JPS60258918A - Manufacture of sic-si heat equalizing tube for manufacturing gas impermeable semiconductor - Google Patents

Abstract

PURPOSE:To reduce the contents of copper and an alkali metal in a heat equalizing tube to an allowable concentration by selectively removing the copper and the alkali metal treating silicon compounds with a mixed acid containing nitric acid and fluoric acid. CONSTITUTION:Silicon nitride powder is treated with a mixed acid of equal quantity nitric acid, fluoric acid and water, impurities of copper and an alkali metal are removed and high purity silicon nitride is made. Silicon carbide is also treated with the mixed acid in the same way, the copper and the alkali metal are selectively removed and high purity silicon carbide powder is made. Powder mainly consisting of high purity silicon carbide is added with a caking agent such as tar pitch and mixed, made to a shape of pipe and a burned product is made by means of caking agent being burnt and carbonized. The burnt product is buried in packed powder consisting of high purity silicon nitride and heated at a high temperature of approx. 2,000 deg.C. An SiC-Si heat equalizing tube for manufacturing a gas impermeable semiconductor with the content of copper 20ppm or less and the content of alkali metal 100ppm or less can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a gas-impermeable 5iC-8i soaking tube for semiconductor manufacturing, which is designed to prevent 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 in the diffusion furnace is transferred to a quartz tube as a bare tube loaded inside the soaking tube. This is a member that uniformly irradiates the semiconductor material inside the quartz tube and uniformly fires the semiconductor material inside 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, so the temperature rise and fall rates are slow. This hindered semiconductor manufacturing efficiency. In addition, since these soaking tubes have a high porosity, during operation, alkaline substances that evaporate from the furnace wall at high temperatures easily pass through the soaking tubes and devitrify the quartz tube inside. It has the disadvantage that it partially passes through quartz and contaminates semiconductor materials.

For this reason, recrystallized silicon carbide tubes have recently been considered as soaking tubes. This soaking tube has high thermal conductivity and excellent spalling properties, so it can stably heat the semiconductor material, and has the advantage of being able to efficiently manufacture semiconductors with fast temperature rise and fall rates. are doing. However, on the other hand, since it has an apparent porosity of around 20%, it still has the same problem as the above-mentioned oxide sintered tube in that it is easy for alkaline substances vaporized during operation to pass through.

In order to improve this drawback, a 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 has high temperatures during operation because impurities such as copper are mixed in during the process of recrystallizing the sintered silicon carbide and impregnating the metal silicon, especially during the process of impregnating the metal silicon. Copper evaporates from the soaking tube itself, passes through the quartz tube inside the soaking tube, contaminates the semiconductor material, and only semiconductors with a short lifetime and many etch pit crystal dislocations can be obtained. . The occurrence of these etch pits has been a fatal drawback particularly in the production of junction semiconductors such as polar and linear semiconductors.

One possible way to prevent this is to use high-purity metallic silicon in the process of impregnating the recrystallized silicon carbide body with metallic silicon. Although using such metallic silicon increases the cost, it is An improvement in purity is observed. However, this still does not fully meet the requirements.

In view of these various problems, the present inventor has attempted to manufacture an 81C-81 type soaking tube that will not cause copper to volatilize from the 5IC-8i type soaking tube and contaminate semiconductor materials even under high temperatures during operation. and conducted extensive research. As a result, 5iC-8i
It goes without saying that the volatilization of copper from the system heat soaking tubes is related to the copper content in the heat soaking tubes, but it is also clear that volatilization progresses depending on the conditions even if the content is minute. It was assumed that the presence of other impurities in the soaking tube was involved in the volatilization of copper. After various investigations into other impurities in the soaking tube, it was determined that it was the alkali metals mixed in that promoted the volatilization of copper.

Therefore, we further explored various relationships between the content ratios of copper and alkali metals, and found that when the copper content exceeds 20 ppm,
The volatilization of copper from the soaking tube is related to the mixing of alkali metals, but even if the copper content is 20 ppm or less, if the alkali metal content exceeds 100 ppm, the volatilization of copper will proceed. I discovered that. Note that the influence of alkali metals is the greatest in promoting the movement of copper ions, and in the case of iron, aluminum, etc., the influence is relatively small, so when the copper content is low, there is no need for the IC to consider their presence.

However, it is still not possible to prevent copper volatilization even if only the copper content is limited. In other words, as mentioned above, the alkali metal promotes the movement of copper ions, so 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.

5- Thus, by limiting the copper content to 20 ppm or less and the alkali metal content to 100 ppm or less in the gas-impermeable 5iC-8i soaking tube, the It has been found that volatilization of copper is prevented, and it is possible to produce a semiconductor with an extremely long lifetime and no etch pits, and it is also possible to prevent devitrification and cracking of the quartz tube inside the soaking tube.

However, according to the conventional manufacturing method, it is difficult to manufacture such high-purity 5IC-81 soaking tubes because copper and other substances are mixed in during the impregnation process of metal silicon into recrystallized silicon carbide as mentioned above. be.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a method for producing a 5IC-81 soaked tube in which the refining process is improved so that copper and alkali metals are reduced to the above-mentioned allowable concentrations and a 9SiC-81 soaked tube is obtained. It is.

61 [Summary of the invention] That is, 5iC for gas impermeable semiconductor manufacturing according to the present invention
-81 series soaking tubes are manufactured by treating a silicon compound with a mixed acid containing nitric acid and hydrofluoric acid, selectively removing copper and alkali metals from K, and reducing the copper content in the soaking tube by 20%.
ppm or less, and the alkali metal content is 100 ppm or less.
ppm or less.

[Embodiments of the invention]

The method for manufacturing the gas-impermeable 5iC-8i soaking tube according to the present invention will be described below by way of 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 high purity powder that can be used as a filling powder. of silicon nitride.

Commercially available silicon carbide was then treated with a mixed acid in the same manner as the silicon nitride described above to selectively remove copper and alkali metals.
High purity silicon carbide powder.

Then, a binder such as tar pitch is added to and mixed with this powder whose main component is high-purity silicon carbide.
After molding into a shape, the binder in this molded product is
A fired body is produced by firing and carbonizing at a temperature of 00°C.

Then, this fired body is embedded in the above-mentioned powder mainly made of high-purity silicon nitride and heat-treated at a high temperature of about 2000°C. 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. Thus the copper content is 20 p.
ptn or less and the alkali metal content is 100p
To manufacture an 81C-Si soaking tube for semiconductor manufacturing that is impermeable to gases below pm.

Note that the composition of the soaking tube of the present invention is usually silicon carbide 70 to 9
5% by weight and 30 to 5% by weight of free silicon, and its porosity cannot be unconditionally determined depending on the state of the pores at the time of manufacturing the silicon carbide body, but in the case of non-connected pores, the porosity should be 3 or less. If this is done, gas impermeability can be maintained sufficiently.

First, 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. The amount of iron mixed in is 20
It is desirable to suppress it to 0.00 ppm or less.

Next, one embodiment of this invention will be described.

Example 1 First, commercially available silicon nitride powder with a particle size of 1 to 3 m was treated with a mixed acid mixture of equal volumes of nitric acid, hydrofluoric acid, and water at a temperature of 60°C.
Silicon nitride powder (containing 1 ppm or less of copper and 5 ppm of sodium) was prepared as a stuffing powder. Next, the silicon carbide powder was treated in the same manner with the above mixed acid to obtain a silicon carbide powder containing 1 ppm or less of copper and 4 Ppnl of sodium. After adding phenol resin to this silicon carbide powder and Lanzopra resin (containing 5 ppm of copper and 4.9 ppm of sodium) and kneading them, they were granulated and dried, and then molded using a rubber press to form an outer diameter of 120 mm. Simple, inner diameter 105cm, length 1500+m
A molded body was made. Next, this molded body was fired at 800°C, and then embedded in the silicon nitride powder.
5i by heating at a temperature of 500 to 2100℃ and recrystallizing
A C-81 type soaking tube was obtained. This soaking tube contains 16 free silicon
．． It contained 4% by weight, had a porosity of 0.7cm, and was gas impermeable. In addition, the copper content in this soaking tube is 3 ppm.
, sodium was 10 ppm, and iron was 200 ppm.

Example 2 A mixed powder consisting of high purity silica powder and returned powder obtained by treating the fired body used in Example 1 with a mixed acid in the same manner as in Example 1 (containing 2 Ppm% copper and 10 ppm sodium)
5iC-191-based recrystallized material (Cu 10-3 ppm% (containing 55 ppm of sodium) was obtained. Next, this recrystallized product was mixed with silicon powder (copper 42pp) with a particle size of 1 to 5m.
2000 m, containing 400 ppm of sodium)
It was heated to ~2100°C to impregnate silicon into its pores to obtain a 5tc-ss soaking tube. This soaking tube contained 12.1% by weight of free silicon, had a porosity of 0.5, and was gas impermeable. In addition, the content of copper in this soaking tube is 7pp"%, sodium is 95ppm, and iron is 1000%.
It was ppm.

Next, three types of experimental examples conducted as comparative examples with respect to the above-mentioned examples will be explained.

Comparative Examples 1 to 3 Commercially available silicon nitride powder (copper 18 ppm, na) IJum 7
A phenol resin was added to and mixed with lamp black (containing 0 ppm of copper and 20 ppm of sodium), and then molded and fired in the same manner as in Example 1 to obtain a sintered body. Next, this sintered body was mixed with a mixed powder (copper 10 ppm, sodium 30 ppm) consisting of silica powder and returned powder.
ppm) and heated and recrystallized at 1500 to 2050°C to obtain a gas-permeable SiC-Si recrystallized body (copper 16%) with a porosity of 15mm and containing 3.0% by weight of free silicon.
5 ppm.

60.3 ppm of sodium) was obtained. Subsequently, this recrystallized product was prepared as silicon powder containing 20 ppm of copper, 400 ppm of sodium (Comparative Example 1), and 40 ppm of copper.

N) Silicon powder containing 2 o o ppm of IJum (Comparative Example 2), 60 ppm of copper, and 600 ppm of sodium
Embedded in silicon powder containing m (Comparative Example 3) 15
By heating at 00 to 2100°C to impregnate silicon into the pores, three types of StC-si soaking tubes containing 15.7% by weight of free silicon and having a porosity of 0.7cm were obtained. . The content of copper and slurry in these soaking tubes is as follows: Comparative Example 1 contains 19.5 ppm of copper, 111% sodium, and 125 ppm of sodium.
Comparative Example 2 contained 22 ppm of copper and 90 ppm of sodium.
n! Yes, and Comparative Example 3 contained 26 ppm of copper and 15 ppm of sodium.
It contained 1 ppm.

Now, the following tests were conducted on the five types of etc-SI soaking tubes obtained in Example 1.2 and Comparative Examples 1 to 3. First, these 5IC-81 type heat soaking tubes were attached to a diffusion furnace, and then a quartz tube containing a bipolar material was inserted into these heat soaking tubes. And 1250
The operation of manufacturing semiconductors by heating them to .degree. 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.

13- =14- As is clear from the table above, the 5iC-8L soaking tubes (Examples 1 and 2) containing 20 ppm or less of copper and 100 ppm or less of alkali metals do not retain quartz glass even after being used for more than a year. The tube was not colored, and the semiconductor produced had a long lifetime and was of extremely high quality with no etch bit crystal transition. On the other hand, even if copper is less than 20 ppm, alkali metals are less than 100 ppm.
m or more 5IC-8, i system soaking tube (comparative example 1) is 1 to
After three months of use, the quartz glass tube became colored red, and the resulting semiconductor had many etch bits, had a short lifetime, and suffered from frequent pulse noise defects. Also, even if the alkali metal content is 1100 pp or less, the copper content is 20 ppp or less.
The SiC-81-based soaking tube (comparative example 2) containing more than m
Similarly, quartz glass tubes were colored, and the semiconductors obtained were of low quality.

) [Effects of the Invention] As detailed above, the SiC-Si soaking tube for semiconductor manufacturing manufactured according to the present invention has a particularly low concentration of impurities such as copper and alkali metals, so it cannot be exposed to high temperatures during operation. Even so, copper will not volatilize from the heat soaking tube itself unlike in the conventional case.

As a result, the quartz glass tube contained in this soaking tube does not devitrify, and the semiconductors manufactured here have a long lifetime and are of extremely high quality with no etch bits. , shows remarkable effects on manufacturing of linear and other junction semiconductors. Furthermore, the conventional 5I
Since high thermal conductivity and high heat resistance similar to C-81 type soaking tubes are ensured, 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] A step of treating a silicon compound with a mixed acid containing nitric acid and hydrofluoric acid to selectively remove copper and alkali metals in the silicon compound, and using the silicon compound subjected to the above treatment as a raw material. Gas impermeable 5 with a copper content of 20 ppm or less and an alkali metal content of 100 ppm or less when used as
1. A method for manufacturing an 81C-81 type soaking tube for manufacturing a gas-impermeable semiconductor made of silicon carbide and free silicon, the method comprising the step of manufacturing a tc-st type soaking tube.