U.S. patent application number 09/401307 was filed with the patent office on 2002-09-05 for gas distribution apparatus for semiconductor processing.
Invention is credited to HUBACEK, JEROME.
Application Number | 20020123230 09/401307 |
Document ID | / |
Family ID | 23587197 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020123230 |
Kind Code |
A1 |
HUBACEK, JEROME |
September 5, 2002 |
GAS DISTRIBUTION APPARATUS FOR SEMICONDUCTOR PROCESSING
Abstract
A baffle plate of a showerhead gas distribution system and
method of using the baffle plate wherein the baffle plate is
effective for reducing particle and/or metal contamination during
processing of semiconductor substrates such as silicon wafers. The
showerhead can be a showerhead electrode of a plasma processing
chamber such as an etch reactor. The baffle plate comprises silicon
on at least one surface thereof and is adapted to fit in a baffle
chamber of the gas distribution system such that the silicon
containing surface is adjacent to and faces the showerhead. The
silicon containing baffle plate can consist entirely of silicon or
silicon carbide of at least 99.999% purity. The silicon can be
single crystal silicon or polycrystalline and the silicon carbide
can be CVD silicon carbide, sintered silicon carbide, non-sintered
silicon carbide or combination thereof. The non-sintered silicon
carbide can be silicon carbide formed by reaction synthesis of
silicon vapor with a carbon material such as graphite. Openings in
the silicon containing baffle plate can be offset from openings in
the showerhead to avoid a line-of-sight between plasma in the
chamber and the openings in the silicon containing baffle
plate.
Inventors: |
HUBACEK, JEROME; (FREMONT,
CA) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
23587197 |
Appl. No.: |
09/401307 |
Filed: |
September 23, 1999 |
Current U.S.
Class: |
438/712 |
Current CPC
Class: |
C23C 16/45565 20130101;
H01J 2237/022 20130101; H01J 37/3244 20130101; H01L 21/67017
20130101; C23C 16/45591 20130101; C23C 16/509 20130101 |
Class at
Publication: |
438/712 |
International
Class: |
C23F 001/02; H01L
021/302; H01L 021/461 |
Claims
What is claimed is:
1. A silicon containing baffle plate which reduces particle and/or
metal contamination during processing of a semiconductor substrate,
the baffle plate being adapted to fit within the baffle chamber of
a showerhead gas distribution system, the baffle plate comprising
silicon on at least one surface thereof and being adapted to fit
within the baffle chamber such that the silicon containing surface
is adjacent to and facing the showerhead.
2. The baffle plate of claim 1, wherein the silicon carbide baffle
plate consists essentially of silicon or silicon carbide having a
purity of at least 99.999%.
3. The baffle plate of claim 1, wherein the silicon containing
baffle plate is comprised entirely of single crystal silicon,
polycrystalline silicon, non-sintered silicon carbide, sintered
silicon carbide, bulk CVD silicon carbide, sintered silicon carbide
with a CVD coating of silicon carbide, graphite coated with silicon
carbide, reaction synthesized silicon carbide, or combination
thereof.
4. The baffle plate of claim 1, wherein the silicon containing
baffle plate includes openings therethrough for passage of process
gas, the openings being offset from openings in the showerhead when
the silicon containing baffle plate is mounted in the baffle
chamber.
5. The baffle plate of claim 1, wherein the silicon containing
baffle plate is a drop-in replacement for a lower aluminum baffle
plate in a baffle chamber having three aluminum baffle plates.
6. The baffle plate of claim 1, wherein the silicon containing
baffle plate is comprised entirely of a non-sintered silicon
carbide material.
7. The baffle plate of claim 6, wherein the non-sintered silicon
carbide material consists essentially of silicon carbide formed by
reaction synthesis of silicon vapor with a carbon material.
8. A plasma processing chamber including the silicon containing
baffle of claim 1 as part of a gas distribution system, the gas
distribution system including an elastomer bonded showerhead
electrode of silicon and a baffle chamber, the silicon containing
baffle plate being mounted in the baffle chamber with the silicon
containing surface facing the showerhead electrode, the silicon
containing baffle plate being effective to reduce metal
contamination by an order of magnitude during plasma processing of
a semiconductor substrate in the chamber compared to metal
contamination produced under the same processing conditions but
using an aluminum baffle plate in place of the silicon containing
baffle plate.
9. The plasma processing chamber of claim 8, further comprising a
semiconductor wafer supported on an electrostatic chuck having a
silicon edge ring and a plasma confinement ring comprised of a
stacked array of quartz rings.
10. A method of reducing particle and/or metal contamination during
processing of a substrate in a reaction chamber wherein a gas
distribution system includes a showerhead, a baffle chamber through
which process gas passes to the showerhead, and a silicon
containing baffle plate located in the baffle chamber, the method
comprising: supplying a semiconductor substrate to the reaction
chamber; supplying process gas into the baffle chamber, the process
gas passing through the silicon containing baffle plate into a
space between the silicon containing baffle plate and the
showerhead followed by passing through the showerhead and into an
interior of the reaction chamber; and processing the semiconductor
substrate with the process gas passing through the showerhead.
11. The method of claim 10, wherein the semiconductor substrate
comprises a wafer supported on an electrostatic chuck having a
silicon edge ring, the showerhead electrode is made of silicon and
energizes the process gas into a plasma which is confined within a
plasma confinement ring comprising a stacked array of quartz
rings.
12. The method of claim 11, further comprising etching a layer on
the semiconductor substrate by supplying RF power to the showerhead
electrode such that the process gas forms a plasma in contact with
an exposed surface of the semiconductor substrate.
13. The method of claim 10, wherein the semiconductor substrate
comprises a silicon or gallium arsenide wafer and the method
includes dry etching a dielectric, semiconductive or conductive
layer of material on the wafer.
14. The method of claim 10, wherein the method includes depositing
a layer of material on the semiconductor substrate.
15. The method of claim 10, wherein the showerhead comprises a
showerhead electrode elastomer bonded to a temperature-controlled
member, the method including withdrawing heat from the showerhead
electrode by passing coolant through the temperature-controlled
member.
16. The method of claim 10, wherein aluminum baffle plates are
located in the baffle chamber between the silicon containing baffle
plate and a gas inlet supplying the process gas to the baffle
chamber, the process gas passing through the aluminum baffle plates
prior to passing through the silicon containing baffle plate.
17. The method of claim 10, wherein the process gas passes through
openings in the silicon containing baffle plate which are offset
from openings in the showerhead, the offset being sufficient to
prevent a line-of-sight between the plasma in the chamber and the
openings in the silicon containing baffle plate.
18. The process of claim 10, wherein openings are etched through
exposed portions of a dielectric layer of the substrate to an
electrically conductive or semiconductive layer of the
substrate.
19. The process of claim 18, wherein the etching step is carried
out as part of a process of manufacturing a damascene
structure.
20. A method of processing a semiconductor wafer with the gas
distribution system of claim 1, wherein the method includes
replacing a lower baffle plate of a gas distribution system with
the silicon containing baffle plate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to reaction chambers used for
processing semiconductor substrates, such as integrated circuit
wafers, and specifically to improvements in the gas distribution
system used in these reaction chambers.
BACKGROUND OF THE INVENTION
[0002] Semiconductor processing includes deposition processes such
as chemical vapor deposition (CVD) of metal, dielectric and
semiconducting materials, etching of such layers, ashing of
photoresist masking layers, etc. In the case of etching, plasma
etching is conventionally used to etch metal, dielectric and
semiconducting materials. A parallel plate plasma reactor typically
includes a gas chamber including one or more baffles, a showerhead
electrode through which etching gas passes, a pedestal supporting
the silicon wafer on a bottom electrode, an RF power source, and a
gas injection source for supplying gas to the gas chamber. Gas is
ionized by the electrode to form plasma and the plasma etches the
wafer supported below the showerhead electrode.
[0003] Showerhead electrodes for plasma processing of semiconductor
substrates are disclosed in commonly assigned U.S. Pat. Nos.
5,074,456; 5,472,565; 5,534,751; and 5,569,356. Other showerhead
electrode gas distribution systems are disclosed in U.S. Pat. Nos.
4,209,357; 4,263,088; 4,270,999; 4,297,162; 4,534,816; 4,579,618;
4,590,042; 4,593,540; 4,612,077; 4,780,169; 4,854,263; 5,006,220;
5,134,965; 5,494,713; 5,529,657; 5,593,540; 5,595,627; 5,614,055;
5,716,485; 5,746,875 and 5,888,907. Of these, the '816 patent
discloses a single wafer plasma etching chamber wherein the upper
electrode assembly includes an electrode of stainless steel,
aluminum or copper and a baffle of conductive material or sintered
graphite.
[0004] A common requirement in integrated circuit fabrication is
the etching of openings such as contacts and vias in dielectric
materials. The dielectric materials include doped silicon oxide
such as fluorinated silicon oxide (FSG), undoped silicon oxide such
as silicon dioxide, silicate glasses such as boron phosphate
silicate glass (BPSG) and phosphate silicate glass (PSG), doped or
undoped thermally grown silicon oxide, doped or undoped TEOS
deposited silicon oxide, etc. The dielectric dopants include boron,
phosphorus and/or arsenic. The dielectric can overlie a conductive
or semiconductive layer such as polycrystalline silicon, metals
such as aluminum, copper, titanium, tungsten, molybdenum or alloys
thereof, nitrides such as titanium nitride, metal suicides such as
titanium silicide, cobalt silicide, tungsten silicide, molybdenum
silicide, etc. A plasma etching technique, wherein a parallel plate
plasma reactor is used for etching openings in silicon oxide, is
disclosed in U.S. Pat. No. 5,013,398.
[0005] U.S. Pat. No. 5,736,457 describes single and dual
"damascene" metallization processes. In the "single damascene"
approach, vias and conductors are formed in separate steps wherein
a metallization pattern for either conductors or vias is etched
into a dielectric layer, a metal layer is filled into the etched
grooves or via holes in the dielectric layer, and the excess metal
is removed by chemical mechanical planarization (CMP) or by an etch
back process. In the "dual damascene" approach, the metallization
patterns for the vias and conductors are etched in a dielectric
layer and the etched grooves and via openings are filled with metal
in a single metal filling and excess metal removal process.
[0006] There is a need in the art of semiconductor processing for
improved reactor designs wherein contamination due to metals and/or
particles is reduced and the time between wet cleans is increased
to improved wafer production efficiency. Although efforts have been
made to improve reactor designs, any improvements which achieve the
abovementioned goals are highly desirable, particularly in the
field of oxide etching.
SUMMARY OF THE INVENTION
[0007] The invention provides a baffle plate which reduces particle
and/or metal contamination during processing of a semiconductor
substrate. The baffle plate is adapted to fit within the baffle
chamber of a showerhead gas distribution system such that a silicon
containing surface of the baffle plate is adjacent to and facing
the showerhead. The baffle plate can consist essentially of silicon
or a silicon compound such as silicon carbide. A preferred baffle
plate material is silicon carbide having a purity of at least
99.999% and/or a porosity of 10 to 30%. The silicon carbide baffle
plate can be made entirely of non-sintered silicon carbide,
sintered silicon carbide, bulk CVD silicon carbide, sintered
silicon carbide with a CVD coating of silicon carbide, graphite
coated with silicon carbide, reaction synthesized silicon carbide,
or combination thereof.
[0008] According to one aspect of the invention, the silicon
containing baffle plate can be used as a drop-in replacement for an
aluminum baffle plate. When mounted in a baffle chamber, the
silicon containing baffle plate can include openings therethrough
for passage of process gas, wherein the openings are offset from
openings in the showerhead. In order to provide a plenum between
the silicon containing baffle plate and an adjacent aluminum baffle
plate, the silicon containing baffle plate can include a rim
extending around the periphery thereof.
[0009] In use, the silicon containing baffle plate can be part of a
gas distribution system of a plasma processing chamber wherein the
gas distribution system includes a showerhead electrode and the
silicon containing baffle plate is mounted in a baffle chamber such
that the silicon containing surface faces the showerhead electrode
and an opposite side of the silicon containing baffle plate faces
an aluminum baffle plate. In such an arrangement, the silicon
containing baffle plate is effective to reduce metal contamination
by at least an order of magnitude during plasma processing of a
semiconductor substrate in the chamber compared to the metal
contamination produced under the same processing conditions but
using an aluminum baffle plate in place of the silicon containing
baffle plate.
[0010] The invention also provides a method of reducing particle
and/or metal contamination during processing of a substrate in a
reaction chamber wherein a gas distribution system includes a
showerhead, a baffle chamber through which process gas passes to
the showerhead, and a silicon containing baffle plate located in
the baffle chamber, the method comprising supplying a semiconductor
substrate to the reaction chamber, supplying process gas into the
baffle chamber, the process gas passing through the silicon
containing baffle plate into a space between the silicon containing
baffle plate and the showerhead followed by passing through the
showerhead and into an interior of the reaction chamber, and
processing the semiconductor substrate with the process gas passing
through the showerhead.
[0011] According to a preferred method, the showerhead is a
showerhead electrode which energizes the process gas passing
therethrough into a plasma state. The method can comprise etching a
layer on the semiconductor substrate by supplying RF power to the
showerhead electrode such that the process gas forms a plasma in
contact with an exposed surface of the semiconductor substrate. For
example, the semiconductor substrate can comprise a silicon or
gallium arsenide wafer and the method can include dry etching a
dielectric, semiconductive or conductive layer of material on the
wafer. Alternatively, the method can include depositing a layer of
material on the semiconductor substrate. In the case where the
showerhead comprises a showerhead electrode attached to a
temperature-controlled member, the method can include withdrawing
heat from the showerhead electrode by passing coolant through the
temperature-controlled member. In the case of etching, openings can
be etched through exposed portions of a dielectric layer of the
substrate to an electrically conductive or semiconductive layer of
the substrate. For example, the etching step can be carried out as
part of a process of manufacturing a damascene structure. Further,
the method can include replacing an aluminum baffle plate of a gas
distribution system with the silicon containing baffle plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The objects and advantages of the invention will be
understood by reading the following detailed description in
conjunction with the drawings in which:
[0013] FIG. 1 is a side sectional view of a showerhead electrode
assembly for single wafer processing in accordance with the
invention;
[0014] FIG. 2 is a side sectional view of an elastomer bonded
showerhead electrode assembly according to an embodiment of the
invention; and
[0015] FIG. 3 is a side sectional view of a portion of the
arrangement shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] For a better understanding of the invention, the following
detailed description refers to the accompanying drawings, wherein
preferred exemplary embodiments of the present invention are
illustrated and described. In addition, the reference numbers used
to identify like elements in the drawings are the same
throughout.
[0017] According to the present invention, contamination of
semiconductor substrates can be substantially reduced during
processing in a plasma reaction chamber which includes a showerhead
for distributing process gas. An example of such a plasma
processing system is a parallel plate type reactor wherein an
individual semiconductor wafer is supported on a bottom electrode
and the upper electrode comprises a showerhead electrode. During
processing in such reactors, plasma attacks the showerhead
electrode and other interior parts of the reactor. In a parallel
plate reactor wherein the plasma is confined in a narrow zone
defined by a wafer on an electrostatic chuck ("ESC") having a
silicon edge ring, a silicon showerhead electrode and a stacked
array of quartz confinement rings, it has surprisingly been found
that the aluminum baffle plate adjacent the showerhead electrode is
attacked by the plasma to a sufficient extent to cause metal and
particle contamination of the wafer.
[0018] In a typical showerhead having a baffle plate arrangement,
process gas enters a plenum and passes through one or more baffle
plates prior to exiting through the showerhead. In a plasma
processing chamber utilizing such an arrangement, it has been
discovered that plasma attacks the baffle plate adjacent the
showerhead in the vicinity of the holes in the showerhead. Over
time, an erosion pattern (identical to the hole pattern in the
showerhead) develops on the underside of the baffle plate with the
result that aluminum enters the interior of the plasma and forms a
difficult to remove polymer. For instance, in the case of an oxide
etch chamber wherein the process gas contains fluorine, the
aluminum combines with the fluorine to form an AlF-containing
polymer. With increasing aluminum in the polymer, the polymer
becomes more dense leading to dust particles and flakes in the etch
chamber. Such particles are referred to as "adders" when they are
found on processed wafers. Because such adders can cause defective
integrated circuits, it is desirable to minimize the number of
adders on a processed wafer. Further, in order to obtain high
production efficiency, it is desirable to maximize the time between
when a plasma reactor must be subjected to a "wet clean" to restore
process reproducibility. That is, while it is common to conduct a
plasma cleaning step during each wafer process cycle, after a
certain number of wafers are processed the build-up of byproducts
in the reactor leads to process drift outside the process window.
During such wet cleaning, it is necessary to shut down production
and chemically clean the inside of the chamber.
[0019] According to the invention, it has surprisingly been
discovered that (1) the number of particles which cause device
failures or adversely impact yield of the processed wafers can be
significantly reduced, (2) contamination by aluminum can be reduced
by at least an order of magnitude, preferably at least 2 orders of
magnitude, and/or (3) the time between wet cleans necessary for
repeatable wafer processing can be extended by at least 100%,
preferably by 200% or more, e.g. from 4000 rf minutes (as in the
case of an aluminum baffle plate) to 12,000 or more rf minutes ("rf
minutes" refers to the total length of time that the wafers are
processed by plasma in the reactor before the next wet cleaning of
the reactor). Such highly beneficial results can be obtained by
utilizing a silicon containing baffle plate adjacent the
showerhead. The showerhead arrangement can be used in any type of
semiconductor processing apparatus wherein it is desired to
distribute process gas over a semiconductor substrate. Such
apparatus includes CVD systems, ashers, capacitive coupled plasma
reactors, inductive coupled plasma reactors, ECR reactors, and the
like.
[0020] In accordance with a preferred embodiment of the invention,
the silicon containing baffle plate is incorporated in a showerhead
electrode 10 of a single wafer etcher, as shown in FIG. 1. Such a
showerhead electrode 10 is typically used with an electrostatic
chuck having a flat bottom electrode on which a wafer is supported
spaced 1 to 2 cm below the electrode 10. Such chucking arrangements
provide temperature control of the wafer by supplying backside He
pressure which controls the rate of heat transfer between the wafer
and the chuck.
[0021] The showerhead electrode assembly shown in FIG. 1 is a
consumable part which must be replaced periodically. Because the
electrode assembly is attached to a temperature-controlled member,
for ease of replacement, the upper surface of the outer edge of the
silicon electrode 10 can be bonded to a graphite support ring 12
with indium which has a melting point of about 156.degree. C.
However, the electrode can be attached by other techniques, such as
by an elastomeric joint, explained below in connection with FIGS. 2
and 3.
[0022] The electrode 10 shown in FIG. 1 is a planar disk having
uniform thickness from center to edge thereof and an outer flange
on ring 12 is clamped by an aluminum clamping ring 16 to an
aluminum temperature-controlled member 14 having water cooling
channels 13. Water is circulated in the cooling channels 13 by
water inlet/outlet connections 13a. A plasma confinement ring 17
comprised of a stack of spaced-apart quartz rings surrounds the
outer periphery of electrode 10. The plasma confinement ring 17 is
bolted to a dielectric (e.g., quartz) annular ring 18 which in turn
is bolted to a dielectric housing 18a. The purpose and function of
confinement ring 17 is to cause a pressure differential in the
reactor and increase the electrical resistance between the reaction
chamber walls and the plasma thereby confining the plasma between
the upper and lower electrodes. A radially inwardly extending
flange of clamping ring 16 engages the outer flange of graphite
support ring 12. Thus, no clamping pressure is applied directly
against the exposed surface of electrode 10.
[0023] Process gas from a gas supply is supplied to electrode 10
through a central hole 20 in the temperature-controlled member 14.
The gas then is distributed through one or more vertically spaced
apart baffle plates 22 and passes through gas distribution holes
(not shown) in the electrode 10 to evenly disperse the process gas
into reaction chamber 24. In order to provide enhanced heat
conduction from electrode 10 to temperature-controlled member 14,
process gas can be supplied to fill open spaces between opposed
surfaces of temperature-controlled member 14 and support ring 12.
In addition, gas passage 27 connected to a gas passage (not shown)
in the annular ring 18 or confinement ring 17 allows pressure to be
monitored in the reaction chamber 24. To maintain process gas under
pressure between temperature-controlled member 14 and support ring
12, a first O-ring seal 28 is provided between an inner surface of
support ring 12 and an opposed surface of temperature-controlled
member 14 and a second O-ring seal 29 is provided between an outer
part of an upper surface of support ring 12 and an opposed surface
of member 14. In order to maintain the vacuum environment in
chamber 24, additional O-rings 30, 32 are provided between
temperature-controlled member 14 and cylindrical member 18b and
between cylindrical member 18b and housing 18a.
[0024] In accordance with the invention, the lower baffle 22a is
made of and/or coated with silicon or a silicon compound such as
silicon carbide. The silicon can comprise single crystal or
polycrystalline silicon of high purity such as 99.999% or above.
The silicon carbide can be a high purity commercially produced
silicon carbide such as CVD silicon carbide material available from
manufacturers such as Morton International, Inc. of Woburn, Mass.,
Sanzo Metal, Inc. of Tamani, Japan, NGK Insulator, Ltd. of Nagoya,
Japan, or sintered silicon carbide materials available from Cercom,
Inc., of Vista, Calif., Carborundum, Inc., of Costa Mesa, Calif.
and Ceradyne, Inc. of Costa Mesa, Calif. Silicon carbide produced
by graphite conversion using silicon vapor is available from Poco
Graphite, Inc. of Decatur, Tex.
[0025] In addition to silicon and silicon carbide, other suitable
but less preferred aluminum-free materials which may or may not be
incorporated in the lower baffle plate and/or other parts of the
gas distribution system include non-oxide ceramics such as silicon
nitride, boron carbide, boron nitride, etc., oxide materials such
as quartz, silicon oxide, etc., thermoplastics such as "VESPEL",
"PEEK", "TEFLON", etc., and high purity graphite. However, in a
showerhead electrode used for etching, baffle plates made of
non-electrically conductive material can lead to subtle differences
in rf characteristics of the etch tool whereas baffle plates made
of graphite are aggressively attacked by oxygen plasmas used in
dielectric etch processes leading to particle problems and high
wear of the graphite. In contrast, sputtering of silicon and
silicon carbide baffle plates by the plasma produces silicon or
silicon and carbon, both of which are abundantly present on the
wafer being processed and in the etch gases. Further, silicon and
silicon carbide exhibit good wear characteristics in such a plasma
environment.
[0026] According to a preferred embodiment of the invention, the
lower baffle plate can be made of a highly pure silicon carbide,
e.g., at least about 99.999% pure. An especially preferred silicon
carbide from a cost perspective is a non-sintered form of silicon
carbide made by graphite conversion wherein a shaped piece of
graphite is reacted with silicon vapor at temperatures such as
1600.degree. C. to convert the graphite to silicon carbide. The
starting graphite is preferably a fine particle, low porosity high
purity graphite. As a result of the conversion to silicon carbide
by the silicon vapor, the bulk silicon carbide can have a porosity
ranging from 10 to 30%, e.g., around 20%. If desired, the silicon
carbide can be coated with a layer of CVD SiC. The SiC prepared in
this manner exhibits thermal conductivity on the order of about 80
W/m.multidot.k at room temperature, compressive strength of at
least about 80,000 psi, fracture toughness of at least about 2.10
MPa-m.sup.-2, and tensile strength of at least about 15,000
psi.
[0027] The silicon or silicon carbide baffle plate can be designed
as a drop-in replacement for existing aluminum baffle plates or as
a part of any gas distribution system wherein it is desired to
reduce contamination attributable to that particular part. For
example, the silicon containing baffle plate can be used as a
drop-in replacement for the aluminum baffle plate of an Exelan.RTM.
or 4520XLE.RTM., both of which are manufactured by the assignee of
the present application, LAM Research Corporation.
[0028] The silicon containing baffle according to the invention
provides reduced particle contamination, reduced metal
contamination and increased production efficiency due to the
increase in time between wet cleans. Such improvements appear
possible because silicon and silicon carbide are more resistant and
less contaminating than an aluminum baffle plate. That is, since
the lower baffle is directly behind the showerhead electrode, a
line-of-sight exists between it and the plasma via the holes in the
showerhead electrode. Ions generated in the plasma are accelerated
through the showerhead holes towards the baffle, causing the baffle
surface to be sputtered. As a result, the plasma chamber is
contaminated with aluminum and other trace metals contained in the
standard aluminum baffle plate. Once the chamber is coated with the
aluminum, the aluminum combines with the polymer generated during
the plasma etching process, creating a dusty or flaky polymer that
can be deposited on a wafer in the chamber. Such particle defects
reduce the yield of the wafer. The silicon and silicon carbide
(SiC) baffle plates according to the invention outperformed baffle
plates made of aluminum (Al), graphite, pyrolytic graphite, SiC
coated graphite, Vespel.RTM., and quartz in one or more of the
categories set forth in the following table.
1 Property Electrical Contaminates Physical Particles SiC good best
good best Al best worst best poor Graphite good good marginal poor
Pyrolytic good good marginal poor Graphite SiC Coated good good
good poor Graphite Vespel .RTM. poor good poor good Silicon
marginal good marginal unknown Quartz poor good poor unknown
[0029] In a comparison of an aluminum baffle plate to a silicon
containing baffle plate, wafers etched in a plasma chamber having a
showerhead electrode with a silicon containing baffle plate
exhibited on average one-half or less "adders" (i.e., particles)
compared to the same process reactors using an aluminum baffle.
Further, in comparing the time between wet cleans used to restore
process repeatability measured in rf minutes, the plasma etch
reactor with the silicon containing baffle plate did not require
wet cleaning for 15,000 rf minutes or even 25,000 rf to over 29,000
rf minutes compared to only 4000 rf minutes for the aluminum baffle
plate. Such dramatic improvement in production efficiency makes the
silicon containing baffle plate a highly economical replacement
part for existing aluminum baffle plates.
[0030] Because the electrode assembly is a consumable part, it is
desirable to use non-contaminating materials for the parts of the
electrode assembly which are contacted by the plasma. Depending on
the process gas chemistry, such materials are preferably
aluminum-free conductive, semiconductive or insulating materials
including glass, ceramic and/or polymer materials such as single
crystal or polycrystalline silicon, quartz, carbides of silicon,
boron, titanium, tantalum, niobium and/or zirconium, nitrides of
silicon, boron, titanium, tantalum and/or zirconium, oxides of
silicon, boron, titanium, tantalum, niobium and/or zirconium,
silicides of titanium, tungsten, tantalum and/or cobalt, pyrolytic
graphite, diamond, etc. Materials made of silicon, carbon, nitrogen
and/or oxygen are most preferred for surfaces in a plasma reaction
chamber.
[0031] The electrode preferably consists of an electrically
conductive material such as a planar silicon (e.g., single crystal
silicon), graphite or silicon carbide electrode disc having uniform
thickness from the center to the outer edge thereof. However,
electrodes having nonuniform thickness, different materials and/or
without process gas distribution holes could also be used with the
electrode assembly according to the invention. In a preferred
embodiment, the electrode is a showerhead electrode provided with a
plurality of spaced apart gas discharge passages which are of a
size and distribution suitable for supplying a process gas which is
energized by the electrode and forms a plasma in the reaction
chamber beneath the electrode.
[0032] FIG. 2 shows a showerhead electrode arrangement 40 which can
be substituted for the electrode assembly constituted by electrode
10 and support ring 12 shown in FIG. 1. The electrode 40 differs
from the In-bonded assembly shown in FIG. 1 in that electrode 42 is
bonded to support ring 44 by an elastomeric joint 46 which can be
located in a recess 48, as shown in FIG. 3. The recess 48 extends
continuously around the support ring 44 between an inner wall (not
shown) and an outer wall 50 of the support ring 44. Each wall 50
can be as thin as possible, e.g. about 30 mils wide, which allows
the elastomer to form a thin layer (e.g. about 2 .mu.m thick in the
case where the elastomer includes 0.7 to 2 .mu.m sized filler) in
the area in contact with each wall 50 and a thicker layer (e.g.
about 0.0025 inch) in the recess 48. The recess formed by the walls
can be extremely shallow, e.g. about 2 mils deep, which provides a
very thin elastomeric joint having enough strength to adhesively
bond the electrode to the support ring yet allow movement of the
electrode relative to the support ring during temperature cycling
of the electrode assembly. Additionally, the walls of the recess
can protect the elastomeric joint from attack by the plasma
environment in the reactor.
[0033] The electrode assembly dimensions can be adapted to meet the
demands of the intended use of the electrode assembly. As an
example, if the electrode is used to process an 8 inch wafer, the
electrode can have a diameter slightly less than 9 inches and the
support ring can have a width at the interface between the
electrode and the support ring slightly less than 0.5 inch. For
example, the support ring at the interface can have an inner
diameter of 8 inches and an outer diameter at the interface of 8.8
inches. In such a case, the interface between the electrode and
support ring can have a width of about 0.4 inch and the recess can
have a width of 0.34 inch if the walls are 0.030 inch wide.
[0034] The elastomeric joint can comprise any suitable elastomeric
material such as a polymer material compatible with a vacuum
environment and resistant to thermal degradation at high
temperatures such as above 200.degree. C. The elastomer material
can optionally include a filler of electrically and/or thermally
conductive particles or other shaped filler such as wire mesh,
woven or non-woven conductive fabric, etc. Polymeric materials
which can be used in plasma environments above 160.degree. C.
include polyimide, polyketone, polyetherketone, polyether sulfone,
polyethylene terephthalate, fluoroethylene propylene copolymers,
cellulose, triacetates, silicone, and rubber. Examples of high
purity elastomeric materials include one-component room temperature
curing adhesives available from General Electric as RTV 133 and RTV
167, a one-component flowable heat-curable (e.g., over 100.degree.
C.) adhesive available from General Electric as TSE 3221, and a
two-part addition cure elastomer available from Dow Corning as
"SILASTIC." An especially preferred elastomer is a
polydimethylsiloxane containing elastomer such as a catalyst cured,
e.g. Pt-cured, elastomer available from Rhodia as V217, an
elastomer stable at temperatures of 250.degree. C. and higher.
[0035] In the case where the elastomer is an electrically
conductive elastomer, the electrically conductive filler material
can comprise particles of a an electrically conductive metal or
metal alloy. A preferred metal for use in the impurity sensitive
environment of a plasma reaction chamber is an aluminum alloy such
as a 5-20 weight % silicon containing aluminum base alloy. For
example, the aluminum alloy can include about 15 wt % silicon.
However, in order to reduce the possibility for contamination from
aluminum, it may be desirable to use aluminum-free electrically
conductive filler such as silicon powder or silicon carbide powder.
Details of the elastomeric joint can be found in commonly-owned
U.S. patent application Ser. No. 09/107,471 filed Jun. 30, 1998,
the entire disclosure of which is hereby incorporated by
reference.
[0036] The silicon containing baffle plate can be used for various
plasma processes including plasma etching of various dielectric
layers such as doped silicon oxide such as fluorinated silicon
oxide (FSG), undoped silicon oxide such as silicon dioxide,
spin-on-glass (SOG), silicate glasses such as boron phosphate
silicate glass (BPSG) and phosphate silicate glass (PSG), doped or
undoped thermally grown silicon oxide, doped or undoped TEOS
deposited silicon oxide, etc. The dielectric dopants include boron,
phosphorus and/or arsenic. The dielectric can overlie a conductive
or semiconductive layer such as polycrystalline silicon, metals
such as aluminum, copper, titanium, tungsten, molybdenum or alloys
thereof, nitrides such as titanium nitride, metal suicides such as
titanium silicide, cobalt silicide, tungsten silicide, molybdenum
silicide, etc. For instance, the gas distribution system according
to the invention can be used for plasma etching a damascene
structure.
[0037] The plasma can be a high density plasma produced in various
types of plasma reactors. Such plasma reactors typically have high
energy sources which use RF energy, microwave energy, magnetic
fields, etc. to produce the high density plasma. For instance, the
high density plasma could be produced in a transformer coupled
plasma (TCP.TM.) which is also called inductively coupled plasma
reactor, an electron-cyclotron resonance (ECR) plasma reactor, a
helicon plasma reactor, or the like. An example of a high flow
plasma reactor which can provide a high density plasma is disclosed
in commonly owned U.S. Pat. No. 5,820,723, the disclosure of which
is hereby incorporated by reference.
[0038] The present invention has been described with reference to
preferred embodiments. However, it will be readily apparent to
those skilled in the art that it is possible to embody the
invention in specific forms other than as described above without
departing from the spirit of the invention. The preferred
embodiment is illustrative and should not be considered restrictive
in any way. The scope of the invention is given by the appended
claims, rather than the preceding description, and all variations
and equivalents which fall within the range of the claims are
intended to be embraced therein.
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