Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
1998-12-22
2001-03-20
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S444100, C219S468100, C219S553000, C118S725000
Reexamination Certificate
active
06204489
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the invention
This invention relates to a heater in which a heating element is embedded in a ceramic substrate and a method of manufacturing the same for treating a substance to be heated, such as semiconductor wafer.
(2) Related Art Statement
Attention is now paid to dense ceramics as a substrate for an electrostatic chuck. In equipment for manufacturing a semiconductor, a halogen corrosive gas such as ClF
3
is frequently used as an etching gas or a cleaning gas. Moreover, for rapidly heating and cooling a semiconductor wafer while holding it, it is desired that a substrate of an electrostatic chuck has a high heat conductivity and a thermal shock-resistance to prevent destruction due to rapid thermal changes. Dense aluminum nitride has high corrosive-resistance against the above halogen corrosion gas. Moreover, aluminum nitride is known as a material with high thermal conductivity with a volume resistivity of 10
14
&OHgr;cm or over at room temperature and high thermal shock-resistance. It is therefore considered preferable that a substrate of an electrostatic chuck as an equipment for manufacturing a semiconductor is formed of an aluminum nitride sintered body. It is proposed that a substrate of a ceramic heater or a heater with a built-in high frequency electrode is formed of aluminum nitride.
NGK Insulators, Ltd. discloses in Japanese examined patent publication No. 7-50736 that a resistance heating element and an electrostatic chuck electrode are embedded in a substrate of aluminum nitride or a resistance heating element and an electrode for generating a high frequency are embedded therein.
When a resistance heating element and a high frequency electrode were embedded in a aluminum nitride substrate to make an electrode for generating high frequency waves and the electrode was operated at a high temperature, for example, 600° C. or over, the state of the high frequency waves or the state of the high frequency plasma often became unstable. Moreover, when a resistance heating element and an electrostatic chuck electrode were embedded in the aluminum nitride substrate to make an electrostatic chuck and the equipment was operated at a high temperature, for example, 600° C. or over, the electrostatic adsorption power in the electrostatic chuck became unstable locally or with the passage of time.
SUMMARY OF THE INVENTION
It is an object to stabilize the operational state in every portion of the heater or the operational state of the heater with the passage of time, the heater comprising a substrate of a ceramic material, a heating element embedded in the substrate, and a heating surface for dealing with a substance to be heated on the substrate.
This invention relates to a heater comprising a substrate having a heating surface to treat a substance to be heated on the substrate, a heating element embedded in the substrate, and a resistance control part, wherein the substrate comprises a first ceramic material and the resistance control part comprises a second ceramic material which has higher volume resistivity than that of the first ceramic material.
This invention also relates to a method of manufacturing the above heater comprising the steps of preparing a substrate preform to be sintered as a ceramic substrate, providing a part to be sintered as a resistance control part in the substrate, and hot-pressing and sintering the substrate preform and the part. present inventors investigated causes of generating the instability in, for example, the high frequency condition of the high frequency electrode. As a result, they found that leak current, which flows between the heating element in the substrate and the high frequency electrode, disturbs the high frequency condition.
To solve the problem, they found that a resistance control part which is formed of a second ceramic material having a higher volume resistivity than that of a first ceramic material of the substrate is provided in the substrate and thereby the influence of the leak current is restrained or controlled. They reached this invention based on the above discovery.
It is particularly known that the volume resistivity of aluminum nitride shows a behavior like a semiconductor and decreases with an increase in temperature. According to this invention, by using aluminum nitride as a resistance control part, the high frequency condition and electrostatic adsorption power even at a range of 600 to 1200° C. can be stabilized.
The above resistance control part is preferably in a layer-like form, and thereby the leak current can be restrained over a wide range of the heating surface of the substrate.
REFERENCES:
patent: 5280156 (1994-01-01), Niori et al.
patent: 5382469 (1995-01-01), Kubota et al.
patent: 5566043 (1996-10-01), Kawada et al.
patent: 5663865 (1997-09-01), Kawada et al.
patent: 5665260 (1997-09-01), Kawada
patent: 5777543 (1998-07-01), Aida et al.
patent: 5800618 (1998-09-01), Niori et al.
patent: 5811761 (1998-09-01), Kita et al.
patent: 296 23 184 U (1997-11-01), None
patent: 6-232243 (1994-08-01), None
patent: 7-50736 (1995-02-01), None
patent: 8-97272 (1996-04-01), None
Araki Kiyoshi
Katsuda Yuji
Ohashi Tsuneaki
Burr & Brown
Jeffery John A.
NGK Insulators Ltd.
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