JP5416041B2 - Single crystal substrate and method for manufacturing single crystal substrate - Google Patents

Description

  The present invention relates to a single crystal substrate that can be suitably used for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal and a method for manufacturing the same.

  Bismuth-substituted rare earth iron garnet single crystal grown on a single crystal substrate mainly by liquid phase epitaxy as a material for Faraday rotators used in optical isolators, optical circulators, optical magnetic field sensors, etc., which are indispensable in optical communication networks A membrane is used.

  In order to deposit this bismuth-substituted rare earth iron garnet single crystal film with high quality by epitaxial growth, the lattice constant difference between the bismuth-substituted rare earth iron garnet film and the single crystal substrate from the deposition temperature to room temperature is as small as possible. That is, it is necessary to use a single crystal substrate having a small lattice constant difference at room temperature and a close linear expansion coefficient.

As a single crystal substrate satisfying such a condition, Ca _x Nb _y Ga _z O ₁₂ (2.9 <x <3.1, 1.6 <y <1.8, 3.1 < z <3.3) Single crystals (hereinafter abbreviated as CNGG single crystals) have been proposed.
Patent Document 1 describes the crystal growth method of the CNGG crystal and the crystal quality.

The CNGG single crystal substrate used in this liquid phase epitaxial method can be pulled up by the Czochralski (hereinafter also referred to as CZ) method which is rich in mass productivity.
This CNGG single crystal substrate has an important lattice constant value of 12.50Å as a substrate crystal, which is close to the lattice constant of a bismuth-substituted rare earth iron garnet single crystal film, and has a coefficient of thermal expansion from room temperature to 850 ° C. It is attracting attention because it is as large as 10 × 10 ⁻⁶ / ° C., which is close to a substituted rare earth iron garnet single crystal film.
For this reason, as shown in Patent Document 2, the crystal pulling condition by the CZ method has been studied.

Japanese Patent Laid-Open No. 10-139596 JP 2005-89223 A

  However, as shown in FIG. 4 of Patent Document 2, a CNGG crystal having a composition formula as described in Patent Document 1 has a solid-liquid interface shape that protrudes upward when the single crystal is pulled up by the CZ method. However, there is a drawback that the diameter can only be raised by a method that is extremely difficult to control the diameter, resulting in a large problem in mass productivity.

  The present invention has been made in view of the above problems, and has a high quality indispensable for growing a bismuth-substituted rare earth iron garnet single crystal by liquid phase epitaxial growth. It is an object of the present invention to provide a single crystal substrate having a compositional formula that has a value that approximates the lattice constant of the material and that has a thermal expansion coefficient that is approximate, and that can be grown by an industrially advantageous CZ method, and a method for producing the same .

In order to solve the above-described problems, the present invention provides a single crystal substrate for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal having the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3.1) I will provide a.

Thus, the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9). By using a substrate made of a single crystal represented by <z <3.1), the garnet crystal structure can be stabilized and the quality can be improved. In addition, since the distortion is small and the crystal structure is stable, the production by the CZ method is easy, which is suitable for mass production.
In addition, its physical properties (lattice constant, linear thermal expansion coefficient, etc.) are very similar to those of bismuth-substituted rare earth iron garnet single crystals, and it is very useful as a substrate for liquid phase epitaxial growth of bismuth-substituted rare earth iron garnet single crystals. Is a suitable composition.
That is, the single crystal substrate is suitable for liquid phase epitaxial growth of a high-quality bismuth-substituted rare earth iron garnet single crystal, and is easy and inexpensive to mass-produce.

Here, it is preferable that the x satisfies the relationship x = 2 × y1 + y2.
Thus, when the relationship of x = 2 × y1 + y2 is satisfied, the single crystal becomes electrically neutral and becomes a high-quality single crystal with fewer crystal defects. Therefore, a suitable substrate can be obtained by growing bismuth-substituted rare earth iron garnet crystals by liquid phase epitaxy.

The present invention is also a method for producing a single crystal substrate for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal, and the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2 .9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3.1), and then pulling up the single crystal Provided is a method for manufacturing a single crystal substrate, wherein the single crystal substrate is manufactured by processing a single crystal into a substrate.

Thus, the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9). By using a single crystal represented by <z <3.1), the formula amount in the single crystal becomes stable, and a single crystal with good crystallinity can be easily pulled up by the CZ method. Then, by processing such a single crystal into a substrate through a general processing process, a substrate suitable for growing a bismuth-substituted rare earth iron garnet single crystal by a liquid phase epitaxial method is manufactured with high productivity. Can do.

Here, it is preferable that x satisfies the relationship x = 2 × y1 + y2.
Thus, by satisfying the relationship x = 2 × y1 + y2, x can be an electrically neutral single crystal, and a single crystal substrate with higher crystallinity can be obtained.

  As described above, according to the present invention, a single crystal substrate having a composition formula suitable for growing a bismuth-substituted rare earth iron garnet single crystal by liquid phase epitaxial growth and growing by an industrially advantageous CZ method, and its A manufacturing method is provided.

Hereinafter, the present invention will be described more specifically.
As described above, a single crystal substrate having a compositional formula that has a value that approximates the lattice constant of the bismuth-substituted rare earth iron garnet single crystal film and that also has a thermal expansion coefficient that can be grown by an industrially advantageous CZ method. The development of was awaited.

  Therefore, as a result of intensive studies, the present inventor can manufacture a high-quality single crystal by overcoming the compositional problems in the CNGG single crystal described in Patent Document 1, for example. The present invention has been completed by finding out what can be done.

Specifically, the present inventors tried to grow CNGG crystals by the Czochralski method based on the descriptions in Patent Documents 1 and 2.
However, as described above, in the method described in Patent Document 2, it is difficult to control the crystal including the diameter of the crystal to be pulled up, and the target bismuth-substituted rare earth iron garnet crystal has not been obtained.

Then, this inventor considered as follows why the crystal growth of the CNGG crystal as described in patent documents 1 and 2 becomes difficult.
The Ca ₃ Nb _1.7 Ga _3.2 O ₁₂ composition, which is a typical composition of the CNGG crystal described in Patent Document 1, is almost neutral electrically. That means
The number of cations is (2 ⁺ ) × 3 + (5 ⁺ ) × 1.7 + (3 ⁺ ) × 3.2 = 24.1
The number of anions is (2 ⁻ ) × 12 = 24
And is almost consistent.

On the other hand, the garnet crystal structure is generally represented by {c} ₃ {a} ₂ (d) ₃ O ₁₂ .
The CNGG crystal has no problem with the formula amount of 3.0 for the {c} site, but the {a} site is insufficient with Nb ⁵⁺ alone and Ga ³⁺ with a small ionic radius has to be forced to enter this site. (D) For the site, when Ga ³⁺ enters 0.3 formula amount into the {a} site, it becomes 2.9 formula amount.
For this reason, there is a possibility that defects may occur. Therefore, the CNGG crystal is easily distorted, and it is presumed that the growth is difficult because the crystal is distorted.
If the amount of Ga or Nb is increased, the number of cations increases this time, the electric neutrality cannot be maintained, and crystal growth becomes difficult.

On the other hand, as a result of intensive studies, the present inventor has solved the above problem occurring in the CNGG crystal with a new composition, that is, Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0 .9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3.1) and found that the problem can be solved, and the present invention has been completed.
For example, a composition of Ca _3.0 Nb _1.0 Ti _1.0 Ga _3.0 O ₁₂ can be electrically neutral. That means
The number of cations is (2 ⁺ ) × 3.0 + (5 ⁺ ) × 1.0 + (4 ⁺ ) × 1.0 + (3 ⁺ ) × 3.0 = 24.0
The number of anions is (2 ⁻ ) × 12 = 24.0
And can be matched perfectly.

