Electric resistance heating devices – Heating devices – Radiant heater
Reexamination Certificate
2001-05-25
2003-06-24
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Radiant heater
C392S497000, C338S208000, C219S444100, C423S447700
Reexamination Certificate
active
06584279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heater sealed with a carbon wire heating element therein and more particularly to a heater sealed with a carbon wire heating element in which a carbon wire of carbon fibers having a particular crystal structure is sealed as a heating element, resulting in obtaining a heater sealed with a carbon wire heating element excellent in stable resistance when the current is flowing and particularly in anti-aging characteristic.
2. Description of the Related Art
Heaters using a carbon heating element therein have excellent properties in raising and lowering the temperature due to a small heat capacity as compared to heaters using a metal heating element, and offering a wide industrial application to various types of heating apparatus.
In the field of the semiconductor manufacturing, especially, silicon wafers are subjected to various heat treatments in the process thereof. Moreover, such heat treatments are in need of strict temperature control while it is essential to maintain a clean atmosphere for heat treatment in which no particles such as dust or the like are present. For this purpose, it is required to meet various conditions; that is, the heater used for the heat treatment must show an excellent uniformity in heating performance and the heater will not give off contaminating substances during the process.
In general, heaters having a structure in which carbon heating elements are sealed within support members of quartz glass material together with the atmosphere of a non-oxidizing gas are widely used as a heater for semiconductor manufacturing processes.
The inventors developed, in the past, a heater for semiconductor heat treatment apparatus and proposed the same in Japanese Patent Application H10-254513, in which fine carbon fibers are bound into a carbon bundle and a plurality of such bundles are woven into a carbon wire heating element to be filled in the quartz glass support member together with a non-oxidizing gas.
This type of carbon wire heating element not only shares the advantages required for the carbon heating element such as an excellent property to raise and lower the temperature and a high temperature resistance but also an extra advantage of having more flexibility than the heating elements made of solid carbon material because said carbon wire heating element is manufactured by binding a plurality of fine carbon single fibers into a bundle and weaving a plurality of such bundles to such an extent that various structures and configurations are easily realized.
Therefore, the heater having a clean and heat-resistant support member of high purity quartz glass support member in which this type of heating element is sealed together with a non-oxidizing gas is free from a risk of giving off particles and is most suitable to the semiconductor manufacturing heater.
It is to be noted here that the carbon wires used for the conventional heater of this type were manufactured by following a baking process to carbonize the fiber form precursor at a temperature in the neighborhood of about 1300° C. and that the quality of the product is maintained by improving the purity of materials to suppress the concentration of contained impurities thereof at a level of 10 ppm or less.
Recently, however, it was recently observed that said conventional carbon wires for the heating element were often used at a temperature higher than the prescribed temperature needed for firing and the disadvantage that the heater performance such as electric resistance thereof or the like becomes unstable has been pointed out.
More specifically,
{circle around (1)} The crystal structure of carbon single fibers composing the carbon wire gradually changes under the heat to lower the carbon wire resistance (&OHgr;/m) gradually to such an extent that a change in the resistance of the whole heater due to aging takes place; and
{circle around (2)} The chemicals adhered to the carbon wires are liberated by the heat in the form of a gas to change the inner pressure inside the quartz glass member filled with the carbon wires during the long service life thereof with the result that the performance of the heating element is affected.
It is not rare that such heater sealed with the carbon wire heating element as being put to the industrial use including said heater for the heat treatment of semiconductor wafers has an instantaneous temperature as high as 1800° C. when the current flows. Therefore, any solution of such problem has been much in demand.
SUMMARY OF THE INVENTION
The present invention is made to solve the problems present in the conventional carbon wire heating element and its object is to provide an excellent heater sealed with a carbon wire heating element which has a stable resistance when the current is flowing and particularly a stable resistance free from aging; that is, the heating performance of the heater will not change throughout a long service period.
Therefore, the present invention provides a heater sealed with carbon wire heating element comprising a heating element composed of carbon wires each being prepared by knitting carbon single fibers into a knitted cord or a braid, each carbon single fiber having a crystal structure with a interlayer spacing d (002) thereof being 0.343 or less and a crystallite size Lc (002) thereof being 4.0 nm or more; and a quartz glass member sealed with said heating element.
Further, the present invention also provide a heater sealed with carbon wire heating element, in a preferred mode of embodiment, characterized in that said heating element is prepared by binding a plurality of carbon single fibers into a bundle, each single fiber having a diameter of 5 through 15 &mgr;m and knitting a plurality of such bundles into a knitted cord or a braid.
Specifically, a heater sealed with carbon wire sealing element which is characterized in being prepared by binding 3000 through 6000 carbon single fibers into a bundle and knitting 6 through 12 such bundles into a knitted cord or a braid having a diameter of 1.5 through 3.0 mm is proposed.
Still further, the present invention provides a heater sealed with carbon wire sealing element which is characterized in that said carbon single fibers contain ash contents of 1 ppm or less.
Still further, the present invention provides a heater sealed with carbon wire sealing element which is characterized in that said heating element composed of carbon wire prepared by knitting carbon single fibers into a knitted cord or braid is subjected to a heat treatment at a temperature of 2000° C. or more in an inert gas atmosphere.
Still further, the present invention provides a heater sealed with carbon wire sealing element which is characterized in that said quartz glass member is provided with two terminals between which said carbon wire heating element is extended, at least one of said two terminals being provided with a mechanism to adjust a tension exerted on said carbon wire heating element.
The structural feature of the heater sealed with carbon wire sealing element according to the present invention is in that the heating element is composed of carbon wires each being prepared by knitting carbon single fibers into a knitted cord or a braid, each carbon single fiber having a crystal structure with a interlayer spacing d (002) thereof being 0.343 or less and a crystallite size Lc (002) thereof being 4.0 nm; and a quartz glass member sealed with said heating element.
Furthermore, said interlayer spacing d (002) and said crystallite size Lc (002) are measured using Gakushin-method for X-ray diffraction of carbon (Japan Society for the Promotion of Science, Committee 117, Carbon, 1963[36], 25).
The carbon wire heating element composed of carbon fibers having a special crystal structure is obtained by subjecting a carbon wire for the ordinary heating element to a heat treatment at a temperature of 2000° C. or more in an inert gas atmosphere.
The carbon wire heating element according to the present invention will not undergo any change in
Kobayashi Masakazu
Konn Tomio
Nagata Tomohiro
Nakao Ken
Saito Norihiko
Dahbour Fadi H.
Toshiba Ceramics Co. Ltd.
Walberg Teresa
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