JPS5850960B2 - How to grow band-shaped silicon crystals - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for growing band-shaped silicon crystals.

Conventionally, band-shaped silicon crystals have been obtained using an apparatus as shown in FIG.

In FIG. 1, a is a plan view, and b is a sectional view taken along line AA' in FIG.

In FIGS. 1a and 1b, a crucible 12 made of quartz glass containing a silicon melt 11 is provided with a pair of dies 13a having a slit (gap) made of carbon,
Install 13b.

The tips of the pair of dies 13a, 13b are sharpened into a knife shape, and the pair of dies 13a, 13b are fixed with support rods 14a, 14b.

Bolts 15a are attached to both ends of the support rods 14a and 14b.
, 15b are provided to firmly fix the pair of dies 13a, 13b.

Furthermore, a pair of plate-shaped main heaters 16a and 16b are provided outside the quartz crucible 12.

This plate-shaped main heater 16a. 16b is provided in the longitudinal direction of the pair of dies 13a, 13b and the quartz crucible 12, and is provided parallel to the support rod 14at14b.

Furthermore, this plate-shaped main heater 16a. A slit 17 is provided in 16b to control the resistance value.
Further, the upper portions of the plate-shaped main heaters 16a and 16b, that is, the pair of dies 13a.

The portion located at the upper end of 13b (where it grows) is tapered.

Polycrystalline silicon is placed in the quartz crucible 12 of the growth apparatus configured in this manner, and plate-shaped main heaters 16a, 16b are placed in the quartz crucible 12.
The temperature is set to about 1500°C.

Then, the polycrystalline silicon becomes a silicon melt 11, and this silicon melt 11 rises through the slits of the pair of dies 13a and 13b to the tip by capillary action.

A seed crystal is brought into contact with this rising silicon melt 11,
By gradually pulling up the seed crystal, a band-shaped silicon crystal 18 grows.

The band-shaped silicon crystal thus obtained has a shape similar to the shape of the slit of the pair of dies 13a, 13b. For example, the width of the slit of the pair of dies 13a, 13b is 0.3 mm, When the thickness is 40 mm, the obtained band-shaped silicon crystal has a thickness of 0.3 mm ± 30 μm.
1 width was 40rran±0.5 mm.

By the way, many of the band-shaped silicon crystals obtained by the above method are used as substrates for semiconductor solar cells in the obtained state.

Therefore, for example, rather than using silicon crystal obtained by the Czochralski method as a substrate for a semiconductor solar cell,
It has the great feature that it can be obtained at low cost.

Recently, attempts have been made to obtain wide band-shaped silicon crystals using the method described above in order to further reduce the cost.

For example, the slit width of the pair of dies 13a and 13b is 0.3
If the length is maintained at mm and the length is set to 100 mm, a band-shaped silicon crystal having a thickness of 0.3 mm and a width of 100 mm can theoretically be obtained.

However, according to experiments conducted by the present inventors, it was not possible to obtain a band-shaped silicon crystal having a thickness of 0.3 mrrt and a width of 100 mm as described above.

Therefore, the present inventors investigated how wide band-shaped silicon crystals can be obtained with a relatively good yield (~80% or more) using the method described above, and found that the maximum width is 70 to 80 mm. found.

For example, the width of the slit of a pair of dies is 70 mrIL to 80 mrIL.
If it exceeds mm, for example, the silicon melt may solidify in the longitudinal direction of a pair of dies, resulting in a yield of less than 80% (usually less than 50%), and there is no reason to increase the width of the band-shaped silicon crystal. understood.

Therefore, the inventors of the present invention have found that when the length of the slits of a pair of dies is increased to, for example, 100 degrees or more, as described above,
For example, in order to investigate the reason why the silicon melt solidifies at the longitudinal ends of a pair of dies, the temperature at the tips of a pair of dies was measured.

To measure this temperature, as shown in the perspective view of FIG.
A plurality of thermocouples 20a and 20b made of rhodium (Rh) were provided.

The width of the pair of dies 13a and 13b shown in FIG. 2 is approximately 165 mm, and the width of the thermocouples 20a and 20b is
They were installed at intervals between the plates.

As shown in FIG. 2, a pair of dies 13a, 13
As a result of measuring the temperature at the tip of b, it was found that the temperature distribution was as shown in FIG.

Note that FIG. 3 shows the temperature distribution centered on the center of the die.

As is clear from the temperature distribution in FIG. 3, when the width of the pair of dies 13a, 13b becomes wider than 80 mm, the pair of dies 13a.

It was found that the temperature at the tip of 13b was 1445°C or less on average, and was, for example, 3°C to 15°C lower on average than the center.

Therefore, if we consider the above-mentioned point that when the width of a pair of dies exceeds 70 to 80 mm, the silicon melt solidifies at the ends of the dies, and the temperature distribution of this pair of dies, Since the temperature at the tip was 3°C or more lower than 1450°C, it is thought that the silicon melt solidified in the longitudinal direction of the pair of dies.

That is, it is considered that if the temperature at the tips of the pair of dies is around 1450°C, the area where the crystal grows is maintained at around 1412°C, making it possible to perform the desired crystal growth.

In order to address this problem, the present inventors attempted to increase the temperature distribution of the pair of dies at the ends in the longitudinal direction.

As one of the methods, an auxiliary heater was installed along the short side of the crucible to grow band-shaped silicon crystals.

However, when this auxiliary heater is provided, for example, the thickness is 0.3
When attempting to grow a band-shaped silicon crystal with a width of 160 mm, a problem occurred in that the silicon melt solidified as in the case without the auxiliary heater.

The reason for this is thought to be that even if an auxiliary heater is provided in the short side direction of the crucible, the temperature at the longitudinal ends of the pair of dies does not change.

Therefore, the present invention addresses the above-mentioned problems and provides a growth method that allows the width of a pair of dies to be approximately 160 mm and obtain a band-shaped silicon crystal having a width of approximately 160 m1 corresponding to the width of the pair of dies. It is.

That is, in the present invention, it is possible to obtain a band-shaped silicon crystal having a width of, for example, 160 mm by simply reciprocating a pair of dies in the longitudinal direction of the crucible without providing an auxiliary heater or the like in the direction of the short side of the crucible. It's a method.

A basic example of the present invention will be explained below with reference to the drawings.

FIG. 4 is a cross-sectional view of an example in which a wider width of the band-shaped silicon crystal can be obtained.

That is, the rotational movement of a DC motor (not shown) is controlled by a combination of a gear 49a and a spur gear 490, and a pair of dies 13a fixed to support rods 14a and 14b connected to the spur gear 49.
, 13b are reciprocated from side to side to stir the silicon melt 11 in the crucible 12 and its atmospheric gas,
The temperature at the tips of a pair of dies is made uniform, thereby making it possible to obtain wide band-shaped silicon crystals.The experimental results will be explained in detail below.

First, a pair of dies 13a. The thickness of the slit 17 of 13b is 0.3 mm, the width is 160 mm, and the reciprocating speed of the pair of dies is 2rILrIL/sec.

711!7+1/second, 12 degrees/second, the pair of dies 13a, 13b is reciprocated from one end of the quartz crucible 12 to the other in parallel with the long side direction of the main heater 16a16b, as shown in FIG. and the temperature of the pair of die tips (
When the average value) was measured, the result was as shown in Fig. 5.

In FIG. 5, if a is the reciprocating speed of the pair of dies 13a and 13b of 7/sec, b is 2/sec,
This is a case where C is 12 hours/second.

As is clear from the experimental results shown in Figure 5, when the reciprocating speed is set to 71nrIL/sec, the average temperature at the tips of the pair of dies is 1450°C ± 1°C, and when the reciprocating speed is set to 2mm /second, the average temperature of the tips of the pair of dies, especially at the ends, is 1450'C-7℃~13℃, and when the reciprocating speed is 12 degrees/second, the temperature of the tips of the pair of dies is The average temperature of the parts was 1450°C±4°C.

Therefore, the average temperature of the pair of die tips is 1450.
In order to keep the temperature within ±2°C, the speed of the reciprocating movement of the pair of dies must be around 7 m/s (5 mrIL/s to 10 rItr).
IL/sec).

Note that the temperature of the experimental data in Figure 5 is an average value, and if you consider its dispersion, the temperature fluctuation is 2 to 3 times.
C±8°C to 12°C.

Further, in experiments conducted by the present inventors, it has been found that when the reciprocating speed of the pair of dies is 5/sec to 10/sec, a temperature distribution similar to the curve shown in FIG. 5a is exhibited.

The reason why the temperature at the tips of the pair of dies changes as shown in Figure 5 a, b, and c when the speed of the reciprocating motion of the pair of dies is changed in this way is that, for example, the speed of the reciprocating motion of the pair of dies When is about 2 mrtt/sec (less than 5 mm/sec), the silicon melt 11 in the quartz crucible 12 is not stirred, and its atmospheric gas is also not stirred, making it almost the same as when the pair of dies are not moved. If the speed of the reciprocating movement of the pair of dies is about 12 mm/sec (more than 10 mm/sec), the silicon melt 11 in the quartz crucible will be shaken so much that temperature variations in the silicon melt will occur.

For this reason, the speed of the reciprocating movement of the pair of dies may be set to 5 mm/sec to 10 m/sec.

Furthermore, the present inventors set the thickness of the slit of the pair of dies 13a and 13b to 0.3 m7fL and the width to 160 mm, and grew a band-shaped silicon crystal while reciprocating the pair of dies at a speed of 7 m/sec. We conducted an experiment.

As a result, the shape of the grown band-shaped silicon crystal has a thickness of 0.
3 mrn±10 μm, width 160±0.3 mm
As a result, we were able to obtain a band-shaped silicon crystal that was almost similar in shape to the slits of a pair of dies.

Further, based on the above-mentioned experimental results, the present inventors investigated the yield, dislocation density, impurity concentration, and degree of surface roughness of band-shaped silicon crystals with respect to the speed of reciprocating motion.

The results are shown in FIG. 6, FIG. 7, FIG. 8, and FIG. 9, respectively, with a 0 mark.

As is clear from these figures, if the reciprocating motion of the pair of dies is set to 5 mm/sec to 10 mm/sec, the yield will reach over 80%, the dislocation density will be less than 100 cr/L-2, and the impurity concentration will also decrease. 1×1014/cr? It was a high-quality band-shaped 4-crystalline silico with a size of less than L, and the surface unevenness was about 10 μm.

Therefore, when used as a solar cell, the conversion efficiency is 10% on average due to the low damage rate during the element fabrication process and high quality.
reach.

As is clear from the embodiments described above, by reciprocating a pair of dies at a speed of 5 to 1 ornrn/sec as in the present invention, the amount of growth per unit time can be greatly improved and very high quality can be achieved. Yield of band-shaped silicon crystals is 80%.
You can grow more than that.

In addition, the present inventors have also discovered that the die support rod 14 of the apparatus shown in FIG.
Gas outflow pipe 100a to a and 14b.

100b is attached so that it moves together with the pair of dies 13a, 13b, and the gas outlet pipes 100a, 10
For example, gas was supplied to the silicon melt rising alternately from a pair of die tips, ie, slits, from 0b.

Note that the flow rate of Ar gas at this time was approximately 7 mm/sec.

When Ar gas is alternately supplied to the die tip in this way,
The gas in the quartz crucible 12 is stirred, the temperature at the tip of the die becomes uniform, and a band-shaped silicon crystal can be obtained with a higher yield than in the above example, that is, when no gas is supplied.

The yield results were as shown by the * mark in FIG.

The results of the dislocation density when Ar gas was supplied were as shown by the * marks in FIG. 7, the impurity concentration was as shown by the * marks in FIG. 8, and the surface irregularities were as shown by the * marks in FIG. 9.

In addition, in the growth apparatus shown in Fig. 4, the slit 17 of the main heater
If the temperature at the end of the die is controlled by changing the zero width or interval, or by changing the thickness of the main heater,
Yield, etc. improves slightly.

Similarly, if a heat shield plate is provided above the crucible 12,
The temperature distribution at the tip of the die is more uniform than in FIG. 5a, and the yield is further improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a growth apparatus for growing band-shaped silicon crystals, in which Fig. a is a plan view, Fig. B is a cross-sectional view taken along the plane A-A' in Fig. A, and Fig. 2 shows a pair of die tips. FIG. 3 is a diagram showing the temperature distribution when the width of a pair of dies is changed in the apparatus of FIG. 1, and FIG. 4 is a diagram for explaining the present invention. FIG. 5 is a plan view showing a mechanism that allows the pair of dies to reciprocate in the growth apparatus shown in FIG. 1, and FIG. 5 shows the temperature distribution when the pair of dies in FIG. Figures 6 to 9 are curve diagrams for explaining the effects of the present invention, and Figure 6 shows the yield (%) versus the reciprocating speed (mm/sec) of a pair of dies;
Figure 7 shows the dislocation density (crrL-2) versus the reciprocating speed (cm/sec) of a pair of dies, and Figure 8 shows the impurity concentration (crrt-2) versus the reciprocating speed (Cmm/sec) of a pair of dies.
3), Figure 9 shows the reciprocating speed of the pair of dies, Cmm/sec)
FIG. 10 shows the degree of unevenness of the surface of the band-shaped silicon crystal relative to the surface of the band-shaped silicon crystal. 11...Silicon melt, 12...Quartz crucible, 13a and 13b...Die, 14a and 14b...Support rod, 15...・Bolts, 16a and 16b... Main heater, 17.
...Slit provided in the main heater, 49a
...Gear, 49b...Spur gear.

Claims (1)

[Scope of Claims] 1. A silicon melt is contained in a crucible, a pair of dies having slits is disposed in the crucible, and the slits of the pair of dies are arranged such that the silicon melt rises by capillary action. The method is controlled by a pair of main heaters provided facing each other on the outside of the crucible, and the seed crystal is brought into contact with the rising silicon melt through the slits of the pair of dies under control by the main heater, and the seed crystal is pulled up. When growing a band-shaped silicon crystal regulated by the pair of dies, after bringing the seed crystal into contact with the silicon melt in the pair of dies having the slits, the main heater is A method for growing a band-shaped silicon crystal characterized by reciprocating motion at a speed of 10 plates. 2. After a pair of dies having slits are brought into contact with the silicon melt, they are reciprocated in the longitudinal direction of the main heater at a speed of 5 to 10 mm per second, and the tips of the pair of dies are heated with an inert gas. A patented method for growing band-shaped silicon crystals characterized by supplying. 3. The method for growing a band-shaped silicon crystal according to claim 2, wherein the inert gas is supplied at a flow rate of 5 to 10 minutes per second. 4. The method for growing a band-shaped silicon crystal according to claim 2, wherein the inert gas is argon. 5. Growth of a band-shaped silicon crystal according to claim 1, wherein the main heater is plate-shaped, and the plate-shaped heater is provided with slits, and the width of the slit or the interval between the slits is changed. Method. 6. The method of growing a band-shaped silicon crystal according to claim 1, wherein the main heater is plate-shaped, and the thickness of both ends of the plate-shaped heater is changed. 7. The method for growing a band-shaped silicon crystal according to claim 1, characterized in that a heat shielding plate is provided above the crucible.