Silicon powder forming method, silicon block and use

Abstract

A silicon powder forming method, comprising the following steps: placing a mold (1) filled with a silicon powder under the condition of a first pressure P1 for a first pressure time T1, so as to obtain a silicon block, wherein 50MPa≤P1≤600MPa, and 7min≤T1≤15min; the medium that applies the first pressure is a liquid. The present invention further relates to a silicon block and a use. By controlling the pressure, the formed silicon block is easily removed from the mold (1) without being crushed or raising dust, and is also easily crushed during filling, the particle size distribution after crushing being easily controlled. The formed silicon block can be directly applied to Czochralski crystal production, and the packing density is increased to 0.18 g / cm3-0.25 g / cm3.

Description

Silicon powder molding method, silicon block and application Technical Field

[0001] The present application relates to the field of single crystal growth technology, and in particular to a silicon powder molding method, a silicon block and applications. Background Art

[0002] Since the particle size of native polysilicon powder is small (particle size 0.1μm to 1000μm), its loading density is low, that is, the weight loaded in the same space is small, which directly affects the weight of the crucible before the use of the CZ vertical single crystal furnace. It cannot be used in the process of re-charging (continuous feeding crystal pulling technology) of the CZ vertical single crystal furnace. Technical issues

[0003] The present application provides a silicon powder molding method, silicon blocks and applications, which solve the problem that silicon powder cannot be directly used in the production of Czochralski single crystals. Technical Solutions

[0004] According to the first embodiment of the present application, the silicon powder molding method includes:

[0005] The mold containing silicon powder is placed under a first pressure P1 for a first pressure time T1, satisfying 50 MPa≤P1≤600 MPa and 7 min≤T1≤15 min, to obtain a silicon block;

[0006] The medium applying the first pressure is liquid.

[0007] Optionally, the first pressure P1 condition is achieved by increasing the pressure, and the pressure increasing step includes increasing the pressure to the first pressure P1 by a first pressure increasing rate v1, satisfying 20 MPa / s≤v1≤30 MPa / s.

[0008] Optionally, the particle size of the silicon powder is 0.1 μm to 1000 μm.

[0009] Optionally, the mold includes a first surface and a second surface that are opposite to each other, the first surface and the second surface are connected via a third surface, and the first surface and the third surface receive the first pressure P1.

[0010] Optionally, the first surface, the second surface and the third surface receive the first pressure P1.

[0011] Optionally, a pressure deviation PD of the first pressure P1 applied to the first surface, the second surface, and the third surface satisfies: -5 MPa≤PD≤5 MPa.

[0012] Optionally, the mold filled with silicon powder is placed under a second pressure condition P2 for a second pressure time T2, satisfying 50MPa≤P2≤600MPa, 1min≤T2≤15min.

[0013] The mold filled with silicon powder is placed under a third pressure P3 for a third pressure time T3, satisfying 100 MPa≤P3≤600 MPa, 1 min≤T3≤6 min.

[0014] Optionally, after the pressurization process is completed, a first pressure relief process is applied to the mold, and the first pressure relief process includes: reducing the pressure to a pressure P n , lasting T n Time, meet: 10MPa≤P n ≤100MPa, 1min≤T n ≤2min.

[0015] Optionally, the mold is made of polyurethane material, and the density ρ0 of the polyurethane material satisfies: 1.00 g / cm 3 ≤ρ0≤1.01g / cm 3 .

[0016] Optionally, the silicon powder is loaded into multiple molds with equal spacing between adjacent molds to ensure that the same pressure is applied to the multiple molds.

[0017] Optionally, the wear rate G of the mold satisfies: G<G0, where G0 is the material loss in g / cm 2 ;

[0018] The G0 satisfies: 0<G0≤0.1g / cm 2 .

[0019] Optionally, the mold includes a cover and a cylinder, the cover seals the cylinder, and the silicon powder is installed in the cylinder.

[0020] Optionally, a protective sleeve is provided on the outer periphery of the cover body, and the protective sleeve is provided on at least a portion of the cover body.

[0021] Optionally, the edge of the cover body includes steps, and the steps surround the cover body.

[0022] In the second embodiment of the present application, a silicon block is provided. The silicon block is prepared by the above method.

[0023] Optionally, the silicon block is crushed to form first particles, and based on the mass of the silicon block, the mass percentage of the first particles to the silicon block is ≥97%, and the particle size D1 of the first particles satisfies: 10 mm ≤ D1.

[0024] Optionally, the silicon block is crushed to form second particles, and based on the mass of the silicon block, the mass percentage of the second particles in the silicon block is ≤3%, and the particle size D2 of the second particles satisfies: D2<10 mm.

[0025] The third embodiment of the present application provides a silicon block obtained by the above-mentioned silicon powder molding method or the application of the above-mentioned silicon block in the production of Czochralski single crystals. Beneficial effects

[0026] The present application provides a silicon powder molding method according to the embodiments of the present application, which has at least the following technical effects:

[0027] (1) The present invention uses pressure control to make it easy to remove the formed silicon block from the mold without breaking or generating dust. The silicon block of the present invention is easy to break, and the particle size distribution after breaking is easy to control.

[0028] (2) The silicon blocks prepared in this application can be directly used for Czochralski single crystal production, and the charging density is increased to 0.18 g / cm 3 ~0.25g / cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0030] FIG1 is a perspective diagram of the exploded structure of a mold according to an embodiment of the present application;

[0031] FIG2 is a schematic diagram of the exploded structure of the mold according to an embodiment of the present application;

[0032] FIG3 is a front view of a mold according to an embodiment of the present application;

[0033] FIG4 is a cross-sectional view taken along line BB in FIG3 .

[0034] The marks in the figure are respectively represented as follows: 1-mold, 100-cylinder, 110-first surface, 120-second surface, 130-third surface, 200-cover, 201-step, 300-protective cover. Modes for Carrying Out the Invention

[0035] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0036] During the preparation of crystal rods, silicon powder cannot be directly fed into the feedstock and needs to be converted into silicon rods or silicon blocks. In order to improve the filling rate, the present application provides a silicon powder molding method, comprising the following steps: placing a mold 1 filled with silicon powder under a first pressure P1 condition, maintaining the first pressure time T1, satisfying 50MPa≤P1≤600MPa, 7min≤T1≤15min, to obtain a silicon block; the medium for applying the first pressure is a liquid.

[0037] In the present application, liquid pressurization is specifically used as follows: the mold 1 is placed in a closed container filled with liquid, and the pressurization system is gradually applied to each surface of the mold 1 to apply equal pressure, so that the distance between the silicon powders is reduced without changing the appearance and shape, thereby increasing the compaction density and improving the physical properties of the material.

[0038] In some embodiments, the pressurization method employed herein is isostatic pressing. The principle is as follows: Using Pascal's principle, a mold 1 containing silicon powder is placed in a sealed, ultra-high-claw container. A booster pump continuously pressurizes water or oil into the sealed container, increasing the hydraulic pressure within the container. The high-pressure liquid (oil or water) uniformly applies pressure to the surface of the mold 1.

[0039] In some embodiments, the mold 1 is a rubber made of polyurethane material, and hydraulic pressure is applied to the surface of the rubber sleeve, compressing the silicon powder granules in the sleeve to form it. Since the characteristic of isostatic pressing is equal pressure in all directions, the silicon powder blank after molding has uniform density, uniform structure, isotropy, and can also form a regularly shaped product. In some embodiments, the value of the first pressure P1 (MPa) can be any value of 50, 100, 150, 200, 250, 300, 250, 300, 350, 400, 450, 500, 550, 600, or a range consisting of any two values. In some embodiments, the value of the first pressure time T1 (min) can be any value of 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two values.

[0040] If the pressure is too low, the compaction density will be affected and the work time will be wasted. If the pressure is too high, although it will not affect the compaction density of the product, it will shorten the life of the equipment and make it difficult to break the silicon block after molding.

[0041] In some embodiments, the first pressure P1 condition is achieved by increasing the pressure. The increasing pressure step includes increasing the pressure to the first pressure P1 at a first pressure increasing rate v1, satisfying 20 MPa / s ≤ v1 ≤ 30 MPa / s. For example, the first pressure increasing rate v1 (MPa / s) can be any value selected from 20, 25, and 30, or a range consisting of any two values.

[0042] In some embodiments, the particle size of the silicon powder ranges from 0.1 μm to 1000 μm. For example, the particle size (μm) of the silicon powder can be any value selected from 0.1, 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, or a range consisting of any two values.

[0043] In some embodiments, the mold 1 includes a first surface 110 and a second surface 120 disposed opposite to each other. The first surface 110 and the second surface 120 are connected by a third surface 130 . The first surface 110 and the third surface 130 receive a first pressure P1 .

[0044] In some embodiments, the first side 110 , the second side 120 , and the third side 130 receive a first pressure P1 .

[0045] In some embodiments, the pressure deviation PD of the first pressure P1 applied to the first surface 110, the second surface 120, and the third surface 130 satisfies: -5MPa≤PD≤5MPa, such as the value of PD (MPa) is any value of -5, -3, -2, 0, 1, 3, 5, or a range consisting of any two values.

[0046] In some embodiments, the mold 1 containing silicon powder is placed under a second pressure P2 for a second pressure time T2, satisfying the following: 50 MPa ≤ P2 ≤ 600 MPa, and 1 min ≤ T2 ≤ 15 min. For example, the second pressure P2 (MPa) can be any value selected from 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, or 600, or a range consisting of any two values. The second pressure time T2 (min) can be any value selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, or a range consisting of any two values. In some embodiments, 1 min ≤ T2 ≤ 15 min, or 1 min ≤ T2 ≤ 3 min, or 7 min ≤ T2 ≤ 15 min.

[0047] In some embodiments, the mold containing silicon powder is subjected to a third pressure P3 for a third pressure time T3, satisfying the following conditions: 100 MPa ≤ P3 ≤ 600 MPa, and 1 min ≤ T3 ≤ 6 min. For example, the third pressure P3 (MPa) can be any value selected from 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, or 600, or a range consisting of any two values. The third pressure time T3 (min) can be any value selected from 1, 2, 3, 4, 5, or 6, or a range consisting of any two values. In some embodiments, 3 min ≤ T3 ≤ 6 min, or 2 min ≤ T3 ≤ 5 min.

[0048] In some embodiments, the mold 1 containing silicon powder is subjected to a fourth pressure P4 for a fourth pressure time T4, satisfying the conditions of 300 MPa ≤ P4 ≤ 600 MPa and 4 min ≤ T4 ≤ 8 min. For example, the fourth pressure P4 (MPa) can be any value selected from 300, 350, 400, 450, 500, 550, and 600, or a range consisting of any two values, and the fourth pressure time T4 (min) can be any value selected from 4, 5, 6, 7, and 8, or a range consisting of any two values.

[0049] In some embodiments, after the pressurization process is completed, a first pressure relief process is applied to the mold 1. The first pressure relief process includes: reducing the pressure to a pressure P n , lasting T n Time, meet: 10MPa≤P n ≤100MPa, 1min≤T n ≤2min. n The value of (MPa) is any value among 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or a range consisting of any two values. n The value of (min) can be any value among 1, 1.5, 2, or a range consisting of any two values.

[0050] In some embodiments, the pressure relief rate v2 satisfies 20 MPa / s≤v2≤30 MPa / s. For example, the pressure relief rate v2 (MPa / s) can be any value among 20, 25, 30, or a range consisting of any two values.

[0051] In some embodiments, the present application controls the pressure range and pressure application time of the present application by selecting a first pressure increase rate or a pressure release rate.

[0052] In some embodiments, the pressurization time of the present application does not include the time of the pressure increase process or the pressure release process. The present application reduces working hours by quickly increasing and releasing pressure.

[0053] In some embodiments, the mold is made of polyurethane material, and the density ρ0 of the polyurethane material satisfies: 1.00 g / cm 3 ≤ρ0≤1.01g / cm 3 .

[0054] In some embodiments, the mold includes a cover 200 and a cylinder 100 , the cover 200 covers the cylinder 100 , and silicon powder is filled in the cylinder 100 .

[0055] In some embodiments, the inner diameter of the barrel 100 is 137 mm to 141 mm.

[0056] In some embodiments, the outer diameter of the barrel 100 is 154 mm to 160 mm.

[0057] In some embodiments, the height of the cylinder 100 is 691 mm to 697 mm.

[0058] In some embodiments, a protective cover 300 is provided on the outer periphery of the cover 200 , and the protective cover 300 covers at least a portion of the cover 200 .

[0059] In some embodiments, the protective cover 300 is disposed on the outer periphery of the cover body 200 .

[0060] In some embodiments, the edge of the cover 200 includes a step 201 , and the step 201 surrounds the cover 200 .

[0061] In some embodiments, the wear rate G of the mold 1 satisfies: G<G0, where G0 is the material loss in g / cm 2 ; G0 satisfies: 0<G0≤0.1g / cm 2 .

[0062] In some embodiments, silicon powder is loaded into a plurality of molds, and the intervals between adjacent molds are equal.

[0063] In some embodiments, the spacing between adjacent molds 1 is the same as the diameter of the cylinder 100 .

[0064] In some embodiments, G0 is the material loss measured by the abrasion tester under specified conditions, and the unit of material loss is g / cm 2 .

[0065] The present application further provides a silicon block prepared by the above method.

[0066] In some embodiments, the silicon block is crushed to form first particles. Based on the mass of the silicon block, the first particles account for ≥97% of the mass of the silicon block, and the particle size D1 of the first particles satisfies: 10 mm ≤ D1.

[0067] In some embodiments, the particle size D1 of the first particles satisfies the following: 10 mm ≤ D1 ≤ 150 mm. For example, the particle size D1 (mm) of the first particles is any value selected from 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150, or a range consisting of any two values. In other embodiments, the particle size D1 of the first particles satisfies the following: 10 mm ≤ D1 ≤ 70 mm.

[0068] In some embodiments, the silicon ingot is crushed to form second particles, where the second particles account for ≤3% of the mass of the silicon ingot, and the particle size D2 of the second particles satisfies the following: D2 < 10 mm. For example, if the particle size of the second particles is 3 mm ≤ D2 < 10 mm, the percentage is 2-3%. If the particle size of the second particles is 0 mm < D2 < 3 mm, the percentage is ≤ 1%. The silicon ingot obtained in this application has a reasonable particle size distribution after crushing, and a reasonable particle size distribution is formed during the crystal ingot preparation and feeding process, facilitating the feeding operation.

[0069] The crushing method in the present application can be artificial crushing or mechanical vibration crushing. In some embodiments, artificial crushing is adopted.

[0070] Example 1: Load the raw polysilicon powder into the mold 1, as shown in Figures 1 to 4. The mold 1 of the present application is made of polyurethane material. After the loading is completed, use a scraper to scrape or flatten the silicon powder at the loading port, cover the cover 200 and the protective cover 300 to seal the cylinder 100. After the sealing is completed, the mold 1 filled with raw polysilicon powder is placed in the equipment, and the liquid is injected to the set height. The equipment starts to run. During the process, the pressure is set as follows: the pressure is increased to 100MPa at a rate of 20MPa / s for a time range of 15min. After the pressure is released to normal pressure at 30Mpa / s, the furnace is opened to extract the liquid and the mold 1 is taken out; during the pressure application process, the liquid evenly transmits the pressure to all sides of the mold 1, and the pressure deviation between any two sides of the mold 1 is within the range of ±5MPa. Use pure water to rinse the surface of the mold 1. After rinsing, wipe off the residual pure water on the surface of the mold 1, and then unseal and demould; seal and package.

[0071] Examples 2 to 4: The pressurization method is the same as that of Example 1, except that the pressure value and pressurization time are adjusted. The specific parameters are shown in Table 1.

[0072] Comparative Example 1: The pressurization method is the same as that of Example 1, except that the pressure value and pressurization time are adjusted. The specific parameters are shown in Table 1.

[0073] Comparative Example 2: The silicon powder was not pressurized.

[0074] Calculation method: charging ratio = (B + C) / A * 100%, where A is the theoretical charging amount of the crucible, in kg, B is the mass of the silicon powder blocks after pressing and crushing, in kg, and C is the mass of other materials such as doping elements, in kg.

[0075] Table 1 Preparation parameters and results of Examples 1 to 4 and Comparative Examples 1 to 2

[0076] It can be seen from the data of Examples 1 to 4 and Comparative Examples 1 to 2 that the method of the present application increases the charging ratio from 6% in the powder state to a maximum of 100%. It can be seen from the data of Example 4 that although the charging ratio is improved, when the pressurization pressure is too low, it will affect the compaction density and consume labor time.

[0077] Example 5: The preparation method is the same as that of Example 1, except that the pressure and time are adjusted. The pressure is increased to 100 MPa at a pressure increase rate of 20 MPa / s, and the pressurization time is 15 min. After the pressurization is completed, the pressure is increased to 300 MPa at a pressure increase rate of 20 MPa / s, and the pressurization time is 5 min. Specific parameters are shown in Table 2.

[0078] Examples 6 to 15: The preparation method is the same as that of Example 5, except that the pressurization pressure and pressurization time are adjusted. The specific parameters are shown in Table 2.

[0079] Table 2 Preparation parameters and results of Examples 5 to 15

[0080] It can be seen from the results in Table 2 that the present application improves the compaction density by controlling the pressure range and pressure time of pressurization.

[0081] Example 16: The preparation method is the same as that of Example 1, except that the pressure and time are adjusted. The pressure is increased to 50 MPa at a pressure increase rate of 20 MPa / s, and the pressurization time is 1 min. After the pressurization is completed, the pressure is increased to 200 MPa at a pressure increase rate of 20 MPa / s, and the pressurization time is 4 min. Subsequently, the pressure is increased to 400 MPa at a pressure increase rate of 20 MPa / s, and the pressurization is continued for 5 min. Specific parameters are shown in Table 3.

[0082] Example 17 to Example 31: The preparation method is the same as Example 16, except that the pressurization pressure and pressurization time are adjusted. The specific parameters are shown in Table 3.

[0083] Table 3 Preparation parameters and results of Examples 16 to 31

[0084] From the results in Table 3, it can be seen that the present application improves the compaction density by controlling the pressure range and pressure time of pressurization.

[0085] Example 32: The preparation method is the same as that of Example 1, except that the pressure and time are adjusted. The pressure is increased to 50 MPa at a pressure increasing rate of 20 MPa / s, and the pressurization time is 3 minutes. After the pressurization is completed, the pressure is increased to 300 MPa at a pressure increasing rate of 20 MPa / s, and the pressurization time is 4 minutes. Then, the pressure is reduced to 50 MPa at a rate of 20 MPa / s for 1.5 minutes, and then restored to normal pressure at a rate of 20 MPa / s. Specific parameters are shown in Table 4.

[0086] Examples 33 to 45: The preparation method is the same as that of Example 32, except that the pressure and time are adjusted. The specific parameters are shown in Table 4.

[0087] Table 4 Preparation parameters and results of Examples 32 to 45

[0088] The results in Table 4 show that the present invention improves compaction density by controlling the pressure range and duration of pressurization. The pressure relief step has little effect on compaction density, but the dust content during crushing is significantly reduced compared to silicon blocks formed without the pressure relief step.

[0089] In addition, the silicon blocks prepared in the embodiments of the present application have a particle size distribution range after crushing that can be directly used for feeding, and there is no dust pollution during the crushing process.

[0090] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0091] The above is a detailed introduction to a silicon powder molding method, silicon blocks and applications provided by the present application. Specific examples are used in the present application to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for forming silicon powder, wherein: include: Placing the mold (1) filled with silicon powder under a first pressure P1 for a first pressure time T1, satisfying 50MPa≤P1≤600MPa, 7min≤T1≤15min, to obtain a silicon block; The medium applying the first pressure is liquid.

2. The silicon powder molding method according to claim 1, wherein: The first pressure P1 condition is achieved by increasing the pressure, and the pressure increasing step includes increasing the pressure to the first pressure P1 at a first pressure increasing rate v1, satisfying 20 MPa / s≤v1≤30 MPa / s.

3. The silicon powder molding method according to claim 1, wherein: The particle size of the silicon powder is 0.1 to 1000 μm.

4. The silicon powder molding method according to claim 1, wherein: The mold (1) comprises a first surface (110) and a second surface (120) arranged opposite to each other, the first surface (110) and the second surface (120) are connected via a third surface (130), and the first surface (110) and the third surface (130) receive the first pressure P1.

5. The silicon powder molding method according to claim 4, wherein: The first surface (110), the second surface (120) and the third surface (130) receive the first pressure P1; and / or, A pressure deviation PD of the first pressure P1 applied to the first surface (110), the second surface (120) and the third surface (130) satisfies: -5MPa≤PD≤5MPa.

6. The silicon powder molding method according to claim 1, wherein: Also includes, The mold (1) containing silicon powder is placed under a second pressure P2 for a second pressure time T2, satisfying 50MPa≤P2≤600MPa, 1min≤T2≤15min; The mold (1) filled with silicon powder is placed under a third pressure P3 for a third pressure time T3, satisfying 100MPa≤P3≤600MPa, 1min≤T3≤6min.

7. The silicon powder molding method according to any one of claims 1 to 6, wherein: The process further comprises: applying a first pressure relief process to the mold (1) after the pressurization process is completed, wherein the first pressure relief process comprises: reducing the pressure to a pressure P n , lasting T n Time, meet: 10MPa≤P n ≤100MPa, 1min≤T n ≤2min.

8. The silicon powder molding method according to claim 1, wherein: The mold (1) is made of a polyurethane material, and the density ρ0 of the polyurethane material satisfies: 1.00 g / cm 3 ≤ρ0≤1.01g / cm 3 .

9. The silicon powder molding method according to claim 1, wherein: The silicon powder is filled in a plurality of the molds (1), and the spacing between adjacent molds (1) is equal.

10. The silicon powder molding method according to claim 1, wherein: The wear rate G of the mold (1) satisfies: G<G0, wherein G0 is the material loss, in units of g / cm 2 ; The G0 satisfies: 0<G0≤0.

1.

11. The silicon powder molding method according to claim 1, wherein: The mold (1) comprises a cover (200) and a cylinder (100), the cover (200) covers the cylinder (100), and the silicon powder is filled in the cylinder (100); and / or, A protective sleeve (300) is provided on the outer periphery of the cover body (200), and the protective sleeve (300) covers at least a portion of the cover body (200).

12. The silicon powder molding method according to claim 11, wherein: The edge of the cover body (200) comprises a step (201), and the step (201) surrounds the cover body (200).

13. A silicon block, wherein: include: The silicon block is prepared by the silicon powder molding method according to any one of claims 1 to 12.

14. The silicon block according to claim 13, wherein: The silicon block is crushed to form first particles, the mass percentage of the first particles to the silicon block is ≥ 97% based on the mass of the silicon block, and the particle size D1 of the first particles satisfies: 10 mm ≤ D1; and / or, The silicon block is crushed to form second particles. Based on the mass of the silicon block, the mass percentage of the second particles in the silicon block is ≤3%, and the particle size D2 of the second particles satisfies: D2<10 mm.

15. Use of a silicon block obtained by the silicon powder molding method according to any one of claims 1 to 12 or a silicon block according to any one of claims 13 to 14 in the production of Czochralski single crystals.

Images