JPS59182217A - Production of polycrystal silicon wafer - Google Patents

Abstract

PURPOSE:To obtain easily the titled wafer having high quality and characteristics, by forming two or more layers of release agent layers consisting of the topmost layer of SiO2 film layer and an underlying layer of silicon based powder layer on the top of a production dish, and further forming a thin melt layer on the topmost layer. CONSTITUTION:Two or more layers of release agent layers are formed on the top of a production dish 1, and the topmost layer (A4) is an SiO2 film layer formed by sputtering. The underlying layer (A1) is a silicon based powder layer left and formed by applying a release agent prepared by dissolving silicon based powder in an organic solvent to the top of the production dish 1, and heating and drying the release agent. The production dish 1 having the resultant release agent layer (A) is placed on a recovery pan 10 of a turntable mechanism 8, and a silicon base material melt is dropped onto the center thereof. A thin melt layer 3 is formed on the whole surface of the topmost layer (A4) by the centrifugal force, cooled, solidified and peeled. Thus, the aimed polycrystal silicon wafer having high quality and characteristics can be easily obtained without fear or contamination of the release agent nor components of the production dish 1 in the melt.

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 matrix and then obtain wafers by slicing this. In this case, not only does the slicing process take a lot of time, but also about 50% of the ingot is lost during slicing, making the product expensive and making mass production impossible.

Therefore, 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 silicone is sprayed onto the circumferential surface of a rotating drum, and a ribbon-shaped coating is applied to the circumferential surface of the drum. This method is used to form wafers, and when using this method, it is practically impossible to fabricate ribbons with a width of several layers, making it difficult to obtain large-sized solar cell materials.

In addition, the above-mentioned gearing 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 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.

Therefore, in this method, when the upper and lower surfaces and side surfaces of the mold assimilate the above-mentioned melt, the growth of silicon crystal grains (grains) is suppressed, and the vicinity of the parts of the solidified product that are in contact with each of the above-mentioned surfaces is extremely Because the crystal grains become fine and large crystal grains cannot be obtained, and the requirement for large crystal grains μ, which is desirable for silicon wafers for solar cells, etc., cannot be obtained, the sea urchin... The photovoltaic conversion efficiency of the resulting solar cells is also extremely poor at 2 to 3%.

Therefore, the present applicant has already proposed a method for manufacturing polycrystalline silicon wafers that can significantly improve the deficiencies of the above-mentioned methods, by melting a silicon base material and using this melt to form a polycrystalline silicon wafer. 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 device (spin method). ) was proposed.

This spin method has many excellent features, but the thin layer of the solidified melt mentioned above is peeled off (at this time, since the layer is adhered to the manufacturing device, it may be damaged during the peeling process). It was easy to put away, and the work was complicated and required skill, which became a bottleneck in mass production.In addition, according to this method, the melt of the molten silicon base material was transferred to the manufacturing equipment. Since a thin layer of the melt is formed by directly dropping it onto the glass, the components of the manufacturing device are likely to diffuse into the melt, and especially if the tray is made of carbon, this carbon may be dissolved as impurities in the Ti dye. There was a problem in that it got mixed into the liquid and had an adverse effect on the characteristics of the wafer product.

In order to solve this problem, in the past, silicon nitride was applied as a solution in a volatile solvent as a mold release agent to the top surface of the manufacturing device, and a film of several microns was formed on the top surface of the manufacturing device. Attempts have been made to solve the above problem by dropping a melt of the silicon base material onto the upper surface of the layer to form a thin layer of the melt, and solidifying this.

However, in this method of separating the silicone sheet from the manufacturing device by applying a mold release agent to the manufacturing device, it is necessary to simply apply a solution in which the mold release agent is dissolved to the manufacturing device. Therefore, when the melt of the silicon base material is dropped into the manufacturing equipment, the impact causes release agent to be mixed into the melt, which not only tends to deteriorate the properties and quality of the silicon wafer, but also causes the impact to cause the silicon wafer to release. In areas where the molding agent has peeled off and scattered, the melt and the manufacturing equipment end up coming into direct contact, and components from the manufacturing equipment mix into the melt, causing crystal defects, which impair its properties. This had the problem of deteriorating quality.

This invention was devised in view of the current situation, and its purpose is to form a thin layer of melt of a desired size by dropping a melt of silicon base material onto the top surface of a manufacturing device,
When manufacturing polycrystalline silicon unihara by peeling it from the manufacturing device after solidifying it, it is possible to eliminate the risk of mixing the molding agent 1 or the components of the manufacturing device into the melt, and to produce a polycrystalline silicone material with high quality and high properties. It is an object of the present invention to provide a method for manufacturing polycrystalline silicon wafers that allows crystalline silicon wafers to be easily obtained.

In order to achieve such an object, in the present invention, the melt of the silicon base material in the rotating manufacturing device in a desired atmosphere is heated by the centrifugal force caused by the rotation.
In the method for manufacturing a polycrystalline silicon wafer, the method for manufacturing a polycrystalline silicon wafer comprises forming a thin layer of melt with a desired diameter by flowing the melt in the direction of diameter expansion, solidifying this, and then peeling off the thin layer from a manufacturing device. Two or more mold release agent layers are formed on the top surface of the dish, and the top layer of the mold release agent layer is a silicon oxide coating layer formed by sputtering, and the lower layer is a silicon-based film layer formed by sputtering. This is a silicon-based powder layer that remains after coating a mold release agent produced by melting the powder and then heating it at a required temperature to dry the organic solvent. It is intended to manufacture polycrystalline silicon wafers in such a manner as to form polycrystalline silicon wafers.

The present invention will now be described in detail based on an example illustrated in the accompanying drawings.

In this embodiment, the production plate (1) is made of a material such as quartz ('Sing) or carbon (c), which has low reactivity with silicon, and is made of a desired shape such as a circle or a square of various dimensions.
1a) is prepared and can be optionally used.

A plurality of mold release agent layers (A) are formed on the upper surface (1a) of this production plate (1).

The first layer (AI) of this mold release agent layer (A) is silicon nitride (
SisN4) and polyviral: I-ru (PV
A) is applied to the upper surface (1a) of the production plate (1) by means such as a brush or spray, and then dried at high temperature (approximately 600° C. or higher) in a heating furnace to form the mixture. As a result, the silicon nitride solidifies and forms a layer of approximately 50 μm on the upper surface (1a) of the production plate (1), as shown in FIG.

The second layer (A,) is made by heating silicon oxide (Si02) in a heating furnace (approximately 300°C) and depositing the vaporized S'i02 on the first layer (A,) by sputtering to form a thin film. Formed as a layer (approximately 05μ thick). This allows the first
As shown in FIG. 2, on the upper surface of the layer (A,), a roll-forming agent coating layer having a harder hardness than that of the first layer (A,) is formed.

The third layer (AD) is formed on the upper surface of the second layer (AD) in the same manner as the first layer (AI), and its thickness is approximately 50 μm.

The fourth layer (A,) is formed on the upper surface of the third layer (AD) using the same material and method as the second layer (AJ), and its thickness is approximately 1 μm.

In this way, if a mold release agent layer consisting of four layers is formed on the upper surface (1a) of the production plate (1), then the production plate (1) is placed in the equipment as shown in Fig. 5. . That is, the production tray (1) is placed on the collection tray (10) of the turntable mechanism (8), and the production tray (1) is collected around the rotating shaft (9) fixed to the collection tray (10). It is rotated in synchronization with the saucer (10).Next, the silicon base material is put into the crucible (4), heated and melted by the melting heat source (5), and the melt is transferred to the crucible (4). The melt is discharged into the funnel (7) by the transfer of the melt, which is received by the funnel (7), and from the outlet (7), the melt is transferred to the uppermost layer as shown by the dotted line in the figure. It is on the uppermost layer of the mold agent layer A and is dropped approximately at the center thereof.

