JPH0478565B2 - - 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 separate method called casting method (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. The movable part of the mold presses and solidifies the melt, but when using this method, wafers with a predetermined shape can be obtained at once, and desirable results can be expected in terms of mass production. The melt is 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 crystal grains (grains) when the melt solidifies, and the areas near the parts of the solidified product in contact with each of the surfaces are extremely fine. 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 photoelectric conversion efficiency of the battery is also extremely poor at 2 to 3%.

Therefore, in view of the deficiencies of the above-mentioned conventional method, the applicant has already developed a new method for producing polycrystalline silicon sheets (Japanese Patent Application No.
No. 169573) was proposed (cast ribbon method).

In this manufacturing method, molten silicon is supplied to a mold nozzle, but it is not discontinuously supplied but is supplied continuously, and the molten silicon is solidified within the mold nozzle, and this solidified silicon sheet is continuously drawn out. This makes it possible to mass-produce polycrystalline silicon sheets of uniform thickness without worrying about contamination by impurities, and also makes it possible to easily obtain polycrystalline silicon sheets of various thickness dimensions, making it possible to easily produce polycrystalline silicon sheets of uniform thickness in the device processing process.
In addition to eliminating the need for thickness uniformization treatment and improving yield, the above-mentioned method for drawing out the solidified silicon sheet is entrusted to the transfer of the drawing board installed in the mold nozzle, and the solidified silicon sheet is By drawing out the sheet together with this drawing board, it is possible to further reduce the thickness of the crystals, lowering the price per unit area, and even when manufacturing thin products, the presence of the drawing board prevents cracking. This was done so that it would never occur.

<<Problem to be solved by the invention>> However, when using the above-mentioned cast ribbon method, it is of course possible to produce a fairly thin polycrystalline silicon sheet, but it is also possible to reduce the cost and improve the efficiency of solar cells. When considering this, thinning the polycrystalline silicon sheet that is the material is,
Its importance is increasing more and more, and in recent years attempts have been made to adopt effective means of confining light, such as allowing the light incident on the sheet to pass through and reflect on the back surface of the sheet. As a result, the demand for thinner polycrystalline silicon sheets has become even stronger.

Therefore, in order to obtain a thinner product, the width of the product slit in the mold nozzle through which the molten silicon flows must be made smaller, otherwise the solidified silicone sheet will not be pulled out properly. In order to make the polycrystalline silicon sheet larger and thinner, it becomes necessary to apply a large injection pressure to the molten silicon. It becomes especially obvious when

However, when the injection pressure is increased and molten silicon is forced into the product slit of the mold nozzle as described above, a large amount of silicon is formed on the mold nozzle's mating surface and at the lower end of the melting tank for supplying the mold nozzle and molten silicon. From the joint part with the supply port,
Molten silicon will leak out, resulting in an unsatisfactory polycrystalline silicon sheet.

In view of the above-mentioned problems, in claim 1 of the present application, a concave groove is formed on the upper surface of the drawing board, and by drawing out the groove, the molten silicon supplied to the mold nozzle is removed. The molten silicon first flows into this concave groove, and flows into the surrounding extremely thin product slit where the polycrystalline silicon sheet is to be formed, thereby increasing the injection pressure of the molten silicon.
In addition to being able to obtain a sufficiently thin product sheet without making it very large, when producing a product by pulling out a solidified silicone sheet,
The purpose is to allow the protruding strips formed by the groove strips to serve as a reinforcing material so that the thin sheet can be pulled out without damage.

Furthermore, according to claim 2, the depth of the grooves is made larger than the separation wall thickness length of the product slit portion formed to obtain the polycrystalline silicon sheet. We are trying to further improve its effectiveness.

《Means for solving the problem》 In order to achieve the above object, the present application uses claim 1.
After melting the silicon base material in an inert atmosphere, pressure is applied to the molten silicon to continuously send it into a heated mold nozzle, and inside this mold nozzle, When the silicon sheet in which the molten silicon has been solidified is continuously drawn out by a desired drawing means, the drawing means inserts the drawing board loaded and placed on the lower surface of the mold nozzle into the molten silicon and the drawn out substrate. The mold nozzle is continuously transferred in the longitudinal direction of the mold nozzle while the solidified silicon sheet is placed thereon, and the upper surface of the drawing board is provided with a required number of grooves along the transfer direction. The present invention attempts to provide a method for manufacturing a thin polycrystalline silicon sheet characterized in that a strip is formed between the drawer substrate according to claim 1 and the lower surface of the upper mold nozzle of the mold nozzle. The content is that the depth of the concave groove formed in the drawer substrate is greater than the distance between the product slits.

<<Operation>> In the manufacturing method according to claim 1 of the present application, molten silicon is continuously supplied into the mold nozzle, the molten silicon is solidified within the mold nozzle, and the solidified silicon sheet is transferred to the mold nozzle. As it is pulled out, a polycrystalline silicon sheet with the thickness and width that matches the dimensions of the mold nozzle is produced without any traces.
At this time, the molten silicon and the solidified silicon sheet are
Not only will these be pulled out together with the placed drawer board, but due to the grooves formed on the board, the product will have protrusions integrally formed on the thin board. Because it is drawn out,
The protrusions serve as reinforcing materials, and polycrystalline silicon sheets can be efficiently manufactured without fear of cracking even in extremely thin products.

Moreover, molten silicon easily flows into the grooves, and therefore, the molten silicon in the grooves quickly flows into the slits around the grooves, thereby reducing the injection pressure on the molten silicon. Although small, extremely thin products can be reliably produced.

<<Example>> Before describing the method according to the present application in detail, the following will be explained.
To explain the manufacturing apparatus for polycrystalline silicon sheets that can be used to carry out this method, 1 in FIG. A melting tank 3 made of quartz and heated by a heater 4a,
A mold nozzle 5 heated by the mold nozzle 4b is provided.

Here, the illustrated melting tank 3 has a small diameter lower end fine nozzle 3b in its upper tank part 3a, and this is done by injecting an inert gas such as argon into the upper tank part 3a. , no outflow from the nozzle 3b is made unless injection pressure P is applied to the molten silicon Si in the section 3a.

Furthermore, a lower tank part 3c of the melting tank 3 connected to the upper tank part 3a is protruded downwardly, and a slit-shaped lower end connecting passage nozzle 3d is opened at the lower end of the lower tank part 3c.
The lower end connecting passage nozzle 3d is connected to the injection port 5' of the mold nozzle 5, and of course, the lower end connecting passage nozzle 3d is disposed directly below the lower end narrowing nozzle 3b, is larger than the flow cross section of the nozzle 3b, and is connected to the lower tank. A heat insulating material 6 is provided on the outside of the portion 3c so as to block heat in the vertical direction, and the heater 4a is provided adjacent to the lower end connecting passage nozzle 3d.

Here, the mold nozzle 5 consists of an upper mold nozzle 5a and a lower mold nozzle 5b, and a predetermined groove 5c is formed on the upper surface of the lower mold nozzle 5b, so that both parts are 5
If a and 5b are fixed in a stacked state, a running path 5d with a predetermined thickness and a predetermined width is formed, and in this running path 5d, the upper surface of the lower mold nozzle 5b is made of stainless steel. The drawer base plate 7 made by a manufacturer, etc., is fitted and mounted in a penetrating manner so as to be able to slide freely, and as a result, as shown in FIG. A casting channel 8 surrounded by the provided side end raised strips 7a, 7b and the lower surface of the upper mold nozzle 5a is formed at a distance, and as shown in FIG. A puller 7c is provided for pulling it out in the direction of arrow A.

Furthermore, the above-mentioned drawer board 7 has grooves 7d formed on its upper surface, and in the illustrated example, only a plurality of grooves are provided in parallel to the drawing direction of the board 7,
The depth D is larger than the separation wall thickness length d of the product slit 8a formed between the upper surface of the drawer substrate 7 forming a part of the casting channel 8 and the lower surface of the upper mold nozzle 5a. In FIG. 2, W indicates the width of the casting channel 8, and w indicates the width of the concave groove strip 7d.

Therefore, in order to carry out the method according to claim 1 using the above-mentioned apparatus, a silicon base material is put into the upper tank part 3a of the melting tank 3, and the silicon base material is melted (1450°C) by operation of the heater 2. ), and the injection pressure P (100 to 500 mmAq) by the inert gas is applied to the molten silicon.
In addition to the upper surface of the Si, the silicon Si is caused to flow down from the lower end thinning nozzle 3b into the lower tank portion 3c. At this time, the mold nozzle 5 is heated to about 1350° C. by the heaters 4a and 4b.

The molten silicon Si flowing down from the lower end thinning nozzle 3b falls without touching the lower tank part 3c, passes through the lower end connecting passage nozzle 3d, and flows from the injection port 5' of the mold nozzle 5 into the casting channel. 8 will be continuously supplied.

At this time, the drawing substrate 7 is continuously transferred in the direction of arrow A, and as a result, the molten silicon Si solidifies on the substrate 7 and grows into a crystal.

That is, the solidified silicon sheet MSi cooled and solidified in the mold nozzle 5 is continuously drawn out while being placed on the drawing board 7, and at this time,
If the continuous supply amount of molten silicon Si and the drawing speed are appropriately adjusted, products such as polycrystalline silicon sheets can be produced continuously without any trace.

Furthermore, in the present invention, since the concave grooves 7d are formed during the drawing operation of the drawing substrate 7 as described above, the molten silicon Si supplied from the injection port 5' is transferred to the casting channel 8 into which it is difficult to flow. Before flowing into the product slit 8a, it quickly flows into the concave groove 7d, and when the product is pulled out, the molten silicon solidified within the concave groove 7d becomes a protrusion. It is pulled out as a kind of rib and has a predetermined width within the casting channel 8.
It serves as a reinforcing material for thin polycrystalline silicon sheets, so products can be produced quickly without damage.

Furthermore, as mentioned above, the molten silicon Si that has flowed into the concave groove 7d is separated from it by an extremely small distance d.
Product slit 8 of casting channel 8 formed in
As a result, despite the small injection pressure P, the molten silicon quickly spreads into the slit 8a.

Here, the actual injection pressure P is set to 100~100 as described above.
500mmAq, d=0.1~0.2mm in Figure 2,
D=0.4 to 0.8 mm, w=10 to 20 mm, and d=100 mm, and a polycrystalline silicon sheet could be manufactured without damage.

<<Effects of the Invention>> Since the method according to claim 1 of the present application selects the cast ribbon method as described above, it is possible to freely and efficiently produce products with a desired uniform thickness and width with high precision. Therefore, device processing is easy and the yield is improved, and not only can high-quality products free of impurities be provided at low cost, but also a drawer substrate is used as the drawer means, and grooves are formed on it. Since we were able to first allow molten silicon to flow into this, even extremely thin polycrystalline silicon sheets, which was previously impossible,
It can be produced without applying high injection pressure to molten silicon, it can achieve thinner solar cell substrates, which have been in high demand in recent years, at low cost, and it has achieved satisfactory results in terms of high efficiency. Even with such thinning, damage during production can be prevented by reinforcement by the protruding strips made of solidified silicon in the groove strips, and it is also possible to manufacture with a high yield.

According to claim 2, since the depth of the concave groove in claim 1 is formed to be larger than the thickness of the product, the molten silicon flows smoothly, and the effect of claim 1 is further enhanced. It can be made certain.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front explanatory view showing a polycrystalline silicon sheet manufacturing apparatus capable of implementing the method of claim 1 according to the present application, FIG. 2 is an explanatory longitudinal sectional view taken along the - line of FIG. FIG. 1 is an explanatory vertical cross-sectional front view showing a conventional ribbon method polycrystalline silicon sheet manufacturing apparatus. 1a... Inert atmosphere, 5... Mold nozzle, 5a... Upper mold nozzle, 7... Output substrate, 7d... Concave groove strip, 8a... Product slit, Si... Molten silicon, MSi... Solidified silicone sheet, d... separated wall thickness length of product slit, D
...The depth of the groove.

Claims (1)

[Claims] 1. After melting a silicon base material in an inert atmosphere, pressure is applied to the molten silicon to continuously send it into a heated mold nozzle, and When the silicon sheet in which the molten silicon has been solidified is continuously drawn out in this mold nozzle by a desired drawing means, the drawing means inserts the drawing board placed on the lower surface of the mold nozzle. , the above molten silicon and the silicon sheet solidified thereon are continuously transferred in the longitudinal direction of the mold nozzle while being placed thereon, and the upper surface of the drawing board is provided with a sheet attached in the transfer direction. 1. A method for producing a thin polycrystalline silicon sheet, characterized in that a required number of grooves are formed in the thin polycrystalline silicon sheet. 2. A claim in which the depth of the concave groove formed on the drawer substrate is greater than the separation wall thickness of the product slit formed between the drawer substrate and the lower surface of the upper mold nozzle of the mold nozzle. Item 1. The method for producing a thin polycrystalline silicon sheet according to item 1.