JPH02184599A - Production of ferroelectric thin film - Google Patents

Abstract

PURPOSE:To obtain the title high purity thin film having single ferroelectric domain structure by using as substrate ZnO single crystal (0001)-plane. CONSTITUTION:In a Rf-excited (at 100-250W) oxygen plasma atmosphere, Li(oxide), Nb(oxide) and Ta(oxide) as Li, Nb and Ta sources, respectively, are put to temperature regulation, using a Knudsen cell, electron beam heater, etc., so as to each independently obtain a specified evaporation level, followed by simultaneous deposition on a ZnO single crystal (0001) plane subjected to heteroepi growth on either ZnO (0001)-plane single crystal substrate or one of the respective substrate surface of sapphire (0001)-, Si(111)-, GaP(111)-, GaAs(111)-, CdTe(111)- and ZnS(111)-planes kept at 400-800 deg.C through heating, thus obtaining the objective LiNb1-xTaxO3 (0<=x<=1) single crystal thin film in a single ferroelectric domain state.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for producing a ferroelectric thin film, and more specifically, to a method for manufacturing a ferroelectric thin film having high purity and a single ferroelectric domain structure.
The present invention relates to a method for producing a b 1-X Ta)(Ox (0'X<1) single crystal thin film.

<Prior Art> t, iNb, -xraxo, coGx<1)a, has been utilized in the development of applications to various devices by taking advantage of its many excellent properties. For example, surface acoustic wave (SAW) devices that utilize a large electromechanical coupling coefficient, optical waveguides, optical switches, optical modulators, optical couplers, wavelength converters, etc. that utilize electro-optical effects, nonlinear optical effects, etc. Substrate materials for optical ICs, optical IC sensors that utilize refractive index changes that respond sensitively to changes in external fields, optical memories that utilize the optical damage effect caused by impurity doping such as Fe, and eight-dimensional hologram materials, etc. It is used in the applied development field of 1.

Conventionally, such LiNb1-xTa)(Oi (0≦X
≦l) is generally used by cutting out a wafer having a specific crystal plane from a bulk single crystal produced by a pulling method. However, high integration and
Due to the demand for multi-functionality and cost reduction, single-crystal thin film production technologies have been studied and as a result, sputtering method, ion blating method, liquid phase epitaxial method, CVD method, etc.
By the sol-gel method, etc., it has become possible to grow epitaxial crystals on single crystal substrates such as sapphire CR plane, 2 plane), crystal 02 plane), magnesium oxide Mg0 (txt) plane, etc.

On the other hand, LiNb1-xTaxO3 (0≦X≦1) is
Crystallographically, it is a material that belongs to the space group R8c and has large anisotropy in the C-axis direction of one ferroelectric axis.In device development, it is important to form a thin film with a single ferroelectric domain. desirable.

However, each of the above four substrate materials is crystallographically isotropic, and in order to have a single ferroelectric domain structure when used as a substrate and L7, it is necessary to perform poling treatment after thin film fabrication. It is necessary to apply

<Problem to be solved by the invention> As stated above, LiNb1-XTaXo3cO≦X≦
1) In the case of thin film fabrication, depending on the substrate material used, a poling process is required after fabrication, resulting in a lack of efficiency in film fabrication. To solve these problems, it is thought to be effective to use a material with lattice mismatch to the extent that heteroepitaxial growth is possible and a material with high crystallographic anisotropy (polarity) as the substrate material. . However, so far there have been no reports on such convenient substrate materials.

Means for Solving the Problems> Therefore, in order to solve the above problems, the present inventors developed a surface perpendicular to the piezoelectric direction of zinc oxide ZnO, a piezoelectric crystal widely used as a surface acoustic wave device. That is, (00
01) LiNb1-XTaXo3 using the surface as a substrate
(0≦X≦1) By producing a thin IA', Lit (bl-zTaz03 (0≦X≦1
) It was discovered that single-domain (0001) plane single crystal thin films can be produced.

Here, it is a piezoelectric crystal that lacks ZnO, has a space group P6Bm'lC@, and has anisotropy (polarity) in the C-axis direction.

Further, ZnO can be easily grown as a heteroepitaxial crystal on various substrates such as sapphire.

The lattice mismatch between the LiNb03 (0001) plane and the Zn0 (0001) plane is approximately 8.8-.

According to the present invention, metal Li or its oxide is used as the Li source, gold [Nb or its oxide] is used as the Nb source, metal, Ta or its oxide is used as the Ta source in an oxygen gas plasma atmosphere with Rf excitation (100 to 250 W), Knudsensel things,
After adjusting the heating temperature so that a predetermined amount of evaporation could be obtained independently using an electron beam heating device, etc., heteroepitaxial growth was performed on a Zn0 (0001) plane single crystal substrate or various substrates heated and maintained at a predetermined temperature. Z'n0(000
1) LrNb1-XTa with high purity and oriented in the ferroelectric axis direction by simultaneous vapor deposition on a planar thin film ophthalmic crystal substrate
z03 (0≦X≦1) #A-Ferroelectric area (δ001
) surface single crystal thin film can be obtained by poling treatment.

In addition, the device for heating the vaporized V source material in the present invention includes:
The heating device is not limited to the above-mentioned Knudsen cell or electron beam heating device, but any heating device that can heat the vapor deposition raw material to a predetermined temperature may be used.

Effect> According to the present invention, in an oxygen gas plasma atmosphere, without the presence of impurities other than the raw material elements corresponding to the constituent elements of the thin film,
Since the evaporation amount of each constituent element component is controlled independently and multiple components are simultaneously deposited on the substrate, different compositions can be obtained without changing the raw materials.
A high purity LiNJ-XTa) (03 (0≦X≦1) thin film can be obtained.

Furthermore, by using a zinc oxide Zn0 (0001) plane single crystal as a substrate, LtNbl in a single ferroelectric domain state can be obtained.
-)(Tax03 (0≦X≦1) It becomes possible to manufacture a single crystal thin film with good film thickness controllability.

<Examples> Examples of the present invention will be described below. However, the present invention is not limited thereby.

Example 1゜Electron beam heating device (244), Knudsen cell (1
In a vacuum chamber equipped with a working coil for high-frequency plasma generation (machine) and a working coil for high-frequency plasma generation, the inside of the vacuum chamber was first evacuated at 1 x 10 Torr, and then oxygen gas was introduced to 2 x 10 Torr to generate high-frequency plasma [frequency 13.56 MH2]. ) occurred. The Rf power at this time was 200W. Next, zinc Zn (purity 4N) was heated using an electron beam heating device and deposited on the sapphire (0001) surface heated and maintained at 400°C.
An O thin film was prepared.

The resulting ZnO thin film was confirmed to be a (0001) single-crystal thin film by RHEED and X-ray diffraction, and was further etched with a 20-inch HNO solution to make the thin film surface a cocol) zinc surface. I confirmed that it is.

Next, using this ZnO thin film as a substrate, LiNbx x
A thin film of Ta) (0≦X≦1) was prepared.The vacuum chamber was evacuated at 11×10-” Torr’!, and then oxygen gas was introduced to 2×10” Torr to generate high-frequency plasma. At this time, the Rf power was 200 W. Next, metal Nb (purity 4N) and metal Ta (purity 4N) were separately heated using an electron beam heating device, and metal Li (purity 4N) was heated using a Knudsen cell. After setting the heating temperature so that the predetermined amount of evaporation is achieved,
Co-evaporation was performed on the ZnO substrate on the rough 1 layer heated and maintained at 0°C. In this case, the emission current for electron beam heating was set to 150 mA from the Nb source and 50 mA from the Ta source, and the heating temperature of the Knudsen cell was set to 550'C. Approximately 1
By time evaporation, a transparent thin film with a film thickness of 100 mm was obtained.

The prepared thin film was analyzed using a secondary ion mass spectrometer (SIMS).
), it was found that IiNb (1g'rao
It was also confirmed that the diffusion of elements at the interface with the ZnO layer was extremely small. Next, we measured the X-ray diffraction pattern, and as shown in Figure 1, we found that sapphire, ZnO1L iNbg, g Ta (1,10
Only the (0001) plane reflection of 3 was observed, and LiNbo,
It was confirmed that gTao and lOs were also grown as heteroepitaxial single crystals on ZnO. Furthermore, the presence or absence of a domain structure was confirmed by etching using fluoronitric acid)
However, no etch pits or the like indicating a multi-regional structure were observed.

The above experimental results are L + N b 1-X T a
This shows that an X Os (O≦X≦1) single crystal thin film can be heteroepitaxially grown on a ZnO thin film single crystal, and also that it can be grown on a bulk ZnO single crystal substrate.

Example 2 In Example 1, a 5i (ill) crystal was used as the substrate material for producing the ZnO thin film. The conditions for forming the ZnO thin film on the Si substrate are the same as in Example 1.

The crystallinity and polarity of the obtained ZnO'll film were evaluated by RHEED, X-ray diffraction, and etching with a 20'L HNOs solution.

As a result, it was found that this ZnO thin film was a single crystal thin film with (0001) plane orientation. Next, L iN b 1-XTaxos (0≦
X≦1) The thin film was produced under the same film forming conditions as in Example 1. The composition and crystallinity of the obtained thin film were determined by SIMS,
As evaluated by line diffraction method, the composition is L i'Nbo
e It was confirmed that it was a single crystal thin film of Tao O1.

As a result of the above, LiNb1-x on the St (111) substrate
In the direct growth of Taxos (0≦X≦1), the lattice mismatch is very large, about 28 degrees, making heteroepitaxial growth difficult. However, by inserting a thin layer of ZnO as a middle layer, LiN1g-XTaxO3 (0≦ X≦1) This shows that a single crystal thin film can be produced even on a substrate with a large lattice mismatch. still.

LiNb0. It can be seen that the lattice mismatch between the (0001) plane of ZnO and ZnO is about 8 degrees, which is more advantageous than forming a film directly on a Si substrate.

According to the above embodiments, LiNb1-zTaxo
It was shown that s (0≦X≦1) single crystal thin film can be produced. Note that the substrate material for producing the ZnO single crystal thin film is not limited to the above-mentioned sapphire and Si. That is, substrate materials GaP (111), GaAs (111), and CdTe (1
11) When we performed a film formation experiment similar to the above using ZnS (111), we found that a LiNb1-XTaxO3 (0≦X≦1) single crystal thin film with good crystallinity could be obtained using these substrates. was confirmed.

<Effects of the Invention> According to the present invention, LiNb can be formed without poling treatment after film formation.
1-) It becomes possible to obtain a single crystal thin film with a single ferroelectric domain structure of (TaxO3(0QXQ1).Also, it is possible to obtain a single crystal thin film having a single ferroelectric domain structure of (TaxO3(0QXQ1).
It is also possible to produce an aXo3 (0≦X≦1) single crystal thin film. Therefore, for use in various device development,
In the production of a LiNb1-XTaXo3 (O≦X≦1) single crystal thin film, efficiency and cost reduction can be achieved.

[Brief explanation of the drawing]

The X-ray diagram shows an X-ray diffraction pattern of a thin film obtained in an example according to the present invention.

Claims (2)

[Claims] 1. In an oxygen gas plasma atmosphere, metal L is used as a Li source.
i or its oxide, metal Nb or its oxide as the Nb source, metal Ta or its oxide as the Ta source, and the amount of evaporation is controlled by independently adjusting the heating temperature, and when simultaneously depositing on the substrate, A method for producing a ferroelectric thin film, characterized in that the substrate temperature is maintained at 400 to 800° C. and a zinc oxide single crystal (0001) plane is used as the substrate. 2. The substrate according to claim 1 is made of sapphire (0001
), Si(111), GaP(111), GaAs(1
11) A method for manufacturing a ferroelectric thin film, characterized in that the film is a zinc oxide single crystal (0001) surface that is heteroepitaxially grown on either a CdTe (111) or ZnS (111) surface.