JP2001354497A - Method for producing ferroelectric film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a ferroelectric film in such a manner that the anisotropic axis of the ferroelectric film is arranged properly in one direction parallel to the upper surface of the film. SOLUTION: The ferroelectric film 12 having a Curie temperature higher than the room temperature is deposited on the main surface of a substrate 11. Then, striped upper periodical structure bodies 13, each of which has been formed from an upper stress controlling material and has a length sufficiently long in comparison with a division period 13a in the y-axis direction, are formed on the ferroelectric film 12 in such a manner that upper periodical structure bodies 13 are arranged in nearly parallel with the x-axis direction at the division period 13a so that an interval is provided between the adjacent upper periodical structure bodies. Thereafter, the ferroelectric film 12 is crystallized at a temperature higher than the Curie temperature and gradually cooled to the room temperature. As the coefficient of thermal expansion of the upper periodical structure bodies 13 is larger than that of the substrate 11, the c-axis of the ferroelectric film 12 comprising a crystal body which is converted into the tetragonal crystal system at a temperature of not more than the Curie temperature is arranged properly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a ferroelectric film used for a semiconductor integrated circuit or an electronic component.

[0002]

2. Description of the Related Art A ferroelectric crystal has not only a ferroelectric property typified by a non-linear polarization phenomenon which can be inverted by an electric field direction, but also a ferroelectric crystal.
Since it has properties such as piezoelectric characteristics, pyroelectric characteristics, and electro-optical characteristics, it is applied to various electronic devices in the field of semiconductor integrated circuits and electronic components. 2. Description of the Related Art In recent years, nonvolatile memory elements have attracted attention as new electronic devices that actively utilize ferroelectricity. In addition, surface acoustic wave filters and microactuators using piezoelectric characteristics, infrared sensors using pyroelectric characteristics or waveguide type optical modulators using electro-optical characteristics, and optical shutter arrays for printer heads have been developed. ing. Examples of the ferroelectric material include barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), and bismuth strontium tantalate (SrBi ₂ T).
a ₂ O ₉₎ perovskite oxide and the oxide solid solution as a main component thereof are known, such as, application range is wide.

When a ferroelectric crystal is applied to a device, it is often preferable to use it as a thin film or a thick film rather than a bulk single crystal or bulk ceramic. This is because the thin film shape or the thick film shape is more advantageous in terms of mass productivity, device miniaturization and high integration, low voltage or low cost, and the like. Therefore, development of a film forming technique for forming a ferroelectric substance in the form of a thin film or a thick film is of particular importance. The currently developed ferroelectric film forming technologies include a sol-gel method, a metal organic material pyrolysis method (MOD method), a sputtering method, an organic metal material chemical vapor deposition method (MOCVD method), and a solution material vaporization chemistry. Deposition (LSMCD) or pulsed laser deposition (PLD)
Method).

Generally, a ferroelectric crystal has a characteristic temperature called a Curie temperature which is inherent to a material, and belongs to a paraelectric phase at a temperature higher than the Curie temperature, and belongs to a ferroelectric phase at a temperature lower than the Curie temperature. This is because the thermodynamic stability of the crystal depends on the temperature, and the crystal structure changes (phase transition) around the Curie temperature. For example, at a temperature higher than the Curie temperature, a crystal structure having a central symmetry such as a cubic crystal becomes stable and the ferroelectricity disappears, but at a temperature lower than the Curie temperature, a crystal having no central symmetry such as a tetragonal crystal The structure becomes stable and develops ferroelectricity. In a crystal in a ferroelectric phase, there is a crystal axis orientation exhibiting spontaneous polarization that can be inverted depending on the direction of an electric field and does not disappear even when the electric field is set to 0 (hereinafter referred to as a spontaneous polarization axis). The orientation of the spontaneous polarization axis is related to the aforementioned symmetry of the crystal structure. For example, in the case of a tetragonal ferroelectric such as BaTiO ₃ or PbTiO ₃ , the spontaneous polarization axis coincides with the c-axis of the crystal. On the other hand, most ferroelectrics having a bismuth layer structure such as SrBi ₂ Ta ₂ O ₉ have a direction in which the spontaneous polarization axis is substantially orthogonal to the c-axis.

In view of the above-described properties of ferroelectric crystals, attempts are being actively made to align crystal axes to align spontaneous polarization axes in one direction. If the spontaneous polarization axis is aligned in one direction,
In the direction parallel to this, polarization can be inverted by a small threshold electric field, that is, a coercive electric field, and there is an effect that a large remanent polarization can be obtained even if the electric field is removed. Further, since the dielectric constant, the piezoelectric constant, the pyroelectric coefficient, the electro-optic constant, and the like also have anisotropy with respect to the spontaneous polarization axis, excellent characteristics can be realized as compared with the case where the crystal axis directions are arranged randomly.

[0006] Such a technique for precisely controlling the structure of a ferroelectric crystal has become more realistic in combination with the above-described film forming technique. Normally, a ferroelectric crystal film is homogeneous in a plane parallel to the substrate surface, and grows in a direction perpendicular to the substrate surface, that is, in a film thickness direction, so that the ferroelectric crystal film is anisotropic in a direction normal to the substrate surface. It is possible to form an oriented film in which the crystal axes showing the properties are aligned.
For example, according to a method for manufacturing a ferroelectric thin film structure disclosed in Japanese Patent No. 2834355, an oxide thin film having a NaCl type crystal structure is uniformly formed on a substrate by a plasma-excited MOCVD method. PbZr _x T
By forming a thin film made of i _1-x O ₃ by sputtering, the c-axis, which is the spontaneous polarization axis of PbZr _x Ti _1-x O ₃ , is oriented at a high orientation rate in a direction perpendicular to the substrate surface. A method is disclosed. Using such a method, a ferroelectric nonvolatile memory element having a large memory polarization using a thin film made of cb-axis oriented PbZr _x Ti _1-x O ₃ as a capacitive insulating film, or a c-axis oriented Pb _x La _{1 An} infrared sensor using a thin film made of -xTiO ₃ and having high pyroelectric current detection performance has been developed.

[0007]

As described above,
As a conventional method of manufacturing a ferroelectric film, a method of aligning an anisotropic axis of a crystal in a direction perpendicular to a substrate surface is known. However, some functional devices using ferroelectric crystals exhibit more excellent characteristics when the anisotropic axes of the crystals are aligned in a direction parallel to the substrate surface.

For example, tetragonal ferroelectricity (Pb, L
a) Consider a planar-type optical switch element utilizing the primary electro-optic effect (Pockels effect) of (Zr, Ti) O ₃ (hereinafter abbreviated as PLZT). In this planar optical switch element, a PLZT film is formed on a transparent substrate, the traveling direction of light is the normal direction of the substrate surface, and the polarization plane of the electric field and light is in a plane parallel to the substrate surface. In this case, PLZ
Although the c-axis, which is the anisotropic axis of the crystal of the T film, coincides with the optical axis, since it is oriented in the normal direction of the substrate surface, birefringence due to an electric field does not occur, so that it does not function as an optical switch. Therefore, if the c-axis, which is the optical axis, can be oriented in a direction parallel to the substrate surface, birefringence due to an electric field can be efficiently induced in the plane of polarization of light, so that an excellent optical switch operation can be realized. .

In the case of a non-volatile memory device having a parallel plate capacitor using a bismuth layered structure ferroelectric, the spontaneous polarization axis is oriented substantially perpendicular to the c-axis when the c-axis alignment film is formed. As a result, the amount of polarization that can be reversed becomes extremely small. On the other hand, if the c-axis can be controlled so as to be aligned in a direction parallel to the substrate surface, the amount of polarization following the electric field increases, so that a highly reliable memory element can be obtained.

It is an object of the present invention to form a ferroelectric film so that an anisotropic axis of the ferroelectric film is aligned in one direction parallel to an upper surface of the ferroelectric film.

