Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
1999-10-28
2001-02-06
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S546000, C219S548000, C206S303000
Reexamination Certificate
active
06184507
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a package of a carbon heater used for manufacturing a mono crystal body and a method of forming the same and, more particularly to a package of a carbon heater, which is used as a heat source provided on an apparaties for manufacturing a silicon mono crystal body, such as electronic device parts or the like, the package being obtained by matching the structure and character of the graphite material, with which the carbon heater are made, and a method of obtaining the same.
The manufacturing of a mono crystal body will now be descried in connection with the manufacturing of a mono crystal body of silicon by using a raising system, such as CZ method. However, the invention is also applicable to carbon heaters used as heat source for manufacturing other mono crystals, such as those of germanium and other metals.
PRIOR ART
In the field of electronic communication equipment, mono crystal bodies of silicon (hereinafter referred to as mono crystals) are used as substrates of semiconductor devices and integrated circuits. Silicon mono crystal is obtained by raising via a seed crystal from a molten silicon bath containing molten polycrystalline silicon as material, that is, it is manufactured by growing in so-called liquid phase epitaxy.
Such silicon mono crystals are mostly manufactured in the CZ method. In the CZ method, a carbon heater, i.e., a heater made of graphite material, is used as a heat source for thermally melting polycrystalline silicon in the case of manufacturing silicon mono crystal by using CZ method. This is done so because the graphite material with use of the carbon heater has the following properties.
(A) Graphite material is not molten under normal pressure, and its sublimation temperature is very high.
(B) Graphite material has very high radiation capacity or about 0.8 or above, i.e., nearly 1.0.
(C) Unlike metallic materials which are softened at high temperatures, the high temperature mechanical strength of graphite material is very high; the strength is increased in proportion to the temperature up to a temperature of 250° C.
(D) Graphite material has adequate electric resistance as resistive heat generator, the resistance increasing in proportion to the temperature at temperatures above 500° C. The material thus has very suitable character as the resistive heat generator.
(E) Graphite material has low thermal expansion coefficients.
(F) Graphite material can be readily freely machined. However, since the machining is liable to result in spoiling of the mechanical strength, imitations are imposed on the method of matching and the structure.
(G) Graphite material is far inexpensive compared to other competitive materials, such as platinum, rhodium, tungsten and molybdenum.
(H) High purity graphite material is less subject to gas generation, and is thus suitable as heat source for silicon single crystal raising, in which the product quality is influenced by gas generation.
The carbon heater makes use of the above properties of graphite material. In the meantime, in the carbon heater considerations are paid to increase the electric resistance within a range free from spoiling the mechanical strength. Specifically, as shown in
FIG. 6
, the carbon heater is formed as a cylindrical body
2
of graphite material, and its peripheral wall is formed with axial slit-like notches
3
cut from alternate upper and lower ends to define conductive portions
4
between adjacent notches
3
. The conductive portions
4
are continuous to one another at the alternate upper and lower ends and constitute a single long conductive part. By forming such conductive part, the electric resistance can be increased, so that a high temperature can be obtained. A pair of current application terminals
5
are provided on the conductive part
45
on the diametrically opposite sides thereof. The terminals
5
project from one end of the body
2
. When using the carbon heater as such, it is set with the terminals
5
as legs, so that the afore-mentioned end constitutes the lower end. At the time of the packing, however, the body
2
is inverted, and is put into a packing body with its end with the terminals
5
projecting therefrom as the upper end. Thus, the following description will be made with the end, from which the terminals
5
project, as the upper end. The terminals
5
are angle-like or L-shaped in sectional profile, having portions
51
projecting radially inward or outward. In
FIG. 6
, the portions
51
are shown projecting radially inward.
The carbon heater having the above structure can serve as a very excellent resistive heat generator. However, since it is made of graphite material and has the continuous long conductive part
4
, which is defined by a plurality of axial slit-like notches
3
, it will be readily broken by slight shocks or external forces that are experienced. Particularly, the current application terminals
5
which project from the upper end of the body
2
will be broken or damaged even by slight external forces.
In the case when moving the carbon heater having such a shape to a storage site or a site of use or shipping the carbon heater as a product, considerable cares should be exercised in the packing.
Accordingly, various packages of and methods of packing the above carbon heater have been proposed.
In one example of Method, since the carbon heater is cylindrically hollow in shape, it is put in a box by reinforcing it with buffering materials of indefinite shapes or like fillers fitted in its inside. However, the carbon heater has a diameter of 30 to 10 cm and a height of 30 to 80 cm, and thus requires a great quantity of fillers. A problem is thus posed in connection with the discarding of used fillers.
In addition, in the above packing method it is impossible to protect the pair current application terminals, which project from the upper end of the carbon heater and are very weak in mechanical strength.
Japanese Patent Laid-Open No. 5-51065 proposes packing core materials used for protecting a carbon heater as shown in FIG.
6
. In this case, the core materials are accommodated in the cylindrical body of the carbon heater. Japanese Patent Laid-Open No. 5-51086 proposes carbon heater packing vessels with such core materials inserted therein.
The former proposed core material is a one-piece resin foam member, which is cylindrical such as to be able to be alignedly set in a cylindrical body of a carbon heater and has a lower end flange for supporting the lower end surface of the carbon heater body.
However, this one-piece resin foam core material is light in weight and merely inserted in the carbon heater for reinforcement thereof, and basically does not protect the carbon heater against external forces applied thereto during transport.
In addition, the former proposed core material is considerably voluminous when applied to carbon heaters, and therefore poses considerable problems in its discarding after use.
The latter proposed packing vessel has an integral structure comprising a vessel body for accommodating a carbon heater and pallet member mounted on the underside of the vessel body and having a fork-lift pawl inserting portion.
This packing vessel, however, aims at logical and machinerized carbon heater conveying operations, and is not intended to directly protect a carbon heater during the transport thereof.
SUMMARY OF THE INVENTION
The invention seeks to solve the above problems resulting from use of the conventional packing of the carbon heater, and it has an object of providing a good package of a carbon heater used for manufacturing a mono crystal body by CZ method. The package is obtainable by making effective use of the property of graphite material with which of the carbon heater is manufactured, and free from the conventional environment problems in the discarding of shock absorbing materials and like packing materials. Furthermore, the package is capable of being safely transported to the customer or the like and capable of being easily unpacked by the customer, and also a method of f
Kouno Tadayoshi
Masaoka Akira
Tanaka Saburou
Fuqua Shawntina
Nippon Carbon Co. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Walberg Teresa
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