U.S. patent application number 10/836516 was filed with the patent office on 2005-11-03 for multi-piece baffle plate assembly for a plasma processing system.
Invention is credited to Ferris, David S., Srivastava, Aseem K., Tun, Maw S..
Application Number | 20050241767 10/836516 |
Document ID | / |
Family ID | 35185884 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241767 |
Kind Code |
A1 |
Ferris, David S. ; et
al. |
November 3, 2005 |
Multi-piece baffle plate assembly for a plasma processing
system
Abstract
A plasma processing system includes at least one multi-piece
baffle plate. The multi-piece baffle plate assembly generally
comprises at least one annular shaped ring portion having an
opening and an insert portion dimensioned to sit within the
opening. The individual pieces can be formed of a ceramic material.
The effects caused by thermal gradients in the plate during plasma
processing are minimized.
Inventors: |
Ferris, David S.;
(Rockville, MD) ; Srivastava, Aseem K.;
(Germantown, MD) ; Tun, Maw S.; (Rockville,
MD) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Family ID: |
35185884 |
Appl. No.: |
10/836516 |
Filed: |
April 30, 2004 |
Current U.S.
Class: |
156/345.35 |
Current CPC
Class: |
H01J 37/3244 20130101;
H01J 37/32633 20130101; H01J 37/32623 20130101 |
Class at
Publication: |
156/345.35 |
International
Class: |
C23F 001/00 |
Claims
1. A baffle plate assembly for distributing plasma into an adjacent
process chamber containing a semiconductor wafer to be processed,
comprising: a generally planar multi-piece baffle plate spaced
apart from and fixedly positioned above a wafer to be
processed.
2. The baffle plate assembly of claim 1, wherein the generally
planar multi-piece baffle plate comprises at least one annular
shaped ring portion having an opening and an insert portion
dimensioned to sit within the opening.
3. The baffle plate assembly of claim 2, wherein the opening
comprises an annular recessed portion and the insert portion
comprises a lip adapted to seat on the annular recessed
portion.
4. The baffle plate assembly of claim 3, wherein the annular
recessed portion further comprises at least three pins spaced
equidistantly about the annular recessed portion, wherein the
insert portion is supported by the at least three pins.
5. The baffle plate assembly of claim 1, wherein the multi-piece
baffle plate comprises a non-apertured central portion.
6. The baffle plate assembly of claim 1, wherein the baffle plate
assembly comprises an upper baffle plate and a lower baffle plate,
wherein the upper baffle plate comprises the multi-piece baffle
plate, wherein the multi-piece baffle plate has a non-apertured
central portion.
7. The baffle plate assembly of claim 2, wherein the annular shaped
ring and the insert portion form a gap less than 0.010 inches.
8. The baffle plate assembly of claim 1, wherein the multi-piece
baffle plate is formed of a ceramic material.
9. A plasma processing chamber for processing a semiconductor wafer
contained therein, comprising: a wafer processing cavity into which
a wafer may be inserted for processing, the wafer processing cavity
defined in part by walls including a top wall; and a baffle plate
assembly located adjacent said wafer processing cavity for
distributing energized gas thereinto, said baffle plate assembly
comprising a generally planar upper baffle plate fixedly positioned
above a generally planar lower baffle plate, said upper baffle
plate comprising at least two pieces comprising at least one
annular shaped ring portion having an opening and an insert portion
dimensioned to sit within the opening.
10. The plasma processing chamber of claim 9, wherein said upper
baffle plate is comprised of a ceramic material.
11. The plasma processing chamber of claim 9, wherein the opening
comprises an annular recessed portion and the insert portion
comprises a lip adapted to seat on the annular recessed
portion.
12. The plasma processing chamber of claim 11, wherein the annular
recessed portion further comprises at least three pins spaced
equidistantly about the annular recessed portion, wherein the
insert portion is supported by the at least three pins.
13. The plasma processing chamber of claim 9, wherein the upper
baffle plate comprises a non-apertured central portion.
14. The plasma processing chamber of claim 9, wherein the annular
shaped ring and the insert portion form a gap less than 0.010
inches.
15. The plasma processing chamber of claim 9, wherein the chamber
is adapted to receive a wafer having a diameter of at least 200
millimeters.
