U.S. patent application number 15/589127 was filed with the patent office on 2017-08-24 for inductively coupled plasma source for plasma processing.
The applicant listed for this patent is Mattson Technology, Inc.. Invention is credited to Andreas Kadavanich, Dongsoo Lee, Vladimir Nagorny.
Application Number | 20170243721 15/589127 |
Document ID | / |
Family ID | 46233023 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170243721 |
Kind Code |
A1 |
Nagorny; Vladimir ; et
al. |
August 24, 2017 |
Inductively Coupled Plasma Source for Plasma Processing
Abstract
Plasma processing apparatus and methods are disclosed.
Embodiments of the present disclosure include a processing chamber
having an interior space operable to receive a process gas, a
substrate holder in the interior of the processing chamber operable
to hold a substrate, and at least one dielectric window. A metal
shield is disposed adjacent the dielectric window. The metal shield
can have a peripheral portion and a central portion. The processing
apparatus includes a primary inductive element disposed external to
the processing chamber adjacent the peripheral portion of the metal
shield. The processing apparatus can further include a secondary
inductive element disposed between the central portion of the metal
shield and the dielectric window. The primary and secondary
inductive elements can perform different functions, can have
different structural configurations, and can be operated at
different frequencies.
Inventors: |
Nagorny; Vladimir; (Tracy,
CA) ; Lee; Dongsoo; (Fremont, US) ;
Kadavanich; Andreas; (Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mattson Technology, Inc. |
Fremont |
CA |
US |
|
|
Family ID: |
46233023 |
Appl. No.: |
15/589127 |
Filed: |
May 8, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13325455 |
Dec 14, 2011 |
9653264 |
|
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15589127 |
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61510732 |
Jul 22, 2011 |
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61424452 |
Dec 17, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/321 20130101;
H01J 37/32119 20130101; H01J 37/32669 20130101; H01J 37/32715
20130101; H01J 2237/334 20130101; H01J 37/32651 20130101; H01J
37/3211 20130101; H01J 37/32449 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32 |
Claims
1-20. (canceled)
21. A plasma processing apparatus, comprising: a processing chamber
having an interior space operable to receive a process gas; a
substrate holder in the interior of the processing chamber operable
to hold a substrate; at least one dielectric window; and a first
inductive element disposed external to the processing chamber and
adjacent the dielectric window, the first inductive element
comprising a coil and a magnetic flux concentrator of ferrite
material; a second inductive element disposed over a peripheral
portion of the processing chamber, the second inductive element
comprising a multi-turn coil; and a grounded metal shield
separating the first inductive element and the second inductive
element.
22. The plasma processing apparatus of claim 21, wherein the
magnetic flux concentrator has a truncated shape.
23. The plasma processing apparatus of claim 21, wherein the
magnetic flux concentrator has an L-shape.
24. The plasma processing apparatus of claim 21, wherein the
dielectric window has a relatively flat central portion and an
angled peripheral side portion.
25. The plasma processing apparatus of claim 24, wherein the second
inductive element is adjacent the angled peripheral side portion of
the dielectric window and the first inductive element is adjacent
the relatively flat central portion of the dielectric window.
26. The plasma processing apparatus of claim 21, wherein the
apparatus further includes a Faraday shield located between the
second inductive element and the dielectric window.
27. The plasma processing apparatus of claim 26, wherein the
Faraday shield is grounded.
28. The plasma processing apparatus of claim 26, wherein the metal
shield and the Faraday shield form a unitary body.
29. The plasma processing apparatus of claim 26, wherein the
Faraday shield comprises a slotted metal shield that reduces
capacitive coupling between the second inductive element and a
plasma formed in the process chamber interior.
30. The plasma processing apparatus of claim 21, wherein the metal
shield is disposed around the first inductive element.
31. The plasma processing apparatus of claim 21, wherein the
dielectric window includes a space in a central portion of the
dielectric window for a showerhead to feed process gas into the
interior space.
32. The plasma processing apparatus of claim 21, further comprising
a first RF generator configured to provide electromagnetic energy
at a first frequency to the first inductive element and a second RF
generator configured to provide electromagnetic energy at a second
frequency to the second inductive element.
33. The plasma processing apparatus of claim 32, wherein the first
frequency is different from the second frequency.
34. The plasma processing apparatus of claim 33, wherein the first
frequency is in the range of about 1.75 MHz to about 2.15 MHz and
the second frequency is about 13.56 MHz.
35. A plasma processing apparatus, comprising: a processing chamber
having an interior space operable to receive a process gas; a
substrate holder in the interior of the processing chamber operable
to hold a substrate; at least one dielectric window, the dielectric
window having a relatively flat central portion and an angled
peripheral side portion; and a first inductive element disposed
external to the processing chamber and adjacent the relatively flat
central portion of the dielectric window, the first inductive
element comprising a coil and a magnetic flux concentrator of
ferrite material; a second inductive element disposed over a
peripheral portion of the processing chamber adjacent the angled
peripheral side portion of the dielectric window, the second
inductive element comprising a multi-turn coil; and a grounded
metal shield separating the first inductive element and the second
inductive element; a Faraday shield located between the second
inductive element and the dielectric window, the Faraday shield and
the metal shield forming a unitary body.
36. The plasma processing apparatus of claim 35, wherein the
magnetic flux concentrator has a truncated shape.
37. The plasma processing apparatus of claim 35, wherein the
magnetic flux concentrator has an L-shape.
38. The plasma processing apparatus of claim 35, wherein the
Faraday shield comprises a slotted metal shield that reduces
capacitive coupling between the second inductive element and a
plasma formed in the process chamber interior.
39. The plasma processing apparatus of claim 35, further comprising
a first RF generator configured to provide electromagnetic energy
at a first frequency to the first inductive element and a second RF
generator configured to provide electromagnetic energy at a second
frequency to the second inductive element, wherein the first
frequency is different from the second frequency.
40. The plasma processing apparatus of claim 39, wherein the first
frequency is in the range of about 1.75 MHz to about 2.15 MHz and
the second frequency is about 13.56 MHz.
Description
PRIORITY CLAIM
[0001] The present application claims priority to U.S. Provisional
Patent Application Ser. No. 61/424,452, filed Dec. 17, 2010, and to
U.S. Provisional Patent Application Ser. No. 61/510,732 filed Jul.
22, 2011, which are incorporated herein by reference for all
purposes.
FIELD
[0002] The present disclosure relates generally to plasma
generation and, more particularly, to an apparatus and method for
processing a substrate using a plasma source.
BACKGROUND
[0003] RF plasmas are used in the manufacture of devices such as
integrated circuits, micromechanical devices, flat panel displays,
and other devices. RF plasma sources used in modern plasma etch
applications are required to provide a high plasma uniformity and a
plurality of plasma controls, including independent plasma profile,
plasma density, and ion energy controls. RF plasma sources
typically must be able to sustain a stable plasma in a variety of
process gases and under a variety of different conditions (e.g. gas
flow, gas pressure, etc.). In addition, it is desirable that RF
plasma sources produce a minimum impact on the environment by
operating with reduced energy demands and reduced EM emission.
[0004] Various plasma sources are known for achieving these
stringent plasma process requirements. Multi-frequency capacitively
coupled plasma (CCP) sources have been used for independent control
of ion energy and plasma density. CCP plasma sources, however, have
some intrinsic problems and limitations. For instance: (a) gas
pressure ranges are typically limited to low pressures; (b)
high-density plasma generation requires very high frequency RF,
causing problems with plasma uniformity, emissions, etc.; (c) there
is interference between higher and lower frequency RF sheaths; (d)
the wafer edge area is prone to severe nonuniformity; and (e) a CCP
source has a narrow process window. Accordingly, CCP sources are
not always suitable for certain plasma process operations.
[0005] Inductively coupled plasma (ICP) sources combined with RF
bias have also been used, for example, to provide independent
control of ion energy and plasma density. ICP sources can easily
produce high-density plasma using standard 13.56 MHz and lower
frequency RF power generators. Indeed, it is known to use
multi-coil ICP sources to provide good plasma control and high
plasma density. For instance, in one known ICP source, two coils
are placed on top of a dielectric window separating plasma from the
air. The two coils are powered with an RF generator and the power
distribution function between the coils is assigned to a matcher.
This arrangement can be very complex and expensive. In addition,
the communication between coils above the dielectric window and in
the plasma makes it difficult to provide true independent control
of power distribution into the plasma. This design also limits the
range of power distribution between coils such that the central
coil still receives power when power to the central coil is not
needed, limiting the operational range of the tool.
[0006] A known multi-coil ICP source is disclosed in U.S. Pat. No.
6,267,074. This ICP source uses three separated coils, three power
generators, multiple gas injectors and provides a complete control
over plasma. The ICP source has, however, three generators, three
matchers and an extremely expensive dielectric window with very
complex shape and multiple channels for gas injection. The capital
cost and maintenance cost of such a system is not justified for
most etch processes.
[0007] Another common problem with ICP sources is a severe
sputtering of a dielectric plate separating an ICP coil from a
process chamber due to RF power capacitive coupling from the coil
to plasma and very high voltage (a few kV per turn) applied to the
coil. The sputtering both affects plasma and increases the capital
cost of the tool and its maintenance cost. Overall process
controllability and, finally, process yield deteriorates.
[0008] Yet another common problem with ICP systems is an azimuthal
nonuniformity caused by the capacitive coupling of the coil. Such
azimuthal nonuniformity can be caused for different reasons. One
reason, for example, is that for secondary electrons emitted from
the surface, the sheath is collisionless. These electrons enter the
plasma with energy strongly dependent on the position from where
the electrons were emitted. Electrons that were emitted near the
ends of a coil have significantly higher energy than those emitted
near the center of a coil or away from the coil. Although these
electrons quickly mix in the volume, they do create noticeable
azimuthal plasma nonuniformity.
[0009] To eliminate both sputtering and azimuthal nonuniformity
caused by a capacitive coupling of a coil, one can use a Faraday
shield as disclosed in U.S. Pat. Nos. 7,232,767, 6,551,447, and
U.S. Patent Application Publication No. 2007/0181257. A Faraday
shield also makes matching the coil to the power generator easier,
more stable and less prone to plasma conditions. However, since a
well-designed Faraday shield absorbs the capacitive component of
the RF, the RF power transfer to the plasma is reduced. Further,
since it is the capacitive component of the RF that initiates the
plasma, a well-designed Faraday shield usually requires additional
means for discharge ignition.
[0010] Some Faraday shield designs can also improve the radial
plasma profile for many etch processes without using an additional
coil. In particular, for many processes the bulk etch rate is
center-fast, even if one uses only a single coil near the edge of
the wafer. For instance, one exemplary known Faraday shield design
selectively blocks any power coupling in the center of the source
to correct for an intrinsic center-fast etch profile. However, this
method of controlling the etch profile is inflexible in that the
Faraday shield has to be redesigned for specific process
chemistries, depending on the inherent etch profile of that
chemistry. By adding a second coil, the etch profile can be
adjusted dynamically, without changing the hardware, providing
greatly increased process flexibility.
[0011] The use of a second coil with a Faraday shield in the center
of a plasma source poses its own difficulties. Because of high RF
voltage and requirements for safe spacing between parts, providing
a second coil that is truly independent of a primary coil is a
difficult task. One also has to provide means for the
synchronization of generators (if using different generators) to
prevent the coils from working against each other, further adding
to the cost of the system.
[0012] The root cause of many problems in ICP sources is that every
coil in any ICP source has the same function and works together in
a similar way as other coils, so that the only differences between
the coils is their respective designated areas of the wafer. Thus,
a need exists for a multi-coil ICP source that avoids the
above-mentioned problems and disadvantages. An ICP source that
includes at least one secondary coil that can have a different
structure from the primary coil and is operable to perform a
different function from the primary coil would be particularly
useful.
SUMMARY
[0013] Aspects and advantages of the invention will be set forth in
part in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0014] One exemplary aspect of the present disclosure is directed
to a method of processing a substrate in a plasma processing
apparatus. The plasma processing apparatus includes a processing
chamber having an interior operable to receive a process gas, a
substrate holder operable to hold a substrate, a first inductive
element disposed over the process chamber interior, and a second
inductive element disposed over the process chamber interior. The
method includes placing a substrate on the substrate holder within
the interior of a processing chamber of a processing apparatus and
admitting a process gas into the interior of the processing
chamber. The method further includes energizing the first inductive
element with electromagnetic energy at a first RF frequency and
energizing the second inductive element with electromagnetic energy
at a second RF frequency to generate a plasma in the interior of
the processing chamber. The first RF frequency for the first
inductive element is selected to be sufficiently different from a
second RF frequency for the second inductive element to reduce
cross-talk between the first inductive element and the second
inductive element in the inductive plasma. The method includes
processing the substrate in the plasma.
[0015] Another exemplary aspect of the present disclosure is
directed to a plasma processing apparatus. The plasma processing
apparatus includes a processing chamber having an interior space
operable to receive a process gas and a substrate holder in the
interior of the processing chamber operable to hold a substrate.
The apparatus further includes at least one dielectric window, and
a first inductive element disposed external to the processing
chamber and adjacent the dielectric window. An RF generator is
configured to provide electromagnetic energy to the inductive
element. The first inductive element has a coil and a magnetic flux
concentrator of ferrite material. The magnetic flux concentrator
has a truncated shape or an L-shape.
[0016] Yet another exemplary aspect of the present disclosure is
directed to an apparatus for processing a substrate in a plasma.
The apparatus includes a processing chamber having an interior
space operable to receive a process gas, a substrate holder in the
interior of the processing chamber operable to hold a substrate,
and at least one dielectric window. The apparatus further includes
a primary inductive element proximate a peripheral portion of the
processing chamber and a secondary inductive element proximate a
central portion of the processing chamber. A metal shield is
disposed around the secondary inductive element such that the metal
shield separates the primary inductive element from the secondary
inductive element. A Faraday shield is located between the first
inductive element and the dielectric window. The metal shield and
the Faraday shield form a unitary body.
[0017] Variations and modifications can be made to these exemplary
embodiments of the present disclosure.
[0018] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] A full and enabling disclosure, including the best mode, to
one of ordinary skill in the art, is set forth more particularly in
the remainder of the specification, including reference to the
accompanying figures, in which:
[0020] FIG. 1 depicts a plasma processing apparatus according to an
exemplary embodiment of the present disclosure;
[0021] FIG. 2 depicts an exemplary inductive element according to
an exemplary embodiment of the present disclosure;
[0022] FIG. 3 depicts an exemplary inductive element according to
an exemplary embodiment of the present disclosure;
[0023] FIG. 4 depicts an exemplary inductive element according to
an exemplary embodiment of the present disclosure;
[0024] FIG. 5 depicts an exemplary inductive element according to
an exemplary embodiment of the present disclosure;
[0025] FIG. 6 depicts an exemplary matching circuit for an
inductive element according to an exemplary embodiment of the
present disclosure;
[0026] FIG. 7 depicts a perspective view of an exemplary unibody
metal shield and Faraday shield according to an exemplary
embodiment of the present disclosure;
[0027] FIG. 8 depicts a plan view of an exemplary Faraday shield
that can be used with an inductive element according to an
exemplary embodiment of the present disclosure; and
[0028] FIG. 9 depicts a plasma processing apparatus according to
another exemplary embodiment of the present disclosure.
[0029] FIG. 10 depicts a plasma processing apparatus according to
another exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION
[0030] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used with
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0031] In general, the present disclosure is directed to a plasma
processing apparatus and method that includes two or more inductive
elements, such as a primary coil and a secondary coil. The primary
coil can be separated from the process chamber by a Faraday shield.
The secondary coil can be separated from the primary coil by an
electromagnetic shield to prevent cross-talk between the coils. In
a particular implementation, different RF frequencies are selected
for use on the first and second inductive elements. The frequencies
are selected to reduce cross-talk between the first and second
inductive elements in the plasma, providing for enhanced
independent control of the inductive elements.
[0032] FIG. 1 depicts a plasma processing apparatus 100 according
to an exemplary embodiment of the present disclosure. The plasma
processing apparatus 100 includes a processing chamber defining an
interior space 102. A pedestal or substrate holder 104 is used to
support a substrate 106, such as a semiconductor wafer, within the
interior space 102. A dielectric window 110 is located above the
substrate holder 104. The dielectric window 110 includes a
relatively flat central portion 112 and an angled peripheral
portion 114. The dielectric window 110 includes a space in the
central portion 112 for a showerhead 120 to feed process gas into
the interior space 102.
[0033] The apparatus 100 further includes a plurality of inductive
elements, such as primary inductive element 130 and secondary
inductive element 140, for generating an inductive plasma in the
interior space 102. The inductive elements 130, 140 can include a
coil or antenna element that when supplied with RF power, induces a
plasma in the process gas in the interior space 102 of plasma
processing apparatus 100. For instance, a first RF generator 160
can be configured to provide electromagnetic energy through a
matching network 162 to the primary inductive element 130. A second
RF generator 170 can be configured to provide electromagnetic
energy through a matching network 172 to the secondary inductive
element 140.
[0034] While the present disclosure makes reference to a primary
inductive and a secondary inductive, those of ordinary skill in the
art, should appreciate that the terms primary and secondary are
used for convenience purposes only. The secondary coil can be
operated independent of the primary coil, and vice versa.
[0035] According to aspects of the present disclosure, the
apparatus 100 can include a metal shield portion 152 disposed
around the secondary inductive element 140. As discussed in more
detail below, metal shield portion 152 separates the primary
inductive element 130 and the secondary inductive element 140 to
reduce cross-talk between the inductive elements 130, 140.
Apparatus 100 can further include a Faraday shield 154 disposed
between the primary inductive element 130 and the dielectric window
130. Faraday shield 154 can be a slotted metal shield that reduces
capacitive coupling between the primary inductive element 154 and
the process chamber 102. As illustrated, Faraday shield 154 can fit
over the angled portion of the dielectric shield 110.
[0036] In a particular embodiment, metal shield 152 and Faraday
shield 154 can form a unitary body 150 for ease of manufacturing
and other purposes. FIG. 7 illustrates a unitary body metal
shield/Faraday shield 150 according to an exemplary embodiment of
the present disclosure. The multi-turn coil of the primary
inductive element 130 can be located adjacent the Faraday shield
portion 154 of the unitary body metal shield/Faraday shield 150.
The secondary inductive element 140 can be located proximate the
metal shield portion 152 of metal shield/Faraday shield unitary
body 150, such as between the metal shield portion 152 and the
dielectric window 110.
[0037] The arrangement of the primary inductive element 130 and the
secondary inductive element 140 on opposite sides of the metal
shield 152 allows the primary inductive element 130 and secondary
inductive element 140 to have distinct structural configurations
and to perform different functions. For instance, the primary
inductive element 130 can include a multi-turn coil located
adjacent a peripheral portion of the process chamber. The primary
inductive element 130 can be used for basic plasma generation and
reliable start during the inherently transient ignition stage. The
primary inductive element 130 can be coupled to a powerful RF
generator and expensive auto-tuning matching network and can be
operated at an increased RF frequency, such as at about 13.56
MHz.
[0038] The secondary inductive element 140 can be used for
corrective and supportive functions and for improving the stability
of the plasma during steady state operation. Since the secondary
inductive element 140 can be used primarily for corrective and
supportive functions and improving stability of the plasma during
steady state operation, the secondary inductive element 140 does
not have to be coupled to as powerful an RF generator as the first
inductive element 130 and can be designed differently and cost
effectively to overcome the difficulties associated with previous
designs. As discussed in detail below, the secondary inductive
element 140 can also be operated at a lower frequency, such as at
about 2 MHz, allowing the secondary inductive element 140 to be
very compact and to fit in a limited space on top of the dielectric
window.
[0039] According to exemplary aspects of the present disclosure,
the primary inductive element 130 and the secondary inductive
element 140 are operated at different frequencies. The frequencies
are sufficiently different to reduce cross-talk between the primary
inductive element 130 and the secondary inductive element 140. For
instance, the frequency applied to the primary inductive element
130 can be at least about 1.5 times greater than the frequency
applied to the secondary inductive element 140. In a particular
embodiment, the frequency applied to the primary inductive element
130 can be about 13.56 MHz and the frequency applied to the
secondary inductive element 140 can be in the range of about 1.75
MHz to about 2.15 MHz. Other suitable frequencies can also be used,
such as about 400 kHz, about 4 MHz, and about 27 MHz. While the
present disclosure is discussed with reference to the primary
inductive element 130 being operated at a higher frequency relative
to the secondary inductive element 140, those of ordinary skill in
the art, using the disclosures provided herein, should understand
that the secondary inductive element 140 could be operated at the
higher frequency without deviating from the scope of the present
disclosure.
[0040] Due to the different frequencies that can be applied to the
primary inductive element 130 and the secondary inductive element
140, there is reduced interference between the inductive elements
130, 140. More particularly, the only interaction in the plasma
between the inductive elements 130, 140 is through plasma density.
Accordingly, there is no need for phase synchronization between the
RF generator 160 coupled to the primary inductive element 130 and
the RF generator 170 coupled to the secondary inductive element
140. Power control is independent between the inductive elements.
Additionally, since the inductive elements 130, 140 are operating
at distinctly different frequencies, it is practical to use
frequency tuning of the RF generators 160, 170 for matching the
power delivery into the plasma, greatly simplifying the design and
cost of any additional matching networks.
[0041] Compared to the primary inductive element 130 operated at
13.56 MHz, the secondary inductive element 140 can be operated at
about 2 MHz and can have a larger number of turns and thus operate
at lower current magnitude
I.sub.coil.varies.P.sub.pl/R.sub.plN,
where I.sub.coil is a coil current, P.sub.pl--is a power deposited
in plasma by the coil, R.sub.pl--is plasma resistance and N--is a
number of turns of the coil. Low current allows usage of a regular
medium gauge wires in the coil, rather than large gauge wires or
copper tubes.
[0042] Due to the lower operation frequency (f), the secondary
inductive element 140 with inductance L does not need to operate at
as high a voltage as a coil operated at a higher frequency of the
same diameter D (assuming it deposits into plasma the same power
P.sub.pl and produces plasma with the same parameters,
R.sub.pl):
V.sub.coil.varies.fLI.sub.coil.varies.fDN.sup.2I.sub.coil.varies.fDN
{square root over (P.sub.pl/R.sub.pl)}
and with smaller diameter the voltage is much smaller than that
used for driving the first coil. Because the secondary inductive
element 140 can be operated at a reduced voltage and current, the
secondary inductive element 140 can have a compact design that can
be embedded into the metal shield 150.
[0043] For instance, as illustrated in FIGS. 2-5, the second
inductive element 140 can include a planar coil 142 and a magnetic
flux concentrator 144. The magnetic flux concentrator 144 is made
from a ferrite material. Use of a magnetic flux concentrator with a
proper coil gives high plasma coupling and good energy transfer
efficiency of the secondary inductive element 140, and
significantly reduces its coupling to the metal shield 150. Use of
a lower frequency, such as about 2 MHz, on the secondary inductive
element 140 increases the skin layer, which also improves plasma
heating efficiency.
[0044] According to particular aspects of the present disclosure,
the magnetic flux concentrator 144 can have various shapes,
depending on the primary requirements or constraints of the
apparatus 100. For instance, if the goal is to have a soft profile
control with a smooth power distribution in plasma (e.g. central
area) and space allows the coil to be a bit wider, then the
magnetic flux concentrator 144 can have a planar shape as
illustrated in FIG. 2 or a truncated shape as illustrated in FIG.
4. If space is limited and high efficiency of the secondary
inductive element 140 is important, or strong localization of power
input into the plasma is important, (e.g. near edge), then it can
be desirable to include a magnetic flux concentrator 144 having a
U-shape with ends facing the dielectric window. In some cases, it
may be desirable to provide asymmetric heating with respect to the
coil position (more localized at one edge of the coil). In these
cases, a magnetic flux concentrator 144 having an L-shape with one
end facing the dielectric window may be desirable. The gas
injection profile of the apparatus 100 may also affect the choice
of shape for the magnetic flux concentrator.
[0045] According to aspects of the present disclosure, the
different inductive elements 130 and 140 can carry different
functions. Specifically, only the primary inductive element 130 has
to carry out the most vital function of the plasma generation
during ignition and providing enough priming for the secondary
inductive element 140. This primary inductive element 130 can
participate in the operation of the ICP tool and should have
coupling to both plasma and the grounded shield to stabilize plasma
potential. The Faraday shield 154 associated with the first
inductive element 130 avoids window sputtering and can be used to
supply the coupling to the ground.
[0046] Additional coils can be operated in the presence of good
plasma priming provided by the primary inductive element 130 and as
such, preferably have good plasma coupling and good energy transfer
efficiency to plasma. A secondary inductive element 140 that
includes a magnetic flux concentrator 144 provides both a good
transfer of magnetic flux to plasma volume and at the same time a
good decoupling of the secondary inductive element 140 from the
surrounding metal shield 150. The use of magnetic flux
concentrators 144 and symmetric driving of the secondary conductive
element 140 further reduces the amplitude of the voltage between
coil ends and surrounding grounded elements. This practically
eliminates sputtering of the dome, but at the same time gives some
small capacitive coupling to plasma, which can be used to assist
ignition.
[0047] However, if capacitive coupling is undesirable, a very
simple and thin Faraday shield can be used in combination with this
secondary inductive element 140, such as the Faraday shield 200
illustrated in FIG. 8. Construction of the secondary inductive
element 140 with a planar coil 142 and ferrite (or similar
non-conductive, high magnetic permeability material) magnetic flux
concentrators 144 allows for the very efficient and low cost design
for Faraday shield 200. The Faraday shield 200 of FIG. 8 can be
simply stamped out of a thin (0.25-0.5 mm) sheet metal. The Faraday
shield 200 includes one or two solid metal portions, a first
portion 210 of solid metal and/or a second portion 240 of solid
metal. A plurality of leaf elements 220 cover the planar coil 142.
Radial spike elements 230 connect the leaf elements 220 with
portions 210 and 240 of the Faraday shield 200.
[0048] Since the leaf elements 220 are parallel to the planar coil
142 and do not cover the magnetic flux concentrator 142, the
leaf-type elements 220 do not interfere with magnetic field and
magnetic flux from the magnetic flux concentrator 144 freely enters
the plasma. On the other hand, the spikes 230 connecting all the
leaf-type elements 220 with surrounding portions 210 and 240, do
cross the flux coming out of the magnetic flux concentrators 144
but they have very small total area to interfere with the magnetic
field. The exemplary Faraday shield of FIG. 8 is easy to install
and to include as part of a process chamber. If grounding of the
shield is preferred, then one can place a thin RF ground spiral on
the first portion 210 and/or second portion 240 of the shield to
connect it to the main electromagnetic shield 150. One possible
placement of the Faraday shield 200 is shown in FIG. 7, indicating
position of elements 210, 220 and 240 in the assembly.
[0049] Because the secondary inductive element 140 can be operated
when good priming is provided by the primary inductive element 140,
the matching of the second inductive element 140 to the source can
be simplified. For instance, the match circuit illustrated in FIG.
6 including a simple transformer matcher with just a few switchable
fixed impedance settings covers a wide range of gases and
operational conditions. In fact, each setting covers a wide range
of process parameters (power, gas pressure, gas flow) for each
combination of gases. The impedance setting does not have to be
changed if the recipe requires changing power or increasing or
decreasing the amount of some gas in the mixture. Matching can be
accomplished entirely by tuning the RF generator frequency. Only
large changes of gas composition (e.g. pure Ar to Oxygen or
SF.sub.6 containing mixture) require change of the impedance
setting. The use of two generators essentially allows a low cost
switching circuit without need to reignite plasma. Since the
primary coil is always "ON", one can always provide a satisfactory
algorithm for switching impedance setting in the secondary coil
with low or zero power applied to that coil.
[0050] An ICP source according to exemplary embodiments of the
present disclosure has shown very robust behavior of the source and
very wide process window. The source can easily ignite and sustain
plasma in most process gases (including "difficult" gases like pure
HBr or SF.sub.6) with significantly lower total power than
otherwise was needed if one used only one coil. One could even
sustain these discharges without any bias power. In fact, the use
of the exemplary inductive element arrangement of the present
disclosure actually showed better stability and efficiency than
sources with only one kind of coil or with multiple coils of
similar structure. Despite numerous attempts, instabilities
associated with discharges in electronegative gases, often observed
in other ICP reactors have not been detected.
[0051] FIG. 9 illustrates an exemplary ICP source 300 according to
another exemplary embodiment of the present disclosure. As
illustrated in FIG. 9. the ICP source 300 includes many similar
elements to the reactor 100 of FIG. 1, including a chamber defining
an interior space 302, a pedestal 304 used to support a substrate
306, a dielectric window 310, and a primary inductive element 330
and a secondary inductive element 340. The dielectric window 310
includes a flat central portion and an angled peripheral
portion.
[0052] The ICP source 300 includes a metal shield 352 separating
the primary inductive element 330 and the secondary inductive
element 340. The metal shield 352 can be disposed around the
secondary inductive element 340. The ICP source 300 can further
include a Faraday shield 354 disposed between the primary inductive
element 330 and the angled peripheral portion of the dielectric
window. In a particular implementation, metal shield 352 and
Faraday shield 354 can form a single unitary body 350.
[0053] The ICP source 300 further includes a third inductive
element 360 adjacent a dielectric window 315. Similar to the
secondary inductive element 340, the third inductive element 360
can include a planar coil and a magnetic flux concentrator. The
magnetic flux concentrator can have a planar shape, U-shape,
L-shape, or truncated shape. The third inductive element 360 can he
located at the periphery of the chamber such that the diameter of
the coil of the third inductive element 360 is greater than the
diameter of the coil of the primary inductive element 330. A
plurality of feed gas ports 322 can be used to feed process gas
into the chamber interior 302 proximate the location of the third
inductive element 360. The third inductive element 360 can have a
metal shield portion 356 separating the third inductive element 360
from the first inductive element 330. A Faraday shield 200 can be
disposed between the third inductive element 360 and the dielectric
window 315.
[0054] FIG. 10 illustrates an exemplary ICP source 400 according to
another exemplary embodiment of the present disclosure. ICP source
400 is similar to ICP source 300 of FIG. 9 except that ICP source
400 includes a flat ceiling as opposed to the frusto-conical
ceiling of ICP source 300. As shown in FIG. 10, the ICP source 400
includes a chamber defining an interior space 402, a pedestal 404
used to support a substrate 406, a dielectric window 410, and a
primary inductive element 430 and a secondary inductive element
440.
[0055] The ICP source 400 further includes a third inductive
element 460 adjacent dielectric window 410. Similar to the
secondary inductive element 440, the third inductive element 460
can include a planar coil and a magnetic flux concentrator. The
magnetic flux concentrator can have a planar shape, U-shape,
L-shape, or truncated shape. The third inductive element 460 can be
located at the periphery of the chamber such that the diameter of
the coil of the third inductive element 460 is greater than the
diameter of the coil of the first inductive element 430. A
plurality of feed gas ports 422 can be used to feed process gas
into the chamber interior 402 proximate the location of the
inductive element 460, 440. The third inductive element 460 can
have a metal shield portion 456 separating the third inductive
element 460 from the primary inductive element 430. Optionally, a
Faraday shield can be disposed between the third inductive element
460 and the dielectric window 415.
[0056] The dielectric window 410 is relatively flat across its
entire width and can include thicker portions 415 proximate the
primary inductive element 430. The apparatus can also include a
slotted Faraday shield 455 disposed between the primary inductive
element 430 and the thicker portions 415 of dielectric window 410.
One or more metal shields can be used to separate the various
inductive elements 430, 440, and 460 of ICP source 400. For
instance, a metal shield 452 surrounding secondary inductive
element 440 can be used to separate the secondary inductive element
440 from the primary inductive element 430 and the third inductive
element 460. A metal shield 456 can be used to separate the third
inductive element 460 from the secondary inductive element 440 and
the primary inductive element 430, in a particular embodiment,
metal shields 452 and 456 can form a unitary body 450.
[0057] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
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