JPS6220687B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a gas-impermeable SiC-Si soaking tube for manufacturing semiconductors, which prevents contamination of semiconductor materials. [Technical background of the invention and its problems] In general, a soaking tube for semiconductor manufacturing is installed in a diffusion furnace for semiconductor manufacturing, and the heat from the diffusion furnace is transferred to a quartz tube as a control tube loaded inside the soaking tube. This is a member that emits radiation uniformly and uniformly fires the semiconductor material within the quartz tube. By the way, oxide sintered tubes made of alumina, mullite, etc. have been used as conventional heat soaking tubes, but these heat soaking tubes have low thermal conductivity and spalling resistance, and their temperature rise and fall rates are slow, making them difficult to use for semiconductors. This hindered production efficiency. In addition, since these soaking tubes have a high porosity, alkali substances that reach high temperatures and evaporate from the furnace wall during operation easily pass through the soaking tubes and enter the quartz tubes inside them. When this alkal substance mixes into the quartz tube, the quartz glass crystallizes, resulting in so-called devitrification, which deteriorates the glass structure and furthermore causes cracks, reducing the mechanical strength of the quartz tube and making it brittle. A problem arose. In addition, some of the alkaline substances that evaporated from the furnace wall and easily passed through the soaking tube
It also had the disadvantage of passing through the quartz tube inside and contaminating the semiconductor material. For this reason, recrystallized silicon carbide tubes have recently been considered as soaking tubes. This soaking tube is
Since it has high thermal conductivity and excellent spalling resistance, it has the advantage that it can stably heat the semiconductor material, and that it can quickly heat up and cool down, making it possible to efficiently manufacture semiconductors. However, on the other hand, it has an apparent porosity of around 20%, so
The same problem as the above-mentioned oxide sintered tube with soaking tube still remains in that vaporized alkaline substances easily pass through during operation. In order to improve this drawback, a metal SiC-Si soaking tube has been proposed in which a recrystallized silicon carbide tube is impregnated with molten metal silicon to reduce air permeability. However, this soaking tube becomes hot during operation because impurities such as copper are mixed in during the recrystallization process of the silicon carbide sintered body and the impregnation process with metal silicon, especially during the metal silicon impregnation process. Copper evaporates from the soaking tube itself, passes through the quartz tube inside the soaking tube, and contaminates the semiconductor material, resulting in only a semiconductor with a short lifetime and a large number of etchipite crystal transitions. . The generation of etch pits has been a fatal drawback particularly in the production of bipolar, linear, etc. junction semiconductors. In view of these various problems, the present inventor developed a SiC-Si system that does not volatilize copper from SiC-Si soaking tubes and contaminate semiconductor materials even under high temperatures during operation.
We conducted extensive research in an attempt to manufacture a heat-equalizing tube. As a result, the volatilization of copper from SiC-Si soaking tubes is of course related to the content of copper in the tube, but even if this content is a trace amount, it may vary depending on the conditions. It was found that volatilization progressed, and various other impurities in the soaking tube were investigated, and it was determined that it was the alkali metal mixed in that promoted the volatilization of copper. As a result of further exploring the relationship between the content ratios of copper and alkali metals, we found that the copper content was 20ppm.
If the copper content exceeds
Even if the content of alkali metal is less than 20ppm,
It was found that copper volatilization progresses when the concentration exceeds 100 ppm. Note that the influence of alkali metals is significant in promoting the movement of copper ions, and in the case of iron, aluminum, etc., the effect is relatively small, so there is no need to consider their presence when the copper content is low. Moreover, even if only the content of copper is limited, volatilization of copper cannot be prevented. That is, as mentioned above, when the alkali metal is in excess, the volatilization of copper from the soaking tube progresses even if the copper content is small. Therefore, by limiting both copper and alkali metal, volatilization of copper from the soaking tube can be prevented for the first time. In this way, by limiting the copper content to 20 ppm or less and the alkali metal content to 100 ppm or less in the gas-impermeable SiC-Si soaking tube, it is possible to remove copper from the heat soaking tube. Volatization is prevented, and semiconductors with an extremely long lifetime and no etch pits can be manufactured. Furthermore, since alkaline substances do not evaporate from the soaking tube, the devitrification of the quartz tube, which was caused by alkali metals getting into the quartz tube as described above, can be prevented.
Cracks are also prevented. However, according to the conventional manufacturing method, as mentioned above, copper and other substances are mixed in during the impregnation process of metal silicon into the recrystallized silicon carbide, so it is difficult to produce such high purity products.
It is difficult to manufacture SiC-Si based soaking tubes. [Object of the Invention] Accordingly, the object of the present invention is to produce a SiC-based carbon fiber in which copper and alkali metals are reduced to the above-mentioned permissible concentrations.
The purification process was improved to obtain a Si-based soaking tube.
An object of the present invention is to provide a method for manufacturing a SiC-Si-based soaking tube. [Summary of the Invention] That is, the method for manufacturing a gas-impermeable SiC-Si soaking tube for manufacturing semiconductors according to the present invention is to process silicon nitride or silicon carbide with a mixed acid containing nitric acid and hydrofluoric acid to remove copper and alkali. Selectively remove metal to reduce the copper content in the soaking tube to 20ppm or less,
And the alkali metal content is 100 ppm or less. [Embodiments of the Invention] Hereinafter, a method for manufacturing a gas-impermeable SiC-Si soaking tube according to the present invention will be described by way of an example, but it is needless to say that the method is not limited to this method. First, commercially available silicon nitride powder is treated with a mixed acid mixture of equal volumes of nitric acid, hydrofluoric acid, and water at a temperature of 60°C to remove impurities such as copper and alkali metals, resulting in a high purity powder that can be used as a filling powder. of silicon nitride. Next, commercially available silicon carbide is also treated with a mixed acid in the same manner as the silicon nitride described above to selectively remove copper and alkali metals, resulting in highly pure silicon carbide powder. Then, a binder such as tarpitz is added to and mixed with this powder mainly composed of high-purity silicon carbide, and after molding into a pipe shape using a normal molding machine, the binder in this molded body is heated to approximately 800℃. A fired body is produced by firing and carbonizing at a temperature of . Then, this fired body was embedded in the above-mentioned powder mainly made of high-purity silicon nitride, and heated to 2000℃.
heat treatment at a moderately high temperature. In this high-temperature heat treatment step, silicon nitride decomposes and generates silicon gas. This silicon gas silicifies the carbon in the fired body to produce silicon carbide, and the silicon gas permeates and deposits into the pores in the fired body. In this way, a gas-impermeable SiC-Si soaking tube with a copper content of 20 ppm or less and an alkali metal content of 100 ppm or less is produced. The composition of the soaking tube of the present invention usually consists of 70 to 95% by weight of silicon carbide and 30 to 5% by weight of free silicon, and the porosity thereof generally varies depending on the state of the pores at the time of manufacturing the silicon carbide body. However, in the case of non-communicating pores, gas impermeability can be maintained sufficiently if the porosity is set to 3% or less. In addition, if a large amount of impurities other than copper and alkali metals such as iron, manganese, chromium, etc. are mixed into the soaking tube and have a negative effect on semiconductor materials, it is desirable to suppress the mixing of these impurities. It is desirable to suppress the amount of iron mixed in to 2000 ppm or less. Next, one embodiment of this invention will be described. Example First, commercially available silicon nitride powder with a particle size of 1 to 3 mm was treated with a mixed acid of equal volumes of nitric acid, hydrofluoric acid, and water at a temperature of 60°C.
1ppm, containing 5ppm sodium). Next, silicon carbide powder was treated in the same manner with the above mixed acid to form copper.
Silicon carbide powder containing 1 ppm or less of sodium and 4 ppm of sodium was obtained. After adding phenol resin to this silicon carbide powder and lamp black (containing 5 ppm of copper and 40 ppm of sodium) and kneading them, they are granulated and dried.Then, this is molded using a rubber press, and the outer diameter
A molded body with a diameter of 120 mm, an inner diameter of 105 mm, and a length of 1500 mm was made. Next, this molded body was fired at 800°C, and then embedded in the silicon nitride powder described above and heated to 1500°C.
