U.S. patent application number 12/171556 was filed with the patent office on 2009-01-15 for high temperature cathode for plasma etching.
Invention is credited to Glen Egami, Denis Koosau, Alexander Matyushkin, Boris Yendler.
Application Number | 20090014323 12/171556 |
Document ID | / |
Family ID | 39917440 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090014323 |
Kind Code |
A1 |
Yendler; Boris ; et
al. |
January 15, 2009 |
HIGH TEMPERATURE CATHODE FOR PLASMA ETCHING
Abstract
The present invention generally is a cathode suitable for use in
high temperature plasma etch applications. In one embodiment, the
cathode includes a ceramic electrostatic chuck secured to a base.
The base has cooling conduits formed therein. A rigid support ring
is disposed between the chuck and the base, thereby maintaining the
chuck and the base in a spaced-apart relation.
Inventors: |
Yendler; Boris; (Saratoga,
CA) ; Matyushkin; Alexander; (San Jose, CA) ;
Koosau; Denis; (Pleasanton, CA) ; Egami; Glen;
(San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP - - APPM/TX
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
39917440 |
Appl. No.: |
12/171556 |
Filed: |
July 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60949833 |
Jul 13, 2007 |
|
|
|
Current U.S.
Class: |
204/298.33 |
Current CPC
Class: |
H01L 21/67069 20130101;
H01J 2237/002 20130101; H01J 2237/2001 20130101; H01J 37/20
20130101; H01J 37/32431 20130101 |
Class at
Publication: |
204/298.33 |
International
Class: |
C25B 11/02 20060101
C25B011/02 |
Claims
1. A plasma processing cathode comprising: a base having cooling
conduits formed therein; a ceramic electrostatic chuck secured to
the base; and a rigid support ring disposed between the
electrostatic chuck and the base, the support ring maintaining the
electrostatic chuck to the base in a spaced-apart relation.
2. The cathode of claim 1 further comprising a gas distribution
ring disposed between the base and chuck.
3. The cathode of claim 2 further comprising: a gas passage formed
through the base; and a gas feed formed through the electrostatic
chuck, wherein the passage and feed are not aligned but fluidly
coupled through the gas distribution ring to define a gas delivery
path, wherein gas delivery path extends through the gas
distribution ring.
4. The cathode of claim 3 further comprising: a ceramic baffle disk
disposed in the gas delivery path.
5. The cathode of claim 4, wherein the gas distribution ring
further comprises: a bore having the baffle disk disposed
therein.
6. The cathode of claim 1 further comprising: a gas passage formed
through the base; a gas feed formed through the electrostatic
chuck, wherein the passage and feed are not aligned but fluidly
coupled through the gas distribution ring to define a gas delivery
path; and a ceramic baffle disk disposed in the gas delivery
path.
7. The cathode of claim 1 further comprising: a flat annular
spreader plate disposed in a gap defined between the electrostatic
chuck and the base.
8. The cathode of claim 7, wherein the annular spreader plate is in
contact with the base and spaced-apart from the electrostatic
chuck.
9. The cathode of claim 1 further comprising: a clamp ring securing
the electrostatic chuck to the base, the clamp ring having at least
two thermal chokes disposed in series between portions of the clamp
ring touching the electrostatic chuck and the base.
10. The cathode of claim 1 further comprising: a stem coupled to
the electrostatic chuck and extending through the base; a sleeve
disposed through the stem, wherein a first gap defined between the
stem and base is greater than a second gap defined between the stem
and sleeve; and a seal disposed between a lower end of the stem and
the base, the seal sealing the first gap.
11. The cathode of claim 10, wherein the base further comprises: a
channel coupling the stem coupled to the electrostatic chuck and
extending through the base, the channel venting the first gap
through the base.
12. A plasma processing cathode comprising: a base having cooling
conduits formed therein; a ceramic electrostatic chuck disposed on
the base, the electrostatic chuck having a plurality of gas feeds
extending from a bottom surface of the electrostatic chuck facing
the base to a top surface the electrostatic chuck; a rigid support
ring disposed between the electrostatic chuck and the base, the
support ring maintaining the bottom of the electrostatic chuck and
the base in a spaced-apart relation; a fluid distribution ring
disposed between the base and the electrostatic chuck, a bottom of
the fluid distribution ring spaced from the base to define an
annular channel, the fluid distribution ring having a plurality of
gas passages configured to direct gas through the fluid
distribution ring from the channel to the electrostatic chuck; and
ceramic baffles disposed in the gas passages.
13. The cathode of claim 12, wherein at least one of the ceramic
baffles further comprises: a disk-like body having upper and lower
surfaces; and cross channels formed in the upper and lower
surfaces.
14. The cathode of claim 12, wherein at least one of the ceramic
baffle further comprises: a disk-like body having a perimeter; and
notches formed in the perimeter.
15. The cathode of claim 12 further comprising: an annular spreader
plate disposed in a gap defined between the electrostatic chuck and
the base, wherein the annular spreader plate is in contact with the
base and spaced-apart from the electrostatic chuck.
16. The cathode of claim 12 further comprising: a stem coupled to
the electrostatic chuck and extending through the base; a sleeve
disposed through the stem, wherein a first gap defined between the
stem and base is greater than a second gap defined between the stem
and sleeve; and a seal disposed between a lower end of the stem and
the base, the seal sealing the first gap.
17. A plasma processing cathode comprising: a base having cooling
conduits formed therein; a ceramic electrostatic chuck secured to a
top surface of the base; a rigid support ring disposed between the
electrostatic chuck and the base, the support ring maintaining a
lower surface of the electrostatic chuck spaced-apart from the top
surface of the base; a flat annular spreader plate disposed
radially inward of the support ring in a gap defined between the
lower surface of the electrostatic chuck and the upper surface of
the base; and a seal providing seal between the electrostatic chuck
and the base outward of the spreader plate, the seal sealingly
permitting radial movement of the electrostatic chuck relative to
the plate.
18. The cathode of claim 17 further comprising: a gas passage
formed through the base; a gas feed formed through the
electrostatic chuck, wherein the passage and feed are not aligned
but fluidly coupled through the gas distribution ring to define a
gas delivery path, and a ceramic baffle disk disposed in the gas
delivery path.
19. The cathode of claim 17 further comprising: a stem coupled to
the electrostatic chuck and extending through a cylinder in the
base, an inside diameter of the cylinder configured to maintain a
first gap between the stem and the base; a sleeve disposed through
the stem, wherein the first gap is greater than a second gap
defined between the stem and sleeve; and a seal disposed between a
lower end of the stem and the base, the seal sealing the first
gap.
20. The cathode of claim 17 further comprising: a fluid
distribution ring disposed between the base and the electrostatic
chuck, a bottom of the fluid distribution ring spaced from the base
to define an annular channel, the fluid distribution ring
comprising: a stepped bore formed on a top surface facing the
electrostatic chuck, the bore receiving the baffle therein; a gas
passage having a first end breaking into the stepped bore and a
second end breaking through the bottom of the fluid distribution
ring and exposed to the annular channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit to U.S. Provisional Patent
application Ser. No. 60/949,833, filed on Jul. 13, 2007.
BACKGROUND
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to
semiconductor substrate processing systems. More specifically, the
invention relates to a high temperature cathode suitable for plasma
etching.
[0004] 2. Description of the Related Art
[0005] In semiconductor wafer processing, the trend towards
increasingly smaller feature size and linewidths have placed a
premium on the ability to mask, etch, and deposit material on a
semiconductor workpiece, or wafer, with greater precision. Plasma
etching is of particular importance in obtaining critical
dimensions less than 1.0 micron.
[0006] Typically, plasma etching is accomplished by applying a RF
power to a working gas supplied over a substrate held by a pedestal
in a low pressure environment. The resulting electric field creates
a reaction zone that excites the working gas into a plasma. Ions
migrate towards the boundary of plasma, and accelerate upon leaving
the boundary layer. The accelerated ions produce the energy
required to remove, or etch, the target material, which generally
is a layer of material disposed on the substrate.
[0007] In some plasma etch applications, it is desirable to
maintain the substrate at temperatures in excess of 100 degrees
Celsius, and up to about 400 degrees Celsius, during processing.
