JP3084574B2 - Method for producing polycrystalline silicon sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polycrystalline silicon sheet used for solar cells and other photoelectric conversion elements.

[0002]

2. Description of the Related Art Various methods for producing a polycrystalline silicon sheet have already been carried out. One of the methods is a ribbon method, as shown in FIG. The die c is immersed and raised in the existing molten silicon b, and the molten silicon b pulled out from the upper end c ′ of the die c is cooled and solidified in an inert gas atmosphere outside the die c. In the ribbon technology, since the sheet is formed using the meniscus (surface tension) of the molten silicon b, it is difficult to obtain a polycrystalline silicon sheet having a uniform thickness, and as a result, when using it as a device of a solar cell, However, there is a defect that it is difficult to apply the screen printing method even if an electrode is formed on the electrode.

[0003] Further, since the ribbon technology is intended to utilize the wetness with the molten silicon as described above, not only many consumables such as dies, filaments, and substrates are required, but also carbon with good wettability, Since SiC or the like is used, this becomes a source of impurities to the molten silicon. Furthermore, when the ribbon method is used, crystal growth
Growth of the polycrystalline silicon sheet in the drawing direction,
The growth rate of the crystal cannot be so high, and is not satisfactory in terms of quality and production efficiency.

[0004] A separate casting method (casting method) is also practiced separately, but in this method, a silicon base material is heated to form a melt, which is poured into a mold corresponding to the size of a product wafer. Further, the melt is pressed and solidified by the movable part of the mold, and the melt is solidified. When the same method is used, a wafer having a predetermined shape can be obtained at a time, and a desirable result in terms of mass productivity can be expected. As described above, the melt is pressed from all sides. Therefore, in the same method, the upper and lower surfaces and the side surfaces of the mold suppress the growth of silicon crystal grains (grains) when the melt is solidified, and the vicinity of a portion in contact with each surface of the solidified product is very fine. Since large crystal grains cannot be obtained as crystal grains, and it is not possible to satisfy the demand for large crystal grains that is desirable in a silicon wafer for a solar cell or the like, the solar cell obtained by the wafer cannot be satisfied. The photoelectric conversion efficiency is also 2
It has a defect that is extremely bad at 3%.

In order to solve the above-mentioned difficulties, the present applicant has utilized the advantages of the casting method and supplied molten silicon to the mold nozzle. By solidifying the solidified silicon sheet continuously, it is possible to mass-produce a polycrystalline silicon sheet having a uniform thickness without the risk of contamination by impurities, and various thickness dimensions. To make it easier to get
In the device processing step, a method was proposed in which the uniformity of the thickness was not required and the yield was improved (this method is hereinafter referred to as a cast ribbon method).

This method is carried out using a manufacturing apparatus as shown in FIG. 3. In FIG. 3, reference numeral 1 denotes a furnace having an inert atmosphere 1a of an inert gas such as argon or a vacuum. A silicon melting tube 3 heated by the heaters 2a, 2b and the like, and a mold nozzle 5 heated by the heater 4 are provided. The silicon base material put into the silicon melting tube 3 is melted by the heater 2a. After
Upon receiving the pressure P by 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. I have.

Here, the mold nozzle 5 is a nozzle lower plate 5
b and a nozzle upper lid plate 5c, and a predetermined concave groove 5d is formed on the upper surface of the nozzle lower plate 5b, so that both the plates 5b and 5c are fixed in a stacked state with screws (not shown) or the like. As a result, a casting path 6 having a predetermined thickness and a predetermined width is formed, and reference numeral 7 in the drawing denotes a drawing jig as drawing means.

In order to carry out the cast ribbon method using the casting apparatus, a silicon base material is charged into a silicon melting tube 3 formed of quartz or the like, and the silicon base material is supplied to a heater 2.
a) (1450 ° C.), and a pressure P (0.01 to 0.1 kg / cm 2) by the inert gas is applied to the upper surface of the molten silicon Si.
From the base side of the mold nozzle 5 toward the casting path 6 and the drawing end port 5e, as shown in the drawing, from a temperature higher than the melting point of silicon (MP = 1420 ° C.) to 1300 ° C.
Temperature distribution curve T such that the temperature falls down to the degree
In the casting path 6 near the drawing end port 5e.
Therefore, the temperature is set to be lower than the melting point MP in advance from the solidified region 5f separated by the required length toward the injection port 5a and toward the drawing jig 7, and the mold nozzle under such temperature conditions 5, the molten silicon Si is supplied continuously from the injection port 5a.
As a result, the molten silicon Si flows from the gripping end 7a of the drawing jig 7 to the solidified region 5f in the mold nozzle 5.
By solidification, the solidified silicon sheet MSi is formed.

Thus, the solidified silicon sheet MSi
If There is formed, although the draw the drawer jig 7 continuously towards the arrow D in the longitudinal direction of the mold nozzle 5, the pressure P applied to the time the molten silicon Si is
By setting the operating pressure lower than the initial pressure mentioned above,
It is preferable that the length of the solidified region 5f does not change.
Here, the concave groove 5d is actually about 0.5 mm deep, about 25 mm wide and about 250 mm long . Carbon is used as the material of the mold nozzle, and its body surface is coated with silicon nitride. Suka, Si3 N4 and S
It is used after applying a release material such as iO2 mixture coating.

[0010]

According to the above conventional method, since the area from the solidified area 5f, which is the tip side of the mold nozzle 5, to the drawing jig 7 is controlled in advance to the melting point MP of Si or less. First, the pressure P of molten silicon Si
When the molten silicon Si poured into the casting path 6 when pressed into the mold nozzle 5 by the
The solidified silicon sheet MSi that is drawn out as a result is rapidly crystallized, and as a result, the solidified silicon sheet MSi becomes a crystallite having a large amount of distortion, which causes not only a decrease in the characteristics of the product but also
The sheet surface becomes rough and the solidified silicon sheet MS
i adheres to the mold nozzle 5, and this drawing operation requires a large tensile force, cracks are generated in the product, and the mold nozzle 5 is applied to the mold nozzle 5 by a roughened solidified silicon sheet MSi. There is a problem that the coating is worn out early and its life is shortened.

In view of the drawbacks of the conventional method as described above,
In the first aspect, the temperature distribution curve in advance mold nozzle, so that a high temperature over the entire area above the melting point of silicon, advance to control the heating conditions, followed by a
Required length from the tip side of the mold nozzle to the injection port side
Spaced up solidified region by <br/> Yuku by slowly cooling control only, the crystals were obtained less favorable characteristics eliminates conventional defect distortion, the solidified silicon sheet having a smooth surface The aim is to enable the formation, prevent adhesion to the mold nozzle, thereby reducing the frictional force from the start of drawing, and realize manufacturing without applying extra stress to the solidified silicon sheet that is drawn. That is the purpose.

Further, according to the present invention, when controlling the temperature drop at the tip end of the mold nozzle in claim 1, this is not performed by a heat source for heating, but under a predetermined heating condition by the heat source. Then, by bringing the cooling body into sliding contact with the tip of the mold nozzle, the boundary line between the molten silicon and the solidified silicon sheet can be controlled with high precision, so that a uniform product can be obtained.

Further, by properly controlling the solidified area of the mold nozzle where the solidified silicon sheet is formed to a minimum, the pulling force by the drawing jig is reduced as much as possible.
The purpose is to prevent the product from cracking. Also, when the service life of the above-mentioned coating of the mold nozzle is approaching, the boundary between the solidified area and the molten silicon is gradually moved to a position which can be shifted by moving the cooling body, thereby reducing the wear of the coating. You can also use a location that is not even possible to be thereby coating life such extension bus
Trying to.

[0014]

According to the present invention, in order to attain the above object, the present invention is characterized in that, in an inert atmosphere, after a silicon base material is melted, pressure is applied to the molten silicon. its Note the the warmed mold the nozzle
A first step of causing the molten silicon to flow into the gripping end of the drawer jig brought into contact with the drawer end of the mold nozzle by continuously delivering the molten silicon from the inlet; and from the gripping end of the drawer jig. the lead-out end mouth closer der mold nozzle
Thus, the solidified region separated by a required length toward the injection port side
When the molten silicon down is consolidated to, while applying pressure to the molten silicon, by Hikidasuru be continuously said drawer jig, the solidified silicon sheets consolidated in the mold nozzle, wherein In the cast ribbon method comprising the second step of continuously drawing out from the drawing end of the mold, in the first step , the mold nozzle is heated by a heat source, so that all the molten metal flowing into the gripping end is heated. silicon, without the molten state is held above its melting point, in the second step toward the solidification region of the mold the nozzle from the drawer jig, by gradually lowering the temperature by adjustment of the heat source, the molten silicon the so after forming a solidified silicon sheet by consolidating to reach ibid solidification region, continuous withdrawal of the then drawn jig is started Trying to provide a method for producing polycrystalline silicon sheet, characterized in that the.

Further, in the invention according to claim 2,
The first step in the high frequency according to claim 1, in the cast ribbon method of a second step, the the first step the mold nozzle by leaving heated by a heat source, all the molten silicon flowing to grip for end mouth, In the second step, the cooling body that is in contact with the mold nozzle heated by the heat source is slid from the drawer jig toward the portion near the drawing end opening of the mold nozzle while maintaining the melting point or higher. be to, after forming a solidified silicon sheet by consolidating the molten silicon until reaching the solidification region, that continuous withdrawal of the then drawn jig is to be started, and its contents.

[0016]

According to the method of manufacturing a polycrystalline silicon sheet according to the first aspect, the molten silicon pressurized and supplied by the cast ribbon method flows from the mold nozzle to the inside of the gripping end. The molten state is maintained by the heating conditions.

Next, by adjusting the heat source, the mold nozzle is located closer to the outlet end of the mold nozzle from the drawer jig side.
In it towards the solidification region, it is temperature controlled to go a low temperature by changing heating conditions in slowly, such as temperature drop state Turkey
From, thereby without fine crystals is generated in solidifying a silicon sheet obtained, also eliminates the problem of the surface roughening, after solidification the silicon sheet to solidification region in the mold nozzle is formed, running drawer jig In this case, a large force is not required, so that the product is not cracked, and the coating of the mold nozzle is less worn.

[0018] The temperature lowering control of the claim 2 wherein, to perform the contact means against the mold nozzle cooling body
Since, by the slide and its stop position of the cooling body,
The solidified area of the solidified silicon sheet can be controlled with high precision, and thereby can be made an extremely short solidified area, whereby the pulling force of the drawing jig can be further reduced. Incidentally, if to displace said如Ku those solid region, the boundary vicinity portion between the molten silicon and solidified silicon sheets most coating In the mold nozzle will wear, not wear coating if not places can transfer Succoth, coating life of this result the mold nozzle is the extend significantly.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When the method according to the present invention is carried out using the manufacturing apparatus shown in FIGS . 1 and 2 , the apparatus has substantially the same configuration as that already shown in FIG. In the manufacturing apparatus according to the present invention, the same members are denoted by the same reference numerals, and the difference is that the heat source 10 disposed near the mold nozzle 5 is a large number of independent heat sources. Heaters 10a, 10b, 10
c}, and each of the independent heaters 1
0a, 10b, 10c} can be individually controlled in temperature.

[0020] Therefore, also in the cast ribbon method according to claim 1, in the inert atmosphere within 1a of the furnace body 1, after melting the silicon base material, the melting <br/> silicon of the silicon melt pipe 3 By applying pressure to the Si, the molten silicon Si is continuously sent out into the mold nozzle 5 heated by the heat source 10 so that the molten silicon Si is
And has a first step of flowing into the gripping end 7a of the drawer jig 7 that is in contact with the drawer end 5e of the mold nozzle 5 from the gripping end 7a. It is close to 5e , which is the required length toward the injection port 5a side
Only when the molten silicon down is <br/> consolidated until solidification region 5f spaced to set, while applying a pressure P in the molten silicon Si, it is drawn out continuously drawer jig 7 of the Accordingly, a second step of drawing the solidified silicon sheet MSi solidified in the mold nozzle 5 from the drawing end port 5e is also provided.

Here, in the manufacturing method, in the first step described above, the mold nozzle 5 is connected to the heat source 10 in advance.
When heating by, all the independent heaters 10a, 10b,
10c}, and all the molten silicon Si flowing to the gripping end 7a is maintained at a temperature equal to or higher than its melting point MP to obtain a molten state as shown in FIG. The temperature is controlled so that the temperature can be controlled. Accordingly, the molten silicon Si is filled from the casting path 6 in the mold nozzle 5 to the gripping end 7 a of the drawing jig 7.

Next, in the second step described above, the drawing jig 7 is located near the drawing end port 5 e of the mold nozzle 5.
And solidified by a required length l toward the injection port 5a.
The temperature of the independent heaters 10a and 10b near the right end of the heat source 10 in the figure is gradually controlled toward the region 5f by a PID control method or the like, so that the temperature is gradually lowered. By solidifying the silicon Si until it reaches the solidified region 5f , a solidified silicon sheet MSi is formed, and the boundary line 5g between the solidified silicon sheet MSi and the molten silicon Si becomes as shown in the drawing. Then, the continuous drawing of the drawing jig 7 is started.

[0023] Here, as described above in FIG. 1 (B) and the temperature distribution curve T2 in the case of performing slow cooling control is illustrated, the curve T2 is the melting point of silicon 1450
℃ at the intersection with, so that the above-mentioned boundary line 5g of the molten silicon Si and solidified silicon sheet MSi is formed. In practice, it is preferable that the temperature be lowered at a rate of about 10 ° C. per minute.
From the mold nozzle 5 to the extraction end port 5e is 30
mm (total length of the mold nozzle 5 is 200 to 300 m
m).

Next, the method of claim 2 will be described in detail with reference to FIG. 2. The difference between claim 2 and claim 1 is that the slow temperature lowering control means in the second step includes:
And not due to energization control to the heater which is a heat source 10, supra independent heaters 10a, 10b, a temperature of 10c ‥‥‥ is left of that, the cooling member 11 abuts on the distal end side of the mold nozzle 5, This is slid in the direction of arrow S. Therefore, in order to perform the above-mentioned temperature-lowering control, the cooling body 11 is slid slowly to the left, and the terminal portion 11a is stopped at a predetermined position.
A boundary line 5g is formed and the required length l
Solidified silicon sheet MSi can be formed.

[0025] Here, the cooling body 11 can be used in desired metal, including previously formed the radiation fins 11b, 800 ° C. to 1000 ° C. of about cooling the argon gas to which 12 It is preferable that the time delay can be reduced and the required length 1 can be regulated with high accuracy, as compared with the above-described temperature reduction control using only the heater. Therefore, control such as 1 = 30 mm or less can be easily performed.

[0026]

Since the present invention can be carried out as described above, according to the first aspect, the characteristics of the product can be improved by slowly lowering the temperature, and the surface of the solidified silicon sheet can be smoothed. This eliminates the need for a large pulling force and does not cause cracking of the product during the pull-out operation with the drawer jig, and also reduces the frictional force due to the pull-out operation, thereby reducing the friction of the coating applied to the mold nozzle. Can also be reduced.

According to the second aspect, in addition to the above-mentioned effects of the first aspect, extremely high-precision temperature control can be given to the molten silicon by the movement of the cooling body. Since the growth can be controlled, a product having better characteristics can be obtained, the solidified area of the solidified silicon sheet can be accurately controlled, and the set length can be shortened, so that the tensile force of the product can be further reduced.

[Brief description of the drawings]

FIG. 1 (A) is a vertical sectional front view showing a relationship with a temperature distribution state in a first step of a manufacturing apparatus used for carrying out a method according to claim 1 of the present invention, and FIG. FIG. 3 is a vertical sectional front view showing a relationship with a temperature distribution state in a second step of the manufacturing apparatus.

FIG. 2 is a vertical sectional front view of a main part at the time of temperature control of a manufacturing apparatus used for carrying out the method of claim 2;

FIG. 3 is a longitudinal sectional front view showing a relationship between a temperature distribution state and a conventional polycrystalline silicon sheet manufacturing apparatus by a cast ribbon method.

FIG. 4 is a vertical sectional front view showing a conventional polycrystalline silicon sheet manufacturing apparatus by a ribbon method.

[Explanation of symbols]

Reference Signs List 1a inert atmosphere 5 mold nozzle 5a inlet 5e withdrawal end 5f solidified area 7 drawer jig 7a gripping end 10 heat source 11 cooling body Si molten silicon MSi solidified silicon sheet MP melting point of silicon l required length

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoya Suzuki 2-3-17 Kikusui Gojo, Shiroishi-ku, Sapporo City Inside Hokusan Hokusan Laboratories (72) Inventor Toshiaki Moriya 2-3-1-17 Kikusui Gojo, Shiraishi-ku, Sapporo City No. Hokusan Co., Ltd. Hokusan Laboratory (58) Fields investigated (Int.Cl. ⁷ , DB name) C01B 33/00-33/193 C30B 1/00-35/00 H01L 21/208 H01L 31/04-31 / 06

Claims (2)

(57) [Claims] 1. After melting a silicon base material in an inert atmosphere and applying pressure to the molten silicon, the molten silicon is introduced into a heated mold nozzle through its injection port.
By continuously sending the molten silicon,
A first step of flowing into the gripping end of the drawer jig brought into contact with the drawout end of the mold nozzle, and the drawing end of the mold nozzle from the gripping end near the drawing end ,
Wherein when the <br/> molten silicon down the required length toward the inlet side only until spaced solidified area is consolidated, while applying pressure to the molten silicon, in succession above the drawer jig Hikidasuru Thus, in the cast ribbon method comprising the second step in which the solidified silicon sheet consolidated in the mold nozzle is continuously drawn from the drawing end port , the mold nozzle is heated by a heat source in the first step. and that previously, all of the molten silicon flowing to grip for end mouth, above its melting point in holding to a molten state and without previous mold nozzle from the drawer jig in the second step
Towards serial solidification region, by gradually lowering the temperature by adjustment of the heat source, after forming the solidified silicon sheet by consolidating until the molten silicon ibid solidification region, of the above-described drawer jig A method for producing a polycrystalline silicon sheet, wherein continuous drawing is started. 2. After melting a silicon base material in an inert atmosphere and applying pressure to the molten silicon, the molten silicon is injected into a heated mold nozzle through an injection port.
By continuously sending the molten silicon,
A first step of flowing into the gripping end of the drawer jig brought into contact with the drawout end of the mold nozzle, and the drawing end of the mold nozzle from the gripping end near the drawing end ,
Wherein when the <br/> molten silicon down the required length toward the inlet side only until spaced solidified area is consolidated, while applying pressure to the molten silicon, in succession above the drawer jig Hikidasuru Thus, in the cast ribbon method comprising the second step in which the solidified silicon sheet consolidated in the mold nozzle is continuously drawn from the drawing end port , the mold nozzle is heated by a heat source in the first step. and that previously, all of the molten silicon flowing to grip for end mouth, above its melting point in holding to a molten state and without previous mold nozzle from the drawer jig in the second step
Towards serial solidification region, by sliding the cooling body contact with the mold nozzles being heated by said heat source, it consolidated the molten silicon until reaching the solidification region
After forming the solidified silicon sheet by the
A method for producing a polycrystalline silicon sheet, wherein continuous drawing of the drawn-out jig is started.