JPH0479969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to a method for producing polycrystalline silicon sheets used in solar cells and other photoelectric conversion elements.

<Prior art> Various methods have already been implemented for producing polycrystalline silicon sheets, and one of them, the ribbon method, is a method for manufacturing polycrystalline silicon sheets in a crucible a in an inert gas atmosphere, as shown in Figure 3. die c to molten silicon b existing in
In this ribbon technology, the molten silicon b drawn out from the upper end c' of the die c is cooled and solidified in an inert gas atmosphere outside the die c. Because the sheet is formed using the meniscus (surface tension) of polycrystalline silicon, it is difficult to obtain a polycrystalline silicon sheet with a uniform thickness.As a result, when trying to use it as a solar cell device, it is difficult to form electrodes on it. However, there are deficiencies that make it difficult to apply the screen printing method.

In addition, since ribbon technology attempts to utilize wetting with molten silicon as described above, the die,
Not only will many consumables such as filaments and substrates be required, but carbon, SiC, etc.
etc., this becomes a source of impurities to the molten silicon.

Furthermore, when using the ribbon method, the crystal growth is in the drawing direction of the polycrystalline silicon sheet, and the growth rate of the crystal cannot be increased too much, which is satisfactory from the standpoint of quality and production efficiency. I'm not used to it.

Furthermore, a so-called casting method (casting method) is also carried out, but in this method, the silicon base material is heated to form a melt, this is poured into a mold according to the dimensions of the product wafer, and then the mold is The movable part of the molten liquid is press-molded and solidified, but when using this method, wafers of a predetermined shape can be obtained at once, and desirable results can be expected in terms of mass production. The melt will be pressed down from all sides.

For this reason, in this method, the upper and lower surfaces and side surfaces of the mold suppress the growth of silicon crystals (grains) when the melt solidifies, and the areas near the parts of the solidified product that contact the above-mentioned surfaces have very fine crystals. Because large crystal grains cannot be obtained and the requirement for large crystal grain formation, which is considered desirable for silicon wafers for solar cells, etc., cannot be achieved, solar cells obtained using such wafers cannot be used. However, the photoelectric conversion efficiency of the photoelectric conversion efficiency is extremely poor at 2 to 3%.

A manufacturing method called a spin method as shown in FIG. 4 is also known, and in this method, the turntable d
By placing the lower plate e on top and the upper plate f on top, a cavity h is formed in the casting mold g formed by both plates e and f, and these are placed in an inert gas atmosphere A. From the injection port i which is placed in the interior and opened at the axial center position of the turntable d of the cavity h,
Molten silicon j is injected and filled into the cavity h by the centrifugal force generated by the rotation of the turntable d.

In addition, in order to obtain the above-mentioned molten silicon j, a heater k, a rolling crucible l heated by the heater k, and a funnel m are arranged above the casting mold g, and the silicon base material put into the rolling crucible l is heated by the heater k. After being melted by k, the molten silicon j is rotated about the rotation axis n, so that the molten silicon j flows through the funnel m from the injection port i as described above.

Therefore, when using the spin method, not only is a rotation mechanism for the turntable d and a fairly complicated drive mechanism for placing and removing the casting mold g on the turntable d required, but also Since it is necessary to secure the space necessary for the rotation of the turntable d and to provide various other members for supplying the molten silicon j, the inert gas atmosphere A must also be wide, and as a result, the consumption by the heater and other sources is Not only does it require a large amount of electricity, but an even more serious problem is that centrifugal force is used to expand the molten silicon, which also requires a considerable amount of time, making it difficult to increase the production speed beyond a certain level. The problem is that it becomes difficult.

Therefore, the applicant has already proposed a manufacturing method based on a casting method using a manufacturing apparatus as shown in FIG.

In this method, as shown in the figure, a silicon base material is placed in a crucible o made of quartz or the like, and placed in an inert atmosphere A made of an inert gas such as argon or vacuum. The molten silicon is melted (1450°C) during operation, and pressure q (0.01 to 0.1 Kg/cm ² ) is applied to the molten silicon by an inert gas such as argon.
In addition to _the upper surface _{of the}
The molten silicon is continuously supplied from an injection port S2 in a casting path S1 of a mold nozzle S heated to a temperature of 1300°C to 1420°C.

As a result, the molten silicon Si is solidified in the mold nozzle S, resulting in a solidified silicone sheet.
The tip of the MSi is drawn out of the inert atmosphere A in advance, and its end is fitted into a tensioning jig t, which is directed in the direction of arrow B, which is the longitudinal direction of the mold nozzle S. It is drawn out continuously, and by this, for example, 0.5 mm thick and 25 mm wide.
mm polycrystalline silicon sheets are obtained.

The above manufacturing method certainly makes it possible to mass-produce polycrystalline silicon sheets of uniform thickness without worrying about contamination by impurities, and it also makes it possible to easily obtain polycrystalline silicon sheets of various thickness dimensions, and also in the device processing process.
There is no need for a process to make the thickness uniform, and there is an advantage that the yield can be improved.

However, the method described above actually has a drawback in that it requires a high degree of skill to match the pressure q applied to the molten silicon Si and the drawing speed by the tensioning jig t.

<<Problems to be Solved by the Invention>> The present invention maintains the various advantages of the above-mentioned canting method, and also avoids problems such as difficulty in adjusting the pressure applied to molten silicon and manufacturing mistakes made by unskilled workers. In order to solve this problem, a pulling process using a tensioning jig is performed, but instead of using pressure to flow the molten silicon into the mold, it is possible to use the gravity of the molten silicon to flow into the mold.
By utilizing the vibration imparted to this as an energy source for inflow, the pulling speed of the tensioning jig can be increased within a wide allowable range. The purpose is to make it easier to manufacture.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides a method in which a thin-walled casting channel is penetrated in an inert atmosphere and arranged in a predetermined inclined state including vertical direction. Molten silicon is supplied to the upper end injection port of the heated mold, and vibrations from a vibration source such as mechanical vibration generation means, ultrasonic vibration generation means, etc. are applied to the mold. The silicone is caused to flow down from the upper end injection port into the thin-walled casting channel by its gravity and the above-mentioned vibration, and the silicon sheet in which the molten silicon is solidified in the thin-walled casting channel is continuously pulled out using a desired tensioning jig. It is an object of the present invention to provide a method for manufacturing a polycrystalline silicon sheet characterized by the following.

<<Operation>> According to this method, the molten silicon supplied to the injection port at the upper end of the mold flows downward into the mold due to the action of gravity due to the inclined arrangement of the mold and the vibration caused by the vibration source. The molten silicon solidifies in the mold to become a solidified silicone sheet, but this is pulled out of the inert atmosphere by a tensioning jig, so the drawing speed by the tensioning jig in this case is As long as it is not lost too quickly, the solidified silicon sheet made of molten silicon can be continuously pulled out without any trace, and even if there is a slight deviation in the drawing speed, the polycrystalline silicon sheet as a product can be smoothly drawn out. production can continue.

《Example》 The present invention will be described in detail by means of an illustrated example. Figures 1 and 2 show manufacturing equipment that can be used to carry out the method, which also uses argon gas or vacuum. A crucible 3 heated by a heater 2 is disposed in the furnace body 1 having an active atmosphere 1a, and a mold 4 in the same atmosphere 1a is disposed directly below the lower end supply port 3a. 4, the thin-walled casting channel 4b communicating with the large-opening upper end injection port 4a is arranged in an inclined state, that is, not in a horizontal state as shown in the figure, but in a rising state. The term "inclined" includes a vertical state, and the thin casting path 4b is formed to have a size commensurate with the polycrystalline silicon sheet to be obtained.

Here, the inclination angle of the mold 4 is preferably about 15° to 45°, but it may reach 90° as described above. In the illustrated example, the upper end injection port 4a is located at the center of the mold 4 in the width direction. It is formed in a cylindrical shape and is opened directly below the lower end supply port 4a,
The thin casting channel 4b is formed according to the thickness and width of the polycrystalline silicon to be obtained, and is indicated by 4 in the figure.
Reference character c indicates the outlet end of the thin casting channel 4b which is open at the lower end of the mold 4, and 5a and 5b indicate heaters disposed above and below the mold 4, respectively.

Furthermore, the mold 4 is configured to be subjected to vibration by a vibration source 6 which plays an important role in carrying out the method, and the direction of the vibration is preferably in the longitudinal direction of the mold 4.

The vibration source 6 may be a mechanical vibration generating means or an ultrasonic vibration generating means. In the illustrated example, an ultrasonic vibrator is used, and the vibration generated by the ultrasonic vibration column 6a is Mold 4
7 in the figure.
indicates a gate bubble of the furnace body 1, from which a polycrystalline silicon sheet, which is a product, is pulled out to the outside by a pulling jig 8 as described later.

In order to carry out the present invention using the above-mentioned manufacturing apparatus, the silicon base material in the crucible 3 is melted by the heater 2, and the molten silicon Si at 1450° C. is transferred from the lower end supply port 3a to the upper end injection port 4a of the mold 4. supplied to

At this time, first, the mold 4 is heated to 1450° C. by the heaters 5a and 5b, and the vibration source 6 is operated to apply the ultrasonic vibration column 6 to the mold 4 in the illustrated example.
The power is transmitted through a.

As the mold 4 is tilted, the molten silicon Si injected into the upper end injection port 4a flows into the thin casting channel 4b, which is a narrow gap, by its own weight and the above-mentioned ultrasonic vibration. Go in and
Furthermore, since this flows out from the pull-out end 4c of the mold 4 (during about 2 to 3 seconds), it is received by the tensioning jig 8.

Here, set the heating temperature of mold 4 to 1400℃~1300℃
By controlling this, the molten silicon in the tension jig 8 is solidified, and the molten silicon Si in the mold 4 is also solidified at a part of the drawing end 4c side, thereby forming a solidified silicon sheet MSi. , and then the tensioning jig 8 is continuously pulled out in the direction of arrow D.

In this way, polycrystalline silicon sheets, which are products, can be continuously obtained from the drawer end 4c by ensuring the supply of molten silicon Si.
The frequency of the above ultrasound actually used here is
19.15KHz, power was 450W, and the thin casting channel 4b of the mold 4 had a thickness of 0.5 mm and a width of 25 mm, and the drawing speed with the tension jig 8 was 3 to 5 mm/sec. A polycrystalline silicon sheet with a length of 25 mm could be pulled out approximately 250 mm.

Of course, at this time, the drawing speed of the tensioning jig 8 can be further increased by changing the power and frequency of the ultrasonic waves, the inclination angle of the mold 4, and the temperature of the mold 4.

The material of the mold 4 may be silicon nitride coating on the surface of the carbon body, or
A mixture coating of Si ₃ N ₄ and SiO ₂ was applied and used.

<<Effects of the Invention>> Since the present invention can be carried out as described above, products with desired uniform thickness and width can be freely and efficiently produced with high precision, and device processing is therefore easy. This not only improves the yield and makes it possible to provide high-quality products free of impurities at a low price, but also allows the molten silicon supplied into the mold to flow into the thin-walled casting channel due to its own weight and the vibrations applied. Since molten silicon is forcibly pushed in by external pressure, no skill is required to adjust the pressure and the pull-out speed of the tensioning jig, making it easy to control manufacturing conditions. As a result, productivity can be improved.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional front view showing a polycrystalline silicon sheet manufacturing apparatus that can carry out the method according to the present invention, FIG. 2 is a vertical cross-sectional side view showing the main parts of the same apparatus, and FIG. 3 is a conventional Fig. 4 is a vertical cross-sectional front view showing an apparatus for manufacturing polycrystalline silicon sheets using the conventional ribbon method; FIG. 2 is a longitudinal sectional front view showing an apparatus for manufacturing the same sheet according to the method. 1a...Inert atmosphere, 4...Mold, 4a...Upper end injection port, 4b...Thin casting path, 6...Vibration source, 8...
Tension jig, Si...molten silicon, MSi...solidified silicon sheet.

Claims (1)

[Claims] 1. Molten silicon is supplied to the upper end injection port of the mold, which is in an inert atmosphere and is heated and has a thin casting channel penetrated through it and arranged at a predetermined slope including vertically. At the same time,
By applying vibration from a vibration source such as a mechanical vibration generating means or an ultrasonic vibration generating means to this mold, the molten silicon is caused to flow down from the upper end injection port to the thin casting channel due to the gravity and the above vibration. A method for manufacturing a polycrystalline silicon sheet, characterized in that the silicon sheet in which the molten silicon is solidified in the thin-walled casting channel is continuously pulled out using a desired tensioning jig.