JPS60108398A - Growth of silicon ribbon crystal - Google Patents

Abstract

PURPOSE:In the titled method, to prevent precipitation of silicon carbide on one side of silicon crystal, by using a pair of dies consisting of graphites having different thermal conductivity, respectively. CONSTITUTION:A pair of dies 4a'' and 4b'' are set in the silicon melt 3 in a crucible, seed crystal is brought into contact with the silicon melt 3 which rised in the slits of the dies by capillary phenomena, and it is pulled up under a given condition to form the silicon ribbon crystal 5. A pair of the dies used in the above-mentioned method consist of the die 4a'' (having higher thermal conductivity in the Q1 direction) made of a material obtained by cutting pyrolytic graphite in the direction perpendicular to the deposition face 7 and the die 4b'' (having higher thermal conductivity in the Q2 direction) made of a material obtained by cutting it in the direction parallel to the deposition face. Consequently, the tip part of the die 4a'' has a lower temperature than that of the tip part of the die 4b'' (the solid-liquid interface 6''), so that silicon carbide particles are attached only to the die 4a'' side of the silicon ribbon crystal 5.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method of growing silicon ribbon crystals using a die.

[Technical background of the invention and its problems]

Conventionally, silicon ribbon crystals are pulled by the method shown in FIG. That is, a silicon material is placed in a crucible 1 made of quartz glass with a 4':I+ degree shape, and a silicon melt 3 is produced by heating the silicon material with a pair of opposing plate heaters 2a and 2b. In this silicon melt 3, a pair of dies 4a and 4b made of carbon are set upright. Since carbon is a material that gets wet with the silicon melt, the silicon melt 3 rises through the slots of the dies 4a and 4b due to capillary action and reaches the tips of the dies 4a and 4b. By bringing a seed crystal into contact with this rising silicon melt 3 and pulling up the seed crystal, a silicon/regan crystal 5 defined by the slots of the dies 4a, 4b grows.

By the way, silicon manufactured with such conventional equipment
There are many silicon carbide grains on the surface of the ribbon crystal. The pair of dies 4a and 4b shown in FIG. 1 are usually kerf]? It consists of In this case, dies 4a, 4
The $f'f component of b, the centripetal carbon, is injected into the silicon melt, and due to the eutectic reaction with the silicon melt, silicon and
Exists as carbide grains. This silicon car/S
The die 4a has a relatively low temperature.

It precipitates at the tip of 4b. The precipitated silicon carbide grains are then incorporated into the growing silicon ribbon crystal. Even if an attempt is made to form a P-N junction by diffusing impurities into such a crystal, the diffusion coefficient will be different due to the silicon carbide grains, making it impossible to form a predetermined flat P-N junction. For this reason, when used as a solar cell element, the photoelectric conversion efficiency differs between parts of the silicon ribbon crystal, making it impossible to obtain a solar cell element with a predetermined power.

Moreover, because of the silicon carbide grains, current-voltage characteristics with extremely large leakage currents are observed.

Also, when printing surface electrodes, the mask may be damaged or
The problem of damage due to printing pressure is likely to occur.

[Purpose of the invention]

The present invention has been made in view of the above 41 circumstances, and is designed to prevent silicon carbide grains from precipitating on one side of a silicon ribbon crystal, and to form a P-N junction on the surface where silicon carbide does not precipitate. For example, even when used as a solar cell element, the photoelectric conversion efficiency will not be reduced (silicon material has almost no leakage current).
The purpose is to provide a method for growing ribbon crystals.

[Summary of the invention]

In the present invention, a pair of dies having slits are set upright in a crucible containing a silicon melt, and a seed crystal is brought into contact with the silicon melt rising inside the slit to pull up a ribbon crystal. The present invention is a silicon ribbon crystal growth method characterized in that each of a pair of dies is made of graphite having a different thermal conductivity, such as pyrolytic graphite.

[Embodiments of the invention]

The inventors of the present invention have conducted intensive research to prevent silicon carbide grains from precipitating on one side of a silicon/iron crystal, and have found that it is effective to create a temperature difference between the tips of a pair of dies. There was found.

Dies 4a and 4b in FIG. 1 and solid-liquid interface 6 in the ribbon thickness direction
The shape of is shown in Figure 2. In the case of Fig. 2, dies 4a and 4b
The temperature at the tip is the same, and the solid-liquid interface 6 has a flat shape.

In this case, silicon carbide grains are formed on both sides of the ribbon crystal.

There is a method shown in FIG. 3 as a means for creating a temperature difference at the die tip. The method shown in FIG. 3 uses the temperature gradient of the die to create a difference in the height of the tip of the die. According to this method, the die 4b' on one side (the tip is low) is at a high temperature, the die 4a/ on the other side (the tip is high) is at a low temperature, the solid-liquid interface 6' is inclined, and the silicon carbide Are the grains glue on the low temperature side? It adheres only to the surface of the crystal and does not touch the high temperature side. However, in this method, silicon carbide grains do not adhere to one side of the ribbon crystal, but the pulling yield is significantly reduced, making it unsuitable for mass production.

As a result of further research, the present inventors discovered a method of constructing a pair of dies using graphite with different thermal conductivities as a means of creating a temperature difference at the tip of the die, and adopted i4 Irolytic graphite as the die material. . Pyrolitic graphite is produced from hydrocarbon gas, and carbon atoms are deposited in layers. Therefore, the anisotropy of physical properties is large in the direction parallel to the deposition surface and in the direction perpendicular to the deposition surface. In particular, when comparing the thermal conductivity, it is 470 KcaA7 in the direction parallel to the deposition surface of /7 Irolytic graphite.
'm1Ihr@tl: In the direction perpendicular to the deposition plane of pyrolytic graphite, there is a large difference of 11 Kcal/m-hr·°C. Therefore, by taking advantage of this physical anisotropy, one side of the die is made of a material cut parallel to the deposition surface of pyrolytic graphite, and the deposition surface is configured to be perpendicular to the horizontal direction. The other side is a material cut perpendicular to the deposition surface, and if the deposition surface is configured horizontally, a temperature difference will occur at the die tip due to the large difference in thermal conductivity, and only on the low temperature side. Silicon carbide sticks and does not stick to the high temperature side.

That is, as shown in FIG. 4, the die 4aH is a material cut perpendicularly to the deposition surface 7 of pyrolytic graphite, and is constructed so that the deposition surface 7 is horizontal, and the die 4b'' is It is made of a material cut out in a direction parallel to the deposition surface 7 of 9Irolitic graphite, and is constructed so that the deposition surface 7 is perpendicular to the horizontal direction.

As shown in FIG. 1 of the conventional example, the heat sources of the die are carbon heaters 2a, 2b, and the hot zone configuration is symmetrical with respect to the die. Y has been completed. Therefore, the amount of radiation incident on the dies 4a' and 4b'' is the same.In Fig. 1, the thermal conductivity of the dies 4a and 4b is the same,
, 4b'' are at the same temperature, but in Figure 4, the thermal conductivity of dies 4aII and 4b'' is significantly different.
On the die 4a'' side, the heat transfer is Ql, and the amount of heat transmitted to the tip of the die 4a by thermal conduction is extremely reduced. However, on the die 4 b' side, the heat transfer is Q2, and the decrease in the amount of heat transmitted to the tip of die 4 b' by thermal conduction is
a''. Therefore, only a small amount of heat is transferred to the tip of the die 4a', and a large amount of heat is transferred to the tip of the die 4b''. Therefore, die 4a"
The tip of the die 4b' becomes low temperature, the tip of the die 4b' becomes hot, the solid-liquid interface 6 is inclined, and the silicon carbide grains adhere only to the silicon ribbon surface on the die 4a'' side, and on the die 4b'' side. Do not irradiate the silicon ribbon surface. Also, the heights of the tips of the dies 4a and 4b' are the same.
Therefore, there is no interruption in pulling, and the pulling yield is the same as in the case shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, a pair of dies are made of pyrolytic graphite, one die is provided with the deposition surface in the horizontal direction, and the other die is provided with the deposition surface in the horizontal direction. By arranging the temperature difference between the die tips on both sides, it is possible to prevent silicon carbide grains from adhering to the silicon ribbon surface on the low temperature side. Therefore, silicon
Diffuse impurities on the surface where carbide grains do not stick to P-N
When the junction is formed, a flat PN junction is formed. Therefore, when used as a solar cell element, there is an advantage that a solar cell element having a predetermined /e quae can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing a conventional silicon crystal growth apparatus, FIGS. 2 and 3 are cross-sectional views each showing a conventional die structure, and FIG. 4 is a diagram showing the structure of a conventional silicon crystal growth apparatus. 1η
FIG. 2 is a sectional view showing an example of the structure. 1... Quartz crucible, 2 a r 2 b... Heater, 3... Silicon melt, 4 a, 4 b, 4
g', 4b', 4b'. 4b'...die, 5...su? crystal', 6.6',
6"...solid-liquid interface, 7...deposition surface of pyrolytic graphite. 1123j Takehiko Suzue, Patent Attorney Figure 1 Figure 2 Figure 3 Figure 7 Contents of amendment (1) Details C between page 9, line 12 and page 9, line 13:
``Furthermore, with this invention, we have obtained the result that impurity atoms tend to adhere to the slit surface on the side where a material with low thermal conductivity is used.For this reason, the average impurity concentration in the spin crystal is 5. Several tens of ppm when not using, 1/1 when using the present invention
It becomes 0 ppm, which is a significant decrease. Therefore, the purity in the pin crystal of the present invention is greatly improved,
As a result, a highly efficient solar cell element can be obtained. Furthermore, in the present invention, since the thermal conductivity of each of the pair of gooeys is different, the temperature of each gooey is different. Therefore, thermal strain exists in the thickness direction in the pulled ribbon crystal. By lowering the temperature during pulling or by simple heat treatment, it is possible to divide the crystal into two parts along the thermal strain, making it possible to obtain two IJ, G crystals at the same time. ” to join. Japanese Patent Application Sho Gfl-108398 (5)

Claims (3)

[Claims] (1) A pair of dies each having a slit are placed upright in a crucible containing a silicon melt, and a seed crystal is brought into contact with the silicon melt rising through the slit. Is there silicon to pull up the crystal? In the method of growing a silicon crystal, each of a pair of dies is made of graphite having different thermal conductivity. How to grow crystals. (2) Claim 1, characterized in that each of the pair of dies is made of solid graphite.
Method for growing silicon ribbon crystals as described in Section 1. (3) One side of the pair of dies is provided so that the deposition surface of t4 ilorithic graphite is in the horizontal direction, and the other side of the pair of dies is provided so that the deposition surface of /f ilorithic graphite is perpendicular to the horizontal direction. 3. The method of growing a silicon ribbon crystal according to claim 2, wherein the silicon ribbon crystal is provided in a direction in which the silicon ribbon crystal is grown.