JP2000256098A - Multilayer thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means to easily obtain a perovskite oxide thin film having the (100) orientation, (001) orientation or (111) orientation. SOLUTION: This multilayer thin film has a buffer layer and a perovskite type oxide thin film grown on the buffer layer. The interface between the buffer layer and the perovskite oxide thin film consists of the 111} facet plane. The 110} plane of the cubic, rhombohedral, tetragonal or orthorhombic crystal of the perovskite oxide thin film, or the 101} plane of the tetragonal or orthorhombic crystal, or the 011} plane of the orthorhombic crystal is present almost parallel to the facet plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laminated thin film having a perovskite oxide thin film.

[0002]

2. Description of the Related Art Electronic devices in which various functional films such as a superconducting film, a dielectric film, a ferroelectric film, and a piezoelectric film are formed and integrated on a Si substrate which is a semiconductor crystal substrate have been devised. For example, in a combination of a semiconductor and a superconductor, SQUI
D, Josephson element, superconducting transistor, electromagnetic wave sensor, superconducting wiring LSI, and the like.
I, a dielectric isolation LSI based on SOI technology, and a combination of a semiconductor and a ferroelectric, such as a nonvolatile memory, an infrared sensor, an optical modulator, an optical switch, and an OEIC.
(Optical and electronic integrated circuits: OPTO-ELECTRONIC INTEGRATED CIR
CUITS). In addition, examples of the element using the piezoelectric film include a surface acoustic wave element, a filter, a VCO, and a resonator.

[0003] In these electronic devices, in order to ensure optimum device characteristics and reproducibility thereof, it is desired that the functional film has good crystallinity. In a polycrystalline material with unaligned orientation, the physical quantity is disturbed by grain boundaries,
It is difficult to obtain good device characteristics.

A typical functional film used for a ferroelectric film or the like is a perovskite oxide thin film. When a perovskite oxide thin film is formed on a Si substrate, for example, Japanese Patent Application Laid-Open No. Hei 9-110592 by the present applicant
It is known that a stabilized zirconia thin film or a rare earth oxide thin film is provided as a buffer layer between a perovskite oxide thin film and a substrate, as disclosed in Japanese Patent Application Laid-Open No. 10-223476 and JP-A-10-223476. For example, Japanese Patent Application Laid-Open
In JP-A-223476, in order to form a perovskite-type oxide thin film having a tetragonal (001) orientation, stress caused by lattice misfit between a buffer layer and a perovskite-type oxide thin film is used. Note that in this specification, that the film has the (001) orientation, for example, means that the (001) plane exists substantially parallel to the film surface.

A perovskite oxide thin film having ferroelectricity generally has a polarization axis in the [001] direction in a tetragonal system and in the [111] direction in a rhombohedral system. Therefore, for example, to exhibit excellent functions as a ferroelectric thin film,
The (001) orientation or the (111) orientation is preferred. However, the perovskite-type oxide thin film tends to have a tetragonal (110) orientation or a tetragonal (101) orientation on the buffer layer, so that the tetragonal (001) plane and the rhombohedral ( It is difficult to form a film in which the (111) plane is oriented. Specifically, BaTiO
₃ is easy to form BaZrO ₃ (110) on zirconia (001), so that it is easy to orient (110). Also, P
bTiO ₃ also tends to be (110) or (101) oriented on zirconia (001). Further, Y ₂ O ₃ (11
1) PbZr _x T on CeO ₂ (111)
The fact that i _1-x O ₃ (PZT) is oriented in the (101) orientation is described in Jpn.
J. Appl. Phys. 37 (Pt. 1, No. 9B) 5145-5149 (1998).

The tetragonal (001) orientation and the rhombohedral (11)
1) In order to obtain a perovskite-type oxide thin film oriented in the direction of the polarization axis such as orientation, it is important to grow the thin film in a direction corresponding to these orientations when growing the thin film. For example, when forming a PbTiO ₃ (001) oriented film, the PbTiO ₃ film is tetragonal at room temperature,
Generally, during growth, the cubic crystal is formed as a high-temperature phase. If the PbTiO ₃ film can be grown as a cubic (100) oriented film, after the growth, the film is transformed into a tetragon during cooling and becomes (00)
1) A single orientation film or a 90 ° domain structure film in which (100) orientation and (001) orientation are mixed. PbTi
Whether the O ₃ film has a (001) single orientation film or a 90 ° domain structure film is determined by a difference in thermal expansion coefficient from the substrate and a difference in lattice constant from the buffer layer.

On the other hand, when a perovskite oxide thin film is used as a base layer of a functional film, for example, when a BaTiO ₃ film is used as a base layer to form a Pt (100) oriented film, the base layer must be (100) oriented. Is important. When a conductive perovskite oxide material such as SrRuO ₃ is formed as an electrode layer and a ferroelectric functional film such as PbTiO ₃ is formed thereon, a (001) oriented functional film is obtained. Therefore, it is important that SrRuO ₃ has a (100) orientation or a (001) orientation. In these cases, the perovskite-type oxide thin film formed as an underlayer or an electrode layer is oriented (100) or (0) during growth.
01) It is important to orient.

Therefore, when forming a perovskite oxide thin film on a Si substrate via a buffer layer,
Depending on the crystal system, the growing perovskite oxide thin film is oriented in (100) orientation, (001) orientation or (111) orientation.
Means that can be easily oriented are desired.

[0009]

The object of the present invention is to provide (1)
An object is to provide a means for easily obtaining a perovskite oxide thin film having a (00) orientation, a (001) orientation, or a (111) orientation.

[0010]

This and other objects are achieved by the present invention which is defined below as (1) to (8). (1) A buffer layer and a perovskite-type oxide thin film grown thereon, wherein the interface between the buffer layer and the perovskite-type oxide thin film is constituted by a {111} facet surface; Substantially parallel to the above, the cubic, rhombohedral, tetragonal or orthorhombic {110} plane, tetragonal or orthorhombic {101} plane, or orthorhombic {011} of the perovskite oxide thin film. ｝
A laminated thin film with a plane. (2) The perovskite oxide thin film is (10)
The laminated thin film according to the above (1), which is an alignment film composed of one or two of 0) orientation, (001) orientation, and (010) orientation. (3) The perovskite oxide thin film is (11)
1) The laminated thin film according to the above (1), which is a single alignment film. (4) The laminated thin film according to any one of (1) to (3), wherein the perovskite-type oxide thin film is mainly composed of lead titanate, lead zirconate or a solid solution thereof. (5) The laminate according to any one of the above (1) to (4), wherein the buffer layer contains a rare earth element oxide, zirconium oxide, or zirconium oxide in which a part of Zr is replaced with a rare earth element or an alkaline earth element. Thin film. (6) When the rare earth element and the alkaline earth element are represented by R, the atomic ratio R / (Zr +
R) is 0.2 to 0.75; (7) An underlayer is provided on the opposite side of the perovskite oxide thin film with the buffer layer interposed therebetween, and the underlayer is an oxide obtained by substituting a part of zirconium oxide or Zr with a rare earth element or an alkaline earth element. When zirconium is contained and the rare earth element and the alkaline earth element are represented by R, the atomic ratio R / (Zr + R) in this underlayer is smaller than the atomic ratio R / (Zr + R) in the buffer layer (5). Laminated thin film. (8) The laminated thin film according to any one of the above (1) to (7), which is present on a substrate whose surface is made of a single crystal of Si (100).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The laminated thin film of the present invention is formed on a substrate made of Si single crystal or the like, has a buffer layer on the substrate side, and has a perovskite oxide thin film in contact with the buffer layer. .

Buffer layer The buffer layer is provided between the perovskite oxide thin film and the substrate.

This buffer layer is characterized by having a {111} facet plane as an interface with the perovskite oxide thin film. FIG. 1A schematically shows the surface of a buffer layer formed on the surface of a Si (100) single crystal substrate. Although the buffer layer shown is made of Y ₂ O ₃ , the illustration of oxygen atoms is omitted. In the present invention, the buffer layer has a cubic (100) orientation and a tetragonal (0
Since the epitaxial film has the (01) orientation or the monoclinic (001) orientation, the illustrated facet plane is a {111} facet plane.

In the laminated thin film of the present invention, the buffer layer has
Almost parallel to the {11} facet plane, a cubic, rhombohedral, tetragonal or orthorhombic {110} plane, a tetragonal or orthorhombic {101} plane of a perovskite oxide thin film,
Alternatively, there is an orthorhombic {011} plane. Perovskite-type oxide thin films, such as PbTiO ₃ , are often cubic during film growth. In that case, it may change to rhombohedral, tetragonal, orthorhombic, etc. after cooling. Also, if there is a misfit or the like of the lattice constant between the buffer layer and, or if this is intentionally provided,
For example, it may grow as a tetragonal crystal and remain as it is after cooling, or may change to another crystal system such as a rhombohedral crystal by cooling.

First, a perovskite oxide thin film is
The case of growing as a cubic crystal on the {111} facet plane will be described. FIG. 1B schematically shows the crystal structure of a perovskite oxide represented by the general formula ABO ₃ . In FIG. 1B, illustration of oxygen atoms is omitted. In FIG. 1B, ABO ₃ is cubic. In the following description, for the sake of simplicity, all of the four faces constituting the facet face are (111)
It is assumed that the perovskite oxide grows such that each (111) plane is parallel to the cubic ABO ₃ (110) plane of the perovskite oxide thin film.

The ABO shown in FIG._Three(110) face
Short side length d_SIs the distance between the lattices of the facet plane shown in FIG.
(111) facet plane and cubic
ABO _ThreeABO so that (110) plane is parallel_Threecrystal
Grows. ABO_ThreeAs the thin film grows, facets
The recess formed by the surface is filled, and finally, FIG.
ABO as shown in (c)_ThreeThe surface of the thin film is almost flat
And this surface is substantially parallel to the substrate surface. this
In the process of growing such a thin film, ABO_ThreeCubic crystal of thin film
The (100) plane shows the Y of the buffer layer at the beginning of growth._TwoO_Three(1
The angle is estimated to be about 9.7 ° with respect to the (00) plane. this
The thing is that it grew on the four faces that make up the facet
Each ABO_ThreeThe same is true for crystals. But this
The tilt is ABO on the facet_ThreeAs the thin film grows
Decrease due to crystal lattice distortion and lattice defects,
In the state shown in FIG._Three(10
0) Surface is Y_TwoO_ThreeSubstantially parallel to the (100) plane, ie, the substrate
It is almost parallel to the surface.

When the ABO ₃ thin film is made of a substance that changes to a tetragon during the cooling process after growth, such as PbTiO ₃ , for example, the cubic (100) plane parallel to the substrate surface is used. All or part of tetragonal (00
1) The surface changes to a film having a tetragonal (001) oriented crystal. On the other hand, depending on the composition of the ABO ₃ thin film, the cubic (100) orientation remains after cooling, or
It may change to a rhombohedral, tetragonal or orthorhombic (100) orientation, or orthorhombic (001) or (010) orientation. Further, the ABO ₃ thin film may be a film having a domain structure due to a film thickness, a difference in thermal expansion coefficient with a substrate, a misfit of a lattice constant with a buffer layer, and the like. For example, a Y ₂ O ₃ buffer layer is formed on a Si (100) substrate, and a thickness of 10
When a 0 nm PbTiO ₃ thin film is formed, a domain structure composed of (100) -oriented crystals and (001) -oriented crystals is formed.

Thus, the {111} facet plane of the buffer layer and the cubic {1} of the perovskite oxide thin film
When the perovskite oxide is grown so that the 10 ° plane, that is, the (110) plane or a plane equivalent thereto, is parallel, the cooled perovskite oxide thin film has the following structure. ing.

First, when the perovskite oxide thin film remains cubic after cooling or becomes rhombohedral after cooling, the {110} plane of the cubic or rhombohedral and the buffer layer The {111} facet faces are substantially parallel to each other, and the perovskite oxide thin film has a (100) orientation.

On the other hand, when the perovskite oxide thin film is tetragonal after cooling, the tetragonal {110}
A plane, that is, a (110) plane or a plane equivalent thereto, or a tetragonal {101} plane, that is, a (101) plane or a plane equivalent thereto is substantially parallel to the {111} facet plane. At this time, the perovskite oxide thin film is considered to have a (100) orientation or a (001) orientation. However, in terms of lattice matching, the perovskite-type oxide thin film generally has a {001} plane substantially parallel to a {111} facet plane and a (001) orientation.

When the perovskite oxide thin film is orthorhombic after cooling, the orthorhombic {110}
Plane, ie, (110) plane or equivalent plane, or orthorhombic {101} plane, ie, (101) plane or equivalent plane, or orthorhombic {011} plane, ie, (011) plane Surface or its equivalent is $ 11
It is almost parallel to the 1｝ facet plane. At this time, the perovskite oxide thin film has (100) orientation, (00
It is considered that 1) orientation or (010) orientation.

Next, a case where the perovskite oxide thin film grows as a tetragonal crystal will be described with reference to the drawings. In this description, the four faces constituting the facet plane are all (111) faces, and the perovskite oxide grows such that this face is parallel to the (101) face of the tetragonal perovskite oxide. It will be described as.
B-axis length (= a-axis length) of tetragonal perovskite oxide,
That is, the short side length d of the tetragonal (101) plane shown in FIG.
_{If S} matches the lattice spacing d of the facet plane, then (1
11) The plane parallel to the facet plane is the tetragonal {101} plane of the perovskite oxide, that is, the (101) plane or a plane equivalent thereto. As a result, the surface of the perovskite oxide thin film is Y It becomes almost parallel to the ₂ O ₃ (100) plane and becomes a tetragonal (001) oriented film.

When the perovskite oxide thin film grows as tetragonal, the tetragonal {110} plane may be almost parallel to the {111} facet plane.

The perovskite-type oxide thin film grown as described above becomes an alignment film composed of one or two of (100), (001) and (010) orientations. That is, each of the films becomes a single alignment film or a domain structure film composed of two kinds of these alignments.

Next, a perovskite-type oxide thin film is (1)
11) The case of forming an alignment film will be described.

In the case where twice (2d) the lattice spacing d of the {111} facet plane in FIG. 1A matches the long side length d _{L of the} cubic ABO ₃ (110) plane shown in FIG. When growing, the plane that is almost parallel to the {111} facet is A
BO ₃ {110} plane. FIG. 1B is similar to FIG. 1B in that the plane substantially parallel to the facet plane is the {110} plane, but in the case of FIG. 3, the lattice shown in FIG. grow up. And ABO ₃ after growth
The (111) plane of the thin film is substantially parallel to the substrate surface. The ABO ₃ thin film thus formed usually shows only a (nnn) peak in X-ray diffraction. Therefore, although it is considered that the crystal has a (111) single orientation, it may have a domain structure. In the case where the ferroelectricity of the perovskite oxide thin film is utilized, if the crystal grows as shown in FIG. 3 and changes to a rhombohedral crystal after the growth, the crystal becomes a rhombohedral (111) orientation and the polarization axis becomes This is preferable because the crystal is oriented in the same direction. In addition, even when the phase changes to tetragonal (111) after growth, the component in the tetragonal [001] direction, which is the polarization axis, can be used, so that the function as a ferroelectric film can be used.

The growing perovskite oxide thin film has (100) orientation, (001) orientation, (010) orientation,
Which of the (111) orientations depends mainly on the misfit of the lattice constant between the perovskite oxide and the buffer layer. For example, PbTiO ₃ tends to be a thin film having a (001) orientation, and PZT tends to be a thin film having a (111) orientation, but a desired crystal orientation can be obtained by selecting a substitution element.

Although the size of the facet surface is not particularly limited, if the height of the facet surface, that is, the size when projected on a plane orthogonal to the plane of the buffer layer, is too small,
The projection size is preferably 5 nm or more because the effect of providing the facet surface on the buffer layer surface is reduced. On the other hand, when the projected dimension is large, the surface of the thin film cannot be made flat unless the perovskite oxide thin film is thickened accordingly. However, if the perovskite oxide thin film is thickened, cracks are likely to occur.
Preferably, the projection size is 30 nm or less. Note that the above projected size is determined from a transmission electron micrograph of the cross section of the buffer layer.

The ratio of the facet plane at the interface is
It is preferably at least 80%, more preferably at least 90%. If the ratio of the facet faces is too low, it becomes difficult to grow a perovskite-type oxide thin film as a high-quality epitaxial film. The facet surface ratio in the present specification is an area ratio determined as follows from a transmission electron micrograph of a cross section of the buffer layer. Assuming that the length of the measurement target area on the buffer layer surface (length in the in-plane direction) is B and the total length of surfaces parallel to the in-plane (other than the facet plane) is H, the above ratio is [1- ( H / B) ² ]. The length B of the measurement target area is 1 μm or more.

In order to form a {111} facet surface on the surface, the buffer layer may be composed mainly of a rare earth element oxide, zirconium oxide, or a part of Zr. It is preferable that zirconium oxide substituted with a class element be the main component. Note that the rare earth elements in this specification include Sc and Y. Such a buffer layer can have a facet plane on its surface when it has a cubic (100) orientation, a tetragonal (001) orientation, or a monoclinic (001) orientation.

Rare earth elements and alkaline earth elements are represented by R
When expressed, the composition of the buffer layer is Zr _1-xR_xO_2-Expressed by δ
be able to. Zirconium oxide with x = 0 (ZrO
_Two) Is cubic → tetragonal → monoclinic from high temperature to room temperature
Phase transition, but rare earth element or alkaline earth element
The cubic crystal is stabilized by the addition of silicon. ZrO_TwoRare earth
Oxides to which elements or alkaline earth elements are added
Called stabilized zirconia. In the present invention, ZrO_Two
It is preferable to use rare earth elements as stabilizing elements.
Good.

In the present invention, _{x in} Zr _{1 -x} R _x O ₂ -δ is not particularly limited as long as a facet surface can be formed.
However, Jpn.J.Appl.Phys.27 (8) L1404-L1405 (1988) shows that rare earth element stabilized zirconia becomes tetragonal or monoclinic in the composition range where x is less than 0.2. And J. Appl. Phys. 58 (6) 2407-24
09 (1985) reports that in a composition region of tetragonal or monoclinic, orientation planes other than those to be obtained are mixed, and a single orientation epitaxial film cannot be obtained. However, as a result of repeated investigations by the present inventors, it has been found that epitaxial growth is possible even with a composition where x is less than 0.2 and good crystallinity can be obtained by using a vapor deposition method described later. A high-purity ZrO ₂ film is preferable when an insulating property is required because the insulation resistance is increased and the leak current is reduced. However, in order to facilitate the formation of the facet surface, x is preferably set to 0.2 or more.

On the other hand, when the buffer layer is in contact with the Si single crystal substrate,
In the case where x is formed in a composition region where x exceeds 0.75,
Although it is tetragonal, it is difficult to obtain a (100) single orientation,
Crystals of (111) orientation may be mixed or
Orientation. Therefore, the Si single crystal substrate
When directly forming a buffer layer on Zr, Zr_1-xR_xO _2-
In δ, x ≦ 0.75 or less, particularly 0.50 or less
Is preferred.

However, by forming a buffer layer on an Si single crystal substrate via an appropriate underlayer, the buffer layer can have a cubic (100) single orientation even when x is large. As such an underlayer, a cubic (10) made of zirconium oxide or stabilized zirconia is used.
0) orientation, tetragonal (001) orientation or monoclinic (00
1) An oriented thin film is preferred. In the base layer, x is set to a smaller value than in the buffer layer.

The rare earth element contained in the stabilized zirconia thin film may be appropriately selected according to the lattice constant of the thin film or the substrate in contact with the stabilized zirconia thin film so that the lattice constant of the stabilized zirconia thin film matches that of the stabilized zirconia thin film. The lattice constant of the stabilized zirconia can be changed by changing x while fixing the type of the rare earth element. However, by changing only x, the matching adjustable region is narrow. However, if the rare earth element is changed, the lattice constant can be changed relatively large, so that the matching can be optimized easily. For example, if Pr is used instead of Y, the lattice constant can be increased.

[0036] Although zirconium oxide containing no oxygen defects is represented by the chemical formula ZrO _2, stabilized zirconia, the type of the added stabilizing element, the amount of oxygen is varied by the amount and valence, Zr _1-x Δ in R _x O ₂₋ δ is 0 to
It is in the range of 1.0, and is usually 0 to 0.5.

The buffer layer may have a gradient composition structure in which the composition changes continuously or stepwise. In the case of a gradient composition structure, it is preferable that _x in Zr _{1 -x} R _x O ₂ -δ increases from the back surface side of the buffer layer to the surface side (metal thin film side). In the case where the above-described base layer is provided, if the base layer is considered to be a part of the buffer layer, it can be said that the composition of the buffer layer changes stepwise.

The rare earth elements used for the buffer layer are Sc,
Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, D
at least one of y, Ho, Er, Tm, Yb and Lu
The species may be selected. However, since rare earth element oxides include those which are likely to have a rare earth a-type structure which is hexagonal, it is preferable to select an element which stably forms a cubic oxide. Specifically, Sc, Y, Ce, Eu, G
At least one of d, Tb, Dy, Ho, Er, Tm, Yb, and Lu is preferable, and it may be appropriately selected from these depending on the lattice constant of the oxide and other conditions.

An additive may be introduced into the buffer layer for improving the characteristics. For example, Al and Si have the effect of improving the resistivity of the film. Further, Mn, Fe, C
Transition metal elements such as o and Ni can form levels (trap levels) due to impurities in the film, and the conductivity can be controlled by using these levels.

It should be noted that Z used as an underlayer or a buffer layer
In the rO ₂ thin film, the upper limit of the ratio of Zr is currently about 99.99 mol%. Further, it is difficult to separate ZrO ₂ and HfO ₂ with the current high-purity technology, so that ZrO ₂
Usually indicates the purity of Zr + Hf. Therefore, the purity of ZrO ₂ in the present specification is a value calculated by regarding Hf and Zr as the same elements,
O ₂ has no problem because it functions in the ZrO ₂ thin film of the present invention in exactly the same manner as ZrO ₂ . This is also true for the above stabilized zirconia.

The thickness of the buffer layer is not particularly limited, and may be appropriately set so as to form a facet surface having an appropriate size, but is preferably 5 to 1000 nm, more preferably 25 to 100 nm. If the buffer layer is too thin, it is difficult to form a uniform facet surface, and if it is too thick, cracks may occur in the buffer layer. The thickness of the underlayer may be appropriately determined so that the underlayer becomes a homogeneous epitaxial film, the surface is flat, and no cracks are generated. However, it is usually preferably 2 to 50 nm.

The material used for the perovskite oxide thin film perovskite oxide thin film is not particularly limited, ferroelectric, etc. piezoelectric, it may be appropriately selected depending on the required function, for example, preferred following materials It is.

BaTiO ₃ ; PbTiO ₃ , rare earth element-containing lead titanate, PZT (lead zircon titanate), PLZ
Pb-based perovskite compounds such as T (lead lanthanum zircon titanate); Bi-based perovskite compounds and the like. Various simple, composite, and layered perovskite compounds as described above.

Of the above perovskite-type materials, BaT
Lead-based perovskite compounds such as iO ₃ and PbTiO ₃ are generally represented by the chemical formula ABO ₃ . Here, A and B each represent a cation. A is Ca, Ba, Sr,
1 selected from Pb, K, Na, Li, La and Cd
B or more is preferably one or more selected from Ti, Zr, Ta and Nb.
In the present invention, among these, those exhibiting functionality such as ferroelectricity at a use temperature may be appropriately selected and used according to the purpose.

The ratio A / B in such a perovskite compound is preferably 0.8 to 1.3, and more preferably 0.9 to 1.2.

By setting A / B in such a range, the insulating properties of the dielectric can be ensured and the crystallinity can be improved, so that the dielectric properties or ferroelectric properties can be improved. can do. In contrast, A / B
If it is less than 0.8, the effect of improving the crystallinity cannot be expected, and if A / B exceeds 1.3, it becomes difficult to form a uniform thin film. Such A / B is realized by controlling the film forming conditions.

[0047] In this specification, but are presented as 3 all ratios x of O in the ABO _x such as PbTiO _3, x is not intended to be limited to three. Since some perovskite materials form a stable perovskite structure with oxygen vacancies or oxygen excess, A
In BO _x , the value of x is generally about 2.7 to 3.3. In addition, A / B can be determined by X-ray fluorescence analysis.

ABO used in the present invention_ThreeType perovskite
The compound is A¹⁺B⁵⁺O_Three, A ²⁺B⁴⁺O_Three, A³⁺B
³⁺O_Three, A_XBO_Three, A (B '_0.67B "_0.33) O_Three, A
(B '_{0.3 Three}B "_0.67) O_Three, A (B_0.5 ⁺³B_0.5 ⁺⁵) O_Three,
A (B_0.5 ²⁺B_0.5 ⁶⁺) O_Three, A (B _0.5 ¹⁺B_0.5 ⁷⁺) O_Three,
A³⁺(B_0.5 ²⁺B_0.5 ⁴⁺) O_Three, A (B_0.25 ¹⁺B_0.75 ⁵⁺)
O_Three, A (B_0.5 ³⁺B_0.5 ⁴⁺) O_2.75, A (B_0.5 ²⁺B_0.5
⁵⁺) O_2.75And so on.

Specifically, Pb-based materials such as PZT and PLZT
Perovskite compound, CaTiO _Three, BaTiO_Three, P
bTiO_Three, KTaO_Three, BiFeO_Three, NaTaO_Three, S
rTiO_Three, CdTiO_Three, KNbO_Three, LiNbO_Three, L
iTaO_Three, And their solid solutions.

The above PZT is PbZrO ₃ -Pb
It is a TiO ₃ -based solid solution. PbTiO ₃ : PbZrO ₃
(Molar ratio) is appropriately determined according to required characteristics. PZ
In general, T tends to be tetragonal on the PbTiO ₃ rich side and tends to be rhombohedral on the PbZrO ₃ rich side. Further, the PLZT is a compound which La is doped PZT, according to the notation of ABO _3, for example, _{(Pb 0.89 ~ 0.91 La 0.1 1} ~ 0.09) (Zr 0.65 Ti
_0.35) represented by the O _3.

In the layered perovskite compound, B
i based layered compounds are generally represented by the formula _{Bi 2 A m-1 B m} O 3m + 3. In the above formula, m is an integer of 1 to 5, A
Is any of Bi, Ca, Sr, Ba, Pb and rare earth elements (including Sc and Y), and B is T
i, Ta, or Nb. Specifically, B
i ₄ Ti ₃ O ₁₂ , SrBi ₂ Ta ₂ O ₉ , SrBi ₂ Nb ₂ O ₉
And the like. In the present invention, any of these compounds may be used, or a solid solution thereof may be used.

The lattice constant of the composite perovskite compound (including the layered perovskite compound) itself is an integral multiple of its unit cell (generally, about 5 times at the maximum). In this specification, the lattice constant of a perovskite-type oxide has a relatively large meaning, but in a composite perovskite-type compound, the lattice constant of its unit cell is important. Also,
For example, in a compound having a pseudo-perovskite structure when thinned like SrRuO ₃ , the lattice constant in the pseudo-perovskite is important, not the lattice constant in the crystal structure in the bulk state.

The perovskite compound preferably used in the present invention is a titanate or a titanate-containing perovskite compound such as BaTiO ₃ , SrTi
O ₃ , PLZT, PZT, CaTiO ₃ , PbTiO ₃ ,
Rare earth element-containing lead titanate and the like, and more preferred are BaTiO ₃ , SrTiO ₃ , PZT, PbTiO ₃ ,
Rare earth element-containing lead titanate is particularly preferable, and PbTiO ₃ , R (R is Pr, Nd, Eu, T
b, Dy, Ho, Yb, Y, Sm, Gd, Er and L
at least one rare earth element selected from a), P
It is a rare earth element-containing lead titanate containing b, Ti and O. In particular, PbTiO ₃ is suitable for a memory in spontaneous polarization, dielectric constant, and Curie point.

In the present invention, the rare earth element-containing lead titanate has an atomic ratio of (Pb + R) /Ti=0.8 to 1.3, Pb / (Pb + R) = 0.5 to 0.99, preferably It is preferable to use a composition having a composition in the range of (Pb + R) /Ti=0.9 to 1.2 and Pb / (Pb + R) = 0.7 to 0.97. Rare earth element-containing lead titanate having this composition is disclosed in Japanese Patent Application No. 8-186.
No. 625. Rare earth elements are P
By adding to bTiO ₃ , Ec can be reduced, and the accompanying decrease in the residual polarization value Pr can be suppressed. In addition, in the above composition, a rare-earth element which hardly causes semiconductor conversion is added, so that a perovskite oxide thin film with less leakage is realized. In addition, the present inventors have found that the type and amount of the rare earth element added affect the fatigue property of polarization reversal. In the above composition, the kind and amount of the rare earth element are optimized, so that a perovskite oxide thin film having excellent repetition characteristics is realized.

R substitutes for Pb located at the A site of the basic perovskite composed of a PbTiO ₃ material to deform the crystal. PbTiO ₃ has an a-axis of 0.3897 n
m, c-axis: 0.4147 nm tetragonal perovskite structure, having a polarization axis in the c-axis direction. This crystal deformation slightly reduces the spontaneous polarization because it reduces the ratio of the a-axis to the c-axis, but the voltage (E
c) can be reduced. On the other hand, a rare earth element other than R, for example, Ce, is substituted with an element located at the B site of PbTiO ₃ , so that the crystal cannot be effectively deformed and spontaneous polarization is extremely reduced, which is not preferable for device application. .

In general, lead titanate is composed of Pb: Ti: O =
In the present invention, the ratio of oxygen varies depending on the type and amount of R to be added.
It is about 3.

In the case of rare earth element-containing lead titanate, T
60% by atom or less of Z is Zr, Nb, Ta, Hf and C
e may be substituted with at least one kind of e.

Although a perovskite oxide having ferroelectricity has been mainly described above, a conductive perovskite oxide can also be used in the present invention. The conductive perovskite oxide thin film can be used, for example, as an electrode layer in an electronic device.

Examples of the conductive perovskite oxide are shown below.

ReO ₃ , WO ₃ , M _x ReO ₃ (where M metal, 0 <x <0.
5), MxWO ₃ (where M = metal, 0 <x <0.5), A ₂ P ₈ W ₃₂ O ₁₁₂ (where A = K, Rb, Tl), Na _x Ta _y W _1-y O ₃ (where 0 ≦ x <1,0 <y
<1), RNbO ₃ (where R: one or more rare earth elements (including Sc and Y)), Na _1-x Sr _x NbO ₃ (where 0 ≦ x ≦ 1), RTiO
₃ (wherein, R: comprising one or more rare earth (Sc and _{Y)), Ca n + 1} Ti n O 3n + 1-y ( where, n = 2,3, ..., y > 0 ), CaVO
₃ , SrVO ₃ , R _1-x Sr _x VO ₃ (where R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦ 1), R _1-x Ba _x VO ₃ (where ,
R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦
1), Sr _{n + 1} V _n O _{3n + 1-y} (where n = 1,2,3 ...., y> 0), Ba _{n + 1}
V _n O _{3n + 1-y} (where n = 1,2,3 ...., y> 0), R ₄ BaCu ₅ O
_{1 3-y} (where R: one or more rare earth elements (including Sc and Y), 0 ≦ y), R ₅ SrCu ₆ O ₁₅ (where R: one or more rare earth elements (including Sc and Y) ), R ₂ SrCu ₂ O _6.2 (where R:
One or more rare earths (including Sc and Y)), R _1-x Sr _x VO
₃ (where R: one or more rare earths (including Sc and Y)), CaCrO ₃ , SrCrO ₃ , RMnO ₃ (where R: one or more rare earths (including Sc and Y)), R _1-x Sr _x MnO ₃ (where
R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦
1), R _1-x Ba _x MnO ₃ (where R: one or more rare earth elements (Sc
And Y), 0 ≦ x ≦ 1), Ca _1-x R _x MnO _3-y (where,
R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦
1,0 ≦ y), CaFeO ₃ , SrFeO ₃ , BaFeO ₃ , SrCoO ₃ , BaCoO ₃ , RCoO
₃ (where R: one or more rare earth elements (including Sc and Y)), R _1-x Sr _x CoO ₃ (where R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦ 1), R _1-x Ba _x CoO ₃ (where
R: one or more rare earth elements (including Sc and Y), 0 ≦ x ≦
1), RNiO ₃ (where R: one or more rare earth elements (Sc and
Y (including Y)), RCuO ₃ (where R: one or more rare earth elements (S
c and Y), RNbO ₃ (where R: one or more rare earths (including Sc and Y)), Nb ₁₂ O ₂₉ , CaRuO ₃ , Ca _1-x R _x Ru
_1-y Mn _y O ₃ (wherein, R: one or more rare earth (Sc and Y
), 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), SrRuO ₃ , Ca _1-x Mg _x RuO ₃ (where 0 ≦ x ≦ 1), Ca _1-x Sr _x RuO ₃ (where , 0 <x <1), Ba
RuO ₃ , Ca _1-x Ba _x RuO ₃ (where 0 <x <1), (Ba, Sr) RuO ₃ , Ba
_1-x K _x RuO ₃ (where 0 <x ≦ 1), (R, Na) RuO ₃ (where
R: one or more rare earths (including Sc and Y)), (R, M) Rh
O ₃ (where R: one or more rare earths (including Sc and Y), M = Ca, Sr, Ba), SrIrO ₃ , BaPbO ₃ , (Ba, Sr) PbO _{3- y} (where 0 ≦ y <1), BaPb _1-x Bi _x O ₃ (where 0 <x ≦ 1), Ba _1-x K _x
BiO ₃ (where 0 <x ≦ 1), Sr (Pb, Sb) O _3-y (where 0 ≦ y <
1), Sr (Pb, Bi) O _3-y (where 0 ≦ y <1), Ba (Pb, Sb) O _3-y (where 0 ≦ y <1), Ba (Pb, Bi ) O _3-y (where 0 ≦ y <1), MMoO
₃ (where M = Ca, Sr, Ba), (Ba, Ca, Sr) TiO _3-x (where 0 ≦
x), etc.

Layered perovskite oxide (including K ₂ NiF ₄ type): R _{n + 1} Ni _n O _{3n + 1} (where R: Ba, Sr, rare earth (Sc
And Y), at least one kind of n = 1 to 5),
R _{n + 1} Cu _n O _{3n + 1} (where, R: at least one of Ba, Sr, rare earth (including Sc and Y), n = 1 to 5), Sr ₂ RuO ₄ , S
r ₂ RhO ₄ , Ba ₂ RuO ₄ , Ba ₂ RhO ₄ , etc.

Among these, RCoO ₃ , RMn
O ₃ , RNiO ₃ , R ₂ CuO ₄ , (R, Sr) CoO ₃ ,
(R, Sr, Ca) RuO ₃ , (R, Sr) RuO ₃ , S
rRuO ₃ , (R, Sr) MnO ₃ (R is Y and Sc
And the related compounds are preferred.

The thickness of the perovskite oxide thin film varies depending on the application, but is preferably from 10 to 500 nm, more preferably from 50 to 150 nm, and preferably as thin as not to impair the crystallinity and surface properties. More specifically, in order to fill the irregularities formed by the facets of the buffer layer, the thickness is preferably 30 nm or more,
When the thickness is 0 nm or more, sufficient surface flatness can be obtained.

The crystallinity and surface properties of the buffer layer, the perovskite oxide thin film, and the underlayer can be evaluated by the half width of the rocking curve of the reflection peak in XRD (X-ray diffraction) and the pattern of the RHEED image. it can. The surface property is RHEED
It can be evaluated by image pattern and transmission electron microscope. In addition, RHEED is reflection high energy electron diffraction (Reflection High Energy Electron Diffraction).

In the buffer layer and the underlayer, the half width of the rocking curve of the reflection on the (200) plane or the (002) plane (the (400) plane in the buffer layer having a rare earth c-type structure) in the X-ray diffraction, and the perovskite In the case of the type oxide thin film, for example, in the case of the (111) orientation, the half width of the rocking curve of the (111) plane reflection is 1.50 ° in each case.
It is preferable to have the following crystallinity.
There is no lower limit of the half width of the rocking curve.
At present, the lower limit is generally about 0.7 °, especially about 0.4 °. Also, R
In HEED, when the image is spot-shaped, the surface has irregularities, and when the image is streak-shaped, the surface is flat. In any case, if the RHEED image is sharp, the crystallinity is excellent.

In the laminated thin film of the present invention, the buffer layer and the underlayer are preferably epitaxial films. First, the epitaxial film in this specification needs to be a single orientation film. In this case, the term “single-oriented film” means that, when measurement is performed by X-ray diffraction, the peak intensity of reflection of an object other than the target surface is 10% or less, preferably 5% or less of the maximum peak intensity of the target surface. Is a film. For example, in the (k00) single orientation film, that is, the a-plane single orientation film, the intensity of the reflection peak other than the (k00) surface in the 2θ-θ X-ray diffraction of the film is 10 times of the maximum peak intensity of the (k00) surface reflection. % Or less, preferably 5% or less. In addition,
In this specification, (k00) is a plane of the (100) series,
That is, the display is a generic name for equivalent planes such as (100) and (200). The second condition of the epitaxial film in the present specification is that when the film plane is the xy plane and the film thickness direction is the z axis, the crystals are aligned in the x axis direction, the y axis direction, and the z axis direction. It is oriented. Such orientation can be confirmed by showing a spot-like or streak-like sharp pattern in RHEED evaluation. For example,
In the case where the crystal orientation is disordered in the buffer layer having unevenness on the surface, the RHEED image does not have a sharp spot shape but tends to extend in a ring shape. If the above two conditions are satisfied, it can be said that the film is an epitaxial film.

In the present invention, the perovskite oxide thin film can be an epitaxial film.

Substrate The substrate used in the present invention can be selected from various single crystals such as Si, MgO and SrTiO _3.
0) Substrates having a single crystal surface are most preferred.

Manufacturing Method The method for forming the buffer layer, the perovskite oxide thin film, and the underlayer is not particularly limited, and may be appropriately selected from methods capable of forming these as an epitaxial film on a substrate, especially on a Si single crystal substrate. It is preferable, but it is preferable to use an evaporation method, particularly, an evaporation method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-223476.

Hereinafter, the formation of a buffer layer made of stabilized zirconia will be described as a specific example of the manufacturing method.

In carrying out this manufacturing method, it is desirable to use a vapor deposition apparatus 1 having a configuration as shown in FIG. 11, for example.

The vapor deposition apparatus 1 has a vacuum chamber 1a provided with a vacuum pump P, and a holder 3 for holding a substrate 2 is arranged in a lower portion of the vacuum chamber 1a. The holder 3 is connected to a motor 5 via a rotating shaft 4.
The substrate 2 is rotated by the motor 5 so that the substrate 2 can be rotated in the plane. The above holder 3
Has a built-in heater 6 for heating the substrate 2.

The vapor deposition device 1 includes an oxidizing gas supply device 7, and a nozzle 8 of the oxidizing gas supply device 7 is disposed immediately below the holder 3. Thus, the partial pressure of the oxidizing gas is increased near the substrate 2. Below the holder 3, a Zr evaporator 9 and a rare earth element evaporator 10 are arranged.
In each of these evaporation units, an energy supply device (an electron beam generator, a resistance heating device, etc.) for supplying energy for evaporation is arranged in addition to the respective evaporation sources.

First, a substrate is set on the holder. In this manufacturing method, a homogeneous thin film is formed on a large area substrate, for example, 10
It can be formed over a substrate having an area of ² cm ² or more.
Thereby, the electronic device having the laminated thin film of the present invention can be made extremely inexpensive as compared with the related art. There is no particular upper limit on the area of the substrate.
It is about 00 cm ² . The current semiconductor process mainly uses a 2 to 8 inch Si wafer, particularly a 6 inch type wafer, but this method can cope with this. Further, it is also possible to form a laminated thin film by selectively using a mask or the like instead of the entire surface of the wafer.

When a Si single crystal substrate is used, it is preferable to perform a surface treatment on the substrate before forming the buffer layer. For the surface treatment of the substrate, it is preferable to use a processing method described in, for example, JP-A-9-110592 or Japanese Patent Application No. 9-106776 filed by the present applicant.

After such a surface treatment, the Si crystal on the substrate surface is covered with the Si oxide layer and protected. Then, the Si oxide layer is reduced and removed by a metal such as Zr supplied to the substrate surface when the buffer layer is formed.

Next, the buffer layer is formed by heating the substrate in a vacuum and supplying Zr and rare earth elements and an oxidizing gas to the substrate surface. The heating temperature may be appropriately set so that good crystallinity is obtained and a facet surface is formed. Specifically, the temperature is preferably 400 ° C. or higher for crystallization, and if it is 750 ° C. or higher, a film having excellent crystallinity can be obtained. Also, the dimensions of the facet surface can be controlled by the heating temperature. Although the upper limit of the heating temperature varies depending on the heat resistance of the substrate, it is usually 13
It is about 00 ° C. As the oxidizing gas used here,
Any of oxygen, ozone, atomic oxygen, NO ₂ , radical oxygen and the like may be used, but in the following description, oxygen will be exemplified.

In forming the buffer layer, oxygen gas is continuously supplied into the vacuum evaporation tank while the inside of the vacuum chamber is continuously exhausted by a vacuum pump. The oxygen partial pressure in the vicinity of the substrate is preferably about 10 ^-3 to 10 ^-1 Torr. The upper limit of the oxygen partial pressure is set to 10 ^-1 Torr in order to keep the metal in the evaporation source in the vacuum chamber from deteriorating and keep the evaporation rate constant. When introducing an oxygen gas into the vacuum deposition tank, it is preferable to inject the gas from the vicinity of the substrate surface and create an atmosphere with a high oxygen partial pressure only in the vicinity of the substrate. The reaction can be further accelerated. At this time, since the inside of the vacuum chamber is continuously evacuated, most of the vacuum chamber is 1
The pressure is as low as 0 ^-4 to 10 ^-6 Torr. The supply amount of oxygen gas is preferably 2 to 50 cc / min, more preferably 5 to 25 cc / min. By controlling the supply amount of oxygen gas, the facet surface can be easily formed, and the dimension of the facet surface can be changed. Since the optimal supply amount of oxygen gas is determined by the volume of the vacuum chamber, the pumping speed of the pump, and other factors, an appropriate supply amount is determined in advance.

Each evaporation source is heated and evaporated by an electron beam or the like and supplied to the substrate. In order to form a uniform thin film having a facet surface, the deposition rate is 0.05 to 1.
It is preferably set to 00 nm / s, particularly 0.100 to 0.500 nm / s. By controlling the film forming rate, the facet surface can be easily formed, and the dimension of the facet surface can be changed.

When the film formation area is about 10 cm ² or more,
For example, when forming a film on the surface of a substrate having a diameter of 2 inches,
By rotating the substrate as shown in FIG. 11 and uniformly supplying oxygen gas to the entire surface of the substrate, the oxidation reaction can be promoted throughout the film formation region. As a result, a uniform film having a large area can be formed. At this time,
The rotation speed of the substrate is desirably 10 rpm or more. When the number of rotations is low, the distribution of the film thickness easily occurs in the substrate surface. Although there is no particular upper limit on the number of rotations of the substrate, it is usually about 120 rpm due to the mechanism of the vacuum apparatus.

A thin film made of a rare earth element oxide or a thin film made of zirconium oxide may be formed according to the above-mentioned stabilized zirconia thin film. Further, for example, when forming a rare earth element oxide thin film on a zirconium oxide thin film, when the same rare earth element is used in both thin films, when the zirconium oxide thin film is formed to a predetermined thickness, Zr By stopping the supply and continuously supplying only the rare earth element, both thin films can be formed continuously. In the case where the buffer layer has a gradient composition structure, the supply amount of Zr may be gradually reduced and finally set to zero, and the process may be shifted to the formation of a rare earth element oxide thin film.

The above-described manufacturing method includes a conventional vacuum evaporation method,
As can be clearly seen in comparison with the sputtering method, laser ablation method, etc., it is possible to carry out under the operating conditions where there is no room for impurities and easy to control, so that the target object with high reproducibility and high perfection can be obtained. It is suitable for obtaining.

Note that even when an MBE apparatus is used in this method, a target thin film can be obtained in exactly the same manner.

In forming the perovskite oxide thin film, it is preferable to set the substrate temperature at the time of vapor deposition to 500 to 750 ° C. If the substrate temperature is too low, it is difficult to obtain a film having high crystallinity, and if the substrate temperature is too high, a composition shift due to re-evaporation is likely to occur, and unevenness on the surface of the film tends to increase.
Note that re-evaporation of the raw material can be reduced by introducing a small amount of oxygen radicals into the vacuum chamber at the time of vapor deposition. Specifically, for example, in a PbTiO ₃ thin film, there is an effect of suppressing re-evaporation of Pb or PbO.

In the present invention, the flatness of the surface of the perovskite oxide thin film is generally good, but a sufficient flatness may not be obtained depending on the thickness of the thin film or the method of forming the thin film.
In such a case, the surface of the thin film can be polished and flattened. For polishing, chemical polishing using an alkaline solution or the like, mechanical polishing using colloidal silica or the like, a combination of chemical polishing and mechanical polishing may be used. In addition,
When the surface of the laminated thin film is polished, polishing distortion may remain. When polishing distortion needs to be removed, it is preferable to anneal the laminated thin film. Annealing is preferably 3
At 00-850 ° C, more preferably at 400-750 ° C,
Preferably 1 second to 30 minutes, more preferably 5 to 15 minutes
Do for a minute.

[0086] In applications present invention of a multilayer film, a functional film of high performance on a Si substrate can be formed. Therefore, the laminated thin film of the present invention is suitable for the various electronic devices described above.

When a perovskite oxide thin film is used as an electrode layer when applied to an electronic device, various functional films are usually formed thereon. When a perovskite-type oxide thin film is used as various functional films, an electrode layer is usually formed thereon. As the metal constituting the electrode layer formed on the perovskite oxide thin film, a metal simple substance or an alloy containing at least one of Au, Pt, Ir, Os, Re, Pd, Rh and Ru is preferable.

[0088]

EXAMPLE 1 A ZrO ₂ thin film and Y ₂ O ₃ were formed on a Si (100) single crystal substrate.
A laminated thin film in which a thin film and a PbTiO ₃ thin film were laminated in this order was formed by the following procedure.

First, an Si single crystal wafer (2 inches in diameter, polished and mirror-polished so that the surface becomes the (100) plane)
(250 μm thick disk). This wafer surface was cleaned by etching with a 40% aqueous ammonium fluoride solution.

Next, using the vapor deposition apparatus 1 shown in FIG. 11, the single crystal substrate 2 is fixed to a substrate holder 3 provided with a rotation and heating mechanism installed in a vacuum chamber 1a.
After evacuating to ^-6 Torr by an oil diffusion pump, the substrate is rotated at 20 rpm to protect the substrate cleaning surface with Si oxide while oxygen is introduced into the vicinity of the substrate from the nozzle 8 at a rate of 10 cc / min. , Heated to 600 ° C. As a result, the substrate surface was thermally oxidized, and a Si oxide film having a thickness of about 1 nm was formed on the substrate surface.

Next, the substrate was heated to 900 ° C. and rotated. The rotation speed was 20 rpm. At this time, oxygen gas was introduced from the nozzle at a rate of 10 cc / min.
r was evaporated from the evaporation source and supplied to the surface of the substrate to reduce the Si oxide formed in the previous step and to form a thin film.
The supply amount of the metal Zr was set to 10 nm in terms of the film thickness of ZrO ₂ . This thin film shows ZrO _{2 in} X-ray diffraction.
(002) peak was clearly observed, and it was confirmed that the film was a (001) single-oriented, highly crystalline ZrO ₂ thin film. Furthermore, the ZrO ₂ thin film, as shown in FIG. 4, R
HEED showed a complete streak pattern, and it was confirmed that the surface was flat at the molecular level and was a highly crystalline epitaxial film.

Next, the single crystal substrate on which the ZrO ₂ thin film was formed was used as a substrate, the substrate temperature was 900 ° C., and the substrate rotation speed was 20 rp
By supplying metal Y to the substrate surface under the conditions of m and an oxygen gas introduction rate of 10 cc / min, a Y ₂ O ₃ thin film was formed. The supply amount of the metal Y was set to 40 nm in terms of Y ₂ O ₃ . The RHEED image of this Y ₂ O ₃ thin film was a sharp spot as shown in FIG. From this, this Y ₂
The O ₃ thin film is an epitaxial film having good crystallinity,
In addition, it can be seen that the surface has irregularities. This Y ₂ O ₃
Observation of the cross section of the thin film with a transmission electron microscope revealed that a facet face having a height of 10 nm was present, and the ratio of the facet face was 95% or more.

Next, Pb having a thickness of 300 nm is formed on the Y ₂ O ₃ thin film.
A TiO ₃ thin film was formed. The substrate temperature was 600 ° C., and the substrate rotation speed was 20 rpm. During the film formation, radical oxygen was supplied at a flow rate of 10 sccm to suppress the re-evaporation of Pb. The RHEED image of this PbTiO ₃ thin film was in a sharp streak shape as shown in FIG. This indicates that the PbTiO ₃ thin film has good crystallinity and a flat surface at the molecular level.

The thus obtained PbTiO ₃ / Y ₂ O ₃ / ZrO ₂
FIG. 7 shows an X-ray diffraction chart of the / Si (100) laminated structure. FIG. 7 shows only a peak of a plane equivalent to PbTiO ₃ (001) and a peak of a plane equivalent to PbTiO ₃ (100). Since PbTiO ₃ is tetragonal at room temperature, it can be seen that PbTiO ₃ is a tetragonal domain structure film composed of (001) -oriented crystals and (100) -oriented crystals. Observation of this PbTiO ₃ thin film with a transmission electron microscope confirmed that it had a domain structure. Since PbTiO ₃ during growth is cubic, it can be seen that a cubic (100) oriented film was formed during growth.

Example 2 A ZrO ₂ thin film and a Y ₂ O ₃ thin film were formed on a Si (100) single crystal substrate in the same manner as in Example 1, and a Pb
A PZT thin film represented by (Zr _0.25 Ti _0.75 ) O ₃ was formed by an evaporation method. The substrate temperature was 600 ° C., and the substrate rotation speed was 20 rpm. During the film formation, radical oxygen was supplied at a flow rate of 10 sccm to suppress the re-evaporation of Pb.

The thus obtained PZT / Y ₂ O ₃ / ZrO ₂ / Si
FIG. 8 shows an X-ray diffraction chart of the (100) laminated structure.
In FIG. 8, only the peak of the plane equivalent to PZT (111) is recognized. The half width of the rocking curve of PZT (111) reflection was 1.29 °, and it was confirmed that the orientation was excellent.

Example 3 A stabilized zirconia / Si (100) laminated structure was produced in the same manner as in Example 1 except that a stabilized zirconia thin film was formed in place of the ZrO ₂ thin film and the Y ₂ O ₃ thin film. The composition of the stabilized zirconia thin film was Zr _0.7 Y _0.3 O ₂ -δ, and the substrate temperature, substrate rotation speed and oxygen introduction amount when forming the stabilized zirconia thin film were the same as those when forming the ZrO ₂ thin film in Example 1. I assumed the same.

The RHEED image of the stabilized zirconia thin film had a sharp spot shape as shown in FIG. This indicates that the stabilized zirconia thin film is an epitaxial film having good crystallinity and has irregularities on the surface. FIG. 10 shows a transmission electron micrograph of the cross section of the stabilized zirconia thin film. In FIG. 10, the right side is the Si single crystal substrate side. It can be seen that the interface between the buffer layer and the metal thin film has almost no plane parallel to the substrate surface (vertical plane in the figure), and most of the interface is composed of facet planes. The facet surface ratio of the stabilized zirconia thin film was 90% or more.

When a perovskite-type oxide thin film was formed on the stabilized zirconia thin film in the same manner as in each of the above examples, a thin film having good crystallinity was formed in the same manner as in each of the above examples.

[0100]

When a facet surface is present on the buffer layer surface and a perovskite oxide thin film is formed on the facet surface, the thin film is cubic or tetragonal (100) oriented, tetragonal (001). ) Orientation, or cubic or rhombohedral (111) orientation, has not been reported before, and was found for the first time in the present invention. As described above, it has been known that a ZrO ₂ thin film or a rare earth oxide thin film is used as a buffer layer. However, when a perovskite oxide thin film is directly formed on a flat buffer layer, the (110) orientation And (1
01) It is easy to be oriented. In the present invention, utilizing this, the perovskite type oxide is converted into its (110) plane or (1) plane.
By growing the crystal so that the (01) plane is parallel to the facet plane, a perovskite oxide thin film having (100), (001) or (111) orientation and having good crystallinity can be easily formed. Make it possible. In the present invention, the (100) orientation, the (001) orientation, and the (111) orientation are selected in each crystal system by selecting a lattice constant in the buffer layer and the perovskite oxide thin film.
Any orientation selected from the orientations can be taken.

By using the perovskite-type oxide thin film of the present invention as a functional film such as a ferroelectric, a piezoelectric, or a superconductor, a nonvolatile memory, an infrared sensor, an optical modulator, an optical switch, an OEIC, and a SAW element can be obtained. , VCO, convolver, collimator, memory element, image scanner, thin film bulk resonator, filter, SQUID, Josephson element, superconducting transistor, electromagnetic wave sensor, superconducting wiring LSI, etc.

[Brief description of the drawings]

FIG. 1A is a schematic diagram of a {111} facet surface of a buffer layer surface, and FIG. 1B is an ABO that becomes a cubic (100) orientation film by growing on a {111} facet surface. _It is a schematic diagram showing a type ₃ perovskite crystal, and (c) is a schematic diagram showing a state in which an ABO ₃ thin film is formed on the facet surface of (a).

FIG. 2 is a schematic diagram showing an ABO ₃ type perovskite crystal which becomes a tetragonal (001) orientation film by growing on a {111} facet plane.

FIG. 3 is a schematic diagram showing an ABO ₃ type perovskite crystal that grows on a {111} facet plane and becomes a (111) orientation film.

FIG. 4 is a drawing-substituting photograph showing a crystal structure, which is composed of Si single crystal.
ZrO formed on crystal substrate _TwoIn the RHEED image of the thin film
is there.

FIG. 5 is a drawing substitute photograph showing a crystal structure, and FIG. 4 shows a RHEED image of Y ₂ O ₃ formed on a ZrO ₂ thin film.
It is a RHEED image of a thin film.

FIG. 6 is a drawing substitute photograph showing a crystal structure, and FIG. 5 shows a RHEED image of PbTi formed on a Y ₂ O ₃ thin film.
It is a RHEED image of an O ₃ thin film.

FIG. 7 is an X-ray diffraction chart of a PbTiO ₃ / Y ₂ O ₃ / ZrO ₂ / Si (100) laminated structure.

FIG. 8 is an X-ray diffraction chart of a PZT / Y ₂ O ₃ / ZrO ₂ / Si (100) laminated structure.

FIG. 9 is a drawing-substituting photograph showing a crystal structure, showing RHE of a stabilized zirconia thin film formed on a Si single crystal substrate.
It is an ED image.

FIG. 10 is a drawing substitute photograph showing a crystal structure, wherein Si is
3 is a transmission electron micrograph of a cross section of a stabilized zirconia thin film formed on a single crystal substrate.

FIG. 11 is an explanatory view showing an example of a vapor deposition apparatus used for forming a laminated thin film of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Evaporation apparatus 1a Vacuum tank 2 Substrate 3 Holder 4 Rotating shaft 5 Motor 6 Heater 7 Oxidizing gas supply device 8 Nozzle 9 Zr evaporation part 10 Rare earth element evaporation part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/8242 H01L 39/02 ZAAB 5F083 21/8247 ZAAD 29/788 27/10 651 29/792 29/78 371 37/02 27/14 K 39/02 ZAA // H01L 27/14 F-term (reference) 4G077 AA03 AA07 BB10 BC41 BC43 BC60 DA02 EC09 ED05 ED06 EF02 EF04 HA05 HA11 HA12 SA04 4M114 AA29 BB05 CC09 4M118 AB01 CA16FCB12 FC18 AA17 5F058 BA20 BD01 BD05 BD18 BF12 BF17 BF20 BJ01 5F083 FR05 GA27 GA30 JA02 JA12 JA13 JA14 JA15 JA17 JA43 JA44 JA45 PR05 PR22

Claims (8)

[Claims] A buffer layer and a perovskite-type oxide thin film grown on the buffer layer, wherein an interface between the buffer layer and the perovskite-type oxide thin film is constituted by a {111} facet plane; Substantially parallel to the facet plane, the cubic, rhombohedral, tetragonal or orthorhombic {110} plane, tetragonal or orthorhombic {101} plane, or orthorhombic of the perovskite oxide thin film $ 01
Stacked thin film with 1｝ plane. 2. The method according to claim 1, wherein the perovskite oxide thin film is
The laminated thin film according to claim 1, which is an alignment film composed of one or two of (100) orientation, (001) orientation, and (010) orientation. 3. The thin film of perovskite oxide,
2. The laminated thin film according to claim 1, which is a (111) single-oriented film. 4. The laminated thin film according to claim 1, wherein said perovskite-type oxide thin film mainly contains lead titanate, lead zirconate or a solid solution thereof. 5. The method according to claim 1, wherein the buffer layer comprises a rare earth element oxide,
The laminated thin film according to any one of claims 1 to 4, comprising zirconium oxide or zirconium oxide in which a part of Zr is substituted with a rare earth element or an alkaline earth element. 6. A rare earth element and an alkaline earth element represented by R
In the buffer layer, the atomic ratio R / (Z
The laminated thin film according to claim 5, wherein (r + R) is 0.2 to 0.75. 7. An underlayer on the opposite side of the perovskite oxide thin film with the buffer layer interposed therebetween, wherein the underlayer replaces part of zirconium oxide or Zr with a rare earth element or an alkaline earth element. Containing zirconium oxide and the rare earth element and the alkaline earth element are represented by R, the atomic ratio R / (Zr + R) in this underlayer
Is smaller than the atomic ratio R / (Zr + R) in the buffer layer. 8. The laminated thin film according to claim 1, wherein the surface is present on a substrate composed of a single crystal of Si (100).