At this time, it is preferable to rotate the turntable mechanism (8) 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. and,
This diameter-expanding flowing melt is expanded over the entire surface of the uppermost layer to its outer periphery, and the excess supply of melt is discharged from the outer periphery by centrifugal force. A thin melt layer (3) is formed, which is solidified by natural cooling or by an appropriate cooling means, and as shown in FIG. Formed on top layer.

The silicon base material used is metal-grade silicon, semiconductor-grade high-purity silicon, etc., and the base phase is melted by a heat source 5 for melting, such as an electric heater, provided on the outer circumference of the crucible (4). Melting temperature of the silicon: 1420°C
It is possible to melt this by heating it in consideration of It is desirable to be able to stop the heating at an appropriate time or to control the heating conditions.

In this way, after a silicone sheet with a desired enlarged diameter is formed on the upper surface of the uppermost layer, the sheet is peeled from the uppermost layer, but in this case, welding occurs at the interface between the same silicone sheet and the second uppermost layer. Since the adhesiveness is weak, the sheet can be easily peeled off manually.

In the above embodiments, the case where the mold release agent layer (A) is composed of four layers is explained as an example, but the present invention is not necessarily limited to this, and two or more layers may be used. However, in order to prevent the release agent from being mixed into the silicone notebook, the uppermost layer of the high 11 type agent layer should be formed by the sputtering method, which yields a release agent layer with higher hardness. It is preferable that

As described in 1-1, this invention not only solves the difficulties of the conventional inconto slicing method and ribbon method, but also allows silicon wafers to be formed without being limited by the various sides of the mold as in the parent casting method. Moreover, since two or more mold release agent layers are formed on the upper surface of the manufacturing device, the peeling operation is easy and the silicone sheet is not damaged.

In addition, according to the present invention, since a plurality of mold release agent layers are interposed between the silicon sheet and the manufacturing device, when dropping the silicon matrix melt to form a thin layer of the melt, There is no risk of the mold release agent scattering and other components from the manufacturing equipment getting mixed into the silicone sheet, and as a result, the characteristics and quality of the solar cells etc. can be significantly maintained and improved. The mold release agent layer was formed from a material similar to that of 7 Recon Sea 1, and the uppermost layer was formed by sputtering to form 4i1, so the silicon base material m! There is no possibility that the wafer will be damaged by the impact caused by pouring the Li liquid, and the mold release agent will not be mixed into the melt, and as a result, the properties of the wafer will not deteriorate.

[Brief explanation of the drawing]

1 to 4 are front explanatory views sequentially showing the process of forming a mold release agent layer in the manufacturing method according to the present invention, and FIG.
FIG. 6 is a front perspective view showing the configuration of an example of equipment for manufacturing polycrystalline silicon wafers.
FIG. (A)...Mold agent layer (A,)...1st layer (A...2nd layer (A◇...3rd layer ( A, 3...Fourth layer'C1)...Manufacturer (1a)...''Second side (3)...Melt thin layer Patent applicant's agent Patent Attorney Ifuji Ashi Figure 1 Figure 2 Figure 3 Figure 4 Flash

Claims (1)

[Claims] By causing the melt of the silicon base material on a rotating production plate in a desired atmosphere to flow in the diameter-expanding direction by the centrifugal force caused by the rotation, the desired diameter is formed by the melt. In a polycrystalline silicon wafer manufacturing method in which a thin melt layer is formed, solidified, and then one thin layer is peeled off from a manufacturing device, two or more mold release agent layers are provided on the top surface of the manufacturing device. The uppermost layer of the mold release agent layer is a silicon oxide coating layer formed by sputtering, and the lower layer is a mold release agent produced by dissolving phosphorus powder with an organic solvent, and then applying this. A polycrystalline silicon wafer, characterized in that the layer is a residual silicon powder layer formed by heating at a required temperature and drying an organic solvent, and the thin melt layer is formed on the uppermost layer. manufacturing method.