JPH038579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of coating carbon plates used for manufacturing polycrystalline silicon wafers used in solar cells and other photoelectric conversion elements.

[Conventional technology]

Conventionally, polycrystalline silicon wafers have been manufactured by various methods, but they have had various problems.

That is, the most common ingot method involves casting an ingot in a silicon base material and then slicing it to obtain wafers, but the slicing process is complicated and there is a large loss of material during slicing. This resulted in a high cost product and was not suitable for mass production.

In addition, there are methods that do not involve slicing, such as the ribbon method and the casting method (casting method), but both have the disadvantage that large solar cell materials cannot be obtained. Since the wafer becomes very fine and large crystal grains cannot be obtained, the photoelectric conversion rate of the solar cell obtained with the wafer is 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 since the above-mentioned molten silicon base material solution is directly dropped onto the production plate to form a thin layer of melt, it is possible to In particular, when the plate is made of carbon, carbon is mixed into the melt as a contaminating impurity and has a negative effect on the characteristics of the wafer product.

Therefore, in order to solve this problem, we have already started applying SiC to the surface of carbon production plates.
It has been proposed to form a double film layer with SiN, and in this way, if a molten silicon base material solution is dropped onto the carbon plate and a polycrystalline silicon wafer is manufactured as described above, carbon It has also been confirmed that carbon from the pan can be very effectively prevented from entering the silicon wafer product.

However, in the conventional method of coating a carbon plate with the above-mentioned double film layer, a SiC film is first formed on the surface of the carbon plate by a known method such as CVD, sputtering, or vacuum evaporation.
A SiN film is then formed on the surface of the SiC film by means such as the above-mentioned CVD method.

Therefore, when using such conventional methods, the SiC film must be stacked to a considerable thickness of 1 μm and the SiN film must be stacked to a considerable thickness of about 10 μm. etc., it is necessary to change the material from SiC to SiN, so it is necessary to change the coating material.
Not only does it take about 30 hours, but the above-mentioned SiC film is only physically attached to the carbon of the carbon plate, and the SiN film is only physically attached to the SiC film. Due to use under high temperature conditions during silicon wafer manufacturing, there was a defect that the product was prone to peeling and could only withstand about 10 uses before it eventually became partially peeled.

[Problem that the invention seeks to solve]

The present invention has been made in view of such conventional circumstances, and involves dropping a melt of a silicon base material onto a production plate on which a release agent layer is formed on the upper surface, and forming a thin layer of the melt as desired. When producing a polycrystalline silicon wafer by forming a polycrystalline silicon wafer, solidifying it, and then peeling it from the production plate,
Rather than simply stacking SiC and SiN films in an adhesive state as in the conventional method, the SiC and SiN films are
The double layer is formed integrally in a chemically bonded state, thereby reducing the time required for coating, and the layer thickness can be formed thinner than that of the conventional method. The purpose is to improve the service life by more than double based on the above, thereby making it possible to manufacture polycrystalline silicon wafers with high quality and high characteristics.

[Means for solving problems]

In order to achieve the intended purpose, the method for coating a carbon plate for manufacturing polycrystalline silicon wafers according to the present invention is to coat the surface of the carbon plate to which a silicon base material melt is supplied with polycrystalline silicon via a film forming means. After forming a silicon film, the carbon plate having the polycrystalline silicon film is heat-treated in a nitrogen atmosphere, so that SiC formed by C in the carbon plate and Si in the silicon film is formed on the carbon plate.
and a SiN layer made of N in the atmosphere and Si of the silicon film are simultaneously formed to obtain a coated carbon plate in which the carbon plate, the SiC layer, and the SiN layer are chemically bonded together. do.

[Effect]

In the present invention, carbon plates and
Because the interface with the SiC layer and the interface between the SiC layer and the SiN layer are not simply in an adhesive state but in a chemically bonded state,
It is resistant to temperature and shock, and can withstand repeated use over a long period of time.

〔Example〕

To explain the present invention in detail with reference to the drawings, first, a polycrystalline silicon film 2 is formed and grown on the surface 1' of a carbon plate 1 shaped like a disk. like, known
CVD method, sputtering method, vacuum evaporation method, etc. may be used, and the film thickness may be about 2 to 3 μm.

Next, the carbon plate 1 on which the silicon film 2 has been formed as described above is heated in a nitrogen atmosphere A, and the heating conditions are approximately 1200 to 1300°C for about 1 hour. desirable.

Through the above heat treatment, C in the carbon plate 1 and Si in the silicon film 2 are chemically bonded, and a SiC layer 3 is formed in the lower layer of the film 2, and N in the nitrogen atmosphere A.
Due to chemical bonding with Si of silicon film 2 as above
A Si ₃ N ₄ or SiN layer 4 is formed on the upper layer of each film 2 .

Therefore, the interface between the carbon plate 1 and the SiC layer 3 and the interface between the SiC layer 3 and the SiN layer 4 are chemically bonded, and thus the bond is strong and forms a coating that is extremely difficult to peel off. We were able to.

By the way, the following is a comparison between a carbon plate, a SiC layer, and a SiN layer that are chemically bonded together (the present invention), and a structure in which these are merely physically attached (the conventional example).

In the case of the present invention, the coating film thickness is 2 to 3 μm
This is 1/5 of the conventional coating thickness.
~1/3 would be enough.

In the case of the present invention, the coating time only needed to be about 24 hours, which was shorter than about 30 hours in the conventional example.

In the case of the present invention, the durability is at least 20 times before partial peeling occurs, which is twice the durability of the conventional example.

In the case of the present invention, the polycrystalline silicon wafer manufactured using the carbon plate obtained by the method had a lifetime of 2 μsec, and by using the coated carbon plate, a high-quality wafer product was obtained.

〔Effect of the invention〕

As explained above, when using the method of coating a carbon plate for manufacturing polycrystalline silicon wafers according to the present invention, these effects such as thinning of the coating film, improvement of productivity by shortening the coating time, and durability of the coating film are achieved. can be ensured.

In particular, when using the method of the present invention, a carbon plate,
Since the SiC layer and SiN layer are chemically bonded together, the durability of the coating film is greatly improved, and even an extremely thin coating film can double its service life.

Moreover, the method of the present invention does not use powder materials, but rather forms the above-mentioned layers by heat-treating the polycrystalline silicon film on the surface of the carbon dish in a nitrogen atmosphere.
When producing polycrystalline silicon using the coated carbon plate obtained from the method, the polycrystalline silicon is not contaminated with powder material.

Therefore, the method of the present invention provides a useful coated carbon dish.

[Brief explanation of the drawing]

Fig. 1 is a partially longitudinal front explanatory view showing the carbon plate after the initial process is completed in the carbon plate coating method according to the present invention, and Fig. 2 is a partially longitudinal front explanatory view showing the carbon plate after the process is completed. It is a diagram. 1...Carbon plate body, 1'...Surface of carbon plate body, 2...Silicon film, 3...SiC layer, 4
...SiN layer, A...nitrogen atmosphere.

Claims (1)

[Claims] 1. After forming a polycrystalline silicon film using a film forming means on the surface of the carbon dish to which the silicon base material melt is supplied, the carbon dish having the polycrystalline silicon film is heat-treated in a nitrogen atmosphere. By this, the C of the carbon plate is placed on the carbon plate.
and Si of the silicon film, and an SiN layer of N in the atmosphere and Si of the silicon film are simultaneously formed.
1. A method for coating a carbon plate for manufacturing polycrystalline silicon wafers, characterized by obtaining a coated carbon plate in which a SiN layer and a SiN layer are chemically bonded together.