Method and apparatus for determining angular deviation of grain boundaries in cast single crystal silicon

Abstract

The application discloses a method and a detection device for judging the angle deviation of a crystal boundary in cast single crystal silicon, and relates to the technical field of crystal growth. The method comprises the following steps: cutting a <100> growth crystal direction cast single crystal silicon ingot, wherein the cutting direction is perpendicular to the solidification direction of the cast single crystal silicon ingot, and a single crystal sample is obtained through the cutting; performing etching or photoluminescence testing on the single crystal sample, and obtaining etching pictures or photoluminescence pictures of the single crystal sample; identifying the crystal boundary in the pictures; identifying micro-twins on both sides of the crystal boundary; and judging and calculating the angle deviation θ of the crystal boundary. The judging method is simple and convenient, has high accuracy, can be applied in actual production, and can be effectively used for the guidance of research and development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystal growth, in particular to a method for judging the angle deviation of grain boundaries in cast single crystal silicon and a detection device. BACKGROUND

[0002] Unlike traditional single crystals prepared by the Czochralski method, cast single crystals have a large single feeding amount, and the production cost is lower than that of single crystals prepared by the Czochralski method. At the same time, due to the low dislocation density of cast single crystal silicon wafers, the use of alkali etching process obtains a pyramid-shaped etching surface, which increases the absorption of incident light, so the conversion efficiency is very close to that of Czochralski single crystal products, and is fully applicable to high-efficiency battery technologies such as PERC, and has strong product competitiveness. The single crystal seeds used in the growth of cast single crystals need to be spliced together due to size limitations, and the cast single crystal silicon ingot is generated on the seed crystal.

[0003] The main disadvantages of growing cast single crystal silicon by the above method are: there will be a splicing gap in the splicing of the seed crystal, and the splicing gap in the casting process forms a grain boundary after seeding on the un-melted seed crystal. The actual angle deviation of the grain boundaries formed after seeding of the splicing gap of the adjacent seed crystals cannot be observed by the naked eye, and at the same time, the grain boundaries will also migrate during the growth process, resulting in different angle deviations of the grain boundaries at different growth heights. The angle deviation of such grain boundaries usually needs to be measured using professional equipment, for example, the sample needs to be polished and then analyzed for microstructure using electron backscatter diffraction technology in a scanning electron microscope to obtain the angle deviation of the grain boundary. The detection process is complex and cumbersome, and is difficult to apply in actual production. SUMMARY

[0004] The purpose of the present application is to provide a method for judging the angle deviation of grain boundaries in cast single crystal silicon. The method is simple, easy to implement, and has high accuracy, and is suitable for large-scale production.

[0005] The first aspect of the present application provides a method for judging the angle deviation of grain boundaries in cast single crystal silicon, the judging method comprising:

[0006] cutting a cast single crystal silicon ingot in a <100> growth direction, the cutting direction being perpendicular to the solidification direction of the cast single crystal silicon ingot, and obtaining a single crystal sample by cutting;

[0007] corrosion or photoluminescence testing of the single crystal sample, and obtaining a corrosion picture or a photoluminescence picture of the single crystal sample;

[0008] identifying the grain boundaries in the corrosion picture or the photoluminescence picture;

[0009] identifying the micro-twins on both sides of the grain boundaries;

[0010] judging and calculating the angle deviation θ of the grain boundaries.

[0011] In an implementable mode, the method for identifying the grain boundary is:

[0012] The position of the seed crystal and the splicing joint of the seed crystal of the cast single crystal silicon ingot are known;

[0013] According to the cutting position of the single crystal sample on the cast single crystal silicon ingot, the splicing joint position is corresponded on the single crystal sample, and it is judged whether there is a straight line with a length equal to the length of the splicing joint at the position corresponding to the splicing joint position on the single crystal sample; if there is, the straight line is judged as a grain boundary.

[0014] In an implementable mode, the seed crystal is a cube or a cuboid, and the length of the splicing joint is calculated according to the size of the seed crystal.

[0015] In an implementable mode, the seed crystal and the seed crystal are spliced in a parallel and / or perpendicular manner.

[0016] In an implementable mode, the method for identifying the micro-twin is: identifying a straight line with a length of 1-20 mm in the same region divided by the grain boundary, and if there are at least two parallel or perpendicular 1-20 mm straight lines, it is judged as a micro-twin.

[0017] In an implementable mode, the shape of the single crystal sample is square.

[0018] In an implementable mode, the total thickness deviation of the single crystal sample is less than or equal to 5 mm.

[0019] In an implementable mode, the method for judging and calculating the angle deviation θ of the grain boundary is: selecting two micro-twins on both sides of a single grain boundary, and making the extension lines intersect with the grain boundary; one end of the extension line of the micro-twin away from the grain boundary intersects with the grain boundary, and the other end of the extension line is away from the grain boundary; wherein the extension direction of the extension line of one end of any one of the two selected micro-twins away from the grain boundary is towards the intersection direction of the other micro-twin and the grain boundary, and the included angle formed by the extension lines of the two micro-twins is the angle deviation θ of the grain boundary.

