TWI516645B - Crystalline silicon ingot, manufacture thereof and silicon wafer therefrom - Google Patents

Description

Twin crystal ingot, its manufacturing method and germanium wafer made therefrom

The present invention relates to a crystalline silicon ingot, a method of manufacturing the same, and a silicon wafer made therefrom, and in particular, to the use of a silicon seed layer and based on A directional solidification process produces a high-efficiency, {100} crystal growth twin crystal ingot, a method for producing the same, and a germanium wafer prepared therefrom.

Most solar cells absorb sunlight and produce a photovoltaic effect. At present, most of the materials of solar cells are mainly coffins, mainly because coffins are the second most easily available elements on the earth, and they have the advantages of low material cost, no toxicity, and high stability. And it has a solid foundation in the application of semiconductors.

The solar cells based on coffins include three types: single crystal germanium, polycrystalline germanium and amorphous germanium. The use of polycrystalline germanium as a raw material for solar cells is mainly based on cost considerations because its price is comparable to that of the conventional Czochralski method (CZ method) and the floating zone method (FZ method). The single crystal crucible is relatively cheaper.

The use of polycrystalline germanium in the manufacture of solar cells has traditionally been produced using conventional casting processes. The use of a casting process to prepare polycrystalline germanium, which is then applied to solar cells, is a prior art in the art. Briefly, high purity germanium is melted in a mold (e.g., quartz crucible) and cooled under controlled solidification to form a polycrystalline germanium ingot. Next, the polycrystalline germanium ingot is cut into wafers close to the size of the solar cell and used in the manufacture of solar cells. Polycrystalline produced in this way The tantalum ingot is an aggregate of the crystal grains of the tantalum in which the crystal orientation of the crystal grains with each other is actually random.

In the existing polysilicon, it is difficult to roughen the surface of the wafer to be formed because of the random crystal orientation of the crystal grains. The roughening of the surface can reduce the light reflection and increase the absorption of light energy through the surface of the battery to improve the efficiency of the photovoltaic cell. In addition, the "kneading" formed in the grain boundaries between the existing polycrystalline germanium grains tends to form clusters of nucleation difference rows or form structural defects in the form of a plurality of line difference rows. These rows and the impurities they tend to attract cause a rapid recombination of charge carriers in photovoltaic cells made from existing polycrystalline germanium. This can result in a decrease in the efficiency of the battery. Photovoltaic cells made from such polycrystalline germanium are generally less efficient than equivalent photovoltaic cells made from single crystal germanium, even considering the radial distribution of defects present in single crystal germanium fabricated by the prior art. However, since the fabrication of existing polysilicon is relatively simple and less costly, as well as defect passivation that is effective in battery processing, polysilicon has become a widely used form of tantalum material for the fabrication of photovoltaic cells.

The prior art discloses the use of a single crystal germanium seed layer and a twin crystal ingot based on directional solidification, and generally uses a single crystal germanium cube having a large size and a crystal orientation of {100} as a main seed crystal. It is desirable to use a germanium single crystal solar cell to fabricate a germanium wafer with a crystal orientation of {100} direction because a light-trapping surface is conveniently formed by an etching method. Unfortunately, grains in the {100} crystal orientation during crystallization during the {100} crystal orientation of the grains compete with randomly nucleated grains. In order to maximize the crystal volume of seeding in the ingot, the prior art discloses the area of the seed crystal surrounding the {100} crystal orientation using the boundary of the {111} crystal orientation. This boundary is very successful in suppressing crystals in other crystal orientations. In this way, an ingot having a high performance single crystal germanium and/or a bi-crystal germanium block can be cast, which maximizes the lifetime of minority carriers of the resulting wafer. Used to manufacture high efficiency solar cells. Here, the term "single crystal germanium" means a main body of a single crystal germanium having a uniform crystal crystal orientation over the entire range. The term "bimorph" refers to a body of ruthenium having a uniform crystal orientation in a range of greater than or equal to 50% of the volume of the body, and having another uniform crystal orientation within the remaining volume of the body. . For example, such a twin germanium can contain a crystal The crystallographic single crystal germanium body is adjacent to another single crystal germanium body having a different crystal crystal orientation in the immediate vicinity of the remaining volume of the crystalline germanium. Further, the prior art polycrystalline germanium refers to a crystal enthalpy having a fine distribution of a centimeter scale, and having a plurality of crystals having a random crystal orientation in the main body of the crucible.

However, the prior art of using a single crystal twin seed crystal to form a twin seed layer to achieve a {100} crystal growth growth has not been proposed to control the grain boundary inside the twin crystal ingot, resulting in internal stress of the twin ingot. High, resulting in reduced efficiency of the twine ingot.

Therefore, the technical problem to be solved by the present invention is to provide a high-performance twin crystal ingot having a {100} crystal growth, a method for producing the same, and a tantalum wafer formed therefrom. The grain boundary in the twinned ingot of the present invention is a functional grain boundary, which can relieve stress and thereby improve the efficiency of the twin ingot.

Basically, the present invention utilizes a twin seed layer different from the prior art and manufactures a twin crystal ingot having a good overall crystal quality based on a directional solidification process.

In order to solve the above technical problems, in a preferred embodiment of the present invention, a method for manufacturing a high-performance twin crystal ingot having a {100} crystal growth is firstly prepared by first preparing a plurality of first single crystal twin crystals, wherein Each of the first single crystal twins has a first top surface and a plurality of first side surfaces, the first top surface having a crystal orientation of {100}, and each of the first side surfaces having a crystal orientation of {100}. Next, the manufacturing method of the present invention is to prepare a plurality of second single crystal twins, wherein each of the second single crystal twins has a second top surface and a plurality of second side surfaces, and the crystal orientation of the second top surface is {100}. Next, the manufacturing method of the present invention lays a plurality of first single crystal twins and a plurality of second single crystals on the bottom of the mold, so that each of the first single crystal twins is adjacent to a plurality of second singles. Crystal seed crystals are separated from other first single crystal seed crystals. The plurality of first single crystal twins and the plurality of second single crystal twins constitute a twin seed layer. Specifically, the angle between the crystal orientation of each of the first side surfaces and the crystal orientation of the immediately adjacent second side surface ranges from about 5 to 85 degrees. Next, the manufacturing method of the present invention mounts the raw material into the mold and is placed on the plurality of first single crystals. The seed crystal is seeded with a plurality of second single crystals. Next, the manufacturing method of the present invention heats the mold until the crucible material is completely melted into a crucible soup. Finally, the manufacturing method of the present invention is based on a directional solidification process cooling mold which causes the crucible melt to solidify to form a twinned ingot comprising a seed layer.

A preferred embodiment of the present invention is a high efficiency and {100} crystal growth grown twin ingot comprising a bottom. The twinned ingot of the present invention comprises a seed layer at the bottom. The twin seed layer is composed of a plurality of first single crystal twins and a plurality of second single crystal twins, wherein each of the first single crystal twins is adjacent to a plurality of second single crystal twins, And separated from other first single crystal twins. Each of the first single crystal twins has a first top surface and a plurality of first side surfaces, wherein the first top surface has a crystal orientation of {100}, and each of the first side surfaces has a crystal orientation of {100}. Each of the second single crystal twins has a second top surface and a plurality of second side surfaces, wherein the second top surface has a crystal orientation of {100}. In particular, the angle between the crystal orientation of each of the first side surfaces and the crystal orientation of the immediately adjacent second side surface ranges from about 5 to 85 degrees.

In one embodiment, the included angle is equal to 36.87 degrees, wherein the grain boundary within the twinned ingot is a Σ5 grain boundary.

In one embodiment, each of the first single crystal twins and each of the second single crystal twins are grown in a cube or cube.

In one embodiment, the first side length of each of the first single crystal twins and the second side length of each of the second single crystal twins are about equal to or less than 16 cm.

The tantalum wafer of a preferred embodiment of the present invention is made from the twinned ingot of the present invention. The tantalum wafer of the present invention comprises a plurality of sheet-like germanium single crystals. The top surface and the bottom surface of each of the sheet-like germanium single crystals are exposed, and their crystal orientations are all {100}. The grain boundary between each sheet-like germanium single crystal and its adjacent sheet-like germanium single crystal is a Σ5 grain boundary and/or a Σ3 grain boundary.

With regard to the advantages and spirit of the present invention, the following invention can be The details and the drawings are further understood.

10‧‧‧

12‧‧‧矽 seed layer

122‧‧‧The first single crystal seed crystal

1222‧‧‧First top surface

1224‧‧‧First side surface

124‧‧‧Second single crystal seed crystal

1242‧‧‧Second top surface

1244‧‧‧ second side surface

14‧‧‧heater

15‧‧‧矽 Raw materials

16‧‧‧矽 molten soup

17‧‧‧ solid/liquid phase interface

18‧‧‧矽ingot casting

180‧‧‧ bottom

182‧‧‧ grain boundary

W1‧‧‧first side length

W2‧‧‧Second side length

‧‧‧‧ angle

2‧‧‧矽 wafer

22, 24 ‧ ‧ 片 矽 single crystal

220, 240‧‧‧ top surface

222, 242‧‧‧ bottom surface

26‧‧‧ Grain boundary

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view schematically showing a twinned ingot of a preferred embodiment of the present invention.

Figure 2 is a top view of an example of a seed layer.

3 through 7 are schematic views of a method of manufacturing a twinned ingot in accordance with a preferred embodiment of the present invention.

Figure 8 is a cross-sectional view schematically showing a germanium wafer in accordance with a preferred embodiment of the present invention.

Figure 9 is a top plan view of a mold and twin seed layer employed in accordance with an exemplary embodiment of the present invention.

10 and FIG. 11 are cross-sectional views of the twin-shaped ingots in the vertical growth direction of the mold, the twin seed layer, and the manufacturing method according to the present invention, which are shown in FIG.

Figure 12 is a photograph of a metallographic photograph taken after the bottom section of the twinned ingot shown in Figure 10 has been etched.

Figure 13 is a photograph of a metallographic photograph taken after the top section of the twinned ingot shown in Figure 11 has been etched.

Referring to Figure 1, a twin crystal ingot 18 of a preferred embodiment of the present invention is schematically illustrated in cross-section.

As shown in FIG. 1, the twinned ingot 18 of the present invention comprises a bottom portion 180. In particular, the bottom 180 of the twin ingot 18 comprises a seed layer 12. Twin seed layer 12 It is composed of a plurality of first single crystal twins 122 and a plurality of second single crystal seed crystals 124.

Referring to FIG. 2, an example of a seed layer 12 of the present invention is schematically illustrated in a top view. Figure 2 also shows the mold 10 in which the seed layer 12 is originally rowed at its inner bottom.

As shown in FIG. 2, each of the first single crystal seed crystals 122 is adjacent to a plurality of second single crystal seed crystals 124 and is separated from the other first single crystal seed crystals 122. Each of the first single crystal seed crystals 122 has a first top surface 1222 and a plurality of first side surfaces 1224. Specifically, the crystal orientation of the first top surface 1222 is {100}, for example, (100) as shown in FIG. Also, the crystal orientation of each of the first side surfaces 1224 is {100}, for example, (010) and (100) as shown in FIG. 2.

Each of the second single crystal twins 124 has a second top surface 1242 and a plurality of second side surfaces 1244. In particular, the crystal orientation of the second top surface 1242 is {100}, for example, (100) as shown in FIG. In particular, the angle a between the crystal orientation of each of the first side surfaces 1224 and the crystal orientation of the immediately adjacent second side surface 1244 ranges from about 5 degrees to about 85 degrees. Thereby, in the directional solidification process of the present invention, the grain boundary 182 between the crystal grains is a functional grain boundary such as a Σ3 grain boundary or a Σ5 grain boundary, which can relieve stress and further enhance the twin crystal ingot 18 Performance.

Referring to Figures 3 through 7, the drawings schematically illustrate a method of making the twinned ingot 18 of Figure 1 in a cross-sectional view in accordance with a preferred embodiment of the present invention.

As shown in Fig. 1, first, a manufacturing method of a preferred embodiment of the present invention provides a mold 10. Mold 10 is suitable for melting and cooling the crucible material by a directional solidification process. In practice, the mold 10 can be a quartz crucible.

First, the manufacturing method of the present invention produces a plurality of first single crystal twins 122. As shown in FIG. 2, each of the first single crystal seed crystals 122 has a first top surface 1222 and a plurality of first side surfaces 1224. Specifically, the crystal orientation of the first top surface 1222 is {100}, for example, (100) as shown in FIG. And every The crystal orientation of a first side surface 1224 is {100}, for example, (010) and (100) as shown in FIG.

Next, the manufacturing method of the present invention is to prepare a plurality of second single crystal twins. As shown in FIG. 2, each of the second single crystal seed crystals 124 has a second top surface 1242 and a plurality of second side surfaces 1244. In particular, the crystal orientation of the second top surface 1242 is {100}, for example, (100) as shown in FIG.

As shown in FIGS. 2 and 3, the manufacturing method of the present invention is followed by providing the mold 10. Mold 10 is suitable for melting and cooling the crucible material by a directional solidification process. In practice, the mold 10 can be a quartz crucible.

Also shown in FIG. 2 and FIG. 3, the manufacturing method of the present invention is to lay a plurality of first single crystal seed crystals 122 and a plurality of second single crystal germanium crystals 124 in the bottom of the mold 10, wherein the plurality of A single crystal seed crystal 122 and a plurality of second single crystal seed crystals 124 constitute the seed crystal layer 12. In particular, each of the first single crystal seed crystals 122 is in close proximity to a plurality of second single crystal seed crystals 124 and is separated from the other first single crystal seed crystals 122. In particular, the angle a between the crystal orientation of each of the first side surfaces 1224 and the crystal orientation of the immediately adjacent second side surface 1244 ranges from about 5 degrees to about 85 degrees.

As shown in FIG. 4, next, the raw material 15 is mounted in the mold 10 according to the method of the present invention, and is placed in a plurality of first single crystal seed crystals 122 and a plurality of second single crystal germanium seeds 124 (twisted crystals). Layer 12).

Also shown in Fig. 4, next, the mold 10 containing the seed layer 12 and the tantalum material 15 is placed in a directional solid crystal furnace in accordance with the method of the present invention. FIG. 4 only shows that the heater 14 in the crystal growth furnace is representative.

As shown in Fig. 5, next, the method of the present invention heats the mold 10 until the crucible material 15 is completely melted into the crucible soup 16, and the twin layer 12 is not melted or a portion thereof is melted.

As shown in Figure 6, the method of the present invention is based on directional condensation. The solid-state cooling mold 10 causes the crucible soup 16 to be seeded by the twin seed layer 12 and solidified toward the opening direction of the mold 10. During the solidification of the crucible soup 16, as shown in Fig. 6, the solid/liquid phase interface 17 of the leading edge of the solidified crucible single crystal (122, 124) moves toward the opening direction of the mold 10. In practice, the directional solidification block (not shown in Figures 6 and 7) is placed below the mold 10 and indirectly in contact with the mold 10. The method of the present invention controls the temperature gradient from the heater 14 to the die 10, the temperature gradient from the bottom of the crucible 16 to the top of the directional solidification block, or the heat transfer flux, etc., to achieve Directional solidification process. The arrows that are drawn downward under the bottom of the die 10 in Figures 6 and 7 represent the direction of heat transfer flux.

As shown in Figure 7, finally, the method of the present invention continues with the directional solidification process cooling die 10 to complete the twinned ingot 18. The twinned ingot 18 can finally cast a high-performance mono-like crystal crucible according to the arrangement of the first single crystal germanium seed crystal 122 and the second single crystal twin crystal seed crystal 124 of the twin seed layer 12. An ingot of a twin-crystalline block. In the present case, the term "monocrystalline single crystal" refers to a host of crystalline germanium having a uniform crystal orientation in a range exceeding 75% of the volume of the body, wherein, for example, such a single crystal germanium may contain The bulk of the single crystal germanium adjacent to the polycrystalline region, or it may comprise a large, continuous uniform germanium crystal, some or all of which further comprise other crystal oriented germanium smaller crystals. The term "bimorph" is as described above and will not be described herein.

In particular, by using the twin seed layer 12 as shown in FIG. 2, the twin seed layer 12 produced according to the manufacturing method of the present invention, in the directional solidification process, the intergranular grain boundaries 182 are Σ3 grain boundaries or Functional grain boundaries such as 晶5 grain boundaries can alleviate stress and obtain high-performance twin crystal ingots 18.

In one embodiment, the angle α between the crystal orientation of each of the first side surfaces 1224 and the crystal orientation of the immediately adjacent second side surface 1244 is equal to 36.87 degrees, wherein the grain boundary 182 of the twinned ingot 18 is Σ5 grain boundary. Σ5 functional grain boundary mitigation stress is more obvious, and the performance of twin crystal ingot 18 is further improved.

In a specific embodiment, each of the first single crystal twins 122 Each of the second single crystal twins 124 is grown into a cube or cube.

In one embodiment, as shown in FIG. 2, the first side length w1 of each of the first single crystal twins 122 and the second side length w2 of each of the second single crystal seed crystals 124 are approximately equal to Or less than 16cm.

Referring to FIG. 8, a tantalum wafer 2 is schematically illustrated in a cross-sectional view of a preferred embodiment of the present invention. The tantalum wafer 2 of the present invention is made from the twin ingot 18 of the present invention.

As shown in Fig. 8, the tantalum wafer 2 of the present invention comprises a plurality of sheet-like germanium single crystals (22, 24). The sheet-like germanium single crystal 22 is grown from the first single crystal seed crystal 122 in FIG. 3 along [100]. The sheet-like germanium single crystal 24 is grown from the second single crystal seed crystal 124 in Fig. 3 along [100].

In particular, the top surface (220, 240) and the bottom surface (222, 242) of each of the sheet-like germanium single crystals (22, 24) are exposed, and their crystal orientations are all {100}. The grain boundary 26 between each of the sheet-like germanium single crystals (22, 24) and its adjacent sheet-like germanium single crystals (22, 24) is a germanium 5 grain boundary and/or a germanium 3 grain boundary.

Please refer to FIG. 9 to FIG. 13 for related photographs and metallographic photographs of an example of the present invention. Figure 9 is a top plan view of the mold 10 used in this example and the seed layer 12 composed of the first single crystal seed crystal 122 and the second single crystal seed crystal 124.

10 and FIG. 11 are the vertical growth directions of the twin crystal ingot 18 produced by the mold 10, the twin seed layer 12, and the manufacturing method according to the present invention, and corresponding to the dotted line in FIG. Cross-section photo. Figure 10 is a cross-sectional photograph of the bottom of the twine ingot 18. Figure 11 is a cross-sectional photograph of the top of the twine ingot 18. The photographs of Figs. 10 and 11 show that the crystal shape and grain boundary of the first single crystal germanium seed crystal 122 and the second single crystal germanium seed crystal 124 disposed at the bottom of the mold 10 can be maintained to the twin crystal ingot 18 the top of.

Figure 12 is a photograph of a metallographic photograph taken after the bottom section of the twinned ingot 18 shown in Figure 10 has been etched. Figure 13 is a photograph of a metallographic photograph taken after the top section of the twinned ingot 18 shown in Figure 11 has been etched. The photographs of Fig. 12 and Fig. 13 can confirm that defects occur mostly at the grain boundaries between the germanium single crystals. Unlike the twin crystal ingots produced by the single crystal twin seed layer used in the prior art, the top defects rapidly grow and spread. The twin seed layer 12 and the twin crystal ingot 18 used in the present invention have a stable Σ5 grain boundary and/or a Σ3 grain boundary during the growth process, and it is apparent that the defect generation rate at the top of the twin crystal ingot 18 is low and the defect area is small. For FIG. 12, FIG. 13 is a photomicrograph made image analysis, in the range of 6cm × 6cm, the silicon ingot 18 at the bottom of the defect area 1.7cm ^2, while the top of the defect area 1.2cm ^2. It was converted into a commercially available 15.6 cm × 15.6 cm germanium wafer having a defect area of 8.112 cm ² at the top and a defect density of 3.33%. However, a typical twinned ingot has a defect density of 30.00% at the top. Obviously, the defect density of the top of the twinned ingot can be reduced by 26.67% by the manufacturing method of the present invention.

The features and spirit of the present invention are intended to be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents that are within the scope of the invention as claimed. Therefore, the scope of the patent application of the present invention should be construed broadly in the light of the above description, so that it covers all possible changes and arrangements.

10‧‧‧

12‧‧‧矽 seed layer

122‧‧‧The first single crystal seed crystal

1222‧‧‧First top surface

1224‧‧‧First side surface

124‧‧‧Second single crystal seed crystal

1242‧‧‧Second top surface

1244‧‧‧ second side surface

W1‧‧‧first side length

W2‧‧‧Second side length

‧‧‧‧ angle

Claims (12)

A method for manufacturing a twin crystal ingot comprising the steps of: preparing a plurality of first single crystal twins, wherein each of the first single crystal twins has a first top surface and a plurality of first side surfaces, The crystal orientation of the first top surface is {100}, and the crystal orientation of each of the first side surfaces is {100}; a plurality of second single crystal twin crystal seeds are prepared, wherein each of the second single crystal twin crystal seeds has a first a top surface and a plurality of second side surfaces, wherein the second top surface has a crystal orientation of {100}; laying the plurality of first single crystal twins and the plurality of second single crystals in a single mold a bottom portion, such that each of the first single crystal twin crystal species is adjacent to the plurality of second single crystal twin crystal seeds, and is separated from the other first single crystal twin crystal seeds, wherein the crystal orientation of each of the first side surfaces is adjacent to One of the angles between the crystal orientations of the second side surface ranges from about 5 degrees to about 85 degrees; a raw material is loaded into the mold, and the plurality of first single crystal twins are placed in the mold a second single crystal seed crystal; heating the mold until the crucible material is completely melted into a crucible; and cooling the mold based on a directional solidification process Solidifying molten metal to form the plurality of single crystal silicon comprising a first plurality of the kinds of the second single crystal silicon ingot of silicon species. The method of claim 1, wherein the included angle is equal to 36.87 degrees. The method of claim 2, wherein the twinned ingot has a plurality of grain boundaries, the grain boundaries being Σ5 grain boundaries. The method of claim 1, wherein each of the first single crystal twins and each of the second single crystals are formed into a rectangular parallelepiped or a cube. The method of claim 4, wherein the first side length of each of the first single crystal twins and the second side length of each of the second single crystal twins are about equal to or less than 16 cm. A twinned ingot comprising a bottom portion, wherein the bottom portion comprises a seed crystal layer, the twin seed layer is composed of a plurality of first single crystal twin crystal seeds and a plurality of second single crystal twin crystal seeds And each of the first single crystal twin crystal series is adjacent to the plurality of second single crystal twin crystal seeds, and is separated from the other first single crystal twin crystal seeds, each of the first single crystal twin crystal seeds has a first top a surface and a plurality of first side surfaces, the first top surface has a crystal orientation of {100}, each of the first side surfaces has a crystal orientation of {100}, and each of the second single crystal twins has a second top a surface and a plurality of second side surfaces having a crystal orientation of {100}, and an angle between a crystal orientation of each of the first side surfaces and a crystal orientation of the immediately adjacent second side surface is about From 5 degrees to 85 degrees. The twinned ingot of claim 6, wherein the included angle is equal to 36.87 degrees. The twinned ingot according to claim 7, wherein the twinned ingot has a plurality of grain boundaries, the grain boundaries being Σ5 grain boundaries. The twinned ingot according to claim 6, wherein each of the first single crystal twins and each of the second single crystal twins form a rectangular parallelepiped or a cube. The twinned ingot according to claim 9, wherein the first side length of each of the first single crystal twins and the second side length of each of the second single crystal twins are about equal to or less than 16cm. A germanium wafer comprising a plurality of sheet-like germanium single crystals, wherein: a top surface of each of the sheet-like germanium single crystals and a bottom surface have a crystal orientation of {100}, and each of the sheet-like germanium single crystals Grain boundary between the adjacent sheet-like germanium single crystal It is a 晶5 grain boundary and/or a Σ3 grain boundary. The wafer according to claim 11 is made of a twinned ingot as described in any one of claims 6 to 10.