JPH0218314A - Production of polycrystalline silicon sheet - Google Patents

Abstract

PURPOSE:To produce polycrystalline silicon sheet having a specified thickness and a specified breadth without causing interruption by flowing down molten silicon into a mold nozzle in a pressurized inactive gas atmosphere, and drawing out solidified silicon continuously. CONSTITUTION:An Si parent material in a melting tube 3 for Si is melted in an inactive gas atmosphere 1a, and molten Si is fallen down under a pressure P from a small-sized nozzle 3c at a foot end of the melting tube 3 into a vacant space 9b in a falling tube 9 connected to beneath the melting tube 3 for Si. The molten Si having been fallen is allowed to pass through a connecting nozzle 9a at a foot end of the falling tube 9, then transported further into a mold nozzle 5 connected to the nozzle 9a. Solidified Si(MSi) formed in the mold nozzle 5 is drawn out continuously with a jig 7 to obtain thus a polycrystalline silicon sheet.

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, as shown in Fig. 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. When attempting to form electrodes thereon, there is a defect that makes it difficult to apply the screen printing method.

In addition, as mentioned above, ribbon technology attempts to utilize wetting with molten silicon, so the die.

Not only does this require many consumables such as filaments and substrates, but also carbon, SiC, etc., which have good wettability, become a source of impurities in 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. is not.

Furthermore, a separate method called the casting method (#PI 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 movable part of the mold presses and solidifies the melt, but when using this method, -
Although wafers having a predetermined shape can be obtained each time and desirable results are expected in terms of mass productivity, the melt is pressed down from all sides as described above.

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 in 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%.

Therefore, in order to solve the above-mentioned difficulties, the applicant has already utilized the advantages of the casting method to supply molten silicon to the mold nozzle, but it is not discontinuous but continuous, and the molten silicon is supplied within the mold nozzle. It solidified,
By continuously drawing out this solidified silicon sheet, it is possible to produce polycrystalline silicon sheets of uniform thickness without worrying about contamination with impurities, and it is also possible to easily obtain sheets of various thickness dimensions. In this way, we proposed a method that eliminates the need for thickness uniformization in the device processing process and also aims to improve yield.

This is done using manufacturing equipment as shown in Figure 3.
In the figure, l is a furnace body with an inert atmosphere 1a made of an inert gas such as argon or vacuum, and inside this is a heater 2a.
, 2b is provided, and a mold nozzle 5 is heated by a heater 4. After the silicon base material introduced into the silicon melting tube 3 is melted by the heater 2a, Under the pressure P of an inert gas or the like, the molten silicon Si is sequentially fed into the mold nozzle 5 through the supply port 3a of the silicon melting tube 3 and the injection port 5a of the mold nozzle 5. There is.

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, so that both plates can be attached by screws or the like (not shown). By fixing 5b and 5c in a stacked state, a casting channel 8 having a predetermined thickness and a predetermined width is formed,
In the figure, numeral 7 indicates a pulling jig as a pulling means.

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 is melted (
1450'0) L, pressure P due to the inert gas
(0.01 to 0.1 kg/cm') was added to the upper surface of the molten silicon Si, and heated to 1300°C in advance by the heater 4.
The molten silicon Si is continuously poured into the mold nozzle 5 through the injection port 5a after being heated to a temperature of ~1420°C.
supply.

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

Here, when the solidified silicon sheet was pulled out by 2501 cm from the groove 5d with a depth of 0.5 mm and a width of 25 mm, the width of the polycrystalline silicon sheet as a product was 0.5 mm.
The material of the mold nozzle is either silicon nitride coating on the surface of the carbon acid body, or 5izN4 and 5iOz.
It is best to use a mixture coating.

However, when implementing the above method, molten silicon is melted at 1450°C, and the supply port 3a of the silicon melting tube 3 is
It is also necessary to provide a heater 2b to prevent the silicon from solidifying inside the mold, and the mold nozzle 5 installed next to it is heated by the heater 4 to a temperature approximately 50° C. lower than that of the molten silicon. Otherwise, it will not be possible to properly form the solidified silicon sheet MSi within the mold nozzle 5.

However, in the manufacturing method using the manufacturing apparatus shown in FIG. 1 above, 1.
The heat of the heaters 2a and 2b that heats the silicon melting tube 3 is
Since the temperature of the mold nozzle 5 inevitably increases, it becomes difficult to set the above-mentioned temperature difference of about 50° C., and a good product cannot be obtained.

In order to overcome these difficulties, we also attempted to use a manufacturing apparatus as shown in FIG.

In this device, the above-mentioned supply port 3a is formed into a long supply port 3b that extends to a lower part, 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.

(Problems to be Solved by the Invention) The present invention aims to eliminate the deficiencies of the conventional method and its improvement method, and aims to supply molten silicon flowing down under pressure from a silicon melting tube to a long supply port as described above. Instead of supplying the molten silicon to the mold nozzle through the silicon molten tube, the molten silicon described in ``-h'' is passed through a falling pipe that is continuous with the silicon melting tube and falls downward without touching it. By improving the supply into the mold nozzle, the heater that heats the silicon melting tube and the mold nozzle can be separated sufficiently, and the falling molten silicon can be prevented from being affected by heat from the outside. The supplied molten silicon and the mold nozzle are
The purpose is to ensure that the required temperature difference can be maintained.

(Means for Solving the Problems) In order to achieve the above object, the present invention melts a silicon base material in a silicon melting tube in an inert atmosphere, and then applies pressure to the molten silicon. Silicone melt
Molten silicon commensurate with the pressure was extruded from a narrow nozzle at the lower end of the tube, and the falling molten silicon was allowed to fall into a hollow space in a falling tube connected below the silicon melting tube. After that, the falling molten silicon passes through the lower end connecting passage nozzle of the above falling pipe, and is further sent into the mold nozzle connected to this lower end connecting passage nozzle, and in this mold nozzle, the molten silicon flows into the mold nozzle. It is an object of the present invention to provide a method for producing a polycrystalline silicon sheet, characterized in that a silicon sheet made of solidified molten silicon is continuously drawn out by a desired drawing means.

(Function) The molten silicon in the silicon melting tube, which is under pressure in an inert atmosphere, flows down into the falling tube from the narrow nozzle at its lower end at an amount corresponding to the pressure, and this falling molten silicon flows down into the falling tube. After falling without touching the tube and thus without being substantially cooled by the external temperature, it is continuously fed into the mold nozzle via the lower end connecting passage nozzle of the falling tube, in which: The molten silicon solidifies, and at this time the solidified silicon sheet is pulled out of the mold nozzle, so a polycrystalline silicon sheet with the thickness and width that matches the dimensions of the mold nozzle is produced without being cut off. That will happen.

(Example) To describe in detail the case where the present invention is implemented using the manufacturing apparatus shown in FIG.
, heaters 2a, 2b, silicon melting tube 3, heater 4
, mold nozzle 5, casting path 6, tension jig 7, and heat insulating material 8 are substantially the same as those in FIGS. 3 and 4, but the difference is that the silicon melting tube The lower end thinning nozzle 3c, which is open at the lower end of 3, is normally opened to such an extent that 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 there is no outflow, and in reality, the diameter of this lower end thinning nozzle 3c should be about 1.2wn. Additional tubes are shown.

A further important difference is that, in the illustrated example, a falling pipe 8 of the same thickness is protruded downwardly and is connected to the silicon melting pipe 3, and a lower end connecting passage is opened at the lower end of the falling pipe 9. Nozzle 9
The point a is connected to the injection port 5a of the mold nozzle 5, and this lower end connecting passage nozzle 8a is opened in the shape of a slit as shown in FIG. 2(b), and of course has a narrow lower end. The insulating material 8 is located directly below the nozzle 3c and is larger than the flow cross section of the nozzle 3c, and the heat insulating material 8 is located on the outer circumferential side of the downflow pipe 9 to block heat in the vertical direction. Furthermore, the heater 2b is provided adjacent to the lower end connecting passage nozzle 9d.

To carry out the present invention by using the above manufacturing apparatus,
The silicon base material in the silicon melting tube 3 is melted (1450°C) by the heater 2a, and the resulting molten silicon Si is heated to a pressure P (0,0
1kg/crn') (7) Application grin, lower end thin 11.
/ The mold nozzle 5 is caused to flow down from the nozzle 3C into the downflow pipe θ, 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 above-mentioned nozzle lower end thinning nozzle 3c falls through the hollow space 9b in the pipe without touching the falling pipe 8, and passes through the lower end connecting passage nozzle 8a which is opened directly below. Thus, it is continuously supplied into the casting channel 6 from the injection port 5a of the mold nozzle 5.

Therefore, after that, the pulling jig 7 is pulled in the direction of the arrow A as shown in the conventional example, and the solidified silicone MSi that has been cooled and solidified in the mold nozzle 5 is continuously pulled out, and the molten silicon Si continuous supply of
If the drawing speed is properly adjusted, the product, which is a polycrystalline silicon sheet, can be produced continuously without being cut off.

By applying a pressure P of <0.01 kg/ctn' as described above, when the depth of the groove 5d of the mold nozzle is 0.5 m and the width is 25 m, 50 to 100 layers can be formed in about 10 seconds. It was possible to pull the polycrystalline silicon sheet at the drawing speed of the layer.

(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 and yields are improved, and high-quality products free of impurities can be provided at low prices. However, the following effects can be achieved.

In other words, the molten silicon is allowed to fall through the downflow tube, eliminating the risk of solidification due to heat being taken away from the outside while falling.As a result, the gap between the silicon melting tube side and the mold nozzle side is eliminated. By placing a heat insulating material on the top and bottom, it is possible to block the influence of heat from above and below without any problems, so it is possible to keep the temperature on the mold nozzle side at a temperature below 1350°C and at a high temperature such as 1450°C on the silicon melting tube side. It is possible to set the difference, and as a result, the molten silicon injected into the mold nozzle can be quickly solidified into solidified silicon (MSi), and the pulling speed can be increased accordingly, which improves productivity. There are high expectations for improvement.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view of a manufacturing apparatus that can be used to carry out the present invention, and FIGS. 2(a) and 2(b) are respectively a-a-
A-line cross-sectional view and a bottom view of the falling pipe; FIG. 3 is a longitudinal cross-sectional front explanatory view of a manufacturing device that can carry out the conventional polycrystalline silicon sheet manufacturing method; and FIG. 4 is a manufacturing device based on an improved version of the same device. FIG. 5 is a vertical front explanatory view showing a conventional ribbon method polycrystalline silicon sheet manufacturing apparatus. 1a...Inert atmosphere 3...Silicon melting tube 3c...Lower end thinning nozzle 511...Mold nozzle 7...As a drawing means Tension jig 9...
... Falling pipe 9a ... Lower end connection passage nozzle 9b ... Pipe cavity P ... Pressure Si ... Molten silicon MSi ... Solidified silicon sheet

Claims (1)

[Claims] After melting the silicon base material in the silicon melting tube in an inert atmosphere, pressure is applied to the molten silicon to extrude and drop molten silicon commensurate with the pressure from the lower end fine nozzle of the silicon melting tube. After causing the falling molten silicon to fall 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. The molten silicon passes through and is further delivered into a mold nozzle connected to this lower end connecting passage nozzle, and the solidified silicon sheet of the molten silicon is continuously drawn out by a desired drawing means within this mold nozzle. A method for producing a polycrystalline silicon sheet, characterized in that: