JPH10189887A - Electorde for ferroelectric body and ferroelectric device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a ferroelectric body, in which film fatigue caused by the repetitively alternate polarization of a ferroelectric body can be reduced, and residual polarization the ferroelectric body can be prevented from being reduced and to provide a non-volatile memory device which can be improved in data write characteristic and attaining lower power consumption. SOLUTION: A ferroelectric electorde (a lower electorde 8 or an upper electorde 10) which is laminated on a ferroelectric body 9 for the formation of a laminated structure has substantially the same crystal structure as the ferroelectric body 9 and is formed of an electrically conductive oxide. Specifically, the ferroelectric electrode is formed of ReO3 , which is of crystal structure where a hole is located at an A-site, and metal ion, enter in the hole of ReO3 from the ferroelectric body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferroelectric electrode and a ferroelectric device using the same. In particular, in the present invention, a ferroelectric electrode used to form a laminated structure with a ferroelectric used for an information storage section of a nonvolatile memory element, and a ferroelectric and a ferroelectric electrode formed by laminating the ferroelectric electrode The present invention relates to a ferroelectric device equipped with a nonvolatile memory element.

[0002]

2. Description of the Related Art A nonvolatile storage device using a ferroelectric material for an information storage section of a nonvolatile storage element has been developed.
As a typical nonvolatile memory element, for example, FeRAM
2. Description of the Related Art A nonvolatile storage element employing a (Ferroelectric Random Access Memory) structure is known.

[0003] A nonvolatile memory element employing a FeRAM structure is formed in a one-transistor / one-capacitor structure formed by a series circuit of a switching element and a capacitance element constituting an information storage part. The switching element includes a channel formation region, an insulator (gate insulator), a control electrode (gate electrode), and a pair of semiconductor regions used as a source region and a drain region. The capacitive element includes a lower electrode, a ferroelectric, and an upper electrode, and the lower electrode, the ferroelectric, and the upper electrode are sequentially stacked.

[0004] The ferroelectric material of the capacitive element has a characteristic that it has remanent polarization so that stored contents are not lost even when the power is turned off. Further, low voltage operation can be realized by employing a ferroelectric substance, so that low power consumption of the nonvolatile memory element can be promoted. PZT (lead titanium zirconate:
PbZr _x Ti _1-x O ₃ ) is used.

[0005] A single-layer thin film of Pt or a composite thin film of Pt and Ti is used for the lower electrode serving as a ferroelectric base film of the capacitor element. The Pt of this electrode material is S
It is deposited on the surface of an i-substrate (semiconductor substrate) or a SiO ₂ thin film used as an interlayer insulating film. When Pt is deposited by a sputtering method in the manufacturing process, Pt is (11)
1) Easy orientation. The ferroelectric formed on Pt having the (111) orientation is easily oriented, and the ferroelectric having the orientation has large remanent polarization, so that the information writing characteristics can be improved. Furthermore, since Pt is a noble metal and is basically not oxidized, no paraelectric material composed of Pt oxide is formed between the ferroelectric and the lower electrode. In other words, Pt has a feature that no paraelectric material is formed near the interface between the ferroelectric and the lower electrode, which reduces the substantial capacitance of the entire capacitive element.

[0006]

In a nonvolatile memory element mounted on a nonvolatile memory device, when a single-layer thin film of Pt or a composite thin film containing Pt is used for a lower electrode of a capacitor element, as described above. Has excellent features. However, by repeatedly performing the information rewriting operation and repeatedly performing the polarization reversal of the ferroelectric, film fatigue occurs in which the magnitude of the remanent polarization of the ferroelectric decreases. Film fatigue of ferroelectrics is caused by the fact that unnecessary substances are deposited on the Pt surface at the interface between the ferroelectrics and the lower electrode due to an electric field repeatedly applied between the electrodes of the capacitor. The present inventor has considered. Unwanted substances deposited on the Pt surface include Pb ions, which are ferroelectric composition substances, Si substrates and SiO _2.
Si ions, which are constituent materials of the thin film, O ions of the SiO ₂ thin film, and compounds composed of these ions are conceivable. That is, the information writing characteristics of the capacitor deteriorate with time.

