JPH0228395Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a sintering container that is optimal for use in sintering a compound semiconductor thin film coated on a substrate, and is particularly useful when heat-treating a relatively large-area substrate. It is effective.

Sintered films of compound semiconductors, such as CdS and CdTe, are used alone or as composite layers in photoconductive devices, optical amplifiers, photovoltaic devices, and the like. Such sintered films are usually made by applying high-purity fine powder such as CdS together with CdCl ₂ as a fluxing agent and other trace additives onto a glass or porcelain substrate, drying it, and then applying an inert gas such as N ₂ as the main agent. It is made by firing in a warm atmosphere. In this case, the calcination is usually carried out in a container, since CdCl ₂ as a flux is volatile at high temperatures and the CdCl ₂ concentration in the atmosphere influences the properties of the resulting sintered film.

Conventionally, containers made of dense alumina porcelain have generally been used as such firing containers. This is because alumina porcelain has fewer impurities that impair the properties of the sintered film, can withstand highly corrosive CdCl ₂ vapor, and has a small porosity and is less susceptible to contamination.

However, when it is desired to fire a large substrate with a size of 300 to 500 mm or more, the following major problem occurs with the alumina porcelain container. First, making such a firing container itself is extremely difficult and extremely expensive. However, a more fundamental problem is that alumina porcelain has low thermal shock resistance, so in order to avoid damage due to heating, the heating rate must be extremely slow, and when firing in a tunnel furnace,
This means that there are considerable limitations in terms of both the properties and productivity of the sintered film.

In addition, alumina porcelain has low thermal conductivity, so when the container becomes large, there is a significant delay in temperature rise inside the container, which not only makes it difficult to apply accurate heat treatment to the substrate to be fired, but also makes it difficult to heat the substrate in the center and surrounding areas. Another major problem is that severe unevenness in firing occurs between parts, resulting in non-uniform properties. Other problems also arise, such as difficulty in improving the dimensional accuracy of the container and the large weight of the container, making it difficult to handle.

The present invention has been made in view of these points, and is intended to provide a baking container that eliminates the above-mentioned problems. The baking container of the present invention consists of a shallow box-shaped container made of high-density graphite and a lid made of the same material that loosely fits into the box-shaped container, and the lid is connected to at least the inner wall surface and inner bottom surface of the box-shaped container. The inside is coated with a silicon carbide thin film. The purpose of this thin film is to prevent contamination of the semiconductor sintered film due to shedding of fine graphite powder and to improve the durability of the firing container. The shape of the baking container of the present invention consists of a shallow box-shaped container 1 and a lid 2 that loosely fits into the container, as shown in the cross section in the drawing.
The lid 2 has one or more pores 3 as required.
will be established. Further, 4 is a thin film of silicon carbide,
An example is shown in which the entire surface of the container is coated. 5 is a substrate to be fired. Graphite's thermal conductivity and thermal shock resistance are orders of magnitude higher than that of alumina porcelain, and since it is not hard, it is easy to machine and achieve dimensional accuracy, and it also has excellent corrosion resistance against CdCl ₂ etc. I have it too. In addition, the oxidation resistance is sufficient up to about 600°C, which is the temperature at which CdS is fired, and since CdS is usually fired in a gas mainly composed of N ₂ , there are no problems. However, since there is a risk of fine powder adhering to graphite containers during handling or falling off during heating and cooling processes, the silicon carbide thin film of the present invention is applied to at least the inner wall surface and inner bottom surface of the container 1 and the lid. It is extremely effective to prevent such problems from occurring if a graphite container is coated on both the inside and the inside.

The firing container of the present invention is not only manufactured by mechanical processing from a graphite block, but also by pressure-molding a mixture of fine coke particles and pitch, followed by firing, pitch impregnation, etc.
It can also be produced by firing, graphitizing, and surface coating.

The method for coating with silicon carbide is to heat a graphite firing container to a high temperature of 1200°C or higher, and then add silicon-containing gas such as silicon tetrachloride, methyltrichlorosilicon, dimethyldichlorosilicon, etc. to methane if necessary. By passing hydrogen gas as a carrier gas in a state mixed with gaseous hydrocarbons such as propane and acetylene, silicon carbide is generated by thermal decomposition on the graphite surface,
A method of forming a film is recommended. When a silicon carbide film is formed on the surface of graphite through such treatment, fine graphite powder may adhere to the firing container when it comes into contact with it, or fall off during the heating and cooling process, contaminating the contents. It is possible to prevent this from happening.

In addition, as this treatment fills the pores in the surface layer of graphite with silicon carbide, it is possible to reduce the diffusion and accumulation of CdCl ₂ vapor generated during the firing of the semiconductor sintered film into the graphite pores. .

Next, an embodiment of the present invention will be described.

A high-density graphite block with a porosity of 15% and an ash content of 900 ppm was ground to produce a firing container with external dimensions of 360 x 360 x 45 mm and the structure shown in the drawing (however, before silicon carbide coating was formed). . Next, the graphite firing container was heated to 1450°C in a hydrogen stream containing 2 vol% of dimethyldichlorosilicon to deposit silicon carbide on the surface, producing a silicon carbide-coated firing container.

Next, 100g of CdS fine powder with a purity of 99.99%CdCl ₂ 10
A paste consisting of 1 g and 30 g of propylene glycol was applied onto a 300 x 300 x 3 mm borosilicate glass substrate by screen printing and dried at 120°C for 3 hours. This substrate was placed in the above-mentioned firing container and passed through a tunnel furnace having a total length of 4 m. Maximum temperature is 650
℃, and the atmosphere was 99% N ₂ and 1% O ₂ . The CdS sintered film obtained under these firing conditions is yellow and translucent, free from defects, highly conductive, and CdS−
It was found that it is suitable for Cu ₂ S-based and CdS-CdTe-based solar cells.

For comparison, in the above example, when the coating with silicon carbide was not performed and the other conditions were the same as in the example, hands were stained black when handling the container, and the surface of the obtained CdS sintered film was Brown or black spots appeared here and there, and it was found that these areas had insufficient light transmittance and conductivity, making them unsuitable for use in the solar cell described above.

As is clear from the above description, by using the firing container according to the present invention, a compound semiconductor thin film having a large area and excellent properties can be obtained. Although the above embodiment describes the firing of a CdS film, the firing container of the present invention can be used for CdSe, CdTe, ZnS, and ZnSe.
Alternatively, the same can be applied to solid solutions thereof.

[Brief explanation of drawings]

The drawing is a sectional view showing an embodiment of the baking container of the present invention. 1... Container body, 2... Lid, 3... Small hole, 4...
...Silicon carbide thin film, 5...Substrate to be fired.

Claims (1)

[Scope of utility model registration request] It consists of a shallow box-shaped container made of high-density graphite and a lid made of the same material that fits loosely with the container, and the entire inner and outer surfaces of the container and the lid are coated with a silicon carbide thin film. Container for firing.