U.S. patent application number 09/814972 was filed with the patent office on 2001-10-04 for gas distribution apparatus for semiconductor processing.
Invention is credited to Dhindsa, Rajinder, Hao, Fangli, Lenz, Eric.
Application Number | 20010027026 09/814972 |
Document ID | / |
Family ID | 23347196 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010027026 |
Kind Code |
A1 |
Dhindsa, Rajinder ; et
al. |
October 4, 2001 |
Gas distribution apparatus for semiconductor processing
Abstract
A gas distribution system for uniformly or non-uniformly
distributing gas across the surface of a semiconductor substrate.
The gas distribution system includes a support plate and a
showerhead which are secured together to define a gas distribution
chamber therebetween. A baffle assembly including one or more
baffle plates is located within the gas distribution chamber. The
baffle arrangement includes a first gas supply supplying process
gas to a central portion of the baffle chamber and a second gas
supply supplying a second process gas to a peripheral region of the
baffle chamber. Because the pressure of the gas is greater at
locations closer to the outlets of the first and second gas
supplies, the gas pressure at the backside of the showerhead can be
made more uniform than in the case with a single gas supply. In one
arrangement, the first and second gas supplies open into a plenum
between a top baffle plate and a temperature controlled support
member wherein the plenum is divided into the central and
peripheral regions by an O-ring. In a second arrangement, the first
gas supply opens into the central region above an upper baffle
plate and the second gas supply opens into the periphery of a
plenum between the upper baffle plate and a lower baffle plate.
Inventors: |
Dhindsa, Rajinder; (San
Jose, CA) ; Hao, Fangli; (Cupertino, CA) ;
Lenz, Eric; (Pleasanton, CA) |
Correspondence
Address: |
Peter K. Skiff
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P. O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
23347196 |
Appl. No.: |
09/814972 |
Filed: |
March 23, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09814972 |
Mar 23, 2001 |
|
|
|
09343690 |
Jun 30, 1999 |
|
|
|
6245192 |
|
|
|
|
Current U.S.
Class: |
438/712 |
Current CPC
Class: |
C23C 16/45572 20130101;
C23C 16/45565 20130101; H01J 37/3244 20130101; C23C 16/455
20130101 |
Class at
Publication: |
438/712 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. A gas distribution system useful for a reaction chamber used in
semiconductor substrate processing, comprising: a support member
having a recess in a lower surface thereof, the support member
having a first gas supply opening into a central area of the recess
and a second gas supply opening into a peripheral area of the
recess: a baffle arrangement located in the recess such that gas
from the first gas supply passes through first openings in the
baffle arrangement and gas from the second gas supply passes
through second openings in the baffle arrangement; and a showerhead
supported by the support member such that the gas passing through
the first and second openings mixes together and passes through a
third set of openings in the showerhead.
2. The gas distribution system of claim 1, wherein the showerhead
is a top electrode and the support member is a
temperature-controlled member of a plasma reaction chamber.
3. The gas distribution system of claim 1, wherein the support
member comprises a support ring attached to a
temperature-controlled member.
4. The gas distribution system of claim 1, wherein the baffle
arrangement includes upper and lower baffle plates, the second gas
supply suppling gas to one or more gas flow channels located
between the upper and lower baffle plates, the gas from the second
gas supply flowing through the channels in a direction from an
outer region of the baffle plates towards an inner region of the
baffle plates.
5. The gas distribution system of claim 4, wherein the channels are
formed in a lower surface of the upper baffle plate and/or in an
upper surface of the lower baffle plate.
6. The gas distribution system of claim 5, wherein the upper
surface of the lower baffle plate is in thermal contact with the
lower surface of the upper baffle plate.
7. The gas distribution system of claim 5, wherein the showerhead
is an electrode, the upper and lower baffle plates are of an
electrically conductive material and the upper surface of the lower
baffle plate is in electrical contact with the lower surface of the
upper baffle plate.
8. The gas distribution system of claim 1, wherein the baffle
arrangement includes upper and lower baffle plates, the gas passing
through the first and second openings mixes in gas flow channels
located between the lower baffle plate and the showerhead.
9. The gas distribution system of claim 8, wherein the channels are
formed in a lower surface of the lower baffle plate and/or in an
upper surface of the showerhead, the lower surface of the lower
baffle plate being in contact with the upper surface of the
showerhead.
10. The gas distribution system of claim 8, wherein the showerhead
is an electrode, the upper and lower baffle plates are of an
electrically conductive material and the channels are formed in a
lower surface of the lower baffle plate and/or in an upper surface
of the showerhead, the lower surface of the lower baffle plate
being in electrical and thermal contact with the upper surface of
the showerhead.
11. The gas distribution system of claim 1, wherein the showerhead
comprises a showerhead electrode.
12. The gas distribution system of claim 1, wherein the baffle
arrangement includes a baffle plate and a seal member, the seal
member separating a space between the baffle plate and the support
member into central and peripheral regions, the first gas supply
opening into the central region and the second gas supply opening
into the peripheral region.
13. The gas distribution system of claim 12, wherein the seal
member is an O-ring.
14. The gas distribution system of claim 1, further comprising a
first mass flow controller connected to the first gas supply, a
second mass flow controller connected to the second gas supply, and
a controller connected to the first and second mass flow
controllers so as to adjust gas chemistry and/or flow rates of the
process gas supplied by the first and second gas supplies.
15. A method of processing a substrate in a reaction chamber
wherein a gas distribution system includes a support member
defining a baffle chamber therein, the support member having a
first gas supply opening into a central area of the baffle chamber
and a second gas supply opening into a peripheral area of the
baffle chamber, a baffle arrangement located in the baffle chamber
such that gas from the first gas supply passes through first
openings in baffle arrangement and gas from the second gas supply
passes through second openings in the baffle arrangement, and a
showerhead supported by the support member such that the gas
passing through the first and second openings mixes together and
passes through third openings in the showerhead, the method
comprising: supplying a semiconductor substrate to the reaction
chamber; supplying process gas to the first and second gas supplies
such that the process gas flows through the baffle arrangement
without mixing until the process gas passes through the baffle
arrangement after which the mixed process gas passes through the
showerhead and into an interior of the reaction chamber; and
processing the semiconductor substrate with the process gas passing
through the showerhead.
16. The method of claim 15, wherein the showerhead is a showerhead
electrode which energizes the process gas passing therethrough into
a plasma state.
17. The method of claim 16, 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.
18. The method of claim 15, wherein the semiconductor substrate
comprises a silicon wafer and the method includes dry etching a
dielectric, semiconductive or conductive layer of material on the
wafer.
19. The method of claim 15, wherein the method includes depositing
a layer of material on the semiconductor substrate.
20. The method of claim 15, wherein the showerhead comprises a
showerhead electrode and the support member comprises a
temperature-controlled member, the method including withdrawing
heat from the showerhead electrode by passing coolant through the
temperature-controlled member.
21. The method of claim 15, wherein the baffle arrangement includes
upper and lower baffle plates, the second gas supply supplies gas
to one or more gas flow channels located between the upper and
lower baffle plates, the gas from the second gas supply flowing
through the channels in a direction from an outer region of the
baffle plates towards an inner region of the baffle plates.
22. The method of claim 15, further comprising adjusting flow rate
and/or gas pressure of the process gas supplied to the first gas
supply and adjusting flow rate and/or gas pressure of the process
gas supplied to the second gas supply such that a desired gas
pressure distribution is provided across the backside of the
showerhead.
23. The method of claim 15, wherein the baffle arrangement includes
upper and lower baffle plates, the method further comprising
cooling the showerhead by withdrawing heat from the showerhead
through contacting surfaces of the showerhead, the lower baffle
plate, the upper baffle plate and/or the support member.
24. The method of claim 15, wherein the baffle arrangement includes
upper and lower baffle plates, the gas passing through the first
and second openings mixes in radially spaced apart annular gas flow
channels located between the lower baffle plate and the
showerhead.
25. The method of claim 24, wherein the channels are formed in a
lower surface of the lower baffle plate and/or in an upper surface
of the showerhead, the lower surface of the lower baffle plate
being in contact with the upper surface of the showerhead such that
heat is removed from the showerhead during processing of the
semiconductor substrate.
26. The method of claim 15, wherein the process gas flowing through
the first gas supply has the same gas chemistry as the process gas
flowing through the second gas supply.
27. The method of claim 15, wherein the process gas flowing through
the first gas supply has a different gas chemistry than the process
gas flowing through the second gas supply.
28. The method of claim 15, wherein the substrate is a
semiconductor wafer which is etched in at least first and second
steps, the process gas passing through the first gas supply being
regulated relative to the process gas passing through the second
gas supply to compensate for edge-fast and center-fast etch
conditions during the first and second steps.
