JPH0410531A - Vertical diffusion furnace - Google Patents

Abstract

PURPOSE:To enable the inside of the title vertical diffusion furnace to be kept in a high purity gas atmosphere by a method wherein a processing gas leading-in pipe is provided in the vertical direction from the bottom part to the topmost part in the processing space of the diffusion furnace; the length and inner diameter of the processing gas leading-in pipe exposed in the processing space specified; and a SiC film in specific thickness is formed on the inner and outer surfaces of the leading-in pipe. CONSTITUTION:A processing gas leading-in pipe 33 is provided in a processing space 8 of a diffusion furnace 10 so as to lead-in specific processing gas. The length of the processing gas leading-in pipe 33 exposed in the processing space 8 is 1000mm-1300mm. Besides, the inner and outer diameters of the pipe 33 are almost equalized respectively to be 5-20mm and 6-20mm extending over the whole length. Furthermore, a SiC film in thickness of 20-500mum is formed on both inner and outer surfaces by CVD(chemical vapor deposition) process. Finally, it is recommended that, as for the basic material of the processing gas leading-in pipe 33, the SiC film is formed into a high purity SiC pipe by the CVD process.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a vertical diffusion furnace used in a heat treatment process for semiconductors.

BACKGROUND OF THE INVENTION In the past, vertical diffusion furnaces have been developed for semiconductor heat treatment processes, such as oxidation, diffusion, annealing, and the like. The characteristics of the vertical diffusion furnace are that the temperature distribution is more uniform than that of the horizontal furnace, that the gas flow is better than that of the horizontal furnace, which improves the accuracy of the film thickness distribution in the wafer, and that the S1 wafer has a larger diameter. However, it is difficult to process it in a horizontal furnace.

Initially, liner tubes used in vertical diffusion furnaces were mainly made of quartz glass, but since quartz glass allows the radiant heat of the heater to pass through it, the effectiveness of SiC tubes as a soaking tube has increased. It's being looked around. The SiC tube also has the effect of preventing metal vapor (Na, Fe, Cu, AJ, etc.) discharged from the heater in a high temperature state from passing through the furnace core tube and contaminating the processing space.

However, simply using a SiC tube as a heat soaking tube cannot prevent trace amounts of metal vapor from entering, and improvements have been desired.

Therefore, in view of the problems of the prior art, the applicant proposed in Japanese Patent Application No. 1-165259 that it is possible to introduce a gas between the soaking tube and the furnace core tube to prevent metal from entering. We proposed a vertical diffusion furnace that can keep the introduction space airtight.

Problems to be Solved by the Invention However, in the diffusion furnace of Japanese Patent Application No. 1-165259, the processing gas introduction tube installed in the furnace was made of quartz glass, so it was impossible to prevent trace amounts of metal vapor from entering. There was a drawback.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a vertical diffusion furnace which eliminates the above-mentioned drawbacks and allows a higher purity gas atmosphere to be maintained in the furnace.

SUMMARY OF THE INVENTION To achieve the above-mentioned object, the subject matter of the present invention is a vertical diffusion furnace according to claim 1.

Means for Solving the Problems The vertical diffusion furnace of the present invention is a vertical diffusion furnace having a furnace core tube opened downward, a heater provided on the outside of the furnace core tube, and a heat insulator provided on the outside of the heater. A processing gas introduction pipe is provided vertically from the bottom to the top of the processing space of the diffusion furnace, and the length of the processing gas introduction pipe exposed to the processing space is 800 to 150 mm.
0 mm, the inner diameter of the processing gas introduction tube is 5 to 20 mm, and a SiC film with a thickness of 20 to 500 μm is formed on the inner and outer surfaces of the processing gas introduction tube by CVD. In the case of a SiC furnace core tube, a soaking tube is not required. In the case of a quartz glass furnace core tube, it is better to install a heat equalizing tube.

Effect: The inner and outer surfaces of the processing gas introduction pipe are coated with a thickness of 20 to 50 mm by CVD.
Since a 0 μm SiC film is formed, the surface can be highly purified, and accordingly, the processing space in the furnace can also be highly purified.

Embodiments Hereinafter, embodiments of the vertical diffusion furnace according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a vertical diffusion furnace 10. As shown in FIG. The vertical diffusion furnace 10 includes a core tube 12 (also called a reaction tube or a process tube) that has a generally cylindrical shape. Furnace core tube 1
2 is opened downward, and the semiconductor wafer 9 is inserted through the opening.
It is configured to take in and out. The furnace core tube 12 is made of quartz glass, and the processing space 8 is formed inside thereof. A large number of semiconductor wafers 9 are installed in the processing space 8 using wafer holding members 28 .

A processing waste introducing pipe 33 is provided in the processing space, and is configured to introduce a predetermined processing waste. Similarly, a processing waste discharge pipe 34 is provided to discharge processing gas.

The length of the portion of the processing gas introduction pipe 33 exposed to the processing space is 1000 to 1300 mm.

In the illustrated example, this length is 1100 mm. Further, the inner diameter and outer diameter of the processing gas introduction pipe 33 are substantially uniform over the entire length, and the inner diameter is 5 to 20 mm and the outer diameter is 6 to 22+ nm, respectively. In the illustrated example, the inner diameter is 12 mm and the outer diameter is 16 mm.

Furthermore, CVD is applied to the inner and outer surfaces of the processing gas introduction pipe 33.
A SiC film is formed by (chemical vapor deposition). SiC
The thickness of the membrane is between 20 and 500 μm, preferably between 50 and 100 μm for best effectiveness.

The most suitable example of a method for forming a SiC film by CVD is a burning method. For example, after forming a SiC film on the outer surface of a carbon rod or tube, the carbon rod or tube is annealed to obtain a SiC tube.

Note that the base material of the processing gas introduction pipe 33 is SiC made by CVD.
It is preferable to form a high-purity SiC tube by forming a membrane.

The wafer holding member 28 has a plurality of heat shield plates 24. Also,
The structure is such that the held wafer is rotated around a vertical axis. The wafer holding member 28 is installed on the furnace lid 16, and the furnace lid 16 is fixed to the base 17. A nut (not shown) is fixed to one end of the base 17. The nut meshes with the feed screw 18.

When the feed screw 18 rotates, the base 17 is fed in the vertical direction (arrow C). By rotating the feed screw 18 in this manner, the wafer is moved. In addition, there is one feed screw,
A guide shaft is provided, which in FIG. 1 is located behind the front lead screw.

A soaking tube 11 is provided outside the furnace core tube 12. The soaking tube 11 has an overall cylindrical shape and is open downward. A tapered curved part is provided at the upper part of the soaking tube 11,
It has a so-called R shape. This curved portion may be constructed integrally with the heat soaking tube body, or may be manufactured separately as a lid and fitted or bonded. When considering gas sealing properties, an adhesive type is preferable to a fitted type. By forming the upper part of the heat soaking tube into an R shape in this manner, thermal shock resistance can be improved compared to the case where the tube has a flat shape. Furthermore, thermal efficiency can also be improved.

The soaking tube 11 is made of SiC or SiC impregnated with Si. Considering oxidation resistance, gas permeability, etc., Si impregnated with Si
C is preferable.

An exhaust pipe 20 is provided above the soaking tube 11. A flange 21 is provided at the end of the exhaust pipe 20. A gas pipe (not shown) can be connected to this flange 21 via a Teflon O-ring. A large number of cooling fins 22 are installed on the outside of the exhaust pipe 20.

A stainless steel pedestal 15 is attached to the outer periphery of the lower end of the soaking tube 11.
is the provision.

A stainless steel member 29 is screwed and installed under the pedestal 15. A soaking tube 11 is installed on the member 29, and an O-ring 30 made of Teflon is provided at the contact portion between the soaking tube 11 and the member 29 to improve the airtightness of the furnace.

A gas introduction pipe 23 is installed in the member 29 as a gas introduction means, and is configured to introduce gas into the space 26 between the furnace core tube and the soaking tube (arrow A). In this embodiment, gas introduction pipes 23 are provided at two opposing locations. The gas introduced by the gas introduction pipe 23, for example, nitrogen gas containing hydrochloric acid gas, is discharged from the exhaust pipe 20 provided above the soaking tube 11 through a gas pipe (not shown) (arrow B).

A stainless steel member 25 is provided between the member 29 and the furnace cover 16.
are arranged and screwed to the member 29. Part 2
O-rings 31 and 19 made of Teflon are provided between the member 9 and the member 25 and between the member 25 and the furnace lid 16 to improve the airtightness of the furnace.

A furnace core tube 12 is installed on the member 25, and an O-ring 31 made of Teflon is provided at the contact portion between the furnace core tube 12 and the member 25. If only the furnace core tube is to be replaced, it can be replaced by removing the screws fixing the member 25 to the member 29 and moving it downward together with the furnace lid 16.

The pedestal 15, the member 29, the member 25, and the furnace lid 16 may be made hollow and configured to be cooled.

A heater 13 is arranged outside the soaking tube 11. A heat insulating body 14 made of, for example, heat insulating fiber is formed on the outside of the heater 13.

The gas flow rate can be adjusted depending on the conditions of use.

In order to clarify the effect of gas flow, we investigated the inside of a silicon wafer oxide film when oxidation treatment was performed by flowing nitrogen gas containing hydrochloric acid gas at 51'/min and when oxidation treatment was performed without flowing any gas. The content of sodium and nickel was measured. An oxide film having a thickness of approximately 1000 angstroms was formed. The results are shown in Table 1. From Table 1, it is clear that the intrusion of metal vapor can be prevented by flowing gas between the furnace core tube and the soaking tube.

Next, in order to clarify the effect of the heat dissipation fins, the temperature at the flange end face of the waste exhaust pipe with heat dissipation fins and the gas pipe without fins was measured. The results are shown in Table 2. Table 2 reveals that the temperature of the flange portion of the waste exhaust pipe can be significantly reduced by providing the fins.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing an embodiment of a vertical diffusion furnace according to the present invention, and Figure 2 shows the furnace shown in Figure 1 with the furnace lid and base moved downward to take in and out wafers. It is a schematic diagram. 10...Vertical diffusion furnace 12...Furnace core tube 11...Soaking tube 13...Heater 14...Insulator 23...Gas introduction means 20...Gas exhaust pipe 22... Heat dissipation fin 1st collector

Claims (1)

[Claims] In a vertical diffusion furnace that has a furnace core tube that opens downward, a heater installed outside the core tube, and a heat insulator installed outside the heater, processing gas is introduced vertically from the bottom to the top of the processing space of the diffusion furnace. A tube is provided, the length of the processing gas introduction pipe exposed to the processing space is set to 800 to 1500 mm, the inner diameter of the processing gas introduction pipe is set to 5 to 20 mm, and the inner and outer surfaces of the processing gas introduction pipe are coated with a thickness of 20 to 20 mm by CVD. 500μm
A diffusion furnace characterized by forming a SiC film.