JP6350405B2 - Method for producing oxide single crystal - Google Patents

Description

  The present invention relates to a method for producing an oxide single crystal.

  Conventionally, oxide single crystals have been used for various applications, but there are cases where strict requirements are imposed on the range of lattice constants of seed substrate crystals and the like used for epitaxial growth.

  For example, a Bi-RIG (bismuth-substituted rare earth iron garnet) thin film crystal used for a communication optical isolator is grown by using a liquid phase epitaxial growth method using a SGGG (Substituted Gadolinium Gallium Garnet) substrate as a seed substrate crystal. In order to stabilize the growth of the Bi-RIG thin film crystal, there is a strict requirement for the range of the lattice constant of SGGG that is the seed substrate crystal.

The SGGG crystal is grown by the melt method, and the pulling method is often used. When growing an SGGG crystal by the pulling method, first, a predetermined amount of Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ and CaCO ₃ mixed in advance in a crucible is charged, and the raw material in the crucible is heated and melted in a high-frequency furnace or the like. A raw material melt is obtained. The seed crystal is brought into contact with the raw material melt in the crucible, and the single crystal can be grown by gradually pulling up while rotating the seed crystal.

  The amount of each raw material charged into the crucible is determined by the target lattice constant specification range (12.496 ± 0.001%) of the SGGG crystal to be grown, and an optimum amount of charging is obtained through repeated experiments.

For example, in Patent Document 1, a predetermined amount of Gd ₂ O ₃ , CaO, Ga ₂ O ₃ , MgO, ZrO ₂ and AO ₂ (A is an element selected from Si, Ge, or Ti) is charged in a crucible. It is disclosed that oxide garnet crystals are produced by heating and melting by high frequency induction and then pulling a single crystal from this melt by the Czochralski method.

Japanese Patent Publication No. 07-076156

  However, when the inventors of the present invention conducted a test, as in Patent Document 1, even when a raw material having a specific blending ratio was used, the lattice constant of the SGGG crystal obtained varied greatly, and SGGG having a desired lattice constant was obtained. In some cases, crystals could not be obtained. In addition to SGGG crystals, when a raw material containing gallium oxide is used and an oxide single crystal is grown by a melt method, the lattice constant varies greatly, and crystals having a desired lattice constant may not be obtained.

  Thus, in view of the above-described problems of the conventional technology, an oxide single crystal having a desired lattice constant is obtained when a single crystal containing gallium oxide is used to grow an oxide single crystal by a melt method. It aims at providing the manufacturing method of the oxide single crystal obtained.

In order to solve the above problems, according to one embodiment of the present invention, an oxide by a melt method using a raw material composed of Gd ₂ O ₃ , CaCO ₃ , Ga ₂ O ₃ , MgO, and ZrO ₂ is used. A method for producing a single crystal comprising:
When the melting point of the oxide single crystal to be produced is Tm,
From the formation of the raw material melt until the growth of the single crystal is completed, it is possible to provide a method for producing an oxide single crystal in which the surface temperature T of the raw material melt is controlled so as to satisfy the following formula (1). .

Tm + 5 ≦ T ≦ Tm + 30 (1)

  According to one embodiment of the present invention, an oxide single crystal having a desired lattice constant is obtained when an oxide single crystal is grown by a melt method using a raw material containing gallium oxide. A method can be provided.

The structural example of a single crystal growth apparatus.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.

  One structural example of the manufacturing method of the oxide single crystal of this embodiment is demonstrated below.

The manufacturing method of the oxide single crystal of this embodiment is related with the manufacturing method of the oxide single crystal by the melt method using the raw material containing a gallium oxide.
And when melting | fusing point of the oxide single crystal to manufacture is set to Tm, it can control so that the surface temperature T of raw material melt may satisfy | fill the following formula | equation (1).
T ≦ Tm + 30 (1)
The inventors of the present invention have studied the cause of the large variation in lattice constant when a single crystal containing gallium oxide is used to grow an oxide single crystal by the melt method, focusing on the surface temperature of the raw material melt. It was.

