JPH0479968B2 - - 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 drawbacks 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%.

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 drawing out the solidified silicon sheets, polycrystalline silicon sheets of uniform thickness can be mass-produced without worrying about contamination by impurities, and they can be produced in various thicknesses and dimensions. We proposed a method to improve yield by making it easier to obtain products and by eliminating the need for uniform thickness processing during the device processing process.

The first method is to use a manufacturing apparatus as shown in FIG. A silicon melting tube 3 heated by heaters 2a and 2b and a mold nozzle 5 heated by heater 4 are provided, and the silicon base material charged into the silicone melting tube 3 is After being melted by the inert gas, the molten silicon Si is subjected to pressure P caused by an inert gas or the like, and the molten silicon Si sequentially passes through the supply port 3a of the silicon melting tube 3 and the injection port 5a of the mold nozzle 5 to the mold nozzle 5. It's starting to be sent inward.

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.
Both plates 5b and 5c are fixed in a stacked state using screws 5e shown in the figure, thereby forming a casting channel 6 having a predetermined thickness and a predetermined width. It shows.

To carry out the first method using this manufacturing apparatus, a silicon melting tube 3 made of quartz or the like is required.
A silicon base material is put in the inside, and it is melted (1450°C) by operating the heater 2a, and the pressure P (0.01 to 0.1 Kg/cm ² ) due to the inert gas is applied to the upper surface of the molten silicon Si. In addition, the molten silicon Si is continuously supplied from the injection port 5a into the mold nozzle 5, which has been previously heated to a temperature of 1300° C. to 1420° C. by the heater 4.

As a result, the molten silicon Si becomes a solidified silicon sheet MSi in the mold nozzle 5, but its tip is drawn out of the furnace body 1 in advance, and its end is fitted into the tension jig 7. The tension jig 7 is continuously pulled out in the direction of arrow A, which is the longitudinal direction of the mold nozzle 5.

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. Apply silicon nitride coating or
It is preferable to use 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, the applicant further proposed a second method that can be carried out using a manufacturing apparatus as shown in FIG.

The items in Figure 6 above are the same as those in Figure 5: furnace body 1, inert atmosphere 1a, heaters 2a, 2b, silicon melting tube 3, heater 4, mold nozzle 5, casting path 6, tension jig 7, heat insulation. The presence of the material 8 is substantially the same as that described above, and the difference is that the lower end fine nozzle 3b that opens at the lower end of the silicon melting tube 3 is to the extent that molten silicon does not normally flow out naturally. 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.
3c in the figure shows a pressure applying tube connected to the upper end of the silicon melting tube 3 via an O-ring 3d.

A further difference is the above silicon melting tube 3.
In the illustrated example, a falling flow pipe 9 of the same thickness is provided below, and a lower end connecting passage nozzle 9a in the form of a slit or the like opened at the lower end of the falling flow pipe 9 is connected to the mold nozzle 5. It is connected to the inlet 5a, and of course is arranged directly below the lower end thin nozzle 3b, and is formed larger than the flow cross section of the nozzle 3b. The heater 2b is disposed on the outer circumferential side of the heater 2b so as to provide vertical heat isolation, and the heater 2b is provided adjacent to the lower end connecting passage nozzle 9a.

In order to carry out the second method described above using the above manufacturing apparatus, the silicon base material in the silicon melting tube 3 is melted (1450° C.) by the heater 2a,
The resulting molten silicon Si is heated by applying pressure P (0.01Kg/cm ² ) using argon gas, etc.
The mold nozzle 5 is caused to flow down from the lower end fine nozzle 3b into the downflow pipe 9, and 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 3b described 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.

Thereafter, as explained in the first method, the pulling jig 7 is pulled in the direction of the arrow A to continuously pull out the solidified silicon sheet MSi that has been cooled and solidified in the mold nozzle 5. If the continuous supply amount and drawing speed are properly adjusted, the polycrystalline silicon sheet product can be produced continuously without any traces.

However, in both the first and second methods described above, since the purpose is to draw out a polycrystalline silicon sheet with a uniform thickness and width, the molten silicon is not solidified in the casting path in the mold nozzle. The polycrystalline silicon sheet is formed to have a uniform thickness and width in accordance with the dimensions of the polycrystalline silicon sheet to be obtained, and it is true that highly accurate dimensions can be obtained. When pulling out the solidified silicone sheet, it must be pulled out with a fairly large tensile force due to the frictional resistance between the sheet and the mold nozzle.

Not only that, the body expansion when molten silicon Si solidifies into solidified silicon sheet MSi is approximately 10%.
As a result, as described above, the carbon screws 5e that fix the nozzle lower plate 5b and the nozzle upper cover plate 5c may be damaged, or the mold nozzle 5 may be deformed.

<<Problems to be Solved by the Invention>> The present invention solves the problem of how to easily draw out the polycrystalline silicon sheet and the deformation of the mold nozzle itself and screws in the first and second methods. In order to solve the problem of damage to the mold nozzle, the tip of the nozzle upper cover plate forms a casting path that can freely rotate in the vertical direction, and the solidified silicon sheet passes through this casting path. By doing so, the body expansion during solidification of molten silicon is absorbed by the rotation of the nozzle top cover plate, thereby eliminating damage to the mold nozzle and reducing the labor and power consumed in operating the extraction means. Its purpose is to improve productivity.

<<Means for Solving the Problems>> In order to achieve the above object, the present application melts a silicon base material in an inert atmosphere and then applies pressure to the molten silicon to melt it into a nozzle lower plate. The nozzle top cover plate is placed and fixed on the mold nozzle to continuously feed the molten silicon into the casting path of the heated mold nozzle. When the solidified silicon sheet of the molten silicon is continuously pulled out using a desired tensioning jig in the solidified silicon sheet forming groove that opens at the outlet, the body expansion of the molten silicon during solidification is measured by the nozzle. An object of the present invention is to provide a method for manufacturing a polycrystalline silicon sheet, characterized in that absorption is caused by rotational escape by pushing up a vertically movable plate part that is pivotally connected to a fixed plate part of the upper cover plate. It is.

<<Operation>> In the present application, the molten silicon in the silicon melting tube flows out under pressure and is supplied into the mold nozzle, and the molten silicon flows into the solidified silicon sheet forming groove and solidifies, and this is removed by the drawing means. The vertically moving plate part of the nozzle top cover plate of the mold nozzle, which constitutes the solidified silicon sheet forming groove, is pushed upward by the body expansion when the molten silicon solidifies. Since the mold nozzle rotates, no force due to unreasonable body expansion is applied to the mold nozzle, and as a result, not only is there no need for a large tensile force from a tension jig, but there is also the risk of deforming the mold nozzle or breaking screws. There's no need to put it away.

<<Example>> This application is described in FIGS. 5 and 6 above, FIG. 1 showing the vicinity of the mold nozzle, and FIGS. 2 to 4 showing the nozzle lower plate 5b and nozzle upper cover plate 5c of the same mold nozzle, respectively. If you explain in detail using
As the manufacturing apparatus, the one shown in FIGS. 5 and 6 described above may be used, and in this case, it is preferable to use the following mold nozzle 5.

That is, the nozzle lower plate 5b as shown in FIGS. 2a and 2b and the nozzle upper cover plate 5c as shown in FIGS. , these are fixed by screws 5e as locking screws made of the same carbon as the same member.

The nozzle lower plate 5b has a standing wall 5g standing perpendicularly from the front end of the horizontal substrate 5f, and abutting protrusions 5h, 5h are provided projecting from both widthwise ends of the standing wall 5g toward the tensioning jig 7 side. The entire structure is formed into an L-shape as shown in FIG. 2a.

Although the manufacturing apparatus shown in FIG. 5 or 6 may be used to carry out the present invention, the manufacturing apparatus shown in FIG.
In the illustrated embodiment, the manufacturing apparatus shown in FIG. 5 is used.

Next, as shown in FIG.
j is stood upright, and the abutting protrusion portion 5 extends from both widthwise ends of the upright wall 5j toward the side opposite to the tension jig 7.
K and 5k are provided protrudingly, and the whole is also formed in an L-shape as shown in FIG. 3a.

Further, the nozzle upper cover plate 5c is provided with the same groove 5d on its lower surface, and when the nozzle upper cover plate 5c is placed on the nozzle lower plate 5b, the abutting protrusion between the two 5h, 5h, 5k, and 5k, and insert the screw 5e into the insertion hole 51 of the nozzle upper cover plate 5c.
It is screwed into the fastening screw hole 5m of the nozzle lower plate 5b.

An L-shaped casting path 6 is formed in the mold nozzle 5 assembled in this way, and the casting path 6 includes a vertical falling part 6a that opens the injection port 5a, and a falling part 6a that opens the injection port 5a. It is in a penetrating state with an L-shaped molten silicon chamber 6c formed by a transverse section 6b extending horizontally from the section 6a, and a solidified silicon sheet forming groove 6e that opens continuously to the outlet 6d of the mold nozzle 5. .

Furthermore, what is important here is that the horizontal substrate 5i is mounted on the fixed plate portion 5n on the side of the mounting upright wall 5j.
and a vertically movable plate portion 5q on the tension jig 7 side, the substrate side of which is pivotally connected by a carbon pivot pin 5p.

In the illustrated example, shaft bearing protrusions 5r are provided protrudingly on both sides in the width direction on the base end side of the vertical moving plate part 5q, and the central shaft bearing part 5s of the fixed plate part 5n is fitted between the shaft bearing protrusions 5r. , is pivotally connected to the center shaft bearing part 5s by a pivot pin 5p screwed from both sides of the shaft bearing protrusion 5r, so that the arrow B in FIG.
The vertically moving plate portion 5q is rotatable in the direction.

To carry out the present invention using the above-mentioned apparatus, the temperature of the mold nozzle 5 is set to 1300° C. to
Maintaining the temperature at 1420°C, obtain molten silicon at 1450°C in the silicon melting tube 3 made of quartz, then introduce argon gas to give the molten silicon 0.01Kg/cm ² ~
Applying a pressure of 0.1 Kg/ ^cm2 , the above-mentioned molten silicon Si flows into the mold nozzle 5, and this molten silicon sheet MSi solidified in the solidified silicon sheet forming groove 6e is pulled and cured at a speed of 10 mm per second. It is pulled out using the tool 7, and as a result, the mold nozzle 5 has a thickness of 0.5 mm and a width of 25 mm, as per the above-mentioned dimensions.
We were able to pull out a polycrystalline silicon sheet.

At this time, when solidifying the molten silicon, the solidified silicon sheet MSi is formed with body expansion, but at this time, the vertically movable plate portion 5q of the mold nozzle 5 is pushed up, and the pulling force by the tension jig 7 is also increased. Otherwise, the mold nozzle 5 may be deformed,
No damage to the pivot pin 5p was observed.

<<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. Therefore, device processing is easy and the yield is high. In addition to being able to provide high-quality products free of impurities at a low price, it also has the following effects.

In other words, by passing the solidified silicone sheet through a casting path in which the tip of the mold nozzle can freely rotate vertically, the pulling force of the tensioning jig is small, and the dimensional accuracy is high.
It can be manufactured without problems such as deformation of the mold nozzle or damage to the pivot pin, and productivity can be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view showing the main parts of a manufacturing apparatus that can be used to carry out the present invention, FIGS. Figures a and b are a longitudinal sectional front view and a bottom view showing the nozzle top cover plate of the same nozzle, Figure 4 is a plan view of the mold nozzle, and Figure 5 is a manufacturing method that can be carried out using the conventional polycrystalline silicon sheet manufacturing method. FIG. 6 is a vertical front explanatory view showing a manufacturing device based on an improved version of the above device, and FIG. 7 is a vertical front explanatory view showing a conventional ribbon method polycrystalline silicon sheet manufacturing device. . 1a...Inert atmosphere, 5...Mold nozzle, 5
a... Inlet, 5b... Nozzle lower plate, 5n... Fixed plate part, 5q... Vertical moving plate part, 6... Casting path, 6c... Molten silicon chamber, 6d... Outlet, 6e... Solidified silicon sheet forming groove, P …pressure, Si…molten silicon,
MSi...Solidified silicone sheet.

Claims (1)

[Claims] 1 After melting the silicon base material in an inert atmosphere, by applying pressure to the molten silicon, the nozzle top cover plate is placed and fixed on the nozzle bottom plate to form a heated mold. The molten silicon is continuously fed into the casting path in the nozzle, and the molten silicon is solidified in the solidified silicon sheet forming groove which is continuous with the molten silicon chamber with the inlet opening and the outlet opening in the casting path. When the molten silicon sheet is continuously pulled out using a desired tensioning jig, the body expansion during solidification of the molten silicon is controlled by the vertical movement of the nozzle upper cover plate, which is pivoted to the fixed plate part. A method for manufacturing a polycrystalline silicon sheet, characterized in that absorption is caused by rotational escape by pushing up a plate part.