Abstrict
An electric heater has multiple zones, wherein the multiple zones
include at least one zone which is subject to high loading (e.g.
bottom zone) and, at least one zone is a non-metal heating element,
and the rest of the zones (e.g. middle zone and top zone) are metal
resistance heating elements of light gauge overbent.
Claims
What is claimed is:
1. A cylindrically shaped multi-zone electric heater for a semiconductor
processing equipment, wherein the heater comprises multiple zones
aligned to form a cylindrical shape and the multiple zones include
at least one zone which is subject to high loading, the said at
least one zone comprises a non-metal heating element, and the rest
of the zones comprise metal resistance heating elements.
2. The electric heater for a semiconductor processing equipment
as claimed in claim 1, wherein the one or more zones of which heating
elements are non-metal heating elements correspond to the said at
least one end zone.
3. The electric heater for a semiconductor processing equipment
as claimed in claim 1, wherein the metal resistance heating element
is of light gauge wire overbent.
4. The electric heater for a semiconductor processing equipment
as claimed in claim 1, wherein the non-metal resistance heating
element is of molybdenum-di-silicide.
5. The electric heater for a semiconductor processing equipment
as claimed in claim 1, wherein each zone comprises a heating element
and one or more blocks which hold the heating elements and consist
of thermal insulation bodies, the blocks being replaceable in block
unit.
6. The electric heater for a semiconductor processing equipment
as claimed in claim 2, wherein the metal resistance heating element
is of light gauge wire overbent.
7. The electric heater for a semiconductor processing equipment
as claimed in claim 2, wherein the non-metal resistance heating
element is of molybdenum-di-silicide.
8. The electric heater for a semiconductor processing equipment
as claimed in claim 2, wherein each zone comprises a heating element
and one or more blocks which hold the heating elements and consist
of thermal insulation bodies, the blocks being replaceable in block
unit.
Description TECHNICAL FIELD
The present invention relates to an electric heater which is preferably
used for an apparatus to perform heat treatments such as oxidation,
diffusion, and/or CVD on semiconductor wafers.
BACKGROUND ART
Conventionally, an electric heater for a batch type heat-treating
equipment for semiconductor wafers is known, such as one employing
a metal resistance heating element (cf. Japanese Patent Unexamined
Publication No. 2001-267261 bulletin), and another employing a non-metal
resistance heating element (cf. Japanese Patent Bulletin No. 3307924).
A heating element as described in Japanese Patent Unexamined Publication
No. 2001-267261 bulletin employs, as a metal wire, a Kanthal (brand
name) wire made of iron/chrome/aluminum system or a similar material,
of around 1 3 mm wire diameter called "light gauge". Besides,
a heating element which employs a Kanthal wire or a similar material,
of around 7 10 mm wire diameter called "heavy gauge" is
used. In case of a heater which employs either of a Kanthal wire
and its equivalents as a material of a heating element, the temperature
of the heating element can reach 1250 1300 degrees Celsius at maximum
when the heater temperature is 1200 degrees Celsius; and because
the heating element starts to creep and is susceptible to damage
at temperatures of above 1200 degrees Celsius, the set temperature
of the heat treating equipment employing this type of heating element
is limited to temperatures not higher than 1200 degrees Celsius
or so. Additionally, at one end zone of a heater, for example, at
the bottom zone of a vertical furnace, unfavorable thermal insulation
condition due to charging, discharging of the work, and existence
of moving section can cause increased loading; so that a problem
with such a zone has been that deformation and/or breaking of a
metal resistance heating element can occur more frequently.
Then, employing a non-metal resistance heating element as described
in the Japanese Patent Bulletin No.3307924 would enable an application
of a heater at higher temperatures compared with a heater which
employs a metal resistance heating element; however, because a non-metal
resistance heating element is expensive, fragile and easy to break,
a problem with such a heating element has been that not only its
initial cost but also repair cost on failure are high.
In view of the above-mentioned fact, the purpose of the present
invention is to provide an electric heater for semiconductor processing
equipments which is inexpensive and usable without problems even
at high temperature.