16. A downstream plasma treatment device for treating a substrate,
comprising, in combination: a gas source; a plasma generating
component in fluid communication with the gas source, the plasma
generating component comprising a plasma tube and a plasma
generator coupled to the plasma tube for generating a plasma within
the plasma tube from the gas source; and a process chamber in fluid
communication with the plasma tube, wherein the process chamber
comprises a baffle plate assembly comprising a generally planar
multi-piece baffle plate spaced apart from and fixedly positioned
above the substrate to be processed.
17. The downstream plasma treatment device of claim 16, wherein the
multi-piece baffle plate is formed of a ceramic material.
18. The downstream plasma treatment device of claim 16, wherein the
generally planar multi-piece baffle plate comprises at least one
annular shaped ring portion having an opening and an insert portion
dimensioned to sit within the opening.
19. The downstream plasma treatment device of claim 18, wherein the
opening comprises an annular recessed portion and the insert
portion comprises a lip adapted to seat on the annular recessed
portion.
20. The downstream plasma treatment device of claim 19, wherein the
annular recessed portion further comprises at least three pins
spaced equidistantly about the annular recessed portion, wherein
the insert portion is supported by the at least three pins.
21. The downstream plasma treatment device of claim 16, wherein the
multi-piece baffle plate comprises a non-apertured central
portion.
22. The downstream plasma treatment device of claim 18, wherein the
annular shaped ring and the insert portion form a gap less than
0.010 inches.
23. A downstream plasma treatment device for treating a substrate,
comprising, in combination: a gas source; a plasma generating
component in fluid communication with the gas source, the plasma
generating component comprising a plasma tube and a plasma
generator coupled to the plasma tube for generating a plasma within
the plasma tube from the gas source; and a process chamber in fluid
communication with the plasma tube, wherein the process chamber
comprises a baffle plate assembly comprising a generally planar
upper baffle plate fixedly positioned above a generally planar
lower baffle plate, said upper baffle plate comprising at least two
pieces comprising at least one annular shaped ring portion having
an opening and an insert portion dimensioned to sit within the
opening.
24. The downstream plasma treatment device of claim 23, wherein the
upper baffle plate is formed of a ceramic material.
25. The downstream plasma treatment device of claim 23, wherein the
upper baffle plate comprises at least one annular shaped ring
portion having an opening and an insert portion dimensioned to sit
within the opening.
26. The downstream plasma treatment device of claim 25, wherein the
opening comprises an annular recessed portion and the insert
portion comprises a lip adapted to seat on the annular recessed
portion.
27. The downstream plasma treatment device of claim 26, wherein the
annular recessed portion further comprises at least three pins
spaced equidistantly about the annular recessed portion, wherein
the insert portion is supported by the at least three pins.
28. The downstream plasma treatment device of claim 23, wherein the
upper baffle plate comprises a non-apertured central portion.
29. The downstream plasma treatment device of claim 25, wherein the
annular shaped ring and the insert portion form a gap less than
0.010 inches.
30. A method for preventing cracking of a ceramic baffle plate
having a radius greater than 4 inches during a plasma mediated
process, wherein the plasma mediated process subjects the ceramic
baffle plate to a thermal temperature gradient across the plate,
the method comprising: forming the ceramic baffle plate into at
least two pieces, wherein a gap formed by the at least two pieces
is less than 0.010 inches; and exposing the least two pieces of the
ceramic baffle plate to plasma formed during the plasma mediated
process.
31. The method of claim 30, wherein the at least two pieces
comprises at least one annular shaped ring portion having an
opening and an insert portion dimensioned to sit within the
opening.
32. The method of claim 30, wherein exposing the at least two
pieces of the ceramic baffle plate to plasma subjects the at least
two pieces to hoop stresses less than a material stress for the
ceramic.
Description
BACKGROUND
[0001] In the manufacture of integrated circuits, photolithography
techniques are used to form integrated circuit patterns on a
substrate, such a silicon wafer. Typically, the substrate is coated
with a photoresist, portions of which are exposed to ultraviolet
(UV) radiation through a mask to image a desired circuit pattern on
the photoresist. The portions of the photoresist left unexposed to
the UV radiation are removed by a processing solution, leaving only
the exposed portions on the substrate. These remaining exposed
portions may be baked during a photostabilization process to enable
the photoresist to withstand subsequent processing.
[0002] After such processing, in which the integrated circuit
components are formed, it is generally necessary to remove the
baked photoresist from the wafer. In addition, residue that has
been introduced on the substrate surface through processes such as
etching must be removed. Typically, the photoresist is "ashed" or
"burned" and the ashed or burned photoresist, along with the
residue, is "stripped" or "cleaned" from the surface of the
substrate.
[0003] One manner of removing photoresist and residues is by
rapidly heating the photoresist-covered substrate in a vacuum
chamber to a preset temperature by infrared radiation, and
directing microwave-energized or radio frequency (RF) energized
reactive gases (i.e., a plasma) toward the heated substrate
surface. In the resulting process, the reactive plasma reacts with
the photoresist to ash it for subsequent removal from the
wafer.
[0004] It is important that the ashing process occur at
substantially the same rate across the surface of the wafer. To
insure such uniform ashing of the photoresist, the process
conditions should be precisely controlled. Process conditions that
must be so controlled include the temperature of the process
chamber and the temperature of the wafer.
[0005] Known gas distribution or baffle plate assemblies for
uniformly directing energized plasma onto a wafer surface generally
comprise one or two parallel apertured plates that are typically
made of quartz, or in the case of two parallel plates, an upper
quartz plate and a lower metal plate. Quartz is generally chosen
for its ability to withstand high process temperatures. However,
the use of quartz makes acceptable wafer and process temperature
uniformity difficult to obtain. The temperature non-uniformities
may be caused by the large temperature gradients that can develop
across the surface of a quartz plate due to its poor thermal
conductivity characteristics. In addition, undesirable infrared
(IR) wavelength absorption characteristics of quartz add to the
thermal energy absorbed by the baffle plate. As a result, process
uniformity and system throughput are adversely affected.
[0006] For plasma tools requiring the use of fluorine chemistries,
the upper quartz plate may be further coated with a sapphire
coating. The presence of the sapphire coating prevents etching of
the plate from exposure to the reactive fluorine species. A solid,
single plate could be fabricated entirely from sapphire; however,
this is generally considered by those in the art to be cost
prohibitive. The sapphire coated quartz plate may additionally
include a central impingement disc formed of a ceramic material to
deflect the incoming plasma jet into the process chamber plenum and
also reduces the high temperature exposure to the coated sapphire
material.
[0007] Several problems of these types of baffle plate assemblies
are known to exist. For example, with regard to the sapphire coated
plates, the sapphire coating tends to flake off after protracted
use, which is believed to be due to unequal and non-conformal
sidewall coating of the apertures disposed therein relative to the
top and bottom surfaces of the plate. Still further, periodic
replacement of the sapphire coated plate and/or ceramic disc leads
to higher end costs since the sapphire coating adds significant
cost to the quartz plate.
[0008] Solid ceramic baffle plates can be used to resolve many of
the problems facing the prior art. However, subjecting solid
ceramic plates of the size utilized in plasma process chambers to a
thermal gradient during operation of the plasma can result in
catastrophic failure. At a baffle plate radius greater than about 5
inches, the so-called "hoop" stresses in the plate can exceed the
capability of the ceramic material causing the plate to crack.
Cracking of the plate deleteriously results in particle generation
as well as contaminates the process chamber, thereby requiring
expensive downtime, repair, and replacement.
[0009] Accordingly, there is a need in the art for an improved
baffle plate assembly that maintains plasma uniformity and can
withstand the various conditions utilized during the plasma
process, e.g., withstands thermal gradient related stresses, and/or
is economical viable, and/or is compatible with fluorine
chemistries, and/or the like.
BRIEF SUMMARY
[0010] Disclosed herein are multi-piece baffle plate assemblies,
plasma processing chambers, and plasma processing systems. In one
embodiment, the multi-piece baffle plate assembly comprises a
generally planar multi-piece baffle plate spaced apart from and
fixedly positioned above a wafer to be processed.
[0011] A plasma processing chamber for processing a semiconductor
wafer contained therein, comprises a wafer processing cavity into
which a wafer may be inserted for processing, the wafer processing
cavity defined in part by walls including a top wall; and a baffle
plate assembly located adjacent said wafer processing cavity for
distributing energized gas thereinto, said baffle plate assembly
comprising a generally planar upper baffle plate fixedly positioned
above a generally planar lower baffle plate, said upper baffle
plate comprising at least two pieces comprising at least one
annular shaped ring portion having an opening and an insert portion
dimensioned to sit within the opening.
[0012] A downstream plasma treatment device for treating a
substrate, comprises, in combination a gas source; a plasma
generating component in fluid communication with the gas source,
the plasma generating component comprising a plasma tube and a
plasma generator coupled to the plasma tube for generating a plasma
within the plasma tube from the gas source; and a process chamber
in fluid communication with the plasma tube, wherein the process
chamber comprises a baffle plate assembly comprising a generally
planar multi-piece baffle plate spaced apart from and fixedly
positioned above the substrate to be processed.
[0013] In another embodiment, a downstream plasma treatment device
for treating a substrate, comprises, in combination a gas source; a
plasma generating component in fluid communication with the gas
source, the plasma generating component comprising a plasma tube
and a plasma generator coupled to the plasma tube for generating a
plasma within the plasma tube from the gas source; and a process
chamber in fluid communication with the plasma tube, wherein the
process chamber comprises a baffle plate assembly comprising a
generally planar upper baffle plate fixedly positioned above a
generally planar lower baffle plate, said upper baffle plate
comprising at least two pieces comprising at least one annular
shaped ring portion having an opening and an insert portion
dimensioned to sit within the opening.
[0014] A method for preventing cracking of a ceramic baffle plate
having a radius greater than 4 inches during a plasma mediated
process, wherein the plasma mediated process subjects the ceramic
baffle plate to a thermal temperature gradient across the plate
comprises forming the ceramic baffle plate into at least two
pieces, wherein a gap formed by the at least two pieces is less
than 0.010 inches; and exposing the least two pieces of the ceramic
baffle plate to plasma formed during the plasma mediated
process.
[0015] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Referring now to the figures, which are exemplary
embodiments and wherein like elements are numbered alike:
[0017] FIG. 1 is a sectional view of an exemplary photoresist asher
into which is incorporated a first embodiment of a baffle plate
assembly constructed according to the present disclosure;
[0018] FIG. 2 graphically illustrates tangential stress in a
ceramic baffle plate at a given thermal gradient;
[0019] FIG. 3 is an exploded perspective view of a single layered
multi-piece baffle plate assembly;
[0020] FIG. 4 is a cross sectional view of the single layered
multi-piece baffle plate assembly taken along lines 4-4;
[0021] FIG. 5 is a plan view of an exemplary insert portion for a
single layered multi-piece baffle plate assembly; and
[0022] FIG. 6 is a cross sectional view of the exemplary insert
portion taken along lines 6-6.
DETAILED DESCRIPTION
[0023] Referring now to the drawings, FIG. 1 illustrates an
exemplary photoresist asher 10, generally comprising a gas box 12,
a microwave plasma generator assembly 14, a process chamber 16
defining an interior cavity in which is processed a semiconductor
substrate such as a wafer 18, and a radiant heater assembly 20 for
heating the wafer 18 situated at the bottom of the process chamber.
A temperature probe 24, such as a thermocouple, is used to monitor
the temperature of the wafer 18 during operation. A vacuum pump 26
is used to evacuate the process chamber 16 for processes requiring
vacuum conditions.
[0024] An optional monochromator 28 is used to monitor the optical
emission characteristics of gases within the chamber to aid in
process endpoint determination. The wafer 18 is introduced into and
removed from the process chamber 16 via an appropriate load lock
mechanism (not shown) via entry/exit passageway 30. Alternately,
the wafer 18 may be introduced directly into the process chamber 16
through the entry/exit passageway 30 if the tool is not equipped
with a load lock. Although the present disclosure is shown and
characterized as being implemented within a photoresist asher, it
may also be used in other semiconductor manufacturing equipment,
such as residue removal and strip processes. For example,
downstream axial flow plasma apparatuses particularly suitable for
modification in the present disclosure are plasma ashers, such as
for example, those microwave plasma ashers available under the
trade name RadiantStrip320 and commercially available from Axcelis
Technologies Corporation. Portions of the microwave plasma asher
are described in U.S. Pat. Nos. 5,498,308 and 4,341,592, and PCT
International Application No. WO/97/37055, herein incorporated by
reference in their entireties. As will be discussed below, the
disclosure is not intended to be limited to any particular plasma
asher in this or in the following embodiments. For instance, the
processing plasma can be formed using a parallel-plate,
capacitively coupled plasma source, an inductively coupled plasma
source, and any combination thereof, with and without DC magnet
systems. Alternately, the processing plasma can be formed using
electron cyclotron resonance. In yet another embodiment, the
processing plasma is formed from the launching of a Helicon wave.
In yet another embodiment, the processing plasma is formed from a
propagating surface wave.
[0025] In operation, a desired mixture of gases is introduced into
a plasma tube 32 from gas box 12 through an inlet conduit 34. The
plasma tube 32 can be made of alumina (Al.sub.2O.sub.3) or sapphire
to accommodate fluorine chemistries without etching, degradation,
and/or other issues associated with fluorine chemistries. The gases
forming the desired mixture are stored in separate supplies (not
shown) and mixed in the gas box 12 by means of valves 36 and piping
38. One example of a desired gas mixture is nitrogen-forming gas
(primarily nitrogen with a small percentage of hydrogen), and
oxygen. A fluorine containing gas, such as carbon tetrafluoride
(CF.sub.4), may be added to the gas mixture to increase ashing
rates for certain processes.
[0026] The desired gas mixture is energized by the microwave plasma
generator assembly 14 to form a reactive plasma that will ash
photoresist on the wafer 18 in the process chamber 16 when heated
by the radiant heater assembly 20. A magnetron 40 generates
microwave energy that is coupled to a waveguide 42. Microwave
energy is fed from the waveguide through apertures (not shown) in
microwave enclosure 44, which surrounds the plasma tube 32.
[0027] An outer quartz cooling tube 46 surrounds the plasma tube
32, slightly separated therefrom. Pressurized air is fed into the
gap between the tubes 32 and 46 to effectively cool the tube 32
during operation. The microwave enclosure 44 can be segmented into
sections shown by phantom lines 45. Segmentation of the enclosure
44 can provide uniform microwave power distribution across the
length of the alumna or sapphire plasma tube, and protects it from
overheating by preventing an unacceptably large thermal gradient
from developing along its axial length when suitable input power is
provided. Each segment of the enclosures 44 is separately fed with
microwave energy that passes through the quartz tube 46 and the
alumna or sapphire tube 32 passing therethrough.
[0028] The gas mixture within the plasma tube 32 is energized to
create a plasma. Microwave traps 48 and 50 can be provided at the
ends of the microwave enclosure 44 to prevent microwave leakage.
Energized plasma (typically having a temperature of about
150.degree. C.) enters the process chamber 16 through an opening 51
in the top wall 52 thereof.
[0029] Positioned between the top wall 52 of the plasma chamber 16
and the wafer 18 being processed is a multi-piece baffle plate
assembly 54. Although shown as a single layered multi-piece baffle
plate assembly, it is contemplated that the multi-piece baffle
plate may take the form of a dual- layered multi-piece baffle plate
assembly comprising upper and lower baffle plates, wherein the
upper baffle plate is formed of the multiple pieces in the manner
described with respect to the single layered multi-piece baffle
plate assembly. In either embodiment, the multi-piece baffle plate
assemblies evenly distribute the reactive plasma across the surface
of the wafer 18 being processed. Moreover, the multi-piece
construction can minimize heat stresses during operation, which
have been observed to cause catastrophic failure in ceramic type
baffle plate assemblies having layers fabricated from a single
piece of the ceramic material.
[0030] For example, as shown in FIG. 2, exposing a ceramic
(alumina) baffle plate assembly to a thermal gradient across the
baffle plate can result in cracking of the plate during operation
as a result of hoop stresses. Ceramic materials suitable for use as
baffle plates are generally stronger in compression than tension.
Because of this, hoop stresses caused by thermal gradients
occurring in the plate during plasma processing can exceed the
material strength. In this particular example, the tensile strength
of the ceramic was about 1E8 MPa to about 2E8 MPa, which is the
maximum shown for about a 4 to about a 5 inch plate radius. The use
of multi-piece construction as disclosed herein, permits the use of
materials such as ceramics for fabrication of the baffle plate(s)
without causing premature cracking by preventing the hoop stresses
from exceeding the material strength. As such, ceramic multi-piece
baffle plate assemblies provide an inexpensive alternative to
sapphire coated baffle plate assemblies and eliminate the problems
associated with the use of sapphire coatings. The multi-piece
ceramic baffle plate is especially desirable for processes
including fluorine chemistries.
[0031] With reference back to FIG. 1, in operation, the reactive
plasma passes through the multi-piece baffle plate 54 and can be
used to ash the photoresist and/or residues on the wafer 18. The
radiant heater assembly 20 comprises a plurality of tungsten
halogen lamps 58 residing in a reflector 56 that reflects and
redirects the heat generated by the lamps toward the backside of
the wafer 18 positioned within the process chamber 16 on quartz or
ceramic pins 68. One or more temperature sensors 72, such as
thermocouples, can be mounted on the interior of process chamber
sidewall 53 to provide an indication of wall temperature.
[0032] The single layered multi-piece baffle plate assembly 54
comprises a generally planar gas distribution central portion 74,
having apertures 76 therein, surrounded by a flange 78. The flange
78 surrounds the central portion and seats intermediate the process
chamber sidewall 53 and top wall 52. Seals 79 and 81, respectively,
provide airtight connections between the flange 78 and the sidewall
53, and between the flange 78 and the top wall 52. The seals 79 and
81 reside in grooves located in the flange 78. The flange 78 also
provides mounting holes (not shown) for mounting to the top wall 52
and sidewall 53.
[0033] As shown more clearly in FIGS. 3-6, the illustrated single
layered multi-piece baffle plate assembly 54 comprises a two-piece
construction. However, although the figures illustrate a two-piece
construction, greater than two pieces are contemplated and may
actually be desired for certain applications. Moreover, it should
be apparent to those skilled in the art that the shapes of the
various pieces to form the baffle plate are not intended to be
limited to any particular shape or aperture pattern. It has been
found that the use of multiple pieces to form the baffle plate
advantageously relieves the thermal stresses introduced during
plasma operation, the design of which is virtually limitless as
will be appreciated by those skilled in the art in view of this
disclosure.
[0034] In FIG. 3, there is illustrated an exploded perspective view
of the multi-piece baffle plate assembly 54. The multi-piece baffle
plate assembly 54 generally comprises a generally annular shaped
ring 90 and an insert portion 92 centrally located within an
opening 94 defined by the generally annular shaped ring 90. As
illustrated, the exemplary single layered multi-piece baffle plate
54 comprises a hexagonally shaped opening 94 and a hexagonally
shaped insert portion 92. In this embodiment, the hexagonal shape
was chosen to accommodate a desired flow pattern for a particular
plasma ashing application. As previously described, the annular
ring as well as the number of pieces forming the single layered
baffle plate assembly can define any opening shape. Again, although
applicant refers to an annular ring, it is contemplated that the
various pieces do not include an annular ring. Rather, the multiple
pieces are configured and constructed so as to form a single layer
of the baffle plate. A locking means would be included to maintain
the baffle plate in a generally planar configuration and is well
within the skill of those in the art.
[0035] FIG. 4 illustrates a cross sectional view of the single
layered multi-piece baffle plate assembly 54. The opening 94 of the
annular shaped ring 90 includes a recessed portion 96 dimensioned
to receive a shoulder portion 98 formed about an outer edge of the
inert portion 92 (shown more clearly in FIG. 6). Optionally, three
or more support pins 100 are radially disposed in the shoulder 98
at equidistant positions about the annular recessed portion to
minimize scraping (and possible particle generation) between the
insert portion and the annular shaped ring. A gap formed between
the insert portion 92 and the annular shaped ring 90 is less than
about 0.010 inches to allow radial expansion during plasma
operation and provide a net surface that is wetted by the plasma as
if the baffle plate were formed a single unitary piece. FIGS. 5 and
6 depict the insert portion 92. As shown, the insert portion 92
includes a non-apertured central portion.
[0036] The so-formed single layered multi-piece baffle plate
generally includes a plurality of apertures, wherein the apertures
are arranged in a radial (or concentric multiply circular) pattern.
The single layered multi-piece baffle plate may or may not include
a non-apertured central portion as may be desired for certain
plasma applications. The design of the baffle plate assembly
(single or dual layered) is generally determined by applied gas
dynamics, materials engineering, and process data to insure correct
pressure, gas flows, and temperature gradients within the process
chamber.
[0037] In the case of a dual layered multi-piece baffle plate
assembly, the upper baffle plate and/or the lower baffle plate can
be comprised of multiple pieces in the manner previously described.
For example, the upper baffle plate can be formed of multiple
pieces, wherein the lower baffle plate is formed of a single
unitary piece. In the dual layered configuration, the apertures in
the upper baffle plate are slightly larger than the apertures in
the lower baffle plate. Moreover, it may be preferred to have a
central non-apertured portion within the upper baffle plate. In
this manner, the non-apertured portion diverts the energized gases
from the plasma tube radially outward to the remaining apertured
area of the upper baffle plate so as to prevent the radially inward
portion of the wafer being preferentially processed before the
outward portion of the wafer. The distance between the upper and
lower baffle plates, in part, determines the pattern of gas flow
through the dual layered baffle plate assembly. Apertures are
provided in the radially inner portion of the lower baffle plate
but generally not in the radial external portion. The surface area
of the radially inner portion of the lower baffle plate is
sufficient to cover the wafer residing therein below. In one
embodiment, the apertures are generally positioned equidistant from
each other in all directions. That is, any three apertures that are
mutually immediately adjacent to each other form an equilateral
triangle. Other distributions of holes on the baffle plates may
also be of used for specific applications such as, for example,
larger holes on the outer diameters but smaller holes on the inside
diameters so as to improve ash uniformity. Moreover, it is noted
that the dual layered baffle plate assembly is generally compact,
requiring less than one-inch vertical space within the process
chamber.
[0038] The upper multi-piece baffle plate is preferably formed from
a ceramic material. Suitable ceramic materials include, but are
note intended to be limited to, alumina (various aluminum oxides),
zirconium dioxides, various carbides such as silicon carbide, boron
carbide, various nitrides such as silicon nitride, aluminum
nitride, boron nitride, quartz, silicon dioxides, various
oxynitrides such as silicon oxynitride, and the like as well as
stabilized ceramics with elements such as magnesium, yttrium,
praseodymia, haffiium, and the like. Optionally, the lower single
piece baffle plate can be the same or of a different material,
typically anodized aluminum.
[0039] The disclosure is further illustrated by the following
non-limiting examples.
EXAMPLES
[0040] In the following examples, a plasma asher was configured
with a dual layered multi-piece baffle plate assembly and
separately with a conventional dual layered baffle plate assembly.
Typical data were acquired and analyzed, comparing the two
configurations. The upper baffle plate of the dual layered
multi-piece baffle plate assembly was of a two-piece construction
similar to that shown in FIGS. 3-6 and formed from high purity
alumina. The baffle plate assemblies for the two configurations
were identical with the exception of the multi-piece construction
of the upper baffle plate in the dual layered multi-piece baffle
plate assembly. The baffle plate assemblies were subjected to a low
temperature plasma ashing process (120.degree. C.) and a high
temperature plasma ashing process (270.degree. C.). Gas flow,
pressure and microwave power were identical. The results are shown
in Tables 1 and 2, respectively. Ashing rate and plasma uniformity
were compared for the two baffle plate assemblies.
1TABLE 1 Standard Baffle Plate Ash Rate Deviation % Non- Standard
Type (.mu.m/min) (.mu.m/min) uniformity (1.sigma.) Deviation
(1.sigma.) Control 0.13 0.002 8.71 0.012 Multi-piece 0.12 0.001
11.14 0.209 Ceramic
[0041]
2TABLE 2 Standard Baffle Plate Ash Rate Deviation % Non- Standard
Type (.mu.m/min) (.mu.m/min) uniformity (1.sigma.) Deviation
(1.sigma.) Control 7.75 0.10 4.1 0.26 Multi-piece 7.27 0.02 4.75
0.16 Ceramic
[0042] The results indicate that the use of the multi-piece
construction provided similar ashing behavior.
[0043] In this example, the generation of particle adders greater
than 0.12 nanometers that were deposited onto the wafer during
plasma ashing was monitored. The results are shown in Table 3.
3 TABLE 3 Ash Rate Standard Baffle Plate Type (.mu.m/min) Deviation
(1.sigma.) Control 53 16.82 Multi-piece Ceramic 87 10.02
[0044] The results show that the use of the ceramic multi-piece did
not contribute significantly to particle adder generation.
[0045] In this example, time to end point was monitored for a
plasma ashing process. Photoresist was coated onto 300 millimeter
wafers at a thickness of 1.0 micron. The results are shown in Table
4.
4 TABLE 4 Time to Standard Baffle Plate Endpoint (Seconds)
Deviation Control 10.43 0.41633 Multi-piece Ceramic 11.80
0.1000
[0046] The results show that the time for ashing the photoresist
was not significantly different for the plasma asher configured
with the multi-piece ceramic baffle plate assembly as
described.
[0047] While the disclosure has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
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