JP2018052745A - Evaluation method of non-magnetic garnet single crystal substrate, production method of non-magnetic garnet single crystal substrate, and non-magnetic garnet single crystal substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method of a SGGG single crystal substrate for evaluating simply ease of cracking of the substrate, in a process for producing the substrate.SOLUTION: An evaluation method (S5) of a non-magnetic garnet single crystal substrate includes: etching the surface of the non-magnetic garnet single crystal C split into a prescribed thickness (S6); measuring a center position P2 of a growth striation by observing the growth striation of the etched substrate SA (S7); and evaluating ease of cracking of the substrate based on a distance between the center position P2 of the growth striation and a center position P1 of the substrate (S8).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for evaluating a nonmagnetic garnet single crystal substrate, a method for producing a nonmagnetic garnet single crystal substrate, and a nonmagnetic garnet single crystal substrate.

A Bi-substituted rare earth iron garnet (abbreviated as RIG) is widely used as a material for a Faraday rotator applied to a communication optical isolator. This RIG single crystal film has a liquid phase using a non-magnetic garnet (SGGG) substrate in which Ca, Mg, and Zr are added to a gadolinium gallium garnet single crystal (GGG: Gd ₃ Ga ₅ O ₁₂ ) as a seed substrate crystal. It is grown by an epitaxial (Liquid Phase Epitaxy: abbreviated as LPE) growth method (see, for example, Patent Documents 1 and 2 below). In order to stabilize the growth of the RIG single crystal film, it is necessary to match the lattice constants of the RIG single crystal film and the nonmagnetic garnet (SGGG) which is the seed substrate crystal. This SGGG substrate is produced by cutting an SGGG single crystal, and the nonmagnetic garnet single crystal is, for example, a CaMgZr-substituted gadolinium gallium garnet (SGGG) single crystal, (Gd _3−x Ca _x ) (Ga _5-x-2y Mg _y Zr _{x + y} ) O ₁₂ , (GdCa) ₃ (GaMgZr) ₅ O _12, etc.

The non-magnetic garnet (SGGG) single crystal used for the substrate is grown by a rotary pulling method of Czochralski (CZ) method. A predetermined amount of premixed Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , and CaCO ₃ is charged into a crucible, heated and melted in a high-frequency furnace to obtain a raw material melt, and then the raw material melt in the crucible The SGGG single crystal is grown by bringing the seed crystal into contact and gradually pulling up the seed crystal while rotating the seed crystal (see, for example, Patent Document 3 below). Next, the shoulder portion of the SGGG single crystal ingot is cut by a device such as an inner peripheral blade cutting machine to obtain a straight body portion, which is ground into a cylindrical shape, and an inner peripheral blade cutting machine, a wire saw, or the like After cutting into a wafer having a desired thickness, the wafer is polished under desired conditions to produce the non-magnetic garnet single crystal substrate (see, for example, Patent Document 4 below).

JP 2003-238294 A JP 2003-238295 A JP 2005-029400 A Japanese Patent Laying-Open No. 2015-086108

  Incidentally, as described above, in order to stabilize the growth of the RIG single crystal film, it is necessary to match the lattice constants of the RIG single crystal film and the nonmagnetic garnet (SGGG) single crystal substrate which is a seed substrate crystal. If these lattice constants are different, the SGGG single crystal substrate may be cracked when the RIG single crystal film is grown by LPE. This lattice constant can generally be measured by an X-ray diffraction apparatus (XRD). However, the measurement with this apparatus is performed in a state in which the substrate is finished, for example, in a state in which the substrate surface is polished and finished on a mirror surface. In addition, this measurement takes about one hour at one measurement point including measurement preparation and takes time. For this reason, the lattice constant has been measured only for evaluation such as sample evaluation of the final substrate. Therefore, after pulling up the single crystal, it was difficult to identify (evaluate) the quality of the lattice constant in the wafer-like substrate manufacturing process. In view of the above situation, an object of the present invention is to provide an SGGG single crystal substrate evaluation method that simply evaluates the ease of cracking of a substrate in a step of manufacturing the substrate.

  The present inventor has found that a growth fringe substantially equivalent to a growth fringe (striation) by X-ray topography can be easily detected in the etching process. The present inventor confirmed that the growth stripes obtained in this etching process are concentric growth stripes observed by photographing with X-ray topography, which is disclosed in an application (Japanese Patent Application No. 2006-025880) filed by the present applicant. When the center of the region is within 8 mm from the center in the SGGG single crystal substrate surface, the dispersion of the lattice constant is reduced, and the SGGG single crystal based on the knowledge that the SGGG single crystal substrate can be stably grown without breaking the SGGG single crystal substrate. The present invention was completed by finding that the method can be applied to a method for evaluating the ease of cracking of a crystal substrate.

  According to the first aspect of the present invention, etching the surface of the nonmagnetic garnet single crystal divided into a predetermined thickness, and observing the growth stripes on the etched substrate, the center position of the growth stripes is determined. There is provided an evaluation method for a non-magnetic garnet single crystal substrate, which includes measuring and evaluating the easiness of cracking of the substrate based on the distance between the center position of the growth stripe and the center position of the substrate.

  According to a second aspect of the present invention, in the first aspect, there is provided a method for evaluating a nonmagnetic garnet single crystal substrate, wherein the growth stripes are observed by visually observing an etched substrate illuminated with light. Provided.

  According to the third aspect of the present invention, there is provided a method for evaluating a magnetic garnet single crystal substrate, wherein in the first or second aspect, the etching amount of the etching process is 1.5 μm or more and 4 μm or less.

  According to the fourth aspect of the present invention, in any one of the first to third aspects, evaluating the ease of cracking of the substrate is that the distance between the center position of the growth stripe and the center position of the substrate is 8 mm. Evaluation of a non-magnetic garnet single crystal substrate that evaluates that it is easy to crack and is poor when it exceeds, and that it is hard to break and is good when the distance between the center position of the substrate and the center position of the growth stripe is within 8 mm A method is provided.

  According to the fifth aspect of the present invention, in any one of the first to fourth aspects, the evaluation of the ease of cracking of the substrate includes the distance between the center position of the growth fringe and the center position of the substrate, and non- There is provided a method for evaluating a nonmagnetic garnet single crystal substrate based on a distance from an interface inversion position when a magnetic garnet single crystal is manufactured.

  According to the sixth aspect of the present invention, in the fifth aspect, the evaluation of the ease of cracking of the substrate is easy to crack when the distance between the center position of the growth stripe and the center position of the substrate exceeds 8 mm. Non-magnetic garnet which is evaluated as being defective and evaluated as being difficult to break when the distance between the center position of the growth stripe and the center position of the substrate is within 8 mm and the distance from the interface inversion position is 40 mm or more. A method for evaluating a single crystal substrate is provided.

  According to a seventh aspect of the present invention, there is provided a method for producing a nonmagnetic garnet single crystal substrate, including the method for evaluating a nonmagnetic garnet single crystal substrate according to any one of the first to sixth aspects.

  According to an eighth aspect of the present invention, the method includes selecting a substrate based on an evaluation result obtained by the evaluation method for a nonmagnetic garnet single crystal substrate according to any one of the first to sixth aspects. Manufacturing method of magnetic garnet single crystal substrate.

  According to a ninth aspect of the present invention, there is provided a nonmagnetic garnet single crystal substrate manufactured from a straight body portion of a nonmagnetic garnet single crystal having a shoulder portion and a straight body portion, and is 40 mm or more from the interface inversion position. There is provided a non-magnetic garnet single crystal substrate manufactured from a straight body portion at a position and having a distance between the center position of the growth stripe and the center position of the substrate within 8 mm.

  According to the present invention, in the process of manufacturing a substrate from an SGGG single crystal, it is possible to easily evaluate the ease of cracking of the substrate.

  Moreover, since the manufacturing method of the SGGG single crystal substrate which concerns on this embodiment includes the evaluation method of the SGGG board | substrate which evaluates the ease of cracking of a board | substrate easily, the outstanding SGGG single crystal board | substrate can be manufactured easily. .

  Further, the SGGG single crystal substrate according to this embodiment can be suitably used for liquid phase epitaxial growth because cracking when used for liquid phase epitaxial growth is suppressed.

(A) is a flowchart which shows an example of the manufacturing method of a nonmagnetic garnet single crystal, (B) is a flowchart which shows an example of the manufacturing method of the SGGG single crystal substrate which concerns on this embodiment. It is a figure which shows an example of a nonmagnetic garnet single crystal. It is a figure which shows an example of the observation of the growth fringe of a board | substrate. (A) is a figure which shows the result of having observed the growth stripe of the board | substrate which carried out the etching process, (B) is a figure which shows the result of having observed the growth stripe on the board | substrate of (A) by the X-ray topography method. It is a figure explaining an example of the measurement of the center position of a growth stripe.

  The present invention will be described below with reference to the drawings. However, the present invention is not limited to this. Further, in the drawings, in order to describe the embodiment, the scale is appropriately changed and expressed by partially enlarging or emphasizing the description. In the following drawings, directions in the drawings may be described using an XYZ coordinate system. In this XYZ coordinate system, a plane parallel to the horizontal plane is defined as an XY plane. A direction perpendicular to the XY plane is expressed as a Z direction. In each of the X direction, the Y direction, and the Z direction, the direction of the arrow in the figure is the + direction, and the direction opposite to the arrow direction is the − direction. For example, the + Z direction is upward and the −Z direction is downward.

  Embodiments according to the present invention will be described below. First, an example of a manufacturing method (growing method) of a non-magnetic garnet (SGGG) single crystal will be briefly described. FIG. 1A is a flowchart showing an example of a method for producing an SGGG single crystal. FIG. 2 is a diagram illustrating an example of an SGGG single crystal.

For example, as shown in FIG. 2, the SGGG single crystal C is obtained by growing the shoulder portion 1 and the straight body portion 2 by a rotational pulling method. The SGGG single crystal C is, for example, a CaMgZr-substituted gadolinium / gallium / garnet single crystal (SGGG single crystal). SGGG monocrystal C, for example, a composition _{formula: (Gd 3-x Ca x} ) (Ga 5-x-2y Mg y Zr x + y) O 12 ( wherein, x is 0 ≦ x <3 real, y Has a composition represented by 0 ≦ y <2.5). Note that SGGG single crystal C is not limited to the above-described composition, and may contain other components.

  The SGGG single crystal C is grown (manufactured) using, for example, a crystal growing apparatus. The crystal growth apparatus used for the growth of the SGGG single crystal C is not particularly limited, and a known crystal growth apparatus capable of growing a crystal by a rotational pulling method can be used. For example, the crystal growth apparatus disclosed in JP-A-2015-134700 can be used as the crystal growth apparatus.

The SGGG single crystal C is grown by growing the shoulder 1 in step S1 of FIG. First, the crucible is filled with raw materials. As a raw material of the SGGG single crystal C, for example, gadolinium oxide (Gd ₂ O ₃ ), calcium carbonate (CaCO ₃ ), gallium oxide (Ga ₂ O ₃ ), magnesium oxide (MgO), and zirconium oxide (ZrO ₂ ) are used. The mixing ratio of these raw materials is determined by, for example, the composition of the single crystal to be grown and the growth conditions. In addition, a raw material is not limited to said thing, It is arbitrary. Subsequently, the raw material is melted by heating the crucible filled with the raw material in the furnace of the crystal growing apparatus. The melting temperature of the raw material is appropriately set according to, for example, the melting temperature of the raw material. Next, the seed crystal is brought into contact with the raw material melt to gradually lower the temperature, and at the same time, the seed shaft is pulled upward at a predetermined speed while gradually rotating the pulling shaft holding the seed crystal at a predetermined speed. This is performed by sequentially crystallizing the raw material melt on the lower side of the crystal. In the growth of the shoulder portion 1, the shoulder portion 1 having a desired diameter can be grown by adjusting the temperature, adjusting the pulling speed and rotating speed of the pulling shaft, and the like. For example, the shoulder 1 has a convex shape (eg, conical shape) on the raw material melt side in order to propagate dislocations generated by, for example, quenching the melt by the seed crystal during seeding to the crystal side surface. Cultivate. The convex portion can be formed into a desired shape by controlling the convection of the raw material melt, for example.

  Subsequently, when the crystal diameter of the shoulder 1 becomes a desired size, an interface inversion operation is performed in step S2 shown in FIG. In order to suppress the occurrence of distortion associated with facet growth by the interface inversion operation, the interface shape is made flat from a convex shape. Specifically, the interface is flattened by stopping the pulling of the crystal and increasing the rotation of the crystal. In the present specification, the shoulder 1 is from when the seed crystal is brought into contact with the raw material melt to start pulling up to when the interface inversion is completed. In this specification, the interface inversion position is a position where the interface inversion operation is started.

  Subsequently, after completion of the interface reversal, in step S3 shown in FIG. 1 (A), the pulling up of the seed crystal is resumed and the straight body portion 2 is grown. In the final stage of the growth of the straight body part 2 shown in FIG. 2, for example, the straight body part 2 is grown so that the lower end 2a of the straight body part 2 has a conical shape. This is to suppress the occurrence of transition that occurs when the straight body 2 is separated from the raw material melt and cooled.

  Through the above steps, SGGG single crystal C (see FIG. 2) having a desired diameter and length is grown. Then, the grown SGGG single crystal C is taken out from the crystal growth apparatus, subjected to annealing treatment to remove thermal strain, and then a nonmagnetic garnet single crystal substrate S (SGGG single crystal substrate S) having a thickness conforming to the standard. To be processed.

  By the way, the SGGG single crystal C is not a coincidence molten crystal, and the added elements (Ca, Mg, Zr) slightly show segregation, and the lattice constant changes depending on the concentration of each added element. . In particular, since the segregation of Zr that affects the lattice constant is larger than that of other constituent elements, the growth of single crystals by the rotary pulling method causes the Zr composition to fluctuate due to supercooling at the solid-liquid interface. Observed as stripes.

  Therefore, the relationship between the growth stripe (striation) and Zr which affects the lattice constant was examined. As a result, there is a relationship between the position of the center of the growth stripe (striation) and the center of the single crystal substrate, which are observed concentrically in the X-ray topography of the SGGG single crystal substrate, and the variation in the in-plane lattice constant. I found out. As disclosed in Japanese Patent Application No. 2006-025880, in particular, a concentric growth observed by X-ray topography on an SGGG single crystal substrate in which the position of the straight body portion is 40 mm or more from the interface inversion position When the center of the stripe is a region within 8 mm from the center of the SGGG single crystal substrate surface, it was confirmed that the dispersion of the lattice constant was reduced and stable LPE growth was possible without breaking the SGGG single crystal substrate. This makes it possible to identify the quality of the lattice constant by observing the growth stripes (striations) by X-ray topography without using an expensive X-ray diffraction apparatus (XRD).

  However, in the identification method by X-ray topography, for example, one piece is cut out from the effective portion 2b (see FIG. 2) of the straight body portion of the SGGG single crystal ingot, the warp of the substrate is removed by surface grinding, and polishing is performed. A substrate made into a mirror surface by processing or the like is photographed by X-ray topography. In the present specification, the “effective portion” means a portion of the straight body portion used for the SGGG single crystal substrate. For this reason, the measurement by X-ray topography requires about 40 minutes including the measurement preparation for each piece, and although it can be measured more easily than the measurement by the above-mentioned X-ray diffraction apparatus (XRD), a single crystal substrate is used. As an identification method in the manufacturing process, there is room for improvement in that it requires labor and time for measurement. For example, as a method for identifying the quality of each single crystal substrate, in the X-ray topography identification method, for example, when all about 70 substrates of the effective portion of the straight body portion of the SGGG single crystal C ingot are photographed, one sheet Since it takes about 40 minutes per operation, it takes about 46 hours in total, so observing the growth fringes on all the substrates has room for improvement in terms of work efficiency. For this reason, as a method of discriminating the quality of the sample in a short time, there are cases where the determination is made only with two substrates cut out from the top side 2d and the bottom side 2e of the effective portion 2b of the straight body portion. In this case, it was not possible to eliminate the crack defect even in the effective portion of the straight body portion of the substrate that was identified as having a good evaluation result.

  The SGGG single crystal substrate evaluation method, which is one of the features of the present invention, is to replace the X-ray topography observation, etching the surface of the substrate, and to show growth fringes that appear by etching processing almost equivalent to the growth fringes. By observing, the ease of cracking of the substrate is evaluated. This etching process is characterized in that it is one step of the manufacturing process of the SGGG single crystal substrate.

  Hereinafter, the manufacturing method of the SGGG single crystal substrate and the evaluation method of the SGGG single crystal substrate according to the present embodiment will be described in detail. FIG. 1B is a flowchart of a method for manufacturing an SGGG single crystal substrate according to the present embodiment.

  The manufacturing method of the SGGG single crystal substrate according to the present embodiment is a method of manufacturing the SGGG single crystal substrate S (see FIG. 2) from the SGGG single crystal C, and the evaluation of the SGGG single crystal for evaluating the fragility of the substrate. Including methods. In the SGGG single crystal C (see FIG. 2) used for manufacturing the SGGG single crystal substrate, for example, the effective portion 2b (see FIG. 2) of the SGGG single crystal C grown by the crystal growth apparatus described above has an inner peripheral blade. It is separated from the straight body part 2 by a cutting device or the like. In the SGGG single crystal C, the internal strain due to the interface inversion remains in the portion 2c from the interface inversion position to the upper end of the effective part 2b, which may cause cracks or cracks after crystal growth or during crystal processing. Further, as will be described later in Table 1, the SGGG single crystal substrate S may be cracked when a single crystal film such as RIG is manufactured by the LPE growth method using the SGGG single crystal substrate. For this reason, it is preferable that the length L1 from the interface reversal position to the upper end of the effective portion 2b is 40 mm or more. In this case, when the SGGG single crystal substrate S is used for the LPE growth method, a good SGGG single crystal substrate S which is difficult to break can be manufactured. Further, the straight body portion is horizontally cut by a cutting device or the like at a portion above the lower end portion 2a, so that the crystal is faced in the orientation (111) and becomes the lower end of the effective portion 2b. Thereafter, the effective portion 2b is trimmed by a cylindrical grinder.

  In the method for manufacturing the SGGG single crystal substrate, first, in step S4 shown in FIG. 1B, the effective portion 2b is divided by a predetermined thickness. For example, the effective portion 2b (see FIG. 2) is sliced and divided into a predetermined thickness by a cutting device such as a wire saw. Although this thickness is not specifically limited, For example, it is about 0.6 mm.

  Subsequently, in step S6 shown in FIG. 1B, the divided SGGG single crystal C substrate is etched. In the etching process, for example, the entire surface of the substrate surface and side surfaces are etched in order to prevent chipping of the substrate end face and scratches on the surface. In an ordinary SGGG single crystal substrate manufacturing method, following the etching process, in step S10 shown in FIG. 1 (B), mirror processing is performed to complete the SGGG single crystal substrate. Step S10 will be described later.

  The inventor has found that in the etching process of step S6, an etching pattern can be formed on the substrate surface that is substantially equivalent to a growth pattern by X-ray topography. Then, the present inventor has concentric circles in which the growth fringes obtained in this etching process are observed by photographing with X-ray topography disclosed in the above-mentioned application (Japanese Patent Application No. 2006-025880). Based on the knowledge that when the center of the growth stripe is in the region within 8 mm from the center of the SGGG single crystal substrate surface, the dispersion of the lattice constant becomes small, and stable LPE growth without breaking the SGGG single crystal substrate is possible. The present invention was found to be applicable to a method for evaluating the ease of cracking of a substrate, and the SGGG single crystal substrate evaluation method according to this embodiment was completed.

  Hereinafter, the evaluation method of the SGGG single crystal substrate according to the present embodiment will be described. In the SGGG single crystal substrate evaluation method S5 according to the present embodiment, as shown in FIG. 1 (B), the surface of the substrate having a predetermined thickness in step S4 described above is etched in step S6, and step S7 is performed. In step S8, the growth fringes of the etched substrate are observed to measure the center position of the growth fringes. In step S8, the substrate is easily cracked based on the distance between the center position of the growth fringes and the center position of the substrate. To evaluate.

  The etching process in step S6 is the same as the etching process that is normally performed in the process of manufacturing the SGGG single crystal substrate, for example. The etching process is performed, for example, by holding the substrate with a rack or the like and immersing it in an etching solution. The etching solution is a solution that is usually used for etching an oxide single crystal. For example, a mineral acid such as phosphoric acid, sulfuric acid, nitric acid, and hydrofluoric acid can be used. Among them, phosphoric acid and sulfuric acid are 1: 1. It is preferable to use a mixed solution (generally referred to as phosphoric sulfate) mixed at a ratio of The concentration of the acid in the etching solution is not particularly limited, and is a known concentration that is usually used for etching an oxide single crystal. The etching amount is preferably 1.5 μm or more and 4 μm or less. When the etching amount is less than 1.5 μm, the etching amount is small, so that scratches and cracks are not prevented. Moreover, when the etching amount exceeds 4 μm, the thickness of the finally manufactured substrate may be smaller than a set value (target value). The etching amount can be controlled, for example, by adjusting the processing time of the substrate with the etching solution. By this etching process, the surface of the substrate becomes a satin finish. After the treatment with the etchant, the substrate is washed with pure water or the like, and the etching process is completed.

  After completion of the etching process, in step S7 shown in FIG. 1B, the growth fringes of the substrate are observed, and the center position of the growth fringes is measured. For the observation of the growth stripes on the substrate, for example, the substrate illuminated with light is observed. FIG. 3 is a diagram illustrating an example of observation of growth stripes on the substrate. For example, as shown in FIG. 3, the substrate SA after etching is placed on a light-transmitting member 4 such as a glass plate, and the illumination device 5 is observed from below the light-transmitting member 4. The substrate SA that has been transmitted and illuminated by irradiating light can be observed by visual observation. By observing the growth stripes on the substrate in this way, the growth stripes (reference numeral Q1 shown in FIG. 4A) inside the substrate can be observed. As described above, the growth fringe has a subtle composition, particularly the additive element concentration (in the case of SGGG, the amount of Ca, Mg, and Zr taken into the crystal) due to periodic temperature changes and crystal growth rate changes during crystal growth. However, since the refractive index of the crystal slightly changes as the composition of the crystal surface changes due to the etching, it is possible to observe a stripe substantially equivalent to the growth stripe.

  By the way, in the case of a mirror-finished substrate, which is a finished surface, the light passes through even if light is irradiated, so it is impossible to observe the growth fringes inside the substrate. Generally, the X-ray topography method is used to observe the growth fringes. Used for. Conversely, in the X-ray topography method, if the surface of the substrate is uneven, X-rays are scattered and an image cannot be acquired.

  On the other hand, the surface of the substrate SA after the etching process described above has irregularities of several μm, and on the surface having irregularities of several μm, the irradiated light is diffusely reflected inside the substrate and transmitted through the substrate. It is possible to observe growth fringes on the surface. FIG. 4A is a view showing the result of observing the growth stripes of the substrate after etching the substrate in step S7, and FIG. 4B is a diagram showing the growth of the substrate of FIG. It is a figure which shows the result of having observed the fringe. Note that the growth fringes are denoted by reference sign Q1 in FIG. 4A and denoted by reference sign Q2 in FIG. 4B. In FIG. 4A, the growth fringes Q1 are indicated by dotted lines, but the growth fringes Q1 are visually observed in the same manner as the growth fringes Q2 in FIG. 4B. Table 1 shows the results of measuring and comparing the distance between the center position P2 of the growth fringe and the center position P1 of the substrate by X-ray topography and observation after etching on the same substrate. As can be seen from FIGS. 4A and 4B and Table 1, the measured growth fringe center positions P2 are substantially the same. Thereby, it turns out that it can replace with X-ray topography and observation after an etching process is possible.

  For example, a general incandescent bulb, a fluorescent lamp, and a light emitting diode (LED) can be used as the illumination device 5 (see FIG. 3) used for the observation of the growth stripes. For this reason, the growth fringes can be easily observed with an inexpensive apparatus. Further, the growth fringes can be easily observed with an inexpensive apparatus because the growth fringes of the substrate are visually observed with the transmitted illumination as described above. The observation of the growth fringes is not limited to visual observation with transmitted illumination, and may be performed by other means or methods. For example, the observation of growth fringes may be performed by epi-illumination, may be performed using an observation device such as a microscope (stereomicroscope), or may be performed using an imaging device such as a camera (digital camera, video camera). Or you may observe through a polarizing filter.

  In step S7, the center position of the growth fringe is measured when observing the growth fringe on the substrate as described above. The measurement of the center position of the growth stripe can be performed visually. The center position of the growth fringe is determined, for example, by measuring the center position of the innermost (most central side) growth fringe among the plurality of growth fringes observed visually. For example, the center position of the growth stripe is measured by placing a sheet member 6 formed of a transparent material or the like on a substrate illuminated with light, as shown in FIG. This is performed by recording the outer shape of the pattern and the center position of the growth stripe measured as described above. In this case, the center position of the substrate may be measured and recorded on the sheet. If the innermost (most central) growth stripe is not clear, the center of the growth stripe located outside the innermost growth stripe may be set as the center position of the growth stripe. In addition, when the outline of the growth stripe is unclear, for example, when the growth stripe or the inside (center side) of the growth stripe is observed in light and dark, the center of the growth stripe observed in light and dark can be used as the center position of the growth stripe. Good. Moreover, the measuring method of the center position of the growth stripe is not limited to the above example, and is arbitrary. For example, the growth fringe may be measured using an image acquired by an imaging device such as a camera (digital camera, video camera). In this case, you may measure using a computer apparatus.

  Subsequently, in step S8 shown in FIG. 1B, the ease of cracking of the substrate is evaluated based on the distance between the center position of the growth stripe and the center position of the substrate.

  As described in Japanese Patent Application No. 2006-025880 filed by the present applicant, the center of the growth stripes (striations) observed in the X-ray topography of the non-magnetic garnet (SGGG) single crystal substrate and the center of the single crystal substrate And the variation of the in-plane lattice constant, and the position of the straight body portion is observed with X-ray topography on a single crystal substrate 40 mm or more from the interface inversion position. When the center of the concentric growth stripe is within 8 mm from the center of the SGGG single crystal substrate surface, it is confirmed that the dispersion of the lattice constant is reduced and stable LPE growth is possible without breaking the SGGG single crystal substrate. Has been. As described above, in this embodiment, instead of the X-ray topography, the center position of the growth stripe can be obtained by observation after etching processing. Therefore, the SGGG single crystal substrate according to this embodiment This evaluation method can easily evaluate the ease of cracking when the substrate is used in the LPE growth method.

  More specifically, as a result of investigating the relationship between the distance between the center position of the substrate and the center position of the growth stripe and the crack defect when used in the LPE growth method, as shown in Table 1, the center position of the growth stripe is It is recognized that when the distance from the center position of the substrate is large, the substrate breaks when the substrate is used in the LPE growth method. When the distance of the center position of the growth stripe exceeds 8 mm, a problem that the substrate breaks occurs. Therefore, in this step S8, when the distance between the center position of the growth stripe and the center position of the substrate exceeds 8 mm, it is evaluated that it is easily broken and defective, and the distance between the center position of the substrate and the center position of the growth stripe is In the case of 8 mm or less, it is evaluated as being difficult to break and good. Further, as shown in Table 1, when the distance from the interface inversion position on the substrate is 40 mm or more, it is recognized that the substrate is difficult to break when used in the LPE growth method. When the distance is less than 40 mm, when the substrate is used in the LPE growth method, it is recognized that the substrate is easily broken and defective. As described above, the evaluation of easiness of cracking when the substrate is used in the LPE growth method is performed based on the distance between the center position of the growth stripe and the center position of the substrate and the distance from the interface inversion position of the substrate. preferable. For example, when the substrate is 40 mm or more from the interface inversion position and the distance between the center position of the substrate and the center position of the growth stripe is within 8 mm, it is preferable that the substrate is difficult to break when used in the LPE growth method. evaluate.

  In addition, regarding the distance between the center position of the substrate and the center position of the growth stripe and the variation in the lattice constant in the plane of the substrate, as described in Japanese Patent Application No. When the distance is 40 mm or more and the distance between the center position of the substrate and the center position of the growth stripe is 8 mm or less, the variation of the lattice constant in the plane of the substrate is 0.002 mm or less and the variation is small. When used in the LPE growth method, it is difficult to break and is good. On the other hand, when the distance between the center position of the substrate and the center position of the growth stripe exceeds 8 mm, the variation of the lattice constant in the plane of the substrate exceeds 0.002 mm, and the variation is large, so that it is easily broken. As described above, the evaluation of the variation of the lattice constant in the plane of the substrate can be evaluated based on the distance between the center position of the growth stripe and the center position of the substrate. The center position of the growth stripe and the center position of the substrate can be evaluated. And the distance from the interface inversion position of the substrate.

  Note that the evaluation of the ease of cracking of the substrate in this step S8 may not be performed on all the substrates obtained by dividing the effective portion 2b. For example, you may perform with respect to the at least one part board | substrate which divided | segmented the effective part 2b. In this case, it is possible to easily evaluate whether or not at least the SGGG single crystal C used for production is good. For example, the evaluation of the ease of cracking of the substrate in this step S8 may be performed on the top substrate 2d and the bottom substrate 2e (see FIG. 2) of the effective portion 2b.

  Subsequently, in step S9 shown in FIG. 1B, a substrate is selected based on the evaluation result obtained in step S8. For example, in step S8, a substrate that is determined to be difficult to break when the substrate is used in the LPE growth method is selected. As described above, since a good substrate can be selected, time for processing a defective substrate can be omitted. Whether or not this step S9 is performed is arbitrary. For example, as described above, it is possible to easily determine whether the SGGG single crystal C used for manufacturing is good by performing the evaluation in step S8 on at least a part of the substrate obtained by dividing the effective portion 2b. When used for evaluation, this step S9 may not be performed.

  When the evaluation of the substrate is observed after the etching process as in the method for evaluating the SGGG single crystal substrate, the etching process is one process of the substrate manufacturing process, and the evaluation of the substrate itself is about 3 minutes per one sheet. The man-hours are small and the time required is short. For this reason, this SGGG single crystal substrate evaluation method can evaluate the total number of substrates as required. Incidentally, in the case of X-ray topography, the measurement time is as long as 40 minutes per sheet because it takes time to process the substrate until measurement.

  Subsequently, in step S10 shown in FIG. 1B, the substrate is mirror-finished. For example, polishing by mechanical polishing using colloidal silica or the like is performed, and the substrate surface is mirror-finished. Through the above steps, the SGGG single crystal substrate S is completed. In addition, the method of mirror finishing of a board | substrate is not limited to the said method, It is arbitrary. For example, the mirror finishing may be performed by chemical physical polishing.

  As shown in FIG. 2, the SGGG single crystal substrate S manufactured by the above manufacturing method or the like has a SGGG single crystal manufactured from the straight body portion 2 of the SGGG single crystal C including the shoulder portion 1 and the straight body portion 2. The substrate S is manufactured from the straight body portion 2 at a position 40 mm or more from the interface inversion position, and the distance between the center position of the growth stripe and the center position of the substrate is within 8 mm. Since the SGGG single crystal substrate is suppressed from cracking when used for liquid phase epitaxial growth as described above, it can be suitably used for liquid phase epitaxial growth.

  As described above, the SGGG single crystal substrate evaluation method according to the present embodiment can easily evaluate the ease of cracking of the substrate in the process of manufacturing the substrate from the SGGG single crystal. Moreover, the evaluation method of the SGGG substrate according to the present embodiment can easily evaluate the fragility of the substrate, and can evaluate the substrate by observing the growth fringes of all the substrates obtained by dividing the SGGG single crystal C. Since it is possible, it becomes possible to suppress the crack defect which arises when carrying out liquid phase epitaxial growth.

  Moreover, since the manufacturing method of the SGGG single crystal substrate which concerns on this embodiment includes the evaluation method of the SGGG board | substrate which evaluates the ease of cracking of a board | substrate easily, the outstanding SGGG single crystal board | substrate can be manufactured easily. .

  Further, the SGGG single crystal substrate according to this embodiment can be suitably used for liquid phase epitaxial growth because cracking when used for liquid phase epitaxial growth is suppressed.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples.

(Examples 1-5, Comparative Examples 1-2)
A mixed amount of Gd ₂ O ₃ , Ga ₂ O ₃ , MgO, ZrO ₂ , and CaCO ₃ is used as a raw material, charged in a predetermined amount into an iridium crucible having a diameter of 150 mm and a height of 150 mm, and heated and melted to 1750 ° C. in a high-frequency heating furnace. After obtaining the raw material melt, the shoulder was grown until the diameter reached 80 mm by pulling it up at a speed of 3 mm per hour while rotating the seed crystal 5 times per minute. Thereafter, the number of rotations of the crystal was increased to 20 times per minute, and interface inversion was performed. Then, the crystal was grown until the length of the straight body portion became 100 mm, to obtain an SGGG single crystal.

  Next, the effective part of the straight barrel part is separated from the obtained SGGG single crystal at a position of 40 mm from the interface inversion position, and the separated effective part is subjected to cylindrical grinding and processed to a diameter of 3 inches, depending on the crystal orientation The orientation flat was applied by grinding. Next, using a multi-wire saw, the substrate was cut into a thickness of 0.6 mm to 0.7 mm and divided into a plurality of pieces, and the irregularities attached with the wire saw were removed with a polishing machine. This substrate is housed in a substrate cleaning cassette, and after etching is performed by immersing the entire substrate in phosphoric acid prepared in an etching tank for 2 to 3 and a half hours, cleaning with pure water and drying are performed. went. This process was repeated to prepare a total of 70 substrates. Next, as shown in FIG. 3, a glass plate (translucent member 4) is placed on the lighting device 5, and the etched substrate SA is placed on the glass plate, and below the glass plate. The center position of the growth fringe projected on the surface of the substrate SA by irradiation with light and the center position of the substrate were measured, and the distance between the center position of the growth fringe and the center position of the substrate was measured.

  The time required from the observation of the growth fringe of the substrate to the measurement of the distance between the center position of the growth fringe and the center position of the substrate requires 3 minutes per substrate, and it is necessary to complete the measurement of all 70 substrates. The time spent was about 4 hours.

  FIG. 5 is a diagram illustrating an example of measurement of the center position of the growth stripe. As for the details of the growth fringe measurement, as shown in FIG. 5, a 200 mm × 200 mm square glass plate (translucent member 4) is prepared on the illumination device 5, and the substrate SA after etching processing is formed on the glass plate. , And irradiated with light from the illuminating device 5, the inside of the substrate was transmitted and the growth fringes inside the substrate were visually observed. Next, a 3-inch circle, which is a direct line of the substrate, is accurately drawn on the transparent sheet member 6 of about 0.1 mm placed on the substrate SA, and a quadrilateral (square) is in contact with the four points of the circle. And the intersection of the diagonal lines was determined as the position P1 of the center of the substrate and recorded on the sheet member 6. Then, the transparent sheet member 6 is overlaid on the substrate SA, fine adjustment is performed so that the 3 inch circle drawn on the sheet member 6 and the outer periphery of the substrate SA overlap, and the growth observed through the sheet member 6 Based on the stripe, the center position P2 of the growth stripe was measured and recorded on the sheet member 6. The distance between the center position P1 of the substrate SA and the center position P2 of the growth stripe was measured. In Example 1, the substrate was 45 mm from the interface inversion position. Example 2 was measured at 50 mm, Example 3 at 55 mm, Example 4 at 60 mm, Example 5 at 90 mm, Comparative Example 1 at 20 mm, and Comparative Example 2 at 30 mm. The results are shown in Table 1.

  After measuring the growth stripes, a polished SGGG single crystal substrate was completed.

  Further, regarding the obtained 70 substrates, the deviation from the center in the substrate plane at the center of the concentric growth stripes observed by X-ray topography was measured. About Examples 1-5 and Comparative Examples 1-2, the same board | substrate was measured. The results are shown in Table 1. Thereafter, using this substrate, a RIG single crystal film was grown by a liquid phase epitaxial method. The crack defect at this time was confirmed. About Example 1-5 and Comparative Examples 1-2, the result of the malfunction of the crack of a board | substrate when it grew on the same board | substrate was described in Table 1. In Table 1, “cracking” indicates that there was a defect in substrate cracking, and “good” indicates that there was no substrate cracking.

  Hereinafter, the results will be described. From Table 1, it is confirmed that the X-ray topography and the center position of the growth fringe after etching are almost the same. This confirms that observation after etching processing is possible instead of X-ray topography.

  In addition, the center of the concentric growth stripe observed after the etching process is a region within 8 mm from the center in the SGGG single crystal substrate surface, in which the position of the straight body portion is 40 mm or more from the interface inversion position. This single crystal substrate was good with no occurrence of defective cracking during the growth of the RIG single crystal film.

  The technical scope of the present invention is not limited to the aspects described in the above-described embodiments. One or more of the requirements described in the above embodiments and the like may be omitted. In addition, the requirements described in the above-described embodiments and the like can be combined as appropriate. In addition, as long as it is permitted by law, the disclosure of all documents cited in the above-described embodiments and the like is incorporated as a part of the description of the text.

C ... Nonmagnetic garnet single crystal 1 ... Shoulder 2 ... Straight body 2b ... Effective portion S ... Nonmagnetic garnet single crystal substrate P1 ... Center position P2 of substrate ... Growth fringe center position Q1 ... growth stripes S4-S10 ... nonmagnetic garnet single crystal substrate manufacturing method S5 (S6-S8) ... nonmagnetic garnet single crystal substrate evaluation method

Claims (9)

Etching the surface of the non-magnetic garnet single crystal divided into a predetermined thickness;
Observe the growth fringes of the etched substrate, measure the position of the center of the growth fringes, and evaluate the ease of cracking of the substrate based on the distance between the center position of the growth fringes and the center position of the substrate And a method for evaluating a non-magnetic garnet single crystal substrate.   The method for evaluating a non-magnetic garnet single crystal substrate according to claim 1, wherein the growth fringes are observed by visually observing the etched substrate illuminated with light.   The method for evaluating a nonmagnetic garnet single crystal substrate according to claim 1 or 2, wherein an etching amount in the etching process is 1.5 µm or more and 4 µm or less.   When the distance between the center position of the growth stripe and the center position of the substrate exceeds 8 mm, the evaluation of the ease of cracking of the substrate is evaluated as being easy to break and defective, and the center position of the substrate and the center of the growth stripe The method for evaluating a nonmagnetic garnet single crystal substrate according to any one of claims 1 to 3, wherein when the distance to the position is within 8 mm, it is evaluated as being difficult to break and good.   The evaluation of the fragility of the substrate is performed based on the distance between the center position of the growth stripe and the center position of the substrate, and the distance from the interface inversion position when the nonmagnetic garnet single crystal is manufactured. Item 5. A method for evaluating a non-magnetic garnet single crystal substrate according to Item 4.   The evaluation of the easiness of cracking of the substrate is evaluated as being easily broken and defective when the distance between the center position of the growth stripe and the center position of the substrate exceeds 8 mm, and the center position of the growth stripe and the center of the substrate are evaluated. The method for evaluating a non-magnetic garnet single crystal substrate according to claim 5, wherein when the distance to the position is within 8 mm and the distance from the interface inversion position is 40 mm or more, it is evaluated as being hard to break and good.   The manufacturing method of a nonmagnetic garnet single crystal substrate including the evaluation method of the nonmagnetic garnet single crystal substrate as described in any one of Claims 1-6.   The nonmagnetic of Claim 8 including selecting a board | substrate based on the evaluation result obtained by the evaluation method of the nonmagnetic garnet single-crystal board | substrate as described in any one of Claims 1-6. A method of manufacturing a garnet single crystal substrate. A nonmagnetic garnet single crystal substrate manufactured from a straight body of a nonmagnetic garnet single crystal having a shoulder and a straight body,
A non-magnetic garnet single crystal substrate manufactured from the straight body portion at a position 40 mm or more from the interface reversal position and having a distance between the center position of the growth stripe and the center position of the substrate within 8 mm.