Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Reexamination Certificate
1998-08-24
2001-02-13
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
C264S625000, C264S666000, C264S682000
Reexamination Certificate
active
06187704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heater member formed from silicon carbide, which exhibits high durability in an oxidizing atmosphere, in a vacuum atmosphere, and even in a corrosive atmosphere, and which has excellent temperature uniformity.
2. Description of the Related Art
A metallic material such as a nickel chrome alloy or a carbon material such as graphite is generally employed for a heating body of a heater member used in various types of thermal treatment equipment or in heating furnaces. In these heaters, the metallic material is corroded by oxidation or is partially melted due to heating at temperatures of 1,000° C. or more and cannot withstand use at high temperatures. On the other hand, although carbon materials have excellent heat resistance, they generate carbon monoxide or carbon dioxide when used in an oxidized atmosphere such as in the ambient air and are gradually worn away. For this reason, there exists a drawback in that a sufficient life duration cannot be obtained.
In semiconductor manufacturing processes such as large scale integration (LSI) of recent years, a process for oxidizing a silicon surface, a process for diffusing a dopant element such as phosphorus or boron in silicon, and the like each require heating processing at temperatures of 1,000° C. or higher, and also require the heating of a silicon wafer directly from a lower portion thereof to form various functional films. When a heater member formed of a metallic material or containing a significant amount of a heavy metal is used in such a process, there is a possibility that a wafer be contaminated during the process. Further, gases having special corrosiveness must be used during the various processings or during post-treatment furnace washing. Accordingly, in consideration of the ease of reaction with such gases, it cannot be said that a heater member formed of a metallic material or a heater member formed of a carbon material can be suitably used.
In view of the above-described circumstances, there has been the need for a heater member which is stable in any of various atmospheres, such as an oxidizing atmosphere and a corrosive-gas atmosphere, and which does not cause any contamination due to the metallic elements contained therein. In recent years, a ceramic heater member is used to satisfy this purpose, and particularly, silicon carbide which has a high heat resistance has come to be noticed. Silicone carbide currently used is porous silicone carbide which causes relatively less contamination by metal and which can be obtained without the addition of a metal-based sintering auxiliary. However, this material has drawbacks in that abnormal heat generation is caused by localized non-uniformity of the resistance distribution and deterioration in performance over time is caused by a reduction in the mechanical strength.
In order to overcome the above-described drawbacks, a silicon carbide rich film is formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD) on the surface of a conventional heater member formed of a carbon material or the like, to improve resistance to a corrosive atmosphere and the like. However, in this case, the silicon carbide film is a thin film and thus separates from a base material due to the difference between the coefficients of thermal expansion of the base material and the coating film, thereby resulting in deterioration of durability.
Accordingly, a silicon carbide sintering process and a sintered body with no harmful additives, which are suitable for the above-described fields of application, are desired. For example, there have been proposed the following methods in which a gas or a solution, containing silicon and carbon, is used as a raw material: (1) a method for producing a sintered body in such a manner that very fine powder is formed by vapor phase epitaxy and is used as a material for the sintered body; and (2) a method for producing a plate-shaped molded body (sintered body) directly by vapor phase epitaxy.
However, these methods each have disadvantages in that productivity is low and cost is high. Further, the above method (1) also has disadvantages in that the resultant powder is too fine and particles are apt to be generated even after sintering, and method (2) has disadvantages in that it is difficult to obtain a thick molded body and it is not easy for the obtained molded body to have a volume resistivity of 10 &OHgr;cm or less which is suitable for a heater member.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above-described circumstances, and an object thereof is to provide a heater member which exhibits high durability in an oxidizing atmosphere, in a vacuum atmosphere, and even in a corrosive atmosphere, and which has excellent uniformity of temperature.
As a result of studies, the present inventors have found that when a sintered body of silicon carbide obtained by a specific production method is used as a heater member, the sintered body exhibits very excellent properties, and the present inventors thus arrived at the present invention.
The heater member of the present invention is formed by a silicon carbide sintered body which has a density of 2.9 g/cm
3
or higher and which is obtained by sintering a homogeneous mixture of silicon carbide powder and a non-metal-based sintering auxiliary.
The non-metal-based sintering auxiliary is preferably an organic compound which produces carbon upon heating. Further, the non-metal-based sintering auxiliary may be present in such a manner as to cover the surface of the silicon carbide powder.
The silicon carbide sintered body can be obtained by hot-pressing the mixture in a non-oxidizing atmosphere. The resultant silicon carbide sintered body preferably has a volume resistivity of 10 &OHgr;cm or less.
The silicon carbide powder can be produced by a production process comprising the steps of: solidifying a mixture of a silicon source containing at least one liquid silicon compound, a carbon source containing at least one liquid organic compound that produces carbon upon heating, and a polymerization catalyst or a cross-linking catalyst, to obtain a solid product; and heating and sintering the resultant solid product in a non-oxidizing atmosphere.
The total content of impurity elements contained in the silicon carbide sintered body is preferably 1 ppm or less.
In accordance with the present invention, when the silicon carbide powder is sintered, only a non-metal-based sintering auxiliary is used as the sintering auxiliary, and no metal-based sintering auxiliary comprising a metal such as boron, aluminum or beryllium or a compound thereof and no carbon-based sintering auxiliary such as carbon black or graphite are used. For this reason, there can be provided a heater member which has a high purity sintered body, and which has a low number of foreign matters at grain boundaries, and which, due to the intrinsic properties of silicon carbide, exhibits higher durability even under severe conditions such as an atmosphere of corrosive gas than a conventional carbon material does, and which has excellent uniformity in temperature.
Further, when powder of the silicon carbide sintered body obtained by the production process of the present invention is used as a material for the silicon carbide sintered body, a sintered body of a higher purity can be obtained, and the total content of elements other than silicon, carbon and oxygen can be 1 ppm or less.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will hereinafter be described in further detail.
Silicon carbide powder used as a raw material for the heater member made of silicon carbide according to the present invention may be &agr;-type, &bgr;-type, amorphous type, or a mixture thereof. Particularly, &bgr;-type silicon carbide powder is preferably used from the standpoint of the coefficient of thermal expansion of the sintered body. The grade of the &bgr;-type silicon carbide powder is not particularly limited. For example, a commercially av
Satou Akira
Takahashi Yoshitomo
Wada Hiroaki
Bridgestone Corporation
Group Karl
Oliff & Berridg,e PLC
LandOfFree
Process for making heater member does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for making heater member, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for making heater member will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2568231