JP2001122629A - Oxide electrode thin film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the difficulty in the strict composition control of an SrRuO3 thin film used as an electrode material effective for decreasing leak current in a ferroelectric capacitor as the lamination order of an SrO surface and RuO2 surface are easily alternated and a laminar structure SRn+1RUnO3n+1 ((n) is an integer of >=1) is resulted. SOLUTION: Two targets, SrOx(0x2) are used in a film making stage by laser abrasion and while the intensity vibration of a reflection high-velocity electron beam diffraction RHEED is observed, SrO-atom layers and RuO2-atom layers 3 are alternately deposited on a (100) Si substrate by alternating the targets at the point of the time the growth of one atom layer is completed, by which the Srn+1RUnO3n+1 ((n) is an integer of >=1) oxide electrode thin film subjected to the strict composition control is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates in general formula Sr n _{+ 1} used for the oxide devices such as ferroelectric memories Ru _n O _{3n + 1}
The present invention relates to an oxide electrode thin film represented by (n is an integer of 1 or more) and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, the development of nonvolatile memories using ferroelectrics has been rapidly progressing. Pb as ferroelectric
Zr _1-x Ti _x O ₃ (PZT), Ba _1-x Sr _x TiO ₃ (B
Materials such as ST) and SrBi ₂ Ta ₂ O ₉ (SBT) have attracted attention. Among them, a PZT material having a composition near the rhombohedral-tetragonal phase boundary (MPB) has excellent remanent polarization and coercive electric field characteristics. It is the most practical material.

[0003] Ferroelectric memories are classified into a ferroelectric capacitor type using a ferroelectric material as a capacitor to form a 1T / 1C structure or the like, and an MFSFET type using a ferroelectric material as a gate insulating film instead of SiO _2. Is done. 1T /
In the 1C-type ferroelectric capacitor structure, an electrode layer is formed on a substrate such as silicon (Si), and a ferroelectric layer is formed thereon. Significantly affects characteristics. The characteristics required as the electrode material of the ferroelectric capacitor are as follows: (1) The electric resistance is sufficiently low. (2) The mismatch between the lattice constant and the ferroelectric material is small. (3) High heat resistance. (4) Low reactivity. (5) High diffusion barrier properties. (6) Good adhesion to substrates and ferroelectrics. And so on.

Conventionally, Pt has been used as an electrode material for PZT-based ferroelectrics. Pt has a strong self-orientation property because it has a face-centered cubic lattice (FCC) structure, which is a close-packed structure. When Pt is formed on an amorphous material such as SiO ₂ , it is strongly oriented to (111) and a ferroelectric substance thereon The film also has good orientation. However, because of the strong orientation, columnar crystals grow,
There is a problem that Pb and the like are easily diffused into the base along the grain boundaries. There was also a problem in the adhesion between Pt and SiO ₂ .

In order to improve the adhesion between Pt and SiO ₂ , a diffusion barrier layer made of Ti or Pb is used as a diffusion barrier layer.
Even if iN or the like is used, the electrode structure becomes complicated, Ti is oxidized, Ti diffuses into Pt, and the crystallinity of PZT is reduced, resulting in PE hysteresis characteristics, leak current characteristics, and fatigue characteristics. Electrical characteristics such as deterioration.

As described above, since there are many problems with the Pt electrode, conductive oxide electrode materials such as RuO _x and IrO ₂ have been studied. Above all, SrRuO ₃ having a perovskite structure has the same crystal structure as PZT, so it has excellent bonding properties at the interface, easily realizes epitaxial growth of PZT, and also has excellent characteristics as a diffusion barrier layer of Pb. I have. Therefore, ferroelectric capacitors using SrRuO ₃ as electrodes have been actively studied. ((1) Appl. Phys. Lett., 63 2570-2572 (199
3)).

[0007]

However, SrRuO ₃
When used as an oxide electrode thin film, there were the following problems.

SrRuO ₃ has a perovskite structure, that is, a structure in which SrO layers and RuO ₂ layers are alternately stacked. The SrO layer can be also viewed as a NaCl structure, by perovskite structure and NaCl structure is laminated by periodically alternating the c-axis direction, layered perovskite structure _{Sr n + 1 Ru n O 3n} + 1 (n is 1 Above integer). When n = 1, Sr also called K ₂ NiF ₄ structure
₂ RuO ₄ , Sr ₃ Ru ₂ O ₇ when n = 2, and SrRuO ₃ when n = ∞.

The SrRuO ₃ thin film shows metal conductivity when produced under a relatively high oxygen partial pressure ((2) Jpn. J. Ap.
pl. Phys., 35 6212 (1996)). On the other hand, Sr ₂ RuO
_{No. 4} has anisotropy in electric conductivity, reflecting its anisotropic crystal structure, and shows semiconductor conductivity in the interplane direction despite showing metal conductivity in the in-plane direction of c-plane. (3) Appl. Phys. Lett., 60 1138 (1992). That is, it is considered that metal conductivity is expressed by the itinerary nature of electrons involved in the covalent bond of the Ru4d-O2p orbital. X-ray diffraction revealed that Sr ₃ Ru ₂ O ₇ also had a layered structure ((4) Mater. R
es. Bull., 26 763 (1991)), and is therefore expected to exhibit anisotropic electrical conductivity as well.

From the above considerations, it was found that S
If _{r n + 1 Ru n O 3n} + 1 (n is an integer of 1 or more) used,
If three-dimensional isotropic electrical conductivity is required, SrRu
O ₃ is most desirable, and when two-dimensional anisotropic electric conductivity is required, a layered structure such as Sr ₂ RuO ₄ is most desirable. Conversely, by strictly controlling the composition and the laminated structure,
It should be possible to make an oxide electrode with any electrical conductivity in any direction.

However, the composition deviation between the target and the product
Laser abrasion of thin film production method, which has the advantage of less
Even in the Sr._{n + 1}Ru_nO_{3n + 1}(N is 1
It is difficult to strictly control the composition of
Was. That is, the SrO layer and RuO _TwoThe order in which the layers are stacked
It is easy to be replaced easily and usually under low oxygen partial pressure
In the case of the film forming conditions of
Genus Ru tends to remain on target, SrRuO_ThreeTarget
Even when a pit is used, the deposited oxide electrode thin film is S
r Excessive composition is likely.

[0012] Therefore, the present invention has the general formula _{Sr n + 1 Ru n O 3n} + 1 (n is an integer of 1 or more) while strictly control the composition of the compound consisting of (001) direction in the epitaxial growth on a variety of substrates An object of the present invention is to provide an oxide electrode thin film obtained by the above method and a method for manufacturing the same.

[0013]

Oxide electrode film according to claim 1, wherein Means for Solving the Problems], in oxide electrode film used for the oxide devices such as ferroelectric memory, the general formula _{Sr n + 1 Ru n O 3n} + 1
(N is an integer of 1 or more).

According to a second aspect of the present invention, there is provided an oxide electrode thin film comprising:
uO ₃ , Sr ₂ RuO ₄ , and Sr ₃ Ru ₂ O ₇ , characterized by being made of at least one of the above compounds.

A method for producing an oxide electrode thin film according to claim 3.
Is the oxidation used in oxide devices such as ferroelectric memories.
In the method for manufacturing an object electrode thin film, the oxide electrode thin film
Sr _{n + 1}Ru_nO_{3n + 1}(N is an integer of 1 or more) and S
rO_xA first target member made of (0x2);
uO_x(0x2) and a second target member
It is characterized by being.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an oxide electrode thin film, wherein a laser energy density on a target surface is 0.5 to 3.0 J / cm by using a laser ablation method.
Characterized by ^two.

A method for producing an oxide electrode thin film according to claim 5.
Means that reflection high-speed electron diffraction RHE
The intensity vibration of the ED changes from the maximum to the minimum and then to the maximum again
Laser beam irradiation and replacement of target material
Periodically for the first and second target members.
By repeating, the perovskite structure SrRuO _Three
It is characterized by obtaining.

According to a sixth aspect of the present invention, there is provided a method for manufacturing an oxide electrode thin film, comprising the steps of: starting reflection of a laser beam;
Interrupting the laser beam irradiation and exchanging the target member when the intensity vibration of the ED is reduced from the maximum to the minimum and becomes the maximum again, a step of performing twice for the first target member and once for the second target member, It is characterized by obtaining a layered perovskite structure Sr ₂ RuO ₄ by repeating periodically.

According to a seventh aspect of the present invention, there is provided a method for producing an oxide electrode thin film, comprising the steps of: starting reflection of a laser beam;
The interruption of the laser beam irradiation and the replacement of the target member performed when the intensity vibration of the ED changes from the maximum to the minimum and then to the maximum again are performed twice for the first target member, once for the second target member, and once for the first target member. Performing the process once for the target member and once for the second target member,
It is characterized by obtaining a layered perovskite structure Sr ₃ Ru ₂ O ₇ by repeating periodically.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a view showing a first embodiment of an oxide electrode thin film according to the present invention.

By a laser ablation method using an SrO target, a laser energy density on the target surface is 1 J / cm ² , a substrate temperature is 700 ° C., and an oxygen partial pressure is 3
(100) S terminated with TiO _{2 under} the condition of mTorr
A single atomic layer of SrO 2 was deposited on the TO substrate 1. However, the target composition, the substrate temperature, the oxygen partial pressure, and the substrate plane orientation are not limited to these. Here, the ablation was stopped when the laser energy density and the RHEED oscillation once passed the minimum point and reached the maximum again.

[0023] Replace the target, the laser ablation method using RuO ₂ target, the laser energy density 1 J / cm ² on the target surface, a substrate temperature of 700 ° C., under conditions of oxygen partial pressure 3 mTorr, RuO ₂
One monolayer 3 was deposited. However, the laser energy density, target composition, substrate temperature, oxygen partial pressure, and substrate plane orientation are not limited to these. Again, RHEE
Ablation was interrupted when the D-vibration once passed the minimum point and reached a maximum again.

As described above, the process of exchanging the target at each maximum point of the RHEED oscillation and sequentially depositing one atomic layer of SrO and one atomic layer of RuO ₂ one by one is repeated 100 times to form a thin film having a thickness of about 50 nm. Formed.

The obtained SrRuO ₃ thin film is an epitaxial film having (001) SrRuO ₃ / (001) STO orientation perpendicular to the surface and [100] SrRuO ₃ // [100] STO orientation in the plane. 4 resistance in the surface
When the electrical resistivity was measured by the terminal method,
A value on the order of 200 μcm was obtained, and exhibited a metallic resistance temperature dependency over a wide temperature range from 100 K to room temperature. Further, as a result of the composition analysis by ICP, Sr:
Ru was also 1: 1. That is, the composition could be controlled.

As described above, when the RHEED oscillation reaches a maximum, two targets of SrO _x (0x2) and RuO _x (0x2) are alternately deposited to perform the deposition for each atomic layer, so that SrRuO ₃ is strictly contained. It is possible to control the composition appropriately.

(Embodiment 2) FIG. 2 is a view showing a second embodiment of the oxide electrode thin film of the present invention.

By a laser ablation method using an SrO target, a laser energy density on the target surface is 1 J / cm ² , a substrate temperature is 700 ° C., and an oxygen partial pressure is 3
(100) S terminated with TiO _{2 under} the condition of mTorr
Two SrO atomic layers 22 were deposited on the TO substrate 21. However, the laser energy density, target composition, substrate temperature, oxygen partial pressure, and substrate plane orientation are not limited to these. Here, the ablation was stopped when the RHEED vibration reached the second maximum.

The target was exchanged, and a laser ablation method using a RuO ₂ target was used under the conditions of a laser energy density on the target surface of 1 J / cm ² , a substrate temperature of 700 ° C., and an oxygen partial pressure of 3 mTorr to obtain RuO _2.
One monolayer 23 was deposited. However, the laser energy density, target composition, substrate temperature, oxygen partial pressure, and substrate plane orientation are not limited to these. Again, RHE
Ablation was stopped when the ED oscillation reached a maximum.

According to the above procedure, the target is exchanged at the maximum point of the RHEED oscillation, and the SrO monolayer 22,
The process of depositing two RuO ₂ atomic layers 23 one by one was repeated 100 times to form a thin film having a thickness of about 70 nm.

The obtained Sr ₂ RuO ₄ thin film is oriented (001) Sr ₂ RuO ₄ / (001) STO perpendicular to the surface and [100] Sr ₂ RuO ₄ // [100] STO in the plane. Is an epitaxial film having a resistance within the surface of 4
When the electrical resistivity was measured by the terminal method,
A value on the order of 200 μcm was obtained, and exhibited a metallic resistance temperature dependency over a wide temperature range from 100 K to room temperature. At this time, the resistance between the Au electrodes 24 and 25 in FIG. 2 at room temperature was = 30 mcm, and showed semiconductor-like resistance temperature dependence over a wide temperature range from 100K to room temperature. Further, as a result of composition analysis by ICP, Sr: R
u was 2: 1. That is, the composition could be controlled.

Sr ₃ Ru ₂ O ₇ can be produced in a similar manner. In this case, the process of exchanging the target at the maximum point of the RHEED oscillation, depositing two SrO atomic layers, one RuO ₂ monolayer, one SrO monoatomic layer, and one RuO ₂ monoatomic layer is performed. Just repeat.

In the device as shown in FIG.
By combining rRuO ₃ , Sr ₂ RuO ₄ , and Sr ₃ Ru ₂ O ₇ , an oxide electrode thin film having low resistance both in the plane parallel to the substrate and between the planes can be manufactured.

As described above, when the RHEED oscillation reaches a maximum, the two targets SrO _x (0x2) and RuO _x (0x2) are alternately deposited to perform deposition for each atomic layer, thereby obtaining Sr ₂ RuO _4. Strict composition control of Sr ₃ Ru ₂ O ₇ is possible.

[0035]

As described above, according to the oxide electrode thin film and the method of manufacturing the same of the present invention, SrO _x (0x2) and RuO _x (0x2) at the time when the RHEED oscillation is maximized.
Since then alternating the two targets performing deposition for each one atomic layer, on a variety of substrates (001) orientation Sr _{n + 1} Ru n
O _{3n + 1} (n is an integer of 1 or more) oxide electrode thin film can be epitaxially grown under strict composition control. The oxide electrode thin film and the method of manufacturing the same of the present invention can locally control the electrical conductivity and oxygen deficiency of the electrode layer, and optimize electronic devices such as a dielectric capacitor memory, a ferroelectric capacitor memory, and an MFSFET. It can be realized with a simple structure.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an SrRuO ₃ oxide electrode thin film showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view of an Sr ₂ RuO ₄ oxide electrode thin film showing one embodiment of the present invention.

[Explanation of Codes] 1. TiO ₂ terminated (100) STO substrate SrO monolayer 3. RuO ₂ monoatomic layer 21. 22. (100) STO substrate terminated with TiO ₂ SrO monoatomic layer 23. RuO ₂ monoatomic layer 24. Au electrode 25. Au electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroshi Miyazawa 3-3-5 Yamato, Suwa-shi, Nagano F-term in Seiko Epson Corporation (reference) 4G048 AA05 AB01 AC02 AD02 AD08 AE05 4K029 BA50 BB07 BD00 CA01 DB05 DB14 DB20 5G301 CA02 CA21 CD02 CE01 5G307 GA08 GC02

Claims (7)

[Claims] 1. A oxide electrode film used for the oxide devices such as ferroelectric memory, wherein the oxide electrode films, the general formula _{Sr n + 1 Ru n O 3n} + 1 (n is an integer of 1 or more) An oxide electrode thin film comprising a compound represented by the formula: 2. A compound represented by the general formula _{Sr n + 1 Ru n O 3n} + 1 (n is an integer of 1 or more) is, SrRuO _3, Sr ₂ Ru
_2. The oxide electrode thin film according to claim 1, wherein O ₄ and Sr ₃ Ru ₂ O ₇ are formed of at least one of the compounds. 3. A strong manufacturing method of an oxide electrode film used for the oxide devices such as ferroelectric memory, the oxide electrode film is _{Sr n + 1 Ru n O 3n} + 1 (n 1 or more integer) A method of manufacturing an oxide electrode thin film, comprising using a first target member made of SrO _x (0x2) and a second target member made of RuO _x (0x2). 4. A laser energy density on a target surface of 0.5 to 3.
4. The method for producing an oxide electrode thin film according to claim 3, wherein the thickness is 0 J / cm ² . 5. The method according to claim 1, further comprising: interrupting the laser beam irradiation and exchanging the target member when the intensity oscillation of the reflection high-energy electron diffraction RHEED is changed from a maximum to a minimum after the start of the laser beam irradiation, and then returns to a maximum again. The perovskite structure S
The method for producing an oxide electrode thin film according to claim ₃ , wherein rRuO ₃ is obtained. 6. The method according to claim 1, further comprising the step of interrupting the laser beam irradiation and exchanging the target member when the intensity oscillation of the reflection high-energy electron beam diffraction RHEED is changed from a maximum to a minimum and becomes a maximum again after the start of the laser beam irradiation. Is performed twice and the second target member is performed once, and the layered perovskite structure Sr is periodically repeated.
_{4. The} method for producing an oxide electrode thin film according to claim 3, wherein ₂ RuO ₄ is obtained. 7. The method according to claim 1, wherein after the laser beam irradiation is started, the interruption of the laser beam irradiation and the replacement of the target member performed when the intensity oscillation of the reflection high-energy electron diffraction RHEED is reduced from a maximum to a minimum and becomes a maximum again. Is repeated twice, once for the second target member, once for the first target member, and once for the second target member, to thereby obtain a layered perovskite structure Sr ₃ Ru ₂ O _7. 4. The method for producing an oxide electrode thin film according to claim 3, wherein