JP6369453B2 - Nonmagnetic garnet single crystal growth method - Google Patents

Description

The present invention relates a rotary pulling method _{(Gd 3-x Ca x)} (Ga 5-x-2y Zr x + y Mg y) nonmagnetic garnet represented by O ₁₂ (SGGG) single crystal to a method for growing, in particular Further, the present invention relates to a method for growing a nonmagnetic garnet single crystal whose dislocation density is within the standard.

  Bi-substituted rare earth iron garnet (Bi-RIG) is widely used as a material for a Faraday rotator used in communication optical isolators, and this Bi-RIG single crystal film is A non-magnetic garnet (SGGG) substrate is used as a seed substrate crystal and grown by a liquid phase epitaxy (LPE) growth method (see Patent Documents 1 and 2). In addition, in order to stabilize the growth of the Bi-RIG single crystal film, strict standards are set for the dislocation density of SGGG which is a seed substrate crystal.

The SGGG single crystal is grown by a rotational pulling method such as Czochralski (CZ) method, and premixed Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ and CaCO ₃ are placed in a crucible. After preparing a fixed quantity and heating and melting in a high-frequency furnace to obtain a raw material melt, the seed crystal is brought into contact with the raw material melt in the crucible, and the seed crystal is gradually pulled up while rotating the seed crystal to grow an SGGG single crystal. (See Patent Document 3). The diameter control of the SGGG single crystal during growth is performed automatically (auto diameter control: ADC), but the initial stage of growth of the SGGG single crystal is the value of the crystal weight used for the diameter calculation processing data of the ADC. Is small, and it is difficult to accurately perform the diameter calculation process, so manual control is performed, and automatic control becomes possible when the crystal diameter is approximately φ25 mm or more.

  Then, the upper and lower portions of the straight body portion of the grown SGGG single crystal ingot are cut into a wafer shape with an inner peripheral cutting machine to obtain an evaluation sample, and the evaluation sample is used as a mirror surface by using a polishing liquid such as colloidal silica. The SGGG substrate is finished, and the lattice constant and dislocation density of the SGGG substrate are measured to make a pass / fail judgment with respect to the standard.

JP 2003-238294 A JP 2003-238295 A JP 2005-029400 A

By the way, when the present inventor conducted an evaluation test on the conventional method in which the diameter control is manually performed and the crystal diameter is approximately φ25 mm or more, and the method is switched automatically, the average per field of 6.3 mm ² regarding the dislocation density of the SGGG substrate. It was found that the standard of 0.1 or less was not satisfied, and the conventional method had a problem that required improvement.

  The present invention has been made paying attention to such problems, and the object of the present invention is to provide a method for growing a nonmagnetic garnet single crystal in which the dislocation density is within the standard.

  Therefore, when the present inventors diligently investigated the cause of the dislocation density of the SGGG substrate grown by the conventional method being out of specification, the diameter of the SGGG crystal suddenly increased in the second half of manual control, and When the timing of diameter control to switch to automatic was too early, the fluctuation of the diameter became large, and it was confirmed that the dislocation was caused by the rapid diameter increase. The present invention has been completed by such technical discovery.

That is, the invention according to claim 1
How to train by rotation pulling method (including x = 0, y = 0) (Gd 3-x Ca x) (Ga 5-x-2y Zr x + y Mg y) magnetic garnet single crystal represented by O ₁₂ In the method of growing a non-magnetic garnet single crystal that is switched from manual to automatic diameter control of the crystal,
When the crystal diameter during growth is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance is 2.7 mm or less, and the timing of diameter control for switching from manual to automatic is greater than φ33 mm It is characterized by that.

According to the method for growing a non-magnetic garnet single crystal according to the present invention,
During crystal growth, when the crystal diameter is between 25 mm and 35 mm, the increase in diameter per 1 mm of crystal pulling distance is 2.7 mm or less, and the timing of diameter control to switch from manual to automatic is when the crystal diameter is 33 mm or more. Therefore, since the diameter of the single crystal to be grown does not increase rapidly, it becomes possible to suppress the occurrence of dislocations.

  For this reason, it has the effect that the nonmagnetic garnet single crystal whose dislocation density is within the standard can be stably grown.

105 field per area 6.3 mm ² plan view of the SGGG substrate average dislocation number is observed to (in one row 27 place × 4 columns, a total of 105 field for the center to 3 Ke duplicates). Diameter per 1 mm of crystal pulling distance according to Examples 1 to 7 and Comparative Examples 7 to 10 in which the crystal diameter when the diameter control is switched from manual to automatic (ADC) satisfies both the conditions of φ33 mm or more specified in the present invention increase (mm) "diameter increase per crystal pulling distance 1 mm (mm)" indicates the average dislocation number per field of view 6.3mm ² (/6.3mm ²⁾ when changing the diameter Skew "average The graph which shows the relationship with the number of dislocations (/6.3mm < ² >). Diameter control for switching from manual to automatic (ADC) according to Examples 1-7 and Comparative Examples 1-2, 4 and 6 in which the increase in diameter per 1 mm of the crystal pulling distance satisfies the condition of 2.7 mm or less specified in the present invention. field 6.3mm average dislocation number per ^{2 (/6.3mm 2)} indicates "ADC start diameter (mm)" and "average dislocation number when changing the crystal diameter (mm) at the timing of (/ 6 .3 mm ² ) ”. The relationship between “diameter increase (mm) per 1 mm of crystal pulling distance” and “ADC start diameter (mm)” according to Examples 1 to 7 and Comparative Examples 1 to 10 is shown, and the diameter control is automatically performed manually. Example 1 in which the crystal diameter when switching to (ADC) satisfies both the condition of φ33 mm or more specified in the present invention and the increase in diameter per 1 mm of the crystal pulling distance satisfies the condition of 2.7 mm or less specified in the present invention. FIG. 7 is a graph showing that 7 is within the standard (that is, pass “◯”), and Comparative Examples 1 to 10 that do not satisfy at least one of the above conditions are out of the standard (that is, fail “×”).

  Embodiments according to the present invention will be described below.

  First, when the present inventor investigated a lot whose dislocation density was out of specification, the SGGG single crystal diameter increased rapidly in the second half of manual control, and the pulling distance required for growth The diameter from φ15mm to φ25mm is 5.0mm, while the crystal diameter from φ25mm to 35mm grows at 1.7mm, and the timing of diameter control to switch from manual to automatic (ADC) It was when φ36.8 mm. Further, when the diameter increase of the SGGG single crystal is converted into a crystal diameter that increases per pulling distance of 1 mm (hereinafter sometimes referred to as “diameter inclination”), the former is 2.0 mm, while the latter is 6 mm. It was confirmed that the growth was as rapid as .9 mm.

  Further, in order to investigate the situation where dislocations propagate to the straight body portion of the SGGG single crystal ingot, the shoulder portion of the ingot is cut along the (112) plane orthogonal to the pulling-up axis (111) plane, When observed under polarized light by immersing in diiodomethane, the crystal diameter, which is the area of manual diameter control, propagates to the straight body perpendicular to the solid-liquid interface starting from dislocations generated at the in-plane center near φ30 mm. It was speculated that this sudden increase in diameter increased the stress on the crystal and caused dislocations.

  By the way, it is effective to make the temperature gradient in the growth atmosphere and the raw material melt steep in order to moderate the increase of the crystal diameter. As a method for realizing this, a work coil that generates a high frequency and heats the crucible It is conceivable to adjust the position of the crucible so that the heat generation at the lower part of the crucible becomes strong, thereby strengthening the “natural convection” (convection caused by the temperature difference in the raw material melt) in the raw material melt.

  Therefore, when SGGG single crystal was grown in a situation where “natural convection” was strengthened, the above-mentioned “diameter inclination” from a crystal diameter of φ25 mm to φ35 mm was 6.9 mm to 1.8 mm of the lot according to the conventional method. The dislocation generated in this portion can be suppressed.

  Next, under the above-mentioned conditions, when the diameter control timing for switching from manual to automatic (ADC) to reduce the shoulder scrap weight is when the crystal diameter is 30 mm, the crystal diameter fluctuates greatly after the ADC starts. Dislocation occurred at this position and propagated to the straight body of the SGGG single crystal ingot. In the conventional method, the crystal grew rapidly from φ25 mm to φ35 mm (the “diameter slope” was 6.9 mm), so it was estimated that the temperature gradient in the crucible radial direction in this range of raw material melt was small. It was. Note that it is actually difficult to measure the temperature of this portion because of the structure of the growth furnace.

  Therefore, based on the conditions confirmed in the examples described below, the inventors have found a method of manually controlling the diameter until the diameter of the crystal to be grown is less than 33 mm.

  Specifically, the diameter increase during the crystal pulling distance of 1 mm when the diameter of the growing crystal is between φ25 mm and φ35 mm is 2.7 mm (that is, “diameter slope” 2.7 mm) or less, and from manual to automatic By making the diameter control timing for switching the crystal diameter φ33 mm or more, an SGGG single crystal having a dislocation density within the standard can be obtained.

  In addition, it is not preferable to increase the diameter of the crystal at the timing of diameter control switching from manual to automatic (that is, the timing to start ADC) because the weight of the shoulder scrap increases and the raw material cost increases. Therefore, it is preferable that the crystal diameter at the timing of starting the ADC is set to φ33 mm or more as described above, and as small as possible in order to suppress an increase in raw material cost.

  Examples of the present invention will be specifically described below with reference to comparative examples.

[Example 1]
A predetermined amount of premixed Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , and CaCO ₃ is charged into an iridium crucible having a diameter of 150 mm and a height of 150 mm, and is heated and melted to 1750 ° C. in a high-frequency heating furnace. After obtaining the melt, the seed crystal is pulled up at a speed of 3 mm per hour while rotating the seed crystal 5 times per minute, and the gadolinium whose diameter is φ80 mm, which is the diameter of the straight body part, is the shoulder part and the subsequent part is gadolinium・ Gallium garnet single crystals were grown.

  As shown in Table 1, when the crystal diameter was between 25 mm and 35 mm, the increase in diameter per mm of crystal pulling distance (mm) was 2.7 mm, and the ADC starting diameter (mm) was 33.0 mm.

  The obtained single crystal was cut into a wafer shape with an inner peripheral blade and finished to a mirror surface using a polishing liquid such as colloidal silica to obtain an SGGG substrate, and then the dislocation density of the SGGG substrate was measured.

The dislocation density was measured by a method of observing the average number of dislocations with respect to 105 visual fields per area of 6.3 mm ^{2 of the} SGGG substrate shown in FIG.

As a result of the measurement, as shown in Table 1, the average number of dislocations was 0.06 (/6.3 mm ² ), and the dislocation density of all five growths was within the standard (see FIGS. 2 to 3).

[Example 2]
The diameter increase (mm) per 1 mm of the crystal pulling distance between the crystal diameters of φ25 mm and φ35 mm shown in Table 1 is 2.7 mm as in Example 1, and only the ADC starting diameter (mm) is 34.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which was the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 0.08 (/6.3 mm ² ), and all five growths were performed. The dislocation density was within specifications (see FIGS. 2 to 3).

[Example 3]
The position of the work coil is finely adjusted so that the strength of “natural convection” in the raw material melt changes, and the crystal diameter shown in Table 1 is between 25 mm and 35 mm and the increase in diameter per mm of crystal pulling distance (mm) is In the same manner as in Example 1 except that 2.4 mm and the ADC starting diameter (mm) is 35.0 mm, the shoulder portion is up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter. A single gadolinium gallium garnet single crystal was grown.

And as in Example 1, when the dislocation density of the obtained GGG substrate was measured, as shown in Table 1, the average number of dislocations was 0.02 (/6.3 mm ² ), and all five growth times The dislocation density was within specifications (see FIGS. 2 to 3).

[Example 4]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 2.0 mm, and the ADC starting diameter (mm) is 35.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1. As shown in Table 1, the average number of dislocations was 0 (/6.3 mm ² ), and the dislocation density for all five growths was Was within the standard (see FIGS. 2 to 3).

[Example 5]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 2.0 mm, and the ADC starting diameter (mm) is 37.8 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, when the dislocation density of the obtained GGG substrate was measured, as shown in Table 1, the average number of dislocations was 0.05 (/6.3 mm ² ), and all five growth times were performed. The dislocation density was within specifications (see FIGS. 2 to 3).

[Example 6]
By finely adjusting the position of the work coil, the crystal diameter shown in Table 1 is 1.9 mm and the ADC starting diameter (mm) is 36.2 mm per crystal pulling distance 1 mm between φ25 mm and φ35 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 0.01 (/6.3 mm ² ), and all five growth times The dislocation density was within specifications (see FIGS. 2 to 3).

[Example 7]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 1.8 mm, and the ADC starting diameter (mm) is 36.8 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1. As shown in Table 1, the average number of dislocations was 0 (/6.3 mm ² ), and the dislocation density for all five growths was Was within the standard (see FIGS. 2 to 3).

[Comparative Example 1]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is 1.9 mm and the ADC starting diameter (mm) is 25.0 mm per 1 mm of crystal pulling distance between φ25 mm and φ35 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 1.1 (/6.3 mm ² ), and all three growths were performed. The dislocation density was out of specification (see FIG. 3).

[Comparative Example 2]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 2.1 mm, and the ADC starting diameter (mm) is 28.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, when the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1, the average number of dislocations was 0.8 (/6.3 mm ² ) as shown in Table 1. The dislocation density was out of specification (see FIG. 3).

[Comparative Example 3]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between 25 mm and 35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 5.0 mm, and the ADC starting diameter (mm) is 30.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

And as in Example 1, when the dislocation density of the obtained GGG substrate was measured, as shown in Table 1, the average number of dislocations was 0.9 (/6.3 mm ² ), and all three growth times The dislocation density was out of specification.

[Comparative Example 4]
The diameter increase (mm) per 1 mm of the crystal pulling distance between the crystal diameters of 25 mm and 35 mm shown in Table 1 is 2.7 mm as in Example 1, and only the ADC starting diameter (mm) is 32.1 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which was the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 0.3 (/6.3 mm ² ), and all three growth times were observed. The dislocation density was out of specification (see FIG. 3).

[Comparative Example 5]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between Φ25 mm and Φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 2.8 mm, and the ADC starting diameter (mm) is 32.1 mm A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, when the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1, the average number of dislocations was 0.4 (/6.3 mm ² ) as shown in Table 1. The dislocation density was out of specification.

[Comparative Example 6]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is 2.6 mm and the ADC starting diameter (mm) is 32.5 mm per crystal pulling distance 1 mm between φ25 mm and φ35 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 0.3 (/6.3 mm ² ), and all three growth times were observed. The dislocation density was out of specification (see FIG. 3).

[Comparative Example 7]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance (mm) is 3.6 mm, and the ADC starting diameter (mm) is 33.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, when the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1, the average number of dislocations was 0.4 (/6.3 mm ² ) as shown in Table 1. The dislocation density was out of specification (see FIG. 2).

[Comparative Example 8]
By finely adjusting the position of the work coil, the crystal diameter shown in Table 1 is between φ25 mm and φ35 mm, the diameter increase per mm of crystal pulling distance (mm) is 3.6 mm, and the ADC starting diameter (mm) is 34.0 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, when the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1, the average number of dislocations was 0.4 (/6.3 mm ² ) as shown in Table 1. The dislocation density was out of specification (see FIG. 2).

[Comparative Example 9]
The position of the work coil is finely adjusted, and the crystal diameter shown in Table 1 is between Φ25 mm and Φ35 mm. The increase in diameter per mm of crystal pulling distance (mm) is 5.4 mm, and the ADC starting diameter (mm) is 36.8 mm A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, as in Example 1, the dislocation density of the obtained GGG substrate was measured. As shown in Table 1, the average number of dislocations was 0.7 (/6.3 mm ² ), and all three growths were performed. The dislocation density was out of specification (see FIG. 2).

[Comparative Example 10]
By finely adjusting the position of the work coil, the crystal diameter shown in Table 1 is 6.9 mm and the ADC starting diameter (mm) is 38.3 mm per 1 mm of crystal pulling distance between φ25 mm and φ35 mm. A gadolinium / gallium / garnet single crystal was grown in the same manner as in Example 1 except that the shoulder diameter was obtained up to φ80 mm, which is the crystal diameter of the straight body portion, and the straight body portion thereafter.

Then, when the dislocation density of the obtained GGG substrate was measured in the same manner as in Example 1, the average number of dislocations was 0.4 (/6.3 mm ² ) as shown in Table 1. The dislocation density was out of specification (see FIG. 2).

"Confirmation"
1. Requirements for diameter increase (mm) per 1 mm of crystal pulling distance when the crystal diameter is between φ25 mm and φ35 mm From the data shown in FIG. 2 based on Table 2 and Table 2 below, the crystal diameter during growth is from φ25 mm In Comparative Examples 7 to 10 not satisfying the requirement that the diameter increase per 1 mm of the crystal pulling distance between φ35 mm is “2.7 mm or less”, the average number of dislocations is 0.1 (/6.3 mm ² ) or less. It is confirmed that the standard is not satisfied (that is, a failure “x”).

2. Requirements for timing of diameter control to switch from manual to automatic From the data shown in FIG. 3 based on the following Table 3 and Table 3, the timing of diameter control to switch from manual to automatic is when the crystal diameter is “φ33 mm or more” In Comparative Examples 1-2, 4, and 6 that do not satisfy the requirements, it is confirmed that the average number of dislocations does not satisfy the standard of 0.1 (/6.3 mm ² ) or less (that is, the failure is “x”).

3. Examples 1 to 7 satisfying each requirement and Comparative Examples 1 to 10 not satisfying at least one requirement
From the data shown in FIG. 4, the diameter increase during the crystal pulling distance of 1 mm or less between φ25 mm and φ35 mm during growth is required to be “2.7 mm or less”, and the diameter control is switched from manual to automatic. In Examples 1 to 7 that satisfy both the requirements for the crystal diameter of “φ33 mm or more”, the average number of dislocations satisfies the standard of 0.1 (/6.3 mm ² ) or less (that is, “ O ”) was confirmed, and in Comparative Examples 1 to 10 that did not satisfy at least one of the above requirements, the average number of dislocations did not satisfy the standard of 0.1 (/6.3 mm ² ) or less (ie, failed) “×”) is confirmed.

  When a nonmagnetic garnet substrate obtained from a nonmagnetic garnet single crystal having a dislocation density within the standard according to the present invention is used, the magnetic garnet single crystal film grown on the substrate is a high-quality film free from crystal defects Therefore, it has industrial applicability that is used as a material for Faraday rotators for optical elements such as optical isolators.

Claims (1)

How to train by rotation pulling method (including x = 0, y = 0) (Gd 3-x Ca x) (Ga 5-x-2y Zr x + y Mg y) magnetic garnet single crystal represented by O ₁₂ In the method of growing a non-magnetic garnet single crystal that is switched from manual to automatic diameter control of the crystal,
When the crystal diameter during growth is between φ25 mm and φ35 mm, the increase in diameter per mm of crystal pulling distance is 2.7 mm or less, and the timing of diameter control for switching from manual to automatic is greater than φ33 mm A method for growing a non-magnetic garnet single crystal.

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