JPH0313167B2 - - 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, and the most common method is to cast an ingot in a predetermined shape from a silicon base material and then obtain the wafer by slicing the ingot. However, not only does the slicing process take a lot of time, but also about 50% of the ingot is lost during slicing, making mass production impossible due to high product costs.

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 present applicant has already developed a method for manufacturing polycrystalline silicon wafers that can significantly improve the defects of the above methods, by melting a silicon base material and using this melt to create polycrystalline silicon wafers made of quartz or carbon. A thin layer of molten liquid with a desired expanded diameter is formed by dripping onto a rotating production plate, effectively utilizing centrifugal force, and after the layer solidifies, this is peeled off from the production plate (spin method). ) was proposed.

This spin method has many excellent features, but when the thin layer of solidified melt mentioned above is peeled off, the layer adheres to the production plate, so it may be damaged during the peeling process. It is easy to store, and the work is extremely complicated and requires skill, which has become a bottleneck in mass production.

In addition, the above-mentioned adhesion phenomenon becomes stronger as the temperature of the melt increases, so it is not possible to raise the temperature too high in consideration of peeling, and as a result, it is difficult to handle wafers for solar cells, etc. However, even though it is known that raising the temperature to high temperatures produces large crystal grains, which is desirable in terms of improving properties, this cannot be achieved.

The present invention was devised in view of the current situation, and its purpose is to provide a wafer with large crystal grains that is easy to manufacture and is desirable for wafers for solar cells, etc. The present invention aims to provide a method for manufacturing polycrystalline silicon wafers that can be mass-produced without any problems.

In order to achieve such an object, in the present invention, a production plate is rotated using a turntable or the like in a desired atmosphere, and the melt of the silicon base material on the production plate is By causing the melt to flow in the direction of diameter expansion due to the centrifugal force caused by rotation, a thin layer of the melt with a desired diameter is formed by the melt,
In a method for manufacturing a polycrystalline silicon wafer in which the thin layer is peeled off from a production plate after solidifying the melt, the production plate is formed of a porous material, and after the thin layer of melt is solidified on the upper surface of the production plate, the thin layer is peeled off from the production plate. A corrosive solution is applied to the production plate, and the thin layer of the melt solidified by the solution leached onto the upper surface of the production plate is dissolved on the surface of the production plate, and the thin layer is peeled off from the production plate. The aim is to manufacture crystalline silicon wafers.

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

FIG. 1 shows a state in which a solidified silicon sheet 2 with a desired enlarged diameter is formed on the upper surface 1a of the manufacturing tray 1, which is the wafer forming plane.

To form such a silicon sheet 2, as shown in FIG. Then, discharge into funnel 7,
Once received by the funnel 7, the melt is dropped from the outlet 7' onto the approximate center of the upper surface 1a, as shown by the dotted line in the figure.

At this time, it is preferable to rotate the turntable mechanism 8 in advance, but the rotation may be started simultaneously or after the dropping is completed before the melt solidifies, and the centrifugal force caused by the rotation causes the melt to flows in the direction of diameter expansion.

Here, the production plate 1 is made of a porous material such as carbon (C), which has little reactivity with silicon, and has a wafer forming plane 1a of a desired shape such as a circle or a square of various dimensions. , this is optionally used, but if the above-mentioned melt supply amount is sufficient, the diameter-expanding flow melt will flow onto the wafer forming plane 1.
The diameter is expanded over the entire surface of 1a to the outer periphery, and the surplus melt is released from the outer periphery by centrifugal force. As a result, a thin layer of melt that matches the shape of the upper surface 1a is formed, and this is released naturally. It is solidified by cooling or an appropriate cooling means, and a polycrystalline silicon wafer is formed on the upper surface 1a of the production plate 1, as shown in FIG.

The silicon base material used is metallic grade silicon, semiconductor grade high purity silicon, etc., and the base material is melted by a heat source 5 for melting such as an electric heater disposed on the outer periphery of the crucible 4. It is possible to melt the silicon by heating it in consideration of the melting temperature of 1420°C, and the heat source 5 can be an electric heat source as shown in the illustrated example or a high-frequency heating device. Of course, it is desirable to be able to stop the heating at appropriate times and to be able to control the heating conditions.

The turntable mechanism 8 is mounted on a production tray 10 to a collection tray 10 to which the rotating shaft 9 is fixed.
is placed on the collection tray 10 with the coaxial 9 as the center of rotation.
and the production plate 1 are rotated synchronously.

After the silicone sheet 2 with the desired enlarged diameter is formed on the upper surface 1a of the manufacturing pan 1 in this way, the manufacturing pan 1
is removed from the collecting tray 10, and a corrosive liquid 3 is applied to the tray 1 by, for example, dipping means as shown in FIG.

In this case, of course, the silicone sheet 2 formed on the upper surface 1a of the production plate 1 should not be immersed in the corrosive solution 3.

Corrosive solution 3 for the above silicone sheet 2
A particularly suitable aqueous solution of hydrofluoric acid and nitric acid is a mixed aqueous solution of hydrofluoric acid and nitric acid.In this case, if the corrosive solution 3 corrodes the silicone sheet 2 excessively, the characteristics and quality of the silicone sheet 2 may be affected. This is undesirable because it lowers the water content, and therefore, aqua regia is undesirable because it dissolves the silicone sheet 2 excessively.

In the embodiment of FIG.
Since the production pan 1 is made of a porous material, the corrosive solution 3 is inhaled by capillary action through the continuous pores of the production pan 1. , it oozes out from the entire area on the upper surface 1a of the production pan 1 and dissolves the surface 2a of the silicone sheet 2 that is attached to the production pan 1.

Thus, after the required time has elapsed, the adhesive surface 2a of the silicone sheet 2 can be completely peeled off from the upper surface 1a of the production plate 1 due to the above-mentioned melting, and the worker lifts the silicone sheet 2 manually or by machine and cleans it. After this, a polycrystalline silicon wafer is obtained by applying product finishing.

Here, to show a specific example according to the present invention, 50% by volume
1:5 hydrofluoric acid aqueous solution and 35% by volume nitric acid aqueous solution
A corrosive solution was prepared by mixing in a volume ratio of 1, and a production plate was immersed in this mixed aqueous solution to about half its height.

As a result, after about 15 to 20 minutes, the silicone sheet adhering to the production plate can be separated from the production plate, and the peeled surface of the silicone sheet obtained in this way can prevent any dissolution that may cause problems. We confirmed that the situation has not changed.

In addition, when trying to shorten the time required for the above-mentioned peeling, the mixing ratio of hydrofluoric acid and nitric acid should be changed, for example, to 2:
The proportion of hydrofluoric acid may be increased as appropriate, such as 5.

As described above, according to the present invention, the difficulties of the conventional ingot slicing method and ribbon method are of course solved, and the production plate is not limited by the various sides of the mold unlike the existing casting method. The silicone sheet solidifies as it is placed, and during this solidification, the adhered silicone sheet is suctioned through the continuous holes in the production plate and dissolved uniformly over the entire surface by a corrosive solution that oozes out from the entire top surface, making it extremely easy to break. It can be peeled off from the production plate without any problem.

In addition, according to this invention, since the bonded surface of the silicon sheet can be reliably melted, it can be easily peeled off even if the melting temperature of the silicon base material is raised and the degree of bonding increases. Silicon wafers with large crystal grains, which are considered desirable, can be easily formed under sufficiently high temperature conditions.

Furthermore, according to the present invention, it is extremely easy to separate the silicon sheet and the production plate, and the production plate can be reused, making it suitable for mass production and reducing the cost of silicon wafers. can.

[Brief explanation of the drawing]

The drawings are process diagrams showing one embodiment of the manufacturing method according to the present invention.
The figure is a partially cutaway explanatory perspective view of the equipment used to carry out the method for manufacturing polycrystalline silicon wafers previously proposed by the applicant, and Figure 3 shows a state in which the manufacturing dish is immersed in a corrosive solution. FIG. 4 is an explanatory view showing a state in which the silicone sheet and the production tray are separated. DESCRIPTION OF SYMBOLS 1... Production plate, 1a... Upper surface of production plate (wafer forming plane), 2... Silicon sheet, 2a... Bonding surface, 3... Corrosive solution.

Claims (1)

[Claims] 1. In a desired atmosphere, the melt of the silicon base material on the rotating production plate is caused to flow in the direction of diameter expansion due to the centrifugal force caused by the rotation. Forming a thin layer of melt with a desired diameter,
In a method for manufacturing a polycrystalline silicon wafer in which the thin layer is peeled off from a production plate after solidifying the melt, the production plate is formed of a porous material, and after solidifying a thin layer of melt on the upper surface of the production plate, the production plate is A corrosive solution was applied to the plate, and the solution that oozed out onto the top surface of the production plate dissolved the surface of the solidified melt thin layer that was attached to the production plate, so that the thin layer was peeled off from the production plate. A method for manufacturing a polycrystalline silicon wafer, characterized by: 2. The method for manufacturing a polycrystalline silicon wafer according to claim 1, wherein the corrosive solution is a mixed aqueous solution of hydrofluoric acid and nitric acid. 3. The method for manufacturing a polycrystalline silicon wafer according to claim 2, wherein the volume mixing ratio of hydrofluoric acid and nitric acid is 1 part of 50 volume % hydrofluoric acid to 5 parts of 35 volume % nitric acid.