Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-10-29
2001-03-20
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S544000
Reexamination Certificate
active
06204486
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a heater unit for semiconductor processing, and in particular to a heater unit having a resistance heating element embedded in a metallic base.
BACKGROUND OF THE INVENTION
Conventionally, heater units having a resistance heating element embedded in a metallic base have been widely used in susceptors and electrostatic chucks for semiconductor processing. The resistance heating element typically consists of a sheath heater including a sheath tube made of stainless steel. Typically, a stainless steel sheath heater is cast into an aluminum base, clamped between a pair of aluminum or stainless plates, or interposed between a pair of plates which are joined together by welding along the outer edge.
FIG. 7
shows a conventional cast heater unit
10
including a base
11
having a stainless steel sheath heater
12
cast therein. The stainless steel sheath heater
12
typically comprises a stainless steel sheath pipe, a resistance heater wire received in the sheath pipe, and an insulator which electrically insulates the resistance heater wire from the sheath pipe. The sheath heater
12
is bent into a desired shape, and is cast into the aluminum base
11
. The aluminum base
11
is then machined and polished to a desired finish.
FIG. 8
shows a conventional clamped heater unit
13
. In this case, the metallic base consists of a lower base
14
and an upper base
15
, each made of an aluminum or stainless steel plate. A sheath heater
12
is received in a groove
14
a
formed in the lower base
14
, and the upper base
15
is placed closely over the lower base
14
. The upper and lower bases
14
and
15
are then firmly joined with each other by fastening them together with threaded bolts.
FIG. 9
shows a conventional welded heater unit
16
. In this case also, the metallic base consists of a lower base
17
and an upper base
18
, each made of an aluminum or stainless steel plate. Likewise, a sheath heater
12
is placed in a groove
17
a
formed in the lower base
17
, and the upper base
18
is placed closely over the lower base
17
. The upper and lower bases
17
and
18
are then firmly joined with each other by welding them together along their edges
19
.
Each of the above described conventional arrangements uses a sheath heater which is bent into a meandering shape, and embedded in the base. It is desirable to sharply bend the sheath heater so that the sheath heater may extend uniformly in a fine pitch to the end of rapidly and uniformly heating the base. However, there is some difficulty in bending the sheath heater at sharp angles without causing excessive stress to the sheath heater.
Also, in the case of the cast heater unit, the metallic base typically consists of aluminum which has a relatively low melting point (typically about 540° C.), and the cast heater unit using such a metallic base is therefore unsuitable for use in a high temperature environment exceeding 500° C. in temperature. Also, because of the sheath tube is typically made of stainless steel which has a substantially different thermal expansion coefficient from that of aluminum, the resulting thermal stress may cause deformation at high temperatures, and repeated applications of such a thermal stress may cause a breaking of the heater wire and/or a deformation of the heater unit.
In the case of the clamped heater unit, a certain gap is created between the upper and lower bases and/or between the sheath heater and the base, and this gap impairs heat transfer. It may prevent a highly responsive temperature control, and may cause localized temperature rises. Localized temperature rises are known to impair the durability of the resistance heater wire.
A welded heater unit is not much different from a clamped heater unit in these respects, and has the additional problem of distortion due to the heat at the time of welding.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide a heater unit for semiconductor processing which is capable of quickly raising temperature, and heating uniformly.
A second object of the present invention is to provide a heater unit for semiconductor processing which allows a selection of materials from a wide range, and can be therefore adapted for use in high temperature environments.
A third object of the present invention is to provide a heater unit for semiconductor processing which is durable in use.
A fourth object of the present invention is to provide a heater unit for semiconductor processing which is suited for highly responsive temperature control.
According to the present invention, these and other objects can be accomplished by providing a heater unit, comprising; a lower metallic base; an upper metallic base placed closely over an upper surface of the lower base; and a resistance heater wire received in a groove defined between opposing surfaces of the lower and upper bases; wherein ceramic powder or other electrically insulating powder is filled in the groove to keep the heater wire at least away from a wall surface of the groove.
Because the heater wire can be directly installed in the groove of the base without the intervention of a sheath pipe, it is possible to bend the heater wire in a desired dense pattern so that the heater unit can be heated both rapidly and uniformly. Also, the electrically insulating powder filled in the groove improves the heat transfer, and this even further enhances the above mentioned advantages of the present invention.
To facilitate the placement of the heater wire in the groove, and prevent the heater wire from touching the base which is made of metallic material, spacers may be provided at a plurality of locations along the length of the heater wire for electrically insulating the heater wire from an adjacent surface of the upper and lower bases. The spacers may each consist of an annular member through which the heater wire is passed. The spacer preferably consists of ceramic or other materials which can withstand high temperatures without losing their required mechanical properties.
The upper and lower metallic bases are joined with each other most preferably by a bonding method selected from a group consisting of brazing, soldering and diffusion bonding. But, they may also be joined with each other by clamping, welding or any other known methods.
REFERENCES:
patent: 2359983 (1944-10-01), Fry
patent: 3110795 (1963-11-01), Bremer
patent: 3436816 (1969-04-01), Lemelson
Amakawa Tsutomu
Futakuchiya Jun
Ishiwata Hidenori
Masaki Takashi
Miyaji Shinya
Marger & Johnson & McCollom, P.C.
NHK Spring Co. Ltd.
Paik Sang
LandOfFree
Heater unit for semiconductor processing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heater unit for semiconductor processing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heater unit for semiconductor processing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478693