JP6933424B1 - How to grow SGGG single crystal and SGGG single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use an SGGG used for a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal substrate used for liquid-phase epitaxial growth of an oxide garnet single crystal film applied to a Faraday rotor of a high-power optical isolator. To provide a method for growing a single crystal. SOLUTION: This is a method for growing an SGGG single crystal represented by the composition formula (Gd, Ca, Ga, Mg, Zr) 8O12 by a rotation pulling method accompanied by a rotation reversal operation, and eight metal elements in the above composition formula. Among them, the raw material melt is set so that the total number of Gd elements and Ca elements is set in the range of 3.035 or more and 3.045 or less, and the number of Zr elements is set in the range of more than 0.640 and 0.650 or less. It is characterized in that the composition is prepared and grown. [Selection diagram] None

Description

The present invention relates to a method for growing a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal.

Optical isolators have a Faraday rotator that rotates the plane of polarization of incident light by applying a magnetic field, and in recent years, optical isolators have been used not only in the field of optical communication but also in fiber laser processing machines. It has become. Further, as a material for a Faraday rotator used in an optical isolator, an oxide garnet single crystal film such as a rare earth iron garnet (RIG) is known.

In the oxide garnet single crystal film, a CaMgZr-substituted gadolinium gallium garnet (Substituted Gd ₃ Ga ₅ O ₁₂ : SGGG) single crystal is used as a non-magnetic garnet single crystal substrate (seed crystal substrate), and a liquid phase epitaxial (Liquid) is used. It can be obtained by Phase Epitaxy (LPE) growth. The CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal is (Gd _3-x Ca _x ) (Ga _5-x-2y Mg _y Zr _{x + y} ) O ₁₂ , (Gd, Ca) ₃ (Ga). , Mg, Zr) ₅ O ₁₂ , (Gd, Ca, Ga, Mg, Zr) ₈ O _{12 and the} like.

As a method for growing a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal, a rotary pulling method such as the Czochralski (CZ) method is known. _{In the CZ method, a predetermined amount of Gd 2} O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , and CaCO ₃ mixed in advance is charged in a crucible arranged in a crystal growth furnace, and the raw material is heated and melted in the growth furnace. After obtaining the 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 to grow a single crystal. An SGGG single crystal having a shoulder and a straight body. Ingots are grown by the CZ method.

In order to process the grown SGGG single crystal ingot into a substrate shape, the shoulder portion of the SGGG single crystal ingot is cut by a device such as an inner peripheral blade cutting machine, and the obtained straight body portion is ground into a cylindrical shape and then inside. The wafer is cut into a wafer of a desired thickness with a peripheral blade cutting machine or a wire saw, and then the obtained wafer is polished under desired conditions to produce the non-magnetic garnet single crystal substrate (seed crystal substrate). ing.

In the growth of the SGGG single crystal ingot by the rotary pulling method such as the CZ method, first, the conical shoulder portion whose crystal diameter is gradually increased from the seed crystal is grown. The shoulders are grown using the "natural convection" of the melt generated by the temperature difference of the melt. On the upper surface of the melt in the crucible, the melt flows from the outer circumference toward the center, and the melt flows so as to slip into the melt under the seed crystal. In order to carry out crystal growth, the seed crystal is rotated relatively slowly, and the solid-liquid interface shape of the shoulder part that is grown becomes a convex shape toward the bottom of the crucible, reflecting the "natural convection" of the melt. go.

In the central portion of the shoulder portion, a portion (a portion called a core) having a high growth speed is formed due to the anisotropy of the crystal. Since the core has a slightly different lattice constant from its peripheral portion, distortion occurs between the core and its periphery, and a RIG single crystal film is used using an SGGG single crystal substrate (non-magnetic garnet single crystal substrate) in which the core exists. When liquid phase epitaxial (LPE) growth occurs, cracks occur in the RIG single crystal film. Therefore, the SGGG single crystal substrate having the core cannot be used as the seed crystal substrate.

Therefore, when growing an SGGG single crystal ingot by a rotation pulling method such as the CZ method, the rotation speed of the crystal (seed crystal) is rapidly increased at the stage where the crystal diameter of the shoulder is increased, and "forced" in the melt. "Convection" is generated to create a competitive state with the above "natural convection", the convex shape of the shoulder is melted to make the solid-liquid interface shape almost flat, and then a non-magnetic garnet single crystal substrate (for seed crystals). We are training a straight body that can be used as a substrate). A series of operations for rapidly increasing the rotation speed of the crystal to make the solid-liquid interface shape almost flat is called an "interface reversal operation", and the "interface reversal operation" causes the solid-liquid interface shape of the shoulder to be changed. Flattening is called "interfacial inversion".

The CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal is composed of 8 metal elements represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _{12 and 12 oxygen atoms.} Each element, not a coincident molten crystal, shows a slight segregation. As a result, the crystal composition is slightly different between the upper part and the lower part of the grown straight body portion, and it appears as a difference in lattice constant. Further, since the composition of the raw material remaining in the crucible after the crystal growth and the composition of the initial raw material are different, the initial raw materials (Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , which are premixed as described above, are used. When an _{SGGG single crystal is grown with (a raw material composed of CaCO 3} ), and in the subsequent growth, a raw material having the same composition as the initial composition is additionally charged to the raw material (raw material residue) remaining in the crucible, and the lattice is grown for each growth. The constants deviated, and as the SGGG single crystal was repeatedly grown, the lattice constant of the SGGG single crystal substrate sometimes did not fall within the desired numerical range. If the lattice constant deviates with each growth, cracks are likely to occur in the straight body grown during crystal cooling after the growth, and in particular, the diameter of the straight body is 80 mm or more and the length of the straight body is long. There was a problem that became noticeable when the diameter was 95 mm or more.

Therefore, in Patent Document 1, the total number of Gd elements and Ca elements is 3.06 or more among the eight metal elements represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _12. The composition of the raw material melt is prepared so as to be set in the range of 08 or less, and the state of the core existing in the center of the shoulder immediately before the above "interfacial inversion operation" is appropriately set (that is, the core is shouldered). It discloses a method of preventing it by forming it in a region within 31% of the radial direction of the shoulder portion from the center of the portion). According to the growing method disclosed in Patent Document 1, even if continuous growing with an additional charge of the raw material is performed, the deviation of the lattice constant for each growing is suppressed, and the straight body portion grown during crystal cooling after the growing is completed. Since cracks are less likely to occur in the segagaga single crystal, it is possible to grow the SGGG single crystal with good yield. The range of the lattice constant of the SGGG single crystal by this growing method is "12.4950 Å to 12.4990 Å", and the RIG single crystal film is formed by using the SGGG single crystal substrate (seed crystal substrate) outside this range. It is known that LPE growth causes a large deterioration in yield. Therefore, in order to stabilize the yield of LPE growth in the RIG single crystal film and reduce the variation in quality, the lattice constant of the SGGG single crystal substrate (seed crystal substrate) is controlled in the range of +/- 0.001 Å. Is required.

Japanese Unexamined Patent Publication No. 2017-20864

By the way, an optical isolator having a Faraday rotator made of a RIG single crystal film or the like has come to be widely used not only in the field of optical communication but also in a fiber laser machine as described above. In particular, optical isolators used in fiber laser processing machines have been required in recent years to withstand high output. Therefore, the RIG single crystal film applied to the optical isolator of the fiber laser machine has a larger lattice constant, which is superior.

However, the lattice constant of the RIG single crystal film is determined by the lattice constant of the SGGG single crystal substrate during liquid phase epitaxial (LPE) growth, and the range of the lattice constant of the SGGG single crystal by the growing method disclosed in Patent Document 1 is Since it is the above "12.4950 Å to 12.4990 Å", the SGGG single crystal having a lattice constant near the lower limit (12.4950 Å) is applied to the optical isolator (high output optical isolator) of the fiber laser processing machine. There was a problem that the RIG single crystal film could not be used as an SGGG single crystal substrate.

The present invention has been made by paying attention to such a problem, and the problem is that the lower limit of the lattice constant in the above range is relatively large, and the straight cylinder grown during crystal cooling after the growth is completed. An object of the present invention is to provide a method for growing an SGGG single crystal in which cracks are unlikely to occur in a portion.

Therefore, in order to solve the above-mentioned problems, the present inventors have repeated experiments and studies on a new policy of initial charge based on the growing method disclosed in Patent Document 1, and as a result, the above-mentioned composition formula (Gd, Ca) , Ga, Mg, Zr) ₈ Of the eight metal elements in the SGGG single crystal represented by O ₁₂ , "the total number of Gd elements and Ca elements" is not only controlled within a predetermined numerical range, but also the composition of Zr is controlled. I came to find that it can be solved by making fine adjustments. The method of avoiding crystal cracking during crystal cooling by appropriately setting the state of the core existing in the center of the shoulder immediately before the above-mentioned "interface inversion operation" is the same as the growing method disclosed in Patent Document 1. Is.

That is, the first invention according to the present invention is
In the method for growing a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _{12 by a rotation pulling method accompanied by a rotation inversion operation,}
Of the eight metal elements in the above composition formula, the total number of Gd elements and Ca elements is set in the range of 3.040 or more and 3.045 or less, and the number of Zr elements is set in the range of 0.645 or more and 0.650 or less. It is characterized in that the composition of the raw material melt is prepared and grown so as to be carried out.

The second invention is
In the SGGG single crystal represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _12,
Of the eight metal elements in the above composition formula, the total number of Gd elements and Ca elements is 3.072 or more and 3.076 or less, and the number of Zr elements is 0.660 or more and 0.670 or less. It is a feature.

According to the growing method according to the present invention
Composition formula of SGGG single crystal (Gd, Ca, Ga, Mg, Zr) Of the ₈ metal elements in 8 O ₁₂ , the total number of Gd and Ca elements is 3.040 or more and 3.045 or less, Zr element. In order to prepare and grow the composition of the raw material melt so that the number of the raw material melts is set in the range of 0.645 or more and 0.650 or less, only the total number of Gd element and Ca element is set in the predetermined numerical range (3). It is possible to stably grow an SGGG single crystal having a relatively large lattice constant as compared with the growing method of Patent Document 1 in which .06 or more and 3.08 or less) are managed.

Therefore, it has an effect of being able to provide an SGGG single crystal substrate (seed crystal substrate) used for LPE growth of a RIG single crystal film applied to a high-power optical isolator.

Hereinafter, embodiments of the present invention will be described in detail.

In the method of growing an SGGG single crystal by a rotary pulling method such as the CZ method in which an additional charge of a raw material is accompanied in the crucible, deterioration of the heat insulating material and deformation of the crucible shape in the crystal growing furnace progress as the number of times of growing increases. Therefore, it is basically difficult to reproduce the raw material melting state (furnace state) for each crystal growth in the same manner as the initial raw material melting state, and the amount of Ga evaporation cannot be matched within the permissible range for each crystal growth. .. Therefore, even if the additional charge composition is determined by keeping the segregation coefficient of each metal element represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _{12 constant and the SGGG single crystal is grown, the composition is composed.} The deviation gradually increases. In particular, the fluctuation of the Ga amount due to evaporation is difficult to control, and the fluctuation of the Ga amount affects the fluctuation of the lattice constant in the SGGG single crystal.

In the growing method disclosed in Patent Document 1, the "total number of Gd elements and Ca elements" fluctuates in the direction of maintaining 8 of the metal elements of the SGGG single crystal represented by the above composition formula, and the variation in the amount of Ga. However, in the growing method according to the present invention, in addition to the above-mentioned "total number of Gd element and Ca element", the fluctuation amount of Ga amount is also compensated by the number of Zr elements.

When the above-mentioned "total number of Gd element and Ca element" fluctuates so as to compensate for the fluctuation in the amount of Ga, if this fluctuation amount is large, crystal cracking occurs during crystal cooling after the completion of crystal growth. As described in.

In the growing method disclosed in Patent Document 1, among the eight metal elements in the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O ₁₂ , the "total number of Gd elements and Ca elements" is 3.060. When the content is set to 3.080 or less, the lattice constant can be stably grown in the range of "12.4950 Å to 124.990 Å" even if the SGGG single crystal is continuously grown with an additional charge of the raw material.

In the present invention, a new measure for initial charge is found based on the breeding method disclosed in Patent Document 1. That is, in the growing method according to the present invention, the "total number of Gd elements and Ca elements" is 3.040 or more among the eight metal elements in the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _12. The number should be 3.045 or less, which is lower than the "total number of Gd element and Ca element" in Patent Document 1. Further, the composition is set so that the "number of Zr elements" is in the range of 0.645 or more and 0.650 or less. The "number of Zr elements" has a correlation with the lattice constant, and increasing the value of the "number of Zr elements" tends to increase the lattice constant. Therefore, by managing the "number of Zr elements", it is possible to manage the lattice constant in a large direction. The "number of Zr elements" is generally 0.63, and by managing the "number of Zr elements" to be larger, the lattice constant can be managed to be larger. In particular, it is more preferable to set the "number of Zr elements" in the melt composition to be 0.645.

Next, the "total number of Gd elements and Ca elements" was set in the range of 3.040 or more and 3.045 or less, and the "number of Zr elements" was set in the range of 0.645 or more and 0.650 or less. As a result of analyzing the single crystal grown with the composition of the raw material melt, _{among the eight metal elements in the composition formula (Gd, Ca, Ga, Mg, Zr) 8} O ₁₂ , "the total number of Gd elements and Ca elements" Is 3.072 or more and 3.076 or less, and the "number of Zr elements" is in the range of 0.660 or more and 0.670 or less. When growing a single crystal, the "total number of Gd elements and Ca elements" increased from 0.030 to 0.036, and the "number of Zr elements" also increased from 0.015 to 0.020. .. It is presumed that the fluctuation of Ga was complemented by "Gd element and Ca element" and Zr element. In particular, by increasing the "number of Zr elements", the number of Zr elements in a single crystal is in the range of 0.660 or more and 0.670 or less, and the lattice constant can be increased. The lattice constant at this time was in the range of "12.4970 Å to 12.4990 Å", and the fluctuation range could be narrowed to 0.002 Å.

Next, a method for growing the SGGG single crystal will be described.

In the growth of the SGGG single crystal, cracks may occur in the straight body portion grown during crystal cooling after the growth is completed, resulting in crystal cracking. Crystal cracking during crystal cooling occurs when the core existing in the center of the shoulder immediately before the above-mentioned "interfacial inversion operation" is formed in a region exceeding 31% in the radial direction of the shoulder from the center of the shoulder, that is, "interfacial". It occurs remarkably when the size of the core existing in the center of the shoulder immediately before the "reversal operation" exceeds 31% in the radial direction of the shoulder, and the diameter of the straight body of the SGGG single crystal is 80 mm or more. Therefore, it occurs remarkably when the length of the straight body portion is 95 mm or more. The core existing in the shoulder is a region generated due to the growth of crystal facets, and appears near the center of the shoulder.

As described above, since the core has a larger lattice constant than the peripheral portion, distortion occurs at the boundary between the peripheral portion and the core. When the core region in the central portion of the crystal is large, the strain causes crystal cracking during crystal cooling.

For this reason, in the growth of SGGG single crystals, as described above, the core region is changed in the flow of the melt by using a technique called "interface inversion" (interface inversion operation) to flatten the solid-liquid interface, and then the straight body portion. We are training. Since the core does not exist in the straight body portion by the interface inversion operation, it is possible to reduce the distribution of the lattice constants in the wafer plane when the straight body portion of the SGGG single crystal is thinly cut into a wafer shape. In order to reduce the core size, it is effective to shorten the length of the shoulder portion.

Hereinafter, examples of the present invention will be specifically described.

[Example 1]
Composition formula (Gd, Ca, Ga, Mg , Zr) is 3.04 zero "Total number of Gd element and Ca element" of SGGG single crystal represented by ₈ O _12, "the number of Zr element" is 0.645 The amount of each element in the raw material melt was determined so as to be individual.

Then, by the Czochralski (CZ) method, the SGGG single crystal was grown so that the length of the shoulder portion was 75 mm, the diameter of the straight body portion was 80.5 mm, and the length of the straight body portion was 95 mm.

No crystal cracking occurred during cooling in the straight body portion of the obtained SGGG single crystal.

Furthermore, the straight body portion of the SGGG single crystal just before the end of growth was cut to obtain a 3-inch wafer (sample 1.1, sample 1.2 and sample 1.3) having a thickness of about 0.6 mm, and ICP and fluorescent X-rays were obtained. When the composition analysis was carried out in, the "total number of Gd element and Ca element", "number of Zr element", and lattice constant were the results shown in Table 1.

In each of the wafers (Sample 1.1, Sample 1.2 and Sample 1.3), the "total number of Gd elements and Ca elements" in the eight metal elements is in the range of 3.072 or more and 3.076 or less. The "number of Zr elements" also fell within the range of 0.660 to 0.670.

In addition, the lattice constant of each wafer falls within the range of "12.4970 Å to 12.4990 Å", and the SGGG single crystal substrate (for seed crystals) used for LPE growth of the RIG single crystal film applied to high-power optical isolators. It could be used as a substrate), and no cracks occurred in the wafer.

[Comparative Example 1]
Under the same conditions as in Example 1, 3.04 0 "Total number of Gd element and Ca element" of SGGG single crystal, "Zr number of elements" is 0.640 or a (0.645 or more requirements The amount of each element in the raw material melt was determined so as to be (not satisfied).

Then, the SGGG single crystal was grown so that the length of the shoulder portion was 75 mm, the diameter of the straight body portion was 80.5 mm, and the length of the straight body portion was 95 mm.

A 3-inch wafer (Sample 2.1 and Sample 2.2) having a thickness of about 0.6 mm was obtained by cutting the straight body portion just before the end of growing the SGGG single crystal, and the composition was analyzed by ICP and fluorescent X-ray. However, the "total number of Gd elements and Ca elements", "number of Zr elements", and the lattice constant are the results shown in Table 2.

Regarding the wafer (Sample 2.1), the "total number of Gd elements and Ca elements" among the eight metal elements was 3.071, which did not fall within the range of 3.072 or more and 3.076 or less, but the wafer. In (Sample 2.2), the "total number of Gd elements and Ca elements" among the eight metal elements was 3.073, which was in the range of 3.072 or more and 3.076 or less, and any wafer (sample). No cracks occurred in 2.1 and sample 2.2).

However, the "number of Zr elements" did not fall within the range of 0.660 to 0.670, and the lattice constant did not fall within the range of "12.4970 Å to 12.4990 Å". Therefore, it could not be used as an SGGG single crystal substrate (seed crystal substrate) used for LPE growth of a RIG single crystal film applied to a high-power optical isolator.

[Example 2]
The composition as in Example 1, i.e., formula (Gd, Ca, Ga, Mg , Zr) 8 O "Total number of Gd element and Ca element" of SGGG single crystal represented by ₁₂ 3.04 0, The amount of each element in the raw material melt is determined so that the "number of Zr elements" is 0.645, the raw material in the pit is melted, and then this condition is maintained for 24 hours or more to evaporate Ga. After urging, the SGGG single crystal was grown so that the length of the shoulder portion was 75 mm, the diameter of the straight body portion was 80.5 mm, and the length of the straight body portion was 95 mm.

Then, the straight body portion of the SGGG single crystal just before the end of growth was cut to obtain a 3-inch wafer (sample 3.1) having a thickness of about 0.6 mm, and the composition was analyzed by ICP and fluorescent X-ray. The "total number of Gd elements and Ca elements", "number of Zr elements", and the lattice constant are the results shown in Table 3.

Due to the increase in the amount of evaporation of Ga, the "total number of Gd elements and Ca elements" of the wafer (Sample 3.1) increased to 3.076, but the "number of Zr elements" was 0.660. It decreased slightly from Example 1.

In addition, the lattice constant of the wafer falls within the range of "12.4970 Å to 12.4990 Å", and the SGGG single crystal substrate (seed crystal substrate) used for LPE growth of the RIG single crystal film applied to high-power optical isolators. ), And the wafer did not crack.

With the same composition as in Example 1, it was confirmed that the lattice constant was within the target range even if the amount of evaporation of Ga increased slightly.

According to the method of the present invention, the total number of Gd elements and Ca elements among the eight metal elements in the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O ₁₂ of the SGGG single crystal is 3.040 or more 3 In order to prepare and grow the composition of the raw material melt so that the number of .045 elements and the number of Zr elements are set in the range of 0.645 or more and 0.650 or less, the total number of Gd elements and Ca elements is adjusted. It is possible to stably grow an SGGG single crystal having a relatively large lattice constant as compared with the method of Patent Document 1 which manages within a predetermined numerical range. Therefore, the grown SGGG single crystal has industrial applicability to be applied as an SGGG single crystal substrate for LPE growth of a RIG single crystal film used for a high-power optical isolator.

Claims (2)

In the method for growing a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _{12 by a rotation pulling method accompanied by a rotation inversion operation,}
Among the eight metal elements in the above composition formula, the total number of Gd elements and Ca elements is set in the range of 3.040 or more and 3.045 or less, and the number of Zr elements is set in the range of 0.645 or more and 0.650 or less. A method for growing an SGGG single crystal, which comprises preparing and growing the composition of the raw material melt so as to be carried out. In the SGGG single crystal represented by the composition formula (Gd, Ca, Ga, Mg, Zr) ₈ O _12,
Of the eight metal elements in the above composition formula, the total number of Gd elements and Ca elements is 3.072 or more and 3.076 or less, and the number of Zr elements is 0.660 or more and 0.670 or less. Characterized SGGG single crystal.