Significant challenges in substrate support design must be overcome
in order to successfully process substrates at such high
temperatures. For example, the large differences in thermal
expansion encountered between ceramic and metal components may
result in damage to the ceramic component. Moreover, high
temperature regions of the substrate support must be isolated from
polymer seals generally utilized to prevent leakage between the
internal regions of the substrate support, which is typically
maintained at substantially ambient pressures, and the vacuum
environment surrounding the substrate support. Furthermore, such
challenges must be overcome while providing good control of the
substrate temperature distribution across the diameter of the
substrate. The inability to control substrate temperature
uniformity has an adverse effect on process uniformity both within
a single substrate and between substrates, device yield and overall
quality of processed substrates.
[0008] Therefore, there is a need in the art for an improved
substrate support suitable for use in high temperature plasma etch
applications.
SUMMARY
[0009] The present invention generally is a cathode suitable for
use in high temperature plasma etch applications. In one
embodiment, the cathode includes a ceramic electrostatic chuck
secured to a base. The base has cooling conduits formed therein. A
rigid support ring is disposed between the chuck and the base,
thereby maintaining the chuck and the base in a spaced-apart
relation.
[0010] In at least one other embodiment, a cathode includes a gas
distribution ring disposed between the base and chuck.
[0011] In at least one other embodiment, a cathode further includes
a gas passage formed through the base and a gas feed formed through
the chuck. The passage and feed are not aligned but fluidly coupled
through a gas distribution ring to define a gas delivery path.
[0012] In at least one other embodiment, a ceramic baffle disk is
disposed in the gas delivery path.
[0013] In at least one other embodiment, a cathode further includes
an annular spreader plate disposed in a gap defined between the
chuck and the base, wherein the annular spreader plate touches the
base but not the chuck.
[0014] In at least one other embodiment, a clamp ring is utilized
to secure the chuck to the base. The clamp ring includes a least
two thermal chokes disposed in series between portions of the clamp
ring touching the chuck and the base.
[0015] In at least one other embodiment, the cathode further
includes a stem and a sleeve. The stem is coupled to the chuck and
extends through the base. The sleeve is disposed through the stem
such that a first gap defined between the stem and base is greater
than a second gap defined between the stem and sleeve. A seal
disposed between a lower end of the stem and the base to seal the
first gap.
[0016] In at least one other embodiment, the base further includes
a channel coupling the stem to the chuck and extending through the
base. The channel vents the first gap through the base.
[0017] In another embodiment, a plasma processing cathode includes
a base, a ceramic electrostatic chuck and rigid support ring
maintaining a bottom of the electrostatic chuck and the base in a
spaced-apart relation. The electrostatic chuck has a plurality of
gas feeds extending from the bottom surface of the electrostatic
chuck to a top surface the electrostatic chuck. A fluid
distribution ring is disposed between the base and the
electrostatic chuck. The fluid distribution ring is spaced from the
base to define an annular channel therebetween. The fluid
distribution ring includes a plurality of gas passages configured
to direct gas through the fluid distribution ring from the channel
to the electrostatic chuck. A plurality of ceramic baffles are
disposed in the gas passages.
[0018] In yet another embodiment, a plasma processing cathode
includes a base having cooling conduits formed therein, a ceramic
electrostatic chuck secured to a top surface of the base, and a
rigid support ring disposed between the electrostatic chuck and the
base. The support ring maintains a lower surface of the
electrostatic chuck spaced-apart from the top surface of the base.
A flat annular spreader plate is disposed radially inward of the
support ring in a gap defined between the lower surface of the
electrostatic chuck and the upper surface of the base. A seal is
provided to seal the electrostatic chuck to the base in a location
outward of the spreader plate, the seal sealingly permitting radial
movement of the electrostatic chuck relative to the plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0020] FIG. 1 is a sectional perspective view of one embodiment of
a substrate support assembly suitable for use in a plasma etch
chamber;
[0021] FIG. 2 is a partial sectional view of the substrate support
assembly of FIG. 1 depicting one embodiment of a gas distribution
ring;
[0022] FIG. 3A is a partial plan view of a portion of the gas
distribution ring disposed on a cooling base, the gas distribution
ring having a baffle disk covering a gas inlet formed through the
ring;
[0023] FIG. 3B is a partial plan view of the gas distribution ring
of FIG. 3A with the baffle disk removed to show the gas inlet;
[0024] FIG. 4 is another partial sectional view of the substrate
support assembly of FIG. 1 through the gas distribution ring;
[0025] FIG. 5 is a perspective view of one embodiment of a baffle
disk;
[0026] FIG. 6 is a partial sectional view of the substrate support
assembly of FIG. 1 through an inner gas feed;
[0027] FIG. 7 is a partial sectional view of a substrate support
assembly utilizing an E-seal between a cooling base and
electrostatic chuck; and
[0028] FIG. 8 is a sectional perspective view of another embodiment
of a substrate support assembly suitable for use in a plasma etch
chamber.
[0029] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is to be noted, however, that
the appended drawings illustrate only typical embodiments of this
invention and are therefore not to be considered limiting of its
scope, for the invention may admit to other equally effective
embodiments.
DETAILED DESCRIPTION
[0030] FIG. 1 is a sectional isometric view of one embodiment of a
high temperature cathode 100 suitable for plasma etching. The
cathode 100 may be advantageously utilized in plasma etch reactors,
such as the AdvantEdge.TM. Etch reactor, available from Applied
Materials, Inc., of Santa Clara, Calif., among other etch reactors,
including suitable reactors available from other manufacturers.
[0031] FIG. 1 is one embodiment of a cathode 100. The cathode 100
generally includes an electrostatic chuck 104 secured to a cooling
base 102. A stem 106 extends from a bottom of the electrostatic
chuck 104. The stem 106 may be coupled to the electrostatic chuck
104 by braising or other suitable method. The stem 106 is generally
fabricated from a conductive material such as stainless steel.
[0032] The electrostatic chuck 104 is supported above the cooling
base 102 in a spaced-apart relation. In the embodiment depicted in
FIG. 1, a support ring 110 is provided between the cooling base 102
and electrostatic chuck 104, such that a gap 118 is maintained
between the underside of the electrostatic chuck 104 and the upper
surface of the cooling base 102. The gap 118 limits the heat
transfer between the electrostatic chuck 104 and cooling base 102.
In one embodiment, the distance across the gap 118 between the
electrostatic chuck 104 and cooling base 102 is about 0.025 to
about 0.045 inches.
[0033] To further minimize heat transfer between the electrostatic
chuck 104 and cooling base 102, the support ring 110 may be made of
a material having a low coefficient of thermal conductivity
relative to the base, such as titanium, among other materials. In
other embodiments, the support ring 110 may be fabricated from hard
anodized aluminum, high temperature plastics or other suitable
material. In other embodiments, the support ring 110 is fabricated
from a rigid material so that the dimension across the gap 118 is
maintained while clamping the chuck 104 to the base 102. In the
embodiment depicted in FIG. 1, the support ring 110 is fabricated
from a rigid plastic, for example a polyimide such as
VESPEL.RTM..
[0034] In one embodiment, the support ring 110 touches less than 15
percent, for example, 10 percent, of the bottom surface of the
electrostatic chuck 104. In the embodiment depicted in FIG. 1, the
top or crown of the support ring 110 contacting the electrostatic
chuck 104 is narrowed to provide a heat choke. Alternatively, the
heat flow can be restricted through the ring 110 by choking heat
transfer at the bottom of the support ring 110 by means of
decreasing contact area between the ring 110 and the cooling base
102 ("reverse crown").
[0035] The cooling base 102 is fabricated from a material having
good heat transfer, for example, a metal such as stainless steel or
aluminum. The cooling base 102 includes one or more fluid conduits
152 formed therein. The conduits 152 are coupled to a fluid source
such that the temperature of the cooling base 102 may be
selectively heated or cooled. Examples of cooling bases having
conduits formed therein to regulate temperature thereof as
described in U.S. patent application Ser. No. 10/960,874 filed Oct.
7, 2004, which is hereby incorporated by reference in its
entirety.
[0036] The cooling base 102 also includes a cylinder 150 extending
from the lower surface of the cooling base 102. An inside diameter
154 of the cylinder 150 is configured such that a gap 112 is
maintained between the cooling base 102 and the stem 106. The lower
end of the cylinder 150 includes an inwardly-extending lip 156
which accommodates a gland that secures an o-ring 116. The o-ring
116 provides a pressure barrier between the cooling base 102 and
the stem 106.
[0037] A shield 108 is utilized to manage the temperature of the
stem 106 so that heat passing from the electrostatic chuck 104 does
not damage the o-ring 116. The shield 108 increases amount of heat
transfer from the stem 106 by about two times. The shield 108
includes a flange 162 and a sleeve 160. The sleeve 160 fits inside
the stem 106, such that the heat transfer from the stem 106 is
predominantly to the sleeve 160. The sleeve 160 may have a close
fit to the stem 106, or have a gap defined therebetween which is
less than the gap 112 defined between the stem 106 and the inside
diameter 154 of the cooling base 102. The shield 108 provides
enough thermal sink to allow the electrostatic chuck 104 to be
operated at temperatures in excess of 300 degrees Celsius without
damaging the seal 116.
[0038] The heat removal from the shaft 106 may be conducted by
radiation and conduction. The heat removal has to be limited in
order to prevent damage to the electrostatic chuck 104 due to high
thermal stresses in the ceramic chuck material. Potentially, the
gap 112 between the shaft 106 and the cooling base 102 may be
filled with helium supplied for substrate cooling due to seal
leakage. The pressure of the helium in the gap 112 will change
significantly during the process cycle, which can lead to an
additional repeating thermal stress and breakdown of the shaft 106.
In order to evacuate helium leaked into the gap 112 and prevent
unpredictable heat transfer from the shaft 106 to the cooling base
102, the gap 112 may be connected to the chamber by a small channel
192, thereby dumping any helium that may be present in the gap 112
into the chamber in which the cathode is installed. The channel 192
may include a sintered ceramic plug 194 to prevent arcing in the
channel 192. Although the channel 192 is shown through the cylinder
150, the channel 192 may be formed in other locations, for example,
through the main portion of the base 102 above the conduits
152.
[0039] The electrostatic chuck 104 is typically fabricated from
aluminum nitride or other suitable material. The electrostatic
chuck 104 includes a resistive heater 122 and at least one chucking
electrode 120. In one embodiment, the heater 122 is disposed in the
middle of the electrostatic chuck 104, while the chucking electrode
120 is disposed between the heater 122 and the upper surface 130.
The chucking electrode 120 is also provided with RF power to
sustain a plasma within a processing chamber during etching. Power
to the chucking electrode 120 and the heater 122 are generally
provided through electrical feeds 124, 126 which extend through the
hollow interior of the stem 106 and shield 108 to facilitate
coupling of the chucking electrode 120 and heater 122 to power
sources not shown.
[0040] A secondary electrode 128 may be disposed below the chucking
electrode 120. The outer edge of the secondary electrode 128
extends beyond the outside edge of the chucking electrode 120.
Since the upper surface 130 of the electrostatic chuck 104 is
smaller than the substrate fixed on top of the chuck to prevent
damage to the chuck by plasma at the edge of the substrate during
processing, the electrical field at the edge of the substrate may
be distorted and provide a so-called "tilted" etch profile. The
secondary electrode 128 is connected to the main RF terminal as the
chucking electrode 120 and is provided with generally same
electrical potential during etch process. The secondary electrode
128 may also be utilized to prevent and/or remove material
deposited on a process kit (e.g., a process ring) supported on a
ledge 190 outward and below the upper surface 130 of the
electrostatic chuck 104.
[0041] The upper surface 130 of the electrostatic chuck 104
generally includes a plurality of mesas 132 separated by a groove
network 134. The mesas may include surface features 144, such as
bumps, projections, embossments, texture and the like, which are
utilized to tailor heat transfer and chucking characteristics of
the surface 130. Helium or other suitable heat transfer gas is
provided to the groove network 134 through an inner gas feed 140
formed through the electrostatic chuck 104.
[0042] The upper surface 130 of the electrostatic chuck 104
additionally includes an outer peripheral channel 136 which is
separated from the groove network 134 by an annular ridge 138.
Helium or other suitable heat transfer gas is provided to the outer
peripheral channel 136 by an outer gas feed 140 so that the gases
delivered to the groove network 134 and the outer peripheral
channel 136 may be independently controlled. Optionally, one or
more gas feeds 140, 142 may be provided to provide a desired
distribution of gas in the groove network 134 and outer peripheral
channel 136. In the embodiment depicted in FIG. 1, one inner gas
feed 142 and twelve equally spaced outer gas feeds 140 are formed
through the electrostatic chuck 104. Although only one is shown, a
plurality of lift pin holes 146 are formed through the cooling base
102 and electrostatic chuck 104.
[0043] Optionally, a second annular outer channel (not shown) may
be disposed adjacent the outer peripheral channel 136. The second
annular outer channel may be utilized to collect contaminants and
to decrease the contamination of the rest of chuck surface, thereby
increasing chucking performance.
[0044] FIG. 2 depicts a partial cross-sectional view of one
embodiment of the clamp ring 114 of the cathode 100. The clamp ring
114 is fabricated from a rigid material, such as anodized aluminum,
titanium, or other suitable material. The material of the clamp
ring 114 may be selected to have a low thermal conductivity so that
heat transfer between the electrostatic chuck 104 and base 102 is
minimized. The clamp ring 114 generally includes an annular body
202 having a flange 204 extending inwardly therefrom. The distal
end of the flange 204 includes a downwardly extending lip 206. The
flange 204 and lip 206 are dimensioned such that the lip 206
contacts a mounting flange 212 extending radially outward below the
ledge 190 of the electrostatic chuck 104 when clamped.
[0045] In one embodiment, the clamp ring 114 may be configured to
minimize the heat transfer between the electrostatic chuck 104 and
the clamp ring 114, thereby preventing or minimizing the formation
of lateral temperature gradients in the chuck 104. In one
embodiment, the lip 206 may be segmented around the circumference
of the flange 204 to minimize the contact between the clamp ring
114 and the electrostatic chuck 104. In another embodiment, the
flange 204 may include a region of reduced cross-section as to
create a thermal choke between the lip 206 and the body 202,
thereby limiting heat transfer therebetween. In another embodiment,
a thermal insulation ring 210 may be provided between the lip 206
and the mounting flange 212. The insulation ring 210 may be
fabricated from a material having a coefficient of thermal
conductivity less than at least one of or both of the electrostatic
chuck 104 and ring 114.
[0046] The body 202 includes a threaded hole 216 configured to
accept a fastener 222. The fastener 222 extends through a clearance
hole 218 formed through the cooling base 102. The clearance hole
218 has a diameter sufficient to accommodate differences in thermal
expansion between the clamp ring 114 and the cooling base 102 while
fastened. One or more washers 220 are utilized to prevent the head
of the fastener 222 from extending or binding in the clearance hole
218. A counter bore 226 is provided through the cooling base 202 to
facilitate access to the fastener 222. The fastener 222 and washers
220 may be fabricated from a suitable material, and in one
embodiment, are fabricated from at nickel alloy, such as
HASTELLOY.RTM.. In one embodiment, springs (not shown) may be
disposed between the head of the fastener 222 and cooling base 102
to bias the clamp ring 114 against the electrostatic chuck 104.
[0047] The body 202 may additionally include a ridge 208 extending
from a lower surface thereof. The ridge 208 maintains the body 202
in a spaced-apart relation relative to an upper surface 214 of the
cooling base 102. The ridge 208 provides a thermal choke between
the body 202 and the cooling base 102, such that heat transfer from
the periphery of the electrostatic chuck 104 to the cooling base
102 through the clamp ring 114 is minimized. Optionally, the ridge
208 may be segmented into discrete portions to further limit the
heat transfer between the body 202 and the cooling base 102.
[0048] Also depicted in FIG. 2 is a gas distribution ring 230. The
gas distribution ring is configured to provide gas to the outer gas
feeds 140. The gas distribution ring 230 is disposed in a stepped
recess 232 formed in the upper surface 214 of the cooling base 102.
A plurality of fasteners 234 are arranged to engage a threaded hole
236 formed in the cooling base 102 to secure the gas distribution
ring 230. A plurality of inner and outer ring seals 238 are
provided between the gas distribution ring 230 and the base 102 and
the stepped recess 232 of the base 102.
[0049] A bottom 254 of gas distribution ring 230 is maintained in a
spaced-apart relation with a bottom 256 of the stepped recess 232,
there by defining an annular channel 250 into which gas is feed
through the base 102. One or more feed holes 252 are formed through
the gas distribution ring 230 to allow gases in the channel to pass
through the gas distribution ring 230.
[0050] The gas distribution ring 230 also includes a stepped
counter bore 240. An upper portion of the stepped counter bore 240
is configured to receive a baffle disk 244. Each baffle disk 244 is
circumscribed by a baffle seal 242 that provides a seal between the
gas distribution ring 230 and a lower surface of the electrostatic
chuck 104. The baffle seal 242 additionally sealingly circumscribes
the outer gas feed 140. In one embodiment, the seals 238, 242 are
fabricated from a high temperature elastomer, such as a
perfluoroelastomer, one example of which is KALREZ.RTM.. In one
embodiment, the feed holes 252 break into the stepped counter bore
240 to allow gases to pass from the annular channel 250 through the
gas distribution ring 230 and eventually through the outer gas feed
140 of the electrostatic chuck 104.
[0051] Referring additionally to FIGS. 3A and 3B, the baffle disk
244 is provided to prevent a direct line of sight exposure of
grounded surfaces of the cathode 100 and the electrically charged
substrate disposed on top of the electrostatic chuck 104 during
processing. The baffle disk 244, made from electrically
non-conductive material such as a ceramic material, prevents
electrical discharge (e.g., arcing) within the cathode 100. In one
embodiment, the baffle disk 244 is made of alumina
(Al.sub.2O.sub.3).
[0052] In the embodiment depicted in FIG. 3A, the baffle disk 244
and gas distribution ring 230 are shown with the electrostatic
chuck 104 removed. The location of the outer gas feed 140 is shown
in phantom. FIG. 3B depicts the gas distribution ring 230 with the
baffle disk 244 removed such that the head of the fastener 234
disposed in the lower region of the stepped bore 240 is shown. With
the baffle disk 244 removed in FIG. 3B, the gas feed hole 252
formed through the gas distribution ring 230 is visible. The gas
feed hole 252 couples the stepped counter bore 240 with a gas
source (not shown) with a passage 402 formed through the cooling
base 102, as shown in FIG. 4.
[0053] As also illustrated in FIGS. 2 and 4, the support ring 110
may be retained on a ledge 224 formed on the periphery of the gas
distribution ring 230. Alternatively, the support ring 110 may be
located in a groove formed in at least one of the electrostatic
chuck 104 or cooling base 102.
[0054] FIG. 5 depicts one embodiment of the baffle disk 244. In the
embodiment depicted in FIG. 5, the upper and lower surfaces of the
baffle disk 244 respectively include cross channels 502, 504,
formed therein to enhance gas flow around the baffle disk 244. The
baffle disk 244 may also include notches 506 formed in the
perimeter of the plate 244 to further enhance flow from the lower
surface to the upper surface of the baffle disk 244.
[0055] FIG. 6 is another partial cross-sectional view of the
cathode 100 illustrating a baffle disk 244 utilized below the inner
gas feed 142. The baffle disk 244 is retained in a stepped bore
602, which is also utilized to retain a baffle seal 242. The baffle
seal 242 provide a seal around the inner gas feed 142. Optionally,
one or more of the seals described herein may be replace by an
E-seal 702, such as shown in FIG. 7. The E-seal 702 may be
fabricated from a flexible metal and configured to provide a high
temperature seal when compressed between the cooling base 102 and
electrostatic chuck 104. In one embodiment, the E-seal 702 is
fabricated from Ni-plated INCONEL.RTM. 718 material. The E-seals
702 allow relative movement of the parts due to thermal expansion
or contraction during heating and cooling while providing vacuum
sealing of the area.
[0056] Returning to FIG. 6, a lower region of the stepped bore 602
is coupled to a gas passage 604 utilized to couple the groove
network 134 to a gas source (not shown) through the inner gas feed
142. As illustrated in FIG. 6, the gas passage 604 and the inner
gas feed 142 are offset to prevent line of sight alignment as
discussed above. Additionally, the baffle disk 244 further
obstructs the alignment between the feed 142 and passage 604 to
provide an extra measure of protection without adversely affecting
the flow of gas through the feed 142 from the passage 604.
[0057] FIG. 8 depicts another embodiment of a cathode 800. The
cathode 800 is substantially similar to the cathode 100 and
includes a spreader plate 802 disposed in a recess 804 of a cooling
base 102. Annular seals, shown as E-seals 702, may be provided on
each side of the spreader plate 802 to isolate the spreader plate
802 from gas pressure changes due to inadvertent gas leakage within
the cathode 800. Alternatively, the E-seals 702 may allow a portion
of the gap 118, for example the region containing the spreader
plate 802, to be selectively flooded with a heat transfer gas such
as helium to assist in regulating the heat transfer between the
cooling base 102 and electrostatic chuck 104.
[0058] In one embodiment, the gap 118 between the bottom of the
electrostatic 104 and the top of the cooling base 102 is configured
to can accommodate a thin (e.g., about 0.020 to 0.060 inches)
spreader plate 802. The spreader plate 802 is made of sturdy
material with high thermal conductivity and high electrical
resistivity (e.g., aluminum nitride, aluminum oxide, and the like).
The spreader plate 802 beneficially makes heat flow from the
electrostatic chuck 104 to the cooling base 102 more uniform by
"spreading" any thermal non-uniformities caused by local features
in the electrostatic chuck 104 or the base 102, such as backside He
holes, or lift-pin holes, as well as caused by the heater 122
disposed in the chuck, imperfections with regard to the coolant
channel pattern, and coolant temperature changes in the channel.
The spreader plate 802 also allows greater distance between the
electrostatic chuck 104 and the cooling base 102 without danger of
igniting secondary plasma in the gap between the chuck and the
cooling base due to electrical discharge in the filling gas in the
gap. One example of a spreader plate which may be adapted to
benefit from the invention is described in U.S. patent application
Ser. No. 10/440,365, filed May 16, 2003, which is incorporated by
reference in its entirety. The interior surfaces of a plasma etch
processing chamber, such as in previously incorporated U.S. patent
application Ser. Nos. 10/440,365 and 10/960,874 may be fabricated
from, and/or coated with, a yttria comprising material. Examples of
such yttria comprising surfaces include shields, process kits, wall
liners, chamber walls, showerheads and gas delivery nozzles, among
others.
[0059] In operation within a plasma etch reactor, heat produced by
the heater 122 embedded in the electrostatic chuck 104 and heat
gained by the chuck 104 from plasma is rejected to the cooling base
102 through the gap 118 and gap 112. In at least one embodiment,
the base 102 and chuck 104 do not touch, and that the stem 108
coupled to the chuck 104 only comes close to the base 102 proximate
the seal 116, such that the chuck and stem assembly essentially
does not contact the base. The gap 118, which in one embodiment, is
filled with helium, reduces the heat flux to the cooling base 102
in order to keep the surface of the electrostatic chuck 104 at
significantly higher temperature than the cooling base 102. In some
embodiments, a spreader plate 802 is utilized to reduce temperature
non-uniformity, created by heater 122 due to a non-optimized heater
power distribution and/or uneven cooling by the cooling base 102.
The stem 106 is used to keep terminals of the electrostatic chuck
104 under atmospheric pressure in order to prevent arcing between
terminals as well as between terminal and other parts. The stem 106
is long enough to allow placement of the o-ring 116 at a distance
sufficient to allow heat removal from the stem 106 to occur at a
rate suitable to prevent damage to the stem 106 or chuck 104, while
reducing the temperature at the bottom of the stem 106 to a
temperature below the melting point of the material of the o-ring
116.
[0060] Thus, embodiments of a cathode suitable for high temperature
plasma etching have been provided. The cathode allows ceramic
electrostatic chucks to operate at temperatures up to 450 degree
Celsius in conjunction with cooling bases maintained in the range
of about 20 to about 80 degree Celsius while preventing damage to
cathode components due to thermal stress or exposure to high
temperatures.
[0061] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
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