ferroelectric capacitor element according to claim 3, wherein the crystal grain size of the upper electrode in the portion in contact with the ferroelectric is formed substantially uniformly. 5. The ferroelectric capacitor according to claim 2, wherein the ferroelectric film has a thickness of 100 nm or less, and a capacity defining port defined by the lower electrode is 50 × 50 μm ² or less. element. 6. The ferroelectric capacitive element according to claim 5, wherein the ferroelectric capacitive element is a ferroelectric capacitive element that generates a residual polarization amount of at least 15 μC / cm ² by 1.8 V pulse wave switching. Ferroelectric film manufacturing method for forming a ferroelectric film across an insulating film formed on a substrate and a conductor embedded in the insulating film so that at least a part of the surface of the insulating film is exposed A step of forming a conductor patterned in a predetermined shape on the substrate, a step of forming an insulating film so as to cover the conductor on the substrate, and a predetermined region of the insulating film. Removing at least a part of the surface of the conductive film, and exposing at least a part of the constituent metal elements of the ferroelectric precursor and the ferroelectric film on the insulating film and the exposed conductor And a step of forming a precursor film by mixing with a paraelectric precursor containing a metal element, and a step of crystallizing the precursor film to form the ferroelectric film. A method of manufacturing a ferroelectric film. Manufacture of a capacitive element comprising a ferroelectric film formed over an insulating film formed on a substrate and a lower electrode embedded in the insulating film so that at least a part of the surface thereof is exposed. A method comprising: forming a lower electrode on the substrate; forming a first insulating film on the substrate so as to cover the lower electrode; and a predetermined region of the first insulating film Removing at least a part of the surface of the lower electrode, and forming a ferroelectric precursor and a constituent metal element of the ferroelectric film on the first insulating film and the exposed lower electrode. A step of mixing a paraelectric precursor containing at least a part of a metal element to form a precursor film; a step of forming an upper electrode on the precursor film; and a second insulation on the upper electrode. Forming a film; and crystallizing the precursor film to produce the ferroelectric And a step of forming a body film. A method of manufacturing a ferroelectric capacitor element, comprising: 9. The method of manufacturing a ferroelectric capacitor element according to claim 8, wherein after the upper electrode is formed on the precursor film, the precursor film is crystallized to form the ferroelectric film. 9. The method for manufacturing a ferroelectric capacitor element according to claim 8, wherein after forming the second insulating film on the upper electrode, the precursor film is crystallized to form the ferroelectric film.

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