[0011]

In order to achieve the above object, the present invention provides a method for crystallizing a ferroelectric film on a substrate at a temperature higher than the Curie temperature, and then reducing the temperature of the ferroelectric to room temperature. When the temperature is decreased to a different value, different stresses are applied to the ferroelectric material in one direction parallel to the substrate surface and another direction parallel to the substrate surface and intersecting the one direction in the ferroelectric material. Thus, the c-axis of the ferroelectric film is aligned in a direction parallel to the substrate surface.

More specifically, a method of manufacturing a ferroelectric film according to the present invention includes a first step of forming a ferroelectric film having a Curie temperature higher than room temperature on a substrate; A second step of crystallizing the ferroelectric film by raising the temperature to a temperature higher than the Curie temperature, and a step of moving the substrate in a direction parallel to the substrate surface of the crystallized ferroelectric film with respect to the ferroelectric film. A third step of lowering the substrate temperature to room temperature while applying a tensile stress greater than the other direction parallel to the plane and intersecting the one direction, or applying a compressive stress greater than the one direction in the other direction. Steps.

According to the method of manufacturing a ferroelectric film of the present invention,
If the substrate temperature becomes equal to or lower than the Curie temperature during the temperature drop in the third step, the crystal isotropically deforms and tries to be distorted. In the third step, however, the in-plane parallel to the interface between the substrate and the ferroelectric film is formed. By applying a stress in two directions crossing each other in one direction while applying a tensile stress in one direction higher than the other direction, or applying a compressive stress in the other direction larger than one direction. Anisotropy of the strain is induced by the mechanical action, and the anisotropic axis can be oriented in one direction in the substrate plane. This is a method utilizing the property that the ferroelectric crystal relaxes the energy of the strain and approaches the state where the internal strain energy is minimized.

In the method for producing a ferroelectric film according to the present invention,
In the first step, the upper stress control material is deposited on the ferroelectric film, and the deposited upper stress control material is divided substantially in parallel so as to be spaced at a predetermined period in one direction. Forming a stripe-shaped upper periodic structure having a length sufficiently larger than a predetermined period in the other direction from the upper stress control material, wherein the coefficient of thermal expansion of the upper stress control material is It is preferably larger than the coefficient of thermal expansion. In this way, when the upper periodic structure has a larger coefficient of thermal expansion than the ferroelectric film, the upper periodic structure is divided in one direction and has a stripe shape continuous in the other direction. Therefore, a large compressive stress is selectively applied to the other direction of the ferroelectric film when the temperature is lowered. on the other hand,
When the substrate has a smaller coefficient of thermal expansion than the ferroelectric film, the stress mainly due to the difference in the coefficient of thermal expansion between the substrate and the ferroelectric film is applied in one direction of the ferroelectric film. When the temperature is lowered, a large tensile stress is selectively applied to one direction of the ferroelectric film.

In this case, the first step includes a step of forming a lower buffer layer made of a lower stress control material over the entire surface of the substrate before forming the ferroelectric film, Preferably, the coefficient of thermal expansion of the material is greater than the coefficient of thermal expansion of the lower stress control material. In this way, on the substrate in advance,
By forming a lower buffer layer made of a lower stress control material having a lower coefficient of thermal expansion than that of the upper stress control material, one direction can be reduced to a relatively lower coefficient of thermal expansion of the lower buffer layer. Since it is governed, the restriction on the selection of the substrate material is reduced.

In this case, in the first step, a lower stress control material is deposited on the substrate before the ferroelectric film is formed, and the deposited lower stress control material is moved in another direction. The lower periodic structure is formed from the lower stress control material by dividing the lower stress control material into a stripe-shaped lower periodic structure having a sufficiently large length compared to the predetermined period. It is preferable that the thermal expansion coefficient of the upper stress control material is larger than the thermal expansion coefficient of the lower stress control material. Thus, between the substrate and the ferroelectric film, the direction in which the upper periodic structure and the stripe extend, which are made of the lower stress control material having a lower coefficient of thermal expansion than that of the upper stress control material, intersects each other. By forming the stripe-shaped lower periodic structure, if the lower periodic structure has a smaller coefficient of thermal expansion than the ferroelectric film, the lower periodic structure is continuous in one direction. And since it is divided in the other direction, a large tensile stress is selectively applied to one direction of the ferroelectric film when the temperature is lowered.

In the method for producing a ferroelectric film according to the present invention,
In the first step, the upper stress control material is deposited on the ferroelectric film, and the deposited upper stress control material is divided substantially in parallel so as to be spaced at predetermined intervals in other directions. Forming a stripe-shaped upper periodic structure having a length sufficiently greater than a predetermined period in one direction from the upper stress control material, wherein the coefficient of thermal expansion of the upper stress control material is lower than the thermal expansion coefficient of the substrate. It is preferably smaller than the expansion coefficient. With this configuration, the direction in which the stripes extend in the upper periodic structure having the stripe shape is one direction, and the thermal expansion coefficient of the upper stress control material is smaller than the thermal expansion coefficient of the substrate. When the body has a smaller coefficient of thermal expansion than the ferroelectric film, a large compressive stress is selectively applied to the other direction of the ferroelectric film when the temperature is lowered. On the other hand, when the substrate has a higher coefficient of thermal expansion than the ferroelectric film, stress mainly due to the difference in the coefficient of thermal expansion between the substrate and the ferroelectric film is applied in one direction of the ferroelectric film. Therefore, a large tensile stress is selectively applied to one direction of the ferroelectric film when the temperature is lowered.

In this case, the first step includes a step of forming a lower buffer layer made of a lower stress control material on the entire surface of the substrate before forming the ferroelectric film. Preferably, the coefficient of thermal expansion of the material is smaller than the coefficient of thermal expansion of the lower stress control material. In this way, on the substrate in advance,
By forming a lower buffer layer made of a lower stress control material having a thermal expansion coefficient larger than that of the upper stress control material, the other direction can be made to have a relatively large thermal expansion coefficient of the lower buffer layer. Since it is governed, the restriction on the selection of the substrate material is reduced.

In this case, the first step is to deposit a lower stress control material on the substrate before forming the ferroelectric film, and to deposit the deposited lower stress control material in one direction. By forming the lower periodic structure in a stripe shape having a length sufficiently larger than the predetermined period in the other direction from the lower stress control material by dividing the substrate substantially in parallel so as to leave an interval at a predetermined period. Preferably, the thermal expansion coefficient of the upper stress control material is smaller than the thermal expansion coefficient of the lower stress control material. Thus, between the substrate and the ferroelectric film, the direction in which the upper periodic structure and the stripe extend, which are made of the lower stress control material having a thermal expansion coefficient larger than the thermal expansion coefficient of the upper stress control material, intersect each other. By forming the stripe-shaped lower periodic structure, if the lower periodic structure has a larger coefficient of thermal expansion than the ferroelectric film, the lower periodic structure is continuous in the other direction. In addition, since the ferroelectric film is divided in one direction, a large compressive stress is selectively applied to the other direction of the ferroelectric film when the temperature is lowered.

In the method for producing a ferroelectric film according to the present invention,
In the first step, before forming the ferroelectric film, a lower stress control material is deposited on the substrate, and the deposited lower stress control material is spaced at a predetermined period in one direction. Forming a stripe-shaped lower periodic structure having a length sufficiently larger than a predetermined period in the other direction from the lower stress control material by dividing the lower stress control material substantially parallel to the lower stress control material. Is preferably larger than the coefficient of thermal expansion of the substrate. In this way, when the lower periodic structure has a larger coefficient of thermal expansion than the ferroelectric film, the lower periodic structure is divided in one direction and has a stripe shape continuous in the other direction. Therefore, a large compressive stress is selectively applied to the other direction of the ferroelectric film when the temperature is lowered. On the other hand, when the substrate has a smaller coefficient of thermal expansion than the ferroelectric film, stress mainly due to the difference in the coefficient of thermal expansion between the substrate and the ferroelectric film is applied in one direction of the ferroelectric film. Therefore, a large tensile stress is selectively applied to one direction of the ferroelectric film when the temperature is lowered.

In this case, the first step includes a step of forming an upper buffer layer made of an upper stress control material over the entire surface of the ferroelectric film, wherein the coefficient of thermal expansion of the lower stress control material is controlled by the upper stress control material. It is preferably larger than the thermal expansion coefficient of the material. As described above, since the upper buffer layer made of the upper stress control material having a lower coefficient of thermal expansion than the lower stress control material is formed on the ferroelectric film, one direction is the upper buffer layer. Is governed by the relatively low coefficient of thermal expansion of the substrate, so that the selection restrictions when selecting the substrate material are reduced.

In the method for producing a ferroelectric film according to the present invention,
In the first step, before forming the ferroelectric film, a lower stress control material is deposited on the substrate, and the deposited lower stress control material is spaced at predetermined intervals in the other direction. Forming a stripe-shaped lower periodic structure having a sufficiently large length in one direction from the lower stress control material by dividing the lower stress control material substantially parallel to the lower stress control material. Is preferably smaller than the coefficient of thermal expansion of the substrate. As described above, when the lower periodic structure has a smaller coefficient of thermal expansion than the ferroelectric film, the lower periodic structure is divided in the other direction and forms a stripe shape continuous in one direction. Therefore, a large compressive stress is selectively applied to the other direction of the ferroelectric film when the temperature is lowered. On the other hand, when the substrate has a higher coefficient of thermal expansion than the ferroelectric film, stress mainly due to the difference in the coefficient of thermal expansion between the substrate and the ferroelectric film is applied in one direction of the ferroelectric film. Therefore, a large tensile stress is selectively applied to one direction of the ferroelectric film when the temperature is lowered.

In this case, the first step includes a step of forming an upper buffer layer made of an upper stress control material on the entire surface of the ferroelectric film, wherein the coefficient of thermal expansion of the lower stress control material is controlled by the upper stress control material. It is preferably smaller than the thermal expansion coefficient of the material. With this configuration, an upper buffer layer made of an upper stress control material having a coefficient of thermal expansion larger than that of the lower stress control material is formed on the ferroelectric film, so that the upper buffer layer is oriented in the other direction. Since the layer is governed by the relatively large coefficient of thermal expansion of the layer, the selection restriction when selecting the substrate material is reduced.

In the method for producing a ferroelectric film according to the present invention,
Preferably, the substrate, the upper stress control material or the lower stress control material is made of a conductor. In this case, the substrate or the periodic structure can be used as an electrode. By connecting the electrode to an external circuit, an electric signal is given in a direction perpendicular or parallel to the surface of the substrate, and a DC electric field is applied to the substrate surface. Can be generated. Therefore, the spontaneous polarization of the ferroelectric film can be aligned in a direction parallel to the substrate surface not only by the mechanical action but also by the electrical action of the periodic structure.

In the method for producing a ferroelectric film according to the present invention,
It is preferable that the substrate, the upper stress control material or the lower stress control material is a four-fold rotationally symmetric crystal having a four-fold rotationally symmetric crystal structure in a plane parallel to the substrate surface. In this way, most of the ferroelectrics are cubic or tetragonal,
Because of the rotational symmetry, the symmetry of the crystal is easily matched in a plane parallel to the substrate surface, so that the anisotropic axis can be easily aligned in one direction.

In this case, the lattice constant of the four-fold rotationally symmetric crystal in the rotationally symmetric plane or a lattice constant obtained by multiplying the lattice constant by 1 / √2 and the lattice constant of the ferroelectric film at a temperature equal to or higher than the Curie temperature. It is preferable that the lattice mismatch with the constant is approximately 10% or less. In this way, not only the symmetry of the crystal but also the lattice mismatch is suppressed to about 10% or less, and the arrangement regularity of the ferroelectric crystal is increased, so that the anisotropic axes are further aligned in one direction. It can be easier.

In the method for producing a ferroelectric film according to the present invention,
If the upper or lower stress control material is aluminum
(Al), gold (Au), platinum (Pt), iridium (I
r), iridium oxide (IrO_2-x ) (Where x is 0
<X <1, the same applies hereinafter), ruthenium oxide (R
uO_2-x ), Strontium ruthenate (SrRuO)
_3-x ), Rhenium oxide (ReO)_2-x ), Silicon oxide
(SiO_Two ), Silicon nitride (Si_ThreeN_Four), Titanium nitride
(TiN), magnesium oxide (MgO), titanium titanate
Trontium (SrTiO_Three ), Aluminum oxide (A
l_TwoO_Three), Spinel (MgAl_TwoO_Four), Aluminum acid
Lantern (LaAlO)_Three ), Tantalum aluminate
Strontium (SrAl_xTa_1-xO_Three ), Zirconium oxide
(ZrO_Two ), Yttrium oxide (Y_TwoO_Three),I
Thorium-stabilized zirconium oxide (Y_TwoO_Three-Dope
d ZrO_Two ) Or titanium oxide (TiO 2)_Two )
Is preferred.

In the method for producing a ferroelectric film according to the present invention,
The third step is a step of generating a DC electric field parallel to one direction in the ferroelectric film by applying a DC voltage to the upper periodic structure, wherein the upper periodic structure is made of a conductor. It is preferred to include. In this way, the upper periodic structure is divided in one direction at a predetermined period, and a DC voltage distribution is applied along one direction, so that the DC voltage is applied in a direction parallel to the one direction in the ferroelectric film. A world can be created. In a ferroelectric material in which the c-axis becomes the spontaneous polarization axis, when a DC electric field is applied in one direction when the temperature is lowered from the Curie temperature, the c-axis is aligned in the one direction and the polarization is electrostatically induced. Positive and negative directions can be aligned. This allows
In addition to eliminating the need for a new polarization treatment after film formation, the primary electro-optic that requires a polarization orientation in one direction is required because the remaining 90-degree domain that does not contribute to externally output polarization can be suppressed. The effects and the like are easily expressed.

In the method for producing a ferroelectric film according to the present invention,
The lower periodic structure is made of a conductor, and the third step is a step of generating a DC electric field parallel to one direction in the ferroelectric film by applying a DC voltage to the lower periodic structure. It is preferred to include. In this manner, as described above, it is not necessary to perform a new polarization process after the film formation, and it is possible to suppress the remaining 90-degree domain that does not contribute to the polarization that can be output to the outside. Facilitates the development of the necessary primary electro-optic effect and the like.

In the method for producing a ferroelectric film according to the present invention,
It is preferable that the ferroelectric film has a cubic crystal structure at a temperature equal to or higher than the Curie temperature and has a tetragonal crystal structure at a temperature equal to or lower than the Curie temperature.

In the method of manufacturing a ferroelectric film according to the present invention,
It is preferable that the ferroelectric film contains an oxide having a perovskite structure or a solid solution of an oxide having a perovskite structure.

In the method of manufacturing a ferroelectric film according to the present invention,
Preferably, the substrate is made of a single crystal.

In this case, the single crystal is made of silicon (S
i), magnesium oxide (MgO), strontium titanate (SrTiO ₃ ), sapphire (α-Al
₂ O ₃ ), spinel (MgAl ₂ O ₄ ), lanthanum aluminate (LaAlO ₃ ), strontium tantalate aluminate (SrAl _x Ta _1-x O ₃ ), zirconium oxide (ZrO ₂ ), yttrium oxide (Y ₂ O) _3), yttrium-stabilized zirconium oxide (Y ₂ O ₃ -doped
ZrO ₂ ) or titanium oxide (TiO ₂ ).

[0034]

(First Embodiment) A first embodiment of the present invention.
An embodiment will be described with reference to the drawings.

FIGS. 1A and 1B show a first embodiment of the present invention.
1A shows a planar structure, and FIG. 1B shows a ferroelectric film obtained by the method for manufacturing a ferroelectric film according to the embodiment, and FIG. 1B shows a line Ib-Ib in FIG. 2 shows a cross-sectional configuration.

As shown in FIG. 1B, a ferroelectric film 12 having a Curie temperature higher than room temperature is deposited on the main surface of the substrate 11. An upper stress control material is formed on the ferroelectric film 12 and is disposed at a predetermined division period 13a in the x-axis direction in the drawing and substantially parallel to each other with an interval therebetween, in the y-axis direction orthogonal to the x-axis direction. Divided cycle 13a
A stripe-shaped upper periodic structure 13 having a sufficiently large length as compared with the above is formed. Here, as an example, the division period 13a in the x-axis direction of the upper periodic structure 13 is set to about 10 μm to 20 μm, and the length in the y-axis direction is set to about 1000 μm to 5000 μm. Also,
The total length in the x-axis direction of the upper periodic structure 13 is also set to about 1000 μm to 5000 μm, which is equivalent to the length in the y-axis direction.

In such a state, the substrate 11 is put into a furnace, and the ferroelectric film 12 is left at a temperature higher than the Curie temperature of the ferroelectric to be crystallized, and then cooled to room temperature. Here, a material whose thermal expansion coefficient is higher than the thermal expansion coefficient of the substrate 11 is selected as the upper stress control material constituting the upper periodic structure 13.

If the temperature of the ferroelectric film 12 crosses the Curie temperature from the high temperature side to the low Curie temperature side during the temperature drop, the crystal structure of the ferroelectric film 12 loses its isotropy and tends to be distorted. . At this time, the crystal constituting the ferroelectric film 12 is subjected to a thermodynamic crystal restructuring action to approach a state in which the strain energy contained in the crystal is the smallest.

As shown in FIGS. 1A and 1B,
At the interface between the substrate 11 and the ferroelectric film 12, the upper periodic structure 13 is divided in the x-axis direction in a plane parallel to the interface. The structure 13 does not receive much stress. For this reason, the stress relationship in the x-axis direction of the ferroelectric film 12 is determined only by the difference in the coefficient of thermal expansion between the substrate 11 and the ferroelectric film 12. Generally, when the ferroelectric film 12 has a larger coefficient of thermal expansion than the substrate 11 during cooling, a tensile stress is applied to the ferroelectric film 12 in the x-axis direction. This is because the contraction operation of the ferroelectric film 12 is restricted by the substrate 11 whose coefficient of thermal expansion is smaller than that of the ferroelectric film 12. Conversely, the ferroelectric film 12 is
When the thermal expansion coefficient is smaller than 1, a compressive stress is applied to the ferroelectric film 12 in the x-axis direction.

Since the upper surface of the ferroelectric film 12 and the upper periodic structure 13 are continuously in contact with each other in the y-axis direction, the distance between the ferroelectric film 12 and the upper periodic structure 13 A stress relationship different from the x-axis direction is established. The result is the same as that in the x direction. If the ferroelectric film 12 has a larger coefficient of thermal expansion than the upper periodic structure 13, the ferroelectric film 12
Tensile stress is applied in the y-axis direction. Conversely, when the ferroelectric film 12 has a smaller coefficient of thermal expansion than the upper periodic structure 13, compressive stress is applied to the ferroelectric film 12 in the y-axis direction.

However, in the first embodiment, since the condition that the thermal expansion coefficient of the upper stress control material constituting the upper periodic structure 13 is made larger than the thermal expansion coefficient of the substrate 11 is given, A relatively larger tensile stress is applied to the dielectric film 12 in the x-axis direction, a relatively larger compressive stress is applied in the y-axis direction, or
It is self-evident that the state occurs either simultaneously in the y-axis direction.

Therefore, according to the present embodiment, the above-described thermodynamic crystal reconstruction can be controlled by the mechanical action that different stresses are applied in the x-axis direction and the y-axis direction. . Therefore, the anisotropic axis can be oriented only in one direction in a plane parallel to the interface between the substrate 11 and the ferroelectric film 12. That is, here, the crystal axis having the largest lattice constant in the crystal of the ferroelectric film 12 is oriented in the x-axis direction which receives a relatively large tensile stress or receives a relatively small compressive stress. . Therefore, for example, the c-axis of the ferroelectric film 12 made of a tetragonal crystal at or below the Curie temperature is aligned in the x-axis direction.

Hereinafter, an example of a combination of materials of the substrate 11 and the upper stress control material for the upper periodic structure 13 suitable for the present embodiment will be specifically described. Here, a tetragonal perovskite-type ferroelectric represented by lead titanate (PbTiO ₃ ) or barium titanate (BaTiO ₃ ) will be described as an example of the ferroelectric film 12. The same applies to ferroelectric materials.

The perovskite ferroelectrics belonging to the tetragonal system generally have a Curie temperature higher than room temperature and a crystallization temperature higher than the Curie temperature in many cases.
Suitable for the present invention.

Table 1 shows typical values of the coefficient of thermal expansion of the substrate 11, the upper stress control material, or a material that can be used for the lower stress control material described later.

[0046]

[Table 1] As can be seen from Table 1, for example, silicon (S
i), sapphire (α-Al ₂ O ₃ ) or spinel (M
gAl ₂ O ₄ ) for the substrate 11 and aluminum (A
1) If the upper periodic structure 13 is formed by using gold (Au) or magnesium oxide (MgO) as the upper stress control material, the above-mentioned relationship of the coefficient of thermal expansion is established. The c-axis in the crystal is easily oriented in the x-axis direction.

In FIGS. 1A and 1B, the x-axis and the y-axis are exchanged, and the magnitude relationship between the thermal expansion coefficients of the substrate 11 and the upper periodic structure 13 is reversed. By making the coefficient of thermal expansion of the upper stress control material constituting the periodic structure 13 smaller than the coefficient of thermal expansion of the substrate 11, the crystal of the ferroelectric film 12 can be formed in the same manner as described above. The c-axis of the body can be aligned in the x-axis direction.

In this case, a material having a large coefficient of thermal expansion such as MgO, strontium titanate (SrTiO ₃ ), or lanthanum aluminate (LaAlO ₃ ) is used for the substrate 11 and silicon oxide (SiO ₂ ) is used for the upper stress control material.
₂ ), silicon nitride (Si ₃ N ₄ ) or iridium (I
A material having a small coefficient of thermal expansion such as r) may be used.

Further, although not shown, a structure having the same shape, arrangement and function as the upper periodic structure 13 is replaced with the substrate 11 and the ferroelectric film 12 instead of the upper periodic structure 13. The ferroelectric film 12 may be formed in between, that is, before the ferroelectric film 12 is deposited. The structure in this case is called a lower periodic structure, and its constituent material is called a lower stress control material. With this configuration, since an etching process for forming the lower periodic structure can be performed before the ferroelectric film 12 is deposited, damage to the ferroelectric film 12, such as a reduction reaction, can be suppressed.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

FIGS. 2A and 2B show a second embodiment of the present invention.
2A is a plan view of the ferroelectric film obtained by the method for manufacturing a ferroelectric film according to the embodiment, and FIG. 2B is a IIb-IIb line of FIG. 2A. 2 shows a cross-sectional configuration.

As shown in FIG. 2B, a lower buffer layer 14 made of a lower stress control material having a thickness of about 0.1 μm to 1 μm is formed on the main surface of the substrate 11. 1
4, a ferroelectric film 12 having a Curie temperature higher than room temperature is deposited. On the ferroelectric film 12, an upper stress control material is provided, which is arranged at a predetermined division period 13a in the x-axis direction in the drawing and substantially parallel to each other with an interval therebetween, and compared with the division period 13a in the y-axis direction. Stripe-shaped upper periodic structure 13 having a sufficiently large length
Are formed.

In the second embodiment, the lower buffer layer 14 instead of the substrate 11 determines the stress relationship in the x-axis direction in the drawing. As a result, it is possible to greatly reduce the cost and the size of the substrate 11 when selecting the material for the substrate 11.

For example, iridium (Ir) or spinel (MgAl ₂ O ₄ ) has a relatively small coefficient of thermal expansion, but is expensive as a substrate and is difficult to have a large area. Therefore, I
If r or MgAl ₂ O ₄ is uniformly applied on the substrate 11 as a lower stress control material and the applied lower stress control material is used as the lower buffer layer 14, there is no limit on the cost or size of the substrate 11.

As described above, even when the lower buffer layer 14 for applying stress to the ferroelectric film 12 from its lower surface is provided between the substrate 11 and the ferroelectric film 12, the first embodiment Similarly to the first embodiment, the shape of the upper periodic structure 13, the dividing direction in the x-axis direction or the y-axis direction, and the magnitude relationship of the thermal expansion coefficient between the lower buffer layer 14 and the upper periodic structure 13 are different from those of the first embodiment. The same is true.

That is, as shown in FIG. 2A, when the division direction of the stripe of the upper periodic structure 13 is the period in the x-axis direction, the thermal expansion coefficient of the upper stress control material constituting the upper periodic structure 13 Is set to be larger than the coefficient of thermal expansion of the lower stress control material constituting the lower buffer layer 14.
As shown in Table 1, for example, Si, α-Al ₂ O ₃
Alternatively, the lower buffer layer 14 is composed of MgAl ₂ O ₄ , and Al,
If the upper periodic structure 13 is made of Au or MgO,
To satisfy this condition, the c-axis of the crystal of the ferroelectric film 12 is easily oriented in the x-axis direction.

In FIGS. 2A and 2B, the x-axis and the y-axis are exchanged, and the magnitude relationship between the thermal expansion coefficients of the lower buffer layer 14 and the upper periodic structure 13 is reversed. That is, by making the coefficient of thermal expansion of the upper stress control material constituting the upper periodic structure 13 smaller than the coefficient of thermal expansion of the lower stress control material constituting the lower buffer layer 14, the ferroelectric film 12 The c-axis of the crystal can be aligned in the x-axis direction.

In this case, MgO, S
A material having a large coefficient of thermal expansion such as rTiO ₃ or LaAlO ₃ is used, and SiO ₂ , Si ₃ N ₄
Alternatively, a material having a small coefficient of thermal expansion such as Ir may be used.

Further, although not shown, a lower periodic structure having the same shape, arrangement and function as the upper periodic structure 13 is replaced with a substrate 11 and a ferroelectric film, instead of the upper periodic structure 13. 12, that is, before the ferroelectric film 12 is deposited.
After depositing No. 2, an upper buffer layer made of an upper stress control material may be formed on the ferroelectric film 12. With this configuration, since an etching process for forming the lower periodic structure can be performed before the ferroelectric film 12 is deposited, damage to the ferroelectric film 12, such as a reduction reaction, can be suppressed.

(Third Embodiment) Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

FIGS. 3A to 3C show ferroelectric films obtained by the method for manufacturing a ferroelectric film according to the third embodiment of the present invention. FIG. The configuration is shown in FIG.
3B shows a cross-sectional configuration along the line IIIb-IIIb in FIG. 3A, and FIG. 3C shows a cross-sectional configuration along the line IIIc-IIIc in FIG.

As shown in FIGS. 3A to 3C, the difference from the second embodiment is that a lower stress control material is used.
A lower buffer layer provided between the substrate 11 and the ferroelectric film 12 is disposed at a predetermined divisional period 15a in the y-axis direction in the drawing and substantially parallel to each other at intervals, and a divisional period 15a in the x-axis direction. This is a point that the lower periodic structure 15 is formed in a stripe shape having a sufficiently longer length than that of the lower periodic structure 15. Here, the dimensions of the lower periodic structure 15 may be such that the division period 15a in the y-axis direction is about 10 μm to 20 μm, and the length in the x-axis direction is about 1000 μm to 5000 μm. Further, the total length in the y-axis direction of the lower periodic structure 15 is also 1000 μm to 5000 μm, which is equivalent to the length in the x-axis direction.
It should just be about.

The coefficient of thermal expansion is selected so that the upper stress control material forming the upper periodic structure 13 is larger than the lower stress control material forming the lower periodic structure 15.

Also in the third embodiment, the substrate 11 and the lower periodic structure 15
5, a stress relationship applied to the interface of the ferroelectric film 12 in contact with
Anisotropy can be generated in the stress relationship that the upper periodic structure 13 gives to the interface of the ferroelectric film 12 in contact with the upper periodic structure 13. That is, when the division direction of the stripe of the upper periodic structure 13 is the period in the x-axis direction, the thermal expansion coefficient of the upper stress control material forming the upper periodic structure 13
If the condition that the coefficient of thermal expansion of the substrate 11 and the coefficient of thermal expansion of the lower stress control material constituting the lower periodic structure 15 are set to be larger is the same as in each of the above-described embodiments.

In addition, by providing the lower periodic structure 15 between the substrate 11 and the ferroelectric film 12, a function of controlling the stress along the x-axis direction is clearly given, so that the effect is more enhanced. At the same time, restrictions when selecting the material of the substrate 11 are reduced.

The upper periodic structure 13 and the lower periodic structure 15 may be interchanged. That is, the replaced upper periodic structure has a division period in the y-axis direction, and the replaced lower periodic structure has a division period in the x-axis direction. Further, the materials are selected such that the coefficient of thermal expansion is smaller in the replaced upper periodic structure than in the replaced lower periodic structure.

In this embodiment, the stripe direction of the upper periodic structure 13 and the stripe direction of the lower periodic structure 15 are strictly orthogonal because they are described in accordance with the rectangular coordinate system for convenience. However, as long as the intersection angle between the two does not deviate significantly from the right angle, the essence of the present invention is not deviated.

(Fourth Embodiment) Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

FIGS. 4A and 4B show a fourth embodiment of the present invention.
4A is a plan view of a ferroelectric film obtained by the method of manufacturing a ferroelectric film according to the embodiment, and FIG. 4B is a IVb-IVb line of FIG. 2 shows a cross-sectional configuration. 4A and 4B, the same components as those shown in FIGS. 1A and 1B are denoted by the same reference numerals.

In the third embodiment, the upper periodic structure 13 is a conductor made of, for example, Al or Au, and further, as an electrode connected to an electric circuit 50 having a plurality of DC power supplies 51 and a switch circuit 52. Function.

The electric circuit 50 comprises a DC power supply 51 and a switch circuit 52 connected in parallel with each other. When the switch circuit 52 is closed, a DC voltage generated by the DC power supply 51 is applied to the upper periodic structure 13. The upper periodic structure 13 is an electrode that is divided from each other at a predetermined division period 13a in the x-axis direction in the drawing.
If the insulating property of 1 is sufficiently high, a DC voltage is directly applied to a region between the upper periodic structures 13 on the upper surface of the ferroelectric film 12.

As shown in FIG. 4A, in the present embodiment, each of the plurality of upper periodic structures 13 is connected to the DC power supply 51 such that the higher the position is on the left side in the drawing, the higher the potential is. Therefore, the potential uniformly drops from left to right along the x-axis direction, so that the direction of the DC electric field 60 generated above the ferroelectric film 12 is aligned in the x-axis direction.

As shown in FIG. 4A, the electric circuit 50 and the upper periodic structure 13 are connected. However, the switch circuit 51 is left open. After that, as in the first embodiment,
The ferroelectric film 12 is crystallized at a temperature higher than the Curie temperature of the material, and then, with the switch circuit 51 closed, the crystallized ferroelectric film 12 is gradually cooled to room temperature. Here, the materials of the upper stress control material and the substrate are selected so that the thermal expansion coefficient of the upper stress control material constituting the upper periodic structure 13 is higher than the thermal expansion coefficient of the substrate 11. In this case, the crystal arrangement is controlled by the mechanical action due to the anisotropy of the thermal expansion coefficient difference, and the c-axis of the crystal of the ferroelectric film 12 is arranged along the x-axis direction.

Further, in the present embodiment, spontaneous polarization is induced on the c-axis aligned in the x-axis direction, and the direction of the polarization vector (direction from negative to positive) is aligned in one direction. Electrical action is simultaneously applied.

Specifically, when the ferroelectric film 12 is crystallized and then cooled to room temperature, a DC voltage is applied to the ferroelectric film 12 via each of the stripe-shaped upper periodic structures 13. To generate a DC electric field. The magnitude of the generated DC electric field depends on the type of material and the like, but is generally about 20 kV / cm.
-100 kV / cm is desirable. Ferroelectric film 1 during cooling
When the crystal of No. 2 receives such a DC electric field, the positive and negative directions of polarization are electrostatically aligned by the influence of the electric potential distribution in the process of aligning the c-axis of the crystals in the x-axis direction. Can be As a result, it is not only necessary to perform the polarization treatment again after the crystallization step, but also it is possible to suppress the remaining of the 90-degree domain that does not contribute to the polarization output to the outside, so that the direction of the polarization vector is aligned in one direction. Is particularly effective for expressing the necessary piezoelectric effect or pyroelectric effect.

Instead of the upper periodic structure 13, a lower periodic structure made of a conductor may be formed, and this lower periodic structure may be connected to the electric circuit 50.

(Fifth Embodiment) Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.

FIGS. 5A and 5B show a fifth embodiment of the present invention.
5A is a plan view of a ferroelectric film obtained by the method of manufacturing a ferroelectric film according to the embodiment, and FIG. 5B is a line Vb-Vb of FIG. 5A. 2 shows a cross-sectional configuration. Here, in FIGS. 5A and 5B, the same components as those shown in FIGS. 1A and 1B are denoted by the same reference numerals.

In the fifth embodiment, as in the fourth embodiment, a DC voltage is applied to the crystallized ferroelectric film 12 in parallel to the surface of the crystallized ferroelectric film 12 during cooling to room temperature.

As shown in FIG. 5A, in the upper periodic structure 16 according to the present embodiment, both ends in the y-axis direction are not electrically open, and the end in the y-axis direction is one. A so-called comb-shaped electrode connected every other book is formed. With this comb-shaped electrode, the upper surface of the ferroelectric film 12 is divided into two with a division period 16a.
It becomes electrically equipotential at twice the pitch.

The electric circuit 50A is composed of one DC power supply 51 and one switch circuit 52 connecting between both electrodes of the comb-shaped electrode constituted by the upper periodic structure 16. When the switch circuit 52 is closed, a DC electric field is generated in the x-axis direction of the ferroelectric film 12, and the generated electric fields 60A and 60A are generated.
The direction of 0B is an antiparallel direction that is inverted by 180 degrees with respect to each division period 16a.

As shown in FIGS. 5A and 5B,
By forming the upper periodic structure 16 into a comb-shaped electrode shape and applying a DC voltage to the upper periodic structure 16, when gradually cooling from a temperature exceeding the Curie temperature, it is induced in the crystal of the ferroelectric film 12. All the spontaneous polarizations are parallel to the x-axis direction, and the positive and negative directions are alternately inverted, and this inversion is periodically repeated.

Thus, the fifth embodiment is applicable to applications in which the directions of the polarization vectors are allowed to be antiparallel.
For example, it is particularly effective for expressing a primary electro-optic effect. When a ferroelectric having a bismuth layer structure is used for the ferroelectric film 12, the spontaneous polarization axis can be aligned in a direction perpendicular to the substrate surface.

Further, the fifth embodiment has an advantage that the configuration of the electric circuit 50A is simpler than that of the fourth embodiment, and that a high voltage is not generally required.

It is to be noted that, instead of the upper periodic structure 16, a lower periodic structure made of a conductor in the form of a comb electrode is formed.
The lower periodic structure may be connected to the electric circuit 50A.

Although the first to fifth embodiments have been described above, in any of the embodiments, the ferroelectric film 12
The compatibility of the crystal structure of the member (the substrate 11, the upper stress control material and the lower stress control material) in contact with the ferroelectric film 12 in the plane defined by the x-axis direction and the y-axis direction plays an important role. .

In particular, the exemplified tetragonal ferroelectric film 12
In order to align the c-axis, which is an anisotropic axis, in one direction in the plane, the x-axis direction and the <100> axis should be parallel as much as possible when crystallizing at or above the Curie temperature. It is desirable that the orientation is performed so that the y-axis direction is parallel to the <010> axis.

Therefore, in order to produce a ferroelectric crystal having such orientation, it is effective to use a crystal material having four-fold rotational symmetry in the interface with the ferroelectric film 12 for the substrate 11 or the like. Become. This is because when the ferroelectric film 12 is crystallized,
Influenced by the four-fold rotationally symmetric crystal regularity, <100>
This is because a thermodynamic effect is exerted to stabilize the shaft by aligning it at one position.

Further, the magnitude relation between the first lattice constant a in the plane orthogonal to the rotational symmetry axis of the four-fold rotationally symmetric crystal and the second lattice constant b above the Curie temperature of the ferroelectric film 12. Also has great significance. That is, the value of the lattice mismatch represented by the ratio (| ba−a | / b) of the absolute value of the difference between the second lattice constant b and the first lattice constant a with respect to the second lattice constant b is small. As the ferroelectric film 12 becomes more sensitive to the structure of the four-fold rotationally symmetric crystal, the crystallites are more likely to be arranged. The tetragonal ferroelectric crystal described in each of the embodiments is preferable when the lattice mismatch rate is approximately 10% or less, since the effect that crystallites are easily arranged becomes large.

Further, when the first lattice constant a is
Even in the case of a crystal having four-fold rotational symmetry considerably larger than the second lattice constant b, a / √2 or a / 2, which is a third lattice constant in which adjacent crystal sites are replaced, Second
The same effect can be obtained if the lattice mismatch rate between the lattice mismatch b and the lattice constant b is within about 10%.

The four-fold rotationally symmetric crystals satisfying such conditions include magnesium oxide (MgO), strontium titanate (SrTiO ₃ ), and spinel (MgAl
₂ O ₄ ), strontium aluminum tantalate (S
rAl _x Ta _1-x O ₃ ), zirconium oxide (ZrO
₂ ), yttrium-stabilized zirconium oxide (Y ₂ O ₃ −
doped ZrO ₂ ).

[0092]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a ferroelectric film according to one embodiment of the present invention will be described below with reference to the drawings.

FIGS. 6A to 6D show cross-sectional structures in the order of steps in the method of manufacturing a ferroelectric film according to the present embodiment. As shown in [Table 1], magnesium oxide (MgO) having a relatively large coefficient of thermal expansion is used for the single crystal substrate 21 shown in FIG.

First, the Mg layer having the (100) plane orientation of the main surface was used.
After subjecting the single crystal substrate 21 made of O to surface treatment with diluted phosphoric acid or the like, for example, an amorphous PL
A ferroelectric film 22A made of T is deposited. Where PL
T is an oxide having a perovskite structure in which 0 to 20 atomic% of lanthanum oxide (LaO _x ) is added to lead titanate (PbTiO ₃ ), and a ferroelectric material belonging to a tetragonal system near room temperature It is. Spontaneous polarization axis is <001>
(= C-axis), and the Curie temperature is in the range of 100 ° C. to 490 ° C., although it depends on the amount of LaO _x added.
The crystallization temperature needs to be approximately 600 ° C. or higher. In addition, MgO
Has a cubic crystal structure, a lattice constant a of 4.203 °, and a coefficient of thermal expansion of 13.8 × 10 ⁻⁶ / ° C.
Therefore, the single crystal substrate 21 has a crystal structure whose main surface has four-fold rotational symmetry.

Here, the ferroelectric film 22A is deposited using a sol-gel method. Specifically, a PLT-based sol-gel reagent having a solute concentration of 15% or less prepared by using 2-methoxyethanol as a main solvent is spin-coated on the single crystal substrate 21, and then applied to the ferroelectric film 22A. Drying and calcination are performed at a temperature in the range of about 150C to about 400C.

What is important here is to keep the drying and calcination temperatures lower than the crystallization temperature.
This is to prevent crystallization of the ferroelectric film 22A from occurring and to sufficiently evaporate the solvent component to promote drying and polymerization shrinkage. The thickness of the ferroelectric film 22A is desirably 100 nm or less per application, and when the total film thickness is increased, the number of applications is increased. Nevertheless, the total film thickness is preferably less than about 1000 nm, preferably less than about 500 nm. This prevents cracks in the ferroelectric film 22B and separation from the single-crystal substrate 21 in a crystallization step described later, and prevents the ferroelectric film 22B from acting on crystal engineering from the single-crystal substrate 21. This is for the purpose of spreading the entire 22B.

In this embodiment, the amorphous PLT is used.
The sol-gel method was used for depositing the ferroelectric film 22A made of, but not limited to, the organic metal raw material thermal decomposition (MOD) method,
Sputtering method, metal organic chemical vapor deposition (MO
A film formation method such as a CVD method, a solution source chemical vapor deposition (LSMCD) method, or a pulse laser deposition method (PLD) method may be used.

Next, as shown in FIG.
An upper stress control material 23A made of silicon oxide (SiO ₂ ) having a thickness of about 500 nm to about 1000 nm is deposited on the ferroelectric film 22A by using the F sputtering method. SiO ₂ is amorphous and has a coefficient of thermal expansion of 0.35 × 10 ⁻⁶ / ° C. in the case of quartz glass.

[0099] In addition, the top stress control material 2 made of SiO ₂
As a deposition method of 3A, a sol-gel method, a plasma CVD method, spin-on-glass (SOG), or the like can be considered, but SiO ₂ obtained by a sputtering method has a small heat shrinkage,
The sputtering method is preferred because the effect of the difference in thermal expansion coefficient with MgO is more likely to appear.

Next, as shown in FIG. 6 (c), the upper stress control material 23A deposited by using the lithography method and the etching method is, for example, 10 μm to 2 μm in the y-axis direction in the drawing.
The division is performed at a division period 23a of about 0 μm and substantially in parallel, so that the upper stress control member 23A has a sufficiently large length, for example, about 10
The upper periodic structure 23 having a stripe shape of 00 μm is formed. The upper stress control material 23A may be etched by wet etching or dry etching using a buffered hydrofluoric acid (BHF) solution. However, the ferroelectric film 22A made of amorphous PLT is reduced or the composition is altered. And the effects of plasma damage should be minimized.

Next, as shown in FIG. 6D, the crystallization firing temperature is set to about 650 ° C., and the ferroelectric film 2 of the amorphous PLT is formed.
By crystallizing 2A, a ferroelectric film 22B made of PLT crystal is obtained. What is important here is the rate of temperature rise when the temperature is raised to the crystallization firing temperature. It is desirable that the average heating rate is at least 10 ° C./sec or more. By increasing the rate of temperature rise, crystal nuclei of the ferroelectric film 22B can be selectively generated at the interface with the single crystal substrate 21, and during the temperature rise, the single crystal substrate 21 and the ferroelectric This is to prevent generation or accumulation of extra stress between the film 22B and between the ferroelectric film 22B and the upper periodic structure 23, respectively. Conversely, after the crystallization is completed, it is gradually cooled to room temperature at a relatively slow temperature decreasing rate. At this time, the average cooling rate is preferably 0.1 ° C./sec or less.

As described above, according to this embodiment, the stripe extends in the x-axis direction and the coefficient of thermal expansion is
The upper periodic structure 23 smaller than 1 is formed on the ferroelectric film 22A.
Since the crystallized ferroelectric film 22B crosses the Curie temperature to a low temperature side and then gradually cools down to room temperature, the ferroelectric film 22B is relatively formed in the x-axis direction. Therefore, the ferroelectric film 22B has the largest lattice constant, that is, the c-axis is aligned in the x-axis direction.

[0103]

According to the method of manufacturing a ferroelectric film according to the present invention, the crystal anisotropy axis of the ferroelectric is aligned in one direction in a plane parallel to the interface between the substrate and the ferroelectric film. Alternatively, the spontaneous polarization vectors can be aligned parallel or anti-parallel. Therefore, the crystal of the ferroelectric film by the conventional film forming method,
In other words, it is possible to realize new device functions and characteristics that are difficult with crystals in which the anisotropic axis is randomly oriented or crystals oriented perpendicular to the substrate surface, and to reduce the power, increase the output, or increase the sensitivity of the device. Dramatic improvement in performance becomes possible.

[Brief description of the drawings]

FIGS. 1A and 1B show a ferroelectric film obtained by a method for manufacturing a ferroelectric film according to a first embodiment of the present invention, FIG. 1A is a plan view, and FIG. ) Is Ib- of (a).
FIG. 3 is a configuration sectional view taken along line Ib.

FIGS. 2A and 2B show a ferroelectric film obtained by a method for manufacturing a ferroelectric film according to a second embodiment of the present invention, wherein FIG. 2A is a plan view and FIG. ) Is IIb- of (a).
FIG. 2 is a configuration sectional view taken along line IIb.

3A and 3B show a ferroelectric film obtained by a method for manufacturing a ferroelectric film according to a third embodiment of the present invention, FIG. 3A is a plan view, and FIG. ) Is IIIb- of (a).
FIG. 3C is a sectional view taken along line IIIb, and FIG.
FIG. 3 is a sectional view taken along line Ic-IIIc.

FIGS. 4A and 4B show a ferroelectric film obtained by a method for manufacturing a ferroelectric film according to a fourth embodiment of the present invention, FIG. 4A is a plan view, and FIG. ) Is IVb- of (a)
FIG. 4 is a sectional view taken along line IVb.

FIGS. 5A and 5B show a ferroelectric film obtained by a method for manufacturing a ferroelectric film according to a fifth embodiment of the present invention, FIG. 5A is a plan view, and FIG. ) Is Vb− of (a).
FIG. 4 is a sectional view taken along line Vb.

FIGS. 6A to 6D are cross-sectional views illustrating a method of manufacturing a ferroelectric film according to an embodiment of the present invention in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Ferroelectric film 13 Upper periodic structure 13a Division period 14 Lower buffer layer 15 Lower periodic structure 15a Division period 16 Upper periodic structure 16a Division period 21 Single crystal substrate 22A Ferroelectric film (amorphous) 22A Ferroelectric film (crystal) 23A Upper stress control material 23 Upper periodic structure 23a Division period 50 Electric circuit 50A Electric circuit 51 DC power supply 52 Switch circuit 60 Electric field 60A Electric field 60B Electric field

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 41/24 H01L 41/22 A F term (Reference) 4G077 AA03 BC42 BC43 CB08 EA02 FE10 HA06 5F058 BA20 BB06 BB10 BC03 BF01 BH01 BJ01 BJ10 5F083 FR01 GA05 GA27 JA14 JA15 JA17 JA32 JA36 JA38 JA40 JA42 JA44 JA45

Claims (25)

[Claims] A first step of forming a ferroelectric film having a Curie temperature higher than room temperature on a substrate; and setting the substrate temperature to a temperature higher than the Curie temperature. A second step of crystallizing the ferroelectric film, and intersecting the one direction parallel to the substrate surface in one direction parallel to the substrate surface of the crystallized ferroelectric film. A third step of lowering the substrate temperature to room temperature while applying a tensile stress greater than the other direction or a compressive stress greater than the one direction in the other direction. A method for producing a ferroelectric film. 2. The method according to claim 1, wherein, after depositing an upper stress control material on the ferroelectric film, the deposited upper stress control material is spaced at a predetermined period in the one direction. Forming a stripe-shaped upper periodic structure having a length sufficiently larger than the predetermined period in the other direction from the upper stress control material by dividing the upper stress control material substantially parallel to 2. The method according to claim 1, wherein a thermal expansion coefficient of the upper stress control material is larger than a thermal expansion coefficient of the substrate. 3. The method according to claim 1, wherein the first step includes a step of forming a lower buffer layer made of a lower stress control material on the entire surface of the substrate before forming the ferroelectric film. 3. The method according to claim 2, wherein a thermal expansion coefficient of the stress control material is larger than a thermal expansion coefficient of the lower stress control material. 4. The method according to claim 1, further comprising: depositing a lower stress control material on the substrate before forming the ferroelectric film, and depositing the deposited lower stress control material in the other direction. By dividing the lower stress control material substantially parallel so as to be spaced at a predetermined period from the lower stress control material, a stripe-shaped lower periodic structure having a length sufficiently larger than the predetermined period in the one direction. 3. The method according to claim 2, further comprising a step of forming a body, wherein a coefficient of thermal expansion of the upper stress control material is larger than a coefficient of thermal expansion of the lower stress control material. 5. The first step is such that, after depositing an upper stress control material on the ferroelectric film, the deposited upper stress control material is spaced at predetermined intervals in the other direction. Forming a stripe-shaped upper periodic structure having a length that is sufficiently larger than the predetermined period in the one direction from the upper stress control material by dividing the upper stress control material substantially in parallel. 2. The method according to claim 1, wherein a thermal expansion coefficient of the upper stress control material is smaller than a thermal expansion coefficient of the substrate. 6. The method according to claim 1, wherein the first step includes a step of forming a lower buffer layer made of a lower stress control material on the entire surface of the substrate before forming the ferroelectric film. 6. The method according to claim 5, wherein a coefficient of thermal expansion of the stress control material is smaller than a coefficient of thermal expansion of the lower stress control material. 7. The method according to claim 1, wherein the first step includes depositing a lower stress control material on the substrate before forming the ferroelectric film, and disposing the deposited lower stress control material in the one direction. The stripe-shaped lower periodic structure having a length sufficiently larger than the predetermined period in the other direction from the lower stress control material by being divided substantially in parallel so as to be spaced at a predetermined period. 6. The method according to claim 5, further comprising a step of forming a body, wherein a coefficient of thermal expansion of the upper stress control material is smaller than a coefficient of thermal expansion of the lower stress control material. 8. The method according to claim 1, wherein a lower stress control material is deposited on the substrate before the ferroelectric film is formed, and the deposited lower stress control material is moved in the one direction. By dividing the lower stress control material from the lower stress control material substantially in parallel to the predetermined period, the lower periodic structure in a stripe shape having a length sufficiently larger than the predetermined period. The method of claim 1, further comprising forming a body, wherein a coefficient of thermal expansion of the lower stress control material is larger than a coefficient of thermal expansion of the substrate. 9. The first step includes forming an upper buffer layer made of an upper stress control material on the entire surface of the ferroelectric film, wherein the coefficient of thermal expansion of the lower stress control material is 9. The method according to claim 8, wherein the thermal expansion coefficient of the upper stress control material is larger than the thermal expansion coefficient of the upper stress control material. 10. The first step includes, before forming the ferroelectric film, depositing a lower stress control material on the substrate and disposing the deposited lower stress control material in the other direction. By dividing the lower stress control material substantially parallel so as to be spaced at a predetermined period from the lower stress control material, a stripe-shaped lower periodic structure having a length sufficiently larger than the predetermined period in the one direction. The method of claim 1, further comprising forming a body, wherein a coefficient of thermal expansion of the lower stress control material is smaller than a coefficient of thermal expansion of the substrate. 11. The first step includes a step of forming an upper buffer layer made of an upper stress control material on the entire surface of the ferroelectric film, wherein the coefficient of thermal expansion of the lower stress control material is The method for manufacturing a ferroelectric film according to claim 10, wherein the coefficient of thermal expansion is smaller than a coefficient of thermal expansion of the upper stress control material. 12. The method according to claim 1, wherein the substrate is made of a conductor. 13. The substrate according to claim 2, wherein the substrate or the upper stress control material is made of a conductor.
2. The method for producing a ferroelectric film according to claim 1. 14. The substrate or the upper stress control material,
3. A four-fold rotationally symmetric crystal having a four-fold rotationally symmetric crystal structure in a plane parallel to the substrate surface.
12. The method for producing a ferroelectric film according to any one of items 7, 9, and 11. 15. The upper stress control material includes aluminum, gold, platinum, iridium, iridium oxide, ruthenium oxide, strontium ruthenate, rhenium oxide,
Silicon oxide, silicon nitride, titanium nitride, magnesium oxide, strontium titanate, aluminum oxide,
12. A method according to claim 2, comprising spinel, lanthanum aluminate, strontium tantalate aluminate, zirconium oxide, yttrium oxide, yttrium stabilized zirconium oxide or titanium oxide. 3. The method for producing a ferroelectric film according to item 1. 16. The semiconductor device according to claim 3, wherein the substrate or the lower stress control member is made of a conductor.
The method for producing a ferroelectric film according to any one of items 8 and 10. 17. The substrate or the lower stress control material,
11. A four-fold rotationally symmetric crystal having a four-fold rotationally symmetric crystal structure in a plane parallel to the substrate surface. 2. The method for producing a ferroelectric film according to claim 1. 18. The lower stress control material includes aluminum, gold, platinum, iridium, iridium oxide, ruthenium oxide, strontium ruthenate, rhenium oxide,
Silicon oxide, silicon nitride, titanium nitride, magnesium oxide, strontium titanate, aluminum oxide,
A spinel, lanthanum aluminate, strontium tantalate aluminate, zirconium oxide, yttrium oxide, yttrium-stabilized zirconium oxide or titanium oxide, characterized in that it comprises titanium oxide.
The method for producing a ferroelectric film according to any one of 7, 8, and 10. 19. The four-fold rotationally symmetric crystal has a lattice constant in a rotationally symmetric plane or a lattice constant obtained by multiplying the lattice constant by 1 / √2, and a lattice constant of the ferroelectric film at a temperature equal to or higher than the Curie temperature. The lattice mismatch rate with the lattice constant is almost 10
%. The method for producing a ferroelectric film according to claim 14, wherein 20. The upper periodic structure is made of a conductor, and the third step is to apply a DC voltage to the upper periodic structure to apply a DC voltage to the ferroelectric film in the one direction. The method for producing a ferroelectric film according to any one of claims 2 to 4, further comprising a step of generating a parallel direct-current electric field by using a magnetic field. 21. The lower periodic structure is made of a conductor, and the third step is to apply a DC voltage to the lower periodic structure to apply a DC voltage to the ferroelectric film in the one direction. The method for producing a ferroelectric film according to any one of claims 7 to 9, further comprising a step of generating a parallel direct-current electric field by using a magnetic field. 22. The ferroelectric film has a cubic crystal structure at a temperature equal to or higher than the Curie temperature and a tetragonal crystal structure at a temperature equal to or lower than the Curie temperature. Item 2. The method for producing a ferroelectric film according to Item 1. 23. The method according to claim 1, wherein the ferroelectric film includes an oxide having a perovskite structure or a solid solution of an oxide having a perovskite structure. 24. The method according to claim 1, wherein the substrate is made of a single crystal. 25. The single crystal body is silicon, magnesium oxide, strontium titanate, sapphire, spinel, lanthanum aluminate, strontium tantalate aluminate, zirconium oxide, yttrium oxide, yttrium-stabilized zirconium oxide or titanium oxide. The method for manufacturing a ferroelectric film according to claim 24, wherein: