TWI595124B - Manufacturing method of polysilicon ingot - Google Patents

Description

Method for manufacturing polycrystalline germanium ingot

This invention relates to a method of making an ingot, and more particularly to a method of making a polycrystalline ingot.

Silicon wafers play a key role in the semiconductor industry. If the quality of the germanium wafer is poor, the efficiency or electrical performance of the semiconductor device to which the germanium wafer is applied may be adversely affected. Taking solar cells as an example, the photoelectric conversion efficiency of solar cells is limited by the quality of germanium wafers. Depending on the ingot used, current solar cells mainly include single crystal germanium solar cells and polycrystalline germanium solar cells. Compared with single crystal germanium solar cells, the polycrystalline germanium ingots used in polycrystalline germanium solar cells have the advantages of fast growth rate and convenient cutting. However, the current manufacturing method of the polycrystalline tantalum ingot cannot effectively reduce the proportion of defects in the polycrystalline tantalum ingot, resulting in poor slicing yield of the polycrystalline tantalum ingot, and the photoelectric conversion efficiency of the subsequently produced solar cell is not good. Therefore, how to make a polycrystalline niobium ingot with a low defect ratio has become one of the topics of concern to researchers.

The present invention provides a method of producing a polycrystalline tantalum ingot which can produce a polycrystalline tantalum ingot having a low defect ratio.

A method of producing a polycrystalline germanium ingot according to the present invention comprises the following steps. Forming a nucleation layer on the bottom surface of the growth vessel, wherein the nucleation layer comprises a plurality of seed crystals and a first release layer, the seed crystal is disposed on the bottom surface, and the first release layer covers the seed crystal and is exposed by the seed crystal Bottom surface. The raw material is placed in the growth vessel, and the raw material is placed on the nucleation layer. Heating the growing container to melt all the raw materials of the crucible into a crucible melt, and melting the first stripping layer covering the seed crystal by heat, so that each seed crystal is partially exposed by the first stripping layer, and the seed crystal is exposed. Partially in contact with the broth. The bottom of the growth vessel is cooled, and a plurality of tantalum crystal grains are nucleated on the exposed portion of the seed crystal and grow in the growth direction. The bottom of the growing container is continuously cooled until the crucible is completely solidified to form a polycrystalline ingot.

Based on the above, since the seed crystal can provide a dense nucleation point and contributes to a large reduction in the distribution ratio of the large-sized niobium crystal grains formed at the bottom of the polycrystalline niobium ingot, the manufacturing method of the polycrystalline niobium ingot of the present invention can be manufactured. A polycrystalline germanium ingot in which the average grain size of the germanium grains increases from the bottom surface toward the top surface. In the crystal growth process, the grain growth is small and large, and under the control of the crystal growth method, the crystal grains are grown in a single direction and the formation of poor grain boundary defects is suppressed. Therefore, the polycrystalline tantalum ingot produced by the method for producing a polycrystalline tantalum ingot of the present invention can have a low defect ratio.

The above described features and advantages of the invention will be apparent from the following description.

1A to 1F are schematic views showing a manufacturing process of a polycrystalline germanium ingot according to an embodiment of the present invention. Referring to FIG. 1A, a nucleation layer 110 is formed on the bottom surface SB' of the growth vessel 100. The growth container 100 is, for example, a quartz crucible, but is not limited thereto. The nucleation layer 110 includes a plurality of seed crystals 112 and a first release layer 114. The seed crystal 112 is disposed on the bottom surface SB', which is adapted to provide a nucleation point for subsequent crystal growth. The first release layer 114 covers the seed crystal 112 and the bottom surface SB' exposed by the seed crystal 112, and the maximum thickness of the first release layer 114 is approximately equal to the maximum thickness of the seed crystal 112. Further, the thickness of the first release layer 114 covering the seed crystal 112 must be thin enough that the first release layer 114 covering the seed crystal 112 can be melted by heat to expose each of the subsequent heating processes. A localized area of seed crystal 112 provides the desired nucleation sites.

The method of forming the nucleation layer 110 on the bottom surface SB' of the growth vessel 100 may include the following steps. First, a seed crystal 112 is formed on the bottom surface SB'. Next, a release material is formed (e.g., sprayed) on the seed crystal 112 and the bottom surface SB' exposed by the seed crystal 112 to form the first release layer 114. Alternatively, the method of forming the nucleation layer 110 on the bottom surface SB' of the growth vessel 100 may also include the following steps. First, the seed crystal 112 is mixed into a release material (not shown). For example, 100 to 200 grams of seed crystal 112, 150 to 200 grams of release material, 0 to 80 grams of cerium sol, and 150 to 300 grams of water may be mixed together, and the mixture is further mixed It is formed (for example, sprayed) on the bottom surface SB' of the growth vessel 100. The material of the seed crystal 112 includes, for example, cerium oxide, and the average size of the seed crystal 112 is, for example, between 0.05 mm and 50 mm to provide a dense nucleation point, and the ruthenium greatly reduces the large size formed on the bottom of the polycrystalline ruthenium ingot. The distribution ratio of crystal grains. The material of the first release layer 114 includes, for example, tantalum nitride (Si ₃ N ₄ ), but is not limited thereto.

In the present embodiment, the second release layer 114' may be further formed on the side wall surface SS' of the growth vessel 100 before the crucible material is loaded. Thus, at the time of subsequent demolding, the side wall surface of the polycrystalline ingot is facilitated to be separated from the growth vessel 100. In addition, the second release layer 114' may also have the function of blocking impurities, thereby preventing the bismuth melt from adsorbing impurities in the growth vessel 100 during the crystal growth process and affecting the quality of the polycrystalline silicon ingot. The material of the second release layer 114' includes, for example, tantalum nitride, but is not limited thereto. In a preferred embodiment, the thickness of the second release layer 114' is greater than the thickness of the first release layer 114 to maintain the integrity of the second release layer 114' during subsequent heating processes. In still another embodiment, the second release layer 114' may be made of a material having a higher melting point than the melting point of the first release layer 114.

Referring to FIG. 1B, a crucible raw material 120 is placed in the growth vessel 100, wherein the crucible raw material 120 is located on the nucleation layer 110, and the melting point of the crucible raw material 120 is lower than, for example, the second release layer 114' and the first release layer 114. And the melting point of the seed crystal 112. The crucible material 120 can include a plurality of crucible blocks. The block may include a large size block and a small size block.

Next, the growth vessel 100 loaded with the crucible material 120 is placed in a Directional Solidification System (DSS) 10 for a subsequent heating process. The directional solidification system 10 includes, for example, a furnace body 11, an adiabatic chamber 12, a gas conduit 13, a heater 14, and a heat transfer block 15. The heat insulating chamber 12 is disposed in the furnace body 11, and the heat insulating chamber 12 includes a heat insulating cover 12A and a heat insulating plate 12B. The heat insulating cover 12A and the heat insulating plate 12B are adapted to be assembled together. The gas conduit 13 is passed through the furnace body 11 and the adiabatic chamber 12 to provide a gas, such as an inert gas, required for the process. The heater 14 is disposed in the heat insulating chamber 12 and disposed adjacent to the growth vessel 100 to heat the growth vessel 100. The heat conducting block 15 is disposed in the heat insulating chamber 12 and carries the growth container 100. The heat conducting block 15 is in direct or indirect contact with the growth vessel 100, and the heat of the growth vessel 100 can be derived by heat conduction. The material of the heat conductive block 15 may include graphite, but is not limited thereto.

Referring to FIG. 1C, the growth vessel 100 is heated to completely melt the crucible raw material 120 of FIG. 1B into the crucible melt 130, and the first release layer 114 covering the seed crystal 112 is melted by heat, so that each of the seed crystals 112 is first. The release layer 114 is partially exposed, and the exposed portion of the seed crystal 112 is in contact with the crucible soup 130. In this step, the growth vessel 100 is heated to a temperature higher than the melting point of the crucible material 120 and lower than the melting points of the second release layer 114', the first release layer 114, and the seed crystal 112. In the present embodiment, although the first stripping layer 114 and the second stripping layer 114' are made of the same material, since the thickness of the first stripping layer 114 covering the seed crystal 112 is very thin, the seed crystal 112 is covered. The first release layer 114 is also thermally melted without reaching its melting point, so that each of the seed crystals 112 is partially exposed by the first release layer 114. On the other hand, the first release layer 114 covering the region other than the seed crystal 112 can maintain its integrity because of its thick thickness, and can prevent the impurities in the container 100 from being adsorbed and grown in the crystal growth process during the crystal growth process to affect the polysilicon. The quality of the ingot.

In order to prevent the first release layer 114 from being completely melted, the heat insulating cover 12A and the heat insulating plate 12B may be selectively separated to form a micro slit, and the heat H in the heat insulating chamber 12 is led to the furnace body 11 through the slit in a heat convection manner. The heat conducting block 15 located beside the slit is thus cooled. Since the bottom of the growth container 100 is in contact with the heat transfer block 15, the bottom of the growth container 100 is cooled with the heat transfer block 15, thereby lowering the temperature of the seed crystal 112 and the first release layer 114 at the bottom of the growth container 100, so that the seed crystal 112 and the first release layer 114 are not melted by heat.

Referring to FIG. 1D, the temperature field in the growth direction D is controlled based on the directional solidification process. The temperature of the crucible melter 130 is maintained by the heater 14, but the bottom of the growth vessel 100 is cooled, for example, the heat insulating cover 12A and the heat insulating plate 12B are further separated (enlarged slit), and more heat H is transmitted through the slit to the furnace body 11. Thereby, the heat conducting block 15 next to the slit is further cooled. By making the temperature of the bottom of the growth vessel 100 lower than the melting point of the tantalum raw material 120, the plurality of tantalum crystal grains 210 can be nucleated at the portion where the seed crystal 112 is exposed and grow in the growth direction D. By controlling the temperature gradient of the solid-liquid interface (the interface between the germanium die 210 and the tantalum melt 130), thermal stress can be reduced, thereby reducing the occurrence of defects.

Referring to FIG. 1E, the bottom of the growth vessel 100 is continuously cooled until the crucible melt 130 of FIG. 1D is completely solidified to form a polycrystalline ingot casting 200. The polycrystalline silicon ingot 200 has a bottom surface SB, a side wall surface SS, and a top surface ST. The bottom surface SB and the top surface ST are opposed to each other, and the side wall surface SS is connected to the bottom surface SB and the top surface ST. The polycrystalline germanium ingot 200 includes a plurality of germanium grains 210. The germanium crystal grain 210 grows from the bottom surface SB in the growth direction D, and the average grain size of the germanium crystal grain 210 increases from the bottom surface SB in the growth direction D. The growth direction D is parallel to the side wall surface SS and points from the bottom surface SB to the top surface ST.

Referring to FIG. 1E and FIG. 1F, after the crucible melt 130 (see FIG. 1D) is completely solidified, the stripping process can be continued. Before the film is released, the bottom surface SB of the polycrystalline silicon ingot 200 is in contact with the nucleation layer 110, and the side wall surface SS of the polycrystalline silicon ingot 200 is in contact with the second release layer 114'. During the stripping process, the sidewall surface SS of the polycrystalline silicon ingot 200 is separated from the second stripping layer 114', and the bottom of the polycrystalline tantalum ingot 200 is broken, for example, along the broken line in the enlarged view of FIG. 1E, so that the polycrystalline tantalum ingot is ingot. The bottom surface SB of 200 is separated from the nucleation layer 110. Since the area of the fracture surface is very small, the surface roughness (Ra) of the bottom surface SB of the polycrystalline silicon ingot 200 is little affected, so the surface roughness of the bottom surface SB of the polycrystalline silicon ingot 200 is mainly caused by the nucleation layer 110. A release layer 114 is determined. When the first material release layer 114 and the second release film layer 114' are made of the same material, the surface roughness of the bottom surface SB of the polycrystalline silicon ingot 200 and the side wall surface SS may be similar.

The difference in the polycrystalline germanium ingot produced by the method for producing a polycrystalline germanium ingot according to the present invention and the prior art will be described below with reference to Figs. 2A to 5 . 2A to 2C are photographs of the appearance of the wafer, respectively, for showing the grain size of the germanium ingot produced in the method for manufacturing the polycrystalline silicon ingot according to the present invention, the portion near the top surface, the middle portion, and the portion near the bottom surface. . 3A to 3C are photographs of the appearance of the wafer, respectively, for showing the grain size of the germanium ingot produced in the method of manufacturing the polycrystalline germanium ingot according to the prior art, in the portion near the top surface, the middle portion, and the portion near the bottom surface. . Figure 4 is a graph of height-average grain size for comparing polycrystalline tantalum ingots produced by the method of manufacturing a polycrystalline tantalum ingot of the present invention (indicated as ingot A) and prior art (indicated as ingot B). Average grain size at different heights. Figure 6 is a graph of height-to-defect ratio for comparing polycrystalline tantalum ingots produced by the method of manufacturing the polycrystalline tantalum ingot of the present invention (labeled as ingot A) and prior art (indicated as ingot B). The proportion of defects at height.

Referring to FIGS. 2A-2C, 4 and 5, the average grain size of a slice of a polycrystalline germanium ingot (labeled as ingot A) between about 50 mm and 100 mm in height is between 5 mm. Between 9mm; the average grain size of a slice between about 100mm and 150mm in height is between 9mm and 12mm; the average grain size of a slice between about 150mm and 200mm in height is between 12mm and 16mm Between; a slice having a height between about 200 mm and 250 mm has an average grain size between 16 mm and 20 mm. In other words, in the polycrystalline germanium ingot of one embodiment of the present invention, the average grain size of the germanium crystal grains increases from the bottom surface in the growth direction. Further, a defect ratio of a slice between a height of about 50 mm to 100 mm is less than 3%; a defect ratio of a slice between a height of about 100 mm to 150 mm is less than 5%; and a slice of a height of between 150 mm and 200 mm is between The defect ratio is less than 7%; the defect ratio of a slice between about 200 mm and 250 mm in height is less than 9%.

From the metallographic photographs of FIGS. 3A to 3C and the relationship diagrams of FIGS. 4 and 5, it is known that the polycrystalline tantalum ingot (indicated as ingot B) of the prior art grows into a large crystal grain at the bottom of the growth vessel and becomes a defect ratio. Low area. As the height increases, the average grain size of the germanium crystal grains decreases, but the proportion of defects in the polycrystalline germanium ingot rapidly increases, resulting in deterioration of the overall quality of the polycrystalline germanium ingot.

In contrast, the method for fabricating a polycrystalline germanium ingot according to an embodiment of the present invention utilizes a seed crystal to provide a dense nucleation site, and when nucleating, can provide a large number of nucleation sites to rapidly grow crystal grains, and Helps to greatly reduce the distribution ratio of large-sized germanium crystal grains formed at the bottom of the polycrystalline germanium ingot, thereby producing a polycrystalline germanium ingot (indicated as ingot A) in which the average grain size of the germanium crystal grains is increased from the bottom surface toward the top surface. . In the crystal growth process, the grain size is small and large, and under the control of the crystal growth method, the crystal grains are grown in a single direction and the formation of poor grain boundary defects is suppressed. Therefore, the polycrystalline germanium ingot produced by the method for producing a polycrystalline germanium ingot of the present invention may have a low defect ratio, and the subsequently fabricated semiconductor element (such as, but not limited to, a solar cell element) may also have a better ratio. Efficiency or electrical performance. In one embodiment, the defect ratio can be further reduced by high purity seed crystals and the quality of the polycrystalline germanium ingot can be improved.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

10‧‧‧Directional solidification system

11‧‧‧ furnace body

12‧‧‧Insulation room

12A‧‧‧Insulation cover

12B‧‧‧Insulation board

13‧‧‧ gas conduit

14‧‧‧heater

15‧‧‧thermal block

100‧‧‧ growing containers

110‧‧‧Nuclear layer

112‧‧‧ seed crystal

114‧‧‧First release layer

114’‧‧‧Second release layer

120‧‧‧矽Materials

130‧‧‧矽 molten soup

210‧‧‧矽 grain

200‧‧‧Polycrystalline ingots

D‧‧‧ Growth direction

H‧‧‧Hot

SB, SB’‧‧‧ bottom

SS, SS’‧‧‧ side wall

ST‧‧‧ top surface

1A to 1F are schematic views showing a manufacturing process of a polycrystalline germanium ingot according to an embodiment of the present invention. 2A to 2C are photographs of the appearance of the wafer, respectively, for showing the grain size of the germanium ingot produced in the method for manufacturing the polycrystalline silicon ingot according to the present invention, the portion near the top surface, the middle portion, and the portion near the bottom surface. . 3A to 3C are photographs of the appearance of the wafer, respectively, for showing the grain size of the germanium ingot produced in the method of manufacturing the polycrystalline germanium ingot according to the prior art, in the portion near the top surface, the middle portion, and the portion near the bottom surface. . Figure 4 is a graph of height-average grain size for comparing the average grain size of polycrystalline tantalum ingots produced by the method of the present invention and prior art polycrystalline tantalum ingots at different heights. Figure 5 is a graph of height-to-defect ratio for comparing the defect ratios of polycrystalline tantalum ingots produced by the method of the present invention and prior art polycrystalline tantalum ingots at different heights.

10‧‧‧Directional solidification system

11‧‧‧ furnace body

12‧‧‧Insulation room

12A‧‧‧Insulation cover

12B‧‧‧Insulation board

13‧‧‧ gas conduit

14‧‧‧heater

15‧‧‧thermal block

100‧‧‧ growing containers

110‧‧‧Nuclear layer

112‧‧‧ seed crystal

114‧‧‧First release layer

114’‧‧‧Second release layer

130‧‧‧矽 molten soup

210‧‧‧矽 grain

D‧‧‧ Growth direction

H‧‧‧Hot

SB’‧‧‧ bottom

Claims (9)

A method for manufacturing a polycrystalline tantalum ingot, comprising: forming a nucleation layer on a bottom surface of a growth vessel, wherein the nucleation layer comprises a plurality of seed crystals and a first release layer, wherein the seed crystals are disposed on the bottom surface And the first release layer covers the seed crystals and the bottom surface exposed by the seed crystals, wherein the seed crystals have a weight of 100 g to 200 g, and the release material of the first release layer The material of the seed crystals includes ceria, the material of the first release layer comprises tantalum nitride; the growth container is filled with a raw material, and the material is located in the On the nucleation layer; heating the growth vessel to completely melt the crucible material into a crucible melt, and melting the first release layer covering the seed crystals by heat, so that each of the crystal seeds is removed by the first release film The layer is partially exposed, and the exposed portion of the seed crystal is in contact with the crucible melt; the bottom of the growth vessel is cooled, and a plurality of germanium crystal grains are nucleated on a portion where the seed crystals are exposed and along Growing in a growing direction; and continuously cooling the bottom of the growing container, straight The entire molten metal solidification silicon, the polycrystalline silicon ingot is formed. The method for producing a polycrystalline germanium ingot according to claim 1, wherein the method of forming the nucleation layer on the bottom surface of the growth vessel comprises: forming the seed crystals on the bottom surface; and the crystals And forming the first release layer on the bottom surface exposed by the seed crystals. The method for producing a polycrystalline germanium ingot according to claim 1, wherein the method of forming the nucleation layer on the bottom surface of the growth vessel comprises: mixing the seed crystals into the release material; The release material having the seed crystals is formed on the bottom surface of the growth vessel. The method for producing a polycrystalline germanium ingot according to claim 1, wherein the seed crystals have an average size of between 0.05 mm and 50 mm. The method for producing a polycrystalline germanium ingot according to claim 1, further comprising: forming a second release layer on a side wall surface of the growth vessel before loading the crucible material. The method for producing a polycrystalline silicon ingot according to claim 5, wherein the thickness of the second release layer is greater than the thickness of the first release layer. The method for producing a polycrystalline silicon ingot according to claim 5, wherein a melting point of the second release layer is greater than a melting point of the first release layer. The method for manufacturing a polycrystalline germanium ingot according to claim 5, further comprising: separating the sidewall surface of the polycrystalline germanium ingot from the second stripping layer after the solid melting of the crucible melt is completely solidified, and disposing the polycrystalline crucible The bottom surface of the ingot is separated from the nucleation layer. The method for producing a polycrystalline tantalum ingot according to claim 1, wherein the seed crystals and the first release layer have a melting point greater than a melting point of the niobium material.