JP2002359287A - Thin-film element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film element which can easily improve leakage current characteristic at a low cost. SOLUTION: This thin-film element is formed, by forming an electrode 12 and a dielectric thin film 13 in order on a base substrate 11. The dielectric thin film 13 has columnar crystal particles of two kinds of Perovskite oxide, having a (111) face and a (110) face as alignment surfaces and the electrode 12 is made of metal, having a (111) face as an alignment surface; and the (111) face of crystal phase of the dielectric thin film 13 is lattice-matched on part of the (111) face of crystal phase of the electrode 12, and the (110) face is aligned preferentially with the in-surface direction of the dielectric thin film 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film device, and more particularly, to a thin film device such as a thin film capacitor formed by sequentially forming an electrode and a dielectric thin film on a support substrate.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and more sophisticated, there has been an increasing demand for electronic components installed in the electronic devices to be smaller, thinner, and compatible with high frequencies. Capacitors, which are circuit elements necessary for various electronic circuits, are one of them. To meet these demands, thin film capacitors using a dielectric thin film have been used.

Conventionally, a thin film capacitor (thin film capacitor) used for an integrated circuit or the like includes SiO.sub.2 as a dielectric thin film material.
_2. Materials such as Si ₃ N ₄ are used. These substances have high insulating properties, but have a small dielectric constant of about 10.
One of the recent trends in miniaturization is an increase in capacitance per unit area. The capacitance of a capacitor is proportional to the dielectric constant and the electrode area, and is inversely proportional to the film thickness. In order to improve the capacitance while ensuring miniaturization, it is necessary to use a material having a high dielectric constant or reduce the film thickness. However, since the thickness of the film is limited due to problems such as insulation properties, it is necessary to develop a dielectric thin film material having a large dielectric constant in order to reduce the size of the thin film capacitor.

A perovskite-type composite oxide represented by the chemical formula ABO ₃ is known as a dielectric material having a large dielectric constant. For example, BaTiO ₃ , SrTiO ₃ , PbTi
It is known that a material mainly composed of O ₃ or the like has a dielectric constant of 100 to 10,000 in single crystal or ceramic. Fabrication of the above-mentioned thin film capacitor using these materials has been performed for a long time. For example, Japanese Patent Application Laid-Open No. 62-58510 discloses a perovskite-type oxide sintered body represented by ABO _3. A method of forming a dielectric thin film by a sputtering method using a target is disclosed.

[0005] However, as described above, since the thickness of the dielectric thin film is reduced, the insulating property, that is, the leak current characteristic is deteriorated, and therefore, it has not been put to practical use.

In recent years, in order to improve leakage current characteristics,
Several technologies have been published. For example, Jpn.
J. Appl. Phys. Vol. 36 (1997) p
p. 5870-5873 reports a technique for improving the coverage of a dielectric thin film by using the MOCVD method and improving the leak current characteristics.

In Japanese Patent Laid-Open No. 5-195227, the content of alkali metal impurities in a dielectric thin film is set to 1 pp.
It is disclosed that the leakage current characteristics are improved by controlling the leakage current characteristics to m or less.

[0008]

When the above-mentioned MOCVD method is used, a certain thickness is required in order to secure the covering property of the dielectric thin film. Contrary to direction. Further, it is a technique peculiar to the MOCVD method which is excellent in coverage as a method of forming a film in a gas phase, and has a problem that it is difficult to convert it to another method.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 5-195227, there is a problem that controlling the impurity content to 1 ppm or less is not at a practical level and increases the production cost.

Therefore, it is necessary to use a dielectric thin film having a large dielectric constant, such as a perovskite-type composite oxide, in order to reduce the size of the thin film capacitive element. The characteristics deteriorate. As a method for solving this, the above-described technology is disclosed, but there are still problems such as a limited production method and poor productivity.

An object of the present invention is to provide a thin-film element capable of easily and inexpensively improving leakage current characteristics.

