CN113293434A - Seed crystal laying method and monocrystalline silicon casting method - Google Patents

Abstract

The invention provides a seed crystal laying method and a monocrystalline silicon casting method, wherein the seed crystal laying method comprises the following steps: laying a plurality of single crystal seed crystals at the bottom of a casting container, integrally splicing the plurality of single crystal seed crystals into a seed crystal layer, wherein in the single crystal seed crystals spliced on the side surfaces, the two mutually contacted side surfaces have different crystal directions; the multi-block single crystal seed crystals comprise at least one rectangular seed crystal and a plurality of first square seed crystals, the first square seed crystals are spliced to form a base seed crystal part which is integrally square, the long edge of the rectangular seed crystal is aligned and spliced with the side edge of the base seed crystal part, the length of the long edge of the rectangular seed crystal is equal to that of the side edge of the base seed crystal part, and the length of the short edge of the rectangular seed crystal is greater than that of the first square seed crystal. The seed crystal laying method can form a sacrificial region at the outermost periphery of a growing silicon ingot, and further improves the yield of the whole small square ingot by omitting the sacrificial region.

Description

Seed crystal laying method and monocrystalline silicon casting method

Technical Field

The invention relates to the technical field of casting single crystals, in particular to a seed crystal laying method and a single crystal silicon casting method.

Background

Photovoltaic power generation can convert solar energy into electric energy, and is a very clean energy utilization mode. The silicon solar cell is the most common photovoltaic power generation equipment at present, and has the advantages of relatively mature technology and high photoelectric conversion efficiency. The power generation efficiency of the monocrystalline silicon solar cell is higher than that of the polycrystalline silicon solar cell, but the conventional monocrystalline silicon preparation process is a czochralski process, so that the production cost is remarkably higher, and the monocrystalline silicon solar cell becomes one of bottlenecks which restrict the large-scale application of monocrystalline silicon.

Casting techniques refer to melting of the raw materials followed by cooling to form an ingot. Casting techniques are mostly used to prepare polycrystalline materials. With the further development of the technology, on the basis of the conventional polycrystalline silicon casting process, monocrystalline seed crystals are paved at the bottom of a casting container, and a square monocrystalline silicon ingot can be formed after directional solidification. The casting process can reduce the production cost of the monocrystalline silicon to be comparable with that of polycrystalline silicon, and the performance of the solar cell manufactured by the monocrystalline silicon is comparable with that of the monocrystalline silicon prepared by the traditional Czochralski process, so that the performance-price ratio is high, and the commercial application value is very high.

The seed crystal laying method in the traditional monocrystalline silicon casting process comprises the following steps: the square seed crystals with the growth surfaces of (100) are alternately spliced, and the crystal directions of the contacted side surfaces of the adjacent seed crystals are different, so that a crystal boundary is formed in the actual casting process, and the proliferation of dislocation in the crystals is inhibited. After the seed crystals are laid, the silicon material is poured onto the seed crystals, heated and melted, and then cooled to grow crystals, so that silicon ingots growing along crystal faces of the seed crystals are prepared. After the silicon ingot is formed, squaring treatment is needed, specifically, the silicon ingot is divided along the boundary line of the seed crystal to obtain a plurality of small square ingots. However, among the small square ingots divided by such a process, the small square ingots located at the periphery are significantly inferior in quality, which lowers the yield of cast single crystal silicon.

Disclosure of Invention

Based on this, there is a need for a seed crystal laying method capable of improving the quality of a small square ingot located at the outer peripheral portion.

According to one embodiment of the present invention, a seed crystal laying method includes the steps of:

laying a plurality of single crystal seed crystals at the bottom of a casting container, integrally splicing the single crystal seed crystals into a seed crystal layer, wherein the crystal directions of two mutually spliced side surfaces of two adjacent single crystal seed crystals are different; the single crystal seed crystals comprise at least one rectangular seed crystal and a plurality of first square seed crystals, the first square seed crystals are spliced to form a base seed crystal part which is integrally square, the long edge of the rectangular seed crystal is aligned and spliced with the side edge of the base seed crystal part, the length of the long edge of the rectangular seed crystal is equal to that of the side edge of the base seed crystal part, and the length of the short edge of the rectangular seed crystal is greater than that of the first square seed crystal.

In one embodiment, the rectangular seed crystal comprises more than two rectangular seed crystals, and each rectangular seed crystal is spliced with different side edges of the basic seed crystal part.

In one embodiment, two rectangular seed crystals are respectively spliced with two adjacent side edges of the base seed crystal part, at least one second square seed crystal is further included in the plurality of single crystal seed crystals, the side length of the second square seed crystal is equal to the length of the short edge of the rectangular seed crystal, and two adjacent side edges of the second square seed crystal are respectively spliced with two adjacent short edges of the two adjacent rectangular seed crystals.

In one embodiment, the length of the side edge of the first square seed crystal is more than half of the length of the short side edge of the rectangular seed crystal.

In one embodiment, the length of the short side of the rectangular seed crystal is longer than the length of the side of the first square seed crystal by more than 10 mm.

In one embodiment, the length of the short side of the rectangular seed crystal is 10-30 mm longer than that of the side of the first square seed crystal.

In one embodiment, in the adjoining single crystal seed crystal, the difference in orientation between the two side surfaces in contact with each other is 10 ° to 90 °.

In one embodiment, the first square seed crystal has a first growth face and a second growth face which are opposite, and in two first square seed crystals which are laterally spliced, the first growth face of one of the first square seed crystals is arranged to face upward, and the second growth face of the other of the first square seed crystals is arranged to face upward.

Further, a single crystal silicon casting method comprises the seed crystal laying method of any one of the above embodiments, wherein the single crystal seed crystal is single crystal silicon.

In one embodiment, after a plurality of single crystal seeds are integrally spliced into the seed layer, the method further comprises the following steps:

paving a silicon material on a seed crystal layer in the casting container, heating to melt the silicon material, and cooling to cool and grow the molten silicon material to form a silicon ingot;

and dividing the silicon ingot along the direction of the side edge of each first square seed crystal by taking the length of the side edge of the first square seed crystal as the square size, and dividing the silicon ingot along the position, away from the side edge of the basic seed crystal by the square size, on the rectangular seed crystal.

The inventors have found that the proportion of defects in the crystal grown on the seed crystal laid on the outer edge and in contact with the casting vessel is much higher than that of the silicon ingot grown on the seed crystal in the middle region due to impurities, thermal stress, and the like. In the traditional technology, a plurality of square seed crystals are usually directly spliced into a whole seed crystal layer and placed in a casting container for growth of monocrystalline silicon, which inevitably causes more defects and poor quality in the monocrystalline silicon ingot which is positioned at the periphery after being divided.

In the seed crystal laying method of the embodiment, the basic seed crystal part is similar to that in the traditional technology and comprises a plurality of first square seed crystals which are aligned and spliced; the rectangular seed crystal is spliced outside the basic seed crystal part, the long edge of the rectangular seed crystal is aligned with the edge of the basic seed crystal part in length, and the short edge of the rectangular seed crystal is longer than the edge of the first square seed crystal. Because the defects in the growth process are mainly concentrated at the outer edge of the grown single crystal, and the short edge of the rectangular seed crystal arranged on the side edge of the basic seed crystal part is longer, the part of the edge of the rectangular seed crystal far away from the basic seed crystal part can be removed in the subsequent squaring process, the defects in the single crystal material after the squaring can be reduced, and the yield of the cast single crystal is improved.

Drawings

FIG. 1 is a schematic view of a seed crystal placement method of example 1;

FIG. 2 is a schematic illustration of a dividing line in the squaring process of example 1;

FIG. 3 is a PL test puzzle for a head monocrystalline silicon wafer according to example 1;

FIG. 4 is a schematic view of a seed crystal deposition method according to example 2;

FIG. 5 is a schematic illustration of a dividing line in the squaring process of example 2;

FIG. 6 shows a PL test puzzle for a head monocrystalline silicon wafer according to example 2;

FIG. 7 is a schematic view of a seed crystal application method of comparative example 1;

FIG. 8 is a schematic drawing of a dividing line in the squaring process of comparative example 1;

FIG. 9 shows a PL test puzzle for a header monocrystalline silicon wafer according to comparative example 1.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. As used herein, "plurality" includes two and more than two items. As used herein, "above a certain number" should be understood to mean a certain number and a range greater than a certain number.

The inventors have found that the proportion of defects in the crystal grown on the seed crystal laid on the outer edge and in contact with the casting vessel is much higher than that of the silicon ingot grown on the seed crystal in the middle region due to impurities, thermal stress, and the like. In the traditional technology, a plurality of square seed crystals are usually directly spliced into a whole seed crystal layer and placed in a casting container for growth of monocrystalline silicon, which inevitably causes more defects and poor quality in the monocrystalline silicon ingot which is positioned at the periphery after being divided.

According to one embodiment of the present invention, a seed crystal laying method includes the steps of:

laying a plurality of single crystal seed crystals at the bottom of a casting container, integrally splicing the plurality of single crystal seed crystals into a seed crystal layer, wherein the crystal directions of two mutually spliced side surfaces of two adjacent single crystal seed crystals are different; the multi-block single crystal seed crystals comprise at least one rectangular seed crystal and a plurality of first square seed crystals, the first square seed crystals are spliced to form a base seed crystal part which is integrally square, the long edge of the rectangular seed crystal is aligned and spliced with the side edge of the base seed crystal part, the length of the long edge of the rectangular seed crystal is equal to that of the side edge of the base seed crystal part, and the length of the short edge of the rectangular seed crystal is greater than that of the first square seed crystal.

Wherein the casting container may be selected from a crucible, which is commonly used in the art for casting single crystal silicon ingots. Among them, the seed crystal is a small crystal having the same crystal orientation as the crystal to be prepared, and is a seed for growing a single crystal, also called a seed crystal. The seed layer is used to prepare a seeding layer for casting a single crystal, and the molten silicon liquid can be directionally grown to form a single crystal under the guidance of the seeding layer.

In the operation of laying the single crystal seeds at the bottom of the casting container, the crystal orientation of the single crystal seeds is not limited, and the single crystal seeds are laid at the central position of the bottom of the casting container in a closely-arranged mode, so that gaps among the single crystal seeds are as small as possible, and crystal boundaries and dislocations introduced from the gaps of the seeds are reduced.

It will be appreciated that the seed crystal is generally cubic, and in particular quadrangular. The rectangular seed crystal in this context means that, in the process of growing a single crystal, the cross-sectional shape of the single crystal seed crystal in the direction perpendicular to the crystal growth direction is rectangular, and the growth surface is also rectangular. The square seed crystal means that the cross section of the single crystal seed crystal along the direction vertical to the crystal growth direction is square in the crystal growth process, and the growth surface is also square. The first square seed crystal herein merely means that the shape of the seed crystal is the first square, and does not specify that the first square seed crystals are identical. Of course, each first square seed may be identical. Similarly, a rectangular seed crystal herein also means only that the seed crystal is rectangular in shape, and a second square seed crystal herein also means only that the seed crystal is second square in shape.

It is also understood that aligned splicing herein refers to the alignment of two edges end to form a close packed manner when the lengths of the two edges are the same. For example, the base seed crystal part comprises a plurality of first square seed crystals which are aligned and spliced, namely that two adjacent first square seed crystals are contacted with each other by one side, and the two sides are aligned end to end. The whole basic seed crystal part is square, and the long edge of the rectangular seed crystal is the same as the whole side length of the basic seed crystal part and is aligned with the long edge of the rectangular seed crystal part. The method for splicing the plurality of first square seed crystals into the integrally square basic seed crystal part specifically comprises the steps of adopting four, nine, sixteen, twenty-five and other integer square pieces of first square seed crystals and adopting the closest packing mode to form the integrally square basic seed crystal part.

In one particular example, the single crystal seed is selected from a silicon single crystal material. Wherein, the growth crystal face of each single crystal seed crystal is <100 >. Further, since the single crystal seed crystal is generally cut from a silicon ingot, it is limited to the actual production of the single crystal seed crystal, and when the growth plane orientation of the rectangular seed crystal is <100>, the lateral plane orientation is also <100 >. The growth surface crystal orientation of the square single crystal seed crystal spliced with the rectangular single crystal seed crystal is <100>, and the side surface crystal orientation is not <100 >. When a plurality of first square seed crystals in the base seed crystal section are aligned and spliced, the first square seed crystals may include two or more square single crystal seed crystals different in lateral crystal orientation as long as the lateral crystal orientations of the adjacent first square seed crystals are different.

It can be understood that the square basic seed crystal part has four sides, and one rectangular seed crystal is spliced with one side of the basic seed crystal part, so that the rectangular seed crystals spliced on the sides of the basic seed crystal part can have four sides. In one specific example, the rectangular seed crystals are more than two, and each rectangular seed crystal is spliced with different side edges in the basic seed crystal part.

In one specific example, two square seed crystals are respectively spliced with two adjacent sides of the basic seed crystal part. It will be appreciated that the rectangular seed crystal may have two, three or four pieces at this time. When two rectangular seed crystals are arranged, the two rectangular seed crystals can be spliced on two adjacent side edges in the basic seed crystal part. When the rectangular seed crystal has three rectangular seed crystals, the three rectangular seed crystals are necessarily spliced on three sides in the basic seed crystal part, and one side of the three sides is necessarily adjacent to the other two sides. When the rectangular seed crystal has four pieces, the four pieces of rectangular seed crystal are necessarily spliced on four edges in the basic seed crystal part, and two edges of the four edges are necessarily adjacent to the other two edges respectively. When two rectangular seed crystals are spliced on two adjacent sides of the basic seed crystal part, a square recess exists between the adjacent short sides of the two rectangular seed crystals, and the stress of the recess is still concentrated on the silicon ingot growing in the recess during actual growth. Therefore, the single crystal seed crystals can be further arranged to comprise second square seed crystals, the side length of each second square seed crystal is the same as the length of the short side of each rectangular seed crystal, and two adjacent sides of each second square seed crystal are respectively spliced with the short sides of two adjacent rectangular seed crystals. It can be understood from the above description that when two rectangular seed crystals are adjacent, at most one second square seed crystal may be disposed between the two rectangular seed crystals, when three rectangular seed crystals are present, at most two second square seed crystals may be disposed between the three rectangular seed crystals, and when four rectangular seed crystals are present, at most four second square seed crystals may be disposed between the four rectangular seed crystals.

In one specific example, the rectangular seed crystal has four pieces, and the four pieces of rectangular seed crystal are respectively spliced with four edges of the basic seed crystal part, so that the four pieces of rectangular seed crystal integrally surround the basic seed crystal part. Further, there are also four second square seeds.

In one specific example, in the adjoining single crystal seed crystal, the difference in orientation between the two side surfaces in contact with each other is 10 ° to 90 °. When the difference in orientation between the mutually contacting side surfaces of adjoining single crystal seed crystals is 10 to 90 degrees, a grain boundary can be formed at the splicing position of the adjoining single crystal seed crystals, so that dislocation propagation can be suppressed. Further, the difference in orientation between the two side surfaces in contact with each other is 20 ° to 40 °. When the position difference between the mutually contacted side surfaces of the adjacent single crystal seed crystals is 20-40 degrees, a crystal boundary can be formed at the splicing position of the adjacent single crystal seed crystals, and the effect of inhibiting dislocation proliferation is optimal.

In one specific example, in order to make the side faces of the adjoining single crystal seeds have a difference in orientation therebetween, the following arrangement may be made. The first square seed crystal has a first growth face and a second growth face which are opposite to each other, and in two adjacent first square seed crystals, the first growth face of one of the first square seed crystals is arranged upward, and the second growth face of the other of the first square seed crystals is arranged upward. For a first square seed crystal, the second growth surface is the back surface of the first growth surface, the first growth surface can be used as the crystal plane for growing the monocrystalline silicon, and the second growth surface can also be used as the crystal plane for growing the monocrystalline silicon. For the convenience of understanding, the first growth surface is arranged upwards to be arranged in a forward direction, the second growth surface is arranged upwards to be arranged in a reverse direction, and for the square seed crystal, the side surfaces of the forward growth surface and the reverse growth surface are just deflected, so that the side surface difference between the two adjacent first square seed crystals can be ensured. The first square seed crystals used in the arrangement are substantially identical, only the arrangement directions are different, and the specific types of the first square seed crystals required to be used can be saved.

Further, an embodiment of the invention also provides a monocrystalline silicon casting method, which comprises the seed crystal laying method of the embodiment.

In one specific example, after a plurality of single crystal seeds are integrally spliced into a seed layer, the method further comprises the following steps:

and filling silicon-based slurry around the single crystal seed crystal layer, wherein the silicon-based slurry is mixed slurry of silicon nitride and silicon powder or silicon nitride slurry, and drying to form the silicon-based filling strip.

Wherein, the solvent in the silicon-based slurry is water, alcohol or methanol. Of course, other solvents capable of dispersing the silicon-based slurry may also be used. Because the silicon-based filling strips are positioned at the periphery of the single crystal strip, the silicon-based filling strips can play a role in preventing silicon liquid from permeating into the bottom of the seed crystal of the corner block in a high-temperature melting stage.

Furthermore, in the mixed slurry of the silicon nitride and the silicon powder, the mass ratio of the silicon nitride to the silicon powder is (2-10): 1. Silicon nitride is mixed with silicon powder, has combined the great silicon powder of granule and the less silicon nitride of granule, can guarantee to be difficult to the fracture after the drying like this, can play the effect that blocks the monocrystalline seed crystal bottom that the silicon liquid permeates the corner piece in the high temperature melting stage.

In one specific example, after a plurality of single crystal seeds are integrally spliced into a seed layer, the method further comprises the following steps: and paving a silicon material on the seed crystal layer in the casting container, heating to melt the silicon material, and cooling to ensure that the melted silicon material is cooled to grow into a silicon ingot. Specifically, the process of heating to melt the silicon material includes a heating melting stage, a crystal growth stage and an annealing stage.

In the process of the heating and melting stage, the temperature in the casting container is 1500-1540 ℃, and the total time of the heating and melting stage is 26-30 h. After the heating and melting stage, the silicon material is completely melted into silicon liquid. After the melting stage and before the crystal growth stage, the single crystal seed crystal can be not melted at all, and at the moment, the silicon liquid is contacted with the seed crystal unit; the seed crystal unit can be partially melted, and the melted single crystal seed crystal is mixed with the silicon liquid and is contacted with the unmelted seed crystal unit, so that the subsequent crystal growth is facilitated.

The temperature of the crystal growth stage is 1400-1450 ℃, and the total time of the crystal growth stage is 28-32 h.

The temperature of the annealing stage is naturally reduced from 1300 ℃ to 1350 ℃ to 350 ℃ to 450 ℃.

Further, after crystal growth, the method also comprises the step of squaring. Specifically, the silicon ingot is divided in the direction of the side of each first square seed crystal with the side length of the first square seed crystal as the open dimension, and the silicon ingot is divided at a position where the rectangular seed crystal is spaced apart from the side edge of the closest base seed crystal portion by the open dimension. Among them, a single crystal silicon ingot obtained by the slicing is commonly called a "small square ingot" in the art.

It can be understood that since the opening size is determined by the size of the first square seed crystal at the time of opening, and the edge portion of the rectangular seed crystal on the side away from the base seed crystal portion is a portion where defects are more likely to occur, it is necessary to remove the defect. In one specific example, the amount of the removed portion should be reduced as much as possible so as not to affect the yield of single crystal silicon. At this time, the short side of the rectangular seed crystal is longer than the side length of the first square seed crystal but shorter than twice the length of the side of the first square seed crystal, namely the length of the side of the first square seed crystal is longer than half of the length of the short side of the rectangular seed crystal, so that the size of the monocrystalline silicon with more defects to be removed is smaller than that of the first square seed crystal formed by squaring.

The inventors have further studied and found that, when single-crystal silicon is grown, defects generated from the edge portions are mostly concentrated within 10mm from the edge, and thus, in one specific example, the short side of the rectangular seed crystal is longer than the side of the first square seed crystal by 10mm or more. The short side of the rectangular seed crystal is controlled to be longer than the side length of the first square seed crystal by more than 10mm, so that the area with more defects can be removed during squaring, and the quality of the obtained monocrystalline silicon is further improved. Further, the defects generated from the edge portions are substantially all concentrated within 20mm inward from the edges, and thus in one specific example, the short side of the rectangular seed crystal is longer than the side length of the first square seed crystal by 20mm or more. The short side of the rectangular seed crystal is controlled to be longer than the side length of the first square seed crystal by more than 20mm, most of the area which generates defects due to edge growth can be removed during squaring, and the quality of the obtained monocrystalline silicon is further improved.

It will be appreciated that the more the edge regions of the rectangular seed crystal are cut away, the more single crystal silicon is lost and the higher the cost. In order to avoid excessive monocrystalline silicon loss caused by cutting corners, the short side of the rectangular seed crystal is controlled to be 10-30 mm longer than the side of the first square seed crystal. Furthermore, the short side of the rectangular seed crystal is 20 mm-30 mm longer than the side of the first square seed crystal.

In order that the invention may be more readily understood and put into practical effect, reference is also made to the following more specific and detailed examples and comparative examples. The embodiments of the present invention and their advantages will also be apparent from the description of specific examples and comparative examples below, and the performance results.

The raw materials used in the following examples are all commercially available without specific reference.

Example 1

Referring to fig. 1, a plurality of single crystal seeds are laid on the bottom of a crucible, and the plurality of single crystal seeds are integrally combined to form a seed layer 100. The seed layer 100 includes three kinds of single crystal seeds having different cross-sectional shapes, i.e., a first square seed 110, a rectangular seed 120, and a second square seed 130. Wherein, the side length of the first square seed crystal 110 is 159mm, and the thickness is 20 mm; the long side of the rectangular seed crystal 120 is 636mm long, the short side is 179mm long, and the thickness is 20 mm; the second square seed crystal 130 has a side length of 179mm and a thickness of 20 mm.

As can be seen from the context and labels in FIG. 1, the first square seed crystal 110 has a total of 16 seed crystals, all of which are type A, and are labeled "A +" or "A-" in FIG. 1, with "A +" denoting the first square seed crystal 110 in a forward orientation and "A-" denoting the first square seed crystal 110 in an inverted orientation. The rectangular seed crystals 120 are 4 pieces in total, and are all B type seed crystals. The second square seed crystal 130 has 4 pieces, all of which are A type seed crystals, and can be arranged in the forward direction or the reverse direction. The growth surface of each single crystal seed crystal is <100 >.

The first square seed crystal 110 is integrally combined into a square basic seed crystal part 101, which can be seen from the dotted area in fig. 1. The long sides of the rectangular seed crystal 120 are the same as the sides of the basic seed crystal part 101 and are aligned and spliced, and the four rectangular seed crystals 120 are respectively spliced with the four sides of the basic seed crystal part 101. Four second square seed crystals 130 are arranged between two adjacent rectangular seed crystals 120, and two adjacent sides of the second square seed crystals 130 are spliced with the adjacent short sides between the two rectangular seed crystals 120. It can be seen that the seed layer 100 formed by splicing the first square seed crystal 110, the rectangular seed crystal 120 and the second square seed crystal 130 is square overall.

The dashed lines in fig. 2 represent the cut lines designed for the seed layer 100 of fig. 1 after the ingot has been grown. After the grown single crystal silicon is diced, the PL test mosaic of the head single crystal silicon wafer is shown in fig. 3.

Where PL test refers to photoluminescence test and black areas indicate the presence of defects. The 'jigsaw' means that after the head monocrystalline silicon wafer of each small square ingot is respectively tested, all the side views are spliced into a whole picture so as to reflect the defect condition of the whole silicon ingot.

Example 2

Referring to fig. 4, a plurality of single crystal seeds are laid on the bottom of the crucible, and the plurality of single crystal seeds are integrally combined to form a seed layer 200. The seed layer 200 includes three kinds of single crystal seeds having different cross-sectional shapes, i.e., a first square seed 210, a rectangular seed 220, and a second square seed 230. Wherein, the side length of the first square seed crystal 210 is 159mm, and the thickness is 20 mm; the long side of the rectangular seed crystal 120 is 636mm long, the short side is 179mm long, and the thickness is 20 mm; the second square seed crystal 130 has a side length of 179mm and a thickness of 20 mm.

As can be seen from the context and indicia of FIG. 4, the first square seed 210 has a total of 16 pieces, all of which are C-type seeds, and are labeled "C +" or "C-" in FIG. 3, with "C +" denoting the first square seed 210 in a forward orientation and "C-" denoting the first square seed 210 in an inverted orientation. The rectangular seed crystals 220 are 4 pieces in total and are all B type seed crystals. The second square seed crystals 230 have 4 pieces in total, are all type A seed crystals, and can be arranged in the forward direction or the reverse direction. The growth surface of each single crystal seed crystal is <100 >.

The first square seed crystal 210 is integrally combined into a square basic seed crystal portion 201, which can be seen from the dotted area in fig. 4. The long sides of the rectangular seed crystals 220 are the same as the sides of the basic seed crystal part 201 and are spliced in an aligned mode, and the four rectangular seed crystals 220 are respectively spliced with four sides of the basic seed crystal part 201. Four second square seed crystals 230 are arranged between two adjacent rectangular seed crystals 220, and two adjacent sides of the second square seed crystals 230 are spliced with the adjacent short sides between the two rectangular seed crystals 220. It can be seen that the seed layer 200 formed by splicing the first square seed crystal 210, the rectangular seed crystal 220 and the second square seed crystal 230 has a square shape as a whole.

The dotted line in fig. 5 indicates a cut line designed when the seed layer 200 is opened after the silicon ingot is grown. After squaring the grown single crystal silicon, the header single crystal silicon PL test mosaic is shown in fig. 6.

In addition, the main difference between the C-type seed crystal and the a-type seed crystal is the difference between the lateral crystal directions of the seed crystals, which makes the difference in the bit direction between the adjacent C-type seed crystals in the present embodiment different from the difference in the bit direction between the adjacent a-type seed crystals in embodiment 1. It is understood that the first square seed crystal in the basic seed crystal portion is not suitable for the B-type seed crystal, otherwise, the orientation difference between the first square seed crystal and the rectangular seed crystal cannot be formed. Further, in some other embodiments, the first square seed crystal in the basic seed crystal portion can also be spliced by simultaneously selecting a type a seed crystal and a type C seed crystal, and the lateral direction difference formed in this way is different from the above embodiments.

Comparative example 1

Please refer to fig. 7. FIG. 7 shows a comparative placement of a single crystal seed. A plurality of single crystal seed crystals are laid at the bottom of the crucible, and the single crystal seed crystals are integrally spliced into the seed crystal layer 300. The single crystal seed crystals are square seed crystals, the number of the square seed crystals is 36, and the square seed crystals 300 with the size of 6 multiplied by 6 are spliced. The square seed layer 300 has a side length of 159mm and a thickness of 20 mm.

Wherein the square seeds comprise a first square seed 310 of a type a seeds and a second square seed 320 of a type B seeds. The growth surface crystal orientation of the first square seed crystal 310 and the growth surface crystal orientation of the second square seed crystal 320 are both <100>, and the lateral surface crystal orientation is not <100 >.

The dotted line in fig. 8 indicates a cut line designed when the seed layer 300 is opened after the silicon ingot is grown. After squaring the grown single crystal silicon, the header single crystal silicon PL test mosaic is shown in fig. 9.

Referring to fig. 9, it can be seen that a large number of black regions are clearly present in the peripheral edge portion of the silicon ingot. It was shown that the conventional single crystal seed crystal growth method causes a large number of defects in the portion of the grown silicon ingot located at the edge region, which remain in the outermost-located small square ingot, and the area of these defects in these single small square ingots is nearly halved. Resulting in the quality thereof often being difficult to meet. Moreover, the more single crystal seeds are used in the seed crystal layer, the more square ingots positioned at the outermost periphery are finally obtained, and the yield of the cast single crystal silicon is further reduced.

Referring to fig. 3 and fig. 6, it can be seen that the black regions in the peripheral edge portion of the silicon ingot are significantly reduced and only exist in a small portion of the outermost edge region, which greatly improves the yield of the cast single crystal silicon. Examples 1 and 2 the manufacturing method forms a sacrificial region at the outermost periphery of a grown silicon ingot by designing a seed crystal laying method, and improves the yield of the whole small square ingot by omitting the sacrificial region. Compared with the overall size of a small square ingot, the sacrificial area only occupies a small part, the cut leftover materials can be recycled, the production cost cannot be greatly increased due to the fact that the sacrificial area needs to be omitted, and the method has considerable potential for practical application.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A seed crystal laying method is characterized by comprising the following steps:

laying a plurality of single crystal seed crystals at the bottom of a casting container, integrally splicing the single crystal seed crystals into a seed crystal layer, wherein the crystal directions of two mutually spliced side surfaces of two adjacent single crystal seed crystals are different; the single crystal seed crystals comprise at least one rectangular seed crystal and a plurality of first square seed crystals, the first square seed crystals are spliced to form a base seed crystal part which is integrally square, the long edge of the rectangular seed crystal is aligned and spliced with the side edge of the base seed crystal part, the length of the long edge of the rectangular seed crystal is equal to that of the side edge of the base seed crystal part, and the length of the short edge of the rectangular seed crystal is greater than that of the first square seed crystal.

2. A seed crystal placement method as set forth in claim 1, wherein there are more than two rectangular seed crystals, and each of the rectangular seed crystals is joined to a different side of the base seed crystal portion.

3. A seed crystal laying method as claimed in claim 2, wherein two rectangular seed crystals are respectively spliced with two adjacent side edges of the base seed crystal part, at least one second square seed crystal is further included in the plurality of single crystal seed crystals, the side length of the second square seed crystal is equal to the length of the short side of the rectangular seed crystal, and two adjacent side edges of the second square seed crystal are respectively spliced with two adjacent short sides of the two adjacent rectangular seed crystals.

4. The seed crystal laying method as claimed in claim 1, wherein the length of the side of the first square seed crystal is greater than half of the length of the short side of the rectangular seed crystal.

5. The seed crystal placement method according to claim 4, wherein the length of the short side of the rectangular seed crystal is longer than the length of the side of the first square seed crystal by 10mm or more.

6. The seed crystal laying method according to claim 4, wherein the length of the short side of the rectangular seed crystal is 10mm to 30mm longer than the length of the side of the first square seed crystal.

7. A seed crystal placement method according to any one of claims 1 to 6, wherein in the adjoining single crystal seed crystals, the difference in orientation between the two side surfaces in contact with each other is 10 ° to 90 °.

8. A seed crystal placement method according to any one of claims 1 to 6, wherein said first square seed crystal has a first growth face and a second growth face which are opposed to each other, and of two of said first square seed crystals joined laterally, the first growth face of one is disposed upward and the second growth face of the other is disposed upward.

9. A single crystal silicon casting method, characterized by comprising the seed crystal laying method according to any one of claims 1 to 8, wherein the single crystal seed crystal is single crystal silicon.

10. The single crystal silicon casting method as recited in claim 9, further comprising, after integrally piecing a plurality of the single crystal seeds into the seed layer, the step of:

paving a silicon material on a seed crystal layer in the casting container, heating to melt the silicon material, and cooling to cool and grow the molten silicon material to form a silicon ingot;

and dividing the silicon ingot along the direction of the side edge of each first square seed crystal by taking the length of the side edge of the first square seed crystal as the square size, and dividing the silicon ingot along the position, away from the side edge of the basic seed crystal by the square size, on the rectangular seed crystal.

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