And the formula weight of each site of the garnet crystal structure is that the {c} site has 3.0 formula weight of Ca ²⁺ ions having the largest ionic radius, and the {a} site has Nb ⁵⁺ having the next largest ionic radius. Ti ⁴⁺ each contains 1.0 formula weight, total 2.0 formula weight, (d) The cation site of garnet is reasonably easy because there is 3.0 formula weight of Ga ³⁺ with the smallest ion radius at the site. It can be an occupied structure.
As a result, this composition can easily grow crystals and does not generate distortion, so it is possible to grow high-quality large-diameter crystals relatively easily.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
A single crystal substrate of the present invention is for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal, and has a composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3.1).

Thus, the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9). The single crystal substrate represented by <z <3.1) has characteristics such as a lattice constant and a linear thermal expansion coefficient similar to those of a bismuth-substituted rare earth iron garnet single crystal, and has high quality by liquid phase epitaxial growth. A bismuth-substituted rare earth iron garnet single crystal can be grown.
In addition, since the composition formula is such that ions of appropriate ionic radii enter each site of the garnet crystal structure, the strain in the crystal is smaller than the conventional one, the crystal structure is stable, and the CZ method It is easy to grow with a manufacturing method suitable for mass production.

In the case of x ≦ 2.9 or x ≧ 3.1, the lattice constant and the linear thermal expansion coefficient are significantly different from those of the bismuth-substituted rare earth iron garnet single crystal, so that high-quality bismuth-substituted rare earth iron garnet single crystal is produced. It is not suitable for.
In the case of y1, y2 ≦ 0.9 or z ≦ 2.9, the number of cations is reduced, the electric neutrality is not maintained, and crystal growth becomes difficult. In the case of y1, y2 ≧ 1.1 and z ≧ 3.1, the number of cations increases and the electrical neutrality cannot be maintained, and the crystal growth is similarly difficult.
Therefore, in the single crystal substrate of the present invention, x, y1, y2, and z of the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ are 2.9 <x <3.1, 0.9 <y1 <1. It is assumed that the relationship of 1, 0.9 <y2 <1.1, 2.9 <z <3.1 is satisfied.

  Here, it is desirable that x satisfies the relationship of x = 2 × y1 + y2, whereby the number of cations and the number of anions in the single crystal coincide with each other, and it becomes electrically neutral. Therefore, it is possible to obtain a high-quality single crystal with few crystal defects, and a single crystal substrate that is very suitable for liquid phase epitaxial growth of a higher crystalline bismuth-substituted rare earth iron garnet single crystal.

  The single crystal substrate of the present invention as described above can be manufactured by a single crystal manufacturing method as exemplified below, but is not limited to this.

First, the composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3.1) Oxides or carbonates of elements (for example, CaCO ₃ , Nb ₂ O ₅ , TiO ₂ , Ga ₂ O _3, etc.) are mixed in a powder form so as to have a predetermined atomic ratio. And accommodated in a crucible of a single crystal manufacturing apparatus that is kept airtight.

  At this time, x can satisfy the relationship of x = 2 × y1 + y2, whereby an electrically neutral single crystal can be obtained, and a single crystal having higher crystallinity can be obtained. Can do.

Thereafter, the mixture is melted into a melt under a nitrogen atmosphere containing a small amount of oxygen.
Next, by moving the crystal pulling shaft downward, the seed crystal attached to the lower end thereof is brought into contact with the melt in the crucible.
Then, by pulling up while rotating the pulling shaft, the melt adhering to the lower end of the seed crystal is crystallized while solidifying to grow a single crystal.

The single crystal manufactured in this way has a composition formula of Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 < y2 <1.1, 2.9 <z <3.1).
A single crystal having such a composition formula has a stable formula amount in the single crystal and has a smaller amount of defects than conventional ones. And distortion is small, it is highly crystalline compared with the conventional CNGG type crystal | crystallization, and is high quality.
That is, such a single crystal is suitable as a single crystal substrate material for liquid phase epitaxial growth of, for example, a bismuth-substituted rare earth iron garnet single crystal.

