JP3993814B2 - Cutting method of polycrystalline silicon ingot - Google Patents

Description

【００３０】
表１から明らかなように、クラックが見られなかったのは、図３中のＡＢＣから切断した場合のみであることが分かる。このことから、最初にインゴットの側面方向から凝固方向に対して垂直に切断することでクラックのない切断が可能であることが確認された。
【００３１】
また、インゴットのインゴット１０の側面方向から凝固方向に対して垂直に切断した後、凝固方向に対して水平に切断することで、大型のインゴットでもクラックを発生させることなく切断できることが確認された。
【００３２】
【発明の効果】
以上のように、本発明に係る多結晶シリコンインゴットの切断方法によれば、一方向凝固させた多結晶シリコンインゴットを、前記凝固方向に対して垂直に切断する工程と、その後、前記切断された多結晶シリコンインゴットを、前記凝固方向に対して平行に切断する工程と、を有することからインゴット内の残留応力を緩和でき、クラックを生じることなく所望の大きさに切断することが可能となる。
【００３３】
また、多結晶シリコンインゴットの凝固方向に対して垂直に切断した後に、凝固方向に対して水平に切断することで、インゴット内の残留応力を緩和した後に、インゴットを所望の大きさに切断することになる。これにより、大型のインゴットもクラックを発生させることなく所望の大きさに切断することが可能となる。
【図面の簡単な説明】
【図１】本発明に係る切断方法の概略図である。
【図２】本発明に係る他の切断方法の概略図である。
【図３】本発明の実施例を説明するための図である。
【図４】従来のバンドソー型切断装置を示す図である。
【図５】インゴットのの上部と下部の応力状態を模式的に示す図である。
【図６】インゴットの切断面のクラックの状態を模式的に示す図である。
【符号の説明】
１・・・プーリー、２・・・ブレード、３・・・ブレード固定具、４・・・シリコンインゴット、５・・・作業テーブル、６・・・シリコンインゴットの縦断面、７・・・応力の方向、８・・・シリコンインゴットの切断面、９・・・クラック、１０・・・シリコンインゴット、１１・・・固定治具、１３・・・切断位置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cutting a polycrystalline silicon ingot, and more particularly to a method for cutting a polycrystalline silicon ingot that has been unidirectionally solidified.
[0002]
[Prior art]
A solar cell converts incident light energy into electrical energy. Major solar cells are classified into crystalline, amorphous, and compound types depending on the type of materials used. Of these, most of the crystalline silicon solar cells currently on the market are in the market. This crystalline silicon solar cell is further classified into a single crystal type and a polycrystalline type. Single-crystal silicon solar cells have the advantage that the substrate quality is good and the efficiency can be easily increased, but the substrate is expensive to manufacture. On the other hand, the polycrystalline silicon solar cell has the advantage that it can be manufactured at a low cost although it has the disadvantage that it is difficult to increase the efficiency because the quality of the substrate is inferior. In recent years, conversion efficiency of about 18% has been achieved at the research level due to the improvement of the quality of the polycrystalline silicon substrate and the advancement of cell technology.
[0003]
On the other hand, since mass-produced polycrystalline silicon solar cells are low in cost, they have been distributed in the market. However, in recent years, demands are increasing as environmental problems are addressed.
[0004]
A polycrystalline silicon substrate used for a polycrystalline silicon solar cell is generally manufactured by a method called a casting method. This casting method is a method of forming a silicon ingot by pouring a silicon raw material into a mold made of graphite or the like coated with a release material by melting it with a crucible and cooling and solidifying it. Other methods for producing a polycrystalline silicon ingot include a method in which a silicon raw material is melted in a mold and solidified as it is.
[0005]
The silicon ingot thus formed is cut to a desired size and sliced to a desired thickness to obtain a polycrystalline silicon substrate. There is a band saw type cutting apparatus as a general apparatus for cutting a polycrystalline silicon ingot.
[0006]
FIG. 4 is a schematic view of a conventional band saw type cutting device. In FIG. 4, 1 is a pulley, 2 is a blade, 3 is a blade fixture, 4 is a silicon ingot, and 5 is a work table. The silicon ingot 4 is cut by moving the blade 2 downward while driving the endless belt-like blade 2 stretched between the pulleys 1 at an appropriate speed.
[0007]
At this time, the silicon ingot 4 is directly fixed on the work table 5 (see, for example, the specification of Japanese Patent Application No. 2002-280999), or the bottom of the silicon ingot 4 is bonded and fixed to a base material such as carbon with a resin adhesive, The entire base material is cut (for example, see Japanese Patent Application No. 2002-281000). At this time, the casting surface that touched the mold on the side surface of the ingot is removed as an end material.
[0008]
Thereafter, the cut silicon ingot was sliced, and portions other than unnecessary portions called so-called end materials above and below the ingot were used as the silicon substrate.
[0009]
According to the above method, the end material on the side surface of the ingot is cut off by cutting, and the silicon substrate can be obtained simply by cutting to a desired size and then slicing, so that the silicon substrate can be obtained with the least number of man-hours. it can.
[0010]
[Problems to be solved by the invention]
However, according to the above method, when the ingot 4 is first cut horizontally with respect to the solidification direction, a cut crack 9 may occur on the cut surface 8 as shown in FIG. When cracks are generated in this way, the substrate cannot be cut out from that portion, and the yield is greatly reduced.
[0011]
This can be explained as follows. When a polycrystalline silicon ingot is formed by a casting method or the like, the molten silicon in the mold is formed by a so-called unidirectional solidification method in which it is gradually cooled and solidified from the lower part. That is, during the solidification of the ingot, the silicon at the lower part of the ingot is cooled and becomes solid first, and the upper part is not cooled yet and exists as a liquid.
[0012]
Since the molten silicon shrinks when it is cooled after being solidified, as shown in FIG. 5, the upper part of the ingot 4 that is solidified later, although it tries to shrink to the center, the lower part of the ingot 4 that has been solidified first. The force that cannot be contracted by being pulled is left. That is, a load directed toward the center of the ingot 4 is applied. Since the resisting stress acts on the inside of the object under load and balances, the outward stress remains in the upper part of the ingot 4, and conversely, in the lower part of the ingot 4, the load is directed toward the inside of the upper part. Since an opposite outward load is applied, an inward stress remains. FIG. 5 is a schematic diagram of stresses at the upper and lower ingots in the longitudinal section of the ingot.
[0013]
As shown in FIG. 5, the upper and lower portions of the ingot 4 are perpendicular to the solidification direction of the ingot, the upper portion has an outward tensile stress, and the lower portion has an inward compressive stress. . Since the uppermost part of the ingot 4 is open, the stress escapes to some extent, but the inward compressive stress is concentrated most strongly in the lowermost part of the ingot 4.
[0014]
As described above, when the ingot 4 in which the stress in the direction opposite to the direction perpendicular to the solidification direction remains on the top and bottom of the ingot 4 is cut horizontally in the direction of the solidification, the stress in the reverse direction is released at a stroke. As a result, the balance of stress cannot be balanced, and as shown in FIG.
[0015]
This invention is made | formed in view of such a problem, and it aims at providing the cutting method which a crack does not produce in a cut surface.
[0016]
[Means for Solving the Problems]
The method for cutting a polycrystalline silicon ingot according to the present invention comprises a step of cutting a unidirectionally solidified polycrystalline silicon ingot perpendicularly to the solidification direction, and then the cutting of the polycrystalline silicon ingot to the solidified state. Cutting in parallel to the direction and dividing into a plurality of ingots .
[0017]
The method for cutting a polycrystalline silicon ingot of the present invention, the polycrystalline silicon ingot, characterized Rukoto is unidirectional solidification from the bottom of the mold toward the upper by a casting method.
[0018]
The method for cutting a polycrystalline silicon ingot according to the present invention is characterized in that the polycrystalline silicon ingot is divided into a plurality of ingots by an endless belt-like blade stretched between two or more pulleys that are rotationally driven.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for cutting a polycrystalline silicon ingot according to the present invention will be described in detail with reference to the drawings. A method for cutting a polycrystalline silicon ingot according to the present invention is shown in FIG. In FIG. 1, 1 is a pulley, 2 is a blade, 3 is a blade fixture, 5 is a work table, 10 is a silicon ingot, and 11 is a silicon ingot fixing jig. The basic structure of the band saw type cutting machine is the same as the schematic diagram of the general band saw type cutting apparatus shown in FIG.
[0020]
First, the silicon ingot 10 is placed on the work table 5 in a state where the upper and lower portions are located sideways, that is, in a state where the side faces are located on the upper side and the blade 2 is perpendicular to the solidification direction of the silicon ingot 10. Install. At this time, the silicon ingot 10 is pressed and fixed with a fixing jig 11 fixed to the work table 5, or can be cut with high accuracy by being bonded and fixed to a base material such as carbon.
[0021]
Next, the blade 2 is lowered while being orbited and cut perpendicularly to the solidification direction of the silicon ingot 10. The blade rotation speed when cutting is about 50 m / min to 400 m / min, and the blade lowering speed is 15 mm / sec to 50 mm / sec.
[0022]
By cutting perpendicularly from the side surface direction of the silicon ingot 10 to the solidification direction in this way, stress in the direction perpendicular to the solidification direction remaining in the ingot 10 and the direction opposite to the upper and lower directions is relieved. Further, it is possible to perform cutting without causing cracks on the cut surface.
[0023]
The present application is effective even for an ingot having a relatively small temperature difference in the solidification direction and a short ingot length. However, the longer the ingot length, the larger the upper and lower temperature difference and the greater the residual stress.
[0024]
By the way, in recent years, the silicon ingot 10 has been increased in size to, for example, 350 mm × 350 mm × 350 mm from the viewpoint of improving productivity. Therefore, when a 150 mm square ingot is obtained from the silicon ingot 10, the desired ingot 10 cannot be obtained simply by cutting from the side surface direction of the ingot 10 perpendicularly to the solidification direction.
[0025]
An outline of the cutting method in such a case is shown in FIG. In FIG. 2, 12 indicates a silicon ingot after being cut perpendicularly to the solidification direction from the side surface direction of the ingot 10 by the method described above, and 13 indicates a cutting position. The silicon ingot 12 that has been cut perpendicularly to the solidification direction from the side surface direction of the ingot 10 is placed on the work table 5 so that the blade 2 enters horizontally with respect to the solidification (growth). Thereafter, the blade 2 is lowered while being rotated, and is cut at a cutting position 13 that is horizontal with respect to the solidification direction of the ingot 10, whereby a desired silicon ingot 10 (12) divided into four can be obtained.
[0026]
At this time, since the reverse stress remaining on the top and bottom of the ingot 10 is relaxed by cutting first in a direction perpendicular to the solidification direction of the ingot 10, the cutting is performed horizontally with respect to the solidification direction of the ingot 10. Even if it goes, there is no crack on the cut surface. Here, an example has been described in which the upper and lower portions of the silicon ingot 10 are positioned sideways, that is, the side surface is positioned upward, but the side surface of the ingot 10 is cut even when the upper and lower portions of the ingot 10 are positioned upward. If it is after cutting perpendicularly to the solidification direction from the direction, no cracks will occur on the cut surface.
[0027]
Further, the apparatus for fixing the silicon ingot 10 to the work table 5 and lowering the blade 2 of the band saw type cutting machine from above has been described as an example. For example, the silicon ingot 10 is lifted from below with respect to the blade 2 fixed upward. It is possible to cut by cutting, and it is also possible to position the silicon ingot 10 upward and the blade 2 downward.
[0028]
【Example】
Next, an embodiment of the present invention will be described with reference to FIG. The silicon ingot 10 shown in FIG. 3 is solidified in one direction from the bottom to the top in the figure. The dotted line in FIG. 3 indicates the cutting position. That is, the silicon ingot 10 is cut by positioning the blade at the position of these dotted lines and cutting vertically from there. A 350 mm × 350 mm × 350 mm silicon ingot was manufactured by a casting method in which 70 kg of silicon raw material dissolved in a quartz crucible was poured into a mold, and was cut by changing the cutting order. The results are shown in Table 1.
[0029]
[Table 1]

[0030]
As is clear from Table 1, it can be seen that cracks were not observed only when cut from ABC in FIG. From this, it was confirmed that cutting without cracks was possible by first cutting from the side surface direction of the ingot perpendicularly to the solidification direction.
[0031]
Further, it was confirmed that a large ingot can be cut without causing cracks by cutting perpendicularly to the solidification direction from the side surface direction of the ingot 10 of the ingot and then cutting horizontally to the solidification direction.
[0032]
【The invention's effect】
As described above, according to the method for cutting a polycrystalline silicon ingot according to the present invention, the step of cutting the polycrystalline silicon ingot solidified in one direction perpendicularly to the solidification direction, and then the cutting The step of cutting the polycrystalline silicon ingot in parallel to the solidification direction can relieve the residual stress in the ingot and can be cut to a desired size without causing cracks.
[0033]
In addition, after cutting perpendicularly to the solidification direction of the polycrystalline silicon ingot, cutting the ingot to a desired size after relaxing the residual stress in the ingot by cutting horizontally to the solidification direction become. Thereby, a large ingot can be cut into a desired size without generating cracks.
[Brief description of the drawings]
FIG. 1 is a schematic view of a cutting method according to the present invention.
FIG. 2 is a schematic view of another cutting method according to the present invention.
FIG. 3 is a diagram for explaining an embodiment of the present invention.
FIG. 4 is a view showing a conventional band saw type cutting device.
FIG. 5 is a diagram schematically showing the stress state of the upper part and the lower part of the ingot.
FIG. 6 is a diagram schematically showing the state of cracks on the cut surface of the ingot.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Pulley, 2 ... Blade, 3 ... Blade fixing tool, 4 ... Silicon ingot, 5 ... Work table, 6 ... Longitudinal section of silicon ingot, 7 ... Stress Direction, 8 ... cutting surface of silicon ingot, 9 ... crack, 10 ... silicon ingot, 11 ... fixing jig, 13 ... cutting position

Claims (3)

Cutting the unidirectionally solidified polycrystalline silicon ingot perpendicularly to the solidification direction;
And then cutting the cut polycrystalline silicon ingot in parallel to the solidification direction and dividing it into a plurality of ingots . The polycrystalline silicon ingot cutting method of polycrystalline silicon ingot according to claim 1, characterized in Rukoto is unidirectional solidification from the bottom of the mold toward the upper by a casting method. 3. The polycrystalline silicon ingot according to claim 1, wherein the polycrystalline silicon ingot is divided into a plurality of ingots by an endless belt-like blade stretched between two or more pulleys that are rotationally driven. Cutting method.

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