[0020] In the present application, by means of the etching picture or the photoluminescence picture of the single crystal sample, by visual observation, magnifying glass observation or simple image processing software, after knowing the characteristics of the grain boundary and the micro-twin, the grain boundary and the micro-twin can be easily identified, and by using the judgment method of the present application, the deviation value of the grain boundary can be obtained. The method is simple and convenient, has high accuracy, can be applied in actual production, and can be effectively used for research and development guidance.

[0021] The second aspect of the present application provides a detection device, comprising: a grain boundary identification and determination module; the grain boundary identification module identifies straight lines on etching pictures or photoluminescence pictures of a single crystal sample; the single crystal sample is obtained by cutting a cast single crystal silicon ingot in a <100> growth direction, and the cutting direction is perpendicular to the solidification direction of the cast single crystal silicon ingot; the grain boundary identification and determination module pre-knows the positions of a seed crystal and a splicing joint of the seed crystal of the cast single crystal silicon ingot, and determines the positions of the splicing joint on the single crystal sample according to the cutting position of the single crystal sample on the cast single crystal silicon ingot; the positions of the splicing joint are corresponded on the single crystal sample, and it is determined whether there is a straight line equal to the length of the splicing joint on the positions of the splicing joint; if there is, the straight line is determined as a grain boundary.

[0022] and / or;

[0023] a micro-twin identification and determination module; the micro-twin identification and determination module identifies straight lines with a length of 1-20 mm on the etching pictures or photoluminescence pictures of the single crystal sample; if there are at least two straight lines with a length of 1-20 mm parallel to or perpendicular to each other in the same region divided by the grain boundary, it is determined that the straight lines are micro-twins.

[0024] In an implementable manner, the detection device further comprises:

[0025] a grain boundary deviation determination module; the grain boundary determination module calculates the angle deviation θ of the grain boundary according to the included angle between the micro-twin and the grain boundary; the method for determining and calculating the angle deviation θ of the grain boundary is that two micro-twins are selected on both sides of a single grain boundary, and the extended lines of the micro-twins intersect with the grain boundary; one end of the extended line of the micro-twin is intersected with the grain boundary, and the other end of the extended line is away from the grain boundary; wherein the extension direction of the extended line of one end of any one of the two selected micro-twins away from the grain boundary is toward the direction of the intersection of the other micro-twin and the grain boundary, and the included angle formed by the extended lines of the two micro-twins is the angle deviation θ of the grain boundary.

[0026] The detection device related to the second aspect of the present application is mainly applied in the method for determining the angle deviation of the grain boundary of the cast single crystal silicon related to the first aspect of the present application, the grain boundary and the micro-twin can be simply and conveniently identified by using the detection device, the deviation of the grain boundary is determined, the accuracy is high, the detection device can be applied in actual production, and is effectively used for the guidance of research and development. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings described herein are used to provide further understanding of the present application, constitute a part of the present application, and the illustrative embodiments of the present application and the descriptions thereof are used to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0028] Figure 1A flowchart illustrating a method of judging the angle deviation of grain boundaries in cast single crystal silicon according to the present invention is shown.

[0029] Figure 2 A schematic diagram showing one embodiment of seed stitching bottoming of a cast single crystal silicon ingot at the bottom of a crucible is shown.

[0030] Figure 3 A schematic diagram showing another embodiment of seed stitching bottoming of a cast single crystal silicon ingot at the bottom of a crucible is shown.

[0031] Figure 4 A schematic diagram showing the distribution of micro-twins and grain boundaries on a single crystal sample according to the present invention is shown.

[0032] Figure 5 A schematic diagram showing Figure 4 A schematic diagram showing the judgment of the angle deviation of grain boundaries after the micro-twins are extended on a single crystal sample according to the present invention is shown.

[0033] Figure 6 A picture showing the etching of a single crystal sample according to embodiment three of the present invention is shown.

[0034] Figure 7 A picture showing the photoluminescence of a single crystal sample according to embodiment one of the present invention is shown.

[0035] Figure 8 A picture showing the photoluminescence of a single crystal sample according to embodiment two of the present invention is shown. DETAILED DESCRIPTION

[0036] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary of the present disclosure, but is not intended to limit the present disclosure. Also, in the following description, descriptions of well-known functions and constructions are omitted to avoid obscuring the concept of the present disclosure in unnecessary detail.

[0037] Also, the terms "first", "second", etc. are used only for the purpose of description, and are not to be construed as indicating or implying relative importance or a specific number of the technical features indicated. Thus, the features defined with "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise explicitly and specifically limited. The meaning of "several" is one or more, unless otherwise explicitly and specifically limited.

[0038] As Figures 2-3As shown, multiple pieces of seed crystals need to be spliced for use in the growth of cast single crystal, and the cast single crystal silicon ingot is generated on the spliced seed crystals. Due to the existence of splicing gaps in the seed crystal splicing, the splicing joint in the casting process forms a crystal boundary after seeding on the un-melted seed crystal. These crystal boundaries can inhibit the generation of dislocations in the subsequent preparation process of the battery, and improve the crystal quality of the cast single crystal. However, the growth of the crystal boundary will migrate, and the crystal boundary will deviate in the actual growth process. This crystal boundary deviation will affect the dislocation absorption of the subsequent crystal boundary, so understanding the crystal boundary deviation is of great significance for subsequent improvement of the quality of the cast single crystal battery piece. The angle deviation of the crystal boundary in the prior art usually needs to be measured using professional equipment, for example, the sample needs to be polished, and then the electron backscatter diffraction technology is used to analyze the microstructure in the scanning electron microscope to obtain the angle deviation of the crystal boundary. The detection process is complex and cumbersome, and it is difficult to apply in actual production.

[0039] Based on this, the first aspect of the present application discloses a method for judging the angle deviation of the crystal boundary in the cast single crystal silicon, the judging method comprising:

[0040] The cast single crystal silicon ingot with a <100> growth direction is cut, and the cutting direction is perpendicular to the solidification direction of the cast single crystal silicon ingot, and a single crystal sample is obtained by cutting.

[0041] In this step, the growth direction of the cast single crystal silicon ingot is <100>, and the cast single crystal silicon ingot with a <100> growth direction can obtain a pyramid-shaped rough surface in the subsequent preparation of the battery piece, thereby increasing the absorption of incident light, and thus the conversion efficiency is very close to that of the Czochralski single crystal product. The growth direction of the cast single crystal silicon ingot is <100>, and the crystal direction in the growth process of the single crystal is parallel or perpendicular to each other, and the micro-twin growth is perpendicular or parallel to each other.

[0042] In this step, the growth direction of the cast single crystal silicon ingot is <100>, and the cast single crystal silicon ingot with a <100> growth direction can obtain a pyramid-shaped rough surface in the subsequent preparation of the battery piece, thereby increasing the absorption of incident light, and thus the conversion efficiency is very close to that of the Czochralski single crystal product. The growth direction of the cast single crystal silicon ingot is <100>, and the crystal direction in the growth process of the single crystal is parallel or perpendicular to each other, and the micro-twin growth is perpendicular or parallel to each other.

[0043] In an implementable manner, the single crystal sample can be directly a cast single crystal silicon wafer, and the cutting direction of the cast single crystal silicon wafer is perpendicular to the solidification direction of the cast single crystal silicon ingot.

[0044] In an implementable manner, the total thickness deviation of the single crystal sample is less than or equal to 5 mm. If the thickness deviation is too large, it indicates that the upper and lower surfaces of the single crystal sample are not parallel, which can cause the micro-twins originally perpendicular to each other in the same area to become non-perpendicular. However, if the thickness deviation is controlled within 5 mm, the deviation between the micro-twins is very small, which makes the measurement more accurate.

[0045] The single crystal sample is subjected to etching or photoluminescence test, and etching pictures or photoluminescence pictures of the single crystal sample are obtained.

[0046] In this step, the single crystal sample is subjected to etching or photoluminescence test, and etching pictures or photoluminescence pictures after the test are obtained. The pictures are mainly used for subsequent identification of grain boundaries and micro-twins.

[0047] In an implementable manner, the single crystal sample is etched by using a chemical solution, such as a mixed acid of nitric acid and hydrofluoric acid, an alkali solution of sodium hydroxide or potassium hydroxide, so that grain boundaries, micro-twins or other manifestations are formed, thereby facilitating subsequent identification of grain boundaries.

[0048] In a specific embodiment, as shown in Figure 6 A mixed acid of nitric acid and hydrofluoric acid with a weight percentage of nitric acid to hydrofluoric acid = 3:1 is used to react with the single crystal sample. After 10 minutes of reaction, the surface of the single crystal sample is washed clean with water, and an optical camera is used to obtain a picture of the surface of the single crystal sample. In the picture, various lengths of straight lines can be observed in the single crystal sample.

[0049] In another implementable manner, a photoluminescence device is used to obtain the picture. Photoluminescence can reflect defects in the single crystal sample, including dislocations, micro-twins, grain boundaries and other defects. Through the acquisition of the photoluminescence test picture, a picture for subsequent identification of grain boundaries and micro-twins can be effectively obtained. In a specific embodiment, as shown in Figures 7-8 A Semilab PL tester is used to perform photoluminescence test on the single crystal sample, and a photoluminescence picture of the single crystal sample is obtained.

[0050] Grain boundaries in the etching picture or the photoluminescence picture are identified.

[0051] In this step, grain boundaries in the etching picture or the photoluminescence picture of the single crystal sample are identified according to the growth characteristics of the grain boundaries in the cast single crystal silicon ingot.

[0052] In an implementable manner, the method for identifying grain boundaries is as follows:

[0053] The position of the seed crystal and the splicing seam of the seed crystal of the cast single crystal silicon ingot is known.

[0054] According to the cutting position of the single crystal sample on the cast single crystal silicon ingot, the splicing seam position is corresponded on the single crystal sample, and it is judged whether there is a straight line with the length of the splicing seam at the position corresponding to the splicing seam position on the single crystal sample; if there is, the straight line is judged as a grain boundary.

[0055] Figure 2 and Figure 3 It is a schematic diagram of seed splicing and bottom laying of cast single crystal silicon ingot at the bottom of crucible; as Figures 2-3 shown, because the bottom area of the crucible loaded with cast single crystal silicon ingot is large, the bottom of the crucible needs to be covered with seeds, and the seeds are generally obtained by single crystal silicon rod or high-quality cast single crystal silicon ingot, compared with the area of the bottom of the crucible, the size of the seed is small, and it is impossible to cover the bottom of the crucible with one seed, so multiple seeds need to be spliced and laid, as Figure 2 shown, the shape of the seed is generally cuboid or square, and the laying of the seed can be uniformly laid as Figure 2 shown, or irregularly laid as Figure 3 shown, the size of the seed can be set according to actual needs, and the splicing of the seed and the seed forms a splicing seam with a certain length, the splicing seam is a straight line, and the length of the splicing seam can be calculated according to the size of the seed, and the length of the splicing seam is equal to the maximum length of the seed between the single seed and the adjacent seed.

[0056] Specifically, the splicing seam between the seeds will generate grain boundaries along with the solidification growth of the cast single crystal silicon ingot from bottom to top, and the grain boundaries grow along the splicing seams perpendicular to the solidification direction of the cast single crystal silicon ingot, and correspond to the position of the splicing seam, so the position of the grain boundary corresponding to the position of the splicing seam can be accurately identified.

[0057] As Figure 4 the schematic diagram shows, a straight line with a certain length can be observed on the single crystal sample, the position of the grain boundary corresponds to the position of the splicing seam of the seed, and such straight line is generally considered as a grain boundary, and the length of the grain boundary is equal to the length of the splicing seam.

[0058] Because the position and length of the grain boundary on the cast single crystal silicon ingot are adapted to the length and position of the splicing seam of the seed, the position of the grain boundary on the single crystal sample can be judged by pre-knowing the splicing seam position of the seed and the seed.

[0059] In one embodiment, the worker records the picture of the seed crystal after the seed crystal is spliced, for example, the lower left corner of the crucible can be set as the origin (0, 0), and along the point, the X coordinate is set from left to right, and the Y coordinate is set from bottom to top, and the positions of all the seed crystals after splicing are identified; after the single crystal silicon ingot is grown, the worker records the position of the lower left corner of the single crystal silicon ingot as the origin (0, 0), and along the point, the X coordinate is set from left to right, and the Y coordinate is set from bottom to top, and the position of the single crystal silicon ingot after growth is identified; when the single crystal sample is cut, the worker corresponds the position of the entire single crystal silicon ingot with the splicing position of the seed crystal, and if a straight line equal to the length of the splicing seam is found at the position corresponding to the splicing seam of the seed crystal, it can be determined that the straight line is the grain boundary. In one embodiment, the worker can input the seed crystal and the splicing picture of the seed crystal and the picture of the single crystal silicon ingot after growth into various analysis software, such as image processing software or Matlab software, and through simple operation, the automatic correspondence of the seed crystal and the splicing seam of the seed crystal in the single crystal silicon ingot can be automatically obtained; further, the position of the single crystal sample cut from the single crystal silicon ingot can also be easily corresponded on the single crystal silicon ingot, realizing the correspondence of the splicing seam of the seed crystal and the position of the single crystal sample.

[0060] In one embodiment, as shown in FIG. 1, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary. Figure 6 Figure 3 In one embodiment, as shown in FIG. 2, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary.

[0061] In one embodiment, as shown in FIG. 3, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary. Figure 7 Figure 2 In one embodiment, as shown in FIG. 4, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary.

[0062] In one embodiment, as shown in FIG. 5, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary. Figure 8 Figure 3 In one embodiment, as shown in FIG. 6, the seed crystal and the seed crystal of the single crystal silicon ingot are spliced in a staggered manner, and a straight line corresponding to the splicing seam is found on the single crystal silicon sample grown at the position of the splicing seam, and the straight line is the grain boundary.

[0063] Identifying micro-twins on both sides of the grain boundary;

[0064] In this step, the micro-twins in the surface etching picture or the photoluminescence picture of the single crystal sample are identified according to the growth characteristics of the micro-twins. ​​​

[0065] In one embodiment, the micro-twin identification method is to identify a straight line with a length of 1-20 mm in the same region divided by the grain boundary, for example, a straight line with a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, or 20 mm. If there are at least two parallel or perpendicular 1-20 mm straight lines, it is determined to be a micro-twin. Since the main source of twinning is the twinning nucleation and growth caused by local temperature fluctuations or local composition differences at the growth interface during growth, the length of the growth is usually short. According to the experimental data of the inventor, the length of the micro-twin is between 1-20 mm.

[0066] Since the growth direction of the cast single crystal silicon is <100>, the micro-twin nucleates and grows due to local temperature fluctuations or composition differences during seeding and growth. The growth surface of the micro-twin is a symmetrical (111) surface, so the micro-twin usually appears in pairs and is perpendicular or parallel to each other. Since the micro-twin nucleates and grows in a very small local area, the length of the micro-twin is usually short. Since the cast single crystal silicon ingot uses multiple seeds and splices the seeds, there is a crystal direction difference between the seeds and the seeds. Therefore, the micro-twins in the same region divided by the grain boundary are perpendicular or parallel to each other, and the angle relationship between the micro-twins in different regions is related to the crystal direction difference between adjacent seeds.

[0067] As shown in Figure 4 , two grain boundaries form four regions, and each region has multiple straight lines with a length of 1-20 mm (white lines in the figure). These straight lines are perpendicular or parallel to each other in the same region divided by the grain boundary. For such straight lines, it is determined to be a micro-twin. Since the growth direction of the cast single crystal silicon is <100>, the micro-twin is generated due to temperature fluctuations or impurity interference during seeding and growth, and the growth surface is a symmetrical (111) surface. Therefore, the micro-twin basically appears in pairs and is perpendicular or parallel to each other. The (111) surfaces in different seeds have an angle difference due to different processing angles of adjacent seeds. The angle difference is equivalent to the angle deviation of the grain boundary, so the deviation of the grain boundary can be determined by the angle between the micro-twin and the grain boundary.

[0068] Further, select any two perpendicular micro-twins and extend them to intersect with the grain boundary to obtain the angle between the perpendicular micro-twins and the grain boundary. As shown in Figure 4As shown, in the same grain boundary region in the lower left corner, two mutually perpendicular microtwins A and B intersect the grain boundary with their extended lines, resulting in two acute angles α1 and α2. Since the two microtwins are perpendicular, α1 + α2 = 90 degrees. In the same grain boundary region in the lower right corner, two mutually perpendicular microtwins C and D intersect the grain boundary with their extended lines, resulting in two acute angles β1 and β2. Since the two microtwins are perpendicular, β1 + β2 = 90 degrees. α1, α2, β1, and β2 can be measured using a simple angle gauge. The acute angles α1, α2, β1, and β2 are the angles between microtwins A, B, C, and D and the grain boundary, respectively.

[0069] In a specific embodiment, such as Figure 6 As shown, within the same grain boundary region in the upper right corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines are microtwins. The acute angle between the extension of the microtwin and the grain boundary is 50 degrees, and the angle between the microtwin and the grain boundary is also 50 degrees. Similarly, within the same grain boundary region in the lower right corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines are also microtwins. The acute angle between the extension of the microtwin and the grain boundary is 65 degrees, and the angle between the microtwin and the grain boundary is also 65 degrees.

[0070] In a specific embodiment, such as Figure 7 As shown, within the same grain boundary region in the lower left corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines represent microtwins. The acute angle between the extension of the microtwin and the grain boundary is 52 degrees, and the angle between the microtwin and the grain boundary is also 52 degrees. Similarly, within the same grain boundary region in the lower right corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines also represent microtwins. The acute angle between the extension of the microtwin and the grain boundary is 31 degrees, and the angle between the microtwin and the grain boundary is also 31 degrees.

[0071] In a specific embodiment, such as Figure 8 As shown, within the same grain boundary region in the lower left corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines represent microtwins. The acute angle between the extension of the microtwin and the grain boundary is 64 degrees, and the angle between the microtwin and the grain boundary is also 64 degrees. Similarly, within the same grain boundary region in the lower right corner, there are multiple parallel straight lines with lengths ranging from 1 to 20 meters. These lines also represent microtwins. The acute angle between the extension of the microtwin and the grain boundary is 51 degrees, and the angle between the microtwin and the grain boundary is also 51 degrees.

[0072] The angular deviation θ of the grain boundary is determined and calculated.

[0073] In this step, the angular deviation θ of the grain boundary is determined by the angle between the grain boundary and the microtwin.

[0074] In an implementable manner, the calculation method of the grain boundary angle deviation is: two micro-twins on two sides of the single grain boundary are selected respectively, and the extended lines thereof intersect the grain boundary; one end of the extended line of the micro-twin is intersected with the grain boundary, and the other end of the extended line is away from the grain boundary; wherein the extension direction of the extended line of the one end of any one of the two selected micro-twins away from the grain boundary is toward the one end of the other micro-twin intersected with the grain boundary, and the included angle formed by the extended lines of the two micro-twins is the angle deviation θ of the grain boundary.

[0075] As shown in Figure 4 , there are two micro-twins on the opposite sides of the same grain boundary, the left side is micro-twin A and micro-twin B, and the right side is micro-twin C and micro-twin D. The micro-twins A, B, C and D are respectively extended with the grain boundary, and the four acute angles α1, α2, β2 and β1 are respectively formed. The acute angles α1, α2, β1 and β2 are the included angles of the micro-twins A, B, C and D with the grain boundary. Since the growth surface of the micro-twin is the (111) crystal surface family, the included angle of the extended line of the micro-twin with the grain boundary represents the included angle of one of the (111) crystal surfaces with the grain boundary, and the angle deviation of the grain boundary can be determined by measuring the difference of the included angles of the two sides of the grain boundary.

[0076] Further, the micro-twins A, B, C and D are respectively extended with the one end away from the grain boundary. As shown in Figure 5 , one end of the extended line of the micro-twin A is intersected with the grain boundary, and the other end of the extended line extends downward in the direction away from the grain boundary. The intersected one ends of the micro-twins C and D with the grain boundary are both below, that is, the extension direction of the other end of the extended line of the micro-twin away from the grain boundary. The extension direction of the other end of the micro-twin D away from the grain boundary is upward, that is, toward the intersected one end of the micro-twin A with the grain boundary. However, the extension direction of the other end of the micro-twin C away from the grain boundary is downward, that is, away from the intersected one end of the micro-twin A with the grain boundary. Therefore, the angle deviation needs to select the intersected one end of the micro-twin A and the micro-twin D, and take the included angle thereof. Similarly, one end of the extended line of the micro-twin B is intersected with the grain boundary, and the other end of the extended line extends upward in the direction away from the grain boundary. The intersected one end of the micro-twin C with the grain boundary is above the intersected one end of the micro-twin B with the grain boundary, and the extension direction of the other end of the micro-twin C away from the grain boundary is downward, that is, toward the intersected one end of the micro-twin B with the grain boundary. Therefore, the angle deviation θ needs to select the intersected one end of the micro-twin B and the micro-twin C, and take the included angle thereof.

[0077] According to the angle congruence theorem of a triangle, the angle between the extensions of the micro-twin A and the micro-twin C is 180-β1-α1, and the angle between the extensions of the micro-twin B and the micro-twin D is 180-α2-β2, which is not the difference between the angles between the two micro-twins, and thus cannot represent the deviation of the two micro-twins; according to the exterior angle theorem of a triangle, the angle between the extensions of the micro-twin A and the micro-twin D is β1-α1, and the angle between the extensions of the micro-twin B and the micro-twin C is α2-β2; since α1+α2=90 degrees and β1+β2=90, then β1-α1=(90-β2)-(90-α2)=α2-β2; that is, the angle between the extensions of the micro-twin B and the micro-twin C is equal to the angle between the extensions of the micro-twin A and the micro-twin D, which is equal to the angular deviation θ of the grain boundary. The angular deviation of the grain boundary can be calculated by the difference between the angles of the two micro-twins and the grain boundary.

[0078] The second aspect of the present application discloses a detection device, which comprises a grain boundary identification and judgment module; the grain boundary identification module identifies straight lines on etching pictures or photoluminescence pictures of a single crystal sample; the single crystal sample is obtained by cutting a cast single crystal silicon ingot with a <100> growth direction, and the cutting direction is perpendicular to the solidification direction of the cast single crystal silicon ingot; the grain boundary identification and judgment module pre-knows the positions of the seed crystal and the seed crystal splicing seam of the cast single crystal silicon ingot, and according to the cutting position of the single crystal sample on the cast single crystal silicon ingot, the splicing seam position is corresponded on the single crystal sample, and it is judged whether there is a straight line equal to the length of the splicing seam at the splicing seam position; if there is, the straight line is judged as a grain boundary.

[0079] The steps of the judgment method of the grain boundary identification and judgment module are: first, the picture of the splicing seam position of the seed crystal and the seed crystal of the crucible bottom is obtained, and is input into the analysis software of the computer, such as image processing software or Matlab software; after the cast single crystal silicon ingot is completed, the position of the single crystal sample on the cast single crystal silicon ingot is marked; after the cast single crystal sample is etched or tested by photoluminescence, the etching picture or the photoluminescence picture of the single crystal sample is input into the analysis software of the computer, and it is identified whether there is a straight line equal to the length of the splicing seam position by corresponding with the picture of the splicing seam position of the seed crystal and the seed crystal, the straight line is the grain boundary.

[0080] The detection device further comprises a micro-twin identification and judgment module; the micro-twin identification and judgment module identifies straight lines with a length of 1-20 mm on the etching picture or the photoluminescence picture of the single crystal sample; if there are at least two straight lines with a length of 1-20 mm parallel or perpendicular to each other in the same region divided by the grain boundary, it is judged that the straight lines are micro-twins.

[0081] The steps of the judgment method of the micro-twin identification and judgment module are: firstly, identifying the grain boundary on the analysis software on the computer, and identifying whether there are parallel or perpendicular straight lines in the same grain boundary area, the number of the straight lines is at least two, and the length of the straight line is less than 1-20 mm, then the straight line is judged as a micro-twin.

[0082] The detection device also includes a grain boundary deviation judgment module; the grain boundary judgment module calculates the angle deviation θ of the grain boundary according to the included angle between the micro-twin and the grain boundary.

[0083] The steps of the judgment method of the grain boundary deviation judgment module are: selecting any micro-twin and the grain boundary on both sides of the same grain boundary to intersect, wherein when the extension direction of the extension line of any one of the two selected micro-twins away from the grain boundary is towards the intersection end of the other micro-twin and the grain boundary, the included angle formed by the extension lines of the two micro-twins is the angle deviation θ of the grain boundary.

[0084] The steps of the judgment method of the micro-twin identification and judgment module are: on the computer analysis software, the extension line of any micro-twin on both sides of the same grain boundary is selected to intersect with the grain boundary, when among the two selected micro-twins on both sides, the extension direction of the extension line of any one of the micro-twins away from the grain boundary is towards the intersection end of the other micro-twin and the grain boundary, then the two micro-twins are micro-twins meeting the conditions, and the included angle formed by the extension lines of the two micro-twins is the angle deviation θ of the grain boundary.

[0085] The second aspect of the detection device disclosed by the application is mainly applied to the method for judging the grain boundary angle deviation of the cast single crystal silicon disclosed by the first aspect of the application. The detection device can simply and conveniently identify the grain boundary and the micro-twin, and judge the grain boundary deviation, has high accuracy, can be applied in actual production, and is effectively used for the guidance of research and development.

[0086] The following describes in detail a method for judging the grain boundary angle deviation of cast single crystal silicon according to the first aspect of the application through two specific embodiments. It should be understood that the following description is only exemplary and is not a specific limitation on the application.

[0087] Example 1

[0088] Reference Figure 7 The single crystal sample is placed in a photoluminescence device for testing to obtain a photoluminescence image, and the longitudinal grain boundary is identified according to the identification of the grain boundary disclosed in the application;

[0089] The grain boundary in the longitudinal direction is selected, and two micro-twins on both sides of the grain boundary in the longitudinal direction are identified according to the method for identifying the micro-twins on both sides of the grain boundary in the longitudinal direction disclosed in the present application, two micro-twins are selected, and the extension direction of the extension line of one end of any one of the micro-twins away from the grain boundary is toward the intersection end direction of the other micro-twin and the grain boundary, and the included angles α and β of the two micro-twins and the grain boundary in the longitudinal direction are measured. The angle α is 52 degrees, and the angle β is 31 degrees, and the angle deviation θ of the grain boundary is |α-β|=|52 degrees-31 degrees|=21 degrees.

[0090] The angle deviation of the grain boundary is measured by the electron backscattering diffraction technology to be 20.3 degrees, and thus it can be known that the angle error between the 21 degrees measured by the method and the 20.3 degrees measured by the electron backscattering diffraction technology is 21 degrees-20.3 degrees=0.7 degrees, and the measurement deviation is less than 1 degree, which meets the detection standard.

[0091] Example Two

[0092] Reference Figure 8 The single crystal sample is placed into a photoluminescence device for testing to obtain a photoluminescence image, and the grain boundary in the longitudinal direction is identified according to the method for identifying the grain boundary disclosed in the present application.

[0093] The grain boundary in the longitudinal direction is selected, and two micro-twins on both sides of the grain boundary in the longitudinal direction are identified according to the method for identifying the micro-twins on both sides of the grain boundary in the longitudinal direction disclosed in the present application, two micro-twins are selected, and the extension direction of the extension line of one end of any one of the micro-twins away from the grain boundary is toward the intersection end direction of the other micro-twin and the grain boundary, and the included angles α and β of the two micro-twins and the grain boundary in the longitudinal direction are measured.

[0094] The angle α is 64 degrees, and the angle β is 51 degrees, and the angle deviation θ of the grain boundary is |α-β|=64 degrees-51 degrees=13 degrees.

[0095] The angle deviation of the grain boundary is measured by the electron backscattering diffraction technology to be 13.5 degrees, and thus it can be known that the angle error between the 13 degrees measured by the method and the 13.5 degrees measured by the electron backscattering diffraction technology is 13.5 degrees-13 degrees=0.5 degrees, and the measurement deviation is less than 1 degree, which meets the detection standard.

[0096] Example Three

[0097] Reference Figure 6 The single crystal sample is etched according to the etching method in the present application to obtain an etching photo, and the grain boundary in the right transverse direction is identified according to the method for identifying the grain boundary disclosed in the present application.

[0098] Select the right grain boundary in the transverse direction, and identify the microtwins on both sides of the grain boundary in the longitudinal direction according to the microtwin determination method disclosed in this invention. Select two microtwins, wherein the extension direction of the extension line of the end of any one of the microtwins away from the grain boundary is toward the end of the other microtwin that intersects with the grain boundary, and measure the included angles α and β between the two microtwins and the grain boundary in the longitudinal direction.

[0099] Using an angle ruler, we obtain α = 65 degrees and β = 50 degrees. Since α > 45 degrees and β > 45 degrees, the angular deviation of the grain boundary θ = |α - β| = 65 degrees - 50 degrees = 15 degrees.

[0100] The angular deviation of the grain boundary was measured to be 14.4 degrees using electron backscatter diffraction. Therefore, the error between the 15 degrees measured by the judgment method and the angular deviation measured by electron backscatter diffraction is 15 degrees - 14.4 degrees = 0.6 degrees. The measurement deviation is less than 1 degree, which meets the testing standard.

[0101] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0102] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method for determining grain boundary angle deviation in cast single-crystal silicon, characterized in that, The determination method includes: right <100> The cast single-crystal silicon ingot with the growth crystal orientation is cut in a direction perpendicular to the solidification direction of the cast single-crystal silicon ingot to obtain a single-crystal sample. The single crystal sample was subjected to corrosion or photoluminescence tests, and corrosion images or photoluminescence images of the single crystal sample were obtained. Identify grain boundaries in the etched or photoluminescent images; Identify microtwins on both sides of the grain boundary; the method for identifying microtwins is as follows: identify straight lines with a length of 1-20 mm in the same region divided by the grain boundary. If there are at least two straight lines of 1-20 mm that are parallel or perpendicular to each other, they are determined to be microtwins. The angular deviation θ of the grain boundary is determined and calculated. The method for determining and calculating the angular deviation θ of the grain boundary is as follows: two microtwins are selected on both sides of a single grain boundary, and their extensions intersect the grain boundary; one end of the extension of the microtwin intersects the grain boundary, and the other end of the extension is away from the grain boundary; wherein, the extension direction of the extension of the end of any one of the two microtwins away from the grain boundary is towards the end of the other microtwin intersecting the grain boundary, and the included angle formed by the extensions of the two microtwins is the angular deviation θ of the grain boundary.

2. The method for determining grain boundary angle deviation in cast single-crystal silicon as described in claim 1, characterized in that, The method for identifying the grain boundaries is as follows: The location of the splice seam between the seed crystals of the cast single-crystal silicon ingot is known; Based on the cutting position of the single crystal sample on the cast single crystal silicon ingot, the splicing seam position is matched with the single crystal sample, and it is determined whether there is a straight line on the single crystal sample at the position corresponding to the splicing seam position that is equal to the length of the splicing seam; if so, the straight line is determined to be a grain boundary.

3. The method for determining grain boundary angle deviation in cast single-crystal silicon as described in claim 2, characterized in that, The seed crystal is a cube or cuboid, and the length of the splicing seam is calculated based on the size of the seed crystal.

4. The method for determining grain boundary angle deviation in cast single-crystal silicon as described in claim 3, characterized in that, The seed crystals are spliced ​​together in a manner that is parallel and / or perpendicular to each other.

5. The method for determining grain boundary angle deviation in cast single-crystal silicon as described in claim 1, characterized in that: The single crystal sample is square in shape.

6. The method for determining grain boundary angle deviation in cast single-crystal silicon as described in claim 1, characterized in that, The total thickness deviation of the single crystal sample is less than or equal to 5 mm.

7. A detection device, characterized in that, include: Grain boundary identification and judgment module; the grain boundary identification module identifies straight lines in the corrosion image or photoluminescence image of a single crystal sample; The single crystal sample is a pair <100> The cast single crystal silicon ingot with the growth crystal orientation is cut, and the cutting direction is perpendicular to the solidification direction of the cast single crystal silicon ingot. The grain boundary identification and judgment module knows in advance the position of the splicing seam between the seed crystals of the cast single crystal silicon ingot, and determines the cutting position of the single crystal sample on the cast single crystal silicon ingot according to the cutting position of the single crystal sample. The splicing seam position is aligned with the single crystal sample, and it is determined whether there is a straight line at the splicing seam position that is equal to the length of the splicing seam; if so, the straight line is determined to be a grain boundary. and / or; Microtwin identification and judgment module; The microtwin identification and judgment module identifies straight lines with a length between 1-20 mm on the corrosion image or photoluminescence image of the single crystal sample. If there are at least two parallel or perpendicular straight lines with a length of 1-20 mm in the same region divided by the grain boundary, it is judged to be a microtwin.

8. The detection device as described in claim 7, characterized in that, The detection device further includes: A grain boundary deviation judgment module; the grain boundary judgment module calculates the angular deviation θ of the grain boundary based on the angle between the microtwin and the grain boundary; the method for judging and calculating the angular deviation θ of the grain boundary is as follows: two microtwins are selected on both sides of a single grain boundary, and their extensions intersect the grain boundary; one end of the extension of the microtwin intersects the grain boundary, and the other end of the extension is away from the grain boundary; wherein, the extension direction of the end of any one of the two selected microtwins away from the grain boundary is towards the end of the other microtwin intersecting the grain boundary, and the angle formed by the extensions of the two microtwins is the angular deviation θ of the grain boundary.

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