  Thereafter, the grown single crystal is sliced by a cutting device such as an inner peripheral slicer or a wire saw, and then chamfering, lapping, etching, polishing, and the like are performed to form a substrate, thereby completing the single crystal substrate.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
99.99% pure calcium carbonate (CaCO ₃ ) raw material, 99.99% pure niobium oxide (Nb ₂ O ₅ ), 99.99% pure titanium oxide (TiO ₂ ), and 99.99% pure gallium oxide (Ga ₂ O ₃ ) was weighed so as to have a composition formula Ca ₃ NbTiGa ₃ O ₁₂ composition to prepare a raw material formulation.

Then, this preparation was mixed, put into a platinum crucible, and melted using a normal high-frequency heating furnace.
The shape of the platinum crucible was about 150 mm in diameter and about 150 mm in height. Further, as the seed crystal, a GGG crystal (Gd ₃ Ga ₅ O ₁₂ crystal) with a (111) orientation cut into a 10 mm square was used.
The growth was performed in an atmosphere in which the oxygen concentration was 2% and the rest was nitrogen gas, the gas flow rate was 1 liter / min, and crystal growth was performed by the CZ method according to a conventional method.

The grown crystal had a diameter of 80 mm and a length of 120 mm, and a transparent crystal could be obtained.
Both ends of the crystal were cut, and after cylindrical grinding, the wafer was cut into a wafer by an inner peripheral cutting machine, lapping and polishing were performed, and a wafer having a diameter of 76.2 mm and a thickness of 0.8 mm was produced.

When this wafer was etched with hot phosphoric acid, it was dislocation-free crystals.
And as a result of measuring the lattice constant of this crystal, it was 12.5012.
Moreover, as a result of measuring the thermal expansion coefficient from room temperature to 600 ^degreeC, it turned out that it approximates to the value of a common bismuth substituted rare earth iron garnet crystal with 9 * 10 < ^-6 > / degreeC.

Further, according to a conventional method, a bismuth-substituted rare earth iron garnet single crystal film represented by the composition formula (BiTbEu) ₃ (FeGa) ₅ O ₁₂ was grown on both surfaces of the wafer by liquid phase epitaxy according to a conventional method, and taken out at room temperature.
As a result, it was a very clean epitaxial film with no cracks observed.

Then, the epitaxial film is diced to 15 mm square, the wafer portion of the Ca ₃ NbTiGa ₃ O ₁₂ composition is cut with a wire saw, the composition is removed by lapping, and double-side polishing is performed. (BiTbEu) ₃ (FeGa) ₃ O ₁₂ crystal was taken out.
As a result of measuring the insertion loss and extinction ratio of this crystal at a wavelength of 1.55 μm, it was confirmed that the crystals were extremely large extinction ratios, that is, distortions were 0.08 dB and 43 dB, respectively.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims (4)

A single crystal substrate for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal,
Composition formula Ca _x Nb _y1 Ti _y2 Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2.9 <z <3 (1) A single crystal substrate represented by   The single crystal substrate according to claim 1, wherein x satisfies a relationship of x = 2 × y1 + y2. A method for producing a single crystal substrate for liquid phase epitaxial growth of a bismuth-substituted rare earth iron garnet single crystal,
By the Czochralski method, the composition formula Ca _x Nb _{y 1} Ti _{y 2} Ga _z O ₁₂ (2.9 <x <3.1, 0.9 <y1 <1.1, 0.9 <y2 <1.1, 2 . 9 <z <3.1) A method for manufacturing a single crystal substrate, comprising pulling up the single crystal and then processing the single crystal into a substrate to manufacture the single crystal substrate.   4. The method for manufacturing a single crystal substrate according to claim 3, wherein x satisfies a relationship of x = 2 * y1 + y2.