U.S. patent application number 12/143146 was filed with the patent office on 2009-11-05 for plasma process employing multiple zone gas distribution for improved uniformity of critical dimension bias.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Rodolfo P. Belen, Edward P. Hammond, IV, Brian K. Hatcher, Dan Katz, David Palagashvili, Theodoros Panagopoulos, Alexander M. Paterson, Valentin N. Todorow.
Application Number | 20090275206 12/143146 |
Document ID | / |
Family ID | 41256334 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090275206 |
Kind Code |
A1 |
Katz; Dan ; et al. |
November 5, 2009 |
PLASMA PROCESS EMPLOYING MULTIPLE ZONE GAS DISTRIBUTION FOR
IMPROVED UNIFORMITY OF CRITICAL DIMENSION BIAS
Abstract
A passivation species precursor gas is furnished to an inner
zone at a first flow rate, while flowing an etchant species
precursor gas an annular intermediate zone at a second flow rate.
Radial distribution of etch rate is controlled by the ratio of the
first and second flow rates. The radial distribution of etch
critical dimension bias on the wafer is controlled by flow rate of
passivation gas to the wafer edge.
Inventors: |
Katz; Dan; (San Jose,
CA) ; Palagashvili; David; (Mountain View, CA)
; Hatcher; Brian K.; (San Jose, CA) ;
Panagopoulos; Theodoros; (San Jose, CA) ; Todorow;
Valentin N.; (Palo Alto, CA) ; Hammond, IV; Edward
P.; (Hillsborough, CA) ; Paterson; Alexander M.;
(San Jose, CA) ; Belen; Rodolfo P.; (San
Francisco, CA) |
Correspondence
Address: |
LAW OFFICE OF ROBERT M. WALLACE
2112 EASTMAN AVENUE, SUITE 102
VENTURA
CA
93003
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
41256334 |
Appl. No.: |
12/143146 |
Filed: |
June 20, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61126600 |
May 5, 2008 |
|
|
|
Current U.S.
Class: |
438/714 ;
257/E21.214 |
Current CPC
Class: |
H01J 37/32449 20130101;
H01L 21/31116 20130101; H01J 37/3244 20130101 |
Class at
Publication: |
438/714 ;
257/E21.214 |
International
Class: |
H01L 21/302 20060101
H01L021/302 |
Claims
1. A method for etching a surface on a workpiece, comprising:
applying RF plasma source power at first and second independently
controlled power levels to respective inner and outer coil antennas
overlying the ceiling; flowing a first process gas mixture
comprising an etchant species precursor gas and a passivation
species precursor gas to an annular inner zone of gas dispersers in
the ceiling at a first flow rate; flowing a second process gas
mixture comprising an etchant species precursor gas and a
passivation species precursor gas to an annular intermediate zone
of gas dispersers in the ceiling surrounding the inner zone at a
second flow rate; flowing a process gas constituting predominantly
or exclusively a passivation species precursor gas to an annular
outer zone of gas dispersers in the ceiling surrounding the
intermediate zone at a third flow rate; controlling radial
distribution of etch rate across the entirety of the wafer by (a)
controlling the ratio of the first and second power levels in the
inner and outer coil antennas and (b) controlling the ratio of the
first and second flow rates; and controlling radial distribution of
etch critical dimension bias on the wafer by controlling said third
flow rate.
2. The method of claim 1 wherein said surface of said workpiece
comprises a silicon-containing hardmask thin film of one of (a)
silicon nitride or (b) silicon oxide, and said etchant species
precursor gas comprises a fluorocarbon while said passivation
species precursor gas comprises a fluoro-hydrocarbon.
3. The method of claim 1 wherein said surface of said workpiece
comprises a silicon-containing thin film, and said etchant species
precursor gas comprises a fluorine and carbon compound containing a
small or zero atomic fraction of hydrogen while said passivation
species precursor gas comprises a fluorine and carbon compound
containing a significant atomic fraction of hydrogen.
4. The method of claim 3 wherein said significant atomic fraction
is at least 1/5.sup.th and said small atomic fraction is less than
1/5.sup.th.
