JPH0637352B2 - Manufacturing method of lithium oxide single crystal thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a lithium oxide single crystal thin film, and is particularly used for an optical device substrate.

(B) Conventional technology Lithium oxide single crystal LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) is used for application development in various devices by utilizing its many excellent characteristics. For example, a surface acoustic wave (SAW) device utilizing the fact that the electromechanical coupling coefficient is large, an optical waveguide utilizing the electro-optical effect, the nonlinear optical effect, etc., an optical switch, an optical modulator, an optical coupler, a wavelength converter. Substrate materials for optical integrated circuits, such as optical IC sensors that utilize the change in refractive index that is sensitive to changes in the external field, and optical memories and three-dimensional hologram materials that utilize the optical damage effect caused by doping impurities such as Fe. The field of applied research covers a wide range.

Conventionally, such LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) is generally used by cutting out a wafer having a specific crystal plane from a bulk single crystal produced by a pulling method. However, in many devices, it is only the tens of microns thick region of the crystal surface that actually functions, so a method for producing a single crystal thin film with a desired crystal plane orientation instead of an expensive bulk single crystal. Has been studied for a long time, and for example, LiNb
_{As a} thinning method for _1-x Ta _x O ₃ (0 ≦ x ≦ 1), a sputtering method, an ion plating method, a liquid phase epitaxial method, a CVD method, a sol-gel method, etc. have been reported. The choice of substrate material is an important factor in the success or failure of thinning of single crystals, and LiNb has been used as the substrate material used so far.
_1-x Ta _x O ₃ (0 ≦ x ≦ 1) single crystal, quartz (Z plane), sapphire (R plane, Y plane, Z plane), magnesium oxide ((111) plane)
Etc. Among these, a sapphire single crystal having a crystal structure similar to that of LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) is most often used for heteroepitaxial crystal growth using a different material substrate. Among them, in the (102) crystal lattice plane of sapphire, lattice mismatch of LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) single crystal is 6.
It is considered to be suitable for heteroepitaxial crystal growth because it is 7 to 8.3%, which is smaller than other crystal planes. The heteroepitaxial growth of a LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) single crystal thin film on the sapphire single crystal (102) crystal lattice plane is performed by, for example, sputtering (10).
0) LiNb _1-x Ta _x O ₃ (0 ≦ x ≦ 1) on the crystal lattice plane grows (Japanese Patent Publication No. 59-5560), while the ion plating method,
In the sol-gel method, it is reported that the same (102) crystal lattice (R-plane crystal lattice plane) as the substrate grows.

(C) Problems to be Solved by the Invention However, it is difficult to say that the technique for heteroepitaxial growth of a lithium oxide-based single crystal on a sapphire substrate is yet to be established, and its crystallinity is low, and optical application It has not reached the point where it can be sufficiently applied to the surface.

The present invention has been made to solve such a problem, and an object thereof is to provide a method for producing a highly crystalline lithium oxide single crystal thin film that can be used as a substrate for an optical device, for example.

(D) Means for Solving the Problems Therefore, the inventors of the present invention have conducted diligent research on the crystallinity improvement of the lithium oxide based single crystal thin film using the sapphire substrate by the ion plating method, and as a result, in the above heteroepitaxy. , (A) When the (102) crystal lattice plane of the lithium oxide single crystal is parallel to the (102) crystal lattice plane of the sapphire substrate, the [110] direction of the lithium oxide single crystal is [110] of the sapphire substrate. In parallel with the (b) direction, and (b) the crystallinity of the lithium oxide single crystal is improved, the R-plane crystal lattice plane ((102) crystal lattice plane) of the lithium oxide single crystal becomes ( The rotation axis is [110] with respect to the (102) crystal lattice plane, and [10]
The present invention has been achieved by finding the fact that it is inclined in the [0] direction.

According to this invention, the sapphire single crystal surface is
02) A sapphire single crystal substrate was obtained by processing a plane tilted from the crystal lattice plane in the [100] direction by 1 ° to 4 ° with the [112] direction as the axis of rotation, and the formula LiNb ₁ was formed on the processed substrate surface. _-x Ta _x O ₃ However, a lithium oxide single crystal represented by 0 ≦ x ≦ 1) is epitaxially grown to prepare a lithium oxide single crystal thin film having an R-plane crystal lattice plane parallel to the substrate surface. A method for producing a lithium oxide-based single crystal thin film is provided.

In the present invention, a sapphire single crystal substrate having a surface inclined in a specific angle range in a specific direction with respect to a crystal plane is used, and a lithium oxide based single crystal is deposited on the surface to form a single crystal thin film. The greatest feature is that it is manufactured.

It is suitable that the surface of the sapphire single crystal substrate is formed so as to be inclined with respect to the (102) crystal lattice plane of the sapphire substrate in the range of 1 ° to 4 ° with the [110] direction as a rotation axis. Among these, 2 ° to 3.5 ° is preferable, and 3 ° is particularly preferable. If it is out of this range, the crystallinity of the lithium oxide single crystal thin film formed on the surface of the substrate by heteroepitaxy is lowered, and it is not suitable for use as a substrate for optical devices, for example.

The surface of the sapphire single crystal substrate can be processed by ordinary cutting, grinding and polishing steps, and the surface can be identified as the target surface by X-ray diffraction.

