JPS59121190A - Apparatus for preparation of ribbon crystal of silicon - Google Patents

Abstract

PURPOSE:To enable the stable crystal growth for a long period, by protruding a pair of structures upward from the molten silicon in a crucible at the outside of both lengthwise ends of the growing band crystal of silicon, and attaching a heating means to heat the structures. CONSTITUTION:A pair of structures 52a, b are protruded upward from the molten silicon in the crucible 51. The structures are positioned opposite to the ends of the growing ribbon crystal 56 of silicon at the outside of both lengthwise ends. The heater for heating the structures 52a, b is attached to the outer side 54a, b of the structures separately from the heater for the crucible 51 attached to the bottom 53 of the crucible 51. The lengthwise solid-liquid interface of the ribbon crystal is set upwards in concave form and the top of the solid-liquid interface is set almost parallel to the pulling direction of the crystal in the crystal growth process.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an improvement in a band-shaped silicon crystal manufacturing apparatus.

[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 is different from the ingot-shaped silicon crystal obtained by the Czochralski method, and can be used as a substrate for semiconductor solar cells in its obtained shape. Therefore, for example, the big advantage is that it is cheaper than using silicon crystals obtained by the Czochralski method as a substrate for solar cells. have

FIG. 1 is a schematic diagram showing a conventional belt-shaped silicon crystal manufacturing apparatus. 11 in the figure is a crucible, this IV) de
A silicon melt 12 is contained within the silicon melt 11 . One end of a cavity die 13 is immersed in the silicon melt 12. This die 13 defines the silicon melt 12 in a ribbon shape, and has the power to raise the melt 12 to its tip due to capillary action. When pulling a band-shaped silicon crystal, a seed crystal (not shown) is brought into contact with the melt 12 at the upper end of the die 13 and the crystal is pulled up.
is lifted from the tip of the die 13 and solidified to become a band-shaped crystal 14. That is, the solid-liquid interface 15, which is the boundary between the melt 12 and the crystal 14, is located above the tip of the die 13, which allows continuous growth of band-shaped silicon crystals.

By the way, the first drawback when attempting to pull up the entire band-shaped silicon crystal using the above-mentioned apparatus is the danger of contact between the die and the solid-liquid interface. That is, when the solid-liquid interface is lowered due to temperature fluctuations, the two come into contact and the band-shaped silicon crystal 14
is fixed to the die 13. If the solid-liquid interface is set in the opposite direction in order to avoid this drawback, another danger exists. That is, a solid-liquid interface that is too high is no longer affected by the crystal shape defining ability of the die, and normally as the band-shaped crystal is pulled up, its width narrows and eventually breaks. This is the second drawback.

The first and second drawbacks are the height above the die at the solid-liquid interface.
This is to limit the meniscus height, and the meniscus height is lower at both ends of the band-shaped silicon crystal in the longitudinal direction than at the ends orthogonal thereto. For example, when the height hD from the melt surface in the crucible 12 to the tip of the die in FIG. This must be achieved by making the meniscus height at both ends extremely low, 0 to 0.25 [:m]. For this reason, it was not possible to reliably prevent crystal sticking to the die due to the temperature fluctuations, etc., and stable crystal growth could not be performed for a long period of time.

[Purpose of the invention]

An object of the present invention is to provide an apparatus for producing a band-shaped silicon crystal that can increase the distance between the solid-liquid interface and the die at both ends in the longitudinal direction of the band-shaped silicon crystal, and can perform stable crystal growth for a long period of time. .

[Summary of the invention]

First, before giving a detailed explanation of the invention, we will touch on the theoretical consideration of the relationship between the die height and the meniscus height of an infinitely wide band-shaped silicon crystal. An infinitely wide band-shaped crystal has no ends in the horizontal and longitudinal directions, and only its planes need to be considered. Figure 2 shows the results of calculations for silicon. The area below the curve in the figure is the allowable range for the meniscus height. Obviously, the lower the die height is, the wider the allowable range for the meniscus height is, and if the die height is zero, the allowable value is approximately 0. ~8 [fall].

The same thing can be applied to the edge of a band-shaped crystal, and the lower the stiffness, the wider the allowable range of meniscus height. However, the degree of this is small, and the thickness is 0.5 [mm]
The allowable range for band-shaped silicon crystals is only θ~0.8 [mm] even when the die height is zero.

As is clear from the above, when pulling a band-shaped silicon crystal,
It can be seen that in order to expand the permissible range of the meniscus height, it is sufficient to adopt a pulling direction in which the horizontal end essentially does not exist.

Figures 3(a) and 3(b) are schematic diagrams for comparing the present invention and the prior art.Based on these diagrams, we will explain under what circumstances the ends of the band-shaped crystals will become fibrous. I will explain how it disappears. Figure 3(a) shows the prior art.
The solid-liquid interface 31 is set substantially horizontally. In order for the band-shaped silicon crystal 32 to be pulled up with the same width, the portion 34 of the surface of the melt 33, which is the gas-liquid interface, in contact with the solid-liquid interface 31 must be set parallel to the crystal pulling direction. . In order to maintain this condition, the meniscus height cannot be made too high. FIG. 3(b) shows the present invention, in which the solid-liquid interface 31' is set to be concave upward relative to the melt 33'. The end portion 35' of the band-shaped silicon crystal 32 is set to be fixed by the melt 33', and only the surface portion 36' thereof is exposed. The band-shaped silicon crystal 32' is formed into a band shape only by the temperature conditions of the melt. Under such conditions, some of the melt 33' outside the edge of the band-shaped silicon crystal does not contribute to crystal growth.

Therefore, the direction in which the surface 34' of the melt 33' at the edge of the band-shaped silicon crystal comes into contact with the band-shaped silicon crystal does not need to coincide with the upward direction of the crystal, and therefore problems regarding the meniscus height are reduced.

Next, the die shape for setting the solid-liquid interface shape of the upwardly concave shape as shown in FIG. 3(b) will be described.

Taking silicon as an example, when the die height is set to zero, the meniscus height at the face of a band-shaped silicon crystal is approximately 8 [-], as described above, whereas at the end of the band-shaped silicon crystal, the meniscus height is 0.8 [+mn]. ), it is not possible to lift the molten gold, and the shape shown in Figure 1 above cannot be lifted. When used, it is not possible to form a solid-liquid interface as shown in FIG. 3(b'). Therefore, the present inventors investigated the solid-liquid interface of the band-shaped silicon crystal 41 as shown in FIG. In order to raise the belt-shaped crystal, a configuration was considered in which a high die 43 was installed outside the end in the longitudinal direction of the band-shaped crystal. With this configuration, the melt can rise due to capillary action between the side surface 44 of the die 43 and the end portion 42 of the band-shaped silicon crystal.
It became possible to form an upwardly concave solid-liquid interface as shown in b).

The present invention focuses on these points, and 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 contained in a crucible and pulling up the seed crystal. A pair of structures are provided on the outside of both ends in the longitudinal direction of the band-shaped silicon crystal so as to face the ends and protrude upward from the silicon melt in the crucible, and a heating mechanism that heats these structures. The solid-liquid interface in the longitudinal direction of the band-shaped silicon crystal is set concave upward during crystal growth, and the uppermost end of the solid-liquid interface is set substantially parallel to the crystal pulling direction.

〔Effect of the invention〕

According to the present invention, the distance between the solid-liquid interface and the die (structure) can be increased. For this reason.

Can crystal sticking to the die due to temperature changes be reduced and thus crystal growth? Effects such as being able to perform stably for a long time and giving off a metallic odor.

Embodiment FIG. 5 is a schematic configuration diagram showing an apparatus for producing a strip-shaped silicon crystal according to an embodiment of the present invention. In the figure, reference numeral 51 denotes a rectangular carbon crucible, and structures 52a and 52b are provided at both ends of the crucible 51 so as to be higher than the gold and other peripheral parts. A heater (not shown) heats the crucible 51.

are installed on the bottom surface 53 of the crucible 51 and the outer side surfaces 54h, 54b of the structures 52a, 52b. All of these are housed in a metal container (not shown) filled with alcone gas.

There is a drive mechanism (not shown) above the metal container that pulls up the band-shaped silicon crystal, and the structure is such that the band-shaped silicon crystal can be taken out of the metal container through this drive mechanism.

With such a configuration, when a silicon melt is placed in the crucible 51 and electricity is applied in the evening, the silicon melt becomes a melt at a high temperature. The position of the melt surface is indicated by a dotted line 58 in the figure. In this state, the band-shaped seed crystal 55 is inserted into the melt in the crucible 51 while maintaining the illustrated positional relationship. In the figure, a dotted line 56 extending downward from the force λ at both ends of the seed crystal 55 indicates the direction in which the seed crystal 55 is inserted into the melt, and a dotted line 57 indicates the lower end of the seed crystal 55 that has descended. After the seed crystal 55 is adapted to the melt, it is pulled up to obtain a band-shaped silicon melt. At this time, since the solid-liquid interface is set as shown in FIG. 3(b), the total distance between the solid-liquid interface and the structures 54h and 54b can be made relatively large. Therefore, crystal pulling failures caused by temperature changes can be extremely reduced.

In fact, conventionally, pulling the band-shaped crystal failed unless the heater setting temperature was controlled within ±1 [°C], but with this device, it was possible to pull up the crystal without failure even when the heater setting temperature was controlled at ±5 [°C]. Possible.

In addition, the band-shaped silicon crystal pulled in this example was
Although the reason for this is unclear, the number of grain boundaries starting from the edge of the band-shaped silicon crystal was smaller than that of the crystal obtained with the conventional apparatus shown in FIG.

Furthermore, the number of silicon carbide grains incorporated was much smaller than in the band-shaped silicon crystal obtained with the apparatus shown in FIG.

Note that the present invention is not limited to the embodiments described above. In order to cover the edge of the band-shaped silicon crystal with the melt, a structure is installed outside the edge of the band-shaped silicon crystal as a means for raising the melt higher than the surface of the band-shaped silicon crystal, and a structure is installed on the outside of the edge of the band-shaped silicon crystal. It is only necessary to provide means for heating the structure in order to keep the melt in contact with it always in a molten state.

At this time, it is necessary to maintain the structure at a position higher than the surface solid-liquid interface of the band-shaped crystal. As long as the structure satisfies such requirements, it is not limited to the shape of the previous embodiment.

For example, as shown in FIG. 6, recesses may be provided on the inner wall surfaces of both ends to encourage the rise of the silicon melt. In this case, the solid-liquid interface further rose, and the accuracy of the heater setting temperature during the pulling operation could be widened to ±7 [°C]. Furthermore, the heating means for the structure may be high frequency heating, optical heating, ultrasonic heating, or the like in addition to resistance heating. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawings] Fig. 1 is a schematic diagram of a conventional band-shaped silicon crystal production device, and Fig. 2 is a characteristic diagram of the relationship between the meniscus height and die height of an infinitely wide band-shaped crystal. Figure 3(a),
(b) and FIG. 4 are schematic diagrams for explaining the present invention in detail, FIG. 5 is a schematic diagram showing an embodiment of the present invention, and FIG. 6 is a diagram showing a main part configuration of a modified example. be. 37, 31'... solid-liquid interface, 32, 32'...
Band-shaped silicon crystal, 33.34'... silicon melt,
41... Band-shaped silicon crystal, 42... Crystal end, 4
3... Die (structure), 44... Die side surface, 51...
... Crucible, 52a, 52b... Structure, 55...
Seed crystal.

Claims (2)

[Claims] (1) In a band-shaped silicon crystal production device that grows 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, the band-shaped silicon crystal to be grown is grown. A pair of structures are provided on the outside of both ends in the longitudinal direction so as to protrude upward from the silicon melt in the crucible so as to face the ends, and a means for heating these structures is provided. ,
A device for producing a band-shaped silicon crystal, characterized in that the solid-liquid interface in the longitudinal direction of the band-shaped silicon crystal is set concavely upward during crystal growth, and the uppermost end of the solid-liquid interface is set approximately parallel to the crystal pulling direction. . (2) The means for heating the structure heats the structure by a heating mechanism that is different from the heating mechanism that heats the silicon melt in the crucible. An apparatus for manufacturing band-shaped silicon crystals according to scope 1.