  Specifically, the case of an SGGG crystal was examined as an example of a single crystal grown using a raw material containing gallium oxide. In the examination, the SGGG crystal is grown a plurality of times by the pulling method single crystal growth apparatus shown in FIG. 1, and the maximum temperature of the surface of the raw material melt during the single crystal growth and the lattice constant of the grown SGGG crystal Measurements were made. From the measurement results, the existence of a correlation between the maximum temperature of the raw material melt surface and the lattice constant of the single crystal to be grown was examined.

  Here, the structure of the single crystal growing apparatus by the pulling method shown in FIG. 1 will be described.

  FIG. 1 schematically shows a cross section in a plane passing through the central axis of the crucible 11 provided in the single crystal growing apparatus 10.

  In the single crystal growing apparatus 10 by the pulling method shown in FIG. 1, a crucible 11 into which a single crystal raw material is placed is disposed on a crucible shaft 12 in a furnace body 15. In order to heat and melt the single crystal raw material, a (high frequency) heating coil 13 is disposed so as to surround the crucible 11. A heat insulating material 14 is provided around the inner surface of the furnace body 15 around the heating coil 13. In addition, a pulling shaft 16 that can move up and down is provided above the crucible 11 so as to penetrate the heat insulating material 14.

  A seed crystal 18 can be attached to the tip of the pulling shaft 16. The seed crystal 18 is brought into contact with the surface of the raw material melt 17 formed in the crucible 11, and then the seed crystal 18 is rotated by the pulling shaft 16. By pulling up, the crystal 19 can be grown.

  The single crystal growth apparatus 10 shown in FIG. 1 is provided with an observation window (not shown) so that the surface temperature of the raw material melt 17 can be measured from the observation window with a radiation thermometer. .

Then, the SGGG crystal is grown a plurality of times using the single crystal growth apparatus 10 shown in FIG.
In growing the SGGG crystal, first, the raw material powder having the composition shown in Table 1 was filled in the crucible 11 of the single crystal growing apparatus 10 and then heated by the heating coil 13 to form the raw material melt 17. Then, after bringing the seed crystal 18 into contact with the surface of the raw material melt 17, the SGGG crystal was grown by gradually pulling the seed crystal while rotating the seed crystal by the pulling shaft 16.

  In addition, as raw material powder with which the crucible 11 was filled, the raw material was weighed and mixed so as to have the composition shown in Table 1, and then calcined at 1350 ° C. for 6 hours to obtain SGGG.

ＳＧＧＧ結晶を複数回育成したところ、原料融液表面の最高温度は、ＳＧＧＧの融点１７３０℃よりも２℃〜７０℃高く、この範囲内でロット毎に原料融液表面の最高温度が異なっていた。そして、得られたＳＧＧＧ結晶の格子定数はロット毎にばらついていることが確認できた。以上の結果から原料融液表面の最高温度と、育成する単結晶の格子定数との間に相関があることが認められた。原料融液表面の最高温度の変化に伴い、ロット毎に格子定数が変わる原因としては、原料中に含まれる酸化ガリウムの蒸発量が一定ではないために、融液組成も異なり格子定数が安定しないためと考えられる。

When SGGG crystal was grown several times, the maximum temperature of the raw material melt surface was 2 ° C to 70 ° C higher than the melting point of SGGG 1730 ° C, and the maximum temperature of the raw material melt surface was different for each lot within this range. . And it was confirmed that the lattice constant of the obtained SGGG crystal varies from lot to lot. From the above results, it was confirmed that there was a correlation between the maximum temperature of the raw material melt surface and the lattice constant of the single crystal to be grown. The reason why the lattice constant changes from lot to lot as the maximum temperature of the raw material melt surface changes is that the evaporation rate of gallium oxide contained in the raw material is not constant, so the melt composition is different and the lattice constant is not stable. This is probably because of this.

  Therefore, in order to stabilize the evaporation amount of gallium oxide when the raw material powder is melted, the above-described case is performed except that the temperature of the raw material melt is controlled so that the surface temperature of the raw material melt is equal to or lower than the melting point of SGGG + 30 ° C. In the same manner, SGGG crystals were grown.

  As a result of adjusting the high frequency output applied to the heating coil 13 so that the surface temperature of the raw material melt does not rise too much with respect to the melting point of SGGG when the raw material in the crucible 11 is melted, the raw material melt when the raw material is melted is adjusted. The maximum temperature of the liquid surface was 1740 ° C. The obtained crystal was cut into a wafer shape with an inner peripheral blade and the lattice constant was measured to be 12.496 mm. This was confirmed to be within the range of 12.496 ± 0.001 mm which is the specification range of the lattice constant. ICP analysis of the wafer showed Ga weight% of 38.6%, confirming that it had the same composition as the raw material powder.

  From the above results, in the production of an oxide single crystal by a melt method using a raw material containing gallium oxide, the melting point Tm of the oxide single crystal to be produced and the surface temperature T of the raw material melt are expressed by the following equations: It was confirmed that an oxide single crystal having a desired lattice constant can be obtained by controlling so as to satisfy (1).

T ≦ Tm + 30 (1)
The surface temperature of the raw material melt preferably satisfies the above range from the formation of the raw material melt until the growth of the single crystal is completed. The completion of single crystal growth means, for example, when the grown single crystal is separated from the raw material melt in the case of a pulling method.

  According to further studies by the inventors of the present invention, by controlling the surface temperature T of the raw material melt to satisfy the following formula (2), an oxide single crystal having a desired lattice constant can be more reliably obtained. can get.

T ≦ Tm + 20 (2)
The lower limit of the surface temperature T of the raw material melt is not particularly limited, but it is preferable to satisfy Tm ≦ T so that the state of the raw material melt can be stably maintained, and Tm + 5 ≦ T is satisfied. It is more preferable to satisfy.

  Up to this point, the method for producing an oxide single crystal according to the present embodiment has been described with respect to an example in which an SGGG crystal is grown by a pulling method. However, the present invention is not limited to such a form, and a raw material containing gallium oxide is used. It can be applied to a method for producing an oxide single crystal by a melt method. As described above, as a result of the surface temperature of the raw material melt becoming higher, the gallium oxide is evaporated and the composition is shifted. As a result, conventionally, a single crystal having a desired lattice constant has not been obtained. However, it is because the evaporation of gallium oxide can be suppressed by keeping the surface temperature of the raw material melt within a predetermined range, and this phenomenon occurs in the entire melt method.

  As described above, the type of oxide single crystal manufactured in the method for manufacturing an oxide single crystal of the present embodiment is not particularly limited. However, it is preferable to apply the obtained single crystal to the production of an oxide single crystal for uses where the lattice constant is required to be within a predetermined range.

As described above, for the seed crystal substrate and the like used for epitaxial growth, there are cases where strict requirements are made regarding the range of the lattice constant. For this reason, it is preferable that the oxide single crystal manufactured with the manufacturing method of the oxide single crystal of this embodiment is a single crystal used as the raw material of the seed crystal substrate for epitaxial growth. In particular, the oxide single crystal manufactured by the oxide single crystal manufacturing method of the present embodiment is a gallium / gadolinium / garnet crystal that can be used for Bi-RIG (bismuth-substituted rare earth iron garnet) thin film crystal growth and the like. It is more preferable. In addition, the gallium / gadolinium / garnet crystal referred to here includes, in addition to the Gd ₃ Ga ₅ O ₁₂ crystal, an SGGG crystal in which a part thereof is substituted, specifically (GdCa) ₃ (GaMgZr) ₅ O ₁₂ or the like. These crystals are also included.