5. The method of claim 1 wherein said first and second process gas
mixtures are the same.
6. The method of claim 1 wherein: each of the annular zones of gas
dispersers constitute gas dispersers arranged in respective circles
at uniform intervals for each circle; each said flowing is
performed so that the flow rate and pressure at all the gas
dispersers within a given zone is uniform.
7. The method of claim 6 wherein each said flowing comprises
flowing the gas through uniform path lengths to each of the gas
dispersers within a given one of said zones.
8. The method of claim 1 wherein said controlling CD bias comprises
increasing said third flow rate whenever CD bias near an edge of
said workpiece is less than elsewhere on said workpiece, while
controlling etch rate distribution across said workpiece
independently of the distribution of said CD bias.
9. The method of claim 1 wherein said controlling CD bias comprises
decreasing said third flow rate whenever CD bias near an edge of
said workpiece is greater than elsewhere on said workpiece, while
controlling etch rate distribution across said workpiece
independently of the distribution of said CD bias.
10. The method of claim 1 wherein said controlling etch profile
taper comprises increasing said third flow rate whenever etch
profile taper near an edge of said workpiece is less than elsewhere
on said workpiece, while controlling etch rate distribution across
said workpiece independently of the distribution of said CD
bias.
11. The method of claim 1 wherein said controlling etch profile
taper comprises decreasing said third flow rate whenever etch
profile taper near an edge of said workpiece is greater than
elsewhere on said workpiece, while controlling etch rate
distribution across said workpiece independently of the
distribution of said CD bias.
12. A method for etching a surface on a workpiece, comprising:
flowing a first process gas mixture comprising an etchant species
precursor gas and a passivation species precursor gas to an annular
inner zone of gas dispersers in the ceiling at a first flow rate;
flowing a second process gas mixture comprising an etchant species
precursor gas and a passivation species precursor gas to an annular
intermediate zone of gas dispersers in the ceiling surrounding the
inner zone at a second flow rate; flowing a process gas
constituting predominantly or exclusively a passivation species
precursor gas to an annular outer zone of gas dispersers in the
ceiling surrounding the intermediate zone at a third flow rate;
controlling radial distribution of etch rate across the entirety of
the wafer by controlling the ratio of the first and second flow
rates; and controlling radial distribution of etch critical
dimension bias on the wafer by controlling said third flow
rate.
13. The method of claim 12 wherein said surface of said workpiece
comprises a silicon-containing hardmask thin film of one of (a)
silicon nitride or (b) silicon oxide, and said etchant species
precursor gas comprises a fluorocarbon while said passivation
species precursor gas comprises a fluoro-hydrocarbon.
14. The method of claim 12 wherein said surface of said workpiece
comprises a silicon-containing thin film, and said etchant species
precursor gas comprises a fluorine and carbon compound containing a
small or zero atomic fraction of hydrogen while said passivation
species precursor gas comprises a fluorine and carbon compound
containing a significant atomic fraction of hydrogen.
15. The method of claim 14 wherein said significant atomic fraction
is at least 1/5.sup.th and said small atomic fraction is less than
1/5.sup.th.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/126,600, filed May 5, 2008.
BACKGROUND
[0002] In plasma processing of semiconductor wafers, precise
feature profile control has become increasingly important during
gate etching as the critical dimensions of semiconductor devices
continue to scale down below 45 nm. For example, the integrity and
critical dimension (CD) control of the hardmask during gate mask
definition is critical in gate etch applications. For example, for
a polysilicon gate, the hardmask layer overlying the polysilicon
layer can be silicon nitride. For etching of the silicon nitride
hardmask layer, the CD of greatest criticality is the mask length
at the bottom of the hardmask. Likewise, for etching of the
polysilicon gate, the CD of greatest criticality is the gate length
at the bottom of the polysilicon gate. This length typically
defines the all-important channel length of the transistor during
later process steps. Therefore, during definition (etching) of the
hardmask or of the polysilicon gate, it is important to minimize
discrepancy between the required CD and the CD obtained at the end
of the etch step. It is also important to minimize the variation in
the CD bias, the difference between the CD as defined by the mask
and the final CD after the etch process. Finally, it is important
to minimize the CD bias microloading, which is the difference
between the CD bias in regions in which the discrete circuit
features are dense or closely spaced and the CD bias in regions in
which the discrete circuit features are isolated or widely spaced
apart.
