JPS58162029A - Preparation of polycrystalline silicon wafer - Google Patents

Abstract

PURPOSE:To make high module loading density by forming the wafer forming plain having the desired shape of circumference at the surface on the same axis of the rotating center of the turn table, supplying molten liquid of silicon, flowing it in the radius direction by a centrifugal force and by releasing the overflowing liquid from the external circumferencial edge. CONSTITUTION:A silicon low material is put into a crucible 1 and heated until it melts. The molten liquid is dropped to the center of wafer forming plane 6 from the outlet 4' of a funnel 4. The molten liquid flows in the radius direction by a centrifugal force generated by rotation of the turn table 5. The wafer plate 9 having the wafer forming plane 6 of the desired shape such as circular of square shape is prepared, and when sufficient amount of molten liquid is prepared, the liquid flows until the external circumferencial edge and the overflowing liquid is released from the external circumferencial edge and thereby a thin liquid layer 14 matching the shape of the wafer forming plate 6 can be formed. It is then cooled and hardened, completing a polycrystalline silicon wafer.

Description

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

Conventionally, polycrystalline silicon wafers have been manufactured by various methods, and the most common method is to cast an ingot of a predetermined shape from a silicon base material and then obtain wafers by slicing the ingot. In this case, not only does the slicing operation take a lot of time, but also about 50 inches of the ingot is lost during slicing, making the product expensive and making mass production impossible.

Therefore, the ribbon method and the casting method (casting method) have already been implemented as methods that do not rely on slide negative n − [1,/l
In the ribbon method, for example, molten silicon is sprayed onto the surface of a rotating drum to form a ribbon-shaped wafer on the surface, and when this method is used, it is actually possible to manufacture only wafers with a rise width of a few centimeters. However, it is difficult to obtain large-sized solar cell materials.

In addition, in the casting method mentioned above, 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 by the movable parts of the mold. When using this method, wafers with 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 will be done.

For this reason, in this method, the upper and lower surfaces and side surfaces of the mold suppress the growth of L1 silicon crystal grains (grains) during solidification of the melt, and the vicinity of the portions of the solidified product in contact with each of the surfaces is extremely Because the crystal grains become fine and large crystal grains cannot be obtained, it is not possible to satisfy the requirement of large crystal grain generation, which is considered desirable in silicon wafers for solar cells. The photoelectric conversion efficiency of the battery also has a defect that is extremely poor, reaching 2 to 3 inches.

Therefore, the applicant has first attempted to obtain a desired diameter by making the melt of the silicon base material on the turntable flow in the direction of diameter expansion by the centrifugal force generated by the rotation of the turntable in a desired atmosphere. We proposed a method for manufacturing polycrystalline silicon Unihara by forming a thin layer of melt and solidifying it.

However, if the melt is caused to expand in diameter by centrifugal force as described above, a radial force acts on the melt, and the resulting wafer will have a circular plate shape.

However, when trying to create a solar cell module using solar cells manufactured using this method, it becomes difficult to lay the required number of solar cells within a predetermined area. The ratio of the battery 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 circularly formed wafer into semicircular, square, etc. shapes. This method has poor workability and is not economically viable.

The present invention improves the above-described wafer manufacturing method using centrifugal force, and is suitable for manufacturing wafers that can be readily applied to the production of solar cells that can increase module loading density. Even when trying to obtain a wafer, it is possible to easily manufacture a wafer with a desired outer diameter dimension.The first aspect of the invention is characterized by a turntable that can be used to obtain a wafer having a desired outer diameter shape. The tapered Ueno (formation plane is formed coaxially with the rotation center of the mechanism, and a melt of the silicon base material is supplied to the tapered formation plane in a desired atmosphere,
By causing the supplied melt to flow in the radially expanding direction by the shelf center force caused by the rotation of the turntable, the excess supplied melt is discharged from the outer periphery of the wafer forming plane. This is because a thin layer of melt is formed over the entire surface and this is cooled and solidified. First, the above-mentioned invention will be described in detail with reference to drawings. To be more specific, in the example of equipment shown in Fig. 1, a heat source for melting (2) such as an electric heater is installed on the outer circumferential side of the crucible +11.
The silicon base material put into the crucible (0) is heated to the same heat source (2).
), the silicon can be melted by heating it in consideration of its melting temperature of 1420°C, and the heat source (2) may be an electric heating wire as shown in the example, or a high-frequency heating device. Of course, it is desirable to be able to stop the heating at an appropriate time and to control the heating conditions.

In addition, as the silicon base material, metal grade silicon, semiconductor grade high purity silicon, etc. are used, and a crucible (1
) is used as a material such as quartz or graphite, which has little reactivity with silicon, and in the illustrated example, by rotating it around the center of rotation (3) of the crucible t11 as a rolling axis,
The melt of the silicon base material can be discharged from the opening, and a funnel (4) also made of quartz, graphite, etc. is arranged directly below the crucible +11. is also placed under heating conditions by the melting heat #(2), and the turntable mechanism (5) placed directly below it is also placed relatively close so that it can be heated by the same heat source (2).

In the turntable mechanism t5), a wafer forming plane (6) is formed on the turntable (5)', and a collection tray (7) is arranged on the outer circumferential side of the table (5)'. has been done.

In the embodiment shown in FIGS. 1 and 2,
The turntable (5)' is equipped with a rotation shaft (8) and the collection tray (7) fixedly installed via the pedestal (8)', and the wafer forming plane ( 6
) is located on the bottom surface (7)' of the collection tray (7) and is formed as the upper surface of the wafer tray]9) placed at the axial center position.

The collection tray (7) has a raised q peripheral edge 0I that stands up from the outer periphery of the bottom surface (71'), and the peripheral edge α is projected to a higher place than the wafer tray (9), and the quartz , is preferably formed from gelaphite.

On the other hand, in the embodiment shown in FIG. The wafer plate (9) is placed at the center position, and the wafer forming plane (6) of the turntable (5) is set as the top surface of the concave plate (9). It can also be a wafer forming plane (6).

Furthermore, in the same embodiment, the collection tray (7) is separated from the turntable (5), and in the illustrated example, the bottom surface of the collection tray (7) provided at a predetermined fixing point (Iz) A shaft hole 0 is bored in 7)', into which the rotating shaft (8) is loosely fitted.

In order to carry out the first invention using the above equipment example, the silicon base material is put into the crucible f11, heated and melted by the melting heat source (2), and the melt is transferred to the crucible 11+. Discharge the water into the funnel (4), then pour it into the funnel (4).
The melt is received by the turntable (5), and then the melt is dripped from the turntable (41') onto the approximate center of the wafer forming plane (6) as shown by the dotted line in the figure.
) is preferably rotated in advance, but the rotation may be started simultaneously or before the melt solidifies after the completion of dropping, and the centrifugal force caused by the rotation causes the melt to flow in the direction of diameter expansion.

Here, as the wafer dish (9), one having a wafer forming plane (6) of a desired shape such as circular or rectangular of various dimensions is recommended, and this can be arbitrarily selected. If the amount is sufficient, the melt in the expanding diameter flow will flow onto the wafer forming plane (
6), the diameter is expanded at the outer periphery #1t, and the excess supply of melt is released from the outer periphery by centrifugal force, resulting in a melt thin I that matches the shape of the wafer forming plane (6).
I(14) is formed and solidified by natural cooling or by an appropriate cooling means to obtain a multi-result silicon wafer as a product.

When using the above equipment example, the wafer forming plane (6)
The silicon melt ejected from the outer periphery is received by the collection tray (7), where it is cooled and solidified, making it possible to reuse the silicon.

To give a specific example, a wafer plate (9) made of graphite with a thickness of 5 cm is used, and the inner diameter is 180 m.

Using a quartz collection tray (7) with a depth of 20 m, the humidity of the wafer tray (9) is maintained at 800°C to 13'0 using the equipment example shown in Figure 2.
Control the temperature to 0℃, and turn the turntable (5)' to 10℃.
Rotate at 0 to 500 r, p, m, melt the silicon base material of the quartz crucible f11 at 1455°C, and then supply the melt to the wafer forming plane (6) as described above,
A product of 50+a+X50m, diameter 70+m, and 100+s was obtained.

Next, a second invention is the first invention, further comprising an outer surface (9)' that is continuous with the outer edge of the wafer plate (9).
It is characterized by the fact that an anti-wetting agent made of boron nitride or the like is pre-applied as shown in FIG. Depending on various conditions such as the number of silicon melts, the amount of silicon melt supplied, the thickness of the wafer to be obtained, and other mechanical factors, the melt released from the wafer forming plane (6) may scatter onto the collection tray (7). Otherwise, the product may flow down to the outer surface (9)' of the ueno plate (9), and if this is not the case, the product obtained as shown in Fig. , it becomes a dish-shaped thing with a hanging edge B that is solidified integrally with this,
In such a product, the upper hanging edge B must be shaved off.

In the second invention, since the step of applying boron nitride or the like to the outer surface (9)' is added as described above, the wafer plate (9)'
) is repelled by the boron nitride, does not integrate with the melt on the wafer forming plane (6), and is completely collected and collected [+11 +71
accepted.

As described in detail above, the present invention supplies a larger amount of silicon than the amount of silicon required for the resulting wafer product to a wafer forming plane formed into a desired shape, and removes the excess silicon by centrifugal force.
Since the product is emitted from the outer periphery of the wafer forming plane to obtain a product having the same shape as the plane, it is possible to easily obtain a product with the desired specifications by selecting the wafer forming plane, especially when creating a solar cell module. In this case, solar cells that can increase the module loading density can be easily provided without the need for secondary fabric, and circular wafers of various sizes can be used depending on the rotation speed of the turntable and the wafer plate. temperature of,
It can be manufactured without requiring strict control over the height of the funnel, etc.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front explanatory view showing an example of equipment that can be used to carry out the manufacturing method according to the present invention, FIG. 2 is a partially cutaway front view showing a turntable mechanism of the same example of equipment, and FIG. 4 is a partially cutaway front view of the same turntable mechanism according to another embodiment, and FIG. 4 is a partially cutaway front view of the turntable mechanism showing an abnormal state of a product wafer. (5)...Turntable mechanism (6)...Wafer forming plane A...Thin layer of melt O9...-Wetting prevention IE agent patent applicant representative Patent attorney Makoto Ito @ 1 Figure 2 Figure 3 Rod 4 Figure

Claims (1)

[Claims] In the Fi+ turntable mechanism, a wafer forming plane with a desired outer peripheral shape is formed on the top surface coaxially with the rotation center of the mechanism, and the wafer forming plane has a silicon matrix formed in a desired atmosphere. Supplying a melt of the material and causing the supplied melt to flow in the direction of diameter expansion due to the centrifugal force caused by the rotation of the one turntable, thereby releasing the excessively supplied melt from the outer peripheral edge of the wafer forming plane. A method for manufacturing a polycrystalline silicon wafer, characterized in that a thin layer of melt is formed over the entire surface of the wafer forming plane using the supplied melt, and the thin layer is cooled and solidified. (2) The turntable mechanism has a wafer forming plane with a desired outer peripheral shape formed on the top surface coaxially with the rotation center of the mechanism, and the outer surface continuous with the wafer forming plane is wetted with boron nitride or the like. By applying a preventive agent, supplying a silicon base material melt to the wafer forming plane in a desired atmosphere, and causing the supplied melt to flow in the direction of diameter expansion by the centrifugal force caused by the rotation of the turntable mechanism, By discharging the excess melt from the outer periphery of the wafer forming plane, a thin layer of the supplied melt is formed over the entire surface of the wafer forming plane, and this is cooled and solidified. Method for manufacturing polycrystalline silicon wafers.