[0012]

Means for Solving the Problems The present inventors have conducted intensive studies to improve the leakage current characteristics of the dielectric thin film, and as a result, have aligned the orientations of the dielectric thin film and the base electrode formed on the supporting substrate. It has been found that leakage current characteristics can be improved by improving crystallinity. More specifically, not only the orientation in the thickness direction of the polycrystalline thin film but also the orientation in the in-plane direction are made uniform, thereby improving the crystal perfection and orientation of the dielectric thin film.

Here, the in-plane direction refers to a direction perpendicular to the thickness direction of the dielectric thin film, and is generally in-pl.
It is called an. Generally, the orientation of a dielectric thin film in the thickness direction can be measured by X-ray diffraction using an optical system such as a concentration method or a parallel beam method. in-plane
In order to measure diffraction, incident X-rays at a low angle with respect to the dielectric thin film were used, and the detector was placed around the surface normal of the film, that is, on the 2θ _(in- plane ₎ axis centered on the ω axis. Can be measured by a scanning method. Further, by scanning a specific diffraction peak in in-plane diffraction by ω,
The orientation in n-plane can be confirmed.

That is, the thin film element of the present invention is a thin film element in which an electrode and a dielectric thin film are sequentially formed on a supporting substrate, wherein the dielectric thin film has a (111) plane and a (110) plane. It has columnar crystal grains of two kinds of perovskite-type composite oxides having an orientation plane, the electrode is made of a metal having an orientation plane of a (111) plane, and a part of the crystal phase of the electrode has a (111) plane. On top of (11) of the crystalline phase of the dielectric thin film
1) The planes are lattice-matched, and the (110) plane is preferentially oriented in the in-plane direction of the dielectric thin film.

In the thin film element of the present invention, since there is a portion where the preferential orientation in the thickness direction of the dielectric thin film and the electrode at least coincide with each other, the dielectric crystal grains in that portion reflect the crystallinity of the underlying electrode. Crystal growth in the same direction can improve lattice matching between the dielectric thin film and the electrode. As a result of the crystal growth in the aligned orientation, columnar crystal grains having less lattice defects and excellent crystallinity are formed in the dielectric crystal. That is, leakage current characteristics can be improved by improving the crystallinity of the dielectric crystal.

The dielectric thin film has columnar crystal grains of a perovskite-type composite oxide in which the preferred orientation direction in at least the thickness direction is controlled in the (111) direction, and the dielectric thin film has a thickness in the thickness direction of the base electrode. By forming the columnar crystal grains in which the orientations of the preferred orientations are matched, the integrity and orientation of the columnar crystal grains can be improved.

Furthermore, since the (110) plane is preferentially oriented in the direction perpendicular to the thickness direction of the dielectric thin film, that is, in the in-plane direction, the columnar crystal grains have a biaxial orientation of the thickness direction and the in-plane direction. To form a preferentially oriented structure. As a result, not only the integrity and orientation of the columnar crystal particles forming the dielectric thin film formed on the base electrode are improved, but also the gap between adjacent columnar crystal particles can be reduced. . That is, leakage current characteristics can be further improved by reducing macro structural defects such as voids serving as conductive paths.

That is, usually, in the formation of a dielectric thin film by a sputtering method, a CVD method, or the like, columnar crystal grains peculiar to the thin film are formed. If the in-plane orientation is not controlled, the orientation tends to be uniaxial only in the thickness direction, and the columnar crystal grains grow in a random orientation to the in-plane orientation on the electrode, and as a result, the adjacent columnar crystal grains And a crystal containing many defects is formed near the interface between the particles. When the (111) axis stands in the thickness direction, it becomes a six-fold axis, and a six-fold symmetric crystal is formed.
Furthermore, by controlling the orientation in two directions, the thickness direction and the in-plane direction, the interface with the adjacent columnar crystal particles is shared as a hexagonal ridge, so that the gaps between the columnar crystal particles are formed. Since there is an effect of decreasing the leakage current characteristics, the leakage current characteristics are further improved.

As described above, it is considered that the leakage current characteristics are improved by the improvement of the crystallinity of the dielectric crystal itself, the reduction of conductive paths such as voids due to the bidirectional orientation, and the synergistic effect of these two. .

