U.S. patent application number 12/821609 was filed with the patent office on 2011-04-28 for inductively coupled plasma apparatus.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to ANKUR AGARWAL, SAMER BANNA, ZHIGANG CHEN, ANDREW NGUYEN, SHAHID RAUF, MARTIN JEFF SALINAS, VALENTIN N. TODOROW, TSE-CHIANG WANG.
Application Number | 20110094994 12/821609 |
Document ID | / |
Family ID | 43897510 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094994 |
Kind Code |
A1 |
TODOROW; VALENTIN N. ; et
al. |
April 28, 2011 |
INDUCTIVELY COUPLED PLASMA APPARATUS
Abstract
Methods and apparatus for plasma processing are provided herein.
In some embodiments, a plasma processing apparatus includes a
process chamber having an interior processing volume; a first RF
coil disposed proximate the process chamber to couple RF energy
into the processing volume; and a second RF coil disposed proximate
the process chamber to couple RF energy into the processing volume,
the second RF coil disposed coaxially with respect to the first RF
coil, wherein the first and second RF coils are configured such
that RF current flowing through the first RF coil is out of phase
with RF current flowing through the RF second coil.
Inventors: |
TODOROW; VALENTIN N.; (Palo
Alto, CA) ; BANNA; SAMER; (San Jose, CA) ;
AGARWAL; ANKUR; (Mountain View, CA) ; CHEN;
ZHIGANG; (San Jose, CA) ; WANG; TSE-CHIANG;
(Concord, CA) ; NGUYEN; ANDREW; (San Jose, CA)
; SALINAS; MARTIN JEFF; (San Jose, CA) ; RAUF;
SHAHID; (Pleasanton, CA) |
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
43897510 |
Appl. No.: |
12/821609 |
Filed: |
June 23, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61254833 |
Oct 26, 2009 |
|
|
|
Current U.S.
Class: |
216/68 ;
156/345.48 |
Current CPC
Class: |
C23C 16/505 20130101;
H01J 37/321 20130101; H01J 37/3244 20130101; H01J 37/32165
20130101; B44C 1/227 20130101 |
Class at
Publication: |
216/68 ;
156/345.48 |
International
Class: |
C23F 1/08 20060101
C23F001/08; C23F 1/00 20060101 C23F001/00 |
Claims
1. A plasma processing apparatus, comprising: a process chamber
having an interior processing volume; a first RF coil disposed
proximate the process chamber to couple RF energy into the
processing volume; and a second RF coil disposed proximate the
process chamber to couple RF energy into the processing volume, the
second RF coil disposed coaxially with respect to the first RF
coil, wherein the first and second RF coils are configured such
that RF current flowing through the first RF coil is out of phase
with RF current flowing through the second RF coil.
2. The apparatus of claim 1, wherein the first RF coil is wound in
a first direction and wherein the second RF coil is wound in a
second direction opposite the first direction.
3. The apparatus of claim 1, wherein the second RF coil is
coaxially disposed about the first RF coil.
4. The apparatus of claim 1, further comprising: a phase shifter
coupled to either the first or second RF coil for shifting the
phase of the RF current flowing therethrough.
5. The apparatus of claim 4, wherein the phase shifter shifts the
phase of the RF current such that the RF current flowing through
the first RF coil is about 180 degrees out of phase with RF current
flowing through the second RF coil.
6. A plasma processing apparatus, comprising: a process chamber
having an interior processing volume; a first RF coil disposed
proximate the process chamber to couple RF energy into the
processing volume and wound in a first direction; and a second RF
coil disposed proximate the process chamber to couple RF energy
into the processing volume, the second RF coil disposed coaxially
with respect to the first RF coil and wound in a second direction
opposite the first direction such that RF current flows through the
first RF coil in the first direction and through the second RF coil
in the second direction.
7. The apparatus of claim 6, wherein RF current flowing through the
first RF coil is about 180 degrees out of phase with RF current
flowing through the second RF coil.
8. The apparatus of claim 6, wherein the second RF coil is
coaxially disposed about the first RF coil.
9. The apparatus of claim 8, wherein the first RF coil further
comprises a plurality of symmetrically arranged first coil elements
and wherein the second RF coil further comprises a plurality of
symmetrically arranged second coil elements.
10. The apparatus of claim 9, wherein the number of first coil
elements is two and the number of second coil elements is four.
11. The apparatus of claim 9, wherein the number of first coil
elements is four and the number of second coil elements is
four.
12. The apparatus of claim 11, further comprising: an RF feed
structure coupled to each of the first and second coil elements to
provide RF power thereto, the RF feed structure coaxially disposed
with respect to each of the first and second coil elements.
13. The apparatus of claim 12, wherein the RF feed structure
further comprises: a first RF feed coupled to each of the first
coil elements; and a second RF feed coaxially disposed about the
first RF feed and electrically insulated therefrom, the second RF
feed coupled to each of the second coil elements.
14. The apparatus of claim 13, wherein the plurality of first coil
elements is symmetrically disposed about the first RF feed and the
plurality of second coil elements is symmetrically disposed about
the second RF feed.
15. The apparatus of claim 13, wherein the second RF feed further
comprises: a conductive tube having a first end proximate the first
and second coil elements and a second end opposite the first
end.
16. The apparatus of claim 15, wherein the first and second end of
the conductive tube are separated by a length such that a magnetic
field formed by flowing RF current through the first and second RF
feeds has substantially no effect on the symmetry of an electric
field formed by flowing RF current through the first and second RF
coils.
17. The apparatus of claim 13, further comprising: a heater element
disposed between the first and second RF coils and a dielectric lid
of the process chamber.
18. A method of forming a plasma, comprising: providing an RF
signal through a first RF coil; providing the RF signal through a
second RF coil coaxially disposed with respect to the first RF coil
such that the RF signal flows through the second coil out of phase
with respect to the flow of the RF signal through the first coil;
and forming a plasma by coupling the RF signal provided by the
first and second RF coils to a process gas disposed in a process
chamber.
19. The method of claim 18, wherein the first and second RF coils
are wound in opposite directions.
20. The method of claim 18, wherein the RF current flowing through
the first and second RF coils are about 180 degrees out of phase.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application Ser. No. 61/254,833, filed Oct. 26, 2009, which is
herein incorporated by reference in its entirety.
FIELD
[0002] Embodiments of the present invention generally relate to
plasma processing equipment.
BACKGROUND
[0003] Inductively coupled plasma (ICP) process reactors generally
form plasmas by inducing current in a process gas disposed within
the process chamber via one or more inductive coils disposed
outside of the process chamber. The inductive coils may be disposed
externally and separated electrically from the chamber by, for
example, a dielectric lid. When radio frequency (RF) current is fed
to the inductive coils via an RF feed structure from an RF power
supply, an inductively coupled plasma can be formed inside the
chamber from an electric field generated by the inductive
coils.
[0004] In some reactor designs, the reactor may be configured to
have concentric inner and outer inductive coils. The inventors have
discovered that additive electric field properties (due to
destructive interference of the magnetic fields induced by the
coils) between the inner and outer coils can result in
non-uniformities in the electric field distribution of the plasma
formed at the substrate level away from the coils. For example, due
to etch rate non-uniformities caused by the non-uniform electric
field distribution in the plasma, a substrate etched by such a
plasma may result in a non-uniform etch pattern on the substrate,
such as an M-shaped etch pattern, e.g., a center low and edge low
etch surface with peaks between the center and edge. The inventor's
have further observed that adjusting the power ratio between the
inner and outer coils to control the severity of the non-uniformity
is not sufficient to completely eliminate the non-uniformity.
Moreover, in order to meet the critical dimension requirements of
advanced device nodes, e.g., about 32 nm and below, the remaining
etch pattern non-uniformities due to this phenomenon may need to be
further reduced or eliminated.
[0005] Accordingly, the inventors have devised a plasma process
apparatus to better control plasma processing non-uniformity.
SUMMARY
[0006] Methods and apparatus for plasma processing are provided
herein. In some embodiments, a plasma processing apparatus includes
a process chamber having an interior processing volume; a first RF
coil disposed proximate the process chamber to couple RF energy
into the processing volume; and a second RF coil disposed proximate
the process chamber to couple RF energy into the processing volume,
the second RF coil disposed coaxially with respect to the first RF
coil, wherein the first and second RF coils are configured such
that RF current flowing through the first RF coil is out of phase
with RF current flowing through the second RF coil.
[0007] In some embodiments, a plasma processing apparatus includes
a process chamber having an interior processing volume; a first RF
coil disposed proximate the process chamber to couple RF energy
into the processing volume and wound in a first direction; and a
second RF coil disposed proximate the process chamber to couple RF
energy into the processing volume, the second RF coil disposed
coaxially with respect to the first RF coil and wound in a second
direction opposite the first direction such that RF current flows
through the first RF coil in the first direction and through the
second RF coil in the second direction.
[0008] In some embodiments, a method of forming a plasma includes
providing an RF signal through a first RF coil; providing the RF
signal through a second RF coil coaxially disposed with respect to
the first RF coil such that the RF signal flows through the second
coil out of phase with respect to the flow of the RF signal through
the first coil; and forming a plasma by coupling the RF signal
provided by the first and second RF coils to a process gas disposed
in a process chamber. Other and further embodiments of the present
invention are described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Embodiments of the present invention, briefly summarized
above and discussed in greater detail below, can be understood by
reference to the illustrative embodiments of the invention depicted
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.
[0010] FIG. 1 depicts a schematic side view of an inductively
coupled plasma reactor in accordance with some embodiments of the
present invention.
[0011] FIG. 2 depicts a schematic top view of a pair of RF coils of
an inductively coupled plasma reactor in accordance with some
embodiments of the present invention.
[0012] FIGS. 3A-B illustratively depict graphs of etch rate
profiles generated using conventional apparatus and an embodiment
of the inventive apparatus as disclosed herein.
[0013] FIGS. 4A-B depict an RF feed structure in accordance with
some embodiments of the present invention.
[0014] FIGS. 5A-B depict schematic top views of an inductively
coupled plasma apparatus in accordance with some embodiments of the
present invention.
[0015] FIG. 6 depicts a flow chart for a method of forming a plasma
in accordance with some embodiments of the present invention.
[0016] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. The figures are not drawn to scale
and may be simplified for clarity. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation.
DETAILED DESCRIPTION
[0017] Methods and apparatus for plasma processing are provided
herein. The inventive methods and plasma processing apparatus
advantageously provide a more uniform plasma as compared to
conventional apparatus, thus providing a more uniform processing
result on a substrate being processed with the plasma. For example,
a plasma formed utilizing the inventive plasma apparatus has an
improved electric field distribution, which provides a more uniform
plasma and can be utilized to produce a more uniform process, such
as an etch pattern on a surface of a substrate.
[0018] FIG. 1 depicts a schematic side view of an inductively
coupled plasma reactor (reactor 100) in accordance with some
embodiments of the present invention. The reactor 100 may be
utilized alone or, as a processing module of an integrated
semiconductor substrate processing system, or cluster tool, such as
a CENTURA.RTM. integrated semiconductor wafer processing system,
available from Applied Materials, Inc. of Santa Clara, Calif.
Examples of suitable plasma reactors that may advantageously
benefit from modification in accordance with embodiments of the
present invention include inductively coupled plasma etch reactors
such as the DPS.RTM. line of semiconductor equipment (such as the
DPS.RTM., DPS.RTM. II, DPS.RTM. AE, DPS.RTM. G3 poly etcher,
DPS.RTM. G5, or the like) also available from Applied Materials,
Inc. The above listing of semiconductor equipment is illustrative
only, and other etch reactors, and non-etch equipment (such as CVD
reactors, or other semiconductor processing equipment) may also be
suitably modified in accordance with the present teachings.
[0019] The reactor 100 includes an inductively coupled plasma
apparatus 102 disposed atop a process chamber 104. The inductively
coupled plasma apparatus includes an RF feed structure 106 for
coupling an RF power supply 108 to a plurality of RF coils, e.g., a
first RF coil 110 and a second RF coil 112. The plurality of RF
coils are coaxially disposed proximate the process chamber 104 (for
example, above the process chamber) and are configured to
inductively couple RF power into the process chamber 104 to form a
plasma from process gases provided within the process chamber
104.
[0020] The RF power supply 108 is coupled to the RF feed structure
106 via a match network 114. A power divider 105 may be provided to
adjust the RF power respectively delivered to the first and second
RF coils 110, 112. The power divider 105 may be coupled between the
match network 114 and the RF feed structure 106. Alternatively, the
power divider may be a part of the match network 114, in which case
the match network will have two outputs coupled to the RF feed
structure 106--one corresponding to each RF coil 110, 112. The
power divider is discussed in more detail below in accordance with
the embodiments illustrated in FIG. 4.
[0021] The RF feed structure 106 couples the RF current from the
power divider 116 (or the match network 114 where the power divider
is incorporated therein) to the respective RF coils. In some
embodiments, the RF feed structure 106 may be configured to provide
the RF current to the RF coils in a symmetric manner, such that the
RF current is coupled to each coil in a geometrically symmetric
configuration with respect to a central axis of the RF coils, such
as by a coaxial structure.
[0022] The reactor 100 generally includes the process chamber 104
having a conductive body (wall) 130 and a dielectric lid 120 (that
together define a processing volume), a substrate support pedestal
116 disposed within the processing volume, the inductively coupled
plasma apparatus 102, and a controller 140. The wall 130 is
typically coupled to an electrical ground 134. In some embodiments,
the support pedestal 116 may provide a cathode coupled through a
matching network 124 to a biasing power source 122. The biasing
source 122 may illustratively be a source of up to 1000 W at a
frequency of approximately 13.56 MHz that is capable of producing
either continuous or pulsed power, although other frequencies and
powers may be provided as desired for particular applications. In
other embodiments, the source 122 may be a DC or pulsed DC
source.
[0023] In some embodiments, a link (not shown) may be provided to
couple the RF power supply 108 and the biasing source 122 to
facilitate synchronizing the operation of one source to the other.
Either RF source may be the lead, or master, RF generator, while
the other generator follows, or is the slave. The link may further
facilitate operating the RF power supply 108 and the biasing source
122 in perfect synchronization, or in a desired offset, or phase
difference. The phase control may be provided by circuitry disposed
within either or both of the RF source or within the link between
the RF sources. This phase control between the source and bias RF
generators (e.g., 108, 122) may be provided and controlled
independent of the phase control over the RF current flowing in the
plurality of RF coils coupled to the RF power supply 108. Further
details regarding phase control between the source and bias RF
generators may be found in commonly owned, U.S. patent application
Ser. No. 12/465,319, filed May 13, 2009 by S. Banna, et al., and
entitled, "METHOD AND APPARATUS FOR PULSED PLASMA PROCESSING USING
A TIME RESOLVED TUNING SCHEME FOR RF POWER DELIVERY," which is
hereby incorporated by reference in its entirety.
[0024] In some embodiments, the dielectric lid 120 may be
substantially flat. Other modifications of the chamber 104 may have
other types of lids such as, for example, a dome-shaped lid or
other shapes. The inductively coupled plasma apparatus 102 is
typically disposed above the lid 120 and is configured to
inductively couple RF power into the process chamber 104. The
inductively coupled plasma apparatus 102 includes the first and
second coils 110, 112, disposed above the dielectric lid 120. The
relative position, ratio of diameters of each coil, and/or the
number of turns in each coil can each be adjusted as desired to
control, for example, the profile or density of the plasma being
formed via controlling the inductance on each coil. Each of the
first and second coils 110, 112 is coupled through the matching
network 114 via the RF feed structure 106, to the RF power supply
108. The RF power supply 108 may illustratively be capable of
producing up to 4000 W at a tunable frequency in a range from 50
kHz to 13.56 MHz, although other frequencies and powers may be
provided as desired for particular applications.
[0025] The first and second RF coils 110, 112 can be configured
such that the phase of the RF current flowing through the first RF
coil can be out of phase with respect to the phase of the RF
current flowing through the RF second RF coil. As used herein, the
term "out of phase" can be understood to mean that the RF current
flowing through the first RF coil is flowing in an opposite
direction to the RF current flowing through the second RF coil, or
that the phase of the RF current flowing through the first RF coil
is shifted with respect to the RF current flowing through the
second RF coil.
[0026] For example, in conventional apparatus, both RF coils are
typically wound in the same direction. As such, the RF current is
flowing in the same direction in both coils, either clockwise or
counterclockwise. The same direction of the winding dictates that
the RF current flowing in the two RF coils are always in phase. In
the present invention, the inventors have examined providing RF
current out of phase between the two coils by either external means
or by physically winding one of the coils in the opposite
direction, thus altering the original phase. By controlling the
phase between the coils the inventors have discovered the ability
to reduce and eliminate non-uniform etch results, such as the
M-shape etch pattern, and furthermore to control the processing
(such as etch rate) pattern from center high, to edge high or to a
flat and uniform processing pattern. By providing out of phase RF
current between the coils and by controlling the current ratio
between the inner and outer coil the inventors have provided an
apparatus that facilitates control over the processing pattern to
achieve improved uniformity across the substrate.
[0027] By providing out of phase RF current between the coils, the
apparatus reverses the destructive interference between the
electromagnetic fields generated by each coil to be constructive,
and, therefore, the typical constructive electric field plasma
properties within the reactor may be similarly reversed. For
example, the present apparatus may be configured to increase the
electric field proximate each of the first and second coils and
decrease the electric field between the coils by providing out of
phase RF current flowing along the first and second coils. In some
embodiments, such as where the RF current in each of the coils is
completely out of phase (e.g., reverse current flow or 180 phase
difference) the electric fields may be maximized (or localized)
proximate each of the first and second coils and minimized (or
null) between the coils due to destructive interference between
opposing electric fields. The inventors have discovered that a
plasma formed using such a coil configuration can advantageously
have an improved, e.g., a more uniform, electric field distribution
and that components of the plasma may diffuse into the null region
of the electric field to provide a more uniform plasma.
[0028] In some embodiments, the direction of the RF current flowing
through each coil can be controlled by the direction in which the
coils are wound. For example, as illustrated in FIG. 2, the first
RF coil 110 can be wound in a first direction 202 and the second RF
coil 112 can be wound in a second direction 204 which is opposite
the first direction 202. Accordingly, although the phase of the RF
signal provided by the RF power supply 108 is unaltered, the
opposing winding directions 202, 204 of the first and second RF
coils 110, 112 cause the RF current to be out of phase, e.g., to
flow in opposite directions.
[0029] In some embodiments, a power divider, such as a dividing
capacitor, may be provided between the RF feed structure 106 to
control the relative quantity of RF power provided by the RF power
supply 108 to the respective first and second coils. For example,
as shown in FIG. 1, a power divider 105 may be disposed in the line
coupling the RF feed structure 106 to the RF power supply 108 for
controlling the amount of RF power provided to each coil (thereby
facilitating control of plasma characteristics in zones
corresponding to the first and second coils). In some embodiments,
the power divider 105 may be incorporated into the match network
114. In some embodiments, after the power divider 105, RF current
flows to flows to the RF feed structure 106 where it is distributed
to the first and second RF coils 110, 112. Alternatively, the split
RF current may be fed directly to each of the respective first and
second RF coils.
[0030] By adjusting the power ratio in combination with the phase
of the RF signal flowing through each of the first and second
coils, the inventors have discovered that undesired processing
non-uniformities (such as the M-shape etch profile of a substrate
surface) may be controlled. For example, FIGS. 3A-B illustratively
depict graphs of etch rate profiles generated using conventional
apparatus and an embodiment of the inventive apparatus as disclosed
herein. These graphs illustratively depict data from actual tests
and observations performed by the inventors. FIG. 3A depicts an
etch rate profile graph of the etch rate (axis 310) radially along
a substrate surface (axis 312) for a plurality of power ratios
between the first and second coils in a conventional apparatus
(plots 302A, 304A and 306A). While some control over the etch rate
profile can be achieved by adjusting the power ratio in the
conventional apparatus, as shown in FIG. 3A, the inventors have
discovered that any adjustment of the power ratio still results in
inadequate overall uniformity, and in particular, poor edge profile
tenability (e.g., each power ratio provides a limited effect at the
edge of the etch profile).
[0031] In contrast, FIG. 3B depicts an etch rate profile graph of
the etch rate (axis 310) radially along a substrate surface (axis
312) for a plurality of the same power ratios between the first and
second coils in an apparatus in accordance with embodiments of the
present invention having the RF current flowing through the first
and second RF coils 180 degrees out of phase (plots 302B, 304B and
306B). Specifically, by making the same power ratio adjustments in
the inventive apparatus as shown in FIG. 3B, the inventors have
discovered that a significantly greater degree of uniformity
control can be achieved. In addition, greatly improved edge profile
tunability can be also achieved. As can be seen from the graph in
FIG. 3B, the inventive apparatus can provide a substantially
uniform etch rate profile by tuning the power ratio (e.g., 304B)
and can also provide a significantly greater edge profile
tunability as compared to a conventional apparatus. For example, by
controlling the power ratio in a chamber configured to have RF
current flowing through the two RF coils out of phase, the
uniformity profile can be controlled to provide center high and
edge low etch rates, substantially flat etch rates, or center low
and edge high etch rates. As these results are due to the plasma
uniformity, such control is also transferrable to other processes
or results (such as plasma treatment, deposition, annealing, or the
like) where plasma uniformity provides control over such processes
or results.
[0032] Embodiments of an exemplary RF feed structure 106 that may
be utilized in combination with the out of phase RF coil apparatus
disclosed herein are described below and depicted in further detail
in FIGS. 4A-B. Further details regarding the exemplary RF feed
structure may be found in U.S. Patent Application Ser. No.
61/254,838, filed on Oct. 26, 2009, by Z. Chen, et al., and
entitled "RF FEED STRUCTURE FOR PLASMA PROCESSING," which is hereby
incorporated by reference in its entirety. For example, FIGS. 4A-B
depicts the RF feed structure 106 in accordance with some
embodiments of the present invention. As depicted in FIG. 4A, the
RF feed structure 106 may include a first RF feed 402 and a second
RF feed 404 coaxially disposed with respect to the first RF feed
402. The first RF feed 402 is electrically insulated from the
second RF feed 404. In some embodiments, and as illustrated, the
second RF feed 404 is coaxially disposed about the first RF feed
402, for example, along central axis 401. The first and second RF
feeds 402, 404 may be formed of any suitable conducting material
for coupling RF power to RF coils. Exemplary conducting materials
may include copper, aluminum, alloys thereof, or the like. The
first and second RF feeds 402, 404 may be electrically insulated by
one or more insulating materials, such as air, a fluoropolymer
(such as Teflon.RTM.), polyethylene, or the like.
[0033] The first RF feed 402 and the second RF feed 404 are each
coupled to different ones of the first or second RF coils 110, 112.
In some embodiments, the first RF feed 402 may be coupled to the
first RF coil 110. The first RF feed 402 may include one or more of
a conductive wire, cable, bar, tube, or other suitable conductive
element for coupling RF power. In some embodiments, the cross
section of the first RF feed 402 may be substantially circular. The
first RF feed 402 may include a first end 406 and a second end 407.
The second end 407 may be coupled to the match network 114 (as
shown) or to a power divider (as shown in FIG. 1). For example, as
depicted in FIG. 4A, the match network 114 may include a power
divider 430 having two outputs 432, 434. The second end 407 of the
first RF feed 402 may be coupled to one of the two outputs of the
match network 114 (e.g., 432).
[0034] The first end 406 of the first RF feed 402 may be coupled to
the first coil 110. The first end 406 of the first RF feed 402 may
be coupled to the first coil 110 directly, or via some intervening
supporting structure (a base 408 is shown in FIG. 4A). The base 408
may be a circular or other shape and includes symmetrically
arranged coupling points for coupling the first coil 110 thereto.
For example, in FIG. 4A, two terminals 428 are shown disposed on
opposite sides of the base 408 for coupling to two portions of the
first RF coil via, for example, screws 429 (although any suitable
coupling may be provided, such as clamps, welding, or the
like).
[0035] In some embodiments, and as discussed further below in
relation to FIGS. 5A-B, the first RF coil 110 (and/or the second RF
coil 112) may comprise a plurality of interlineated and
symmetrically arranged stacked coils (e.g., two or more). For
example, the first RF coil 110 may comprise a plurality of
conductors that are wound into a coil, with each conductor
occupying the same cylindrical plane. Each interlineated, stacked
coil may further have a leg 410 extending inwardly therefrom
towards a central axis of the coil. In some embodiments, each leg
extends radially inward from the coil towards the central axis of
the coil. Each leg 410 may be symmetrically arranged about the base
408 and/or the first RF feed 402 with respect to each other (for
example two legs 180 degrees apart, three legs 120 degrees apart,
four legs 90 degrees apart, and the like). In some embodiments,
each leg 410 may be a portion of a respective RF coil conductor
that extends inward to make electrical contact with the first RF
feed 402. In some embodiments, the first RF coil 110 may include a
plurality of conductors each having a leg 410 that extends inwardly
from the coil to couple to the base 408 at respective ones of the
symmetrically arranged coupling points (e.g., terminals 428).
[0036] The second RF feed 404 may be a conductive tube 403
coaxially disposed about the first RF feed 402. The second RF feed
404 may further include a first end 412 proximate the first and
second RF coils 110, 112 and a second end 414 opposite the first
end 412. In some embodiments, the second RF coil 112 may be coupled
to the second RF feed 404 at the first end 412 via a flange 416, or
alternatively, directly to the second RF feed 404 (not shown). The
flange 416 may be circular or other in shape and is coaxially
disposed about the second RF feed 404. The flange 416 may further
include symmetrically arranged coupling points to couple the second
RF coil 112 thereto. For example, in FIG. 4A, two terminals 426 are
shown disposed on opposite sides of the second RF feed 404 for
coupling to two portions of the second RF coil 112 via, for
example, screws 427 (although any suitable coupling may be
provided, such as described above with respect to terminals
428).
[0037] Like the first coil 110, and also discussed further below in
relation to FIGS. 5A-B, the second RF coil 112 may comprise a
plurality of interlineated and symmetrically arranged stacked
coils. Each stacked coil may have a leg 418 extending therefrom for
coupling to the flange 416 at a respective one of the symmetrically
arranged coupling points. Accordingly, each leg 418 may be
symmetrically arranged about the flange 216 and/or the second RF
feed 404.
[0038] The second end 414 of the second RF feed 404 may be coupled
to the match network 114 (as shown) or to a power divider (as shown
in FIG. 1). For example, as depicted in FIG. 4A, the match network
114 includes a power divider 430 having two outputs 432, 434. The
second end 414 of the second RF feed 404 may be coupled to one of
the two outputs of the match network 114 (e.g., 434). The second
end 414 of the second RF feed 404 may be coupled to the match
network 114 via a conductive element 420 (such as a conductive
strap). In some embodiments, the first and second ends 412, 414 of
the second RF feed 404 may be separated by a length 422 sufficient
to limit the effects of any magnetic field asymmetry that may be
caused by the conductive element 420. The required length may
depend upon the RF power intended to be used in the process chamber
104, with more power supplied requiring a greater length. In some
embodiments, the length 422 may be between about 2 to about 8
inches (about 5 to about 20 cm). In some embodiments, the length is
such that a magnetic field formed by flowing RF current through the
first and second RF feeds has substantially no effect on the
symmetry of an electric field formed by flowing RF current through
the first and second coils 110, 112.
[0039] In some embodiments, and as illustrated in FIG. 4B, the
conductive element 420 may be replaced with a disk 424. The disk
424 may be fabricated from the same kinds of materials as the
second RF feed 404 and may be the same or different material as the
second RF feed 404. The disk 424 may be coupled to the second RF
feed 404 proximate the second end 414 thereof. The disk 424 may be
an integral part of the second RF feed 404 (as shown), or
alternatively may be coupled to the second RF feed 404, by any
suitable means that provides a robust electrical connection
therebetween, including but not limited to bolting, welding, press
fit of a lip or extension of the disk about the second RF feed 404,
or the like. The disk 424 may be coaxially disposed about the
second RF feed 404. The disk 424 may be coupled to the match
network 114 or to a power divider in any suitable manner, such as
via a conductive strap or the like. The disk 424 advantageously
provides an electric shield that lessens or eliminates any magnetic
field asymmetry due to the offset outputs from the match network
114 (or from the power divider). Accordingly, when a disk 424 is
utilized for coupling RF power, the length 422 of the second RF
feed 204 may be shorter than when the conductive element 420 is
coupled directly to the second RF feed 404. In such embodiments,
the length 422 may be between about 1 to about 6 inches (about 2 to
about 15 cm).
[0040] FIGS. 5A-B depict a schematic top down view of the
inductively coupled plasma apparatus 102 in accordance with some
embodiments of the present invention. As discussed above, the first
and second coils 110, 112 need not be a singular continuous coil,
and may each be a plurality (e.g., two or more) of interlineated
and symmetrically arranged stacked coil elements. Further, the
second RF coil 112 may be coaxially disposed with respect to the
first RF coil 112. In some embodiments, the second RF coil 112 is
coaxially disposed about the first RF coil 112 as shown in FIGS.
5A-B.
[0041] In some embodiments, and illustrated in FIG. 5A, the first
coil 110 may include two interlineated and symmetrically arranged
stacked first coil elements 502A, 502B and the second coil 112
includes four interlineated and symmetrically arranged stacked
second coil elements 508A, 508B, 508C, and 508D. The first coil
elements 502A, 502B may further include legs 504A, 504B extending
inwardly therefrom and coupled to the first RF feed 402. The legs
504A, 504B are substantially equivalent to the legs 410 discussed
above. The legs 504A, 504B are arranged symmetrically about the
first RF feed 402 (e.g., they are opposing each other). Typically,
RF current may flow from the first RF feed 402 through the legs
502A, 502B into the first coil elements 504A, 504B and ultimately
to grounding posts 506A, 506B coupled respectively to the terminal
ends of the first coil elements 502A, 502B. To preserve symmetry,
for example, such as electric field symmetry in the first and
second coils 110, 112, the ground posts 506A, 506B may be disposed
about the first RF feed structure 402 in a substantially similar
symmetrical orientation as the legs 502A, 502B. For example, and as
illustrated in FIG. 5A, the grounding posts 506A, 506B are disposed
in-line with the legs 502A, 502B.
[0042] Similar to the first coil elements, the second coil elements
508A, 508B, 508C, and 508D may further include legs 510A, 510B,
510C, and 510D extending therefrom and coupled to the second RF
feed 204. The legs 510A, 510B, 510C, and 510D are substantially
equivalent to the legs 418 discussed above. The legs 510A, 510B,
510C, and 510D are arranged symmetrically about the second RF feed
404. Typically, RF current may flow from the second RF feed 404
through the legs 510A, 510B, 510C, and 510D into the second coil
elements 508A, 508B, 508C, and 508D respectively and ultimately to
grounding posts 512A, 512B, 512C, and 512D coupled respectively to
the terminal ends of the second coil elements 508A, 508B, 508C, and
508D. To preserve symmetry, for example, such as electric field
symmetry in the first and second coils 110, 112, the ground posts
512A, 512B, 512C, and 512D may be disposed about the first RF feed
structure 402 in a substantially similar symmetrical orientation as
the legs 510A, 510B, 510C, and 510D. For example, and as
illustrated in FIG. 5A, the grounding posts 512A, 512B, 512C, and
512D are disposed in-line with the legs 510A, 510B, 510C, and 510D,
respectively.
[0043] In some embodiments, and as illustrated in FIG. 5A, the
legs/grounding posts of the first coil 110 may oriented at an angle
with respect to the legs/grounding posts of the second coil 112.
However, this is merely exemplary and it is contemplated that any
symmetrical orientation may be utilized, such as the legs/ground
posts of the first coil 110 disposed in-line with the
legs/grounding posts of the second coil 112.
[0044] In some embodiments, and illustrated in FIG. 5B, the first
coil 110 may include four interlineated and symmetrically arranged
stacked first coil elements 502A, 502B, 502C, and 502D. Like the
first coil elements 502A, 502B, the additional first coil elements
502C, 502D may further include legs 504C, 504D extending therefrom
and coupled to the first RF feed 402. The legs 504C, 504D are
substantially equivalent to the legs 410 discussed above. The legs
504A, 504B, 504C, and 504D are arranged symmetrically about the
first RF feed 402. Like the first coil elements 502A, 502B, the
first coil elements 502C, 502D terminate at grounding posts 506C,
506D disposed in-line with legs 504C, 504D. To preserve symmetry,
for example, such as electric field symmetry in the first and
second coils 110, 112, the ground posts 506A, 506B, 506C, and 506D
may be disposed about the first RF feed structure 402 in a
substantially similar symmetrical orientation as the legs 502A,
502B, 502C, and 502D. For example, and as illustrated in FIG. 5B,
the grounding posts 506A, 506B, 506C, and 506D are disposed in-line
with the legs 502A, 502B, 502C, and 502D, respectively. The second
coil elements 508A, 508B, 508C, and 508D and all components (e.g.,
legs/grounding posts) thereof are the same in FIG. 5B as in FIG. 5A
and described above.
[0045] In some embodiments, and as illustrated in FIG. 5B, the
legs/grounding posts of the first coil 110 are oriented at an angle
with respect to the legs/grounding posts of the second coil 112.
However, this is merely exemplary and it is contemplated that any
symmetrical orientation may be utilized, such as the legs/ground
posts of the first coil 110 disposed in-line with the
legs/grounding posts of the second coil 112.
[0046] Although described above using examples of two or four
stacked elements in each coil, it is contemplated that any number
of coil elements can be utilized with either or both of the first
and second coils 110, 112, such as three, six, or any suitable
number and arrangement that preserves symmetry about the first and
second RF feeds 402, 404. For example, three coil elements may be
provided in a coil each rotated 120 degrees with respect to an
adjacent coil element.
[0047] The embodiments of the first and second coils 110, 112
depicted in FIGS. 5A-B can be utilized with any of the embodiments
for altering the phase between the first and second coils as
described above. For example, each of the first coil elements 502
can be wound in an opposite direction to each of the second coil
elements 508 such that RF current flowing through the first coil
elements is out of phase with RF current flowing through the second
coil elements. Alternatively, when a phase shifter is used, the
first and second coil elements 502, 508 can be wound in the same
direction or in an opposite direction.
[0048] Returning to FIG. 1, optionally, one or more electrodes (not
shown) may be electrically coupled to one of the first or second
coils 110, 112, such as the first coil 110. The one or more
electrodes may be two electrodes disposed between the first coil
110 and the second coil 112 and proximate the dielectric lid 120.
Each electrode may be electrically coupled to either the first coil
110 or the second coil 112, and RF power may be provided to the one
or more electrodes via the RF power supply 108 via the inductive
coil to which they are coupled (e.g., the first coil 110 or the
second coil 112).
[0049] In some embodiments, the one or more electrodes may be
movably coupled to one of the one or more inductive coils to
facilitate the relative positioning of the one or more electrodes
with respect to the dielectric lid 120 and/or with respect to each
other. For example, one or more positioning mechanisms may be
coupled to one or more of the electrodes to control the position
thereof. The positioning mechanisms may be any suitable device,
manual or automated, that can facilitate the positioning of the one
or more electrodes as desired, such as devices including lead
screws, linear bearings, stepper motors, wedges, or the like. The
electrical connectors coupling the one or more electrodes to a
particular inductive coil may be flexible to facilitate such
relative movement. For example, in some embodiments, the electrical
connector may include one or more flexible mechanisms, such as a
braided wire or other conductor. A more detailed description of the
electrodes and their utilization in plasma processing apparatus can
be found in U.S. patent application Ser. No. 12/182,342, filed Jul.
30, 2008, titled "Field Enhanced Inductively Coupled Plasma
(FE-ICP) Reactor," which is herein incorporated by reference in its
entirety.
[0050] A heater element 121 may be disposed atop the dielectric lid
120 to facilitate heating the interior of the process chamber 104.
The heater element 121 may be disposed between the dielectric lid
120 and the first and second coils 110, 112. In some embodiments.
the heater element 121 may include a resistive heating element and
may be coupled to a power supply 123, such as an AC power supply,
configured to provide sufficient energy to control the temperature
of the heater element 121 to be between about 50 to about 100
degrees Celsius. In some embodiments, the heater element 121 may be
an open break heater. In some embodiments, the heater element 121
may comprise a no break heater, such as an annular element, thereby
facilitating uniform plasma formation within the process chamber
104.
[0051] During operation, a substrate 114 (such as a semiconductor
wafer or other substrate suitable for plasma processing) may be
placed on the pedestal 116 and process gases may be supplied from a
gas panel 138 through entry ports 126 to form a gaseous mixture 150
within the process chamber 104. The gaseous mixture 150 may be
ignited into a plasma 155 in the process chamber 104 by applying
power from the plasma source 108 to the first and second coils 110,
112 and optionally, the one or more electrodes (not shown). In some
embodiments, power from the bias source 122 may be also provided to
the pedestal 116. The pressure within the interior of the chamber
104 may be controlled using a throttle valve 127 and a vacuum pump
136. The temperature of the chamber wall 130 may be controlled
using liquid-containing conduits (not shown) that run through the
wall 130.
[0052] The temperature of the wafer 114 may be controlled by
stabilizing a temperature of the support pedestal 116. In one
embodiment, helium gas from a gas source 148 may be provided via a
gas conduit 149 to channels defined between the backside of the
wafer 114 and grooves (not shown) disposed in the pedestal surface.
The helium gas is used to facilitate heat transfer between the
pedestal 116 and the wafer 114. During processing, the pedestal 116
may be heated by a resistive heater (not shown) within the pedestal
to a steady state temperature and the helium gas may facilitate
uniform heating of the wafer 114. Using such thermal control, the
wafer 114 may illustratively be maintained at a temperature of
between 0 and 500 degrees Celsius.
[0053] The controller 140 comprises a central processing unit (CPU)
144, a memory 142, and support circuits 146 for the CPU 144 and
facilitates control of the components of the reactor 100 and, as
such, of methods of forming a plasma, such as discussed herein. The
controller 140 may be one of any form of general-purpose computer
processor that can be used in an industrial setting for controlling
various chambers and sub-processors. The memory, or
computer-readable medium, 142 of the CPU 144 may be one or more of
readily available memory such as random access memory (RAM), read
only memory (ROM), floppy disk, hard disk, or any other form of
digital storage, local or remote. The support circuits 446 are
coupled to the CPU 144 for supporting the processor in a
conventional manner. These circuits include cache, power supplies,
clock circuits, input/output circuitry and subsystems, and the
like. The inventive method may be stored in the memory 142 as
software routine that may be executed or invoked to control the
operation of the reactor 100 in the manner described above. The
software routine may also be stored and/or executed by a second CPU
(not shown) that is remotely located from the hardware being
controlled by the CPU 144.
[0054] FIG. 6 depicts a flow chart of a method for forming a plasma
in accordance with some embodiments of the present invention. The
method 600 is described below in accordance with embodiments of the
invention illustrated in FIGS. 1-3, however, the method 600 can be
applied with any embodiments of the invention described herein.
[0055] The method 600 begins at 602 by providing an RF signal
through a first RF coil, such as the first RF coil 110 (although
the "first RF coil" of the method 600 may be either of the RF coils
discussed above). The RF signal may be provided at any suitable
frequency desired for a particular application. Exemplary
frequencies include but are not limited to, a frequency of between
about 100 kHz to about 60 MHz. The RF signal may be provided at any
suitable power, such as up to about 5000 Watts.
[0056] At 604, the RF signal is provided through a second RF coil,
e.g., the second RF coil 112, coaxially disposed with respect to
the first RF coil such that the RF signal flows through the second
coil out of phase with respect to the flow of the RF signal through
the first coil. Any of the above embodiments may be utilized to
control the phase of the RF current flowing through the first and
second coils. For example, as discussed above, to create an out of
phase condition between the first and second coils, the first and
second coils can be wound in opposite directions, e.g., the first
and second directions 202, 204 as illustrated in FIG. 2.
Alternatively or in combination, a phase shifter, such as phase
shifter 302, or blocking capacitors 302, 304, can be utilized to
shift the phase of the RF current flowing through the first and/or
second RF coils such that the RF current flowing through the first
RF coil is out of phase with the RF current flowing through the
second RF coil. In some embodiments, the phase shifter or blocking
capacitor may shift the phase such that the RF current flowing
through the first RF coil is about 180 degrees out of phase with
the RF current flowing through the second RF coil. However, the RF
current need not be about 180 degrees out of phase, and in some
embodiments, the phase may be between about 0 to about +/-180
degrees out of phase.
[0057] At 606, a plasma, such as the plasma 155, may be formed by
coupling the RF signal provided by the first and second RF coils to
a process gas, such as the gaseous mixture 150, disposed in a
process chamber. The process gas may include any suitable process
gas for forming a plasma. In some embodiments, the RF signal may be
provided at an equal power setting to each of the first and second
RF coils. In some embodiments, the RF signal may be provided at a
fixed or an adjustable power ratio of between about 1:0 to about
0:1 between the first and second RF coils. The plasma may be
maintained for a desired period of time using the same or different
settings of the RF current ratio and/or the phase difference of the
RF current flowing through the first and second RF coils.
[0058] Thus, methods and apparatus for plasma processing are
provided herein. The inventive methods and plasma processing
apparatus advantageous reduces additive electric field properties
between adjacent plasma coils in multi-coil plasma apparatus.
Accordingly, a plasma formed utilizing the inventive plasma
apparatus has an improved electric field distribution, and can be
utilized to produce a smoother etch surface.
[0059] 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.
* * * * *