SiC-Si is heated and recrystallized at a temperature of ~2100℃.
A system soaking tube was obtained. This soaking tube contained 16.4% by weight of free silicon, had a porosity of 0.7%, and was gas impermeable. Also, the content of copper in this soaking tube is
3ppm, sodium 10ppm, and iron 200ppm. Next, 3 was carried out as a comparative example for the above example.
An example of a seed experiment will be explained. Commercially available silicon carbide powder (copper 18ppm, sodium
After adding and mixing phenol range to lamp black (containing 70 ppm) and lamp black (containing 4 ppm copper and 20 ppm sodium), molding was carried out in the same manner as in the previous example.
A sintered body was obtained by firing. Next, this sintered body was embedded in a mixed powder of silica powder and charcoal powder (containing 10 ppm copper and 30 ppm sodium) and heated at 1500 to 2050°C.
A gas-permeable SiC-Si recrystallized product (containing 16.5 ppm of copper and 60.3 ppm of sodium) containing 3.0% by weight of free silicon and a porosity of 15% was obtained. Next, this recrystallized product was added to silicon powder containing 20 ppm copper and 400 ppm sodium (Comparative Example 1), copper
Silicon powder containing 40ppm, sodium 200ppm (comparative example 2), and copper 60ppm, sodium 600ppm
Embedded in silicon powder (Comparative Example 3)
The tubes were heated at 1500 to 2100 DEG C. to impregnate silicon into the pores to obtain three types of SiC-Si soaking tubes containing 15.7% by weight of free silicon and having a porosity of 0.7%.
The content of copper and sodium in these soaking tubes is as follows: Comparative Example 1 contains 19.5 ppm of copper and 19.5 ppm of sodium.
125ppm, comparative example 2 has copper 22ppm, sodium
Comparative Example 3 contained 26 ppm of copper and 151 ppm of sodium. Now, the following tests were conducted on the four types of SiC-Si soaking tubes obtained in Examples and Comparative Examples 1 to 3. That is, first, these SiC-Si type soaking tubes were attached to a diffusion furnace, and then a quartz tube containing a bipolar material was inserted into these soaking tubes. The process of manufacturing semiconductors by heating them to 1250°C was continued for one year, and the condition of each quartz tube and the occurrence of etch pits in the manufactured semiconductors were observed. These results are shown in the table below.

〔Effect of the invention〕

As detailed above, the SiC-Si heat soaking tube for semiconductor stands manufactured according to the present invention has a particularly low concentration of impurities such as copper and alkali metals, so it can withstand high temperatures during operation. Unlike conventional methods, copper does not volatilize from the soaking tube itself. As a result, the semiconductors manufactured here have a long lifetime and are of extremely high quality with no etch pits, and are particularly effective in manufacturing bipolar, linear, etc. junction semiconductors. Furthermore, since the soaking tube manufactured according to the present invention has a low concentration of alkali metal, the alkaline substance does not evaporate from the soaking tube itself, and the quartz glass tube installed in the soaking tube does not devitrify. Furthermore, since it has high thermal conductivity and high heat resistance similar to conventional SiC-Si heat soaking tubes, semiconductor manufacturing efficiency is also good.
Furthermore, since the method of the present invention only requires treatment with a mixed acid containing nitric acid and hydrofluoric acid, it can be easily added to conventional processes.

Claims (1)

[Claims] 1. A step of treating silicon nitride or silicon carbide with a mixed acid containing nitric acid and hydrofluoric acid to selectively remove copper and alkali metals in the silicon nitride or silicon carbide; A step of manufacturing a gas-impermeable SiC-Si soaking tube having a copper content of 20 ppm or less and an alkali metal content of 100 ppm or less using the treated silicon nitride or silicon carbide as a raw material. 1. A method for manufacturing a gas-impermeable SiC-Si soaking tube for semiconductor manufacturing, characterized by comprising: