U.S. patent application number 10/308300 was filed with the patent office on 2003-05-01 for substrate support and method of fabricating the same.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Bagley, William A., Kondo, Hideaki, Kowaka, Masahiko, Matsumura, Naomi, Terashi, Akira.
Application Number | 20030079853 10/308300 |
Document ID | / |
Family ID | 25444923 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030079853 |
Kind Code |
A1 |
Matsumura, Naomi ; et
al. |
May 1, 2003 |
Substrate support and method of fabricating the same
Abstract
A substrate support and method of fabricating the same are
provided. Generally, one method of fabrication includes assembling
a subassembly comprising a first reinforcing member and a heating
element, supporting the subassembly at least 40 mm from a bottom of
a mold, encapsulating the supported subassembly with molten
aluminum, and applying pressure to the molten aluminum.
Alternatively, a method of fabrication includes assembling a
subassembly comprising a stud disposed through a heating element
sandwiched between a first reinforcing member and a second
reinforcing member, supporting the subassembly above a bottom of a
mold, encapsulating the subassembly disposed in the mold with
molten aluminum to form a casting, forming a hole in the casting by
removing at least a portion of the stud, and disposing a plug in at
least a portion of the hole.
Inventors: |
Matsumura, Naomi; (Osaka,
JP) ; Kowaka, Masahiko; (Kobe City, JP) ;
Bagley, William A.; (San Jose, CA) ; Terashi,
Akira; (Fuji-shi, JP) ; Kondo, Hideaki;
(Kumagaya-shi, JP) |
Correspondence
Address: |
Applied Materials, Inc.
Patent Counsel
3050 Bowers Avenue
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
25444923 |
Appl. No.: |
10/308300 |
Filed: |
December 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10308300 |
Dec 2, 2002 |
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09921104 |
Aug 1, 2001 |
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6510888 |
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Current U.S.
Class: |
164/110 |
Current CPC
Class: |
Y10T 428/12535 20150115;
B22D 19/02 20130101 |
Class at
Publication: |
164/110 |
International
Class: |
B22C 019/04 |
Claims
What is claimed is:
1. A method of fabricating a substrate support comprising:
disposing a first reinforcing member and a heating element on a
stud to form a subassembly; encapsulating the subassembly in a mold
with molten aluminum to form a casting; and finishing the casting
by removing at least a portion of the stud.
2. The method of claim 1, wherein the disposing step further
comprises: sandwiching the heater element between the first
reinforcing member and a second reinforcing member; and coupling a
backplate to the second reinforcing member and having at least 40
.mu.m spacing therebetween.
3. The method of claim 1, wherein the disposing step further
comprises: sandwiching the heater element between the first
reinforcing member and a second reinforcing member.
4. The method of claim 3, wherein the encapsulation step further
comprises: impregnating the first reinforcing member and the second
reinforcing member with aluminum.
5. The method of claim 1, wherein the encapsulating step further
comprises: supporting the subassembly at least 40 mm from a bottom
of the mold or a backplate coupled to the subassembly; and applying
pressure to the molten aluminum.
6. The method of claim 1, wherein the applying step further
comprises: applying pressure to the molten aluminum to an area of
the molten aluminum at least directly above the subassembly.
7. The method of claim 1, wherein the encapsulation step further
comprises: impregnating the first reinforcing member with
aluminum.
8. The method of claim 1, wherein the encapsulating step further
comprises: providing the entire amount of molten aluminum into the
mold in one shot.
9. The method of claim 1, wherein the finishing step further
comprises: annealing the casting; removing aluminum from at least a
portion of the casting to form an unfinished support; and anodizing
the unfinished support.
10. The method of claim 1, wherein the finishing step further
comprises: filling a void left in the aluminum by the removed
portion of the stud with an aluminum plug.
11. The method of claim 1, wherein the first reinforcing member is
comprised of metal or ceramic.
12. The method of claim 1 wherein the first reinforcing member is
comprised of a ceramic material selected from the group consisting
of aluminum oxide plate, aluminum oxide fiber and aluminum oxide
particle combined with silicon oxide fiber, silicon oxide particle,
silicon carbide fiber or silicon carbide particle.
13. A method of fabricating a substrate support comprising:
assembling a subassembly comprising a stud disposed through a
heating element sandwiched between a first reinforcing member and a
second reinforcing member; supporting the subassembly above a
bottom of a mold; encapsulating the subassembly in the mold with
molten aluminum for form a casting; forming a hole in the casting
by removing at least a portion of the stud; and disposing a plug in
at least a portion of the hole.
14. The method of claim 13, wherein the step of assembling the
subassembly further comprises coupling a backplate to the
subassembly in a spaced-apart relation of at least 40 mm.
15. A method of fabricating a substrate support comprising:
assembling a subassembly comprising a heating element held between
a first reinforcing member and a second reinforcing member by a
plurality of studs; coupling a backplate to the subassembly in a
spaced-apart relation of at least 40 mm; casting the subassembly
supported in a mold with molten aluminum in one shot; applying
pressure to the molten aluminum; and removing at least a portion of
the stud surrounding the casted subassembly.
16. The method of claim 15 further comprising: applying a pressure
of at least 40 MPa to the molten aluminum over an area of the
molten aluminum at least directly above the subassembly.
17. The method of claim 15 further comprises heating the mold to
between about 350 and about 400 degrees Celsius.
18. The method of claim 15 further comprising filling voids left in
the aluminum by the removed portion of the studs with an aluminum
plug.
19. The method of claim 15, wherein the step of applying pressure
further comprises impregnating the first reinforcing member and
second reinforcing members with aluminum.
20. The method of claim 15 further comprising anodizing the
substrate support.
21. A substrate support comprising: a casted aluminum body having
an outer surface; a heating element embedded in the body; a first
reinforcing member embedded in the body; at least one holed formed
within the body between the outer surface and at least the heating
element or the first reinforcing member; and a plug disposed in the
hole between the outer surface and the heating element or the first
reinforcing member.
22. The substrate support of claim 21, wherein the casted aluminum
body is formed in a single shot of aluminum.
23. The substrate support of claim 22, wherein a stud maintains the
heating element and the reinforcing member in a spaced-apart
relation during casting and is at least partially removed from the
hole before insertion of the plug.
24. The substrate support of claim 21, wherein the plug is welded
to the aluminum body.
25. The substrate support of claim 21 further comprising a second
reinforcing member embedded in the body and sandwiching the heating
element with the first reinforcing member.
26. A substrate support fabricated by a process comprising:
disposing a first reinforcing member and a heating element on a
stud to form a subassembly; encapsulating the subassembly in a mold
with molten aluminum to form a casting; and finishing the casting
by removing at least a portion of the stud.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 09/921,104, filed Aug. 1, 2001, which is
hereby incorporated by reference herein in its entirety.
BACKGROUND OF THE DISCLOSURE
[0002] 1. Field of the Invention
[0003] Embodiments of the invention generally provide a substrate
support utilized in semiconductor processing and a method of
fabricating the same.
[0004] 2. Description of the Background Art
[0005] Liquid crystal displays or flat panels are commonly used for
active matrix displays such as computer and television monitors.
Generally, flat panels comprise two glass plates having a layer of
liquid crystal material sandwiched therebetween. At least one of
the glass plates includes at least one conductive film disposed
thereon that is coupled to a power supply. Power supplied to the
conductive film from the power supply changes the orientation of
the crystal material, creating a pattern such as text or graphics
seen on the display. One fabrication process frequently used to
produce flat panels is plasma enhanced chemical vapor deposition
(PECVD).
[0006] Plasma enhanced chemical vapor deposition is generally
employed to deposit thin films on a substrate such as a flat panel
or semiconductor wafer. Plasma enhanced chemical vapor deposition
is generally accomplished by introducing a precursor gas into a
vacuum chamber that contains a substrate. The precursor gas is
typically directed through a distribution plate situated near the
top of the chamber. The precursor gas in the chamber is energized
(e.g., excited) into a plasma by applying RF power to the chamber
from one or more RF sources coupled to the chamber. The excited gas
reacts to form a layer of material on a surface of the substrate
that is positioned on a temperature controlled substrate support.
In applications where the substrate receives a layer of low
temperature polysilicon, the substrate support may be heated in
excess of 400 degrees Celsius. Volatile by-products produced during
the reaction are pumped from the chamber through an exhaust
system.
[0007] Generally, the substrate support utilized to process flat
panel displays are large, often exceeding 550 mm.times.650 mm. The
substrate supports for high temperature use typically are casted,
encapsulating one or more heating elements and thermocouples in an
aluminum body. Due to the size of the substrate support, one or
more reinforcing members are generally disposed within the
substrate support to improve the substrate support's stiffness and
performance at elevated operating temperatures (i.e., in excess of
350 degrees Celsius and approaching 500 degrees Celsius). Although
substrate supports configured in this manner have demonstrated good
processing performance, manufacturing supports has proven
difficult.
[0008] One problem in providing a robust substrate support is that
the reinforcing member may occasionally displace, deform and
sometimes break during the casting process. The reinforcing member
typically includes portions that are unsupported in the pre-cast
state of the substrate support. After assembling the reinforcing
member, the heating elements and thermocouples into a subassembly,
the subassembly is supported in a mold and encapsulated with molten
aluminum. Conventional presses used in the casting process
typically have one or twin rams that provide up to about 500 tons
of pressure that works not whole area of cast surface but local
area flowing the molten aluminum around the subassembly disposed in
the substrate support mold. In this case, there is always
nonuniformity of pressure working on the molten aluminum.
Occasionally, this nonuniformity of the weight and pressure of the
aluminum flowing in the mold during the casting process causes the
reinforcing member to displacement, deformation and sometimes
fracture. Additionally, this casting process results in undesirable
heterogeneous grain size of aluminum cast. Furthermore, such
pressures stress the substrate support up to about 28 MPa, which is
not enough to get a desired uniform micro-grain size within the
aluminum cast.
[0009] Another problem with substrate support formed using this
molding process is the lack of integrity of the aluminum where the
flow of molten aluminum comes back together on the side of the
substrate support furthest from the molten aluminum source. As a
substantial amount of aluminum and time is needed to encapsulate
the heating elements, thermocouples and reinforcing members, the
flow of aluminum may cool causing a seam to be created where the
leading edges of the aluminum flow merges under the subassembly at
less than acceptable temperatures.
[0010] Depending on the temperature of the aluminum when the seam
is formed, the seam may become a source of a variety of defects.
For example, vacuum leaks may propagate through the seam between
the interior of the chamber and the environment surrounding the
chamber. Vacuum leakage may degrade process performance and may
lead to poor heater performance that contributes to pre-mature
heater failure. Moreover, thermal cycling of the substrate support
may cause the substrate support to fracture along the seam, thereby
causing failure and possible release of particulates into the
chamber environment.
[0011] As the cost of materials and manufacturing the substrate
support is great, failure of the substrate support is highly
undesirable. Additionally, if the substrate support fails during
processing, a substrate supported thereon may be damaged. This can
occur after a substantial number of processing steps have been
preformed thereon, thus resulting in the expensive loss of the
substrate support. Moreover, replacing a damaged support in the
process chamber creates a costly loss of substrate throughput while
the process chamber is idled during replacement or repair of the
substrate support. Moreover, as the size of the next generation
substrate supports are increased to accommodate substrates in
excess of 1.44 square meters at operating temperatures approaching
500 degrees Celsius, the aforementioned problems become
increasingly important to resolve.
[0012] Therefore, there is a need for an improved substrate
support.
SUMMARY OF THE INVENTION
[0013] Generally, a substrate support and method of fabricating the
same are provided. In one embodiment, a method of fabricating a
substrate support includes the steps of assembling a subassembly
comprising a first reinforcing member and a heating element,
supporting the subassembly at least 40 mm from a bottom of a mold,
encapsulating the supported subassembly with molten aluminum, and
applying pressure to the molten aluminum.
[0014] In another embodiment, a method of fabricating a substrate
support includes the steps of a method of fabrication includes
assembling a subassembly comprising a stud disposed through a
heating element sandwiched between a first reinforcing member and a
second reinforcing member, supporting the subassembly above a
bottom of a mold, encapsulating the subassembly disposed in the
mold with molten aluminum to form a casting, forming a hole in the
casting by removing at least a portion of the stud, and disposing a
plug in at least a portion of the hole.
[0015] In another aspect of the invention, a substrate support is
provided. In one embodiment, the substrate support includes at
least a first reinforcing member and a heating element disposed
within a cast aluminum body. At least one hole is formed in the
aluminum body between an outer surface and at least the heating
element or the reinforcing member. A plug is disposed in the hole
between the outer surface and the heating element or the
reinforcing member. In another embodiment, the hole houses a stud
during casting that maintains the heating element and the
reinforcing member in a spaced-apart relation and is at least
partially removed from the hole before insertion of the plug.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0017] FIG. 1 depicts a schematic sectional view of one embodiment
of a processing chamber having a substrate support of the present
invention;
[0018] FIG. 2 is one embodiment of a method of fabricating a
substrate support;
[0019] FIG. 3A is a sectional view of one embodiment of a
subassembly;
[0020] FIG. 3B is a plan view of the subassembly of FIG. 3A;
[0021] FIG. 4 is a schematic of the subassembly of FIG. 3A disposed
in a press; and
[0022] FIG. 5 is a sectional view of an embodiment of a substrate
support.
[0023] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0024] The invention generally provides a substrate support and
methods of fabricating a substrate support. The invention is
illustratively described below in reference to a plasma enhanced
chemical vapor deposition system, such as a plasma enhanced
chemical vapor deposition (PECVD) system, available from AKT, a
division of Applied Materials, Inc., Santa Clara, Calif. However,
it should be understood that the invention has utility in other
system configurations such as physical vapor deposition systems,
ion implant systems, etch systems, other chemical vapor deposition
systems and any other system in which processing a substrate on a
substrate support is desired.
[0025] FIG. 1 is a cross sectional view of one embodiment of a
plasma enhanced chemical vapor deposition system 100. The system
100 generally includes a chamber 102 coupled to a gas source 104.
The chamber 102 has walls 106, a bottom 108 and a lid assembly 110
that define a process volume 112. The process volume 112 is
typically accessed through a port (not shown) in the walls 106 that
facilitates movement of the substrate 140 into and out of the
chamber 102. The walls 106 and bottom 108 are typically fabricated
from a unitary block of aluminum or other material compatible for
processing. The lid assembly 110 contains a pumping plenum 114 that
couples the process volume 112 to an exhaust port (that includes
various pumping components, not shown).
[0026] The lid assembly 110 is supported by the walls 106 and can
be removed to service the chamber 102. The lid assembly 110 is
generally comprised of aluminum. A distribution plate 118 is
coupled to an interior side 120 of the lid assembly 110. The
distribution plate 118 is typically fabricated from aluminum. The
center section includes a perforated area through which process and
other gases supplied from the gas source 104 are delivered to the
process volume 112. The perforated area of the distribution plate
118 is configured to provide uniform distribution of gases passing
through the distribution plate 118 into the chamber 102.
[0027] A heated substrate support assembly 138 is centrally
disposed within the chamber 102. The support assembly 138 supports
a substrate 140 during processing. In one embodiment, the substrate
support assembly 138 comprises an aluminum body 124 that
encapsulates at least one embedded heating element 132 and a
thermocouple 190. At least a first reinforcing member 116 is
generally embedded in the body 124 proximate the heating element
132. A second reinforcing member 166 may be disposed within the
body 124 on the side of the heating element 132 opposite the first
reinforcing member 116. The reinforcing members 116 and 166 may be
comprised of metal, ceramic or other stiffening materials. In one
embodiment, the reinforcing members 116 and 166 are comprised of
aluminum oxide fibers. Alternatively, the reinforcing members 116
and 166 may be comprised of aluminum oxide fiber combined with
aluminum oxide particles, silicon carbide fiber, silicon oxide
fiber or similar materials. The reinforcing members 116 and 166 may
include loose material or may be a pre-fabricated shape such as a
plate. Alternatively, the reinforcing members 116 and 166 may
comprise other shapes and geometry. Generally, the reinforcing
members 116 and 166 have some porosity that allows aluminum to
impregnate the members 116, 166 during a casting process described
below.
[0028] The heating element 132, such as an electrode disposed in
the support assembly 138, is coupled to a power source 130 and
controllably heats the support assembly 138 and substrate 140
positioned thereon to a predetermined temperature. Typically, the
heating element 132 maintains the substrate 140 at a uniform
temperature of about 150 to at least about 460 degrees Celsius.
[0029] Generally, the support assembly 138 has a lower side 126 and
an upper side 134 that supports the substrate. The lower side 126
has a stem cover 144 coupled thereto. The stem cover 144 generally
is an aluminum ring coupled to the support assembly 138 that
provides a mounting surface for the attachment of a stem 142
thereto.
[0030] Generally, the stem 142 extends from the stem cover 144 and
couples the support assembly 138 to a lift system (not shown) that
moves the support assembly 138 between an elevated position (as
shown) and a lowered position. A bellows 146 provides a vacuum seal
between the chamber volume 112 and the atmosphere outside the
chamber 102 while facilitating the movement of the support assembly
138. The stem 142 additionally provides a conduit for electrical
and thermocouple leads between the support assembly 138 and other
components of the system 100.
[0031] The support assembly 138 generally is grounded such that RF
power supplied by a power source 122 to the distribution plate 118
(or other electrode positioned within or near the lid assembly of
the chamber) may excite the gases disposed in the process volume
112 between the support assembly 138 and the distribution plate
118. The RF power from the power source 122 is generally selected
commensurate with the size of the substrate to drive the chemical
vapor deposition process.
[0032] The support assembly 138 additionally supports a
circumscribing shadow frame 148. Generally, the shadow frame 148
prevents deposition at the edge of the substrate 140 and support
assembly 138 so that the substrate does not stick to the support
assembly 138.
[0033] The support assembly 138 has a plurality of holes 128
disposed therethrough that accept a plurality of lift pins 150. The
lift pins 150 are typically comprised of ceramic or anodized
aluminum. Generally, the lift pins 150 have first ends 160 that are
substantially flush with or slightly recessed from a upper side 134
of the support assembly 138 when the lift pins 150 are in a normal
position (i.e., retracted relative to the support assembly 138).
The first ends 160 are generally flared to prevent the lift pins
150 from falling through the holes 128. Additionally, the lift pins
150 have a second end 164 that extends beyond the lower side 126 of
the support assembly 138. The lift pins 150 may be actuated
relative to the support assembly 138 by a lift plate 154 to project
from the support surface 130, thereby placing the substrate in a
spaced-apart relation to the support assembly 138.
[0034] The lift plate 154 is disposed proximate the lower side 126
of the support surface. The lift plate 154 is connected to the
actuator by a collar 156 that circumscribes a portion of the stem
142. The bellows 146 includes an upper portion 168 and a lower
portion 170 that allow the stem 142 and collar 156 to move
independently while maintaining the isolation of the process volume
112 from the environment exterior to the chamber 102. Generally,
the lift plate 154 is actuated to cause the lift pins 150 to extend
from the upper side 134 as the support assembly 138 and the lift
plate 154 move closer together relative to one another.
[0035] FIG. 2 depicts a flow chart of one embodiment of a method
200 for fabricating the support assembly 138. Generally, the method
200 begins at step 202 of assembling a subassembly that includes
the reinforcing members 116, 166, the heating element 132 and the
thermocouple 190. At step 204 and step 206, the subassembly 300 is
supported in a mold that is disposed in a press and respectively
encapsulated with aluminum to form a casting. At step 208, the
casting is processed to form an unfinished substrate support. At
step 210, the unfinished substrate support is finished by anodizing
the substrate support assembly 138 and coupling the heating
elements 132 to the appropriate electrical connections, for
example, soldering lead wires to the heating elements 132.
[0036] FIG. 3A depicts one embodiment of a subassembly 300
assembled at step 202. The subassembly 300 generally includes the
first reinforcing member 116, the second reinforcing member 166,
the heating element 132 and the thermocouple 190. A plurality of
studs 302, for example, fasteners, pins, rods, bolts and the like
comprised of a ceramic or metallic material such as stainless
steel, are utilized to support and maintain a predetermined spacing
between the reinforcing members 116, 166, the heating element 132
and the thermocouple 190. The studs 302 vary in number and be
arranged in different patterns, for example, a grid comprising 12
equally spaced studs 302 (see FIG. 3B). The studs 302 generally are
passed through the first reinforcing member 116 and configured to
support the first reinforcing member 116 at least 40 mm from an end
304 of the stud 302. In one embodiment, the position of the first
reinforcing member 116 relative to the end 304 of the studs 302 is
maintained by providing a first ledge 306 in the stud 302 on which
the first reinforcing member 116 rests. Optionally, the stud 302
may incorporate other features or devices such as standoffs,
threads, tapers and the like to maintain the relative positions of
the studs 302 and the first reinforcing member 116.
[0037] The heating elements 132 and the thermocouples 190 are
disposed on the studs 302 proximate the first reinforcing member
116 from the side of the stud 302 opposite the end 304. The heating
elements 132 and the thermocouple 190 are generally disposed
against the first reinforcing member 116 but may be maintained in a
spaced-apart relation to the first reinforcing member 116. In one
embodiment, a spaced-apart relation is maintained by resting the
heating elements 132 and the thermocouple 190 on a second ledge 308
of the stud 302. Alternatively, threads, standoffs, spacers or
geometry such as bosses incorporated into one or both of the
heating elements 132, the thermocouple 190 and first reinforcing
member 116 may be used to maintain the relative spacing
therebetween.
[0038] The second reinforcing member 166 is disposed on the stud
302 proximate the heating element 132. Generally, the second
reinforcing member 166 is disposed against the heating element 132
but may optionally be maintained in a spaced-apart relation by
providing a third ledge 310 on which the second reinforcing member
166 rests. The spacing between the heating elements 132 and the
second reinforcing member 166 may alternatively be maintained as
described above.
[0039] The subassembly 300 may optionally be secured to prevent
movement between the first reinforcing member 116, the second
reinforcing member 166, the heating element 132 and the
thermocouple 190 during casting. In one embodiment, the first
reinforcing member 116 is retained against the first ledge 306 by a
metallic collar 312 pressed on at least some of the studs 302. The
second reinforcing member 166 is retained against the third ledge
by another collar 312 while the heating element 132 and the
thermocouple 190 are respectively retained against the second ledge
308 by another collar 312. The collars 312 are preferably
fabricated from stainless steel. Alternatively, the subassembly 300
may be secured on the studs 302 by other devices such as nuts (with
threaded studs), adhesives, friction on the studs (i.e., press or
snap fit), wire, ceramic string, twine and the like. Optionally,
the first reinforcing member 116, the second reinforcing member
166, the heating element 132 and the thermocouple 190 may include
interlocking geometry integral to the subassembly such as mating
pins and bosses, standoffs, press and snap fits and the like.
[0040] Optionally, the studs 302 may be coupled at their end 304 to
a base plate 314. The base plate 314 is typically comprised of a
metallic material and is utilized to position the subassembly 300
in a predetermined position in the mold 400. In one embodiment, the
base plate 314 is a perforated steel plate having a plurality of
threaded holes to accept the studs 302. The thickness of base plate
314 is at least 40 mm to prevent a deformation during the
casting.
[0041] FIG. 4 depicts a schematic of one embodiment of the
subassembly 300 disposed in the mold 400 which is disposed in the
press 404. Generally, the subassembly 300 is positioned within the
mold 400 such that the subassembly is supported from a bottom 402
of the mold 400 by at least 40 mm at step 204. The back plate 314
that is coupled to the subassembly 300 typically rests in a
predetermined bottom 402 of the mold 400. The back plate 314 may be
located relative the mold 400 in the predetermined position by
dowel pins, geometric interfacing and the like. By maintaining the
subassembly 300 in this position, adequate encapsulation around all
sides of the subassembly 300 is ensured.
[0042] Alternatively, the subassembly 300 may be supported in the
mold 400 in other ways. For example, mold pins (not shown) may
project from the bottom 402 of the mold 400 and support the
subassembly 300. In another configuration, one or more members (not
shown) may extend between other portions of the mold 400 to support
the subassembly 300. The studs 302 may be directly disposed on or
in locating holes in mold bottom 402 while maintaining at least 40
mm between the first reinforcing plate 116 and the mold bottom 402
on subassemblies 300 that do not include the back plate 314.
[0043] The mold 400 is generally heated to minimize the cooling of
the molten aluminum used to encapsulate the subassembly. The mold
400 may be heated through any conventional means including
circulated fluids, resistance heaters and burners. Generally, the
mold 400 is heated to a temperature between about 300 and about 350
degrees Celsius.
[0044] The molten aluminum at about 800 to about 900 degrees
Celsius is generally dispensed into the mold in a single shot at
step 206. The single shot minimizes seam formation at the interface
between shots due to cooling of the aluminum that occurs during
utilizing conventional processes. The aluminum may be dispensed
manually or automatically through an opening in the top of the mold
or one or more other passages (not shown). Generally, aluminum
alloy 6061 is utilized but other alloys may be substituted. The
molten aluminum at about 800 to about 900 degrees Celsius is
generally dispensed into the mold in a single shot at step 206. The
single shot minimizes seam formation at the interface between shots
due to cooling of the aluminum that occurs during utilizing
conventional processes. The aluminum may be dispensed manually or
automatically through an opening in the top of the mold or one or
more other passages (not shown). Generally, aluminum alloy 6061 is
utilized but other alloys may be substituted.
[0045] Once the molten aluminum is in the mold, pressure is applied
to the aluminum to assist the aluminum in flowing around and in
between the components of the subassembly 300. The applied pressure
additionally impregnates the reinforcing members 116 and 166 with
aluminum. In one embodiment, a single ram 406 of the press 404
applies pressure to an area 408 of the molten aluminum above the
subassembly 300. Generally, the area 408 is at least as large as
the area of the subassembly 300 and may include the entire width of
the mold 400. The pressure applied by the ram 406 is generally less
than about 3,000 tons. The space between the support assembly 138
and the bottom 402 of the mold 400 or the base plate 314 enhances
the flow the aluminum therebetween. Optionally, the mold 400 may
include a vacuum applied to the mold's vents (not shown) to assist
the flow of aluminum. The use of a single ram 406 over a large area
408 results in uniformity application of stress, preferably in
excess of about 40 MPa, to the entire area of the support assembly
138, which eliminates the displacement, deformation and fracture of
the reinforcing members 116, 166. The high stress correspondingly
increases the homogeneity of grain size of aluminum cast and
decreases the integrity of any seams or flow lines that may form
during casting. The molten aluminum at about 800 to about 900
degrees Celsius is generally dispensed into the mold in a single
shot at step 206. The single shot minimizes seam formation at the
interface between shots due to cooling of the aluminum that occurs
during utilizing conventional processes. The aluminum may be
dispensed manually or automatically through an opening in the top
of the mold or one or more other passages (not shown). Generally,
aluminum alloy 6061 is utilized but other alloys may be
substituted.
[0046] FIG. 5 depicts one embodiment of the substrate support
assembly 138 in the form of a post-molding casting 500. Generally,
the casting 500 is processed at steps 206 to form an unfinished
processing support. In one embodiment, the processing step 208
generally includes annealing the casting 500 to relieve residual
stresses in the casting 500. In one embodiment, the casting 500 is
annealed at about 510 to about 520 degrees Celsius for about 2 to
about 3 hours.
[0047] Next, the casting is machined to roughly the dimensions of
the finished substrate support assembly 138. The studs 302 are at
least partially removed from the bottom side and replaced with an
aluminum plug 502 that is welded to the substrate support assembly
138. The stem cover 144 is then welded to the substrate support
assembly 138. The support assembly 138 is annealed once more before
a final machining step that brings the substrate support 138 to its
final dimensions. Electrical leads are then attached to the heating
element 132 and fed through the stem 142 which is then welded to
the stem cover 144.
[0048] The surface of the support assembly 138 is then treated to
remove tool marks left by the machining operations. The step of
removing the tool marks may optionally be completely or partially
performed before the second anneal step. The surface treatments may
include grinding, electropolishing, abrasive or bead blasting,
chemical etching and the like. In one embodiment, the substrate
support is treated by blasting the substrate support with aluminum
oxide balls and exposing the support to an alkaline or acid
etchant. At step 210, the substrate support 138 is anodized to
provide a protective finish to the substrate support.
[0049] Although several preferred embodiments which incorporate the
teachings of the present invention have been shown and described in
detail, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
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