JPS6127896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a furnace core tube for a semiconductor diffusion furnace, and particularly to the structure of its joint portion.
Conventionally, quartz glass furnace core tubes have been used in the process tubes of diffusion furnaces used in semiconductor manufacturing processes. The process tube and the quartz glass tube at the tube end are usually connected by spherical mating connection or fitting, as shown in FIGS. 1(a) and 1(b). However, in recent years, as wafers have become larger and diffusion furnaces have become more automated, process tubes made of silicon carbide, silicon nitride, silicon, or composite materials thereof have come into wide use. However, when such a process tube made of silicon carbide or the like is used, a new problem has arisen in that the sealing between the process tube and the quartz glass connecting tube to which it is connected is insufficient. In other words, the joint at the end of the process tube on the gas inlet pipe side is currently made using a conventional quartz glass process tube or a recently used process tube made of silicon carbide, etc., as shown in Figures 2(a) and (b). If a sealing method is adopted, it is difficult to achieve a complete seal due to differences in thermal expansion, etc. Gas leakage due to incomplete sealing here only results in the generation of defective wafers, specifically an increase in the lifetime of stacking faults, an increase in leakage current, and an increase in the ΔNFB value due to MOSVaractor check. Furthermore, leaks of the normally used gas HCl and doping gas caused harm to the human body and damage to peripheral equipment. In the future, the occurrence of these defects will become an issue that must be avoided in highly integrated, high-performance devices such as LSI and VLSI. The cause of gas leaks in silicon carbide process tubes is that no matter how much you polish silicon carbide, it is difficult to obtain a smooth surface as precise as quartz glass, and even if a perfectly smooth surface could be obtained. This is also thought to be due to the difference in expansion between silicon carbide and quartz glass, which creates minute voids here during high-temperature use. For this reason, various attempts have been made to improve this problem, for example, the use of heat-resistant packing was considered, but since the temperature inside the furnace is as high as 1200℃ or more, the joint part is also heated to 250 to 300℃.
The reality is that there is currently no suitable gasket that can withstand the high heat that occurs. Therefore, we made further improvements by extending the tube side end of the process tube and positioning the joint part where the packing is inserted further away.
Attempts have also been made to lower the temperature here.
However, if you do that, for example, the temperature inside the furnace is 1280℃.
In this case, in order to achieve a joint temperature of 200℃, the length of the tube side end must be increased to 300 to 350 mm, and as the furnace core tube becomes larger,
Problems arose in that it was extremely inconvenient to set up and took up a lot of space. This invention is an attempt to solve the above-mentioned problems of the conventional technology.A cooling fin is attached to the gas introduction pipe side end (branch pipe part) of a silicon carbide process tube.
This is intended to lower the temperature at the joint with the quartz glass tube to avoid thermal expansion there, and to completely prevent gas leaks here. That is, the present invention provides a furnace core tube for a diffusion furnace made of silicon carbide, silicon nitride, silicon, or a composite material thereof, which is provided with a large number of fins at the end of the gas introduction tube side;
This is a structure of a furnace core tube for a semiconductor diffusion furnace, which consists of a quartz glass joint tube connected to the core tube, and a heat-resistant packing is further inserted into the joint portion as necessary. The details of the present invention will be explained below based on illustrated embodiments. FIG. 3 is a sectional view of one embodiment of the furnace core tube according to the present invention, in which 1 is the furnace core tube and is made of silicon carbide. A large number of fins 3 are provided at the gas introduction pipe side end 2 of the furnace core tube 1, and a flange 4 is provided at the outer end.
is formed. An example of such a gas introduction pipe side end 2 is an outer diameter of 32φ x inner diameter of 22φ x height of 300 (mm), the flange and fins are 70φ x 5t (mm), and the number of fins is 10. be. The flange 4 on the gas introduction pipe side end 2 of the process tube is made of Teflon, fluoro rubber,