29. The process of claim 15, wherein openings are etched through
exposed portions of a dielectric layer of the substrate to an
electrically conductive or semiconductive layer of the
substrate.
30. The process of claim 29, wherein the etching step is carried
out as part of a process of manufacturing a damascene
structure.
31. The process of claim 29, wherein the semiconductor substrate
includes layers of a photoresist masking layer, a first dielectric
layer, a first stop layer, a second dielectric layer and a second
stop layer, the etching step being carried out such that a trench
patterned in the photoresist layer is etched through the first
dielectric layer to the first stop layer during a first stage of
the etching step and vias or contact openings are etched through
the second dielectric layer to the second stop layer during a
second stage of the etching step, the process gas supplied by the
first and second gas supplies being adjusted such that the process
gas composition and/or flow rates during the first stage is
different from the process gas composition and/or flow rates during
the second stage.
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.
[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 silicides 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] It is desirable to evenly distribute the plasma over the
surface of the wafer in order to obtain uniform etching rates over
the entire surface of the wafer. Current gas distribution chamber
designs include multiple baffles which are optimized to uniformly
distribute etching gas to achieve the desired etching effect at the
wafer. However, the current baffle and showerhead electrode designs
are best suited to empirical optimization for uniform gas
distribution for a particular gap between the wafer and the
showerhead electrode and are difficult to adjust to varying gaps
between the wafer and the showerhead. In addition, conventional gas
distribution designs include baffles having hundreds of openings or
complex, difficult to manufacture geometries to ensure even
distribution of etching gas to the backside of the showerhead
electrode. When etching large, twelve-inch (300 mm) wafers,
controlling the process gas to create a uniform pressure
distribution across the showerhead is even more difficult. The
number of openings and baffles must be increased significantly to
maintain uniform distribution of the etching gas. As the number of
openings in the baffles increase and the number of baffles
increase, the complexity and cost to manufacture such a gas
distribution apparatus increase greatly.
SUMMARY OF THE INVENTION
[0007] The present invention provides a gas distribution system
which is a simple to manufacture design requiring a small number of
baffle plates, while still achieving desired gas distribution
delivered through a showerhead. Gas flow can be optimized for any
size substrate and/or gap between the showerhead and the
semiconductor substrate being processed. In addition, the present
invention can improve heat transfer from a showerhead electrode to
a cooled support plate, thereby creating better temperature
uniformity across the electrode surface. Furthermore, the present
invention can provide generally continuous electrical contact among
the components of a showerhead electrode gas distribution
system.
[0008] A gas distribution apparatus according to the present
invention includes a support plate and a showerhead which are
secured to define a gas distribution chamber. The chamber includes
a baffle assembly including one or more baffle plates which can be
used to achieve a desired pressure distribution across the
showerhead. Multiple gas supplies provide process gas into the gas
distribution chamber where the process gas flows downward through
the baffle assembly and through the showerhead.
[0009] A first embodiment of the invention includes a baffle
assembly having an upper baffle plate. A seal member, such as an
O-ring is at an intermediate location between the upper baffle
plate and the support plate. The seal member divides the space
therebetween into inner and outer regions. Gas from a first gas
supply directs gas into the inner region and gas from a second gas
supply directs gas into the outer region. The arrangement allows
different gas chemistries and/or gas pressures to be provided to
the inner and outer regions. As a result, better control of gas
chemistry and/or gas pressure across the substrate can be achieved
by preselecting process parameters or adjusting such process
parameters during processing of a substrate.
[0010] If desired, middle and/or lower baffle plates can be
arranged to define three plenums. The first plenum is located
between the upper and middle baffle plates. The second plenum is
located between the middle and lower baffle plates, and the third
plenum is located between the lower baffle plate and the
showerhead. The plenums can be used to create a more uniform
process gas pressure distribution across the showerhead.
[0011] In a second embodiment of the present invention the support
member includes a recess in its lower side which defines the gas
distribution chamber. The support member has a first gas outlet
supplying a first process gas into a central area of the recess
chamber and a second gas outlet supplying a second process gas into
a peripheral area of the recess. Secured within the baffle chamber
are an upper baffle plate and a lower baffle plate. The upper
baffle plate is arranged to receive gas exclusively from the first
gas supply and the lower baffle plate is arranged to receive gas
exclusively from the second gas supply. A first set of gas passages
in the upper baffle plate is in fluid connection with gas passages
in the second baffle plate to create a set of flow-connected
passages through which the first process gas passes directly from
the upper baffle plate to the underside of the lower baffle plate.
The second process gas flows through a second set of gas passages
in the lower baffle plate to its underside adjacent the backside of
the showerhead. In this arrangement, the first process gas does not
mix substantially with the second process gas before flowing to the
underside of the lower baffle. The space between the lower baffle
and the showerhead can have spaced apart annular channels which
allow the gases passing through the showerhead to be selectively
controlled, e.g., to achieve uniform or nonuniform gas chemistry
and/or pressure across the showerhead. Gas from both the first gas
supply and the second gas supply flows through a third set of
openings in the showerhead into a region spanning the
substrate.
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 sectional view of a gas distribution chamber
according to the present invention;
[0014] FIG. 2 is an exploded perspective sectional view of a first
embodiment of the present invention;
[0015] FIG. 3 is a sectional view of the first embodiment of the
present invention;
[0016] FIG. 4 is an exploded perspective view of a second
embodiment of the present invention;
[0017] FIG. 5 is a sectional view of the second embodiment;
[0018] FIG. 6 is a perspective sectional view of a lower baffle
plate of the second embodiment of the present invention;
[0019] FIGS. 7A-B show an etching process which can be carried out
with the gas distribution system of the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0020] 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.
[0021] According to the present invention, process gas can be
uniformly distributed from one or more gas supplies to a substrate
positioned underneath a showerhead. The showerhead 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.
[0022] A gas distribution system for a parallel plate plasma
reactor is shown in FIG. 1 wherein a support plate 20 and a
showerhead 22 are secured together to define a sealed gas
distribution chamber 24. A baffle assembly 26, including one or
more baffle plates, is located between the support plate 20 and the
showerhead 22. According to the present invention, the geometry and
arrangement of the baffle assembly 26 is configured to uniformly
distribute gas to a backside 28 of the showerhead 22. In
semiconductor wafer processes such as chemical vapor deposition or
dry-etch plasma processes, the controlled distribution of process
gas across the substrate is desirable in order to increase the
consistency and yield of these processes.
[0023] As seen in FIGS. 2 and 3, in a first embodiment of the
present invention the baffle assembly 26 includes baffle plate 30A
and optional baffle plates 30B and 30C. The baffle plates 30A-30C,
are positioned within a recess 32 defined by a peripheral
upwardly-projecting side 34 of the showerhead 22. The upper baffle
plate 30A is spaced from a bottom surface 36 of the support plate
20 by an O-ring 38. The O-ring 38 divides space between the upper
baffle plate 30A and the support plate 20 into two regions, each of
which can be supplied process gas having different gas chemistries,
pressures and/or flow rates. Gas from a first gas supply 40 flows
into a central region 42 between the upper baffle plate 30A and the
support plate 20. Gas from a second gas supply 44 flows into an
annular channel 44a and then into a peripheral region 46 between
the upper baffle plate 30A and the support plate 20. The middle and
bottom plates 30B, 30C can be arranged below the upper baffle plate
30A to define open plenums 48A, 48B therebetween and an open plenum
48C between the bottom baffle plate 30C and the showerhead 22.
[0024] Each gas supply creates a pressure distribution across the
surface of the upper baffle plate 30A wherein the gas pressure is
highest adjacent the gas supply outlet and decreases in a direction
away from the outlet. Thus, the relative gas pressures between the
peripheral 46 and central 42 regions of the top surface of the
upper baffle plate 30A can be adjusted using first and second mass
flow controllers 50A, 50B which are connected to the first and
second gas supplies 40, 44. Each mass flow controller 50A, 50B can
be supplied a desired gas mixture by adjusting flow rates of two or
more gases supplied from gas supplies 50C, 50D, 50E, 50F, etc.
[0025] Process gas is distributed across the central region 42 and
peripheral region 46 between the upper baffle plate 30A and the
support plate 20, and passes through openings 52A in the upper
baffle plate 30A into the open plenum 48A between the upper and
middle baffle plates 30A, 30B. Thereafter, gas flows downward
through openings 52B in the middle baffle plate 30B into an open
plenum 48B between the middle and bottom baffle plates 30B, 30C,
then through openings 52C in the bottom baffle plate 30C into an
open plenum 48C between the bottom baffle plate 30C and the
showerhead 22, and ultimately through openings 54 in the showerhead
22 before reaching a substrate. Each time the gas enters into an
open plenum, nonuniform pressure distribution is damped as any
nonuniform pressure equalizes somewhat from areas of high pressure
to areas of low pressure. Thus, by configuring the gas distribution
system to define a plurality of plenums 48 between the baffle
plates 30, a substantially uniform pressure distribution can be
achieved at the backside 28 of the showerhead 22.
[0026] A second embodiment of the gas distribution system is shown
in FIGS. 4-6. The baffle assembly of the second embodiment includes
two baffle plates 56A, 56B. The upper baffle plate 56A includes
portions in contact with the support plate 20 and the lower baffle
plate 56B includes portions in contact with the showerhead 22.
Surface to surface contact between the support plate 20, baffle
assembly 26 and the showerhead 22 both facilitates heat transfer
between the showerhead 22, the baffle assembly 26 and the support
plate 20, and can provide an electrically conductive path between
the showerhead 22, baffle assembly 26 and the support plate 20 in
the case where the showerhead is used as a top electrode.
[0027] During processing, the temperature controlled support plate
20 acts as a heat sink, drawing heat from the showerhead 22 through
the baffle assembly 26. For instance, coolant can be circulated
through cooling channels 58 in the support plate 20 to dissipate
heat generated during processing of a substrate.
[0028] In the second embodiment, a first gas supply 60 is
configured to feed gas to a central recess 62 in the upper baffle
plate 56A. A second gas supply 64 feeds gas to an annular manifold
66 which distributes gas to a peripheral region 68 above the lower
baffle plate 56B. The manifold 66 may be integral with the support
plate 20 or can comprise a separate component of the gas
distribution system.
[0029] The upper baffle plate 56A includes radially extending
channels 70 which distribute gas from the generally centrally
located first gas supply 60 to the periphery of the upper baffle
plate 56A. The channels 70 are defined between contact surfaces 72
which contact the bottom surface 36 of the support plate 20. Heat
and electric current flows from the upper baffle plate 56A to the
support plate 20 through the surfaces 72. Similarly, the top
surface of the lower baffle plate 56B includes radially extending
channels 74 which distribute gas from the peripherally located
manifold 66 to an annular channel 76 in a central part of the lower
baffle plate 56B. The radially extending channels 74 are defined
between contact surfaces 78 which thermally and electrically
contact the upper baffle plate 56A. Although the channels 70, 74
and 76 are shown in the upper surfaces of the upper and lower
baffles, they could also be formed in lower surfaces of the support
plate 20 and upper baffle plate.
[0030] Openings 80 located in the radially extending channels 70 in
the upper baffle plate are flow-connected to a first set of
openings 82 in the lower baffle plate 56B. That is, the openings 80
in the upper baffle plate 56A and the first set of openings 82 in
the lower baffle plate 56B define a generally continuous and
uninterrupted fluid pathway from the first gas supply 60 through
the upper and lower baffle plates 56A, 56B. Gas from the second gas
supply 64 flows through a second set of openings 84 in the channels
74 in the lower baffle plate 56B. The flow-connected openings 80,
82 and the second set of openings 84 are arranged to prevent
significant mixing between gas from the first gas supply 60 and the
second gas supply 64. Such an arrangement will allow some gas to
migrate between the upper and lower baffle plates. To prevent such
migration, the upper and lower baffle plates could be adhesively or
metallurgically bonded together in a manner which prevents the two
gases from mixing together.
[0031] Preferably, the flow-connected openings 80, 82 are created
by aligning the openings 80 in the upper baffle plate with the
first set of openings 82 in the lower baffle plate by any suitable
technique such as mating alignment features such as locating pins.
However, other techniques for connecting openings 80 to openings 82
include interposition of a patterned gasket between the upper and
lower baffles or the provision of individual tubes bonded between
the openings in the upper and lower baffle plates.
[0032] The bottom surface of the lower baffle plate 56B includes
annular downwardly-projecting wall portions 86 which thermally and
electrically contact the top surface of the showerhead 22. Both the
flow-connected openings 80, 82 and the second set of openings 84
open into radially spaced annular channels 88 defined by the
downwardly-projecting wall portions 86. The channels 88 could be
formed in the upper surface of the showerhead or the space between
the lower baffle plate and the showerhead could be an open plenum
with or without contact portions therebetween for conducting heat
away from the showerhead and/or supplying electrical power to the
showerhead.
[0033] During semiconductor processing, gas from the first gas
supply 60 flows through flow-connected openings 80, 82 in the upper
baffle plate 56A and the lower baffle plate 56B, and gas from the
second gas supply 64 flows through the second set of openings 84 in
the lower baffle plate 56B. Gas from both the first and second gas
supplies 60, 64 mixes in the channels 88 in the underside of the
lower baffle plate above the top surface of the showerhead 22 and
flows through a third set of openings 90 in the showerhead 22
toward the substrate.
[0034] Across the upper baffle plate 56A, gas pressure is highest
near the centrally located first gas supply 60 and lowest near the
periphery of the upper baffle plate 56A. Process gas flows downward
through the flow-connected openings 82, 84 in the upper and lower
baffle plates 56A, 56B to the open channels 88 in the underside of
the lower baffle plate 56B. In operation, if the first and second
gas supplies deliver gas at the same pressure, gas from the first
gas supply 60 sets up a pressure distribution wherein pressure is
high proximate to the center of the lower baffle plate 56B and low
at the periphery of the lower baffle plate 56B whereas the gas from
the second gas supply 64 sets up a pressure distribution wherein
pressure is high at the periphery and low at the center-of the
lower baffle. Consequently, with the baffle arrangement of the
invention, the pressure seen at the backside of the showerhead can
be made more uniform across the backside of the showerhead.
[0035] In an alternative processing scheme, the gas distribution
system can provide a controlled, nonuniform gas pressure
distribution across the backside 28 of the showerhead 22. For
example, if high gas pressure around the periphery of the backside
28 of the showerhead 22 is desirable, the flow through the second
gas supply 64 can be selectively increased relative to the flow
through the first gas supply 60. Conversely, if relatively high gas
pressure is desirable near the center of the backside 28 of the
showerhead 22, the flow through the first gas supply 60 can be
increased relative to the flow through the second gas supply 64.
Thus, in the case of single wafer processing, the gas distribution
system can supply different gas chemistries to one or more annular
zones above the wafer. Because the gas chemistry, flow rate and
pressure can be made uniform circumferentially around each such
annular zone but varied radially from zone to zone it is possible
to effect uniform processing of a wafer during processes wherein
the processing conditions at the wafer surface vary across the
wafer.
[0036] FIGS. 7A-B show schematics of how a dual-damascene structure
can be etched in a single step in accordance with the invention.
FIG. 7A shows a pre-etch condition wherein an opening 500
corresponding to a trench is provided in a photoresist masking
layer 520 which overlies a stack of a first dielectric layer 540
such as silicon oxide, a first stop layer 560 such as silicon
nitride, a second dielectric layer 580 such as silicon oxide, a
second stop layer 600 such as silicon nitride, and a substrate 620
such as a silicon wafer. In order to obtain etching of vias through
the first stop layer 560 in a single etching step, first stop layer
560 includes an opening 640. FIG. 7B shows the structure after
etching wherein the opening 500 extends through the dielectric
layer 540 to the first stop layer 560 and the opening 640 extends
through the second dielectric 580 to the second stop layer 600.
Such an arrangement can be referred to as a "self-aligned
dual-damascene" structure.
[0037] During the etch process, process gas conditions supplied by
the first and second gas supplies in the first and second
embodiments can be changed relative to each other, e.g., during
etching of the trench 500 a mixture of Ar, oxygen and fluorocarbons
(e.g., CHF.sub.3 and C.sub.4F.sub.8) can be supplied and during
etching of the vias 640 the flow of the oxygen to the central
region of the wafer can be decreased. In the case of etching low-k
dielectric layers, the process gas can include a hydrocarbon such
as C.sub.2H.sub.4 and the hydrocarbon to oxygen gas flow rate ratio
can be varied radially to achieve uniform etching. Thus, according
to the invention the flow of gases to the center and edge of the
wafer can be adjusted to compensate for edge fast etching and
center fast etching conditions in the plasma chamber. For example,
in a conventional plasma etcher, edge fast etch conditions can
occur until the photoresist is eroded after which center fast etch
conditions can occur. With the gas distribution apparatus according
to the invention, more oxygen can be supplied in the center when
the wafer has a photoresist layer whereas when the photoresist
layer is eroded away, the flow of oxygen to the center can be
reduced. As a result, more uniform etching can be achieved by
compensating for the edge-fast and center-fast etch conditions.
[0038] The process of the invention is applicable to 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 silicides such as
titanium silicide, cobalt silicide, tungsten silicide, molydenum
silicide, etc.
[0039] 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.
[0040] 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.
* * * * *