In the thin film element of the present invention, it is desirable that the dielectric thin film contains at least Ba, Sr and Ti as metal elements. As a result, the thin film capacitor has excellent dielectric characteristics and temperature characteristics, and does not contain Pb, which has been pointed out to affect the environment in recent years, so that the load on the environment is reduced.

In the present invention, it is desirable that the electrode is made of Pt. Since the electrode formed on the lower surface of the dielectric thin film is made of Pt, the misfit of the lattice constant between the electrode and the dielectric thin film is reduced, so that the dielectric thin film formed by inheriting the crystallinity of the electrode also results. It has excellent crystallinity and can easily form an orientation.

Further, it is desirable that the supporting substrate is made of sapphire single crystal. This makes it possible to easily form a metal thin film, particularly a Pt thin film, oriented on the (111) plane on each cut surface of sapphire.

The thin film element of the present invention is a thin film element in which an electrode made of Pt and a dielectric thin film containing at least Ba, Sr and Ti as metal elements are sequentially formed on a supporting substrate made of sapphire single crystal. Then, the (111) plane of the crystal phase of the dielectric thin film is lattice-matched on the (111) plane of the crystal phase of some of the electrodes, and the (110) plane is oriented in the in-plane direction of the dielectric thin film. They are preferentially oriented.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin film device according to the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view of a thin-film element comprising the thin-film capacitor of the present invention. The thin-film element is formed by sequentially forming an electrode 12, a dielectric thin film 13, and an electrode 14 on a support substrate 11.

The support substrate 11 is a ceramic substrate such as alumina, a single crystal substrate such as sapphire, MgO or SrTiO ₃ , a silicon substrate coated with SiO ₂ , or a glass substrate.
Considering that the reactivity with the thin film is small and the strength is large even when the plate thickness is reduced, an alumina substrate or a sapphire substrate is desirable. Substrates are preferred.

The material of the electrode 12 formed on the supporting substrate 11 is Pt, Au, Pd, Cu, Ag, Ni, Cr, T
Although not particularly limited, i.e., Al, etc., since the lattice constant of the ferroelectric and the high dielectric having a perovskite structure is about 3.90 angstroms, lattice mismatch, generation of residual stress, and In consideration of the peeling of the film, the change in the interface characteristics, and the like, the smaller the difference between the lattice constants of the dielectric thin film 13 and the electrode material, the better.
Pt, Pd, Al, and Au of 88 to 4.07 are desirable.
Further, Pt, Au, or a solid solution thereof having a (111) preferred orientation in the thickness direction is desirable from the viewpoint of easy control of the preferred orientation in forming the metal thin film (electrode) and the oxidation resistance in forming the dielectric thin film. In particular, Pt is desirable from the viewpoint of stability at the time of forming a dielectric thin film at a high temperature, that is, the point that aggregation of a metal thin film and formation of pores are small.

An adhesion layer may be formed at the interface between the support substrate 11 and the electrode 12 or the interface between the electrode 12 and the dielectric thin film 13 within a range that does not impair the crystal orientation in order to enhance the adhesion. Of course, an adhesion layer may be formed between the dielectric thin film 13 and the electrode 14. The thickness of the electrode 12 is not particularly limited, but is preferably smaller than the thickness of the dielectric thin film 13 in consideration of covering properties. Electrode 1
The formation methods of 2 and 14 are produced by a known method such as a sputtering method or an evaporation method.

The dielectric thin film 13 is made of a perovskite-type composite oxide, and the material is not particularly limited. A perovskite-type composite oxide made of Ba, Sr, and Ti is desirable in consideration of environmental issues, as well as excellent dielectric properties and temperature properties as a thin-film capacitor.

In particular, by using a dielectric thin film 13 of a general formula represented by (Ba _x Sr _{1 -x} ) TiO ₃ (0.4 ≦ x ≦ 0.6), It has excellent dielectric characteristics and temperature characteristics, and does not contain Pb, which has been pointed out to affect the environment in recent years, so that the load on the environment is reduced. Here, when the range of x is smaller than 0.4, the dielectric constant tends to decrease, and when it is larger than 0.6, the temperature characteristic tends to deteriorate.

The thickness of the dielectric thin film 13 is not particularly limited, but is desirably 200 nm or less from the viewpoint of miniaturization (high capacity) of the thin film capacitor. The dielectric thin film 13 is formed by a known method such as a PVD method, a CVD method, and a sol-gel method.

In the thin film capacitor of the present invention, the dielectric thin film 13 has columnar crystal grains of two kinds of perovskite-type composite oxides having (111) plane and (110) plane as oriented planes. In addition, the electrode 12 is made of a metal having the (111) plane as an orientation plane, and the crystal phase of some of the electrodes 12 is (1).
(11) The (111) plane of the crystal phase of the dielectric thin film 13 is lattice-matched on the plane, and (1) faces in the in-plane direction of the dielectric thin film 13.
10) The plane is preferentially oriented.

That is, as shown in the conceptual diagram of FIG.
The dielectric thin film 13 has columnar crystal grains of two kinds of perovskite-type composite oxides having the (111) plane and the (110) plane as orientation planes, and the (111) plane of the crystal phase of the electrode 12; The (111) plane of the crystal phase of the dielectric thin film 13 is oriented in the thickness direction, and the (111) plane of the crystal phase of the dielectric thin film 13 is formed on the (111) plane of the crystal phase of some electrodes 12. are doing.

Further, as shown in FIG. 2B, the (110) plane is preferentially oriented in the in-plane direction of the dielectric thin film 13.

In the above-described thin film capacitor, there is a portion where the preferred orientation in the thickness direction of the dielectric thin film 13 and the electrode 12 at least coincide with each other. The crystal growth of the dielectric thin film 13 and the electrode 12 is good by growing the crystal in the same direction reflecting the above. As a result of the crystal growth in the aligned orientation, the dielectric crystal is formed with columnar crystal grains having less lattice defects and excellent crystallinity. That is, the leak current characteristics can be improved more than the crystallinity of the dielectric crystal.

The dielectric thin film 13 has columnar crystal grains of a perovskite-type composite oxide in which at least the preferred orientation in the thickness direction is controlled in the (111) direction,
By forming the columnar crystal grains in which the orientation of the preferential orientation in the thickness direction of the base electrode is matched, the completeness and orientation of the columnar crystal particles are improved.

Further, since the (110) plane is preferentially oriented in the in-plane direction of the dielectric thin film 13, the columnar crystal grains form a structure preferentially oriented in the thickness direction and the in-plane direction. . As a result, it is possible not only to improve the integrity and orientation of the columnar crystal particles forming the dielectric thin film formed on the base electrode, but also to reduce the gap between adjacent columnar crystal particles, Further, the leak current characteristics can be improved.

In the above example, the basic structure of the thin film capacitor of the present invention has been described, but the support substrate 11, the electrodes 12, 14,
Needless to say, in addition to the dielectric thin film 13, an extraction electrode required for extracting the capacitance, a protective film for ensuring reliability, and the like may be provided. In addition, although an example of one layer of the dielectric thin film has been described, the present invention is not limited to this, and it is a matter of course that a laminated structure in which a plurality of dielectric thin films and electrodes are alternately stacked may be used.

[0038]

[Embodiment] 85 SCC of Ar gas on a sapphire R substrate
M, the atmospheric pressure is 6.9 Pa, the substrate temperature is 250
A Pt electrode was formed by sputtering at an output of 200 W while the temperature was maintained at 200C. A dielectric thin film (hereinafter, also referred to as BST) was formed thereon by RF magnetron sputtering using a target having a purity of 4N made of (Ba _0.5 Sr _0.5 ) TiO ₃ . The formation conditions are as follows: Ar gas is 72 SC
After introducing 18 SCCM of CM and O ₂ gas, keeping the atmosphere pressure at 6.9 Pa and the substrate temperature at 600 ° C. for 1 hour,
It was formed at an output of 300 W. Further, under the same conditions as the base electrode, an Au electrode was formed on the upper portion, and a thin film capacitor was formed. The facing electrode area was 1.0 mm ² .

The electrical characteristics of the obtained thin film capacitor were measured. At an applied voltage of 4 V, a capacitance of 32 nF and a leak current density of 1.4 × 10 ⁻⁸ A / cm ² were obtained. The capacity and leak current were measured using an LCR meter (Agilent 4284).
B) and a high resistance meter (4339B manufactured by Agilent) were measured and calculated. After measurement, X
The orientation of the electrode layer and the dielectric thin film was examined by line diffraction. The preferred orientation orientation in the thickness direction of the BST dielectric thin film was the (111) direction and the (110) direction (FIG. 3), and the preferred orientation orientation in a plane perpendicular thereto was the (1-10) direction. (FIG. 4). The Pt electrode also had a preferred orientation orientation in the thickness direction of the (111) direction (FIG. 3), and a preferred orientation orientation in a plane perpendicular thereto was the (110) direction (FIG. 4).
The fracture surface was observed by SEM and TEM, and the thickness of the electrode and the dielectric thin film was measured. As a result, the thickness of the Pt electrode was 50 nm, and the thickness of the BST dielectric was 150 nm.

3 to 6 will be described in detail.

FIG. 3 shows an X-ray diffraction chart of the BST in the thickness direction. The X-ray diffraction of the surface of the thin film is measured using a laboratory focused X-ray diffractometer (CuKa) of a usual concentrated optical system. did. From the X-ray diffraction results, Pt (lower electrode) is preferentially oriented to (111) in the thickness direction, and (110) and (111) are oriented to the BST (dielectric) thin film in the thickness direction. You can see that. Since the lattice constant of BST is close to that of Pt, BST (111) overlaps with Pt (111), making it difficult to see. Further, a diffraction peak was also observed for Au formed as an upper electrode, and Au was observed.
(111) can be confirmed. From the above, it is understood that the BST has a structure oriented in two different directions in the thickness direction.

FIG. 4 shows an X-ray diffraction chart of the BST in the in-plane direction, and this X-ray diffraction chart shows an in-plane X-ray diffraction pattern. The in-plane X-ray diffraction pattern is obtained by irradiating X-rays from a low angle and scanning the detector in a scanning direction on a trajectory on the same plane as the thin film surface. The information obtained is not the information in the thickness direction of the thin film, but the information on the crystal plane spacing perpendicular to the thickness direction.

From FIG. 4, several diffraction peaks can be confirmed in in-plane diffraction. These peaks can be grouped into two structures oriented in the thickness direction. The in-plane diffraction peaks for the structure in which BST (110) is oriented in the thickness direction are BST (001) and BST (1-1).
0), BST (002), and BST (1-12).
On the other hand, the in-plane diffraction peaks for the tissue oriented in the thickness direction at (111) are BST (1-10) and BST (1).
-11) and BST (2-20).

BST (1-10) is considered as a peak contributed from both tissues. As will be described later with reference to FIG. 7,
Since the in-plane orientation cannot be confirmed from the φ scan of the peak of BST (001), the BST (1-10) shown in FIG.
Is considered to have a large contribution from a tissue oriented in the (111) direction in the thickness direction.

FIG. 5 is an X-ray diffraction chart showing the in-plane orientation of Pt, and FIG. 5 is an X-ray diffraction chart showing the in-plane orientation of Pt as the underlying electrode. Pt confirmed in Fig. 4
(2-20) The in-plane orientation was measured by rotating the thin film sample while satisfying the diffraction condition of the peak. Pt
The diffraction peak of (2-20) showed six-fold symmetry. As a result, it was found that Pt was selectively oriented in the (2-20) direction in the plane. Therefore, it was found that the Pt thin film was oriented in two directions of (111) in the thickness direction and (2-20) in the plane.

FIG. 6 is an X-ray diffraction chart showing the in-plane orientation of BST (1-10). FIG. 6 shows the in-plane orientation of BST (1-10) obtained by rotating and scanning the thin film sample while observing the diffraction conditions of the BST (1-10) peak appearing in the in-plane X-ray diffraction of FIG. FIG. From this, BST (1-10) showed six-fold symmetry similarly to the Pt electrode. It was also found that there was a slight angle shift in the orientation from Pt.

As described above, the structure of BST oriented in (111) direction in the thickness direction is (1-1) in the plane.
0), it was found that it was oriented in two directions. BST (111), BST in the thickness direction are placed above the tissue where Pt (111) is preferentially oriented in the thickness direction.
There are two tissues where (110) is preferentially oriented.
Of these two organizations, BST (111) is BS
It is oriented to T (1-10), and the in-plane Pt (2-2)
It is considered to have lattice matching with the orientation of 0).

FIG. 7 is an X-ray diffraction chart showing the in-plane orientation of BST (001). FIG. 7 shows a thin film while satisfying the diffraction condition of the BST (001) peak appearing in the in-plane X-ray diffraction of FIG. It is a diffraction pattern which shows the in-plane orientation of BST (001) obtained by rotating and scanning a sample. No peak could be confirmed in the φ scan of BST (001). From this, BST (00
1) was found to be non-oriented in the plane. This B
ST (001) is a peak originating only from the BST structure oriented in the thickness direction at (110). Therefore, it is considered that this structure has a random orientation in the plane and does not match Pt. Can be

As can be seen from the drawing, of the two types of structures having different BSTs, one (structure having a (111) orientation in the thickness direction) is also oriented in the plane, and has lattice matching with Pt.
On the other hand, the (structure with (110) orientation in the thickness direction) is random in the plane and has no lattice matching with Pt. It is considered that the composite of these tissues reduces the path of the leakage current and improves the leakage current characteristics.

[0050]

According to the thin film element of the present invention, since the orientation of the dielectric thin film in the film plane and the orientation of the base electrode in the film plane at least partially coincide with each other, the lattice matching between the base electrode and the dielectric thin film is performed. As a result, crystal grains of a dielectric material having few lattice defects and excellent crystallinity are formed, and the leakage current characteristics can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thin film capacitor according to the present invention.

FIG. 2 is a conceptual diagram for explaining the orientation of a dielectric thin film and an electrode.

FIG. 3 is a diagram showing an X-ray diffraction chart in a thickness direction of a dielectric thin film.

FIG. 4 is a diagram showing an in-plane X-ray diffraction chart of a dielectric thin film.

FIG. 5 is a view showing an in-plane X-ray diffraction chart of Pt.

FIG. 6 is a diagram showing an in-plane X-ray diffraction chart of BST (1-10).

FIG. 7 is a view showing an in-plane X-ray diffraction chart of BST (001).

[Explanation of symbols]

 11 ... Support substrate 12, 14 ... Electrode 13 ... Dielectric thin film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E001 AB06 AC10 AE01 AE02 AE03 5E082 AB03 BC35 EE23 FG03 FG26 KK01 5F038 AC05 AC15 AC17 AC18 AC19 EZ05 EZ06 EZ20

Claims (5)

[Claims] 1. A thin film element comprising an electrode and a dielectric thin film sequentially formed on a support substrate, wherein the dielectric thin film is formed of (1)
It has columnar crystal grains of two types of perovskite-type composite oxides having an (11) plane and a (110) plane as an orientation plane, and the electrode is made of a metal having an (111) plane as an orientation plane, and a part of the above-mentioned metal is used. The (111) plane of the crystal phase of the dielectric thin film is lattice-matched on the (111) plane of the crystal phase of the electrode, and the (110) plane is preferentially oriented in the in-plane direction of the dielectric thin film. A thin film element characterized by the above-mentioned. 2. The thin film element according to claim 1, wherein the dielectric thin film contains at least Ba, Sr and Ti as metal elements. 3. The thin film device according to claim 1, wherein the electrode is made of Pt. 4. The thin film device according to claim 1, wherein the support substrate is made of sapphire single crystal. 5. A sapphire single crystal support substrate comprising:
Pt electrode, at least Ba, S as metal element
A thin film element formed by sequentially forming a dielectric thin film containing r and Ti, wherein (111)
On the plane, the (111) plane of the crystal phase of the dielectric thin film is lattice-matched, and (110) in the in-plane direction of the dielectric thin film.
A thin film element characterized in that the plane is preferentially oriented.