JPH0222117A - Production of polycrystalline silicon sheet - Google Patents

Abstract

PURPOSE:To efficiently obtain the title sheet of desired uniform thickness and width in high accuracy by making a molten silicon fed into a mold flow, through its own weight and vibration, into a thin-wall casting channel. CONSTITUTION:A crucible 3 set up in a furnace 1 filled with an inert atmosphere 1a is fed with a silicon matrix, which is then melted by heating with a heater 2 and fed to the pouring port 4a at the upper end of a tilted mold 4 heated beforehand with heaters 5a, 5b and vibrated through a supersonic vibration column 6a from a vibration source 6. And the molten silicon Si, through its own weight and supersonic vibration, is introduced into a thin-wall casting channel 4b of the mold 4, and a solidified silicon sheet MSi discharged through a delivery end 4c is continuously drawn in the arrow D direction using a tensilizing jig 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing 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 shown in Figure 3, in which a polycrystalline silicon sheet is produced in a crucible d in an inert gas atmosphere. A die C is immersed and stood up in molten silicon b existing in the die C, and 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. This ribbon technology uses the meniscus (surface tension) of molten silicon to form a sheet, making it difficult to obtain a polycrystalline silicon sheet with a uniform thickness.As a result, it is difficult to obtain a polycrystalline silicon sheet with a uniform thickness. However, even if one attempts to form electrodes on this, there is a defect that makes it difficult to apply a screen printing method.

In addition, since ribbon technology attempts to utilize wetting with molten silicon as described above, the die, filament,
Not only will it require many consumables such as circuit boards, but
Since carbon, SiC, etc., which have good wettability, are used, they become a source of impurities to the molten silicon.

Furthermore, when using the ribbon method, the crystal growth occurs in the direction in which the polycrystalline silicon sheet is pulled out, and the growth rate of the crystal cannot be increased too much, which should be satisfactory in terms of quality and production efficiency. It is not.

Furthermore, a so-called casting method is also carried out, but in this method, the silicon base material is heated to form a melt, which is poured into a mold according to the dimensions of the product wafer, and then the mold is This method uses a movable part to suppress the melt and solidify it, but when using this method, wafers with a predetermined shape can be obtained in one step, and desirable results in terms of mass production can be expected, but as mentioned above, 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 generation, which is considered desirable for silicon wafers for solar cells, cannot be achieved, the solar cells obtained from the wafer cannot be It also has a defect in that the photoelectric conversion efficiency is extremely poor at 2 to 3%.

Also known is a manufacturing method called the spin method as shown in FIG. A cavity h is formed in the casting mold g formed by e and f, and these are placed in an inert gas atmosphere A, and an injection port i is opened at the axial center position of the turntable d of the cavity h.
Then, 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 rolling crucible 1 and a funnel l heated by the heater are placed above the casting mold g, and the silicon base material put into the rolling crucible l is transferred to the heater k. After melting, the silicon is rotated about the rotation axis n, so that the molten silicon flows through the funnel l 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 lot of power, but an even more serious problem is that centrifugal force causes the molten silicon to expand.
From this point of view as well, it takes a considerable amount of time, making it difficult to increase the manufacturing speed beyond a certain level.

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

This method uses a crucible made of quartz etc. as shown in the figure.
A silicon base material is put in the inside, and it is melted (1450°C) by the operation of the heater p in an inert atmosphere A made of an inert gas such as argon or vacuum. Pressure q (0.01~0.1.
kg/crn”) on the top surface of the molten silicon, and heated to 1300°C in advance by heaters rl, r2, r3.
The molten silicon is heated to a temperature of ~1420 DEG C. and is continuously supplied from the injection port s2 in the casting path S1 of the mold nozzle S.

As a result, the molten silicon Si is solidified in the mold nozzle S to become a solidified silicon sheet MSi, but its tip is drawn out of the inert atmosphere A in advance, and its end is fitted into the tensioning jig t. This tensioning jig t is continuously pulled out in the direction of arrow B, which is the longitudinal direction of the mold nozzle S, and thereby, for example, the thickness is 0.
．． A polycrystalline silicon sheet with a thickness of 5 m and a width of 25 layers is 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, in the above method, the molten silicon S
There is a problem in that a high degree of skill is required to match the pressure q applied to i and the drawing speed by the tensioning jig t.

(Problems to be Solved by the Invention) The present invention retains the various advantages of the above-mentioned canting method, and also solves problems such as difficulties in adjusting the pressure applied to molten silicon and manufacturing failures caused by unskilled workers. In order to solve the problem of frequent occurrence, a pulling process is performed using a pulling jig, but the molten silicon does not flow into the mold using pressure, but instead uses gravity of the molten silicon.

By utilizing the vibration imparted to this as an energy source for inflow, the pulling speed by the tension jig can be increased.
The purpose is to be able to have a large tolerance range, so that it can be manufactured easily even by beginners without requiring any skill.

(Means for Solving the Problems) In order to achieve the above object, the present invention is arranged in an inert atmosphere, in which a thin-walled casting channel is penetrated 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 formed.
It is an object of the present invention to provide a method for producing a polycrystalline silicon sheet, which is characterized in that it is continuously drawn out using a desired tensioning jig.

(Function) According to the pending decision, the molten silicon supplied to the injection port at the upper end of the mold flows down into the mold due to the action of gravity due to the inclined arrangement of the mold and vibrations from the vibration source, causing the molten silicon to flow into the mold. The 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 pulling speed by the tensioning jig in this case is extremely fast. As long as the molten silicon is solidified, the solidified silicon sheet can be continuously drawn out without being interrupted, and polycrystalline silicon sheets can be smoothly produced as products even if there is a slight deviation in the drawing speed. can continue to do so.

(Example) To describe the present invention in detail by means of an illustrated example, FIGS. 1 and 2 show a manufacturing apparatus that can be used to carry out the method,
This is also an inert atmosphere such as argon gas or vacuum 1a
The furnace body l has a crucible 3 heated by a heater 2.
is disposed, and a mold 4 in the same atmosphere la is disposed directly below the lower end supply port 3a, and this mold 4 has the following:
The thin-walled casting channel 4b communicating with the large-opening upper end injection port 4a is arranged in an inclined state as shown in the figure, that is, not in a horizontal state, but in a rising state. This thin-walled casting path 4b includes a vertical state, and is formed to have a size commensurate with the polycrystalline silicon sheet to be obtained.

Here, the inclination angle of the mold 4 is desirably 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, and the thin casting channel 4b is formed according to the thickness and medium length of the polycrystalline silicon to be obtained, and is 4C in the figure. is located at the lower end of the mold 4 and the opening of the thin-walled casting channel 4b is inserted into the drawing end opening 5a, 5.
b indicates heaters disposed above and below the mold 4, respectively.

Furthermore, the mold 4 is configured to receive vibrations from a vibration source 6, which plays an important role in carrying out the method, and the direction of 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 vibrator is transmitted to the mold 4 by an ultrasonic vibration column 6a. In the figure, 7 indicates the gate bubble of the furnace body 1, from which the polycrystalline silicon sheet, which is the 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 manufacturing apparatus, crucible 3
The silicon base material of 14 is melted by heater 2, and thus 14
Molten silicon Si at 50° C. is supplied from the lower end supply port 3 a to the upper end injection port 4 a of the mold 4 .

At this time, the mold 4 is first heated to 1450° C. by the heaters 5a and 5b, and the vibration source 8 is operated to transmit its power to the mold 4 via the ultrasonic vibration column 8a in the illustrated example. I'll keep it.

As a result, the molten silicon Si injected into the upper end injection port 4a enters into the thin casting channel 4b, which is a narrow gap, due to its own weight and the above-mentioned ultrasonic direct motion because the mold 4 is tilted. Then, this flows out from the drawer end 4C of the mold 4 (for about 2 to 3 seconds), and is received by the tension jig A8.

Here, set the heating temperature of mold 4 to 1400°C to 1300°C.
By controlling to
A part of the drawer end 4C side is solidified to form a solidified silicone sheet MSi, and then the tensioning jig 8
is continuously pulled out in the direction of the arrow.

In this way, polycrystalline silicon sheets, which are products, can be obtained continuously from the drawer end 4C by ensuring the supply of molten silicon Si, and the frequency of the ultrasonic waves actually used here is 19 .15KHz, power is 454, and the thin casting path 4b of the mold 4 has a thickness of 0.
．． When using a polycrystalline silicon sheet with a thickness of 0.5 m and a medium length of 25 m, the pulling speed using the tensioning jig 8 was set at 3 to 5 m/sec.
I was able to withdraw it.

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 Si3N4 and 5i.
It was used with a mixture coating of Oz.

(Effect of the invention) Since the present invention can be implemented as described above,
Products with a desired uniform thickness and width can be produced freely and efficiently with high precision. Therefore, device processing is easy, yields are improved, and high-quality products free of impurities can be provided at low prices. Instead, the molten silicon supplied into the mold was made to flow into the thin casting channel due to its own weight and the vibrations applied, so it is similar to when molten silicon is forced into the mold by external pressure. No skill is required to adjust the pressure and the drawing speed of the tensioning jig, and manufacturing conditions can be easily controlled and 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. la...Inert atmosphere 40...Fist/mold 4a...Top end injection port 4b...Thin casting path 6...Vibration source 8... ...Tension jig Si...Melted silicon MSi...Solidified silicon sheet first! Figure Figure Figure

Claims (1)

[Claims] In an inert atmosphere, a thin-walled casting channel is penetrated and arranged at a predetermined slope including vertical,
The molten silicon is supplied to the injection port at the upper end of the heated mold, and the molten silicon is supplied to the mold by applying vibrations from a vibration source such as mechanical vibration generating means or ultrasonic vibration generating means to the mold. Due to the gravity and the above-mentioned vibrations, the molten silicon flows down from the upper end injection port into the thin-walled casting path, and the silicon sheet, in which the molten silicon is solidified, is continuously pulled out by a desired tensioning jig. A method for producing a polycrystalline silicon sheet, characterized by: