JPS6111913B2 - - 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]

Recently, a method for growing band-shaped silicon crystals has been attracting attention as one of the crystal growth techniques. Since this band-shaped silicon crystal is in the form of a thin plate, it can be used as a solar cell substrate in its obtained shape. Because there is no large material loss that occurs when cutting and processing ingot-shaped silicon crystals obtained by the Czyochralski method into wafer shapes, and the processing cost is extremely low, it is attracting attention as an inexpensive silicon crystal substrate. There is.

Band-shaped silicon crystals are produced using the conventional EFG method (Edge-
It is manufactured by a method using a capillary die with a slit, as typified by the defined film-fed growth method. However, when producing band-shaped silicon crystals by this method, there were the following major drawbacks. That is, the distance from the free liquid surface of the silicon melt in which the lower part of the capillary die is immersed to the upper end of the capillary die is, for example, 2 [cm], and a band-shaped silicon crystal with a thickness of 0.5 [cm] is manufactured. In this case, the height of the meniscus (silicon melt between the top of the capillary die and the solid-liquid interface at the bottom of the band-shaped silicon crystal) is at most 0.4 mm at the center of the crystal, and at most 0.25 mm at both ends of the crystal.
[cm] is extremely low. As the temperature decreases, the height of the meniscus also decreases, but as mentioned above, the original meniscus height is low, so the temperature drop is only 1.
If it occurs even at [℃], the crystal end and the capillary die will stick together. On the other hand, if the temperature increases even slightly, the width of the crystal becomes narrower, making it difficult to achieve stable crystal growth over a long period of time.

The above-mentioned drawback is due to the low height of the meniscus, and in order to solve this drawback, the present inventors devised a belt-shaped silicon crystal manufacturing apparatus having a structure as shown in FIG. 1 in FIG. 1 is a crucible, and a silicon melt 2 is accommodated in this crucible 1. 3a and 3b are crucible 1
These are a pair of structures that protrude upward from the silicon melt 2 inside the crucible 1, and are attached to the crucible 1.
Hereinafter, these structures will be referred to as crystal growth dies. Although not shown in the figure, a heater for heating the silicon melt 2 is provided at the bottom of the crucible 1, and a heater for heating the silicon melt 2 is provided at the side of the dies 3a and 3b.
A heater is provided to heat each. These heaters are used to maintain a temperature at which silicon is melted in the crucible and dies 3a, 3b.

A conceptual diagram of the production of band-shaped silicon crystals using this apparatus is shown in FIG. A seed crystal 4 is blended into the silicon melt 2 between a pair of dies 3a and 3b, and when this seed crystal 4 is pulled up in the direction of arrow A in the figure, the die 3a,
A band-shaped silicon crystal 5 having a width approximately defined by an interval of 3b is obtained. At this time, it should be noted that the height H of the meniscus generated on the free liquid surface of the silicon melt 2 is as high as approximately 8 mm at the center of the crystal, and the solid-liquid interface 6 is concave, and the die 3a, The width W of the meniscus generated between 3b and the silicon crystal 5 is approximately 1
It is large [mm]. For this reason, ±5 [℃]
Even if a temperature change of
It does not stick to b, and crystal thinning is also less likely to occur, allowing stable crystal growth to continue.

The thickness of the band-shaped silicon crystal produced with the above apparatus is mainly related to temperature and pulling speed, and the lower the heating temperature of crucible 1 or the slower the pulling speed, the thicker the crystal becomes. The results shown are obtained. Figure 3 shows the crucible set temperature of 2.
Approximate width grown by changing dot and pulling speeds
It shows the thickness of a crystal of 100 [cm]. In addition, the circle mark in the figure indicates when the crucible temperature is low (1445℃).
● indicates the case where the crucible temperature is high (1460℃).

Note that this temperature is the value of the output of a thermocouple installed outside the crucible, and is not the temperature of the silicon melt. From this figure, for example, in order to make the crystal thickness 0.5 [mm], if the crucible temperature setting is high, the pulling speed should be 14 mm.
[m/min], and if the crucible set temperature is low, it is understood that the pulling speed should be set to 18 [m/min]. It is also clear that in order to pull a crystal of a certain thickness at high speed, it is necessary to lower the heating temperature. This is due to the following reasons. In other words, the speed v and temperature for pulling a crystal with a certain width and thickness (more specifically, the temperature gradients dT _l /dZ and dT _s /dZ on the melt side and crystal side, respectively)
Between v=1/L(-K _s dT _s /dZ+K _e dT _l /dZ
)...(1) There is a relationship. Here, L is the latent heat of crystallization, K _s ,
K _l is the thermal conductivity of the crystal and melt, respectively, and Z
dT _s /dZ and dT _l /dZ usually take negative values. Since the temperature at the solid-liquid interface is constant at the melting point of silicon (approximately 1420℃), lowering the crucible heating temperature will reduce the temperature gradient on the melt side in the above equation.
This means that the absolute value |dT _l /dZ| of dT _l /dZ is made smaller, and the speed v becomes larger.

However, the crucible 1 as shown in FIG.
When crystal growth is performed using an apparatus in which the dies 3a and 3b are integrated, if the heating temperature of the crucible 1 is lowered to a certain level or more, the silicon melt 2 will grow into the crucible 1.
The crystals begin to solidify from the wall of the dies 3a, 3.
It sticks to b and growth is interrupted. To prevent this, if the heating of the dies 3a and 3b is increased,
Solidification near b disappears and growth continues, but since the heating of dies 3a and 3b was increased, crucible 1
The temperature of the silicon melt 2 inside increases, which impedes high-speed pulling. Due to these points, a pulling rate higher than that shown in FIG. 3 could not be obtained. This problem also occurs when the dies 3a and 3b are placed in the middle of the crucible 1 as shown in FIG. That is, even if the temperature of the crucible 1 is lowered and solidification progresses from the wall surface of the crucible 1, crystal growth can continue, but the dies 3a, 3
Since b is immersed in silicon melt 2,
The temperature of the silicon melt in the crucible 1 cannot be lowered as desired due to the temperature of the dies 3a and 3b, and on the other hand, if the temperature of the dies 3a and 3b is lowered, the crystal and the dies 3a and 3b will solidify during growth. After all, it is not possible to produce crystals at a speed higher than the above-mentioned pulling speed.

[Purpose of the invention]

An object of the present invention is to increase the distance between the solid-liquid interface at both ends in the width direction of a band-shaped silicon crystal and a die for crystal growth, and to alleviate disturbance in the silicon melt temperature caused by the die. It is an object of the present invention to provide a band-shaped silicon crystal manufacturing apparatus capable of increasing the pulling speed of silicon crystal and stabilizing crystal growth for a long period of time.

[Summary of the invention]

The gist of the present invention is to provide a crucible and a crystal growth die separated from each other to prevent the die from increasing the temperature of the silicon melt in the crucible.

That is, the present invention provides an apparatus for producing band-shaped silicon crystals that grows band-shaped silicon crystals by bringing a seed crystal into contact with a silicon melt housed in a crucible and pulling up the seed crystal. A die for crystal growth is provided above the crucible so as to face the ends on the outside of both ends in the direction, and a heating mechanism for heating these structures is provided, and the die is not brought into contact with the crucible. It is arranged above the free horizontal liquid level of the silicon melt in the crucible.

〔Effect of the invention〕

According to the present invention, mutual interference between the temperatures of the crucible and the die is reduced, and disturbances in the silicon melt temperature due to the die temperature are alleviated, so the temperature of the silicon melt can be set low. Therefore, the pulling speed of the band-shaped silicon crystal can be significantly increased. Furthermore, since the distance between the solid-liquid interface and the die can be increased, crystal growth can be performed stably for a long period of time.

[Embodiments of the invention]

FIG. 5 is a schematic configuration diagram showing a belt-shaped silicon crystal manufacturing apparatus according to an embodiment of the present invention. 11 in the diagram
is a crucible made of graphite, and this crucible 1
1 contains a silicon melt 12. Above the crucible 11 are crystal growth dies 13a and 13.
b are installed respectively. Dies 13a, 13
b is a fixed part 14 provided outside the crucible 11;
a and 14b, respectively, and their lower surfaces are arranged above the free horizontal liquid level of the silicon melt 12. Furthermore, two dies 13a, 13b
The inner spacing is 100 [mm]. Further, a heater (not shown) for heating the crucible 11 is provided at the bottom of the bottom of the crucible 11, and in addition to this, a die 13 is provided.
Heater 15 that independently heats a and 13b
a, 15b are provided on the fixing portions 14a, 14b. It goes without saying that each of the heaters described above is configured to be able to heat the crucibles 11, 13a, and 13b to a temperature higher than the melting point of silicon. In this embodiment, silicon carbide was used as the material for these heaters. Note that 16 in the figure indicates heaters 15a and 15b.
This is a heat shield to prevent the crucible temperature from being disturbed by heat radiation from the sides of the crucible. 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. part (not shown)
is expected to be installed.

6a to 6c are conceptual diagrams when growing a band-shaped silicon crystal using the apparatus of this embodiment. Figure 6a
is the state before crystal growth, and the dies 13a and 13b
The lower ends of each of the silicon melts 12 are positioned approximately 3 to 4 mm above the free horizontal liquid level of the silicon melt 12 in the crucible 11. Next, as shown in FIG. 6b, from above the crucible 11, the dies 13a and 13b are
Lower the narrow seed crystals 17 that are slightly wider than the interval between
It is brought into contact with the silicon melt 12 in the crucible 11.
When seeded in this way, the silicon melt 12 near the seed crystal 17 is lifted, a meniscus 18 shown by hatching in the figure is formed, and the solid-liquid interface 19
is concave. The height of the meniscus 18 from the free liquid surface of the silicon melt 12 to the lower end of the seed crystal 17 is approximately 8 [mm], and the width of the meniscus 18 between the dies 13a, 13b and the side of the seed crystal 17 is approximately 1 [mm]. It was hot. Next, when the seed crystal 17 is pulled upward, the sixth
As shown in FIG. c, a band-shaped silicon crystal 20 grew under the seed crystal 17. At this time, the meniscus 18
maintains the same shape as the seeded state.

Figure 7 shows the results of crystal growth, in which the thickness of a band-shaped silicon crystal with a width of about 100 mm was measured using two different crucible temperature settings and different pulling speeds as in Figure 3 above. It is something. In addition, in the figure, the ○ mark indicates a case where the crucible temperature is low (1435°C), and the ● mark indicates a case where the crucible temperature is high (1450°C). Note that this temperature is not the temperature of the silicon melt and cannot be directly compared with the temperature in FIG. 3. From this figure, for example, to obtain a crystal with a thickness of 0.5 [mm],
If the crucible temperature setting is high, the pulling speed is 30 [mm/
At low temperatures, crystal growth was possible at a speed of 40 mm/min, which was about twice as fast as the conventional example shown in FIG. This is because the temperature of the dies 13a and 13b is lower than that of the silicon melt due to the device of this embodiment.
This is because the crucible temperature could be lowered and the temperature gradient in the melt could be made smaller because it did not affect the temperature in step 2.

In this way, according to this apparatus, the crystal growth die 1
3a and 13b are provided above the crucible without contacting the crucible 11, and the lower ends of the dies 13a and 13b are arranged above the free horizontal liquid surface of the silicon melt 12 in the crucible 11, thereby controlling the temperature of the crucible 11. Even if it is low, sufficiently stable crystal growth can be achieved. Therefore, the pulling speed of the band-shaped silicon crystal 20 can be significantly increased, and the manufacturing cost of the band-shaped silicon crystal can be reduced. Furthermore, since the distance between the solid-liquid interface and the dies 13a, 13b can be increased, it goes without saying that stable crystal growth can be performed for a long period of time.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof.

In the above example, since the relative positions of the crucible and the die are fixed, as crystal growth continues and the free liquid level of the silicon melt decreases, the distance between the free liquid level of the silicon melt and the bottom end of the die increases. . When the distance between the silicon melt surface and the bottom end of the die exceeds 7 to 8 mm, the meniscus moves away from the die, crystal growth takes on a pattern similar to the Czyochralski method, and band-shaped silicon crystals can no longer be obtained. To prevent this, it may be possible to increase the width of the crucible and reduce the ratio of decrease in silicon melt to the amount of grown crystals, but this method is not preferable because it increases the size of the apparatus itself. For this reason, the present inventors manufactured the following apparatus and performed crystal growth. That is, during crystal growth, the positions of the crucible and the crucible heater are continuously raised by an amount corresponding to the lowering of the silicon melt surface. Using this device, we succeeded in growing band-shaped silicon crystals continuously for a longer period of time. In the above example, the crucible and the crucible heater are movable, but the same effect can be obtained by moving the die and the die heater instead.

Moreover, the materials of the crucible, heater, etc. are not limited to those in the embodiments, and can be changed as appropriate according to specifications. Furthermore, the die or crucible may be heated using high frequency waves, light, or ultrasonic waves instead of the resistance heater. Further, the interval between the dies may be determined as appropriate depending on the width of the band-shaped silicon crystal to be grown.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a conventional belt-shaped silicon crystal production device, Fig. 2 is a style diagram showing the state of crystal production using this device, and Fig. 3 is a diagram for explaining the problems of the above device. FIG. 4 is a schematic diagram showing the relationship between pulling speed and crystal thickness, FIG. 4 is a schematic diagram showing another conventional device, and FIG. 5 is a schematic diagram showing a belt-shaped silicon crystal manufacturing device according to an embodiment of the present invention. , Figures 6a to 6c are schematic diagrams showing the state of crystal production using the apparatus of the above embodiment, and Figure 7 is for explaining the effects of the apparatus of the above embodiment, and shows the relationship between the pulling speed and the crystal thickness. It is a characteristic diagram. 11... Crucible, 12... Silicon melt, 13
a, 13b...Crystal growth die, 14a, 14b
...Fixed part, 15a, 15b...Heater, 16...
... Heat shield plate, 17 ... Seed crystal, 18 ... Meniscus, 19 ... Solid-liquid interface, 20 ... Band-shaped silicon crystal.

Claims (1)

[Scope of Claims] 1. In a belt-shaped silicon crystal manufacturing apparatus that grows a belt-shaped silicon crystal by bringing a seed crystal into contact with a silicon melt contained in a crucible and pulling up the seed crystal, a belt-shaped silicon crystal to be grown is used. a pair of structures provided above the crucible to face the ends on the outside of both widthwise ends of the crucible;
means for heating these structures, and the structures are arranged above the free horizontal liquid level of the silicon melt in the crucible without contacting the crucible. Band-shaped silicon crystal production equipment. 2. Claim 1, wherein the means for heating the structure heats the structure using a heating mechanism that is different from the heating mechanism that heats the silicon melt in the crucible. The band-shaped silicon crystal manufacturing apparatus described above.