A gasket 5 made of silicone rubber may be used, and after it is connected to a gas joint tube 6 made of quartz glass, its outer periphery is fixed together with a stopper 7. FIG. 4 shows another embodiment of the present invention, in which the only difference is that a ball joint is used for the structure of the joint part, and the other embodiments are completely the same. Note that the furnace core tube according to the present invention exhibits even more effects when used in combination with an air cooling fan. According to an experiment in which the temperature inside the furnace was set to 1280° C. using the above-mentioned furnace core tube, the surface temperature (joint portion) of the gas introduction tube under various conditions was as shown in FIG. As is clear from the same figure, approximately 150℃ is considered to be the upper limit of safe usage temperature for commercially available heat-resistant packing.
The length of the end of the gas introduction tube to hold the
By providing fins, the width can be significantly shortened compared to the case without fins, and by further combining this with an air cooling fan, the width can be reduced to about 1/3. The length of the gas introduction pipe side end is
If it is within the limit of about 200 mm, it will not cause much trouble during work, but when using heat-resistant packing, it is essential that it can be used for a long period of time. According to the present invention, long-term use of the packing has been confirmed as shown in Examples below. The structure of the fins is not particularly limited as long as it can dissipate heat; for example, the fins may be formed separately from an aluminum or other metal plate and inserted into the end of the gas introduction tube. As described above, according to this invention, the joint seal with the quartz glass joint tube at the gas introduction side end of the furnace core tube for a semiconductor diffusion furnace is perfect, and the joint seal is in a satisfactory state, so that external gas can be sucked in during use. Gas leakage during the previous hydrochloric acid cleaning can now be almost completely avoided. As a result, the occurrence of defective processing ware has been greatly reduced, and the conventional problems of damage to peripheral equipment and harm to the human body have been solved all at once. Furthermore, if a heat-resistant packing is used in this invention, the joint seal will be even more complete, and the gas inlet end of the process tube will be further shortened, which will reduce inconveniences such as damage when installing equipment. can be significantly improved. Example 1 A semiconductor furnace core tube made of silicon carbide shown in FIG. 3 had the shape of the end on the gas introduction side as described above, and a quartz glass connecting tube was connected through a Teflon packing for pre-cleaning. The gas used is Hcl0.3 ^l /min + O ₂ 10 ^l /
min, and the temperature was 1300°C. In order to investigate gas leaks in this case, we wrapped litmus paper around the joint and performed a litmus method to detect the change in color, but no change in color was observed even after 60 days had passed. Also, no abnormalities in the skin were observed. Example 2 When the same experiment as in Example 1 was conducted for 30 days with the heat-resistant packing removed, no discoloration of the litmus paper was observed. Example 3 MOS-Varactor-check (C-V
Using the same silicon carbide tube as in Example 1, the results were obtained when a Teflon packing was used at the joint between the tube and the quartz glass connection tube and when no packing was used. However, the results were as shown in the table below. 【table】

[Brief explanation of the drawing]

Figures 1 (a) and (b) are both explanatory diagrams showing the bonding state of a conventional quartz glass process tube and a quartz glass joint tube, and Figures 2 (a) and (b) are both silicon carbide process tubes. 3 and 4 are cross-sectional views showing the joint structure of the furnace core tube according to the present invention, and FIG. 5 shows the gas introduction tube side end. FIG. 3 is a diagram showing the surface temperature of the gas introduction pipe with respect to the length of the gas introduction pipe. DESCRIPTION OF SYMBOLS 1... Process tube, 2... Gas introduction pipe side end, 3... Fin, 4... Flange, 5... Packing,
7...Quartz glass joint tube.

Claims (1)

[Scope of Claims] 1. A furnace core tube for a diffusion furnace made of silicon carbide, silicon nitride, silicon, or a composite material thereof, provided with a large number of fins at the end on the gas introduction side, and a quartz tube connected to the core tube at a joint portion. A structure of a furnace core tube for a semiconductor diffusion furnace characterized by comprising a glass connecting tube. 2. The structure of a furnace core tube for a semiconductor diffusion furnace according to claim 1, wherein a heat-resistant packing is inserted into the joint portion.