Heating – Work feeding – agitating – discharging or conveying... – Removable furnace bottom section or kiln cart
Patent
1993-12-23
1996-01-02
Bennett, Henry A.
Heating
Work feeding, agitating, discharging or conveying...
Removable furnace bottom section or kiln cart
432214, 432218, 432205, 432152, 432176, F27D 312
Patent
active
054803004
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a vertical heat-treating apparatus constructed so that a vertical holder, which is constructed so as to vertically dispose plate-shaped members (hereinafter referred to as substrates), glass substrates or the like such as a semiconductor wafer or liquid crystal one above the other, can be arranged on a heat insulator, and to a heat insulator therefor.
BACKGROUND OF THE INVENTION
Conventionally, there is known a heat-treating apparatus, for example, as shown in FIG. 6, which is constructed to house a wafer holder 3 in which wafers 4 are disposed one above the other within a furnace tube 2 made of silica glass surrounded by heating a means 1 and which performs various heat treatments, such as oxidation, diffusion, vapor phase deposition and annealing, on the surface area of the wafers 4 placed on the wafer holder 3 while heating and maintaining the wafers 4 within a predetermined temperature range by means of the aforementioned heating means 1.
To minimize the space required for installation of this type of heat-treating apparatus, a vertically-structured heat-treating apparatus furnace is usually used in which the foregoing furnace tube 2 is vertically installed. In such an apparatus, however, to prevent variations in the thickness of thin film to be formed or doped on the surfaces of the wafers 4 and in the diffusate density distribution due to uneven temperature, a heat insulator 5 made of silica glass is provided between a heating area A in the furnace tube 2 and the open end of furnace tube 2 to maintain a uniform temperature in the space where the aforementioned wafers 4 are heat-treated. In addition, the heating means 1, which surrounds the aforementioned furnace tube 2, is located above the heat insulator 5 so that the heat insulator 5 functions as a heat insulating material, thereby preventing heat loss through O-rings 6 provided between the open end of the core tube 2 and another sealing member.
Such an apparatus is constructed so that the wafer holder 3 is placed directly on the aforementioned heat insulator 5. However, the heat insulator 5 is generally formed by vacuum sealing lint-like silica glass wool 5b within a sealed cylindrical body 5a made of silica glass, and consequently the heat insulator has low load resistance properties, thus limiting the number and diameter of wafers which can be disposed thereon.
Yet, since the top surface of the aforementioned heat insulator 5 is always exposed to high temperature due to radiant heat from heating means 1 which surrounds the furnace tube 2 above the insulator, if gas (air) remains in the sealed cylindrical body 5a or if pinholes communicating with outside air occur as a result of subsequent cleaning or the like so that the sealing is lost and cleaning liquid or outside air is allowed to enter, the remaining gas (air) or the air or cleaning liquid which has entered the cylindrical body is rapidly heated, thereby further increasing the internal pressure load by thermal expansion or expansion and vaporization, and thus possibly rupturing and destroying the cylindrical body 5a.
To prevent such destruction, ribs, braces or other reinforcing bars have been provided within the foregoing cylindrical body 5a to increase the pressure resistance. In recent years, however, as the diameter of the wafers 4 has become larger and the core tube 2 has been made larger, the diameter of the foregoing heat insulator 5 has also been made larger, which correspondingly decreases the pressure resistance. Accordingly, the number of the aforementioned reinforcing bars to be provided has to be increased in geometric ratio, which makes it more complicated to manufacture the heat insulator 5 and greatly increases the manufacturing cost. In addition, particularly if the diameter of the aforementioned heat insulator 5 is made as large as about 150 to 200 mm, it would be very difficult to design and manufacture an insulator with a large enough number of reinforcing bars to be sufficient to withstand the pressure in a vac
REFERENCES:
patent: 5000682 (1991-03-01), Heidt et al.
patent: 5330352 (1994-07-01), Watanabe et al.
Kimura Hiroyuki
Okoshi Shinichi
Bennett Henry A.
Ohri Siddharth
Shin-Etsu Quartz Products Co. Ltd.
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