JP4085521B2 - Silicon ingot cutting method - Google Patents

Description

【００４０】
【発明の効果】
以上に説明した通り、本発明のシリコン鋳塊切断方法は、シリコンを連続的に鋳造するシリコン鋳造装置から引き出されるシリコン鋳塊を支障なく高温で切断することにより、鋳造速度が速い場合も、シリコン鋳造装置から切断位置までの距離を抑え、設備高さの低減及びこれによる設備コストの低減、メンテナンスの簡略化等に大きな効果を発揮する。
【図面の簡単な説明】
【図１】本発明の一実施形態を示すシリコン鋳造設備の構成図である。
【図２】ダイヤモンドカッタの一例を示す平面図である。
【図３】図２のＡ−Ａ線矢示図である。
【符号の説明】
１０ シリコン鋳塊
２０ シリコン鋳造装置
２１ チャンバ
２２ 誘導コイル
２３ 無底ルツボ
２４，２５ 保温炉
３０ 鋳塊切断装置
３１ ダイヤモンドカッタ
３２ クランプ機構
３３ 噴霧機構[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cutting a silicon ingot used for manufacturing a solar cell substrate and the like, and more particularly to a method for cutting a silicon ingot drawn from a silicon casting apparatus that continuously casts silicon.
[0002]
[Prior art]
As the solar cell substrate, a silicon wafer cut out from a silicon ingot into a regular thin plate is used. The silicon ingot here is a directional solidified ingot of polycrystalline silicon, and its production is performed by a continuous casting method called electromagnetic casting, for example.
[0003]
Silicon electromagnetic casting uses a cylindrical conductive bottomless crucible divided in the circumferential direction at least in part in the axial direction, and the raw material in the bottomless crucible by an induction coil arranged outside the bottomless crucible A silicon ingot is continuously produced by dissolving silicon and drawing it below the bottomless crucible while solidifying the melt. This casting method can continuously produce a silicon ingot, so that the casting cost can be kept low and the silicon melt in the bottomless crucible can be repelled against the inner surface of the crucible. Since contamination of the melt from the bottomless crucible can be suppressed to a low level, there is a feature that high ingot quality can be secured.
[0004]
The present applicant has paid attention to the electromagnetic casting of silicon from an early stage, and has already started mass production of silicon ingots by this, and has proposed many new technologies in the process (Japanese Patent Nos. 2630417 and 2657240). No., No. 2660225, etc.). As one of the proposed technologies, a silicon ingot continuously produced in the chamber is drawn out from the outlet provided with a non-contact seal at the lower part of the chamber to the lower side of the chamber. Some are cut by a diamond cutter (Japanese Patent No. 2660225). This technology is indispensable for continuing casting for a long time, and plays a very important role in achieving mass production.
[0005]
[Problems to be solved by the invention]
However, the silicon ingot drawn out of the chamber is very hard as compared with a normal metal material, and is a high temperature of several hundred degrees Celsius just below the chamber. As far as the applicant knows, there has been no technology that can cut such a high-temperature, high-hardness silicon ingot without any problem. For this reason, in the past, cutting with a diamond cutter was performed at the stage where the ingot temperature was lowered to near room temperature, that is, considerably below the chamber.
[0006]
In other words, there are two methods for cutting a high-hardness material such as a silicon ingot, such as heat melting cutting using a laser or the like, and cutting cutting using a rotary diamond cutter. This is not applicable to the cutting of silicon ingots. For this reason, only cutting with a rotary diamond cutter can be applied to cutting a silicon ingot.
[0007]
A rotary diamond cutter is made by bonding and fixing diamond powder to the outer periphery of a circular base plate. While rotating this, it is cut into the material, but heat is generated by friction with the material, and this heat generation is left unattended. Then, the diamond peels or wears out early and becomes unusable, or the base plate is distorted. For this reason, in the cutting with a diamond cutter, so-called wet cutting is employed in which cutting is performed while spraying a large amount of cooling / lubricating medium such as water or oil on the cutting portion.
