JPH0328818B2 - - Google Patents

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, most commonly by casting an ingot of a predetermined shape from a silicon base material and slicing it to obtain wafers. However, not only does the slicing process take a lot of time, but about 50% of the ingot is lost during slicing, making the product expensive and impossible to mass produce. .

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, the above-mentioned casting method heats the silicon base material to form a melt, pours it into a mold according to the dimensions of the product wafer, and then presses and molds the melt using the movable parts of the mold. However, when using this method, wafers with a predetermined shape can be obtained at once, and desirable results can be expected from the standpoint of mass production.As mentioned above, the melt is embossed from all sides. will be done.

For this reason, in the above method, the upper and lower surfaces and side surfaces of the mold suppress the growth of silicon crystal grains (grains) when the melt solidifies. Because large grains cannot be obtained as crystal grains, and the requirement for large crystal grain formation, which is considered desirable for silicon wafers for solar cells, etc., cannot be achieved, solar cells obtained using such wafers cannot be used. The photoelectric conversion efficiency of the photoelectric conversion efficiency is also extremely deteriorated to 2 to 3%.

The present invention was developed as a result of studies in view of the problems of the conventional methods described above. distributing the melt and blowing gas onto the melt from a nozzle to cause the melt to flow in the direction of the rising edge;
The second aspect of the present invention is to form a thin layer of melt having a required dimension in which the outer peripheral edge is defined by the rising peripheral edge, and to solidify this by cooling the thin layer in a timely manner. When forming a thin melt film, the nozzle is oscillated in a circular motion so that the gas blown from the nozzle is rotated and radiated toward the outer peripheral edge of the melt of the silicon base material in a manner oblique to the axis. By being characterized in that it solidifies by cooling in a timely manner,
To enable mass production of polycrystalline wafers of a desired size with large crystal grains and a uniform layer thickness using simple equipment without loss of base material, and to transform the silicon base material from a molten state to a solidified state. The aim is to shorten the time required for production, prevent contamination with impurities, and improve productivity.

To explain the present invention in detail with reference to the drawings, the first
In the example of equipment shown in the figure, in an inert atmosphere 1 of vacuum or inert gas such as argon,
A melting heat source 2 such as an electric heater is disposed, and a horizontal plate 3 is disposed in a space 2' heated by the heat source 2 so as to be movable up and down.

Here, the horizontal plate 3 has a peripheral edge 4 extending upward from the outer periphery of the flat plate part 3', and a support pipe 5 is provided downwardly protruding from the axial position of the flat plate part 3'. As the material, it is best to use quartz, graphite, etc., which have little reaction with silicon, and a high-frequency heating device can also be used as the heat source 2, and of course, it is possible to stop the heating at any time or control the heating conditions. It is preferable to leave it there.

Therefore, in Figure 1, silicon base material 6 made of metal grade silicon, semiconductor grade high purity silicon, etc.
is placed at the center of the flat plate part 3' of the horizontal plate 3, and the base material 6 is placed on the flat plate part 3' of the horizontal plate 3.
The melt 7 obtained in this manner is heated and melted by a nozzle 8 and a gas 9 is blown onto the melt 7 thus obtained.

Here, as a means for obtaining the melt 7 on the flat plate part 3', it is possible to melt the solid silicon base material 6 on the flat plate part 3' as described above, but it is possible to melt the silicon base material 6 in advance in a crucible or the like (not shown). The melted liquid may be allowed to flow down onto the flat plate portion, and in such a case, it is desirable to heat the melted liquid 7 using the heat source 2 so as not to solidify the melted liquid 7.

Further, the nozzle 8 is connected to the flat plate portion 3' as shown in FIG.
It is sufficient to place the gas 9 directly above the center and spray the gas 9, which expands in diameter into a conical shape, onto the melt 7 from the nozzle 8, so that the melt 7 quickly rises and flows in four directions around the periphery. The rising edge 4 forms a thin melt layer B with a uniform thickness and the required dimensions define the outer edge A, and the gas 9 used at this time is an inert gas such as Af or He. It is better to use gas.

If the thin melt layer B is obtained in this way,
This will be cooled and solidified, but the cooling means may be to lower the horizontal plate 3 to remove it from the heating space 2'. Even after B is obtained, the thin layer of melt B can be formed while the descending operation is preceded.
Alternatively, it is also possible to cut off the current supply to the melting heat source 2 and cool the horizontal plate 3 while leaving it still, but in order to complete the solidification in a short time, In addition to lowering the horizontal plate 3 as described above, it is preferable to supply the same plate 3 with a refrigerant 10 such as inert gas or water.

When trying to feed the refrigerant 10 in this way, it is sufficient to use, for example, a horizontal plate 3 as shown in FIG. It passes through an outgoing path 12 formed by a partition wall provided in the flat plate portion 3', then passes through a return path 14 through a folding opening 13 of the rising edge 4, and is discharged from an outer circumferential annular path 15 of the support pipe 5.

Next, what is shown in FIG. 2 is an example of equipment that can be used to carry out the second invention, and the difference from that shown in FIG. 1 is that the nozzle 8 is simply left stationary. Rather, the nozzle 8 is installed in an oblique manner with respect to the axis, and in this oblique state, it is rotated in the direction of arrow C, whereby the gas 9 blown from the nozzle 8 is directed to the silicon base material. The point is that the melt 7 of No. 6 is rotated and radiated obliquely to the outer peripheral edge of the melt 7 with respect to the axis.

In carrying out the present invention illustrated in FIGS. 1 and 2, the horizontal plate 3 is rotated about the support pipe 5 as shown by the arrow D in FIG. 2, and the centrifugal force caused by the rotation is Alternatively, the melt 7 of the silicon base material 6 may be made to flow toward the rising edge 4.

In practice, 5.6g of silicon is melted under heating conditions of 1500℃ and heated for 1 hour in an argon gas atmosphere.
Argon gas, which is an inert gas, is first supplied from a mm diameter nozzle.
A polycrystalline silicon wafer with a diameter of 25 cm and a thickness of 0.5 cm was produced by lowering the horizontal plate while blowing with the device shown in the figure, and supplying a refrigerant with Ar gas to the horizontal plate for forced cooling. The efficiency was extremely good at 10%.

Since the present invention manufactures polycrystalline silicon wafers as described above, the melt can be forced to flow extremely quickly by blowing gas onto the melt, which dramatically increases productivity. At the same time, the chances of contamination with impurities can be reduced as much as possible, and products with the required dimensions can be obtained without effort by the rising edge of the horizontal plate, and the thin film formed by flowing to the edge is If the flat plate part of the horizontal plate is kept horizontal, wafers of uniform thickness can be obtained without much effort, and since the upper surface of the thin melt layer is open during solidification, it is not possible to use the conventional ingot slicing method or Not only does it solve the problems of the ribbon method, but it is not restricted by the various sides of the mold as in the existing casting method, and the melt can solidify freely in the minor axis direction, allowing the crystal grains to Since there are no factors that significantly inhibit the growth of crystal grains, large crystal grains grow relatively uniformly, making it possible to obtain a product with high conversion efficiency.

Furthermore, the equipment is relatively simple and compact, its operation is not difficult, and automation elements can be easily introduced in terms of mass production, making it superior to conventional methods.

In the second invention, since the nozzle is made to swing in a circular motion, it is possible to make the melt flow even more smoothly, and the gas emitted by the rotation is evenly distributed over the entire circumference. This results in smooth flow, which can help make the product uniform in thickness.

[Brief explanation of the drawing]

Figures 1 and 2 are front explanatory views showing examples of equipment that can be used to implement the methods according to the first and second inventions, respectively, and Figure 3 is a longitudinal cross-sectional front view showing details of the horizontal plate of the example equipment. It is an explanatory diagram. DESCRIPTION OF SYMBOLS 1... Inert atmosphere, 3... Horizontal plate, 4... Rising periphery, 6... Silicon base material, 7... Melt, 8
...Nozzle, 9...Gas, 10...Refrigerant, A...
Outer peripheral edge, B...Thin layer of melt.

Claims (1)

[Claims] 1. In an inert atmosphere, a melt of a silicon base material is placed on a horizontal plate having a rising edge, and a gas is blown onto the melt from a nozzle. The liquid is made to flow in the direction of the rising edge to form a thin layer of molten liquid having a required dimension whose outer peripheral edge is defined by the rising edge, and this is solidified by being cooled in a timely manner. A method for manufacturing polycrystalline silicon wafers. 2. Claim 1, characterized in that the horizontal plate can be cooled freely with a refrigerant such as water or inert gas.
A method for manufacturing a polycrystalline silicon wafer as described in Section 1. 3. The method for manufacturing a polycrystalline silicon wafer according to claim 1, wherein the gas blown from the nozzle is an inert gas. 4 In an inert atmosphere, a melt of silicon base material is placed on a horizontal plate having a rising edge, and a coaxial liquid is directed toward the rising edge by blowing gas from a nozzle onto the melt. When flowing the melt to form a thin layer of the melt having the required dimensions whose outer peripheral edge is defined by the rising edge, the nozzle is moved in an oscillating circular motion to direct the gas blown from the nozzle to the silicon matrix. 1. A method for producing a polycrystalline silicon wafer, characterized in that the melt is radiated obliquely toward the outer circumference of the melt, and the thin layer of the melt is solidified by timely cooling. 5. The method of manufacturing a polycrystalline silicon wafer according to claim 4, wherein the nozzle is arranged obliquely directly above the center of the horizontal plate.