JPS5950639B2 - Manufacturing equipment for band-shaped silicon crystals - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an apparatus for manufacturing band-shaped silicon crystals.

[Technical background of the invention and its problems]

Since the band-shaped silicon crystal is in the form of a thin plate, unlike the ingot-shaped silicon crystal obtained by the Czochralski method, it can be used as a substrate for a semiconductor solar cell in its obtained shape.

Therefore, it has the great feature that the solar cell is cheaper than when silicon crystal obtained by, for example, the Czochralski method is used as a substrate.

FIG. 1 shows a cross-sectional view of the interior of the furnace for growing band-shaped silicon crystals.

A silicon melt 11 is housed in a quartz glass crucible 12, and a capillary die 13 (13a, 13b) having a slit (gap) made of carbon is placed in the melt 11.
) (hereinafter simply referred to as a die) is installed with its long side direction parallel to the long side direction of the crucible 12.

The tips of the dies 13 are sharply machined into a knife shape, and these dies 13 are strongly fixed to a heat shield plate 14 by a die holder 15.

This heat shield plate 14 prevents the heat radiation of the melt 11 from passing through the die 1.
A window is opened to expose the tip of the die 13, which serves to weaken the die 13 from reaching the tip.

The crucible 12 is a crucible holder 16 made of carbon.
inserted inside.

A pair of plate-shaped resistance heaters 17 (17a, 17b) are provided on the outside of the crucible holder 16.

This heater 17 is installed parallel to the long side direction of the die 13, and a thermocouple 18 in a protective tube installed on the side of the heater detects the temperature and controls the amount of heat generated by the detected output. .

19 is a heat insulation cylinder.

Polycrystalline silicon is placed in the quartz crucible 12 of the growth apparatus configured as described above, and the temperature of the heater 17 is set to approximately 1500°C.
raise.

Then, the polycrystalline silicon becomes a silicon melt 11, and this silicon melt 11 flows through the die 1 due to capillary action.
It rises to the tip of 3.

This rises. By bringing a seed crystal (not shown) into contact with the rising silicon melt 11 from above and then gradually pulling it up, a band-shaped silicon crystal 20 can be grown.

With the conventional apparatus described above, it was impossible to obtain band-shaped crystals larger than the melt in the crucible.

In order to grow a large amount of band-shaped crystals, either increase the crucible capacity and input a large amount of raw material from the beginning, or leave the crucible capacity small and replenish the amount of raw material taken out as band-shaped crystals. It is conceivable to adopt one of two methods: growth while

The former method of increasing the crucible capacity is technically possible.

This is because as the capacity of the crucible increases, the entire furnace including the heater can be increased in size.

However, increasing the capacity not only increases the manufacturing cost of the device and the consumption of electricity, inert gas, cooling water, etc., but also takes into account the operating rate, which goes against the purpose of manufacturing solar cell substrates at low cost. is well predicted.

Furthermore, it is not preferable to leave the raw material in a molten state for a long time from the viewpoint of quality control of the band-shaped crystals.

In other words, it is necessary to avoid deterioration in the quality of the band crystals due to impurity elements melting out from the crucible or die that the melt is in contact with, or impurity elements from the furnace materials entering through the atmospheric gas. I can't do it.

On the other hand, the latter included the following technical problems that had to be solved.

In other words, when a solid raw material is introduced, a drop in temperature of the melt is observed, but this drop in temperature cannot be detected sufficiently with the conventional thermocouple arrangement, and as a result, the solid-liquid interface of the band-shaped crystal lowers, causing the die to drop. It has been difficult to grow long band-shaped silicon crystals with a good yield due to the fixation.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide an apparatus that can mass-produce band-shaped silicon crystals without degrading quality.

[Summary of the invention]

The present invention provides a thermocouple for controlling a resistive heater at a distance from the top of the die, preferably between 13 mm and 19 mm.
It is characterized by being installed in a lowered position with its tip touching the side surface of the die.

〔Effect of the invention〕

According to the present invention, it is possible to detect the drop in liquid temperature that occurs when solid raw materials are directly charged from the outside of the furnace into the crucible, and when this is fed back to the heater output, the heater generates heat. By arranging the control thermocouple in consideration of the time it takes for the crystal to reach the tip of the die, it is possible to not only prevent the band-shaped crystals from sticking, but also to minimize changes in the width.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view of a main part of a belt-shaped silicon crystal manufacturing apparatus according to an embodiment of the present invention.

Components corresponding to those in FIG. 1 are given the same reference numerals as in FIG. 1.

In the conventional device, the thermocouple 18 was located near the heater 17, but in the device of this embodiment, the thermocouple 18 was inserted and fixed into the horizontal hole 21 provided in the die holder 15, and its tip was placed in the vicinity of the heater 17. It is in contact with the side of the die.

It has been observed that when solid raw materials are introduced into conventional equipment, the temperature of the liquid drops.

The amount of decrease in liquid temperature depends on the amount of raw materials input.

Furthermore, there was a certain time delay after the raw material was introduced until the liquid temperature drop affected the solid-liquid interface at the upper end of the die.

It was also found that the time delay varies somewhat depending on the pulling speed of the ribbon crystal.

The following table shows this relationship.

The distance between the silicon melt surface and the top of the die is 50 mm, and it is assumed that changes in liquid temperature are transmitted at a constant speed across this distance, and the time it takes for changes in heater heat to reach the solid-liquid interface at the top of the die is approximately 30 seconds. Taking this into account, the optimal thermocouple position when both changes simultaneously reach the solid-liquid interface was calculated as a distance downward from the top of the die, as shown in the rightmost column of the table.

Since the normal pulling speed is 0 to 30 mm 7' minutes, we set the thermocouple position to 17 mm, and at this position, we drilled a horizontal hole in the die holder and inserted the tip of the thermocouple to start control, but this alone did not provide enough control width. Met.

In other words, it was found that the amount of correction of the heater output was too small.

Therefore, a slit was provided on the silicon melt side of the horizontal hole provided in the die holder so that the thermocouple would be affected by the atmospheric gas.

FIG. 3 is a front view of the die 13 held in the die holder 15, and FIG. 4 is a view of only the die holder 15 viewed from the bottom of FIG. 3.

The diameter of the thermoelectric lamp horizontal hole 21 placed in the thermocouple protection tube is 5 m.
It was confirmed that when the width d of the slit 22 was set to 3 mm, the correction amount of the heater output matched well to the amount of liquid temperature decrease.

Initially, 200 g of polycrystalline silicon raw material was put into the apparatus of this example, and after it was melted, growth was performed while continuously supplying the bulk silicon raw material in an amount corresponding to the growth amount. ) was successfully pulled over a period of approximately 5 hours.

If there is no time constraint, it is possible to perform growth as long as the life of the die continues.

. In addition, in the conventional apparatus, the resistivity of the band-shaped crystals showed a tendency to gradually decrease, but the resistivity of the band-shaped crystals grown with the apparatus of this embodiment showed almost a constant value.

In conventional equipment, the time the melt stays in the crucible,
In other words, this appears to be because the time spent in the furnace differs between what crystallized first and what crystallized later, and the later the time, the higher the concentration of impurity elements becomes.

As described above, the apparatus of this embodiment is suitable for mass producing band-shaped crystals of good quality, and is well suited for the purpose of lowering the price of solar cell substrates.

Note that the present invention is not limited to the above-described embodiments.

Since it is possible that the heat flow and heat capacity will differ depending on the configuration and size of the furnace, the thermocouple position should be set at 13 to 19 mm.
It is quite conceivable that it may be placed outside the range.

Other modifications may be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional belt-shaped silicon crystal manufacturing apparatus, FIG. 2 is a cross-sectional view of a belt-shaped silicon crystal manufacturing apparatus according to an embodiment of the present invention, and FIGS. 3 and 4 show the die holder from the front and bottom. This is a diagram seen from. 11... Silicon melt, 12... Crucible, 13...
・Die, 14... Heat shield plate, 15... Die holder, 17... Heater, 18... Thermocouple, 20...
・Silicon crystal, 21...Horizontal hole, 22...Slit.

Claims (1)

[Scope of Claims] 1. A crucible containing a silicon melt and a capillary die having a slit are disposed in a heating furnace having a resistance heater, and a seed crystal is brought into contact with the melt rising through the slit, In an apparatus for producing a band-shaped silicon crystal by pulling up the seed crystal, the band-shaped silicon crystal is characterized in that a thermocouple for controlling the resistance heater is installed with its tip in contact with a side surface of the capillary die. Crystal manufacturing equipment. 2. The device for manufacturing a band-shaped silicon crystal according to claim 1, wherein the thermoelectric lamp has its tip in contact with the side surface of the capillary die at a position within a range of 13 mm to 19 mm from the upper end of the capillary die. 3. Claim 1, wherein the thermocouple is inserted and fixed into a die holder for fixing the capillary die, provided with a horizontal hole having a slit open to the silicon melt side. A manufacturing device for band-shaped silicon crystals.