The production of this single crystal thin film can be carried out by using various film forming means such as an ordinary sputtering method and an ion plating method. For example, the lithium oxide single crystal thin film of the present invention is produced by the ion plating method. , A sapphire substrate having the above specific surface was placed in a vacuum chamber equipped with an electron beam heating device, a Knudsen cell and a working coil for high frequency plasma generation. First, the vacuum chamber was set to 1 × 10 ^-8 Torr or less. After evacuating to vacuum, oxygen gas was introduced at 1 × 10 ^{−4 to} 5 × 10 ⁻⁴ Torr to generate high-frequency plasma. In this state, metal Nb and metal Ta were heated by an electron beam heating device, and metal Nb was heated by a Knudsen cell. After setting the heating temperature so that each Li has a predetermined evaporation amount independently, the surface of the sapphire substrate is heated and held at 600 to 800 ° C. It can be carried out by depositing at the time.

Note that the object of the present invention can be achieved even if a lithium oxide-based single crystal is used without using either Nb or Ta.

The surface of the lithium oxide single crystal thin film thus manufactured is an R-plane crystal lattice plane with high crystallinity and is formed parallel to the substrate surface.

(E) Action For the (102) crystal lattice plane of the sapphire substrate,
When a lithium oxide single crystal thin film is grown on a sapphire substrate surface inclined in the range of 1 ° to 4 ° with the [110] direction as a rotation axis, the lithium oxide single crystal thin film The R-plane lattice plane grows parallel to the surface of the sapphire substrate to improve the crystallinity of the lithium oxide single crystal thin film.

(F) Example One example of the present invention will be described below. The present invention is not limited to this.

Example 1 Electron beam heating device (2 units), Knudsen cell (1
Machine) and a working coil for high-frequency plasma generation inside, first evacuate the inside of the vacuum chamber to 1 × 10 ^-8 Torr and then add oxygen gas to 2
High frequency plasma was generated by introducing up to × 10 ^-4 Torr. The Rf power at this time was set to 200W. In this state, the sapphire substrate was heated and held at 700 ° C. after the metal Nb and the metal Ta were heated by the electron beam heating device and the metal Li was independently heated by the Knudsen cell so as to have a predetermined evaporation amount. Co-deposited on top. In this case, the electron beam heating emission current was set to 150 mA for Nb source and 50 mA for Ta source, and the heating temperature of the Knudsen cell was set at 550 ° C.
However, in the sapphire substrate, the substrate surface is [100] with the rotation axis in the [110] direction with respect to the R plane.
A substrate tilted by 3 ° was used. Thus, a transparent thin film having a film thickness of about 6000Å was obtained on this substrate after vapor deposition for 2 hours.

The composition of the prepared thin film was measured by the secondary ion mass spectrometer (SIM
S)), the thin film on this plate is LiNb _0.9 Ta _0.1
It was O ₃ and was found to be homogeneous throughout the film.

Next, the crystallinity was evaluated by X-ray diffraction, and as a result, it was found from this thin film that the Li
Rb reflection of Nb _0.9 Ta _0.1 O ₃ (102) (204) (3
Only 06) was observed. That is, it can be seen that an R-plane single crystal thin film was obtained.

As a result of further X-ray precession photography, it was confirmed that LiNb _0.9 Ta _0.1 O ₃ on the substrate showed spot-like diffraction points, and that this thin film was a single crystal thin film.

Next, in order to evaluate the crystallinity, LiNb _0.9 Ta _0.1 O ₃ (1
02) When the half-width of the rocking curve of reflection was measured, as shown in FIG. 2, the half-width (Δω) was about
It is 0.4 °, which is clearly smaller than about 1.0 ° of the comparative example described later, and it can be seen that the crystallinity is improved. This LiNb _0.9 Ta _0.1 O ₃ single crystal thin film is suitable as a substrate for optical devices. Was confirmed.

Comparative Example 1 A LiNb _0.9 Ta _0.1 O ₃ single crystal thin film was prepared in the same manner as in Example 1 except that a sapphire substrate whose surface was parallel to the R-plane lattice plane of this substrate was used in Example 1.

In order to evaluate the crystallinity of the obtained single crystal thin film, the rocking curve full width at half maximum of (102) reflection of LiNb _0.9 Ta _0.1 O ₃ was measured in the same manner as in Example 1, and it is seen in FIG. The full width at half maximum was about 1.0 ° and the crystallinity was low.

(G) Effect of the Invention By using the present invention, it is possible to provide a method for producing a lithium oxide single crystal thin film having high crystallinity which can be applied to, for example, an optical device substrate.

[Brief description of drawings]

FIG. 1 shows the LiNb _0.9 Ta _0.1 O ₃ obtained in the example of the present invention.
FIG. 2 is an X-ray diffraction pattern of the single crystal thin film, and FIG. 2 is a (102) plane reflection rocking curve diagram of the LiNb _0.9 Ta _0.1 O ₃ single crystal thin films obtained in Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] 1. A sapphire single crystal surface is provided with (102)
The [110] direction is the axis of rotation with respect to the crystal lattice plane and [1
[00] direction to form a sapphire single crystal substrate with a surface inclined by 1 to 4 degrees.
A lithium oxide single crystal thin film having an R-plane crystal lattice plane parallel to the substrate surface, which is obtained by epitaxially growing a lithium oxide single crystal represented by _1-x Ta _x O ₃ (where 0 ≦ x ≦ 1) A method for producing a lithium oxide single crystal thin film, which comprises: