JPH0479970B2 - - 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, as shown in Fig. 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., there is a defect that 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%.

Therefore, in order to solve the above-mentioned difficulties, the applicant has already utilized the advantages of the above-mentioned casting method to supply molten silicon to the mold nozzle. By continuously pulling out this solidified silicone sheet,
It enables mass production of polycrystalline silicon sheets with a uniform thickness without worrying about contamination by impurities, and it also makes it possible to easily obtain sheets of various thicknesses and dimensions, making it possible to uniformize the thickness even in the device processing process. We proposed a method that would eliminate the need for such processes and improve yields.

This is carried out using a manufacturing apparatus as shown in Fig. 5, in which 1 is a furnace body having an inert atmosphere 1a made of inert gas such as argon or vacuum;
This includes a silicon melting tube 3 heated by heaters 2a and 2b, and a mold nozzle 5 heated by a heater 4. After being melted by the heater 2a, the molten silicon Si is sequentially passed through the supply port 3a of the silicon melting tube 3 and the injection port 5a of the mold nozzle 5 under the pressure p of an inert gas or the like. It is designed to be fed into the mold nozzle 5.

Here, the mold nozzle 5 consists of a nozzle lower plate 5b and a nozzle upper cover plate 5c, and a predetermined groove 5d is formed on the upper surface of the nozzle lower plate 5b.
By fixing both plates 5b and 5c in a stacked state using screws (not shown), a casting path 6 of a predetermined thickness and width is formed. There is.

In order to carry out the above method using this manufacturing apparatus, a silicon base material is placed in a silicon melting tube 3 made of quartz or the like, and the silicon base material is placed in a heater 2a.
The molten silicon Si is melted ( ^at 1450°C) by operation of
The molten silicon Si is continuously supplied from the injection port 5a into the mold nozzle 5 heated to a temperature of 1300°C to 1420°C.

As a result, the molten silicon Si is solidified in the mold nozzle 5, resulting in a solidified silicone sheet.
The tip of the MSi is drawn out of the furnace body 1 in advance, and its terminal end is fitted into the above-mentioned tensioning jig 7, and this tensioning jig 7 is moved toward the arrow A in the longitudinal direction of the mold nozzle 5. It is drawn out continuously.

Here, the depth of the groove 5d is 0.5 mm, and the width is 25 mm.
When the solidified silicon sheet was pulled out by 250 mm, the product polycrystalline silicon sheet had a thickness of 0.5 mm and a width of 25 mm.
As for the material of the mold nozzle, it is preferable to use a carbon main body surface coated with nitrided silicon or a mixture coating of Si ₃ N ₄ and SiO ₂ .

However, when implementing the above method, it is necessary to provide a heater 2b so that the molten silicon is melted at 1450°C and does not solidify inside the supply port 3a of the silicon melting tube 3, and it is also necessary to install a heater 2b next to the heater 2b. Unless the nozzle 5 is heated by the heater 4 to a temperature approximately 50° C. lower than that of the molten silicon, an appropriate solidified silicon sheet MSi cannot be formed within the mold nozzle 5. becomes.

However, in the manufacturing method using the manufacturing apparatus as shown in FIG.
Since the heat of 2b inevitably raises the temperature of the mold nozzle 5, it becomes difficult to set the above-mentioned temperature difference of about 50° C., and a good product cannot be obtained.

Therefore, in order to solve the above-mentioned difficulties, we also attempted to use a manufacturing apparatus as shown in FIG.

In this device, the above-mentioned supply port 3a is extended to a lower part to form a long supply port 3b, and a stepped heating material 8 is disposed directly below the heater 2a. Although heating of the mold nozzle 5 by the heater 2a is avoided, a phenomenon occurs in which the molten silicon Si in the elongated supply port 3b is cooled and solidified.

Therefore, in order to further eliminate the drawbacks of the above-mentioned method, the applicant proposes to supply the molten silicon flowing down under pressure from the silicon melting tube to the mold nozzle through the elongated supply port as described above. By improving the method, the molten silicon is allowed to fall through a falling pipe that is continuous with the silicon melting pipe and protrudes downward without touching it, and is supplied into the mold nozzle. The heater that heats the molten tube and the mold nozzle are sufficiently spaced apart, and the falling molten silicon is prevented from being affected by heat from the outside as much as possible, thereby preventing clumps on the way down. This experiment was conducted to ensure that the supplied molten silicon and the mold nozzle could maintain the required temperature difference.

That is, the above method can be carried out using a manufacturing method as shown in FIG. 3, and the difference in the apparatus from that shown in FIG. 5 is as follows. be.

That is, the lower end thinning nozzle 3c opening at the lower end of the silicon melting tube 3 is thinned to such an extent that the molten silicon does not naturally flow out.
Therefore, unless a pressure p is applied to the molten silicon Si using an inert gas such as argon, it is set so that it will not flow out, and in reality, the diameter of the lower end thinning nozzle 3c is approximately 1.2 mm. By the way,
3d in the figure is an O-ring 3 attached to the upper end of the silicon melting tube 3.
The pressure application pipes connected via e are shown.

A further difference is that a falling pipe 9 of the same thickness as shown in the figure is connected to the silicon melting pipe 3, and a lower end connecting passage nozzle is opened at the lower end of the falling pipe 9. 9a is connected to the injection port 5a of the mold nozzle 5, and this lower end connecting passage nozzle 9a is opened in the shape of a slit as shown in FIG. 4b, and of course has a narrow lower end. It is arranged directly under the growth nozzle 3c,
It is formed larger than the flow cross section of the nozzle 3c, and the heat insulating material 8 is disposed on the outer peripheral side of the downflow pipe 9 so as to perform heat insulation in the vertical direction,
Further, the heater 2b is provided adjacent to the lower end connecting passage nozzle 9a.

Therefore, the method using the above-mentioned manufacturing apparatus is to melt the silicon base material in the silicon melting tube 3 (1450°C) with the heater 2a, and then apply the resulting molten silicon Si to the pressure p ( 0.01
Kg/cm ² ) is applied to cause the mold nozzle 5 to flow down from the lower end fine nozzle 3c into the downflow tube 9. At this time, the temperature of the mold nozzle 5 is heated to about 1350° C. by the heater 4.

The molten silicon Si flowing down from the lower end thinning nozzle 3c mentioned above falls through the hollow space 9b in the pipe without touching the falling pipe 9, and passes through the lower end connecting passage nozzle 9a which is opened directly below. Thus, it is continuously supplied into the casting path 6 from the injection port 5a of the mold nozzle 5.

Then, as explained in the above method, the pulling jig 7 is pulled in the direction of the arrow A, and the solidified silicone sheet is cooled and solidified in the mold nozzle 5.
The MSi is drawn out continuously, and the molten silicon
If the continuous supply of Si and the drawing speed are appropriately adjusted, products in the form of polycrystalline silicon sheets can be produced continuously without any traces.

Incidentally, by applying a pressure p of 0.01 Kg/cm ² as described above, the depth of the concave groove 5d of the mold nozzle is 0.5 mm,
When the width was 25 mm, the polycrystalline silicon sheet could be pulled at a drawing speed of 50 to 100 mm in about 10 seconds.

When using the above method, of course, a certain degree of improved results can be obtained, but in this case as well, the following problems may occur.

That is, as described above, pressure p is applied to the molten silicon Si in the silicon melting tube 3, but in this case, in practice, by fitting the lower end connecting passage nozzle 9a of the downflow tube 9 to the injection port 5a of the mold nozzle 5, It is difficult to ensure a completely sealed state and to prevent pressure from leaking.

For this reason, if the pressure p is increased in anticipation of the leakage of the inert gas, a large amount of molten silicon Si in the silicon melting tube 3 will inadvertently flow down, making it impossible to maintain the integrated continuous production as described above. It becomes difficult to do.

Furthermore, the thinner the casting channel 6 of the mold nozzle 5 is, the more difficult it becomes for molten silicon Si to enter. This is not possible with the control of

<Problems to be Solved by the Invention> The present invention attempts to eliminate the deficiencies of the above-mentioned methods, and the pressure from the silicon melting tube is used only to cause the molten silicon to flow down. This allows the molten silicon to flow into the downflow tube.
When the molten silicon is dropped without touching it, and the molten silicon is supplied to the mold nozzle, the molten silicon is improved so that pressure is applied to the molten silicon by an inert gas from a pressurized air supply path separately provided in the mold nozzle. The heater that heats the silicon melting tube and the mold nozzle are made to be sufficiently spaced apart, and the falling molten silicon is prevented from being affected by heat from the outside as much as possible. Avoid caking,
The supplied molten silicon and mold nozzle are
The first objective is to ensure that the required temperature difference can be maintained.

In addition, in the present invention, pressure is applied to the molten silicon separately to the silicon melting tube and the mold nozzle, so that continuous production of products using a tensioning jig can be easily performed by special pressure adjustment without requiring any skill. The second objective is to make it possible to produce even very thin polycrystalline silicon sheets.

<<Means for Solving the Problems>> In order to achieve the above object, the present invention melts the silicon base material in the silicon melting tube in an inert atmosphere, and then applies pressure to the molten silicon. From the lower end thinning nozzle of the silicon melting tube,
The molten silicon commensurate with the pressure is extruded and dropped, and the falling molten silicon is dropped into the hollow space in the falling pipe connected below the silicon melting pipe, and then the falling molten silicon is It passes through the lower end connecting passage nozzle of the above-mentioned falling pipe and is further sent to the casting path in the mold nozzle connected to this lower end connecting passage nozzle, and the inert gas pressure supply passage provided in the mold nozzle. Pressure is applied to the molten silicon in the casting channel through the mold nozzle, and a silicon sheet of the molten silicon solidified is continuously pulled out by a desired tensioning jig. The present invention aims to provide a method for manufacturing a polycrystalline silicon sheet.

<<Operation>> The molten silicon in the silicon melting tube, which is under pressure in an inert atmosphere, flows down from the lower end fine nozzle into the downflow tube in an amount corresponding to the pressure, and this falling molten silicon flows into the downflow tube. is continuously fed into the mold nozzle via the connecting passage nozzle at the lower end of the downflow pipe, without being touched and thus substantially uncooled by the external temperature. Since pressure is directly applied to the molten silicon in the casting channel, the molten silicon smoothly and reliably enters the casting channel, and even if the casting channel is thin, the molten silicon is guaranteed to enter the channel. By matching the drawing speed of the pulling jig with the pressure caused by this air pressure, normal drawing of polycrystalline silicon becomes possible regardless of the pressure applied to the molten silicon in the silicon melting tube.

<<Example>> To describe in detail the case in which the present invention is carried out using the manufacturing apparatus shown in FIG. 1, the apparatus is similar to that shown in FIG. However, the difference is that a pressurized air supply path 10 is attached to the mold nozzle 5.

In the embodiment shown in FIG. 1, the pressurized air supply path 10 is provided in the mold nozzle 5 and is formed by fixing the end of a pipe to the upper end portion of the nozzle upper cover plate 5c, and the end port 10a of the pipe is formed in the mold nozzle 5. It opens into the injection port 5a of the nozzle 5, and pressurized air such as argon is fed into this pipe from an inert gas supply source (not shown).

FIG. 2 shows another embodiment of the pressurized air supply path 10, in which a mounting body 11 is fixed to the upper end of the mold nozzle 5 to form a pressurized air space 10b communicating with the upper part of the injection port 5a. The lower end connecting passage nozzle 9a is attached to the top plate portion of this mounting body 11, and
A pipe serving as a pressurized air supply path 10 is inserted through the peripheral wall of the container body 11.

In order to carry out the present invention using this, the silicon base material is melted at 1450°C in the silicon melting tube 3, as in the method illustrated in FIG.
A pressure p ₁ is applied inside this silicon melting tube 3 to supply molten silicon into the mold nozzle 5. At this time, the amount of molten silicon to be supplied can be controlled by the pressure value and the time for applying the pressure. can.

Here, to specifically explain using one example, approximately
By supplying 30g of molten silicon Si, it is filled into the tension jig 7 and the casting path 6 of 25 mm x 150 mm x 0.5 mm, and a solidified silicon sheet MSi is formed in the casting path 6. At a speed of /sec,
Pull the tension jig 7 for about 10 seconds (pull 100 mm),
Next, after supplying about 3 g of molten silicon to the mold nozzle 5, inert argon gas is supplied through the pressure supply path 10, and at this time, the pressure p ₂ is set to 0.01 to 0.01.
It was maintained at 0.1Kg/ ^cm2 .

Thereafter, the tension jig 7 was pulled out by about 100 mm at a speed of about 10 mm/sec, and then about 3 g of molten silicon was again supplied, and the solidified silicon sheet MSi was pulled by following the same procedure as above.

In this way, we were able to pull out approximately 600 mm of a 25 mm wide, 0.5 mm thick polycrystalline silicon sheet.

The reason why 3 g of molten silicon was supplied in the above experiment was because silicon having a volume of 25 mm x 100 mm x 0.5 mm weighs approximately 3 g.

Of course, you can supply molten silicon at 0.3g/sec instead of intermittently supplying 3g as described above.
It may be drawn out continuously, and in that case, the argon gas will also be continuously supplied.

<<Effects of the Invention>> Since the present invention can be carried out as described above, products with desired uniform thickness and width can be produced freely and efficiently with high precision, and device processing is also possible. Not only is it easy to use, the yield is improved, and high-quality products free of impurities can be provided at low cost, but since the molten silicon falls through the downflow tube, it absorbs heat while falling from the outside. There is no need to worry about the silicon melting tube being taken away and solidifying, and as a result, it is possible to place a heat insulating material between the silicon melting tube side and the mold nozzle side to block the upper and lower heat effects without any problems. It is also possible to set the temperature on the nozzle side to a temperature below 1350℃ and the silicon melting tube side to a large temperature difference such as 1450℃.As a result, the molten silicon injected into the mold can be quickly heated. It can be solidified to form a solidified silicone sheet MSi, and the pulling speed can be increased accordingly.

Furthermore, in the present invention, the application of pressure for supplying molten silicon and the application of pressure for injecting molten silicon into the mold nozzle are performed separately, so that the desired amount of molten silicon can be accurately supplied. By separately applying a predetermined pressure to the mold nozzle, polycrystalline silicon sheets can be easily pulled out using a pulling jig without requiring any skill, improving productivity and making extremely thin sheets possible. It also becomes possible to manufacture products.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front explanatory view of a manufacturing apparatus that can be used to carry out the present invention, FIG.
The figure is a vertical cross-sectional front explanatory view of a manufacturing apparatus that can be used to carry out the method for manufacturing polycrystalline silicon sheets recently proposed by the applicant, and FIGS. 4a and 4b are respectively a--
A sectional view taken along line A and an end view on the side of the injection port of the mold nozzle, FIG. 5 is a longitudinal sectional front explanatory view of the manufacturing device for the same manufacturing method as previously presented, and FIG. 6 shows the improved manufacturing device of FIG. 5. FIG. 7 is an explanatory vertical cross-sectional view showing a manufacturing apparatus for a method for manufacturing a polycrystalline silicon sheet by a conventional ribbon method. 1a...Inert atmosphere, 3...Silicon melting tube, 3a...Lower end thinning nozzle, 5...Mold nozzle, 6...Casting path, 7...Tension jig, 9...
Falling pipe, 9a... lower end continuous passage nozzle, 9b...
Pipe cavity, 10...Pressure air supply path, p ₁ ...Pressure, p ₂
...Pressure, Si...molten silicon, MSi...solidified silicon sheet.

Claims (1)

[Claims] 1 After melting the silicon base material in the silicon melting tube in an inert atmosphere, pressure is applied to the molten silicon, and molten silicon commensurate with the pressure is extruded from the lower end fine nozzle of the silicon melting tube. After the falling molten silicon falls into the hollow space in the falling pipe connected below the silicon melting pipe, the falling molten silicon passes through the lower end connecting passage nozzle of the falling pipe. , and is further delivered to the casting path in the mold nozzle connected to this lower end connecting passage nozzle, and is also sent to the casting path in the casting path through the inert gas pressure supply path provided in the mold nozzle. Production of a polycrystalline silicon sheet, characterized in that pressure is applied to molten silicon, and a silicon sheet in which the molten silicon is solidified within the mold nozzle is continuously pulled out using a desired tensioning jig. Method.