JP2001163620A - Dielectric thin film, production process of the same and electronic part using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process of an Mg solid solution dielectric thin film having a single phase perovskite structure and also to provide such a thin film material which is produced by the production process and has excellent characteristics. SOLUTION: This production process comprises performing crystal growth in a thermodynamically non-equilibrium state to deposit an oxide having a composition represented by the formula ( A1}1-XMgX) A2}O3 (wherein X>0), on a desired substrate. Thus, by performing the crystal growth in a thermodynamically non-equilibrium state, formation of an ilmenite secondary phase, which is liable to occur in a conventional sintering process, can be inhibited from being caused and a single phase perovskite structure being in a metastable state is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dielectric thin film having a perovskite structure, a method of manufacturing the same, and an electronic component thereof.

[0002]

BACKGROUND ART An oxide thin film material having a perovskite structure represented by a composition formula of {A1} {A2} O ₃ has ferroelectricity, high dielectric constant, electro-optic effect, piezoelectric effect, pyroelectric effect, superconductivity, etc. Because of its extremely diverse functions, it has been applied to a wide range of electronic devices such as capacitor elements, ferroelectric memory elements, and optical sensors. Recently, the development of memory devices that focus on the high dielectric constant characteristics and strong attraction characteristics of perovskite oxide thin films has been spotlighted, and DRAMs (Dynamic Random Access Memory) aiming at high integration by reducing the capacitor area
Access Memory) or MMIC
(Microwave Monolithic Integrated Circuit) is being studied for applications such as highly integrated thin film capacitors for high frequency applications. In particular, perovskite oxide SrT
iO ₃ , BaTiO ₃ , CaTiO _{3 and the} like have a high dielectric constant and a high insulating property, and are attracting attention as materials suitable for those applications.

[0003] In a material system having a perovskite structure as described above, a single component composition cannot satisfy the characteristic requirements of each device. Therefore, {A1} and {A1
2} substitution by other atoms, doping, or non-stoichiometric composition ratio {A1} / {A2} to control the characteristics,
Optimizations have been made for the desired characteristics of each application.

[0004] In particular, when the divalent {A1} site cation is replaced with a cation atom having the same valence having a different ionic radius, the dielectric constant mainly due to the shift of the structural phase transition temperature, the so-called Curie temperature, is increased. The temperature characteristic is remarkably modulated, and the temperature characteristic can be controlled to some extent by selecting the kind of the substituted atom and the amount of substitution. Also, in synchronization with the temperature characteristic modulation,
Other physical properties (such as dielectric constant and frequency characteristics) also change significantly.
For example, SrTiO ₃ ceramics exhibit quantum paraelectricity at a low temperature (<−263 ° C.) due to the quantum fluctuation effect.
Quantum ferroelectric phase is induced at low temperature by replacing Sr ion with Ca ion.

[0005] CaTiO after this substitution₃-SrTiO₃
Constitutes a complete solid solution system, and the composition Sr_{0 . 96}Ca_0.04
TiO₃Approximately 10,000 at 243 ° C
Develop electrical conductivity. On the other hand, SrTiO₃-BaTiO₃Solid
The solution system shows a very high dielectric constant near room temperature,
Sr / (Sr + Ba) = 0 near the cubic structure change boundary.
3 has the highest dielectric constant. Even at room temperature with paraelectric phase
SrTiO₃-BaTiO₃Solid-solution materials are highly dielectric
Suitable for DRAM applications that require performance
R & D is being actively conducted toward. More recently
Is CaTiO ₃-SrTiO₃-BaTiO₃Of 3
Consideration of separation is also being conducted, and high dielectric properties, low loss, frequency
And high stability against temperature.

[0006]

However, within the composition range described above, it is difficult to obtain sufficient characteristics as a capacitor for a high-performance thin-film element requiring high stability in recent years. Other solid solution composition systems are required. As an element that can be substituted for the {A1} site, there is Mg belonging to the same alkaline earth metal group as Ca, Sr, and Ba. However, this Mg is Ca, Sr,
The ionic radius is significantly smaller than that of Ba. For this reason,
Mg has a perovskite structure having an oxygen 12 coordination structure.
{A1} does not form a solid solution, MgTiO ₃ having an ilmenite structure based on an oxygen close-packed structure more stable in terms of electrostatic energy, ZrO ₂ having a fluorite-type structure in which MgO forms a solid solution, rock salt MgO having a mold structure is formed as a secondary phase.

That is, in the conventional powder metallurgy technique, Mg
Cannot be dissolved in the {A1} site of the perovskite structure, and Mg is Mg having an ilmenite structure.
A secondary phase such as TiO ₃ is formed. For example, {A} TiO ₃
-MgTiO ₃ (where {A} = Ca, Sr, Ba,
Pb) does not form a solid solution and shows a two-phase separated microstructure of perovskite {A} TiO ₃ and ilmenite MgTiO ₃ .

However, Mg is dissolved in the {A1} site,
If it is possible to obtain a single-phase perovskite structure,
Lattice strain, which is considered to be caused by substitution of Mg having a small ionic radius, has a great effect on the dielectric properties of the material, as well as enabling property modulation over a wider range.

The present invention focuses on the above points.
It is an object of the present invention to obtain a single-phase perovskite structure by dissolving g in the {A1} site, and to obtain a thin film material having excellent characteristics by this method.

[0010]

According to the present invention, there is provided a dielectric thin film having a perovskite structure, wherein {A1} is at least one selected from Ca, Sr, Ba and Pb. When {A2} is composed of at least one element selected from Ti and Zr, ({A2}
Characterized by having a composition of _{1} 1-X Mg X)} {A2} O 3 ( provided that X> 0). The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> First, the present invention
Explanation of thin film manufacturing method and thin film embodiment according to the present invention
I will tell. In the conventional powder metallurgy method, ({A1}_1-XMg
_X) {A2} O₃When a material having the composition of
MgTiO with menite structure₃Etc. are generated separately
I will. However, in this embodiment, the thermodynamically non-equilibrium
The desired substrate is formed by a thin film formation technique that performs crystal growth in a state.
Above ({A1}_1-XMg_X) {A2} O ₃(However, X> 0)
Deposit an oxide with a composition. Thermodynamically non-equilibrium state
Crystal growth in the normal state
The formation of a secondary phase that is
A lobskite structure is formed.

Thus, ({A1}_1-XMg_X) {A2} O
₃Having a composition represented by the formula: ₆Oxygen octahedron
Oxide composed only of shared perovskite structure
A dielectric thin film is obtained. Where {A1} is Ca, S
at least one selected from the group consisting of r, Ba, and Pb
It is a seed element. {A2} is composed of Ti and Zr.
At least one element selected from the group consisting of In addition,
X> 0. Mg has a small ionic radius.
Makes it possible to introduce strain into the dielectric thin film
You. In other words, the lattice of the perovskite structure is distorted
The lattice distortion causes new dielectric properties
And contribute to the dielectric properties.
You.

FIG. 1A shows a state of the structure. In FIG. 1A, an octahedron 12A represents a perovskite structure of {A2} O ₆ oxygen octahedron, and a black circle 12B represents an element.
Represents {A1}

For forming a thin film of perovskite oxide having the above composition, for example, a laser ablation method, M
BE (Molecular Beam Epitaxy) method, CVD (Chemical Vapor
A thin film manufacturing technique such as a porDeposition method, a sol-gel method, or a sputtering method is used. According to these methods,
The film can be formed at a temperature of about 1/2 or less of the firing temperature by the powder metallurgy method.

In film formation at such a low temperature, a metastable structure that cannot be stably provided by a conventional powder metallurgy technique can be present relatively stably. That is, since the powder metallurgy technique brings about a state thermodynamically close to the thermal equilibrium state, the most energy-stable substance is formed.
On the other hand, in the thin film technology for growing a crystal by a low-temperature process, a non-equilibrium state is maintained thermodynamically, so that a metastable structure can be formed. Therefore, a single-phase perovskite structure can be obtained by a low-temperature process even for a dielectric material to which MgTiO ₃ is added, in which a secondary phase is formed by the powder metallurgy technique.

In addition, in the above-mentioned formation of the Mg-dissolved perovskite dielectric thin film, SrTiO ₃ and Nr having a perovskite structure having good lattice matching are added.
TiO ₃ , LaAlO ₃ —Sr ₂ AlTaO ₆ , LaS
By performing epitaxial growth using a single crystal substrate of rAlO ₄ or the like or MgO having a NaCl structure, the perovskite structure of the thin film is stabilized, and Mg is deposited on the {A1} site.
Can further expand the solid solution region.

In actual use as a capacitor, a single crystal substrate of SrTiO ₃ or LaTiO ₃ —SrTiO ₃ doped with Nb having conductivity is used, or has a lattice matching with the single crystal substrate. Ca {A2} O ₃ (where {A2} = V, Cr, Fe, Ru), Sr {A2} O ₃ (where {A2} = V, Cr, Fe, Ru), La which is a perovskite conductive oxide {A2} BO
₃ ({A2} = Ti, Co, Ni, Cu), La
_1−X Sr _X {A2} O ₃ (where {A2} = V, Mn, C
o, X> 0.23), BaPbO ₃ , SrRuO ₃ , Sr
IrO ₃ , Sr ₂ RuO ₄ , Sr ₂ IrO ₄ , (La
_1-X Sr _X ) ₂ CuO ₄ (where X <0.3), La, N
b-doped SrTiO ₃ or the like is epitaxially grown on the single crystal substrate as a lower electrode layer.

The substrate assist effect of performing epitaxial growth of a thin film by selecting such a substrate is because Si has high lattice reactivity with the above-described perovskite dielectric thin film and has high reactivity.
It can also be obtained on a semiconductor substrate. That is, FIG.
As shown in (B), an oxide film 52 that can be epitaxially grown and has lattice matching with a perovskite conductive oxide 54 described later is grown on the Si substrate 50. Then, a perovskite conductive oxide 54 having lattice matching with the perovskite oxide is grown thereon as an electrode layer. Then, an Mg solid solution perovskite dielectric thin film 56 is formed on the perovskite conductive oxide 54. The conductive oxide 58 will be described later.

According to this example, the Mg-dissolved perovskite dielectric thin film of the present embodiment can be formed irrespective of the lattice matching with the substrate, and the Mg-dissolved perovskite dielectric thin film can be manufactured by a method other than epitaxial growth. .

FIG. 2 shows an example of an apparatus for manufacturing a dielectric thin film according to the present embodiment. In this apparatus, a perovskite compound is deposited on a film formation substrate by a laser ablation method, and has a single-phase perovskite structure ({A
_{1} 1-X} Mg X) is to prepare a TiO ₃ dielectric thin film. In FIG. 1, a target 102 is placed in a vacuum chamber 100, and a deposition substrate 10 is placed at a predetermined distance from the target 102. Oxygen gas or ozone 104 is introduced into the vacuum chamber 100, and a laser beam 108 emitted from a laser light source 106 such as an ArF laser oscillator having a wavelength of 193 nm is reflected by a reflection mirror 110 so that the target 1
02 is applied.

As the target 102, for example, a ceramic sintered body produced by a usual powder metallurgy technique is used. The sintered body is obtained by mixing raw material powders to have a desired composition, and then performing preliminary firing, molding, and firing. Conventionally, only the perovskite structure material was used, but in this embodiment, (S
A sintered body of r _0.7 Mg _0.3 ) TiO ₃ is used.
This sintered body is composed of SrTiO ₃ particles having a perovskite structure and MgTiO ₃ having an ilmenite structure relatively uniformly distributed.
It has a microstructure composed of particles. Therefore, at the time of film formation, the target 102 is rotated to form the film in order to ensure uniform scattering of the Sr, Mg, and Ti elements.

When the target 102 is irradiated with the laser beam 108, the target 1
From 02, the excited species are scattered in the oxygen atmosphere, and a thin film having substantially the same composition as the target 102 is formed on the facing film-forming substrate 10. The atmosphere oxygen pressure for forming the thin film is, for example, 1 mTorr, and the substrate temperature is 600 ° C.

A high-resolution transmission electron microscope image showing a cross section of the thin film of the (Sr _0.7 Mg _0.3 ) TiO ₃ perovskite structure manufactured by the above thin film manufacturing apparatus was examined. Thin film is SrT
epitaxial growth on an iO ₃ single crystal substrate,
It was confirmed that there was no next phase or the like.

As described above, according to the present embodiment, on the substrate
By depositing a perovskite oxide represented by ({A1} _1-x Mg _x ) TiO ₃ , a Mg solid solution type dielectric thin film having a single-phase perovskite structure, which is difficult to form by conventional powder metallurgy, is produced. It is possible to do. Also, M
By dissolving g, characteristic modulation can be performed in a wide range, and characteristics corresponding to various devices can be optimized.

Further, Mg ions having a small ionic radius
The solid solution at the {A1} site changes the packing property of the perovskite structure and increases the particle strain. This is expected to improve the dielectric properties. Furthermore, by using a perovskite structure single crystal oxide substrate exhibiting good lattice matching as a substrate of the Mg solid solution dielectric thin film, the perovskite structure of the thin film can be stabilized, and the Mg solid solution region increases. .

<Embodiment 2> Next, an embodiment in which the dielectric thin film having the single-phase perovskite structure of the above embodiment is applied to a thin film capacitor for a DRAM will be described. The capacitor structure of this embodiment has the structure shown in FIG. 1B, and the oxide 52 formed on the Si substrate 50 is made of Mg.
An Al ₂ O ₄ thin film is formed. Then, a SrRuO ₃ thin film is formed thereon as a conductive oxide 54, and (SrRuO ₃₎ is formed thereon as a Mg solid solution perovskite dielectric thin film 56.
_{A 0.7} Mg _0.3 ) TiO ₃ thin film is formed. Further M
On the g solid solution perovskite dielectric thin film 56, an SrRuO ₃ thin film is stacked as a conductive oxide 58. As described above, the MgAl ₂ O ₄ thin film 52 is formed on the Si substrate 100.
The SrRuO ₃ thin films 54 and 58 function as a lower electrode and an upper electrode, respectively, as a buffer layer for forming the conductive oxide 54 thereon.

In the thin film capacitor having such a configuration, the MgAl ₂ O ₄ thin film 52 is epitaxially grown on the Si substrate 50 with a perfect plane orientation, and the SrRuO ₃ thin film 54 is further grown thereon. I have. That is, since the lower electrode layer is a conductive oxide having a perovskite structure, the (Sr _0.7 Mg _0.3 ) TiO ₃ thin film, which is the Mg solid solution perovskite dielectric thin film 56,
Epitaxial growth is easily performed on the lower electrode layer 54.

Therefore, in the capacitor element of the present embodiment, the above-mentioned Mg solid solution perovskite dielectric thin film structure can be formed stably, and the problem of adhesion between the dielectric thin film and the electrode seen when using a Pt electrode. In addition, the diffusion of the constituent elements that induce the deterioration of the fatigue characteristics, in particular, the oxygen can be avoided.

Epitaxial growth on Si substrate 50
As the oxide film 52, MgAl₂O ₄In addition, MgO,
CeO₂, Α-Al₂O₃, YSZ (Yttrium stable
Zirconium oxide) can be used. A pair of electrodes
As the lobskite conductive oxides 54 and 58, Ca
{A3} O₃(However, {A3} = V, Cr, Fe, Ru), S
r {A3} O₃(However, {A3} = V, Cr, Fe, Ru),
La {A3} O₃(However, {A3} = Ti, Co, Ni, C
u), La_1-XSr_X{A3} O₃(However, {A3} = V,
Mn, Co, X> 0.23), BaPbO₃, S
rRuO₃, SrIrO₃, Sr₂RuO₄, Sr₂I
rO₄, (La_1-XSr_X)₂CuO₄(However, X <
0.3), SrTiO doped with La and Nb₃Use
Can be.

<Other Embodiments> The present invention has many embodiments, and various modifications can be made based on the above disclosure. For example, in the above-described embodiment, a case has been described in which a Mg solid solution dielectric thin film having a single-phase perovskite structure is manufactured as a dielectric thin film applied to a memory element or the like. However, the present invention is not limited thereto. It can be applied to a dielectric thin film of an electronic component. For example, M
By applying as a high-frequency compatible capacitor for MIC or a decoupling capacitor for MCM, the functions of these components can be enhanced.

[0031]

As described above, according to the present invention,
The thin film forming method for performing thermodynamic crystal growth in a non-equilibrium state, on the desired substrate _{({A1} 1-X Mg} X) {A2} O 3
Since an oxide having a composition (where X> 0) is deposited, Mg can be dissolved in {A1} to obtain a single-phase perovskite structure, and further, a thin film having excellent characteristics There is an effect that a material can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a single-phase perovskite structure and a laminated state according to an embodiment.

FIG. 2 is a block diagram illustrating an example of an apparatus for manufacturing a dielectric thin film having a perovskite structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Film-forming board 50 ... Substrate 52 ... Oxide 54, 58 ... Conductive oxide 56 ... Mg solid volume perovskite dielectric thin film 100 ... Vacuum chamber 102 ... Target 104 ... Oxygen gas 106 ... Laser light source 108 ... Laser beam 110 … Reflection mirror 112… Plume

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoichi Sekiguchi 6-16-20 Ueno, Taito-ku, Tokyo Inside Taiyo Denki Co., Ltd. (72) Inventor Masayuki Fujimoto 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Denki Co., Ltd. F term (reference) 4G047 CA07 CA08 CB08 CC02 CD02 CD08 4G048 AA05 AB05 AC02 AD02 AD08 AE05

Claims (4)

[Claims] 1. A dielectric thin film having a perovskite structure, wherein {A1} is composed of at least one element selected from Ca, Sr, Ba and Pb, and {A2} is selected from Ti and Zr. When composed of at least one element, ({A
1} _{1 -X} Mg _X ) {A2} O ₃ (where X> 0), wherein the dielectric thin film has a composition. 2. The production of a dielectric thin film according to claim 1, wherein the dielectric thin film is formed using a powder sintered body containing a compound having a composition of {A1} {A2} O _3. Method. 3. A crystal is grown in a thermodynamically non-equilibrium state by using the powder sintered body.
The method for producing a dielectric thin film according to the above. 4. An electronic component using the dielectric thin film according to claim 1.