[0008]
However, the silicon ingot immediately after exiting the chamber is hot as described above. When wet cutting is performed on such a high-temperature silicon ingot, the high-temperature ingot is locally quenched due to the effect of vaporization and heat dissipation of the medium, and cracks and residual stress are generated due to thermal distortion. For this reason, wet cutting with a rotary diamond cutter has been performed at the stage where the ingot temperature has dropped to near room temperature, that is, considerably below the chamber.
[0009]
When the casting speed is slow, the distance that the ingot descends is small while the ingot temperature drops to near room temperature, and does not have a large effect on the equipment height etc. Recently, the ingot speed has been increased by various devices. Along with this, the diamond cutter has to be positioned several tens of meters below the chamber, and an increase in equipment height due to the lowered cutting position has become a very big problem.
[0010]
An object of the present invention is to provide a silicon ingot cutting method capable of cutting a high-temperature silicon ingot drawn out from a silicon casting apparatus that continuously casts silicon without any trouble directly under the casting apparatus.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors repeated various cutting experiments using a rotary diamond cutter in order to develop a method for cutting a high-temperature silicon ingot. As a result, if the ingot temperature is up to 650 ° C., the silicon ingot can be cut without any trouble by dry cutting without directly supplying a lubricating cooling medium such as water or oil to the cutting portion, and a relatively long cutter life can be obtained. It was found that it was secured. In addition, by providing a cut or opening in the outer periphery of the cutter or supplying a small amount of water or oil to the outer periphery, the cutter life can be further extended without adversely affecting the ingot. I also found out.
[0012]
The silicon ingot cutting method of the present invention has been developed based on such knowledge, and the ingot temperature of the silicon ingot drawn from the silicon casting apparatus for continuously casting silicon is measured by a rotary diamond cutter. Dry cutting is performed in the range of 250 to 650 ° C.
[0013]
The rotary diamond cutter preferably has a configuration that promotes cooling of the blade portion by the cutter cooling means. The cutter cooling means, there is an open mouth formed at predetermined intervals in the circumferential direction to cut and / or the outer peripheral surface near which is formed at predetermined intervals in the circumferential direction on the outer peripheral surface. Further, it is also effective cutter cooling means to supply a small amount of lubricating cooling liquid to the outer peripheral portion of the diamond cutter by spraying or coating, and it is particularly preferable to use in combination with notches or openings.
[0014]
In the silicon ingot cutting method of the present invention, dry cutting is employed, and the lubricating coolant is not directly supplied to the cut portion. Therefore, despite the ingot temperature being 250 ° C. or higher, thermal strain due to local rapid cooling ( Generation of cracks and residual stress) is prevented. Further, since the ingot temperature is limited to 650 ° C. or less (preferably 600 ° C. or less), diamond peeling or abrasion is suppressed despite a dry cutting, and a relatively long cutter life is ensured. . As a result, the high-temperature silicon ingot is cut directly under the silicon casting apparatus without any trouble.
[0015]
However, when the ingot temperature at the time of cutting exceeds 650 ° C., the cutter life is extremely deteriorated due to diamond carbonization. Moreover, when a mechanical impact is given to an ingot at a high temperature exceeding 650 ° C., there is a high risk of the ingot breaking. Furthermore, if the ingot is pulled out of the casting apparatus at such a high temperature, there is a risk of cracking due to thermal shock. On the other hand, when the ingot temperature at the time of cutting is less than 250 ° C., the distance from the casting apparatus to the cutting position becomes long, and an increase in equipment height becomes a problem. By the way, in order to make a silicon ingot less than 250 ° C., it takes about 25 hours even if it is not heated. When the casting speed is 2 mm / min, the distance from the casting apparatus to the cutting position is 3m or more.
[0016]
When a notch is provided on the outer peripheral surface of the diamond cutter or an opening is provided in the vicinity of the outer peripheral surface, air agitation is promoted and the heat radiation area is increased, so that the cooling of the diamond blade is promoted, and the cutter Life is further extended. Similarly, the outer peripheral portion of the diamond cutter, even when the cooling fluid was fed by Rikyo spray or coating, cooling of the diamond blade portion is promoted by the vaporization of the feed, even extending the cutter life. Further, the supply liquid is removed from the cutter by the vaporization and the supply of the liquid to the cutting portion is avoided, so that local rapid cooling of the ingot is prevented. When the liquid is supplied to the outer periphery of the cutter provided with cuts and openings, the cutter life is particularly effectively extended.
[0017]
The silicon casting apparatus includes not only an apparatus that continues casting substantially indefinitely but also a semi-continuous apparatus that continuously manufactures an ingot of a predetermined length. The raw material heating is not limited to the electromagnetic heating described above, and plasma heating or the like is also possible, and these can be used together. The cutting of the silicon ingot drawn out from the casting apparatus can be performed in a state where the ingot is descending or in a state where the descending is temporarily stopped. In the case where cutting is performed in a state in which the descent is temporarily stopped, the casting unit temporarily stops the supply of raw materials by limiting heating, for example.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a silicon casting facility showing an embodiment of the present invention, FIG. 2 is a plan view of a diamond cutter, and FIG. 3 is a view taken along line AA in FIG.
[0019]
As shown in FIG. 1, the silicon casting facility includes a silicon casting apparatus 20 that continuously manufactures the silicon ingot 10 and an ingot cutting apparatus 30 provided below the silicon casting apparatus 20.
[0020]
The silicon casting apparatus 20 includes a chamber 21 that houses a continuous casting portion and an ingot heat retaining portion. In the chamber 21, a rectangular tubeless bottomless crucible 23 combined with the induction coil 22 is provided. Below the bottomless crucible 23, a square tube-shaped first heat-retaining furnace 24 is provided, and further below that, a square tube-shaped second heat-retaining furnace 25 is provided.
[0021]
The bottomless crucible 23 is made of water-cooled copper and continuously produces the silicon ingot 10 in cooperation with the induction coil 22. For this production, the bottomless crucible 23 is divided into a plurality in the circumferential direction, leaving the upper end. Further, silicon raw material is introduced into the bottomless crucible 23 from a raw material hopper 27 provided above the chamber 21 through a duct 28. A plasma torch 26 is inserted into the bottomless crucible 23 from above for heating the charged raw material.
[0022]
The first heat-retaining furnace 24 arranged continuously below the bottomless crucible 23 is an induction heating type, and the second heat-retaining furnace 25 below is a temperature gradient type, and these are silicon ingots drawn from the bottomless crucible 23. 10 is given a predetermined temperature gradient in the axial direction. The silicon ingot 10 exiting from the second heat-retaining furnace 25 is drawn out of the chamber 21 from an outlet provided with a non-contact type or soft contact type seal and sent to the slab cutting device 30.
[0023]
The ingot cutting device 30 includes a rotary diamond cutter 31 disposed below the chamber 21 and a plurality of clamp mechanisms 32, 32... Disposed above and below the rotary diamond cutter 31. Is set so that the silicon ingot 10 drawn below the chamber 21 is cut in a temperature range of 250 to 650 ° C.
[0024]
As shown in FIGS. 2 and 3, the diamond cutter 31 of the ingot cutting device 30 has a horizontal circular base plate 31a that is rotationally driven at a predetermined speed and a diamond powder adhered to the outer periphery of the base plate 31a. It has the blade part 31b fixedly formed. As a cooling means for the diamond cutter 31, a large number of cuts 31c, 31c,... Are provided on the outer peripheral surface thereof at predetermined intervals in the circumferential direction. Further, in the vicinity of the outer peripheral surface of the diamond cutter 31, a large number of circular openings 31d, 31d,... Are provided at predetermined intervals in the circumferential direction separately from or along with the cuts 31c, 31c,. Yes.
[0025]
The diamond cutter 31 is cut at a right angle into the silicon ingot 10 drawn below the chamber 21 while rotating at a predetermined speed, thereby dry-cutting the silicon ingot 10 at a fixed position. In the vicinity of the diamond cutter 31, in order to supply a small amount of coolant such as water to the blade 31a of the diamond cutter 31, a spray mechanism 33 for coolant is provided as a cooling means.
[0026]
The plurality of clamp mechanisms 32, 32,... Are fixed to the plurality of columns 34, 34,..., And fix the silicon ingot 10 drawn below the chamber 21 at the top and bottom of the cutting portion when cutting. Except at the time of cutting, the clamp mechanisms 32, 32,... Release the silicon ingot 10 and allow its lowering.
[0027]
Next, a method for manufacturing the silicon ingot 10 using the above silicon casting equipment will be described.
[0028]
The inside of the chamber 21 is maintained in a predetermined inert gas atmosphere (normal pressure). With the bottom of the bottomless crucible 23 closed by a dummy ingot, the initial raw material is charged into the bottomless crucible 23 and melted by the induction coil 22 and the plasma torch 26 to form the raw material melt 11. While continuing to feed the raw material into the bottomless crucible 23, the raw material melt 11 in the bottomless crucible 23 is lowered and solidified. Thereby, the silicon ingot 10 is continuously drawn out from the bottomless crucible 23.
[0029]
The silicon ingot 10 drawn out from the bottomless crucible 23 passes through the first heat insulation furnace 24 and the second heat insulation furnace 25, and is given a predetermined temperature gradient in the axial direction in the process, and then below the chamber 21. Pulled out. The ingot temperature is, for example, about 600 to 800 ° C. at the time when the ingot temperature is drawn to the lower side of the heat-retaining furnace.
[0030]
The silicon ingot 10 drawn out below the chamber 21 passes through the ingot cutting device 30 and continues to grow below it. When the silicon ingot 10 having a predetermined length is manufactured below the diamond cutter 31, the descent of the silicon ingot 10 is temporarily stopped, and the silicon ingot 10 is cut by the ingot cutting device 30. During the temporary stop, the charging of the raw material in the bottomless crucible 23 is stopped and the heating of the raw material in the bottomless crucible 23 is restricted.
[0031]
When the silicon ingot 10 is cut by the ingot cutting device 30, the silicon ingot 10 is held and fixed by the plurality of clamp mechanisms 32, 32,. In this state, the silicon ingot 10 is dry-cut by the diamond cutter 31 without supplying liquid directly to the cutting portion. During cutting, a coolant such as water is sprayed onto the blade 31b of the diamond cutter 31 by the spray mechanism 33. The spray amount is vaporized and cut simultaneously with the spraying so that the dry cutting is not hindered. The amount is small enough not to be supplied to the part.
[0032]
When the cutting is finished, the cut silicon ingot 10 is taken out, casting is resumed, and the silicon ingot 10 having a predetermined length is manufactured below the diamond cutter 31 again. By repeating this, the silicon ingot 10 is continuously manufactured.
[0033]
In the cutting, dry cutting without direct liquid supply to the cutting part is used, so that although the ingot temperature at the time of cutting is 250 ° C. or higher, thermal strain (cracking) due to local rapid cooling. And residual stress) are prevented. In addition, since the ingot temperature at the time of cutting is limited to 650 ° C. or lower, diamond peeling or abrasion is suppressed despite a dry cutting, and a relatively long cutter life is ensured. By such ingot cutting at a high temperature, the distance from the chamber 21 to the diamond cutter 31 is reduced, and the equipment height is suppressed.
[0034]
【Example】
Next, the results of the present invention will be shown and compared with comparative examples to clarify the effects of the present invention.
[0035]
When the silicon ingot 10 drawn downward from the silicon casting apparatus 20 in the form of FIG. 1 is cut by the ingot cutting apparatus 30 by 800 mm, the ingot temperature (distance from the lower end of the heat-retaining furnace to the diamond cutter 31) at the time of cutting is determined. Various changes were made. Further, various cooling means for the diamond cutter 31 were changed.
[0036]
The total height of the silicon casting apparatus is about 8 m. A silicon ingot produced by a silicon casting apparatus is for a solar cell, and has a casting size of 160 mm square and a casting speed of 0.5 to 10 mm / min. In order to prevent cracking due to thermal shock of the silicon ingot drawn out from the silicon casting apparatus, the drawing temperature from the chamber was 650 ° C. except for some comparative examples. The diamond cutter used was obtained by uniformly applying diamond powder having a particle size of about 50 μm to the outer periphery of a base plate having a diameter of 550 mm × 2 mm in thickness and fixing with a fixing agent. The rotation speed was 2540 rpm and the cutting speed was 50 mm / min.
[0037]
Table 1 shows the results of investigation on the influence of the ingot temperature at the time of cutting on the cutter life and the distance from the lower end of the heat-retaining furnace to the cutter. The cutter life is expressed by the area of the silicon ingot, and the cross-sectional area of the ingot is 0.0256 m ² (0.16 m × 0.16 m). For example, when the cutter life is 1 m ² , the ingot is cut 39 times. Indicates that it was possible.
[0038]
As can be seen from Table 1, when the ingot temperature at the time of cutting is 700 ° C., the cutter life is extremely deteriorated. In addition, since cutting is performed at 700 ° C. outside the chamber, the drawing temperature from the chamber is increased from 650 ° C., so that the pulled silicon ingot may be cracked due to thermal shock. On the other hand, by limiting the ingot temperature at the time of cutting to 650 ° C. or less, it is possible to cut more than several tens of times with one cutter, and it is possible to cut about 200 times or more at 600 ° C. or less. . The cutter life is further extended by cutting the outer periphery of the cutter cooling means or spraying water. By using both, the cutter life is 1.5 times that of the case without the cutter cooling means. Reach. On the other hand, when the ingot temperature at the time of cutting is less than 200 ° C., the cutter life is not a problem, but the equipment height due to an increase in the distance from the lower end of the heat insulation furnace to the cutter becomes a problem. The incisions were provided with a width of 5 mm × depth of 25 mm at a pitch of 30 mm.
[0039]
[Table 1]

[0040]
【The invention's effect】
As described above, the silicon ingot cutting method according to the present invention cuts the silicon ingot drawn from the silicon casting apparatus for continuously casting silicon at a high temperature without trouble, so that the silicon ingot can be cut even when the casting speed is high. The distance from the casting device to the cutting position is suppressed, and it has a great effect in reducing the equipment height, reducing the equipment cost, and simplifying the maintenance.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a silicon casting facility showing an embodiment of the present invention.
FIG. 2 is a plan view showing an example of a diamond cutter.
FIG. 3 is a view taken along the line AA in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Silicon ingot 20 Silicon casting apparatus 21 Chamber 22 Inductive coil 23 Bottomless crucible 24, 25 Incubator 30 Ingot cutting apparatus 31 Diamond cutter 32 Clamp mechanism 33 Spray mechanism

Claims (3)

  A silicon ingot cutting method, characterized in that a silicon ingot drawn from a silicon casting apparatus for continuously casting silicon is dry-cut with a rotary diamond cutter in an ingot temperature range of 250 to 650 ° C. A diamond cutter rotary is claimed, characterized in that it comprises an opening formed at predetermined intervals in the circumferential direction on the switching interrupt and / or the outer peripheral surface near which is formed at predetermined intervals in the circumferential direction on the outer peripheral surface Item 2. The method for cutting a silicon ingot according to Item 1.   The silicon ingot cutting method according to claim 1 or 2, wherein a cooling liquid is supplied to the outer peripheral portion of the rotary diamond cutter by spraying or coating.

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