JPS6111915B2 - - 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 and its problems] Because the band-shaped silicon crystal is in the form of a thin plate, unlike the ingot-shaped silicon crystal obtained by the Czyochralski method, it can be used in semiconductor solar cells without changing its shape. Used as a basis. Therefore, it has the great feature that it is cheaper than using, for example, silicon crystal obtained by the Czyochralski method as a substrate for a semiconductor solar cell. FIG. 1 shows a cross-sectional view of the interior of the furnace for growing band-shaped silicon crystals. FIG. 1 shows capillary dies 13, 13a, 13b (hereinafter simply referred to as dies) having slits (gaps) made of carbon in a quartz glass crucible 12 containing a silicon melt 11 in the direction of its long side. The crucible 12 is shown installed so that it is parallel to the long side direction of the crucible 12. die 13
The tips of the dies 13 are sharp and processed into a knife edge shape, and these dies 13 are connected to die holders 14,
14a and 14b, and the die holder 14 is also strongly fixed to a heat shield plate 15. The heat shielding plate 15 serves to weaken the thermal radiation of the silicon melt 11 from reaching the tip of the die 13, and has a window that exposes the tip of the die 13. The crucible 12 is inserted into a crucible holder 16 made of carbon. A pair of plate-shaped heaters 17, 17a, and 17b are provided on the outside of the crucible holder 16. The heater 17 is installed parallel to the longitudinal direction of the die 13 and the crucible holder 16, and cuts are made alternately from above and below, thereby controlling the electrical resistance value. Polycrystalline silicon is placed in the crucible 12 of the belt-shaped silicon crystal manufacturing apparatus constructed as described above, and the temperature inside the furnace is raised to about 1450 [°C]. Then,
Polycrystalline silicon becomes a silicon melt 11, and this silicon melt 11 flows through a die 13 due to capillary action.
rises to the tip of the By bringing a seed crystal (not shown) into contact with the rising silicon melt 11 from above and gradually pulling up the seed crystal, a band-shaped silicon crystal 18 can be grown. However, this type of device has the following problems. In other words, although the temperature distribution at the die tip is extremely important for the growth of band-shaped silicon crystals,
[mm], a temperature difference occurs in the longitudinal direction of the die tip. It was extremely difficult to keep this temperature difference within 3 [°C]. If the temperature difference between the left and right sides in the longitudinal direction of the die tip becomes 3 [℃] or more, sufficient adjustment cannot be made using the auxiliary temperature control mechanisms placed at both longitudinal ends of the die, making it impossible to achieve well-balanced growth. . The relationship between the die 13 and the band-shaped silicon crystal 18 grown in a state where the temperature distribution in the longitudinal direction of the die tip is sufficiently adjusted (temperature difference within 3° C.) is as shown in FIG. However, if the left and right temperature distribution is not adjusted, the band-shaped silicon crystal 18 will grow biased to one side, as shown in FIG. In FIG. 3, since the left side (L side in the figure) of the die 13 is lower temperature than the right side (R side in the figure), the width of the left side increases, and the band-shaped silicon crystal 18 reaches the left end before the right side reaches the target point. This is an example in which the tip of the die 13 and the tip of the die 13 are stuck together. If the temperature difference is not as large as in this example, it is possible to reach the target crystal width. However, it has been difficult to maintain stable growth over a long period of time. [Object of the Invention] An object of the present invention is to be able to easily and reliably control the temperature distribution in the longitudinal direction of the die tip within a certain value, to widen the band-shaped silicon crystal from side to side in a well-balanced manner, and to obtain the desired crystal width. An object of the present invention is to provide an apparatus for producing band-shaped silicon crystals that enables stable growth over a long period of time while maintaining the following properties. [Summary of the Invention] The gist of the present invention is how to reduce the temperature difference between the left and right sides of the die tip in the longitudinal direction and ensure its reproducibility. There are several possible causes of the temperature difference between the left and right sides. The inventors investigated possible factors such as differences in the heat generation distribution of the heaters, differences in the flow of atmospheric gas, and differences in the material and processing/assembly conditions of the heat shield plate, but which of the following could be the cause of the temperature difference? It was difficult to determine whether the However, it has been found that the temperature distribution is reproducible only by changing the die, quartz crucible, etc., which require conversion for each growth, as long as the furnace interior materials are not significantly changed. In other words, if the left end is at a low temperature in a certain furnace configuration,
That trend is expected to be maintained. Also,
According to further intensive research by the present inventors, the easiest and most reliable way to change the temperature situation at both longitudinal ends of the die tip is to change the relative position between the die tip and the top surface of the die holder. It has been experimentally discovered that. The present invention focuses on such points, and the lower end of a capillary die with a slit is immersed in a heated and melted silicon melt housed in a crucible, and seeds are injected into the silicon melt rising through the slit of the die. In a band-shaped silicon crystal manufacturing apparatus that grows and forms a band-shaped silicon crystal by bringing crystals into contact with each other and pulling up the seed crystal, a spacer of a predetermined thickness is disposed between the die and a die holder that fixes the die, Each distance between the tips of both longitudinal ends of the die and the top surface of the holder is variably set. [Effects of the Invention] According to the present invention, by adjusting the thickness of the spacer, it is possible to vary the distances of the tips of both longitudinal ends of the die from the top surface of the die holder. The distribution can be easily adjusted within a certain range. Furthermore, since there is no need to add a complicated mechanism, operability will not deteriorate. Therefore, it is possible to achieve well-balanced widening during crystal growth, and stable growth for a longer period of time is possible. Furthermore, according to experiments conducted by the present inventors, it was possible to reduce the time required to widen a band-shaped silicon crystal to a desired width by about 40% compared to the conventional apparatus. Furthermore, the maximum difference in thickness between the left and right spacers was about 0.4 mm, so
This did not have any adverse effect on the thickness, crystallinity, etc. of the band-shaped silicon crystal. [Embodiment of the Invention] FIG. 4 is a sectional view showing a schematic configuration of a belt-shaped silicon crystal manufacturing apparatus according to an embodiment of the present invention.
The same parts as in Fig. 1 are given the same reference numerals.
A detailed explanation thereof will be omitted. This device differs from the device shown in FIG. 1 in the configuration of the capillary die and die holder, and the arrangement of spacers. That is, the capillary dies 21, 21a, 21b
is different from the conventional die 13 and has a spacer 2 which will be described later.
2, 22a, 22b, 22c and 22d,
In order to play the role of positioning, a step of about 1 mm is provided on the longitudinal plane. The die holders 23, 23a, and 23b are provided with grooves on the left and right sides thereof, respectively, in which the spacers 22 can be accommodated. The spacer 22 is made of carbon and has a length of 15 [mm], a width of 5 [mm], and a thickness of about 3.5 [mm], with 10 increments of 0.05 [mm].
Four sheets were prepared for each type. Figure 5 a-c
5 partially shows the configuration of the main parts of the device, and FIG. 5a shows a state in which spacers 22a and 22c are housed in one piece 23a of the die holder 23.
5b is a front view of the die 21a, and FIG. 5c is a diagram showing the die 21 held in the die holder 23 and fixed with bolts. What is at issue here is the difference (h 1 _{-h 2} ) between the distances h ₁ and h ₂ between the top surface of the holder and the tip of the die as shown in FIG. 5c. Of course, the die tip may protrude upward or downward relative to the upper surface of the holder, and the difference between h ₁ and h ₂ is important, as they are positive in the former case and negative in the latter case. Carefully configure the furnace interior materials, insert four pieces of 0.35 mm thick spacers, and place the die 21 into the die holder 2.
3 and tried crystal growth. After several attempts,
The left side of the tip of the die 21 in the longitudinal direction is always 7
It was found that the temperature was ~9 [°C] lower. This temperature difference is 0
The table below shows the results of appropriately changing the difference between h ₁ and h ₂ to achieve [°C].

[Table] As shown in this table, the height difference is 0.30 [mm]
The spacer thickness for the two on the left is 3.45 so that
[mm], and the two on the right were 3.75 [mm]. In several experiments in which these spacers were inserted in the same way, it was possible to always maintain the desired temperature difference within 3 [° C.]. In addition, if the furnace interior material is significantly changed,
Although the temperature distribution between the left and right sides was sometimes reversed, the temperature difference never exceeded 9 [°C]. and,
There was no need to correct the height difference by more than 0.40 [mm]. When the left side of the top of the die was 7 to 9 degrees Celsius lower than the right side, the band-shaped silicon crystal expanded only to the left, and hardly expanded to the right. Even when the crystal reached the left end, the desired width of 100 [mm] could not be reached because the width was insufficiently widened to the right. Growth was attempted by correcting the height so that the left side of the upper end of the die was 3 to 5 degrees Celsius lower. The difference in height is 0.20
It was [mm]. In this case as well, the crystal widened significantly to the left, so it grew to the left from the center of the die and somehow reached a width of 100 mm with the help of an auxiliary temperature control mechanism. However, overall the temperature was lower on the left side, and the distance between the die tip and the solid-liquid interface was smaller and unstable on the left side than on the right side, so it was difficult to maintain the width of 100 mm for a long time. was difficult. On the other hand, when growth was performed with a height difference of 0.30 [mm] and a temperature difference between the left and right sides of approximately 0 [℃],
The width expansion from left to right was well balanced, and there was no need to use an auxiliary temperature control device for width expansion. Because the width was expanded without much effort, the time it took to reach the desired width of 100 mm was also shortened by a temperature difference of about 3 mm.
The time was 40% shorter than at [℃].
Furthermore, once the width reached 100 mm, it was easy to maintain this width and continue to grow stably until the melt in the crucible ran out. After that, the experiment was repeated, but by correcting the height (h ₁ , h ₂ ) with reference to the temperature distribution of the previous growth experiment, the temperature difference between the left and right sides of the top of the die was always kept at 2.
It was easy to keep the temperature within [°C]. Also,
By making the temperature distribution uniform in the longitudinal direction of the upper end of the die, the thickness of the crystal also became constant. In areas with low temperatures, the solid-liquid interface becomes lower and the crystal thickness increases accordingly, but by correcting the temperature distribution, the tendency for one end of the band-shaped silicon crystal to be thick is also corrected, and the thickness at both ends becomes became almost the same. Having a constant thickness contributes to improving the electrode formation yield during solar cell production. As is clear from the embodiments described above, in order to adjust the degree of protrusion of the die tip from the upper surface of the die holder, by inserting a spacer between the die holder and the die, the distance between the left and right sides in the longitudinal direction of the die tip can be adjusted. temperature distribution could be easily and reliably corrected, and the time required to widen the band-shaped silicon crystal could be shortened. Furthermore, since the temperature balance between the left and right sides of the die is good, it is possible to maintain a constant crystal width without difficulty, and as a result, stable growth over a long period of time has been achieved. In order to reduce the cost of band-shaped silicon crystals, the main aims are to increase the growth rate, increase the width, and prevent growth from being interrupted midway, and the present invention achieves at least the latter two. This will greatly contribute to lowering the cost of solar cells. Note that the present invention is not limited to the embodiments described above. In the example, the heights of the top surface of the die holder and the tip of the die were approximately equal; It may be installed. In this case, even if the die was tilted to change the height in the longitudinal direction of the die tip relative to the carbon, etc., the same effect as described above was obtained. Further, although a spacer is inserted between the die holder and the die, the number of spacers is not limited to four, and the material of the spacer is not limited to carbon. The material of the spacer has excellent heat resistance and silicon vapor resistance.
Any material with low content of harmful impurities and good processability may be used. Also, the spacer does not necessarily need to be fixed to the die holder or die. Furthermore, it is also possible to provide a spacer with a taper and move this spacer relative to the die using an operating jig taken out of the growth furnace, thereby changing the height of the die in accordance with the taper of the spacer. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a schematic configuration of a conventional belt-shaped silicon crystal production apparatus, FIGS. 2 and 3 are schematic diagrams for explaining the problems of the conventional apparatus, and FIG. 5A to 5C are cross-sectional views showing the schematic structure of the embodiment, and FIGS. 5A to 5C are views partially showing the main structure of the above embodiment. 11... Silicon melt, 12... Crucible, 15
... Heat shield plate, 17, 17a, 17b ... Heater, 18 ... Band-shaped silicon crystal, 21, 21a,
21b...Capillary die, 22, 22a-2
2d...Spacer, 23, 23a, 23b...Die holder.

Claims (1)

[Claims] 1. The lower end of a capillary die having a slit is immersed in a heated and melted silicon melt housed in a crucible, and a seed crystal is brought into contact with the silicon melt rising through the slit of the die. In a band-shaped silicon crystal manufacturing apparatus that grows and forms band-shaped silicon crystals by pulling up this seed crystal,
A spacer having a predetermined thickness is disposed between the die and a die holder that fixes the die, and distances between the ends of both longitudinal ends of the die and the top surface of the holder are variably set. Band-shaped silicon crystal manufacturing equipment. 2. The belt-shaped silicon crystal manufacturing apparatus according to claim 1, wherein the spacer is made of carbon.