Specific examples and comparative examples will be described below, but the present invention is not limited to these examples.
[Example 1]
The SGGG single crystal was grown using the single crystal growth apparatus 10 shown in FIG.

As the crucible 11, an iridium crucible having a diameter of 150 mm and a height of 150 mm was prepared. Then, premixed Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , and CaCO ₃ were weighed and mixed in the crucible 11 so as to have the ratio shown in Table 1, and pre-calcined at 1350 ° C. for 6 hours. The raw material powder was filled.

  Then, the crucible 11 is placed on the crucible shaft 12 in the single crystal growth apparatus 10, and a high frequency output is applied to the heating coil 13, whereby the raw material powder in the crucible 11 is heated to 1730 ° C. or more, and the raw material melt 17 Formed. After the raw material melt 17 was formed, the high frequency output was controlled so that the surface temperature of the raw material melt 17 was not excessively higher than the melting point of SGGG to be grown until the growth of the single crystal was completed. Specifically, after the raw material melt was formed, the surface temperature of the raw material melt was controlled to be 5 ° C. or lower than the melting point of the SGGG crystal to be grown until the growth of the single crystal was completed. Therefore, in this example, the maximum temperature of the surface of the raw material melt was grown until the growth of the single crystal was completed after the formation of the raw material melt, that is, until the growth crystal and the raw material melt were separated. The temperature was 5 ° C. higher than the melting point of SGGG crystals.

  The surface temperature of the raw material melt was measured with a radiation thermometer from an observation window (not shown) provided in the single crystal growing apparatus 10.

  After forming the raw material melt 17, an SGGG crystal was grown as a crystal 19 by bringing the seed crystal 18 into contact with the surface of the raw material melt 17 and gradually raising the seed crystal 18 while rotating the seed crystal 18.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade, and the lattice constant was measured using a 4-axis X-ray diffractometer (Model: X'Pert PRO MRD, manufactured by PANalytical), which was 12.496 mm. Therefore, it was confirmed that a single crystal having a desired lattice constant was obtained within the range of 12.496 ± 0.001% which is the specification range of the lattice constant.

  Further, when the wafer was analyzed by an ICP emission analyzer (model: ICPS-8100, manufactured by Shimadzu Corporation), Ga was 38.7% by weight, and it was confirmed that it was almost the same as the composition in the raw material powder.

The results are shown in Table 2.
[Example 2]
Example 1 except that the surface temperature of the raw material melt was controlled to be 20 ° C. or higher than the melting point of the SGGG crystal to be grown until the growth of the single crystal was completed after the raw material melt was formed. In the same manner, SGGG crystals were produced. The maximum temperature on the surface of the raw material melt was 20 ° C. higher than the melting point of the SGGG crystal.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade and the lattice constant was measured using a 4-axis X-ray diffractometer to find 12.496 mm. Therefore, it was confirmed that a single crystal having a desired lattice constant was obtained within the range of 12.496 ± 0.001% which is the specification range of the lattice constant.

  Further, when the wafer was analyzed by an ICP emission spectrometer, Ga was 38.6% by weight, and it was confirmed that it was the same as the composition in the raw material powder.

The results are shown in Table 2.
[Example 3]
Example 1 except that the surface temperature of the raw material melt was controlled to be 30 ° C. higher than the melting point of the SGGG crystal to be grown until the growth of the single crystal was completed after the raw material melt was formed. In the same manner, SGGG crystals were produced. The maximum temperature on the surface of the raw material melt was 30 ° C. higher than the melting point of the SGGG crystal.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade and the lattice constant was measured using a 4-axis X-ray diffractometer to find 12.497 mm. Therefore, it was confirmed that a single crystal having a desired lattice constant was obtained within the range of 12.496 ± 0.001% which is the specification range of the lattice constant.

  Further, when the wafer was analyzed by an ICP emission spectrometer, Ga was 38.5% by weight, and it was confirmed that it was almost the same as the composition in the raw material powder.

The results are shown in Table 2.
[Comparative Example 1]
Example 1 except that the surface temperature of the raw material melt was controlled to be not more than 50 ° C. higher than the melting point of the SGGG crystal to be grown until the growth of the single crystal was completed after the raw material melt was formed. In the same manner, SGGG crystals were produced. The maximum temperature on the surface of the raw material melt was 50 ° C. higher than the melting point of the SGGG crystal.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade, and the lattice constant was measured using a 4-axis X-ray diffractometer. Therefore, it was outside the range of 12.496 ± 0.001 mm which is the specification range of the lattice constant.

  Further, when the wafer was analyzed by an ICP emission spectrometer, Ga was 38.1% by weight, and it was confirmed that the deviation from the composition in the raw material powder was large.

The results are shown in Table 2.
[Comparative Example 2]
Example 1 except that the surface temperature of the raw material melt was controlled to be not more than 35 ° C. higher than the melting point of the SGGG crystal to be grown until the growth of the single crystal was completed after the raw material melt was formed. In the same manner, SGGG crystals were produced. The maximum temperature on the surface of the raw material melt was 35 ° C. higher than the melting point of the SGGG crystal.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade and the lattice constant was measured using a 4-axis X-ray diffractometer to find 12.498 mm. Therefore, it was outside the range of 12.496 ± 0.001 mm which is the specification range of the lattice constant.

  Further, when the wafer was analyzed with an ICP emission analyzer, Ga was 38.4% by weight, and it was confirmed that the deviation from the composition in the raw material powder was large.

  The results are shown in Table 2.

表２に示したように、実施例１〜実施例３においては格子定数の仕様範囲内のＳＧＧＧ結晶を得られることが確認できた。特に実施例１、２においては、格子定数が、格子定数の仕様範囲の中央値となることが確認できた。

As shown in Table 2, in Examples 1 to 3, it was confirmed that SGGG crystals within the lattice constant specification range could be obtained. In particular, in Examples 1 and 2, it was confirmed that the lattice constant was the median value of the specification range of the lattice constant.

  On the other hand, in Comparative Examples 1 and 2, it was confirmed that the SGGG crystal had a lattice constant exceeding the specification range of the lattice constant. As is apparent from the results of ICP emission analysis, this is thought to be because Ga was evaporated during single crystal growth and the composition shifted.

  From the relationship between the above results and the maximum temperature of the surface temperature of the raw material melt when growing the single crystal, the surface temperature of the raw material melt is set to the melting point of the single crystal to be grown + 30 ° C. or less, thereby obtaining a lattice constant. It was confirmed that a single crystal within the specified range, that is, a single crystal having a desired lattice constant can be grown. In particular, it was confirmed that the lattice constant becomes the median value of the specification range of the lattice constant by setting the surface temperature of the raw material melt to the melting point of the single crystal to be grown + 20 ° C. or lower.

Claims (3)

A method for producing an oxide single crystal by a melt method using a raw material composed of Gd ₂ O ₃ , CaCO ₃ , Ga ₂ O ₃ , MgO, and ZrO ₂ ,
When the melting point of the oxide single crystal to be produced is Tm,
A method for producing an oxide single crystal in which the surface temperature T of the raw material melt is controlled so as to satisfy the following formula (1) from the formation of the raw material melt until the growth of the single crystal is completed .
Tm + 5 ≦ T ≦ Tm + 30 (1) The method for producing an oxide single crystal according to claim 1, wherein the surface temperature T of the raw material melt is controlled so as to satisfy the following formula (2) from the formation of the raw material melt until the growth of the single crystal is completed. .
Tm + 5 ≦ T ≦ Tm + 20 (2)   The method for producing an oxide single crystal according to claim 1 or 2, wherein the oxide single crystal to be produced is a gallium / gadolinium / garnet crystal.

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