[0003] Various conventional techniques have been used to meet these
requirements. For instance, trial-and-error techniques have been
used for determining the optimum gas flow rates for the various gas
species in the reactor, the optimum ion energy (determined mainly
by RF bias power on the wafer) and the optimum ion density
(determined mainly by RF source power on the coil antenna). The
foregoing process parameters affect not only CD, CD bias and CD
bias microloading but also affect other performance parameters,
such as etch rate and etch rate uniformity. It may not be possible
to set the process parameters to meet the required performance
parameters such as etch rate and at the same time optimize CD and
minimize CD bias and CD bias microloading. As a result, the process
window, e.g., the allowable ranges of process parameters such as
chamber pressure, gas flow rates, ion energy and ion density, may
be unduly narrow to satisfy all requirements.
[0004] A current problem is that CD bias is non-uniform, decreasing
near the wafer edge. This problem is becoming more acute as device
feature sizes are scaled down to 32 nm and smaller. Part of this
problem is the sharp drop in CD bias at the wafer edge. We believe
that this sharp drop is due to the lack of etch passivation species
to passivate etch by-products. The amount of passivation species
affects etch profile tapering and sidewall etch rate in high aspect
ratio openings. Typically, the greater the amount of passivation
gas present, the greater the etch profile tapering. What is desired
is the etch profile or etch profile tapering be uniform across the
wafer. This will promote a uniform distribution of CD bias. Because
of the lack of passivation gas at the wafer edge, the etch profile
taper is small at the wafer edge and large elsewhere.
SUMMARY
[0005] A method is provided for etching a surface on a workpiece.
The method includes flowing a first process gas mixture including
an etchant species precursor gas and a passivation species
precursor gas to an annular inner zone of gas dispersers in the
ceiling at a first flow rate, while flowing a second process gas
mixture including an etchant species precursor gas and a
passivation species precursor gas to an annular intermediate zone
of gas dispersers in the ceiling surrounding the inner zone at a
second flow rate. The method further includes flowing a process gas
constituting predominantly or exclusively a passivation species
precursor gas to an annular outer zone of gas dispersers in the
ceiling surrounding the intermediate zone at a third flow rate.
Radial distribution of etch rate across the entirety of the wafer
is controlled by controlling the ratio of the first and second flow
rates. The radial distribution of etch critical dimension bias on
the wafer is controlled by controlling the third flow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] So that the manner in which the above recited embodiments of
the invention are attained and can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0007] FIG. 1 depicts a plasma reactor in accordance with a first
embodiment.
[0008] FIGS. 2A, 2B and 2C are different cross-sectional side views
of a ceiling of the reactor of FIG. 1 revealing a gas distribution
assembly within the ceiling.
[0009] FIG. 2D is a top view of a gas feed hub in the reactor of
FIG. 1.
[0010] FIG. 2E is an enlarged cross-sectional side view of a
portion of the ceiling of the reactor of FIG. 1.
[0011] FIG. 3A is a view of the bottom surface of an equal path
length manifold in the gas distribution assembly of FIGS.
2A-2C.
[0012] FIG. 3B is an enlarged portion of the view of FIG. 3A.
[0013] FIG. 4 is a view of the bottom surface of a gas distribution
orifice plate in the gas distribution assembly of FIGS. 2A-2C.
[0014] FIG. 5 depicts a plasma reactor in accordance with a second
embodiment including a gas distribution assembly in the ceiling of
the reactor.
[0015] FIG. 6 is a view of the bottom surface of an equal path
length manifold in the gas distribution assembly of FIG. 5.
[0016] FIG. 7 is a bottom view of a gas distribution orifice plate
in the gas distribution assembly of FIG. 6.
[0017] FIG. 8A is an enlarged view of FIG. 7, illustrating an
embodiment in which each individual orifice of FIG. 7 consists of
seven miniature orifices.
[0018] FIG. 8B is a cross-sectional view corresponding to FIG.
8A.
[0019] FIG. 9 is a flow diagram depicting a hard mask etch process
in accordance with one embodiment.
[0020] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation. It is to be noted,
however, that the appended drawings illustrate only exemplary
embodiments of this invention and are therefore not to be
considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
DETAILED DESCRIPTION
[0021] FIG. 1 depicts a plasma reactor for processing a workpiece
or semiconductor wafer in accordance with a first embodiment. The
reactor has a chamber 100 defined by a cylindrical sidewall 102, a
ceiling 104 and a floor 106. An RF plasma source power applicator
108 is provided and may be an inductive coil antenna overlying the
ceiling 104. The coil antenna 108 may consist of an inner coil 112
and an outer coil 114 surrounding the inner coil. RF power to each
of the coils 112, 114 may be independently controllable and may be
furnished from a common power generator or (as depicted in FIG. 1)
from separate RF power generators 116, 118 coupled to the
respective coils 112, 114 through respective impedance matches 120,
122. The chamber is evacuated by a vacuum pump 124 through the
floor 106. A wafer support pedestal 126 supported at the floor 106
holds a workpiece 128 such as a semiconductor wafer. An RF plasma
bias power generator 130 (or plural RF bias power generators of
different frequencies) may be coupled through an impedance match
132 (or plural respective impedance matches) to an electrode 134
within the pedestal 126.
[0022] In embodiments described below, the gas distribution
apparatus within the ceiling 104 may distribute process gases in
three gas distribution zones that receive process gas from three
independent gas supply lines 141, 142, 143. These three zones are,
in one embodiment, annular concentric zones including inner, middle
and outer zones. The gas mixtures and flow rates in each of the
lines 141, 142, 143 may be independently controlled. For example,
each line 141, 142, 143 may be supplied with process gas from a
respective gas source 144, 145, 146. As will be described below,
the gas supply lines 141, 142, 143 supply process gas for injection
in respective inner, middle and outer gas injection zones below the
ceiling. The gas furnished by the gas supplies 144 and 145 to the
inner and middle gas injection zones is, in one embodiment, a
mixture of an etch species precursor gas and a passivation species
precursor gas, and etch rate distribution across the wafer may be
controlled by the ratio of the flow rates from the gas supplies
144, 145. Gas furnished by the gas supply 146 to the outer gas
injection zone may be a pure or nearly pure passivation species
precursor gas, and radial distribution of CD bias or etch profile
taper may be controlled by varying the gas flow rate from the gas
supply 146. This latter adjustment is independent or nearly
independent of the adjustment of the etch rate distribution.
Typically, the CD bias distribution is non-uniform because it
decreases near the wafer edge, and uniformity is achieved by
increasing the passivation species precursor gas flow rate to the
outer gas injection zone. In this way, two etch performance
parameters, namely (a) distribution of etch rate and (b)
distribution of CD bias, are controlled simultaneously and nearly
independently of one another in the reactor of FIG. 1.
[0023] The ceiling 104 in one embodiment includes a showerhead
orifice plate 150 having an array of gas injection orifices 152
extending through it. In the illustrated embodiment of FIG. 2A, the
orifices 152 are located in three concentric radial zones, namely
an inner zone 154, an annular middle zone 156 and an annular outer
zone 158. A multipath lid 160 overlies the orifice plate 150. A hub
170 may overlie the lid 160. As depicted in FIG. 2A through 2E, the
hub 170 has three concentric channels 171, 172, 173 in its bottom
surface 174. The hub 170 further has three gas supply ports 175,
176, 177 coupled to the gas supply lines 141, 142, 143
respectively, the ports 175, 176, 177 being coupled to respective
ones of the concentric channels 171, 172, 173. Each channel 171,
172, 173 receives process gas from a particular one of the supply
lines 141, 142, 143. The hub 170 may have a passageway or hole (not
shown) extending axially through the hub 170 to enable installation
of an optical interferometric sensor for process end-point
detection.
[0024] In the illustrated embodiment, the lid 160 consists of an
equal path length manifold 162 whose top surface 162b contacts the
hub 170. Referring to FIG. 2E, the equal path length manifold 162
has an array of equal path length channels 180, 190, 200 formed in
its bottom surface 162a. As shown in FIG. 2E, the equal path length
manifold 162 has a radial translation layer 164 overlying the equal
path length channels 180, 190, 200. The radial translation layer
164 has radial channels 220, 230, 240 providing communication
between individual hub channels 171, 172, 173 and respective ones
of the equal path length channels 180, 190, 200, as will be
described in greater detail below. The radial translation layer 164
and the equal path length manifold constitute an integral
structure. Alternatively, they may be formed as separate pieces
that are joined together. The equal path length channels 180, 190,
200 communicate between individual ones of the radial channels 220,
230, 240 and respective ones of the gas injection zones 154, 156,
158. The cross-sectional side views of FIGS. 2A, 2B and 2C are
taken at different angles around the axis of symmetry to reveal
different internal features. In the view of FIG. 2A, the
communication between the inner hub channel 171 and the inner gas
injection zone 154 is exposed. In the view of FIG. 2B, the
communication between the middle hub channel 172 and the middle gas
injection zone 156 is exposed. In the view of FIG. 2C, the
communication between the outer hub channel 173 and the outer gas
injection zone 158 is exposed.
[0025] FIGS. 3A and 3B are top views of equal path length manifold
(EPLM) 162 showing the different equal path length channels 180,
190, 200 correspond to three different groups or types of gas flow
channels, namely the inner zone channels 180, the middle zone
channels 190 and the outer zone channels 200. In the implementation
of FIGS. 3A and 3B, there are eight inner zone channels 180, eight
middle zone channels 190 and eight outer zone channels 200, the
channels of each type being azimuthally distributed in periodic
fashion.
[0026] FIG. 4 is a bottom view of the gas distribution orifice
plate 150 showing how the plural gas injection orifices 152 may be
grouped in different circular zones corresponding to the inner,
middle and outer zones 154, 156, 158 referred to above, including a
set of inner zone orifices 152a, first and second sets of middle
zone orifices 152b-1, 152b-2, and first and second sets of outer
zone orifices 152c-1, 152c-2. A subset of the overlying equal path
length channels 180, 190, 200 is depicted in hidden line in FIG. 4
to show their alignment with the various orifices 152.
[0027] In the illustrated embodiment of FIGS. 3B and 4, each of the
eight inner zone channels 180 consists of a pair of legs 181, 182
forming an acute angle and joined together at an apex 183 from
which the legs 181, 182 radiate toward terminations 184, 185. A gas
inlet hole 186 extends from the apex 183 to the opposite (top)
surface 162b (FIG. 2E) of the EPLM 162. Each termination 184, 185
is aligned with a corresponding one of the orifices 152a of the
inner zone 154 of the orifice plate 150. In this manner, each of
the orifices 152a of the inner zone 154 is aligned with one of the
terminations 184, 185 of the eight inner zone channels 180.
[0028] Referring again to FIGS. 3B and 4, each of the middle zone
channels 190 consists of a radial main leg 191 extending from an
apex 192 and terminating in the middle of a transverse leg 193
forming a "T" with the main leg 191, the two ends of the transverse
leg 193 terminating in the middle of each of respective radial legs
194-1, 194-2, each of the radial legs 194-1, 194-2 having a
radially inward end 195 and a radial outward end 196, each radial
leg 194-1, 194-2 terminating in the middle of a transverse leg 197
at its radially outward end 196 to form a "T". Each transverse leg
has a pair of opposite ends 198-1, 198-2. A gas inlet hole 199
extends from the apex 192 to the opposite (top) surface 162b (FIG.
2A) of the EPLM 162. The first set of orifices 152b-1 in the middle
zone 156 of the orifice plate 150 face the channel ends 195. The
second set of orifices 152b-2 of the middle zone 156 face
respective ones of the channel ends 198-1, 198-2.
[0029] Referring yet again to FIGS. 3B and 4, each of the outer
zone channels 200 consists of a radial main leg 201 extending from
an apex 202 and terminating in the middle of a transverse leg 203
forming a "T" with the main leg 201, the two ends of the transverse
leg 203 terminating in the middle of each of respective radial legs
204-1, 204-2, each of the radial legs 204-1, 204-2 extending
radially to a radial outward end 206, each radial leg 204-1, 204-2
terminating in the middle of a transverse leg 207 at its radially
outward end 206 to form a "T". Each transverse leg 207 has a pair
of opposite ends 208-1, 208-2 terminating in the middle of each of
respective radial legs 210. Each radial leg 210 has a pair of
opposite termination ends 211, 212. Each outer channel 200 has a
total of four channel ends 211 and four channel ends 212. A gas
inlet hole 209 extends from the apex 202 to the opposite (top)
surface 162b (FIG. 2E) of the EPLM 162. The first set of orifices
152c-1 in the outer zone 158 of the orifice plate 150 face the
channel ends 211. The second set of orifices 152c-2 of the outer
zone 158 face the channel ends 212.
[0030] In accordance with one feature, the array of channels 180,
190, 200 in the bottom surface 162a of the EPLM manifold 162 are
configured so that the distances traveled within the EPLM 162 by
process gas to different orifices within inner zone 154 are
uniform. In the illustrated embodiment, the distances traveled
within the EPLM 162 by process gas to different orifices 152 within
the middle zone 156 are uniform. In this same embodiment, the
distances traveled within the EPLM 162 by process gas to different
orifices 152 within the outer zone 158 are uniform. Another feature
is that the arc distances subtended by the various equal path
length channels within the EPLM are all not more than fractions of
a circle, which prevents or minimized inductive coupling to the
gases therein.
[0031] Referring to FIGS. 2A-2E, the radial translation layer 164
of the EPLM 162 provides the gas communication from the inner,
middle and outer concentric channels 171, 172, 173 of the hub 170
to the inner zone, middle zone and outer zone gas inlets 186, 199,
209 of the EPLM 162. Specifically, the radial translation layer 164
provides gas communication between the inner hub channel 171 and
the inner zone gas inlets 186 through the radial channels 220,
between the middle hub channel 172 and the middle zone gas inlets
199 through the radial channels 230, and between the outer hub
channel 173 and the outer zone gas inlets 209 through the radial
channels 240.
[0032] As shown in FIGS. 2A through 2E, the radial translation
layer 164 may have its plural inner zone channels 220 tilted at a
first acute angle A relative to the axis of symmetry. Each inner
zone axial channel 220 has a first end 221 open at the top surface
162b and facing the inner concentric hub channel 171. Each inner
zone axial channel 220 further has a second end in registration
with one of the inner zone gas inlets 186 of the EPLM 162. In this
manner, eight inner zone axial channels 220 provide gas flow from
the inner hub channel 171 to the eight inner zone gas inlets 186 of
the EPLM 162.
[0033] The radial translation layer 164 may have its plural middle
zone axial channels 230 tilted at a second acute angle B relative
to the axis of symmetry. In the illustrated embodiment, each middle
zone axial channel 230 may have a first end 231 open at the top
surface 162b and facing the middle concentric hub channel 172. Each
middle zone axial channel 230 further may have a second end in
registration with one of the middle zone gas inlets 199 of the EPLM
162. In this manner, eight middle zone axial channels 230 may
provide gas flow from the middle hub channel 172 to the eight
middle zone gas inlets 199 of the EPLM 162.
[0034] The radial translation layer 164 may have its plural outer
zone axial channels 240 tilted at a third acute angle C relative to
the axis of symmetry. Each outer zone axial channel 240 has a first
end 241 open at the top surface 162b and facing the outer
concentric hub channel 173. Each outer zone axial channel 240
further may have a second end in registration with one of the outer
zone gas inlets 209 of the EPLM 162. In this manner, eight outer
zone axial channels 240 may provide gas flow from the outer hub
channel 173 to the eight outer zone gas inlets 209 of the EPLM
162.
[0035] The first, second and third acute angles A, B, C may be
progressively smaller to accommodate the different radial locations
of the inner zone gas inlets 186, the middle zone gas inlets 199
and the outer zone gas inlets 209. In the implementation of FIGS.
1-3, the radial distance of the middle and outer zone gas inlets
199, 209, from the axis of symmetry are the same so that the second
and third acute angles B and C are nearly the same. The middle and
outer zone gas inlets 199, 209 have different azimuthal locations
in alternating sequence, as shown in the drawings.
[0036] FIGS. 5 and 6 depict another embodiment employing an EPLM
manifold 462 and an orifice plate 450. In FIG. 5, the three gas
supply lines 141, 142, 143 are coupled directly to the EPLM
manifold 462. An advantage of the embodiment of FIGS. 5 and 6 is
that the hub 170 and radial translation layer 164 of FIG. 1 are
eliminated.
[0037] In the illustrated embodiment of FIGS. 5 and 6, the bottom
surface of the EPLM 462 has gas distribution channels including
inner, middle and outer zone gas input channels 301, 302, 303
coupled to the gas supply lines 141, 142, 143, respectively. The
gas input channels 301, 302, 303 may be formed in a radial
extension 464 of the circular EPLM 462. Gas connections (not shown)
are provided at the outer terminations of the channels between the
gas supply lines 141, 142, 143 and respective ones of the input
channels 301, 302, 303.
[0038] In the illustrated embodiment of FIGS. 5 and 6, the inner
zone input channel 301 in the extension 464 merges with a radial
supply channel 305 within the main circular portion of the manifold
462. The radially inward termination of the supply channel 305 is
coupled to the middle of a half-circular channel 310. The opposite
ends of the half-circular channel 310 are coupled to the middle of
a respective quarter-circular channel 314 through respective radial
short transition channels 312. Each of the opposite ends or
terminations of the quarter-circular channels 314 is coupled
through a respective short radial transition channel 316 to the
middle of a respective arcuate channel 318 having opposite first
and second ends or terminations 318a, 318b. The terminations 318a,
318b may have a common radial location as shown in FIG. 6, and are
aligned with respective ones of a set of inner zone orifices 452-1
of the orifice plate 450 shown in FIG. 7.
[0039] In the illustrated embodiment of FIGS. 5 and 6, the middle
zone input channel 302 in the extension 464 merges with a radial
supply channel 306 within the main circular portion of the manifold
462. The radially inward termination of the supply channel 306 is
coupled to one end of a half-circular channel 332. The opposite end
of the half-circular channel 332 is coupled through a short radial
transition channel 334 to the middle of a half-circular channel
336. The opposite ends of the half-circular channel 336 are each
coupled through a respective short radial transition channel 338 to
the middle of a respective quarter-circular channel 340. Each of
the opposite ends or terminations of the quarter-circular channels
340 is coupled through a respective short radial transition channel
342 to the middle of a respective arcuate channel 344. Each of the
opposing ends or terminations of the arcuate channels 344 is
coupled through a respective short radial transition channel 346 to
the middle of a respective arcuate channel 348 having opposite
first and second ends or terminations 348a, 348b. The terminations
348a, 348b may have a common radial location as shown in FIG. 6,
and are aligned with respective ones of a set of middle zone
orifices 452-2 of the orifice plate 450 shown in FIG. 7.
