A method for detecting dislocation density in fluoride crystals

Abstract

This invention relates to the field of crystal detection technology, specifically to a method for detecting the dislocation density of fluoride crystals, particularly suitable for the dislocation density analysis of calcium fluoride crystals. The method comprises: (1) pre-treating the surface of the fluoride crystal to be tested; (2) corroding the surface of the fluoride crystal to be tested using a corrosion mixture solution, followed by termination of corrosion, wherein the corrosion mixture solution is used to form corrosion pits on the surface of the fluoride crystal to be tested; (3) observing the surface of the fluoride crystal to be tested, counting the number of corrosion pits in the fluoride crystal to be tested, and calculating the dislocation density of the fluoride crystal to be tested based on the number of corrosion pits, wherein the corrosion pits are corrosion pits with dislocation characteristics among the corrosion pits.

Description

Technical Field

[0001] This invention relates to the field of crystal detection technology, specifically to a method for detecting the dislocation density of fluoride crystals, which is particularly suitable for the dislocation density analysis of calcium fluoride crystals. Background Technology

[0002] In recent years, with the widespread application of calcium fluoride (CaF2) crystals in ultraviolet lithography, astronomical observation, reconnaissance, and high-resolution optical instruments, the precision requirements for the stress birefringence parameters of calcium fluoride crystals have become increasingly stringent. Among the factors influencing the stress birefringence of calcium fluoride crystals, dislocations play a crucial role: as typical microscopic defects in crystal structures, the presence of dislocations disrupts the balance between atoms, causing lattice disorder and deformation, leading to lattice distortion. This alters the distribution of energy and stress within the crystal, increasing local strain energy and stress, thus significantly impacting the stress birefringence of calcium fluoride crystals.

[0003] In existing technologies, the dislocation density on the surface of calcium fluoride crystals is mainly measured by chemical etching. This method involves etching calcium fluoride with a suitable etchant and under appropriate etching conditions. Since the lattice distortion energy around defects is higher, the etching rate at defects is faster than at areas without defects. Therefore, after a period of etching, etching pits corresponding to the defects can be observed, and the dislocation density can then be calculated.

[0004] However, as the material requirements for calcium fluoride crystals continue to increase, the precision requirements for dislocation density measurement also increase. Previous studies have mostly focused on observing corrosion pits on the crystal faces of calcium fluoride crystals, and have been accustomed to simply equating corrosion pit density with dislocation density to judge the quality of the crystal. However, the inventors have creatively discovered that corrosion pits are not only generated by dislocations, but also by micro-precipitation defects in the material or by the complete corrosion of defects, which leads to the poor accuracy of existing dislocation density measurement methods. Summary of the Invention

[0005] This invention provides a method for detecting dislocation density in crystals, thereby solving the technical problem of insufficient accuracy in existing dislocation density detection methods.

[0006] This invention provides a method for detecting the dislocation density of fluoride crystals, the method comprising:

[0007] (1) The surface of the fluoride crystal to be tested is pretreated;

[0008] (2) The surface of the fluoride crystal to be tested is corroded by the corrosion mixture solution, and then the corrosion is terminated. The corrosion mixture solution is used to form corrosion pits on the surface of the fluoride crystal to be tested.

[0009] (3) Observe the test surface of the fluoride crystal, count the number of dislocation pits in the fluoride crystal, and calculate the dislocation density of the fluoride crystal based on the number of dislocation pits.

[0010] The dislocation pit is a corrosion pit with dislocation characteristics among the corrosion pits.

[0011] Optionally, in some embodiments of the present invention, the dislocation characteristic is an extension characteristic of the corrosion pit in both the width and depth directions.

[0012] Optionally, in some embodiments of the present invention, step (3) of counting the number of etch pits in the fluoride crystal to be tested includes the following steps:

[0013] Identify the type of corrosion pit in the sampling area, including triangular pyramidal corrosion pits, flat-bottomed corrosion pits, and cone-flat-bottomed corrosion pits;

[0014] The number of the corrosion pits is counted. The corrosion pits consist of triangular pyramidal corrosion pits and cone-shaped flat-bottomed corrosion pits.

[0015] Optionally, in some embodiments of the present invention, after step (2) and before step (3), the following steps are further included:

[0016] The fluoride crystal to be tested after etching is placed in deionized water at a constant temperature to allow it to cool down slowly and prevent it from cracking.

[0017] The fluoride crystals to be tested were rinsed with deionized water.

[0018] Optionally, in some embodiments of the present invention, the pretreatment of the test surface of the fluoride crystal to be tested in step (1) further includes the following steps:

[0019] Cut the fluoride crystal to be tested;

[0020] The diffraction angle deviation of the test crystal plane of the fluoride crystal is determined to be less than ±1°.

[0021] Polish the fluoride crystal to be tested until there are no scratches or broken points on the surface of the fluoride crystal to be tested.

[0022] Optionally, in some embodiments of the present invention, in step (3), the dislocation density of the fluoride crystal to be tested is calculated according to the following formula:

[0023] ρ=N / S

[0024] Where S is the sampling area and N is the number of erosion pits within the sampling area.

[0025] Optionally, in some embodiments of the present invention, the fluoride crystal to be tested is calcium fluoride, and the surface to be tested is the {111} crystal plane of calcium fluoride.

[0026] Optionally, in some embodiments of the present invention, in step (2), the temperature of the corrosion mixture is 45°C-60°C and the corrosion time is 6 min-15 min.

[0027] Optionally, in some embodiments of the present invention, the temperature of the corrosion mixture is 55℃-60℃, the corrosion time is preferably 10min-12min, and the corrosion mixture is a mixture of 4mol / L hydrochloric acid solution and deionized water.

[0028] Optionally, in some embodiments of the present invention, the corrosion mixture is formed by mixing 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:2.

[0029] The beneficial effects of this invention are as follows:

[0030] The detection method of this application, namely, counting the number of etch pits in the fluoride crystal to be tested and calculating the dislocation density of the fluoride crystal to be tested based on the number of etch pits, wherein the etch pits are corrosion pits with dislocation characteristics, can more accurately calculate the dislocation density of the fluoride crystal to be tested and improve the accuracy of dislocation density calculation.

[0031] By further refining the corrosion pits and defining the dislocation characteristics as extensional characteristics in both the width and length directions of the corrosion pits, we can better clarify the judgment criteria for dislocation-induced corrosion pits and improve the accuracy of dislocation density statistics.

[0032] The fluoride crystals to be tested, after being etched, are placed in deionized water at a constant temperature to slowly cool them down and prevent them from cracking.

[0033] By pretreating the surface of the fluoride crystal to be tested, the interference of other irrelevant factors on the dislocation density can be effectively reduced, thereby improving the accuracy of dislocation density measurement.

[0034] By optimizing the ratio of the corrosion mixture solution for fluoride crystals, the corrosion time, and the ambient temperature, clearer corrosion results can be obtained, improving the accuracy of dislocation density measurement. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart illustrating the steps of a method for detecting dislocation density in a crystal provided by the present invention.

[0037] Figure 2 This is a magnified schematic diagram of the corrosion pit types on the {111} crystal plane of calcium fluoride provided by the present invention;

[0038] Figure 3 This is a time-pit shape variation diagram of the triangular pyramidal etch pits on the {111} crystal plane of calcium fluoride provided by the present invention;

[0039] Figure 4 This is a time-pit shape variation diagram of the conical-flat bottom etch pits on the {111} crystal plane of calcium fluoride provided by the present invention;

[0040] Figure 5 This is a time-pit shape variation diagram of the flat-bottomed etch pits on the {111} crystal plane of calcium fluoride provided by the present invention;

[0041] Figure 6 This is the observation result under a microscope of Comparative Example 1 provided by the present invention;

[0042] Figure 7 This is the observation result under a microscope of Comparative Example 2 provided by the present invention;

[0043] Figure 8 This is the observation result of Comparative Example 3 provided by the present invention under a microscope;

[0044] Figure 9 This is the observation result of Comparative Example 4 provided by the present invention under a microscope.

[0045] Figure label:

[0046] α, triangular cone-shaped pits; β, cone-shaped flat-bottomed pits; γ, flat-bottomed pits. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. To fully understand the present invention, numerous specific embodiments and details are mentioned in the following detailed description. Furthermore, it should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. In the following embodiments, the descriptions of each embodiment have different focuses; parts not described in detail in a certain embodiment can be referred to in the relevant descriptions of other embodiments.

[0048] As mentioned earlier, the growth and microscopic characterization of high-quality, large-size calcium fluoride crystals have become a research hotspot in recent years. The precision requirements for dislocation density in calcium fluoride crystals are also constantly increasing. Chemical etching technology, with its advantages of low cost and simple experimental procedures, is currently the main method for studying crystal dislocations. The principle of chemical etching technology is that, under suitable etchant and etching conditions, the lattice distortion energy around defects is higher, resulting in a faster etching rate at defects than at defect-free areas. After a period of etching, corrosion pits corresponding to the defects can be observed.

[0049] Previous studies have mostly focused on observing corrosion pits on the crystal faces of calcium fluoride crystals, and have conventionally equated the density of corrosion pits to dislocation density to judge the quality of the crystal. However, through innovative discoveries, corrosion pits have been found not only to be generated by dislocations, but also to form corrosion pits when micro-precipitation defects or defects in the crystal material are completely corroded. Therefore, the method for measuring the dislocation density of calcium fluoride crystals needs further improvement.

[0050] To address the aforementioned issues, this application provides a method for detecting crystal dislocation density, thereby further improving the accuracy of crystal dislocation density detection and meeting user needs.

[0051] Please see Figure 1 This application achieves the detection of dislocation density in crystals through the following steps:

[0052] Step 100: Pre-treat the test surface of the fluoride crystal to be tested.

[0053] When testing the dislocation density of fluoride crystals, such as fluoride crystals, the surface of the fluoride crystal to be tested needs to be pretreated first. The main reason is that the dislocation density of a crystal is affected by many factors. Even for the same crystal, the measured dislocation density will be different under different conditions. For example, for the same calcium chloride crystal, when the crystal faces are different, such as {110} and {111}, the corrosion morphology, corrosion time and temperature are not the same. Even for fluoride crystals with the same crystal face, when the orientation deviation or polishing does not meet the requirements, the corrosion results cannot be well displayed. For example, when the orientation deviation is greater than 1°, the morphology of the corrosion pit cannot be etched; when the polishing is not good, the morphology of the corrosion is a destructive triangle or the corrosion surface has scratches.

[0054] In a specific testing scenario, when the testing personnel receive the fluoride crystal to be tested, they need to first cut the crystal facets of the fluoride crystal to be tested according to the specified requirements. When cutting the fluoride crystal to be tested, the crystal facets of the fluoride crystal to be tested are mainly cut according to the specified crystal facet requirements by an internal circle cutter or a wire cutter, such as cutting according to the {111} crystal facets. It is preferred to use an internal circle cutter for cutting.

[0055] After the crystal facets of the fluoride crystal to be tested are cut according to the specified requirements, they need to be oriented using an orientation detection device, preferably an X-ray orientation detector. This determines whether the diffraction angle of the crystal facets meets the requirements. If yes, the next step is polishing and grinding; otherwise, the fluoride crystal is recut to improve the accuracy of dislocation density detection. The preferred standard for the diffraction angle is that a deviation of less than ±1° indicates that the cutting result of the crystal facets meets the requirements.

[0056] After the test crystal facets are inspected, the test crystal facets of the fluoride crystal need to be ground and polished to further improve the detection accuracy of the dislocation density of the fluoride crystal. Generally, the grinding and polishing of the fluoride crystal can be considered to be well completed when the surface of the fluoride crystal is polished to the point that there are no scratches or broken points.

[0057] It should be noted that when pre-treating the surface of the fluoride crystal to be tested for dislocation density detection, the pre-treatment content varies depending on the state of the different fluoride crystals. Generally, the pre-treatment mainly includes one or more steps such as cutting, positioning, and polishing, so as to minimize the interference factors of the fluoride crystal to be tested during dislocation density measurement and improve the accuracy of dislocation density measurement data.

[0058] Step 200: The surface of the fluoride crystal to be tested is etched using a corrosion mixture solution, and then the etching is terminated. The corrosion mixture solution is used to form corrosion pits on the surface of the fluoride crystal to be tested.

[0059] For the chemical etching method to measure the dislocation density of crystals, different crystal faces have different requirements for the optimal etching solution and etching environment. The etching time and etching temperature have a significant impact on the dislocation density of the fluoride crystal being tested. The following section will provide a detailed explanation of the dislocation density measurement process of fluoride crystals, which will not be repeated here.

[0060] It should be noted that when immersing the fluoride crystal to be tested into the corrosive mixed solution, the entire fluoride crystal can be immersed, or only one side of the fluoride crystal to be tested can be immersed, i.e., only the surface to be tested can be immersed. This application is not limited to this.

[0061] Step 300: Observe the test surface of the fluoride crystal to be tested, count the number of etch pits in the fluoride crystal to be tested, and calculate the dislocation density of the fluoride crystal to be tested based on the number of etch pits, wherein the etch pits are corrosion pits with dislocation characteristics among the corrosion pits.

[0062] When observing the surface of the fluoride crystal to be tested, it can be done by microscopy. It is preferable to use the 63x magnification of the OPTHOLUX Ⅱ POL-BK type microscope to observe the distribution and morphology of corrosion pits, which can achieve relatively clear observation of corrosion pits.

[0063] It should be noted that in existing technologies, when detecting the dislocation density of fluoride crystals, researchers simply assume that the corrosion pits formed after the fluoride crystal is corroded by the corrosion solution are dislocation pits, thus equating the density of corrosion pits with the density of dislocations to determine the quality of the crystal. However, with the increasing application demands of crystals and the rising requirements for the preparation process and quality evaluation of fluoride crystals, improving the detection accuracy of dislocation density in crystals is an urgent problem to be solved.

[0064] During their research, the inventors made a creative discovery: corrosion pits can be categorized into those with dislocation characteristics (dislocation pits) and those without. In other words, corrosion pits don't only occur at dislocation sites; micro-precipitation defects or defects completely corroded within crystalline materials can also form corrosion pits. Therefore, simply using corrosion pit density as a criterion to measure dislocation density is not entirely accurate.

[0065] The following is a schematic illustration of the process for detecting the dislocation density of the {111} crystal plane of calcium fluoride:

[0066] Example 1

[0067] First, the calcium fluoride crystals used for etching are cut along the {111} plane. The cut samples are then oriented and polished on both sides, ensuring that the crystal surface is free of scratches and breaks. After adjusting the oven to 60 ℃ and keeping it at that temperature for half an hour, the etching solution formed by mixing 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:2 is placed in the oven and left to stand for 15 min.

[0068] After the solution has settled, the polished sample is immersed in a 60 °C etching solution for 10 min. After etching, the sample is placed in insulated deionized water to allow for slow cooling and prevent crystal cracking. The sample is then removed and rinsed thoroughly with deionized water. Finally, the crystal surface is dried with filter paper, and the etched sample is placed under an optical microscope to observe the shape, distribution, and statistical dislocation density of the etching pits on the crystal surface, thereby obtaining... Figure 2 .

[0069] Depend on Figure 2 It can be seen that the corrosion pits on the {111} crystal plane of calcium fluoride crystal are clearly visible, and the corrosion pits have three types: triangular pyramidal pit α, cone-shaped-flat-bottomed pit β, and flat-bottomed pit γ.

[0070] To further understand the defect types corresponding to the morphology of triangular pyramidal pits and flat-bottomed pits, the same corrosion pit on the CaF2{111} crystal surface was tracked and analyzed. The corrosion times of the crystal surface were 6 min, 10 min, 18 min, 24 min, 26 min, and 30 min, respectively. Based on this, graphs showing the changes in depth and width of different corrosion pit types at different times were created.

[0071] from Figure 3 , Figure 4 as well as Figure 5 It can be seen that both the triangular pyramidal pit α and the conical flat-bottomed pit β exhibit extension characteristics in both width and depth, and the corresponding defects clearly possess dislocation characteristics. The lack of depth extension observed in the flat-bottomed pit, however, indicates that it was formed after the corrosion of localized defects. Subsequently, the number of triangular pyramidal pits and conical-flat-bottomed pits caused by dislocations was counted, yielding a dislocation density of approximately 102 in the crystal. 4 dis / cm 2 .

[0072] In other words, by tracking and analyzing different corrosion pits, and comparing them after repeated etching, it can be found that triangular pyramidal corrosion pits and cone-flat-bottomed corrosion pits have extension characteristics in both the width and length directions, while flat-bottomed corrosion pits do not have extension characteristics in both the width and length directions. According to the principle of chemical etching to detect the dislocation density of the calcium fluoride crystal under test, the principle of chemical etching technology is mainly that under suitable etchant and etching conditions, due to the higher distortion energy of the lattice around the defect, the corrosion rate at the defect is faster than that at the defect-free area. After a period of etching, the corrosion corresponding to the defect can be seen. That is, only corrosion pits that change according to the etching time can be considered as dislocation pits, and only corrosion pits with extension characteristics in both the width and length directions can be considered as valid corrosion pits that can be used for dislocation density calculation.

[0073] In other words, in existing methods for calculating dislocation density, researchers do not identify whether corrosion pits have extension characteristics, which leads to significant deviations in the calculation of dislocation density. However, the method proposed in this application only counts corrosion pits with dislocation characteristics, which can effectively solve the problem of significant deviations in the calculation of dislocation density in existing technologies and improve the accuracy of dislocation density calculation.

[0074] Therefore, the solution proposed in this application can further improve the method for detecting dislocation density in crystals and solve the problem of insufficient accuracy in dislocation density measurement in the prior art.

[0075] It should be noted that an important improvement of this solution is the classification of corrosion pits, which clarifies that corrosion pits are divided into dislocation pits with dislocation characteristics and corrosion pits without dislocation characteristics. In the existing technology, corrosion pits are not analyzed, which leads to poor accuracy in dislocation density measurement.

[0076] It should also be noted that the crystal in this application is calcium fluoride crystal. For non-fluoride crystals, there are significant differences in their preparation process and application fields, which are very different from the solution in this application. For example, comparing the preparation processes of silicon carbide crystal and calcium fluoride crystal reveals that they differ in terms of corrosion solution, corrosion temperature, corrosion time, and corrosion container, resulting in huge technical differences.

[0077] Furthermore, in some embodiments of the present invention, after step 200 and before step 300, the following steps are also included:

[0078] Step 291: Place the etched calcium fluoride crystal to be tested into deionized water at a constant temperature to slowly cool the calcium fluoride crystal to prevent it from cracking.

[0079] Step 292: Rinse the calcium fluoride crystals to be tested with deionized water.

[0080] Furthermore, in some embodiments of the present invention, in step 300, the dislocation density of the calcium fluoride crystal to be tested is calculated according to the following formula:

[0081] ρ=N / S

[0082] Where S is the sampling area and N is the number of erosion pits within the sampling area.

[0083] Furthermore, in order to obtain a more accurate method for detecting the dislocation density of the calcium fluoride crystal under test, when sampling the calcium fluoride crystal under test using a microscope, the sampling positions are evenly distributed on the surface under test, and the total number of samples is not less than 8.

[0084] At this point, the dislocation density is calculated using the following formula:

[0085]

[0086] ρ: Dislocation density in crystal, unit: disc / cm 2 ;

[0087] N: Number of dislocation pits within the sampling area, in units of;

[0088] n: Total number of samples, in units;

[0089] S: Sampling area per sample, i.e., the field of view under a 63x magnification lens of an optical microscope, in cm². 2 .

[0090] It should be noted that the morphology of corrosion pits is significantly affected by corrosion time. Even for the same crystal face of the same calcium fluoride crystal to be tested, different corrosion times will result in different corrosion results, and the accuracy of the obtained dislocation density detection will naturally be different.

[0091] In the detection of dislocation density of the {111} crystal plane of calcium fluoride, the temperature of the etching solution is 45℃-60℃ and the etching time is 6min-15min. It is preferred to set the temperature of the etching solution to 55℃-60℃ and the etching time to 10min-12min, which can better obtain the dislocation density of the {111} crystal plane of calcium fluoride.

[0092] The following will still use the detection process of dislocation density of the {111} crystal plane of calcium fluoride as an example to illustrate the process.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that the etching time in this comparative example is 5 minutes.

[0095] First, the calcium fluoride crystals used for etching are cut along the {111} plane. The cut samples are then oriented and polished on both sides, ensuring that the crystal surface is free of scratches and breaks. After adjusting the oven to 60 ℃ and keeping it at that temperature for half an hour, the etching solution formed by mixing 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:2 is placed in the oven and left to stand for 15 min.

[0096] After the solution had settled, the polished sample was immersed in a 60 °C etching solution for 5 min. After etching, the sample was placed in insulated deionized water to allow for slow cooling and prevent crystal cracking. The sample was then removed and rinsed thoroughly with deionized water. Finally, the crystal surface was dried with filter paper, and the etched sample was placed under an optical microscope to observe the shape, distribution, and statistical dislocation density of the etching pits on the crystal surface. The observation results are shown in [Figure number missing]. Figure 6 .Depend on Figure 6 It can be seen that the morphology of the corrosion pits on the {111} crystal plane of calcium fluoride crystal is unclear, making it impossible to accurately identify the type, and the measurement error of dislocation density is relatively large.

[0097] Comparative Example 2

[0098] Compared with Example 1, this comparative example changed the corrosion time to 20 minutes while keeping other treatment conditions unchanged. The observation results are shown in […]. Figure 7 .

[0099] Therefore, by observing the shape and distribution of corrosion pits on the crystal surface and analyzing the statistical dislocation density under an optical microscope after etching, it can be found that: Figure 7 It can be seen that as the corrosion time increases, the size of the corrosion pits becomes larger and corrosion pits accumulate, making it impossible to identify the morphology of the corrosion pits and count the number of dislocation corrosion pits.

[0100] As can be seen from Examples 1, 1, and 2, the morphology of the corrosion pits on the {111} crystal plane of calcium fluoride crystal is significantly affected by the corrosion time. Different corrosion times have a significant impact on the observation of corrosion pits. In the detection of dislocation density on the {111} crystal plane of calcium fluoride, the temperature of the corrosion solution is 45℃-60℃ and the corrosion time is 6min-15min. It is preferred to set the temperature of the corrosion solution to 55℃-60℃ and the corrosion time to 10min-12min, which can better obtain the dislocation density of the {111} crystal plane of calcium fluoride.

[0101] It should also be noted that the morphology of corrosion pits is significantly affected by the corrosive solution mixture. Even for the same crystal face of the same calcium fluoride crystal, different corrosive solutions will result in different corrosion results, and the accuracy of the obtained dislocation density detection will naturally be different.

[0102] In the detection of dislocation density of the {111} crystal plane of calcium fluoride, the corrosion mixture is prepared by mixing 4 mol / L hydrochloric acid solution and deionized water. Preferably, the corrosion mixture is formed by mixing 4 mol / L hydrochloric acid solution and deionized water in a volume ratio of 1:2, which can better obtain the dislocation density of the {111} crystal plane of calcium fluoride.

[0103] The following will still use the detection process of dislocation density of the {111} crystal plane of calcium fluoride as an example to illustrate the process.

[0104] Comparative Example 3

[0105] First, the calcium fluoride crystals used for etching are cut along the {111} plane. The cut samples are then oriented and polished on both sides, ensuring that the crystal surface is free of scratches and breaks. After adjusting the oven to 60 ℃ and keeping it at that temperature for half an hour, the etching solution formed by mixing 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:1 is placed in the oven and left to stand for 15 min.

[0106] After the solution has settled, the polished sample is immersed in a 60 °C etching solution for 10 min. After etching, the sample is placed in insulated deionized water to allow for slow cooling and prevent crystal cracking. The sample is then removed and rinsed thoroughly with deionized water. Finally, the crystal surface is dried with filter paper, and the etched sample is placed under an optical microscope to observe the shape, distribution, and statistical dislocation density of the etching pits on the crystal surface. Figure 8 .Depend on Figure 8 It is known that increasing the volume of hydrochloric acid solution in the etching solution will cause excessive corrosion on the {111} crystal surface of calcium fluoride crystal, with corrosion pits covering the entire crystal surface, affecting the observation of dislocation pits.

[0107] Comparative Example 4

[0108] As shown in Comparative Example 3, a corrosive mixed solution was formed by mixing a 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:3, with other treatment conditions remaining unchanged.

[0109] The etched sample was placed under an optical microscope to observe the shape, distribution, and statistical dislocation density of the etch pits on the crystal surface. Figure 9 It can be seen that increasing the volume of deionized water in the etching solution will affect the crystal corrosion rate. After 10 minutes of etching, the size of the crystal corrosion pit is small, and the corrosion pit is not completely etched and the morphology is not clear.

[0110] Examples 1, 3, and 4 show that both excessively high and low proportions of hydrochloric acid solution in the etching solution affect the morphology of the corrosion pits on the {111} crystal facets of calcium fluoride, making it difficult to detect the dislocation density of the calcium fluoride crystal. For the detection of the dislocation density on the {111} crystal facets of calcium fluoride, the etching solution is prepared by mixing 4 mol / L hydrochloric acid solution and deionized water. Preferably, the etching solution is formed by mixing 4 mol / L hydrochloric acid solution and deionized water at a volume ratio of 1:2, which can better obtain the dislocation density of the {111} crystal facets of calcium fluoride.

[0111] The solution of this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0112] Throughout this specification, the terms "an embodiment," "embodiment," or "specific embodiment" refer to a particular feature, structure, or characteristic described in connection with an embodiment that is included in at least one embodiment of this application, but not necessarily in all embodiments. Therefore, the various representations of the phrases "in one embodiment," "in an embodiment," or "in a specific embodiment" in different places throughout this specification do not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic of any specific embodiment of this application may be combined with one or more other embodiments in any suitable manner. It should be understood that other variations and modifications of the embodiments described and illustrated herein may be based on the teachings herein and will be considered part of the spirit and scope of this application.

[0113] It should also be understood that one or more of the elements shown in the figures may be implemented in a more separate or more integrated manner, or may even be removed because they are inoperable in certain circumstances or provided because they may be useful for a particular application.

[0114] Furthermore, unless otherwise expressly stated, any arrows in the accompanying drawings should be considered illustrative only and not limiting. Additionally, unless otherwise stated, the term "or" as used herein is generally intended to mean "and / or". Where a term is anticipated to provide a separation or combination capability that is unclear, a combination of components or steps will also be considered as indicated.

Claims

1. A method for detecting dislocation density in a fluoride crystal, comprising: The detection method is: (1) pretreating a to-be-detected surface of a to-be-detected fluoride crystal; (2) etching the to-be-detected surface of the to-be-detected fluoride crystal by using an etching mixed solution, and then stopping etching, the etching mixed solution being used to form etching pits on the to-be-detected surface of the to-be-detected fluoride crystal; (3) observing the to-be-detected surface of the to-be-detected fluoride crystal, counting the number of wrong etching pits in the to-be-detected fluoride crystal, and calculating the dislocation density of the to-be-detected fluoride crystal based on the number of the wrong etching pits; Wherein, the wrong etching pit is an etching pit with dislocation characteristics; the to-be-detected fluoride crystal is calcium fluoride, and the to-be-detected surface is the {111} crystal surface of calcium fluoride; the temperature of the etching mixed solution is 45-60°C, and the etching time is 6-15 minutes; the etching mixed solution is formed by mixing 4 mol / L hydrochloric acid solution and deionized water in a volume ratio of 1:2; The dislocation characteristics are the extension characteristics in the width direction and the length direction of the etching pit; Counting the number of wrong etching pits in the to-be-detected fluoride crystal includes the following steps: Identify the etching pit type in the sampling area, which includes triangular pyramidal etching pits, flat bottom etching pits and conical-flat bottom etching pits; Count the number of wrong etching pits, which consists of triangular pyramidal etching pits and conical-flat bottom etching pits.

2. The method of claim 1, wherein the method is performed on a fluoride crystal. After step (2) and before step (3), the following steps are further included: Put the etched to-be-detected fluoride crystal into the constant-temperature deionized water to slowly cool the to-be-detected fluoride crystal to prevent the to-be-detected fluoride crystal from cracking; Rinse the to-be-detected fluoride crystal with deionized water.

3. The method for detecting dislocation density in fluoride crystals according to claim 2, characterized in that, The pretreatment of the to-be-detected surface of the to-be-detected fluoride crystal in step (1) further includes the following steps: Cut the to-be-detected fluoride crystal; Determine whether the diffraction angle deviation of the to-be-detected crystal surface of the to-be-detected fluoride crystal is less than ±1°; If it is less than ±1°, polish the to-be-detected fluoride crystal until there are no scratches and broken points on the surface of the to-be-detected fluoride crystal.

4. The method of claim 3, wherein the method is performed on a fluoride crystal wafer. In step (3), the dislocation density of the to-be-detected fluoride crystal is calculated according to the following formula: ρ=N / S Wherein, S is the sampling area, and N is the number of wrong etching pits in the sampling area.

5. The method of claim 1, wherein the method is performed on a fluoride crystal. The temperature of the etching mixed solution is 55-60°C, the etching time is 10-12 minutes, and the etching mixed solution is a mixed solution made of 4 mol / L hydrochloric acid solution and deionized water.

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