A method for dislocation prevention and control of rare earth garnet thin film

Abstract

The present application relates to a kind of rare earth garnet film dislocation prevention and control method, comprising the following steps: using improved type of rice-shaped fixed-point detection method to arrange test point;The number of different types of dislocations of each test point is recorded to carry out statistics, finally determine the total number of dislocations of substrate and the peak value of the number of dislocations in observation field;Substrate screening and rating are carried out.The improved type of rice-shaped fixed-point detection method used in the present application pays more attention to the regional concentration and peak value characteristics of dislocation distribution, can effectively identify local high-density dislocation area, and grow target film on the surface of high-quality substrate by liquid phase epitaxy technology;After growth is completed, macroscopically observe the cracking and pit defects of the film, and then obtain the qualified rate of the film.The present application realizes the early screening of high-risk substrate, blocks the evolution and transmission of defects in the film growth process from the source, finally significantly improves the qualified rate of target film and the stability of production process, and shortens the test time.

Description

Technical Field

[0001] This invention relates to the field of crystal growth and detection technology, specifically to a method for preventing and controlling dislocations in rare earth garnet thin films. Background Technology

[0002] Rare earth iron garnet single crystal material is a function-oriented single crystal material with a garnet-type crystal structure as its core, composed of rare earth elements, iron, and oxygen. Its unique crystal structure and electron spin characteristics give it irreplaceable application value in fields such as magneto-optics, microwaves, and magnetic storage, making it one of the key basic materials for high-end industries such as modern information communication, precision sensing, and quantum technology.

[0003] Crystal dislocations, as line defects in the atomic arrangement of crystal structures, significantly affect the mechanical, electrical, and optical properties of materials. Therefore, simple and effective observation of dislocation density is crucial for ensuring crystal yield. Crystal growth is a key step in dislocation "source control," which can be achieved by selecting seed crystals with low defect density as "structural templates" for crystal growth, or by optimizing growth process parameters (such as temperature gradient, cooling rate, and melt convection state). However, the latter places stringent requirements on the temperature control precision, atmosphere stability, and flow field regulation capabilities of the growth equipment, and relies on the operator's experience in process adjustments, making it prone to introducing new dislocations due to parameter fluctuations. In contrast, using dislocation-free or low-dislocation seed crystals can prevent the hereditary proliferation of dislocations from the initial stage, offering advantages in terms of operational simplicity and process stability, making it a preferred strategy for low-cost dislocation control.

[0004] Crystal growth techniques based on optimized seed crystals can significantly reduce dislocation density; the dislocation density of high-quality seed crystals is typically less than 10 dislocations / cm². 2 However, in actual production, it was found that even when the dislocation density is less than 10 dislocations / cm², 2 However, problems such as film cracking, shattering, and local dislocation concentration still exist, and the proportion of unqualified products may reach 50%.

[0005] In existing technologies, the dislocation status of rare earth iron garnets is predicted by observing the dislocation density of the substrate. The substrate inspection method generally involves selective etching using acid etching to reveal dislocation defects, followed by observation using an optical microscope to detect the presence of dislocations. Current judgment methods are based on the acid etching method and establish a dislocation density of 10 dislocations / cm² for SGGG wafers. 2 The dislocation density standard meets the current growth requirements for 3-inch rare-earth iron garnet films. However, since larger film sizes are more sensitive to substrate dislocations, a standard of 10 dislocations / cm is recommended. 2 The dislocation density standard is not applicable to the growth of 4-inch rare-earth iron garnet films. To address the problems existing in the prior art, this invention proposes a corresponding solution. Summary of the Invention

[0006] To address the problems existing in the prior art, the improved cross-shaped fixed-point detection method adopted in this invention focuses more on the regional concentration and peak characteristics of dislocation distribution, which can effectively identify local high-density dislocation regions, providing a faster and more accurate detection method, screening high-quality substrates, blocking the evolution and transmission of defects in the target film growth process from the source, and improving the pass rate of rare earth garnet films.

[0007] The technical solution of the present invention is as follows: a method for preventing and controlling dislocations in rare earth garnet thin films, comprising the following steps:

[0008] (1) Substrate processing: Two mutually perpendicular reference lines are determined by X-rays, wherein the first reference line corresponds to the (110) crystal plane and the second reference line corresponds to the (211) crystal plane;

[0009] (2) Testing procedure: Multiple observation fields are distributed according to the requirements of the improved cross-shaped fixed-point detection method; the substrate is acid-etched to obtain corrosion pits, and each observation field is observed, the number of dislocations is recorded and counted, and finally the total number of dislocations in the observation fields of the substrate and the peak number of dislocations in the observation fields are determined. Preferably, the diameter of the corrosion pits ranges from 8μm to 25μm, and the depth ranges from 8μm to 50μm.

[0010] (3) Based on the total number of dislocations in the observation field and the peak number of dislocations in the observation field for each substrate, a diagram showing the relationship between the total number of dislocations and the peak number of dislocations is drawn; wherein the diagram showing the relationship between the total number of dislocations and the peak number of dislocations is divided into 6 regions, each region representing a different substrate grade. Different substrate grades correspond to different yield rates of the target thin film.

[0011] Furthermore, the observation field of the improved star-shaped fixed-point detection method is distributed along the edge of the substrate. <110> <211> Multiple acquisition points are taken perpendicular to the crystal plane system, forming a cross-shaped pattern, and all acquisition points are located on the same plane. Preferably, one observation field of view is located at the center point of the substrate, and the remaining observation fields of view are distributed in six directions, namely, a first perpendicular line of the first reference line passing through the center point of the substrate, a second perpendicular line of the second reference line passing through the center point of the substrate, and both the first and second perpendicular lines are located on the same plane; two straight lines in the same plane that make an angle of 120 degrees with the first perpendicular line, and two straight lines in the same plane that make an angle of 120 degrees with the second perpendicular line.

[0012] In some preferred embodiments, the number of observation fields is 25. The diameter of each observation field is 1 cm, and the edge spacing between adjacent observation fields is 0.1 cm.

[0013] In some preferred embodiments, for a 4-inch substrate, the dislocation total number-dislocation peak value relationship diagram in step (2) includes regions A, B, C, D, E, and F, which correspond to different grades of substrates; region A is a substrate of excellent grade when the total number of dislocations is less than or equal to 212 and the peak value of the number of dislocations in the observation field is less than 50; region B is a substrate of first-class grade when the total number of dislocations is 212 to 314 and the peak value of the number of dislocations in the observation field is less than 50; region C is a substrate of excellent grade when the total number of dislocations is between 212 and ... F is a substrate of excellent grade when the total number of dislocations is between 212 and 314 and the peak value of the number of dislocations in the observation field is less than 50. When the total number of dislocations is less than or equal to 212 and the peak number of dislocations in the observed field of view is greater than 50, the substrate grade is second-class; when the total number of dislocations in region D is 212 to 314 and the peak number of dislocations in the observed field of view is greater than 50, the substrate grade is third-class; when the total number of dislocations in region E is more than 314 and the peak number of dislocations in the observed field of view is less than 50, the substrate grade is fourth-class; when the total number of dislocations in region F is more than 314 and the peak number of dislocations in the observed field of view is greater than or equal to 50, the substrate grade is scrap.

[0014] In some preferred embodiments, observation and statistics are performed using image acquisition devices such as cameras or microscopes.

[0015] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0016] (1) The improved cross-shaped fixed-point detection method adopted in this invention focuses more on the regional concentration and peak characteristics of dislocation distribution, and can effectively identify local high-density dislocation areas. Although the matrix-type 69-point counting method covers more points, it is difficult to highlight such key risk areas. Therefore, this invention has more advantages in terms of the accuracy of substrate screening and subsequent film quality control. Using the "total number of dislocations" and the "peak number of dislocations in the observation field" as core evaluation parameters, the technical problem of inaccurate substrate dislocation density characterization is fundamentally solved from the methodological level. It reduces the cracking rate of the film and improves the product qualification rate, realizes the effective control of dislocation density of rare earth garnet films, significantly improves the qualification rate and performance consistency of film products, and reduces detection time and production costs.

[0017] (2) The improved cross-shaped arrangement of the present invention optimizes the spatial layout of the detection points, thereby reducing redundant observations and improving detection efficiency while ensuring statistical validity. In practical applications, this method can be combined with automated image recognition technology to quickly locate high-risk areas, further reducing human interpretation errors. Compared with the homogenized sampling of the matrix 69-point counting method, the present invention is more suitable for the high sensitivity of rare earth garnet films to local substrate quality, thus achieving better process control and improved yield. Especially in the detection of large-size substrates, the improved cross-shaped fixed-point detection method can accurately capture dislocation clusters with fewer key observation points, avoiding film growth instability caused by local defects. Actual data shows that the pass rate of films prepared from substrates screened using this method can reach 90%, and the detection process time is shortened by about 50%. This method has been successfully applied to the mass production process, verifying its stability and reproducibility.

[0018] (3) This invention establishes a qualitative correlation mechanism between the number of dislocations in the substrate and the final dislocation density of the target thin film. Through systematic characterization of the substrate surface, lattice integrity and stress state, high-risk substrates can be screened out in advance, blocking the evolution and transmission of defects in the thin film growth process from the source, and ultimately significantly improving the pass rate of the target thin film and the stability of the production process. Attached Figure Description

[0019] Figure 1 The existing technology uses a 69-point counting measurement method.

[0020] Figure 2 This is a schematic diagram of the observation field of the improved cross-shaped fixed-point detection method of the present invention.

[0021] Figure 3 This is a diagram showing the relationship between the total number of dislocations and their locations according to an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of substrate grade evaluation based on the relationship between the total number of dislocations and the peak value of dislocations in this invention.

[0023] Figure 5 These are dislocation photographs of the SGGG substrate being tested. Detailed Implementation

[0024] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, are also considered to fall within the scope of the present invention.

[0025] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the disclosure of this invention, those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the scope of protection defined by this invention.

[0026] Growing rare-earth garnet thin films on homogeneous substrates, such as gadolinium gallium garnet (GGG) substrates or calcium magnesium zirconium doped gadolinium gallium garnet (SGGG) substrates, using liquid-phase epitaxy requires, in addition to optimizing growth process parameters, selecting seed crystals or substrates with low defect density as "structural templates" for crystal growth. In other words, the dislocation density of the substrate largely determines the number of dislocations in the rare-earth garnet thin film. One of the objectives of this invention is to quickly select high-quality substrates.

[0027] The current method for characterizing dislocation density on substrates is the matrix 69-point counting method. This method uses a large number of points over a wide area, but the measurement time is long and the accuracy of dislocation characterization is insufficient. Thin films prepared from substrates evaluated using the matrix 69-point counting method still commonly suffer from cracking, fragmentation, and localized dislocation concentration. We found that using the matrix 69-point counting method, when the dislocation density is <103 / cm2... 2 In this case, the stress meter showed concentrated dislocations on the substrate, which is the reason why the cracking rate of rare earth garnet films cannot be reduced. Therefore, this invention changes the method of measuring and evaluating the dislocation density of the substrate.

[0028] Through extensive observation and testing, the inventors discovered that the dislocation concentration on the (211) and (110) characteristic crystal planes has a greater impact on the pass rate of rare earth garnet films. Therefore, this invention proposes an "improved star-shaped fixed-point detection method" to screen substrates. The improved star-shaped fixed-point detection method refers to testing dislocations at fixed observation points after the substrate has been oriented according to a baseline. The observation points include those along the upper edge of the substrate and... <110> <211> Multiple sampling points are taken perpendicular to the crystal plane, forming a cross-shaped pattern, all located on the same plane. Compared to the matrix-style 69-point counting measurement method, the distribution of observation points in this invention provides more accurate location of dislocations, improving detection efficiency, and the smaller observation area significantly reduces observation time.

[0029] Preferably, 25 fixed sampling points are preset as the observation field of view. The number of dislocations is determined by acid etching. The diameter of the observation field of view is 1 cm. The "total number of dislocations in the observation area" and the "peak number of dislocations in the observation field of view" are used as core evaluation parameters. This effectively avoids errors caused by the randomness of sample selection and local mean, and fundamentally solves the technical problem of inaccurate characterization of substrate dislocation density from a methodological perspective. The peak number of dislocations in the observation field of view refers to the highest number of dislocations among all observation fields of view; because excessive concentration of dislocations can easily lead to film cracking.

[0030] The calcium-magnesium-zirconium-doped gadolinium-gallium garnet (SGGG) substrate was characterized to precisely locate dislocation defects within the substrate. The specific steps were as follows:

[0031] (1) Substrate preparation: The crystal rod is oriented by X-ray to form crystallographic shape. <110> <211> The crystal plane system is cut, and the oriented cut crystal rod is cut into substrates along the (111) crystal plane. The uppermost substrate is ground, polished, and acid-etched to detect the number of dislocations. The baseline of the substrate is determined by X-ray, such as... Figure 1 or Figure 2 The white dashed lines in the diagram represent the reference lines of the substrate. This invention requires two mutually perpendicular reference lines, one corresponding to the (110) crystal plane and the other to the (211) crystal plane. Preferably, the diameter of the etched pits ranges from 8 μm to 25 μm, and the depth from 8 μm to 50 μm. For example... Figure 5 The image shows a dislocation photograph of the SGGG substrate.

[0032] (2) Test procedure: The test setup shall be carried out in accordance with the requirements of the improved cross-shaped fixed-point detection method, such as... Figure 2 As shown in the diagram, an observation field of view is set at the center point of the substrate (i.e., Figure 2(Test point 25) Four observation fields are evenly set on the vertical line between the center point of the substrate and the reference line, and observation fields are set on the direction with an angle of 120 degrees to the vertical line. For example, test points 1, 7, 13, and 19 are distributed on the vertical line 5 of the reference line represented by the (110) crystal plane; the angle between the line 1 containing test points 5, 11, 17, and 23 and the vertical line 5 is about 120 degrees; the angle between the line 2 containing test points 3, 9, 15, and 21 and the vertical line 5 is about 120 degrees. The reference line represented by the (211) crystal plane is treated in the same way, and the angle between the line 3 containing test points 6, 12, 18, and 24 and the line 4 containing test points 4, 10, 16, and 22 and the vertical line 6 of the reference line is about 120 degrees. In this way, 25 observation fields are set. These 25 observation fields are located on the upper edge of the substrate and the vertical line 6 of the reference line. <110> <211> The crystal planes are distributed vertically, forming a cross-shaped pattern.

[0033] Each observation field of view is considered a dislocation test point, with a diameter of 1 cm and an edge spacing of 0.1 cm between adjacent observation fields. The dislocation defects on the substrate are visualized as corrosion pits through acid etching; the etching conditions can be adjusted according to specific circumstances. The number of dislocations in each observation field is recorded and statistically analyzed using the naked eye or image acquisition equipment such as cameras and microscopes, ultimately determining the total number of dislocations on the substrate and the peak number of dislocations in each observation field.

[0034] It should be noted that, Figure 2 The numbers of the 25 observation fields are only for the convenience of explaining the number of observation fields and do not represent the order of observation.

[0035] (3) Based on the total number of dislocations in the observation area and the peak number of dislocations in the observation field, draw a diagram showing the relationship between the total number of dislocations and the peak number of dislocations, and screen and rate the substrates.

[0036] The target thin film was grown on the aforementioned substrate. Liquid phase epitaxy was used to grow the target thin film on the surface of the SGGG substrate. After growth, the cracks and pits in the film were macroscopically observed to obtain the dislocation density and yield of the film. Macroscopic observation refers to observation with the naked eye, but image acquisition equipment such as cameras and microscopes can also be used.

[0037] For 4-inch products, this invention establishes a qualitative correlation mechanism between the initial number of dislocations on the substrate and the final dislocation density of the target thin film. See Table 1 for details.

[0038] Table 1. Relationship between total dislocations and peak dislocations with substrate grade.

[0039]

[0040] When the total number of dislocations in the observation area of ​​the substrate is less than 212, and the peak number of dislocations in the observation field is less than 50 (corresponding to...) Figure 4 Region A), the substrate is the best substrate, the substrate grade is excellent, the grown target film is complete, and the pass rate is high.

[0041] When the total number of dislocations in the observation region is 212–314, and the peak number of dislocations in the observation field is less than 50 (corresponding to…) Figure 4 (Region B), the substrate is a better substrate, and the substrate grade is first-class.

[0042] When the total number of dislocations in the observation region is less than 212, and the peak number of dislocations in the observation field is greater than or equal to 50 (corresponding to...) Figure 4 (Region C), the substrate grade is second-class.

[0043] When the total number of dislocations in the observation region is 212–314, and the peak number of dislocations in the observation field is greater than or equal to 50 (corresponding to…), Figure 4 (Region D), the substrate is a second-best substrate, and the substrate grade is third-class.

[0044] Figure 4 In the middle region E, when the total number of dislocations exceeds 314 and the peak number of dislocations in the observation field is less than 50, the substrate grade is fourth-class.

[0045] When the total number of dislocations in the observation region exceeds 314, and the peak number of dislocations in the observation field is greater than or equal to 50 (corresponding to...) Figure 4 Area F), substrates of scrap grade are not used, and the target film has a high probability of cracking and pitting defects.

[0046] Based on the above research, this invention ultimately constructs a method for dislocation prevention and control of rare earth garnet thin films. Using the substrate as the core of quality control, an "improved cross-shaped fixed-point detection method" is employed to count dislocations across the entire observation area of ​​the substrate surface. The total number of dislocations is obtained, and a threshold standard is established (e.g., when the total exceeds a certain critical value, the substrate is judged as high-risk). By preemptively screening out high-risk substrates, the evolution and propagation of defects are blocked from the crystal growth source, ultimately achieving effective control of the dislocation density of rare earth garnet thin films, significantly improving the pass rate and performance consistency of thin film products.

[0047] Example 1:

[0048] Four SGGG crystal rods were designated S1-S4, oriented, and then cut into substrates. The topmost substrate was used for testing. The substrate size was 4 inches. A matrix-style 69-point counting method was used for the measurement of the substrates, and the dislocation density of each substrate was less than 10 dislocations / cm². 2 .

[0049] The improved cross-shaped fixed-point detection method of this invention was used for testing, with 25 observation fields selected as test points, such as... Figure 2As shown. The diameter of each observation field of view is 1 cm, and the edge interval between adjacent observation fields of view is 0.1 cm. After acid etching, according to Figure 2 the improved cross-shaped fixed-point detection method to observe and count the total number of dislocation defects, and obtain Figure 3 the results. Figure 3 is the number of dislocations in each observation field of view area of the observed substrates in samples S1 - S4. The abscissa represents 25 observation fields of view, and the ordinate is the number of dislocations in each observation field of view. The substrates are classified and graded according to the "total number of dislocations in the observation area" and the "peak value of the number of dislocations in the observation field of view". Then, 10 wafers are taken from each ingot for LPE growth of the target thin film. The results of the target thin film are shown in Table 2.

[0050] Table 2 Dislocation Information Table of Samples

[0051]

[0052] Example 2:

[0053] After orienting 1 SGGG ingot (i.e., sample G1 in Table 3) and cutting it into substrates, the topmost substrate is taken for detection. First, the matrix 69-point counting measurement method is used. The test results show that the dislocation density of the measured substrates is less than 10 per cm 2 , which is recorded as the number of qualified ones. Then, it is changed to the improved cross-shaped fixed-point detection method of the present invention for testing. The test results calculated by dislocation density exceed 10 per cm 2 , and they do not meet the dislocation density standard in the prior art. However, using the evaluation method of the present invention, that is, the dislocation total number - dislocation peak value relationship diagram in Table 1 or Figure 4 , 50% of the substrates are recorded as qualified (substrate grades A - E are all counted as qualified). Take 20 4-inch SGGG substrates and perform LPE growth under the same process conditions. The final qualified rate of the thin film is 50%, which is consistent with the test evaluation results of the present invention. The qualified rate of the thin film refers to the ratio of the number of qualified target thin films to the number of substrates.

[0054]

[0055] Among them, the matrix 69-point counting method is calculated according to the area of a 4-inch substrate, which is about 81 square centimeters; while the calculation area of the improved cross-shaped fixed-point detection method is the sum of the areas of 25 observation fields of view, that is, 25 circles with a diameter of 1 cm, which is about 19.6 square centimeters. If the total number of dislocations is the same, the dislocation density obtained by the present invention is higher than that of the traditional detection method. And the inventor found that the dislocations of the SGGG thin film are concentrated on the (110) and (211) crystal planes, and the matrix 69 detection method will cause the dislocation density on the two crystal planes to be low, resulting in a large error in the detection results.

[0056] Another SGGG crystal rod (i.e., sample G2 in Table 3) was tested using the same matrix 69-point counting method and the improved cross-shaped fixed-point detection method of this invention. The test results showed that the dislocation density was less than 10 dislocations / cm². 2 Furthermore, all substrates were deemed qualified based on the evaluation method described in Table 1 of this invention. Twenty 4-inch SGGG substrates were selected and thin film was grown under the same process conditions. The results are summarized in Table 3. The final film qualification rate was 90%. As can be seen from the results in Table 3, although all substrates obtained by the matrix 69-count measurement method were qualified, i.e., meeting the dislocation density standard, the qualification rate of the films obtained after LPE growth fluctuated significantly, ranging from 50% to 90%.

[0057] On the other hand, the improved cross-shaped fixed-point detection method of the present invention reduces the detection time from the original 1h-1.5h to 35min-40min due to the reduced detection range, thereby improving the detection efficiency.

[0058] Table 3. Film pass rate for different testing methods

[0059]

[0060] This method has been successfully applied to mass production, verifying its stability and reproducibility. Detection data can be uploaded to the quality monitoring system in real time, supporting traceability analysis and dynamic optimization of process parameters. Especially when dealing with high-density dislocation clusters, the improved cross-shaped fixed-point detection method exhibits stronger sensitivity and recognition accuracy, effectively avoiding the problem of missed detection of critical defects caused by the homogenization of sampling in traditional methods.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preventing and controlling dislocations in rare earth garnet thin films, characterized in that, Includes the following steps: (1) Substrate processing: Two mutually perpendicular reference lines are determined by X-rays, wherein the first reference line corresponds to the (110) crystal plane and the second reference line corresponds to the (211) crystal plane; (2) Test procedure: Multiple observation fields are distributed according to the requirements of the improved cross-shaped fixed-point detection method; the substrate is acid-etched to obtain corrosion pits, each observation field is observed, the number of dislocations is recorded and counted, and finally the total number of dislocations in the observation fields of the substrate and the peak number of dislocations in the observation fields are determined. (3) Based on the total number of dislocations in the observation field of each substrate and the peak number of dislocations in the observation field, draw a diagram showing the relationship between the total number of dislocations and the peak number of dislocations. The diagram showing the relationship between the total number of dislocations and the peak number of dislocations is divided into 6 regions, each region representing a different substrate grade. Different substrate grades correspond to different yield rates of the target thin film. The observation field of view of the improved star-shaped fixed-point detection method is distributed along the upper edge of the substrate and... <110> <211> Multiple acquisition points are selected in the vertical direction of the crystal plane system, forming an approximate cross shape. All acquisition points are located on the same plane. One observation field of view is located at the center point of the substrate, and the other observation fields of view are distributed in 6 directions, namely the first vertical line (5) of the first reference line passing through the center point of the substrate, the second vertical line (6) of the second reference line passing through the center point of the substrate, the straight line (1) and the straight line (2) with an angle of 120 degrees with the first vertical line (5), and the straight line (3) and the straight line (4) with an angle of 120 degrees with the second vertical line (6). The straight lines (1), (2), (3), and (4) are all located on the same plane as the first vertical line (5) and the second vertical line (6). The number of observation fields is 25; When the substrate size is 4 inches, the dislocation total number - dislocation peak value relationship diagram in step (2) includes regions A, B, C, D, E, and F, which correspond to different grades of substrates; region A is a substrate grade of excellent when the total number of dislocations is less than 212 and the peak value of the dislocations in the observation field is less than 50; region B is a substrate grade of first-class when the total number of dislocations is 212 to 314 and the peak value of the dislocations in the observation field is less than 50; region C is a substrate grade of first-class when the total number of dislocations is less than 212.

12. When the peak number of dislocations in the observed field of view is greater than or equal to 50, the substrate grade is second-class; when the total number of dislocations in region D is 212-314 and the peak number of dislocations in the observed field of view is greater than or equal to 50, the substrate grade is third-class; when the total number of dislocations in region E exceeds 314 and the peak number of dislocations in the observed field of view is less than 50, the substrate grade is fourth-class; when the total number of dislocations in region F exceeds 314 and the peak number of dislocations in the observed field of view is greater than or equal to 50, the substrate grade is scrap.

2. The method for preventing and controlling dislocations in rare earth garnet thin films according to claim 1, characterized in that, The diameter of the observation field of view is 1 cm, and the edge spacing between adjacent observation fields of view is 0.1 cm.

3. The method for preventing and controlling dislocations in rare earth garnet thin films according to claim 1, characterized in that, The corrosion pits range in diameter from 8μm to 25μm and in depth from 8μm to 50μm.

4. The method for preventing and controlling dislocations in rare earth garnet thin films according to claim 1, characterized in that, Observation and statistics are performed using image acquisition equipment.

5. The method for preventing and controlling dislocations in rare earth garnet thin films according to claim 4, characterized in that, The image acquisition device includes a camera or a microscope.

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