Heater unit for semiconductor processing

Details Heater unit for semiconductor processing Heater unit for semiconductor processing

1999-07-01

2001-01-30

Walberg, Teresa (Department: 3742)

Electric heating

Heating devices

With heating unit structure

C219S444100, C118S725000

Reexamination Certificate

active

06180931

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. The present invention also relates to a method for producing such a heater unit.
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. 5
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. 6
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. 7
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 edge
19
.
A cast heater unit demonstrates a favorable heat conductivity owing to the close contact between the metallic base and the heating element. However, the metallic base is typically made of aluminum or an aluminum alloy 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 the casting temperature of aluminum is higher than 700° C., the sheath pipe must be made of a high melting point material such as stainless steel and Inconel. Because the material of the sheath pipe differs in thermal expansion coefficient from the aluminum base, the resulting thermal stress may cause deformation to the heater element under a high temperature condition, and the repeated thermal stress may cause damage to the resistance heater wire and warping of the heater unit.
A clamped heater unit using an aluminum base can be used only in a same temperature range as a cast heater unit. But, because the sheath heater is retained by the base only physically, the repeated thermal stress is less likely to cause damage to the resistance heater wire. On the other hand, a certain gap is created in the groove, and this gap impairs heat transfer. In particular, the contact between the sheath heater and the base, and between the upper and lower bases is not very intimate, and this results in a poor thermal conductivity and 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 method for fabricating such a heater in both economical and reliable manner.
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 element interposed in a groove defined between opposing surfaces of the lower and upper bases; wherein the opposing surfaces of the lower and upper bases, and the resistance heater element are substantially entirely bonded to one another by a metallic bonding which may consist of brazing, soldering or diffusion bonding.
The metallic bonding provides a favorable heat conduction, and can thereby improve the thermal efficiency and prevent local heating. It also allows rapid temperature rises, and uniform heating. Because the base consists of two parts, the material for the base can be selected from a wide range of materials including those capable of withstanding high temperatures and corrosive materials. Preferably, the resistance heater element comprises a sheath heater including a metallic sheath pipe, resistance heater wire received in the sheath pipe, and insulating material filled in the sheath pipe so as to electrically insulate the resistance heater wire from the sheath pipe. The material for the metallic sheath pipe may be selected from a group consisting of aluminum, aluminum alloys, copper, copper alloys, stainless steels, nickel, chromium and iron alloys, such as Inconel®, titanium and titanium alloys. Also, the upper and lower bases may each consist of a material selected from a group consisting of aluminum, aluminum alloys, copper, copper alloys, stainless steels, nickel-based alloys, titanium and titanium alloys.
The method for fabricating the heater unit of the present invention may comprise the steps of: preparing a lower base having a planar top surface; preparing an upper base having a planar bottom surface; placing the upper base over the lower base with a resistance heater element interposed between the top and bottom surfaces of the lower and upper bases so as to cause a plastic deformation to at least one of the top and bottom surfaces of the lower and upper bases until the corresponding surface conform to an outer profile of the heater element, and causing the opposing surfaces of the lower and upper bases, and the resistance heater element substantially entirely bonded to one another by a metallic bonding. The plastic deformation of at least one of the top and bottom surfaces of the lower and upper bases ensures a close contact between the opposing surfaces of the lower and upper bases and the resistance heater element.
The opposing surfaces of the lower and upper bases may consist of simple planar surfaces, and the resistance heater element may be received in a groove which is formed by plastic deformation of at least one of the opposing surfaces of the lower and upper bases. But, more preferably, at least one of the top surface of the lower base and the bottom surface of the upper base is provided with a groove for substantially closely receiving the resistance heater element prior to the plastic deformation. This allows the proper positioning of the resistance heater wire during the fabrication process, and the proper selection of the extent of the plastic deformation that

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