JPH049370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to a method for manufacturing polycrystalline silicon wafers used in solar cells and other photoelectric conversion elements.

<Prior Art> Polycrystalline silicon wafers have traditionally been manufactured by various methods, most commonly by casting an ingot of a predetermined shape from a silicon base material and slicing it. However, this method not only requires a lot of time for slicing, but also results in about 50% of the ingot being lost during slicing, making the product expensive and requiring mass production. is also impossible.

Therefore, the ribbon method and casting method (casting method) have already been implemented as methods that do not involve slicing, but in the ribbon method, for example, molten silicon is sprayed onto the peripheral surface of a rotating drum, and a ribbon-shaped wafer is placed on the peripheral surface of the drum. When using this method, it is actually possible to manufacture ribbons with a width of only a few mm, which has the disadvantage that large-sized solar cell materials cannot be obtained.

In addition, in the above-mentioned casting 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 melt is pressed and molded by the movable parts of the mold. However, when this method is used, wafers of a predetermined shape can be obtained at once, and desirable results can be expected in terms of mass production.As mentioned above, the melt is pressed down from all sides. It turns out.

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 that contact the above-mentioned surfaces are extremely The crystal grains become fine and large crystal grains cannot be obtained, and the requirement for large crystal grain generation, which is considered desirable for silicon wafers for solar cells, etc., cannot be satisfied. The photovoltaic conversion efficiency of solar cells is also extremely poor at 2 to 3%.

Therefore, the applicant first needs to be in the desired atmosphere,
By causing the melt of the silicon base material on the turntable to flow in the direction of diameter expansion due to the centrifugal force generated by the rotation of the turntable, a thin layer of melt with a desired diameter is formed by the melt, and this is solidified. A method for manufacturing polycrystalline silicon wafers was proposed.

However, if the melt is caused to expand in diameter by centrifugal force as described above, a radial force acts on the melt, so
The shape of the obtained wafer is a circular plate.

However, when trying to create a solar cell module using solar cells manufactured in this way, the required number of solar cells must be laid within a predetermined area, so if the outer shape of the solar cell is circular, The ratio of the solar cells to the above-mentioned predetermined area of the module, that is, the module loading density, becomes smaller, and for this reason, solar cells are created by cutting a circular wafer into semicircular, square, etc. shapes. However, this method has poor workability and is not economically viable.

Therefore, the present applicant has improved the above-described wafer manufacturing method using centrifugal force to provide a wafer manufacturing method that can be readily applied to the manufacturing of solar cells that can increase the module loading density.

In this case, equipment as shown in FIG. 1 is prepared, in which a melting heat source 2 such as an electric heater is placed on the outer periphery of the crucible 1.
The silicon base material placed in the crucible 1 can be melted by heating it with the same heat source 2, taking into account the melting temperature of the silicon of 1420°C. It is possible to use a heating wire or a high-frequency heating device, as shown in FIG.

Further, as the silicon base material, metal-grade silicon, semiconductor-grade high-purity silicon, etc. are used, and as the material for the crucible 1, quartz, graphite, etc., which have little reactivity with silicon, are used. By rotating the center of rotation 3 as a rolling axis, the melt of the silicon base material can be discharged from its opening. The funnel 4 is also placed under heating conditions by the heat source 2 for melting, and the turntable mechanism 5 placed directly below it is also placed relatively nearby so that it can be heated by the heat source 2. It is located in

The turntable mechanism 5 has a wafer tray 8 placed on a recovery tray 7 fixedly attached to the rotating shaft 6, and a wafer forming plane 9 is formed on the upper surface of the tray 8.

In order to manufacture polycrystalline silicon wafers using the above equipment, a silicon base material is put into the crucible 1, heated and melted by the melting heat source 2, and the melt is transferred by the rolling movement of the crucible 1. Pour into funnel 4,
Once received by the funnel 4, the melt is dropped from the outlet 4' onto the approximate center of the wafer forming plane 9, as shown by the dotted line in the figure.

At this time, it is preferable to rotate the turntable mechanism 5 in advance, but the rotation may be started at the same time or before the melt solidifies after the dropping is completed, and the centrifugal force caused by the rotation causes the melt to flows in the direction of diameter expansion.

Here, as the wafer plate 8, circular plates of various sizes,
A wafer forming plane 9 having a desired shape such as a rectangular shape is prepared and used as desired. However, if the above-mentioned melt supply amount is sufficient, the diameter-expanding flow of melt will spread over the wafer forming plane 9. The diameter is expanded over the entire surface to the outer periphery, and the excess supply of melt is discharged from the outer periphery by centrifugal force. As a result, a thin layer 14 of melt corresponding to the shape of the wafer forming plane 9 is formed, and this is naturally spread. Solidify by cooling or by appropriate cooling means,
The product, polycrystalline silicon wafer, is obtained.

However, when using the above manufacturing method, the separately prepared wafer tray 8 is placed on the collection tray 7 of the turntable mechanism 5, so the temperature control of the wafer tray is dependent on the location of the collection tray 7. In addition, since the wafer plate 8 is only placed on the table, if it is eccentric from the rotation center of the turntable mechanism 5, when the rotation speed of the turntable mechanism 5 increases, the wafer plate 8 may The wafer tray 8 may fluctuate and may fly outward in some cases, and the wafer tray 8 must be replaced and placed in order to manufacture various desired wafers.
It is undesirable to fix the turntable mechanism 5 to the collection tray 7, and if it were to be fixed, the turntable mechanism 5 would become structurally complicated.

Furthermore, when using the above method, depending on various conditions such as the rotation speed of the turntable 5', the amount of silicon melt supplied, the thickness of the wafer to be obtained, and other mechanical factors, the distance from the wafer forming plane 9 may vary. The released melt may not be scattered to the collection tray 7 and may flow down to the outer surface 8' of the wafer tray 8. In such a case, the obtained product will be transferred to the flat plate part A as shown in FIG. Not only that, but it also becomes a dish-shaped product with a hanging edge B that is solidified integrally with the product, and in the case of such a product, the hanging edge B must be scraped off.

<<Problems to be Solved by the Present Invention>> The present invention has been studied in view of the above-mentioned difficulties.
In particular, the wafer forming plane on which a mold release agent has been applied to the turntable is formed into a desired shape such as a circle or semicircle, and the outer periphery is coated with nitride, which has greater wettability to silicon than the mold release agent. In addition to forming a surplus silicon release plane due to boron,
By forming the height of the wafer forming plane to be equal to or lower than the height of the excess silicon release plane, polycrystalline silicon can be formed into a desired shape such as circular or square, regardless of the shape of the turntable. The wafer can be formed freely by adjusting the application distribution of boron nitride and the mold release agent, and of course the turntable can be used any number of times, and there is no protrusion or dripping of the outer periphery.
Its main purpose is to ensure a clean finish and to allow easy and rapid peeling of the product from the turntable.

<<Example>> The present invention will be described in detail below with reference to the drawings. First, the difference between the above-mentioned equipment examples lies in the turntable mechanism.

That is, as shown in FIG. 3, the turntable mechanism 10 has a turntable 12 fixedly attached to its rotating shaft 11. The table 12 has a coating flat surface 13 formed thereon, and the outer periphery of the flat surface 13. An excess silicon release plane 14 is formed by applying boron nitride to the inner edge 1 of the plane.
4', a wafer forming plane 1 is formed on the plane 13.
5 is formed coaxially with the rotation center of the mechanism 10, and the wafer plate 8 as described above is not used in the present invention.

Here, the shape of the wafer forming plane 15 forms a recess determined by the inner edge 14' so as to have a circular, square or other desired external shape for the shape of the wafer to be obtained, and further, Figures 3 and 4
As shown in the figure, the wafer forming plane 15 does not use the coating plane 13 itself in the recess as it is, but applies a mold release agent 16 such as silicon nitride or silicon carbide (SiC) to the same plane 13. It is. At this time, the mold release agent 16 contains more than the aforementioned boron nitride.
The surface of the agent 16 is used as the wafer forming plane 15 by selecting a material with high wettability to silicon, and in this case, the wafer forming plane 15 and the excess silicon release plane 14 are flush with each other. The height of the wafer forming plane 15 is lower than that of the excess silicon emitting plane 14, and in the illustrated embodiment, the turntable 12
However, in the illustrated embodiment, the turntable 12
However, it includes not only the bottom plate part 17 for forming the coating plane 13 but also an upright peripheral edge part 18 that stands up from the outer peripheral edge of the bottom plate part 17. Part 18
It is best to apply this to the inside of the body.

Therefore, in order to carry out the present invention, the melt of the silicon base material is supplied to the center of the wafer forming plane 15 using the equipment shown in FIG. It is preferable that the device be placed inside a suitable container and filled with an inert gas.

Thus, by the rotation of the turntable mechanism 5,
When the supplied melt flows over the entire surface of the wafer forming plane 15 formed by the mold release agent 16 and attempts to expand the diameter further, the melt flows into the excess silicon release plane 14, but the plane 14 Since it is made of boron nitride and has no wettability with any substance and is stable even at high temperatures, the discharged melt is scattered by the centrifugal force and solidified on the flat surface 14. , can be recovered and reused, and thus, on the mold release agent 16, which has greater wettability to silicon than the boron nitride applied to the wafer forming plane 15, which has been preformed into the desired shape, A thin melt layer 19 is formed over the entire surface by the supplied melt, and this is cooled by natural cooling, strong cooling, etc. to solidify and obtain a product.

Up to this point, if the surface of the mold release agent 16 is at the same level as the excess silicon release plane 14 as described above, the melt portion will not hang down from the wafer forming plane 15 as shown in FIG. Mold release agent 16
When the surface of the molten liquid is located at a lower level than the surplus silicon release plane 14, the inner edge 14' prevents the melt from further expanding its diameter, and the melt protrudes to a higher level than the excess silicon release plane 14. Even if an attempt is made to further expand the diameter of the melted part, as in the case of the previous example,
Excess silicon is emitted and scattered due to the arrangement of the boron nitride discharge plane 14, and a thin melt layer 19 regulated by the inner edge 14' of the plane 14 is eventually formed, which can be cooled and solidified to form a product. can.

Here is a specific example: inner diameter 180mm, depth 20mm
A turntable 5' is formed using a quartz plate, and the center of the turntable 5' is formed by aligning the center of silicon nitride application to form a wafer forming plane 15, and boron nitride is applied to the remaining part by spraying or paste. The turntable mechanism is rotated at 100 to 500 rpm and the temperature is controlled to 800 to 1300℃.
Molten silicon was allowed to flow down to produce a 50 mm x 50 mm rectangular wafer having the same shape as the wafer forming plane 15 and a circular wafer having a diameter of 100 mm.

<<Effects of the Invention>> Since the present invention is realized by the above-described embodiment, there is no need to place a wafer plate on the turntable mechanism, there is no problem caused by involuntary movement of the wafer plate, and boron nitride, By simply changing the application distribution of a mold release agent that has higher wettability to silicon than this, it is possible to easily form any shape of wafer formation plane by using the same turntable as many times as the substrate. Therefore, it is possible to manufacture not only disc-shaped wafers but also polygonal and other arbitrary-shaped wafers without much effort.In particular, when creating solar cell modules, solar cells that can increase the module loading density are two-dimensional. It is possible to easily provide circular wafers without the hassle of subsequent processing, and also to manufacture circular wafers of various sizes without strictly controlling the rotation speed of the turntable. Either the surface of the boron nitride is flush with the surface of the boron nitride, or the surface of the boron nitride is raised, so the outer periphery of the resulting polycrystalline silicon wafer is also
In addition, since the product is obtained on a mold release agent, it is easy to peel it off, and by not using a wafer plate, it is easy to heat the wafer forming surface appropriately. By applying boron nitride, it is also possible to recover the silicon melt scattered by centrifugal force.

[Brief explanation of drawings]

Figure 1 is a partially cutaway front explanatory view of equipment that can be used to carry out the polycrystalline silicon wafer manufacturing method previously proposed by the applicant, and Figure 2 is a diagram showing the turntable mechanism of the equipment. Front view of partial cutout,
FIG. 3 is a partially cutaway front view of the turntable mechanism used to carry out the method according to the present invention, and FIG. 4 is an explanatory plan view of the turntable mechanism. DESCRIPTION OF SYMBOLS 10... Turntable mechanism, 11... Rotating shaft, 12... Turntable, 13... Coating plane, 14... Surplus silicon release plane, 14'...
Inner edge, 15... Wafer forming plane, 16... Mold release agent, 19... Melt thin layer.

Claims (1)

[Claims] 1. A turntable mechanism is provided with a turntable on its upper part, and boron nitride is applied to the outer periphery of the application plane of the turntable to form an excess silicon release plane. A recess with the desired external shape is formed in the center of the table, and a release agent with greater wettability for silicon than the boron nitride described above is applied to the recess, thereby making the wafer forming plane continuous with the surplus silicon release plane. The wafer formation plane and the surplus silicon release plane are flush with each other, or the wafer formation plane is formed at a lower level than the surplus silicon release plane, and the wafer formation plane is formed coaxially with the rotation center of the turntable mechanism. A melt of the silicon base material is supplied to the flat surface in a desired atmosphere, and the supplied melt is caused to flow in the direction of diameter expansion by the centrifugal force generated by the rotation of the turntable mechanism, thereby removing excess melt. By discharging the surplus silicon from the outer peripheral edge of the wafer forming plane to the surplus silicon releasing plane, a thin solution layer is formed over the entire surface of the wafer forming plane by the supplied solution, and the obtained solution is cooled and solidified. A method for producing a polycrystalline silicon wafer, characterized in that the wafer is peeled off from a plane on which the wafer is formed using a molding agent. 2. The method for manufacturing a polycrystalline silicon wafer according to claim 1, wherein the turntable is formed by a lower plate portion and an upright peripheral edge portion that stands up from the outer peripheral end of the turntable.