JPH0154320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an apparatus for producing band-shaped silicon crystals.

[Technical Background of the Invention] Recently, there has been a desire to lower the price of silicon substrates for solar cells as part of efforts to reduce the cost of solar power generation, and band-shaped silicon crystals are produced when cutting and processing ingot crystals. It is viewed as promising because there is no significant material loss and processing costs are low.

The present inventors have proposed a new apparatus for manufacturing band-shaped silicon crystals that allows easy crystal growth and stable growth for a long period of time (Japanese Patent Application No. 58-53534, etc.). Fifth
The figure is a schematic configuration diagram of the above band-shaped silicon crystal manufacturing apparatus. In the figure, reference numeral 11 indicates a crucible made of graphite, and a silicon melt 12 is accommodated in this crucible 11. Crystal growth dies 13a and 13b are installed above the crucible 11, respectively.
The dies 13a and 13b are attached to fixing parts 14a and 14b provided outside the crucible 11, respectively. Further, a heater (not shown) for heating the crucible 11 is provided at the lower bottom of the crucible 11, and in addition to this, heaters 15a and 15b for independently heating the dies 13a and 13b are provided at the fixed parts 14a and 14b. It is provided.

In the figure, 16 is a heat shield for preventing the crucible temperature from being disturbed by heat radiation from the sides of the heaters 15a, 15b. Furthermore, all of the above-mentioned components are housed in a metal container (not shown) filled with argon gas, and above the container there is a pulling drive for pulling the band-shaped silicon crystal upward. (not shown) is provided.

FIG. 6 is a conceptual diagram of band-shaped silicon crystal growth using the above-mentioned apparatus. Crystal growth dies 13a, 13b
When a seed crystal 17 with a width slightly smaller than the spacing is brought into contact with the silicon melt 12, the silicon melt near the seed crystal 17 is lifted up and a meniscus 18 shown by hatching in the figure is formed, and the solid-liquid interface 19 has a concave shape. Become. When the seed crystal 17 is pulled up, a band-shaped silicon crystal 20 having a width defined by the interval between the crystal growth dies 13a and 13b grows below it. meniscus 1
The height of the die 13 (from the free liquid surface of the silicon melt 12 to the bottom of the solid-liquid interface 19) is approximately 7 to 8 mm.
The width of the meniscus 18 between a, 13b and the side of the seed crystal 17 is approximately 1 mm.

According to the above-described belt-shaped silicon crystal manufacturing apparatus, since the height of the meniscus 18 and the distance between the dies 13a, 13b and the solid-liquid interface 19 are large (for example,
Edge-defined Film-fed Growth method (EFG method)
(The meniscus height at the top of the capillary die is approximately 0.25 mm) Even if slight temperature fluctuations occur, the crystal growth dies 13a, 13b and the band-shaped silicon crystal 2
It is characterized in that it is less likely that 0 particles will stick together or that the band-shaped silicon crystal 20 will separate from the meniscus 18 and the crystal will be cut, and that stable growth can be continued for a long time.

[Problems of the Background Art] However, even in the belt-shaped silicon crystal production apparatus shown in FIG. 5, there is a problem in that crystal breakage or sticking occurs when the temperature of the silicon melt changes for some reason. That is, crystal breakage occurs when the liquid temperature rises, and fixation occurs when the liquid temperature falls, resulting in the interruption of crystal growth. Figures 7a and b are diagrams schematically showing when and immediately after crystal breakage is about to occur in the die 13a on the left, respectively, and Figures 8a and b are similarly diagrams showing when crystal breakage is about to occur and when it has occurred. It is a diagram schematically showing immediately after. What should be noted is that the width or height of the meniscus 18 between the die 13a and the crystal 20 changes slightly.

A physical explanation of these interruption phenomena is as follows. When pulling a band-shaped silicon crystal from the free melt surface, the height of the meniscus 18 is usually 7 to 8 mm.
becomes. The solid-liquid interface can be thought of as an isothermal line (isothermal surface) of the silicon melt (1420℃), and its height is affected by the liquid temperature, increasing at high temperatures and decreasing at low temperatures, but Laplace's height related to surface tension Solving the differential pressure equation yields the above meniscus height of 7 to 8 mm.
The reason why the solid-liquid interface 19 is concave in this manufacturing method of band-shaped crystals is because the left and right dies 13a, 13b are heated, so the isothermal line becomes concave. There is a capillary effect between the melt and the crystal 20, and the melt rises to a height of 7 to 8 mm. Now, die 13a on the left side of the crystal.
If a temperature rise occurs in the vicinity, as shown in Figure 7a,
The solid-liquid interface 19 near the left die 13a (i.e.
1420℃ isotherm) according to the right side of the figure. As the pulling continues, the width of the crystal 20 becomes narrower and the distance between the left die 13a and the crystal 20 becomes larger. For this reason, the capillary effect mentioned above becomes small, and the left die 13a is no longer filled with melt, resulting in crystal breakage as shown in FIG. On the contrary, when the temperature decreases near the left die 13a, the solid-liquid interface 19 near the left die 13a shifts to the left side of the figure, as shown in FIG. 8a. Die 13a
If the temperature does not fall below 1420°C, crystal growth will continue with the crystal width becoming slightly wider, but if the temperature drops too much, die 13a and crystal 2
0 is stuck. However, since the temperature in the vertical direction of the die is higher at the bottom, the occurrence rate of the sticking phenomenon is lower than that of crystal breakage.

Conventionally, the following methods have been used to prevent such interruptions. In other words, if crystal breakage is likely to occur, reduce the heater input to lower the crucible temperature or the temperature of the dies 13a, 13b, or slow down the pulling speed to avoid the breakage phenomenon, and if the die and crystal are likely to stick together, On the contrary, sticking was prevented by increasing the crucible temperature or die temperature, or by increasing the pulling speed. However, increasing or decreasing the temperature of the crucible or die takes time to respond due to the heat capacity of the system, and it is often difficult to meet the interruption phenomenon.On the other hand, adjusting the pulling speed has a greater effect on the thickness of the crystal than temperature. It was a disadvantage of giving. In addition, dies 13a and 13b
It is possible to some extent to prevent the discontinuation phenomenon by moving the dies left and right and changing the distance between the two dies, but the distance to be moved is delicate and, for example, increasing the distance between the dies in an attempt to prevent sticking causes crystal breakage. This is a method that requires skill as it can cause problems.

The above-mentioned discontinuation phenomenon occurs due to temperature fluctuations of about ±3°C, and although it is still a small drawback compared to the EFG method, where a similar phenomenon occurs due to temperature fluctuations within ±1°C, it is This was an issue that needed to be overcome in order to achieve continuous growth and, ultimately, to reduce the cost of silicon substrates.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to widen the allowable range of temperature fluctuations that may occur during the growth of band-shaped silicon crystals, and therefore to It is an object of the present invention to provide a band-shaped silicon crystal manufacturing apparatus that can stabilize growth for a long time and reduce manufacturing costs.

[Summary of the Invention] The gist of the present invention that can achieve the above object is to make the opposing surfaces of the pair of crystal growth dies described above be inclined with respect to the vertical direction.

That is, the present invention provides an apparatus for growing a band-shaped silicon crystal by bringing a seed crystal into contact with a silicon melt housed in a crucible and pulling up the seed crystal. a pair of crystal growth dies disposed to face the ends and a means for heating these dies on the outside of the crystal growth dies, the ends of the band-shaped silicon crystal to be grown by the pair of crystal growth dies; The crystal growth die is characterized in that opposing surfaces of the pair of crystal growth dies corresponding to the portions are inclined with respect to the vertical direction.

[Embodiment of the Invention] FIG. 1 is a schematic diagram showing an embodiment of the present invention. Silicon melt 1 in graphite crucible 11
Above the crucible 11, crystal growth dies 13a and 13b are installed at an interval of 10 cm. In addition, a heater for heating the crucible (not shown), a heater for heating the die (not shown)
The structure and the overall structure of the growth apparatus are the same as those described in the explanation of FIG. The feature of the present invention in FIG. 1 is that the dies 13a and 13b are each installed at an angle with respect to the vertical direction.
A pair of dies 13a and 13b are installed with an inclination of 5 degrees so that they are wide at the top and narrow at the bottom. Further, these dies 13a and 13b are movable in the vertical and horizontal directions, respectively.

The stability of band-shaped silicon crystals produced using the above apparatus will be described with reference to FIG.
FIG. 2a shows a case where crystal growth is carried out steadily, which is the same as the case shown in FIG. 5. Figure b shows a case where the temperature rises due to some reason in the vicinity of the die 13a on the left side of the crystal, and as explained in Figure 6, the solid-liquid interface 19 moves away from the die 13a and moves to the right side of the figure, causing the crystal to rise. As the growth continues, the crystal width becomes narrower. In the conventional device, as described above, the gap between the left die 13a and the crystal 20 becomes wide and the melt is no longer stretched between them, resulting in crystal breakage, but with the device of the present invention, the die 13a is tilted. Therefore, even if the crystal width becomes narrow, a stable solid-liquid interface 19 can be formed again when the melt on the left die 13a side becomes slightly lower, as shown in Figure c, and the crystal grows without breaking. can be continued. At this time, there was no need to change the heating amount of the heater or move the die, making growth extremely easy.

As described above, according to the apparatus of this embodiment, although the fluctuation in crystal width is ±0.4 mm, the duration of crystal growth while continuously supplying the raw material silicon is 3 hours on average when using the conventional apparatus. Something that was hot
It lasted over 10 hours.

Incidentally, when the pair of crystal growth dies as described above are tilted such that they are wide at the top and narrow at the bottom, this is not more advantageous than the conventional apparatus in terms of the phenomenon of fixation between the crystal and the die. The following devices are highly effective in preventing sticking phenomena. That is,
FIG. 3 is a schematic diagram of the embodiment, and the improvement is that the crystal growth dies 13a, 13b are tilted so that they are narrow at the top and wide at the bottom. The inclination angle is 5° with respect to the vertical direction. Figure a shows the case where the crystal is growing steadily. Also, Figure b shows a case where a temperature drop occurs due to some reason near the die 13a on the left side of the crystal, and as explained in Figure 8, when the solid-liquid interface 19 approaches the die 13a and the crystal continues to grow, the crystal width increases. becomes wider. In the conventional apparatus, the crystal growth die 13a and the crystal 20 are stuck together as they are, but according to the apparatus of the present invention, the die 13a and the crystal 20 are fixed together.
Because a is tilted, even if the crystal width becomes wider, a stable solid-liquid interface 19 can be formed again when the melt surface on the die 13a side becomes slightly higher, as shown in c in the figure, and the solid-liquid interface 19 is fixed. You can continue to grow without having to By the way, in the configuration of this embodiment, even if no fixation occurs, the crystals with increased width are attached to the dies 13a, 1.
There was a concern that it might not pass above 3b. However, for example, even if the width increases on the left side of the crystal and the crystal and die come into contact above the left die 13a, the solid crystal and die will not stick together, and the crystal will simply be swung to the right. We were able to continue our growth. If the width of the crystal becomes wider than the width of the upper ends of the dies 13a, 13b, the distance between the dies 13a, 13b may be widened as in the conventional device. Furthermore, according to the apparatus of this embodiment, since the sticking phenomenon is less likely to occur, the temperature of the silicon melt can be set low, which has the effect of improving the growth rate.

The inventor further conceived and implemented a belt-shaped crystal growth apparatus that is effective in preventing both crystal breakage and crystal fixation.

That is, FIG. 4 is a schematic diagram of crystal growth performed by the device, and the improvement point is the crystal growth die 13.
a and 13b are narrow at the center and wide at the upper and lower parts. In this embodiment, the inclinations of the dies 13a and 13b were both upward and downward at an angle of 5 degrees with respect to the vertical direction, and the central portions were provided with a curvature. Figure a shows the case where the crystal is growing steadily, and the bottom of the solid-liquid interface 19 is the die 13a, 1
The system was adjusted so that it was located approximately at the vertical center of 3b. That is, the amount of raw material silicon continuously supplied during growth was set to be the same as the amount of grown crystals, and the silicon melt surface was kept constant. Same figure b
2 is a diagram showing a case where a temperature rise occurs near the left die 13a, and in this case, crystal growth continues due to exactly the same effect as in the previous embodiment. Further, in FIG. 3C, a temperature drop occurs near the left die 13a, but since the distance between the crystal 20 and the die 13a is widening downward, sticking is unlikely to occur.

With the apparatus described in this third example, the growth duration was further extended, and no interruption occurred even when growth continued for 24 hours.

In addition, in the above-mentioned embodiment, the inclination angle of the die was set to 5 degrees with respect to the vertical direction, but the inclination angle is not limited to this. Further, in the present invention, in order to prevent the growth interruption phenomenon, an operation of moving the die similar to the conventional technique can also be used. In addition, various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] As described above, by using the belt-shaped silicon crystal manufacturing apparatus according to the present invention, the allowable range of temperature fluctuations during crystal growth is wider than when using a conventional apparatus.
Since the incidence of interruption of crystal growth is extremely low, there is an effect that the growth duration time is improved.
At the same time, there is also the advantage that operations that require skill to prevent growth interruption phenomena, which were necessary in conventional apparatuses, are unnecessary or simplified, and the growth technique becomes easier.

On the other hand, according to the apparatus particularly shown in the second embodiment of the present invention, even if the temperature of the silicon melt contained in the crucible is lowered, a decrease in adhesion is unlikely to occur, and the growth rate is improved by the amount that the melt temperature can be lowered. There is an effect.

In addition, the apparatus of the present invention can change the interval between the crystal growth dies even during growth, and the width of the crystal can be changed arbitrarily, and the use of the die shape according to the present invention has the advantage that this operation becomes easy. .

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing one embodiment of the present invention, Figure 2 is a schematic diagram showing an embodiment of the present invention.
The figure is a schematic diagram illustrating the state of crystal growth according to one embodiment of the present invention, FIGS. 3 and 4 are schematic diagrams illustrating other embodiments of the present invention, and FIG. 5 is a conventional belt-shaped silicon crystal manufacturing apparatus. FIG. 6 is a conceptual diagram of crystal growth using a conventional apparatus, and FIGS. 7 and 8 are schematic diagrams illustrating the phenomenon of interruption of crystal growth in the conventional apparatus. 11... Crucible, 12... Silicon melt, 13
a, 13b...Crystal growth die, 14a, 14b
... Fixed part, 15a, 15b ... Heater for die heating, 16 ... Heat shield, 17 ... Seed crystal, 18
...Meniscus, 19...Solid-liquid interface, 20...Striped silicon crystal.

Claims (1)

[Claims] 1. In an apparatus for growing a band-shaped silicon crystal by bringing a seed crystal into contact with a silicon melt contained in a crucible and pulling up the seed crystal, both ends in the width direction of the band-shaped silicon crystal to be grown are provided. A pair of crystal growth dies are provided on the outside of the part to face the end part, and a means for heating these dies is provided. A belt-shaped silicon crystal manufacturing apparatus characterized in that opposing surfaces of the pair of crystal growth dies corresponding to the end portions are inclined with respect to the vertical direction. 2. The opposing surfaces of the pair of crystal growth dies corresponding to the ends of the band-shaped silicon crystal to be grown are inclined so that the distance between the surfaces is wide at the top and narrow at the bottom. An apparatus for producing band-shaped silicon crystals according to claim 1. 3. The opposing surfaces of the pair of crystal growth dies corresponding to the ends of the band-shaped silicon crystal to be grown are inclined so that the distance between the surfaces is narrow at the top and wide at the bottom. An apparatus for producing band-shaped silicon crystals according to claim 1. 4. The opposing surfaces of the pair of crystal growth dies corresponding to the ends of the band-shaped silicon crystal to be grown are sloped so that the distance between the surfaces is narrow in the center and wide in the upper and lower portions. An apparatus for manufacturing band-shaped silicon crystals according to claim 1, characterized in that the apparatus comprises: 5. The belt-shaped device according to claim 1, wherein the means for heating each of the dies is a heating mechanism that is different from a heating mechanism that heats the silicon in the crucible. Silicon crystal manufacturing equipment. 6. The belt-shaped silicon crystal manufacturing apparatus according to claim 1, wherein the pair of crystal growth dies are each independently movable in the vertical direction and the horizontal direction.