DISCLOSURE OF INVENTION
An electric heater for semiconductor processing equipments according
to the present invention is characterized by a cylindrically shaped
multi-zone electric heater for semiconductor processing equipments
wherein, the multiple zones include at least one zone which is subject
to high loading, the said at least one zone comprises a non-metal
heating element, and the rest of the zones comprise metal resistance
heating elements.
Among metals as a material of a metal resistance heating element,
Kanthal wire (Kanthal A1 wire, Kanthal APM wire, etc.), a material
which bears high temperature, or its substitute is preferred; and
moreover, Kanthal APM wire or its substitute is particularly preferred.
As for geometry of the metal resistance heating element, either
of a thin wire bent to a sinuous shape (light gauge overbent) and
a thick wire formed to a helical coil (heavy gauge helical coil)
is preferred; and, a light gauge metal heating element is more preferred
in that it is light weight and allows for fast heat-up and cool-down.
Further, as stated above, since the only differences between the
light gauge and the heavy gauge heating elements are energy saving
character and heat response character other than the wire weight
(resources saving character), it is desired to use either or both
of the gauges properly, depending on the specifications of the processing
equipment where the heater is employed, or the specifications of
the heater power supply, etc.
As a non-metal resistance heating element, either of ceramics such
as molybdenum-di-silicide (MoSi.sub.2), graphite, and silicon carbide
is preferred, and molybdenum-di-silicide is particularly preferred
in that it suffers little degradation in the atmospheric air. When
graphite or silicon carbide is employed as a non-metal resistance
heating element, it is desired to enclose the heating element in
a heating element container kept under vacuum. The maximum surface
load of molybdenum-di-silicide is 20W/cm.sup.2, whereas that of
Kanthal wire which is a metal wire of iron/chrome/aluminum system
is 2 to 3.5W/cm.sup.2; therefore, employing molybdenum-di-silicide
can render 10 times as greater heat generation at maximum as compared
with a metal wire. Molybdenum-di-silicide can be used at high temperature
range of up to 1800 degrees Celsius; and moreover, since it undertakes
no aging effect, it requires no care about its life-time, providing
another advantage.
Here, a plurality of zones, for example, in a vertical heater,
consist of a bottom zone, a middle zone and a top zone, and in case
where, for example, magnitude of the loading decreases in the order
of the bottom zone, the top zone, and the middle zone, then, the
bottom zone comprises a non-metal resistance heating element, and
the middle zone and the top zone comprise metal resistance heating
elements. In this case, the middle zone and the top zone are typically
controlled independently. The middle zone consists of one or more
zones, and total number of zones is chosen optionally from values
not less than 3.
Because, with an electric heater for a semiconductor processing
equipment according to the present invention, among the multiple
zones is at least one zone which is subject to high loading and
of which heating element is non-metal, risk of failure of the heating
element by overheat in the said zone which is subject to high loading
is eliminated; this allows for an operation of the heater even at
high temperature without causing problems; and since the heating
elements in the rest of the zones are metal, its cost can be reduced,
and risk of their failure by mechanical shock can be reduced as
well. Thus, an electric heater is available which, in view of heat
resistant temperature, bears comparison with an electric heater
employing only non-metal resistance heating elements in all zones,
and moreover, is inexpensive and easy to handle. The electric heater
is suitably employed for high temperature thermal processes such
as CMOS process and/or SOI process.
Usually, the zone which is subject to high loading can be either
the zone into which a mass of heating capacity is introduced from
outside or the end zone on one or both sides with an opening from
which a large amount of heat escapes outwards. Therefore, employing
non-metal heating elements in such zones can yield ease of temperature
control at the time of semi-conductor processing.
It is preferred that each zone consists of one or a plurality of
blocks each of which comprises a heating element and thermal insulation
body holding the heating element so that replacement can be made
by the block. In the case of a vertical furnace where a plurality
of zones consist of a bottom zone, a middle zone, and a top zone,
the bottom zone corresponds to the end zone on the said one side.
For example, the bottom zone may be formed by a pair of half cylinder
blocks put together facing one another, and the middle zone and
the top zone may be formed by a pair of half cylinder blocks put
together facing one another. The bottom zone may be formed simply
by a cylinder block, and the middle zone and the top zone may also
be formed altogether by a cylinder block. In this case, when a heating
element breaks down at any of the blocks, it is physically possible
to replace merely the block including faulty part; moreover, in
case where reuse of the thermal insulation body is allowed, then
replacing the heating element alone is possible, thus enabling repair
of the electric heater at a minimal additional cost.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a vertical sectional view showing an example of a semiconductor
processing equipment in which an electric heater by the present
invention is employed.
FIG. 2 is a perspective view to show an example of a block configuration
of an electric heater by the present invention for a semiconductor
processing equipment.
FIG. 3 is a sectional view of the post-assembly heater along the
III--III Line of FIG. 2.
FIG. 4 is a sectional view of the post-assembly heater along the
IV--IV Line of FIG. 2.
FIG. 5 is a development view watched from inside of an electric
heater by the present invention for a semiconductor processing equipment.
FIG. 6 depicts some perspective views to show some variations (differences
in mode of divisions) of an electric heater for a semiconductor
processing equipment by the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Best mode for carrying out the present invention is explained below,
referring to the drawings.
FIG. 1 shows a vertical diffusion furnace which is an example of
a semiconductor processing equipment, in which an electric heater
by the present invention is employed; the vertical diffusion furnace
comprises a process tube (1) to perform a heat treatment for semiconductor
wafers, an electric heater (2) installed surrounding the process
tube (1), a boat (3) which is mounted on a heat insulating cylinder
(4) and can carry a number of semiconductor wafers, and a flange
cap (5) which supports the heat insulating cylinder (4), performs
a vertical movement (up/down), and closes a boat insertion opening
at the bottom end of the process tube (1) at the time of the treatment.
The electric heater (2) is sectioned in four control zones consisting
of the bottom zone (2a) as the end zone, the middle zones (2b)(2c)
consisting of two zones, and the top zone (2d); the electric heater
(2) consists of two parts, the non-metal resistance heating element
applied part (6) which comprises a non-metal resistance heating
element (12) and composes the bottom zone (2a), and the metal resistance
heating element applied part (7) which comprises metal resistance
heating elements (22) and composes the remaining zones, i.e. the
two middle zones (2b) (2c) and the top zone (2d).
In the electric heater (2) of the first embodiment, the non-metal
resistance heating element applied part (6) is formed as shown in
FIG. 2 by a pair of half cylinder body blocks (6a) (6b) made to
face one another, and the metal resistance heating element applied
part (7) is formed by a pair of half cylinder body blocks (7a)(7b)
made to face one another.
As shown in detail in FIGS. 3 and 5, the non-metal resistance heating
element applied part (6) of the electric heater (2) comprises a
cylindrical main thermal insulation body (11) made of ceramic fiber,
a non-metal resistance heating element (12) installed on an internal
perimeter surface of the cylindrical main thermal insulation body
(11), an inner thermal insulating material layer (13) and an outer
thermal insulating material layer (14) both of which jacket the
main thermal insulation body (11), a flexible ceramic fiber mat
(15) laid between the body (11) and the layers (13)(14) as a buffer,
and a metal shell (16) covering outside perimeter surface of the
outer thermal insulating material layer (14).
The non-metal resistance heating element (12) is made of molybdenum-di-silicide,
formed to a sinuous shape, and supported at the internal perimeter
surface of the main thermal insulation body (11). The non-metal
resistance heating element (12) made of molybdenum-di-silicide has
an advantage that it can be used with a large surface electric power
load density even at high temperature, and this allows each zone
(2a)(2b)(2c)(2d) to heat-up to a predetermined temperature in a
short time; otherwise, the bottom zone (2a) would be hard to heat-up
in comparison with the other zones (2b)(2c)(2d).
Each half cylinder body block (6a) or (6b) of the non-metal resistance
heating element applied part (6) comprises a pair of heater terminals
(12a) or (12b) respectively, so that one can replace just either
of half cylinder body blocks alone (6a)(6b).
As shown in detail in FIGS. 4 and 5, the metal resistance heating
element applied part (7) of the electric heater (2) comprises a
cylindrical main thermal insulation body (21) made of ceramic fiber,
a metal resistance heating element (22) installed on an internal
perimeter surface of the cylindrical main thermal insulation body
(21), an inner thermal insulating material layer (23) and an outer
thermal insulating material layer (24) both of which jacket the
main thermal insulation body (21), a flexible ceramic fiber mat
(25) laid between the body (21) and the layers (23)(24) as a buffer,
and a metal shell (26) covering outside perimeter surface of the
outer thermal insulating material layer (24). To an internal perimeter
surface of the main thermal insulation body (21) of the metal resistance
heating element applied part (7) are formed a plurality of parallel
grooves (27) with a distance in the perimeter direction, each extending
along the length direction of the main thermal insulation body (21).
The metal resistance heating element (22) is made of iron/chrome/aluminum
system metal wire (fe is contained as the main component, and typically
contains Cr 22%, Al 5.8%; e.g Kanthal wire) and has a wire diameter
of around 1 3 mm which is referred to as "light gauge".
The metal resistance heating element (22) is formed to a sinuous
shape and its amplitude is made to be bigger than the width of the
groove (27). Then, the metal resistance heating element (22) is
supported unitedly in the main thermal insulation body (21) by both
sides part in widthwise direction of the metal resistance heating
element (22) entering in the main thermal insulation body (21) from
both sides of the groove (27).
Each half cylinder body block (7a) or (7b) of the metal resistance
heating element applied part (7) comprises a pair of heater terminals
(22a) or (22b) in each of the middle zones (2b)(2c) and the top
zone (2d), so that one can replace merely either of half cylinder
body blocks (7a)(7b).
With the configuration of the above-mentioned electric heater (2)
which splits into the non-metal resistance heating element applied
part (6) and the metal resistance heating element applied part (7),
when a failure occurs such as damage caused by mechanical shock
on the non-metal resistance heating element applied part (6) or
breaking of the wire caused by wear of the metal resistance heating
element applied part (7), it is possible to replace just either
the non-metal resistance heating element applied part (6) or the
metal resistance heating element applied part (7) alone. Moreover,
since the non-metal resistance heating element applied part (6)
and the metal resistance heating element applied part (7) are respectively
formed by a pair of half cylinder body blocks (6a)(6b) and (7a)(7b)
made to face one another, it is even possible to replace just either
of the half cylinder body blocks (6a)(6b)(7a)(7b) alone which has
failed; this allows for ease of repair at a reasonable cost.
In the above-mentioned example, the non-metal resistance heating
element applied part (6) and the metal resistance heating element
applied part (7) are formed by a pair of half cylinder body blocks
(6a)(6b) and (7a)(7b) made to face one another respectively. However,
various forms of divisions other than this embodiment are possible,
and some of those examples are shown in FIG. 6.
In an electric heater (2) shown in FIG. 6(a), the non-metal resistance
heating element applied part (6) and the metal resistance heating
element applied part (7) are formed by a cylinder block (6c) and
(7c) respectively. In an electric heater (2) shown in FIG. 6(b),
a combination of the non-metal resistance heating element applied
part (6) and the metal resistance heating element applied part (7)
is formed by a pair of half cylinder blocks (8)(8) made to face
one another. In an electric heater (2) shown in FIG. 6(c), the non-metal
resistance heating element applied part (6) is formed by a cylinder
block (6c), and the metal resistance heating element applied part
(7) is formed by a pair of half cylinder blocks (7a)(7b) made to
face one another. In an electric heater (2) shown in FIG. 6(d),
the non-metal resistance heating element applied part (6) is formed
by a pair of half cylinder blocks (6a)(6b) made to face one another,
and the metal resistance heating element applied part (7) is formed
by a cylinder block (7c). Additionally, in FIG. 6(a) to (c), the
metal resistance heating element (22) is illustrated as a light
gauge overbent, whereas in FIG. 6(d), the metal resistance heating
element (22) is illustrated as a heavy gauge helical coil.
Although the above-mentioned embodiments describes an electric
heater (2) employed in a vertical furnace, the electric heater (2)
can naturally be employed in a horizontal furnace as well. Moreover,
the electric heater (2) by the present invention may have either
both ends open or one end closed, and its form is not limited. Further,
although the metal resistance heating element (22) has been explained
as that of light gauge sinuous shape, the present invention can
naturally be applied to heavy gauge helical coil as well.
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