[0040] In the illustrated embodiment of FIGS. 5 and 6, the outer
zone input channel 303 in the extension 464 merges with one end of
an outer half-circular supply channel 360 within the main circular
portion of the manifold 462. The opposite end or termination of the
outer supply channel 360 is coupled radially inwardly through a
short radial transition channel 362 to the middle of an inner
half-circular channel 364 concentric with and inside the radius of
the outer supply channel 360. Each one of the opposite ends of the
half-circular channel 364 is coupled radially inwardly through a
respective short radial transition channel 366 to the middle of a
respective quarter-circular channel 368. The quarter-circular
channel 368 is encircled by the half-circular channel 364. Each
opposite end of each quarter-circular channel 368 is coupled
through a respective short radial transition channel 370 to the
middle of a respective arcuate channel 372. Each of the opposite
ends or terminations of the arcuate channels 372 is coupled through
a respective short radial transition channel 374 to the middle of a
respective arcuate channel 376. Each of the opposing ends or
terminations of the arcuate channels 376 is coupled through a
respective short radial transition channel 378 to the middle of a
respective arcuate channel 380 having opposite first and second
ends or terminations 380a, 380b. The terminations 380a, 380b may
have a common radial location as shown in FIG. 6, and are aligned
with respective ones of a set of outer zone orifices 452-3 of the
orifice plate 450 shown in FIG. 7.
[0041] Referring to FIGS. 8A and 8B, each of the orifices 452 in
one embodiment may form a single hole or opening in the top surface
450a of the orifice plate, but branch radially outwardly into seven
smaller holes 453-1, 453-2, 453-3, 453-4, 453-5, 453-6 and 453-7 in
the bottom surface 450b of the orifice plate. FIG. 8A depicts this
feature in the group of inner zone orifices 452-1.
[0042] FIG. 9 is a flow diagram depicting a process in accordance
with one embodiment that can be carried out in the reactor of FIG.
1 (or in the reactor of FIG. 5). The process of FIG. 9 begins by
flowing a first process gas mixture of an etchant species precursor
gas and a passivation species precursor gas to an annular inner
zone of gas dispersers in the ceiling at a first flow rate (block
610 of FIG. 9). The process includes flowing a second process gas
mixture of an etchant species precursor gas and a passivation
species precursor gas to an annular middle zone of gas dispersers
in the ceiling surrounding the inner zone at a second flow rate
(block 615). The process further includes flowing a process gas
which is a pure or nearly pure passivation species precursor gas to
an annular outer zone of gas dispersers in the ceiling surrounding
the middle zone at a third flow rate (block 617). RF plasma source
power is applied at first and second independently controlled power
levels to respective inner and outer coil antennas overlying the
ceiling (block 620). The radial distribution of etch rate across
the entirety of the wafer is obtained by controlling the ratio of
the first and second power levels in the inner and outer coil
antennas and (or, alternatively) by controlling the ratio of the
inner and outer zone (first and second) gas flow rates (block 625).
Uniformity of the radial distribution of either etch critical
dimension (CD) bias or etch profile taper is controlled by
controlling the third flow rate, i.e., the flow rate of the
passivation species precursor gas to the third gas injection zone
(block 630).
[0043] The process may be applied to etching a silicon nitride or
silicon oxide hard mask prior to a gate etch step. In this case the
etchant species precursor may be CF.sub.4 and the passivation
species precursor may be CHF.sub.3. In general, the etchant species
precursor gas is a fluorocarbon (i.e., a species containing no
hydrogen) while the passivation species precursor gas is a
fluoro-hydrocarbon (i.e., a species containing a significant
proportion of hydrogen). More generally, the etchant species
precursor gas contains a high proportion of fluorine and a low
proportion (less than a few percent atomic ratio) or zero amount of
hydrogen, while a significant fraction (20% atomic ratio) of the
passivation species is hydrogen. The gas mixtures flowed to the
inner and middle zones may be identical, while their flow rates are
different and independently controlled.
[0044] The etch critical dimension (CD) bias and the etch profile
taper tend to be less at the wafer edge. In order to improve
uniformity of radial distribution of either or both the CD bias and
the etch profile tapering, the third gas flow rate (the flow rate
of the pure passivation species precursor gas to the outer zone of
gas dispersers) is increased until the nonuniformity in
distribution of CD bias or profile taper has been minimized. An
overcorrection that raises the CD bias or etch profile taper at the
wafer edge above the average value across the wafer requires a
corresponding reduction in the pure passivation species precursor
gas in outer zone of gas dispersers.
[0045] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *