Abstrict
An electric heater for a semiconductor processing equipment according
to the present invention consists of multiple zones wherein, the
multiple zones include at least one zone which is subject to high
loading (e.g. bottom zone), the said at least one zone comprises
a non-metal heating element, and the rest of the zones (e.g. middle
zone and top zone) comprise metal resistance heating elements of
light gauge overbent.
Claims
1. A cylindrically shaped multi-zone electric heater for a semiconductor
processing equipment, 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.
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
[0001] 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
[0002] 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).
[0003] 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.
[0004] 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.
[0005] 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
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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
[0013] 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.
[0014] 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.
[0015] FIG. 3 is a sectional view of the post-assembly heater along
the III-III Line of FIG. 2.
[0016] FIG. 4 is a sectional view of the post-assembly heater along
the IV-IV Line of FIG. 2.
[0017] FIG. 5 is a development view watched from inside of an electric
heater by the present invention for a semiconductor processing equipment.
[0018] 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
[0019] Best mode for carrying out the present invention is explained
below, referring to the drawings.
[0020] 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.
[0021] 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).
[0022] 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.
[0023] 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).
[0024] 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).
[0025] 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).
[0026] 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).
[0027] The metal resistance heating element (22) is made of iron/chrom/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).
[0028] 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).
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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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