The present invention has been made to solve the above-mentioned problems.

Accordingly, it is an object of the present invention to provide a ferroelectric electrode capable of reducing film fatigue caused by repetition of polarization inversion of a ferroelectric and preventing a decrease in remanent polarization of the ferroelectric. .

A further object of the present invention is to provide a non-volatile memory device which uses a ferroelectric electrode as a capacitor of the non-volatile memory device and which can realize low power consumption while improving information writing characteristics. It is in.

[0010]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, there is provided an electrode for a ferroelectric which forms a laminated structure with a ferroelectric having a perovskite crystal structure. It has a crystal structure substantially the same as the perovskite crystal structure of the dielectric and is formed of a conductive oxide.

According to the first aspect of the present invention, the ferroelectric electrode is formed of an oxide, and oxygen is present in a stable state in the oxide. In the vicinity, no oxygen is deposited on the surface of the ferroelectric electrode. As a result, no paraelectric substance (unnecessary substance) is generated at the interface due to the precipitation of oxygen, so that film fatigue caused by repetition of polarization inversion of the ferroelectric substance is reduced,
Effective reduction of remanent polarization of the ferroelectric can be prevented. Further, since the ferroelectric electrode is formed with a crystal structure substantially identical to the ferroelectric perovskite crystal structure, when a ferroelectric crystal is grown on the ferroelectric electrode, In any case of crystal growth of the ferroelectric electrode, crystal growth can be performed while maintaining the crystallinity of the base.

According to a second aspect of the present invention, the ferroelectric electrode according to the first aspect has a crystal structure having a hole at a position of an A site in an ABO ₃ crystal structure. I do.

According to the second aspect of the present invention, the crystal structure of the ferroelectric electrode is not a perfect perovskite crystal structure but a crystal structure having vacancies at the A site of the ABO ₃ crystal structure. Therefore, the metal atoms of the crystal unit located on the ferroelectric electrode-side end surface of the ferroelectric material enter the holes of the crystal unit located on the ferroelectric-side end surface of the ferroelectric electrode. When PZT is used for the ferroelectric, Pb of PZT is filled in the vacancy of the crystal unit.
Atoms enter. In other words, since the ferroelectric electrode and the ferroelectric are atomically bonded, the bonding strength between the ferroelectric electrode and the ferroelectric can be improved. Furthermore, the ferroelectric electrode and the ferroelectric are atomically bonded, and the crystallinity information from the ferroelectric electrode to the ferroelectric, or conversely, from the ferroelectric to the ferroelectric electrode. Is transmitted, the respective crystal growths of the perovskite crystal structure and the crystal structure substantially identical to the perovskite crystal structure can be easily performed.

According to a third aspect of the present invention, the ferroelectric electrode according to the first aspect is formed of ReO ₃ in a polycrystalline state or a single crystalline state.

According to the third aspect of the present invention, the ferroelectric electrode is formed of ReO ₃ , and ReO ₃ has a low resistance value of about 10 ⁻⁵ Ωcm at room temperature. Can be achieved.

According to a fourth aspect of the present invention, there is provided a ferroelectric device, comprising: a ferroelectric having a perovskite crystal structure; and a ferroelectric having substantially the same crystal structure as the perovskite crystal structure of the ferroelectric. A ferroelectric electrode formed of an oxide having the following characteristics: the ferroelectric electrode, the ferroelectric layered on the ferroelectric electrode, and the electrode layered on the ferroelectric substance. Characterized in that the element formed by the above is mounted.

According to the fourth aspect of the present invention, in addition to the function and effect obtained by the ferroelectric electrode according to the first aspect of the present invention, film fatigue of the ferroelectric is reduced in the element. The remanent polarization can be increased. In particular, in a capacitor element in which a ferroelectric material is interposed between electrodes for a ferroelectric material, remanent polarization can be increased, so that information writing characteristics can be improved and sufficient information can be obtained with a low voltage information writing voltage. Can be written, so that low power consumption can be realized.

According to a fifth aspect of the present invention, in the ferroelectric device according to the fourth aspect, an element in which the ferroelectric electrode, the ferroelectric, and the ferroelectric electrode are sequentially stacked is mounted. It is characterized by having done.

According to a sixth aspect of the present invention, in the ferroelectric device according to the fourth or fifth aspect, the ferroelectric material includes PZT, PbTiO ₃ , BaT
Any ferroelectric of iO ₃ or SrBi ₂ Ta ₂ O
_9. A layered dielectric material of Bi ₄ Ti ₃ O ₁₂ is used, and polycrystalline or single crystalline ReO ₃ is used for the ferroelectric electrode.

According to a seventh aspect of the present invention, in the ferroelectric device according to the sixth aspect, the element is a capacitive element used as an information storage unit.

[0021]

Embodiments of the present invention will be described below. FIG. 1 shows an FeRAM according to an embodiment of the present invention.
FIG. 2 is a cross-sectional structural view of a nonvolatile memory device equipped with a nonvolatile memory element (memory cell) adopting a structure. The nonvolatile memory device is formed on the substrate 1, and the nonvolatile memory element M is formed on the main surface of the substrate 1. In this embodiment, a single crystal Si substrate is used as the substrate 1, and this Si substrate is set to a p-type in which a p-type impurity is introduced. The nonvolatile memory element M has a one-transistor / one-capacitor structure formed by a series circuit of a switching element (switching transistor) and a capacitor. The capacitor functions as an information storage unit.

The switching element of the nonvolatile memory element M includes a channel forming region 1A, a gate insulator 2, a control electrode (gate electrode) 3, and a pair of semiconductor regions 4 used as a source region and a drain region.

The channel forming region 1A is formed near the main surface of the substrate 1. Gate insulator 2 is formed at least on the surface of channel formation region 1A. Gate insulator 2
Is formed of, for example, a SiO ₂ thin film.

The control electrode 3 is formed on the surface of the gate insulator 2. The control electrode 3 is formed of, for example, a single layer film of a polycrystalline Si thin film, a silicide thin film, or a high melting point metal thin film, or a composite film in which a silicide thin film or a high melting point metal thin film is laminated on a polycrystalline Si thin film. That is, the control electrode 3 is formed of a so-called gate material. Although not shown,
The control electrode 3 is formed of the same gate material as a word line extending in the same direction as the channel width direction, and is electrically connected to this word line.

A pair of semiconductor regions 4 used as a source region and a drain region are formed on the main surface of the substrate 1 on both sides of the control electrode 3 in the channel length direction. Each semiconductor region 4 is set to an n-type with an n-type impurity introduced. That is, the switching element is an n-channel conductive transistor (MISFET: Metal Insulator Fiel).
d Effect Transistor).

On the switching element, an interlayer insulating film 5 for electrically separating the switching element from the capacitor is formed. In the present embodiment, the interlayer insulating film 5 is a single-layer film of any one of a SiO ₂ film and a Si ₃ N ₄ film, or an S film.
It is formed of a composite film combining the iO ₂ film and the Si ₃ N ₄ film. A connection hole 6 is formed in the interlayer insulating film 5 on one semiconductor region 4 of the switching element. In the connection hole 6, a connection hole wiring 7 for electrically connecting one semiconductor region 4 and the lower electrode 8 of the capacitive element is provided.
Is formed. The connection hole wiring 7 is made of, for example, W, TiW, WS
It is formed of a material having a low resistance value such as i ₂ and TiN and having a high melting point metal or a high melting point metal as a main component. The connection hole wiring 7 is made of polycrystalline Si doped with P and having a low resistance.
A membrane can be used.

Although not shown, a data line (bit line) is electrically connected to the other semiconductor region 4 of the switching element.

The capacitive element comprises a lower electrode 8, a ferroelectric 9,
The upper electrode 10 has a laminated structure in which each of the upper electrodes 10 is sequentially laminated.

The lower electrode 8 of the capacitive element is formed on the surface of the interlayer insulating film 5, and this lower electrode 8 is electrically connected to one semiconductor region 4 of the switching element through the connection hole wiring 7. In the present embodiment, the lower layer electrode 8 is formed as a ferroelectric electrode, and the ferroelectric electrode includes ReO _3.
Thin films are used. This ReO ₃ is an oxide having conductivity and containing oxygen atoms in a stable state.

Oxides similar to ReO ₃ include Re
Each of ₂ O ₇ and ReO ₂ is known. Re ₂ O
₇ is a crystal structure having the largest number of oxygen atoms, but Re ₂ O ₇
Is an insulator and cannot be used as an electrode material. Although ReO ₂ has conductivity, the resistance value of ReO ₂ is larger than ReO ₃ and is not suitable for increasing the signal transmission speed. Re
O ₃ is Al used as a wiring material in semiconductor devices
-10 ^-5 Ωc, which is comparable to the resistance value of Cu wiring of 10 ^-6 Ωcm
m. As will be described later, the crystal structure of ReO ₃ is similar to the perovskite crystal structure, and the crystal structure of ReO ₂ is a rutile crystal structure. Therefore, the crystal structures of ReO ₂ and ReO ₃ are basically different.

FIG. 2 is a crystal structure diagram showing one crystal unit of ReO ₃ which is the lower layer electrode 8 and is used as a ferroelectric electrode. ReO ₃ has an ABO ₃ crystal structure in which vacancies are present at the A site and hexavalent positive Re ions are present at the B site. The greatest features of this ReO ₃ are that the position of the A site is a vacancy and that it has an oxygen octahedron formed by six oxygen atoms surrounding the Re ion. Has substantially the same crystal structure as the perovskite crystal structure. The lower electrode 8 is basically formed in a single crystal state, but may be formed in a polycrystalline state.

The ferroelectric 9 of the capacitor is formed on the surface of the lower electrode (ferroelectric electrode) 8. In the present embodiment, the ferroelectric 9 is made of a PZT thin film or PbTiO.
_Three thin films are used.

FIG. 3 shows one of the ferroelectric materials 9 of PbTiO ₃ .
It is a crystal structure figure showing a crystal unit. PbTiO
₃ is an ionic crystal, and a divalent plus P is added to the A site.
The b ion exists and the tetravalent plus Ti ion exists at the B site. The greatest feature of this PbTiO ₃ is that it has a perovskite crystal structure having an oxygen octahedron surrounding Ti ions. When the A site or the B site shifts from the lattice point, remanent polarization (spontaneous polarization) occurs, and the magnitude of the remanent polarization differs depending on the type of ion. The ferroelectric material 9 has a high remanent polarization of about 50 μC / cm ² at room temperature in the case of PbTiO ₃ . In the present embodiment, the ferroelectric 9 is basically formed in a single crystal state. Note that the ferroelectric material 9 may be formed in a polycrystalline state.

FIG. 4 is a crystal structure diagram showing a layered state between the lower electrode 8 and the ferroelectric 9 at an atomic level. In the ReO ₃ crystal unit located at the end of the lower electrode 8 on the ferroelectric 9 side, the vacancy at the position of the A site is filled with the PbT located at the end of the ferroelectric 9 on the lower electrode 8 side.
Pb ions of the iO ₃ crystal unit enter. That is, the crystal unit of ReO _{3 and} the crystal unit of PbTiO ₃ are mutually connected by sharing the Pb ion of PbTiO ₃ at the A site. Therefore, the adhesive force between the lower electrode 8 and the ferroelectric 9 becomes strong.

Further, PbTiO _3, which is a ferroelectric substance 9, has a perovskite crystal structure, and ReO ₃ has a vacancy in the position of the A site but has an octahedral oxygen and has substantially the same crystal structure as PbTiO _3. MOCVD (Metalo
PbTiO ₃ can be continuously grown on the surface of ReO ₃ by the rganic CVD method.

Further, since the lattice constant in the a-axis direction is 3.9 ° in the PbTiO ₃ crystal unit and the lattice constant in the a-axis direction is 3.7 ° in the ReO ₃ crystal unit, both lattice constants are similar. Therefore, the crystal growth of PbTiO ₃ can be performed according to the crystallinity of ReO ₃ . Moreover, since the lattice constants in the a-axis direction are similar to each other, R
The crystal unit of PbTiO ₃ grown on the surface of eO ₃ tends to be c-axis oriented in a direction coinciding with the direction of the electric field E applied between the lower electrode 8 and the upper electrode 10.
When the PbTiO ₃ crystal unit is c-axis oriented in a direction coinciding with the direction of the electric field E, a large remanent polarization is obtained.

Further, at the interface between the lower electrode 8 and the ferroelectric material 9, Pb ions existing at the position of the A site of PbTiO ₃ enter the vacancies existing at the position of the A site of ReO _3. since the information of the crystal structure of the ReO ₃ is transmitted to the crystal structure of PbTiO _3, allows crystal growth of PbTiO ₃ in accordance crystalline ReO ₃ on the surface of the ReO _3.

The upper electrode 10 of the capacitive element is formed on the surface of the ferroelectric 9. The upper layer electrode 10 is formed of ReO ₃ as a ferroelectric electrode similarly to the lower layer electrode 8 in this embodiment. Similar to the case of performing the crystal growth of PbTiO ₃ on the surface of the ReO _3, allows crystal growth of the ReO ₃ by sputtering on the surface of PbTiO _3. Since the upper electrode 10 does not basically serve as a base for crystal growth of the ferroelectric 9, it is not necessarily required to use the upper electrode 10 as a ferroelectric electrode, that is, R
It need not be formed of eO ₃ .

The nonvolatile memory element M thus configured
The following operation and effect can be obtained in the non-volatile memory device equipped with.

(1) In the capacitive element of the nonvolatile memory element M, at least the lower electrode 8 has substantially the same crystal structure as the perovskite crystal structure as a ferroelectric electrode,
Since the oxide is formed of a conductive oxide, oxygen is present in a stable state in the oxide. Therefore, oxygen is present near the interface with the ferroelectric material 9 and on the surface of the lower electrode 8. Is no longer precipitated. As a result, no paraelectric substance (unnecessary substance) is generated at the interface due to the precipitation of oxygen, so that film fatigue caused by repetition of polarization reversal of the ferroelectric substance 9 is reduced, and Effective reduction of remanent polarization can be prevented. Further, since the lower electrode 8 is formed with a crystal structure substantially the same as the perovskite crystal structure of the ferroelectric 9, when the ferroelectric 9 is crystal-grown on the surface of the lower electrode 8, the underlying crystal The crystal growth can be performed while maintaining the above condition. When the upper electrode 10 is formed of the same material as the lower electrode 8, crystal growth of the upper electrode (ferroelectric electrode) 10 is performed on the surface of the ferroelectric 9 while maintaining the crystallinity of the base. I can do it.

(2) Since at least the lower electrode 8 of the capacitive element is formed of a crystal structure having a hole at the position of the A site of the ABO ₃ crystal structure, the lowermost electrode 8 on the ferroelectric material 9 side is the outermost end. The metal atoms of the crystal unit located on the outermost surface on the side of the lower electrode 8 of the ferroelectric material 9 enter the vacancies of the crystal unit located on the surface. As a result, the lower electrode 8 and the ferroelectric 9 are atomically bonded, so that the bonding strength between the lower electrode 8 and the ferroelectric 9 can be improved. Further, since the lower electrode 8 and the ferroelectric 9 are atomically bonded and crystal information is transmitted from the lower electrode 8 to the ferroelectric 9,
Continuous crystal growth of each of the perovskite crystal structure and the substantially same crystal structure as the perovskite crystal structure can be easily performed.

(3) Since at least the lower electrode 8 of the capacitive element is made of ReO ₃ , ReO ₃ has a low resistance value of about 10 ⁻⁵ Ωcm at room temperature, so that the signal transmission speed can be increased. .

(4) The ferroelectric material 9 in the capacitor element
Since the film fatigue of the film can be reduced and the remanent polarization can be increased, the information writing characteristics can be improved, and sufficient information can be written at a low information writing voltage, so that low power consumption can be realized.

Application Example The present invention relates to a nonvolatile memory element M of the nonvolatile memory device.
In addition to PZT, PbTiO ₃
Can be used. Further, the present invention provides a ferroelectric material 9 of SrBi ₂ Ta ₂ O ₉ , Bi ₄ Ti ₃ O
Any of the _twelve layered dielectrics can be used.

Further, the present invention can be applied to a pyroelectric infrared sensor utilizing a pyroelectric effect using a ferroelectric material.
Further, the present invention can be applied to a pressure sensor utilizing a piezoelectric effect using a ferroelectric material. Pyroelectric infrared sensor,
In any case of the pressure sensor, the ferroelectric electrode having a laminated structure with the ferroelectric material is formed of ReO ₃ .

[0046]

According to the present invention, it is possible to provide a ferroelectric electrode capable of reducing film fatigue caused by repetition of polarization inversion of a ferroelectric and preventing a decrease in remanent polarization of the ferroelectric.

Further, according to the present invention, it is possible to provide a nonvolatile memory device capable of improving information writing characteristics of a nonvolatile memory element and realizing low power consumption.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a nonvolatile memory device according to an embodiment of the present invention.

FIG. 2 is a crystal structure diagram of an electrode of a capacitor in a nonvolatile memory element mounted on the nonvolatile memory device.

FIG. 3 is a crystal structure diagram of a ferroelectric substance of the capacitive element.

FIG. 4 is a crystal structure diagram of a laminated portion of an electrode of the capacitor and a ferroelectric.

[Explanation of symbols]

Reference Signs List 1 substrate, 1A channel formation region, 2 gate insulator, 3 control electrode, 4 semiconductor region, 8 lower electrode, 9
Ferroelectric, 10 upper electrode, M nonvolatile memory element.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/8247 29/788 29/792

Claims (7)

[Claims] 1. An electrode for a ferroelectric which forms a laminated structure with a ferroelectric having a perovskite crystal structure, wherein the electrode has substantially the same crystal structure as the perovskite crystal structure of the ferroelectric and has conductivity. An electrode for a ferroelectric, characterized by being formed of an oxide. 2. The ferroelectric electrode according to claim 1, wherein the ferroelectric electrode has a crystal structure in which vacancies are present at positions of A sites in the ABO ₃ crystal structure. 3. The ferroelectric electrode according to claim 1, wherein the ferroelectric electrode is formed of polycrystalline or single-crystalline ReO ₃ . 4. A ferroelectric material having a perovskite crystal structure; and a ferroelectric electrode having a substantially same crystal structure as the perovskite crystal structure of the ferroelectric material and formed of a conductive oxide. Wherein the ferroelectric electrode, a ferroelectric layer laminated on the ferroelectric electrode, and an element formed of an electrode laminated on the ferroelectric substance are mounted. Dielectric device. 5. The ferroelectric device according to claim 4, wherein an element in which the ferroelectric electrode, the ferroelectric, and the ferroelectric electrode are sequentially stacked is mounted. Body device. 6. The ferroelectric device according to claim 4, wherein the ferroelectric material includes PZT, PbTiO ₃ , and BaTiO.
₃ , any of SrBi ₂ Ta ₂ O ₉ ,
A ferroelectric device, wherein any one of layered dielectric materials of Bi ₄ Ti ₃ O ₁₂ is used, and ReO ₃ in a polycrystalline state or a single crystal state is used for the ferroelectric electrode. 7. The ferroelectric device according to claim 6, wherein the element is a capacitance element used as an information storage unit.