U.S. patent application number 15/197060 was filed with the patent office on 2018-01-04 for selective etch using material modification and rf pulsing.
This patent application is currently assigned to Applied Materials, Inc.. The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to Viachslav Babayan, Bhargav Citla, Srinivas Nemani, Michael Stowell, Chentsau Ying.
Application Number | 20180005850 15/197060 |
Document ID | / |
Family ID | 60785206 |
Filed Date | 2018-01-04 |
United States Patent
Application |
20180005850 |
Kind Code |
A1 |
Citla; Bhargav ; et
al. |
January 4, 2018 |
SELECTIVE ETCH USING MATERIAL MODIFICATION AND RF PULSING
Abstract
Semiconductor systems and methods may include methods of
performing selective etches that include modifying a material on a
semiconductor substrate. The substrate may have at least two
exposed materials on a surface of the semiconductor substrate. The
methods may include forming a low-power plasma within a processing
chamber housing the semiconductor substrate. The low-power plasma
may be a radio-frequency ("RF") plasma, which may be at least
partially formed by an RF bias power operating between about 10 W
and about 100 W in embodiments. The RF bias power may also be
pulsed at a frequency below about 5,000 Hz. The methods may also
include etching one of the at least two exposed materials on the
surface of the semiconductor substrate at a higher etch rate than a
second of the at least two exposed materials on the surface of the
semiconductor substrate.
Inventors: |
Citla; Bhargav; (Fremont,
CA) ; Ying; Chentsau; (Cupertino, CA) ;
Nemani; Srinivas; (Sunnyvale, CA) ; Babayan;
Viachslav; (Sunnyvale, CA) ; Stowell; Michael;
(Loveland, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
60785206 |
Appl. No.: |
15/197060 |
Filed: |
June 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/3115 20130101;
H01L 21/3105 20130101; H01L 21/31116 20130101; H01J 2237/334
20130101; H01L 21/6831 20130101; H01L 21/6833 20130101; H01L
21/68735 20130101; H01J 37/32146 20130101; H01L 21/67069 20130101;
H01J 37/32706 20130101 |
International
Class: |
H01L 21/67 20060101
H01L021/67; H01L 21/683 20060101 H01L021/683; H01L 21/3115 20060101
H01L021/3115; H01L 21/687 20060101 H01L021/687; H01L 21/311
20060101 H01L021/311 |
Claims
1. A method of performing a selective etch, the method comprising:
modifying a material on a semiconductor substrate having at least
two exposed materials on a surface of the semiconductor substrate;
forming a low-power plasma within a processing chamber housing the
semiconductor substrate, wherein the low-power plasma is a
radio-frequency (RF) plasma, and wherein the low-power plasma is at
least partially formed by an RF bias power operating at between
about 10 W and 100 W and at a pulsing frequency below about 5,000
Hz; and etching one of the at least two exposed materials on the
surface of the semiconductor substrate at a higher rate than a
second of the at least two exposed materials on the surface of the
semiconductor substrate.
2. The method of claim 1, wherein the modifying comprises forming a
plasma from a precursor within the processing chamber with the RF
bias power.
3. The method of claim 2, wherein the precursor is selected from
the group consisting of oxygen, hydrogen, or helium.
4. The method of claim 1, wherein each of the at least two exposed
materials on the surface of the semiconductor substrate are
selected from the group consisting of silicon oxide, silicon
nitride, silicon carbide, and silicon oxycarbide.
5. The method of claim 1, wherein the RF bias power at least
partially forming the low-power plasma operates at a duty cycle
below about 50%.
6. The method of claim 1, wherein forming the low-power plasma
further comprises utilizing an RF source power below about 100
W.
7. The method of claim 1, wherein forming the low-power plasma
further comprises utilizing a pulsed DC power.
8. The method of claim 7, wherein the pulsed DC power is applied to
a bipolar electrostatic chuck supporting the semiconductor
substrate.
9. The method of claim 7, wherein the pulsed DC power is applied to
a conductive ring embedded in a shield ring of a pedestal
supporting the semiconductor substrate or embedded in a showerhead
within the processing chamber.
10. A method of removing material from a semiconductor substrate,
the method comprising: modifying a material on a semiconductor
substrate having at least two exposed materials on a surface of the
semiconductor substrate, wherein the modifying comprises forming a
plasma from a precursor with an RF bias power to generate plasma
effluents that modify the material; forming a low-power plasma
within a processing chamber housing the semiconductor substrate,
wherein the low-power plasma is a radio-frequency (RF) plasma, and
wherein the low-power plasma is formed by a pulsed RF bias power
operating at between about 20 W and 50 W at a pulsing frequency
between about 500 Hz and about 2,000 Hz at a duty cycle of between
about 20% and 50%; operating a DC pulsed power on an alternating
frequency with the RF bias power pulsing; and etching one of the at
least two exposed materials on the surface of the semiconductor
substrate at a selectivity of at least about 20:1 with respect to a
second of the at least two exposed materials on the surface of the
semiconductor substrate.
11. The method of claim 10, wherein the modifying comprises a
chemical modification causing a chemical change to the material on
the semiconductor substrate.
12. The method of claim 10, wherein the modifying comprises a
physical modification utilizing an inert precursor.
13. The method of claim 12, wherein the physical modification
comprises damaging bonds of the material on the semiconductor
substrate with ions of the inert precursor.
14. The method of claim 10, wherein forming the low-power plasma
further comprises utilizing an RF source power operating up to
about 100 W.
15. A substrate processing chamber comprising: a pedestal
configured to support a semiconductor substrate; an RF bias power
electrically coupled with the pedestal and configured to generate a
plasma within the processing chamber at a power of between about 20
W and about 50 W, wherein the RF bias power is a pulsing power
configured to pulse at a frequency below about 5,000 Hz; and a DC
pulsing power electrically coupled with the substrate processing
chamber and configured to produce priming particles for the RF bias
plasma.
16. The substrate processing chamber of claim 15, wherein the DC
pulsing power supply is configured to pulse at a frequency to
produce priming particles without developing a plasma sheath.
17. The substrate processing chamber of claim 16, wherein the DC
pulsing power supply is configured to be pulsed on for a duration
of 100 microseconds or less at a duty cycle of less than about
50%.
18. The substrate processing chamber of claim 15, wherein the
pedestal comprises a bipolar electrostatic chuck, and wherein the
DC pulsing power is applied to electrical ground of the bipolar
electrostatic chuck.
19. The substrate processing chamber of claim 15, wherein the
pedestal comprises an electrostatic chuck, and wherein the DC
pulsing power is electrically coupled with a conductive ring
coupled with the pedestal, wherein the conductive ring is
electrically decoupled from the electrostatic chuck and the RF
bias.
20. The substrate processing chamber of claim 15, wherein the DC
pulsing power is electrically coupled with a conductive ring
embedded in a showerhead within the substrate processing chamber.
Description
TECHNICAL FIELD
[0001] The present technology relates to systems and methods for
processing semiconductor materials. More specifically, the present
technology relates to semiconductor material modifications and
hardware modifications for producing a low-power plasma.
BACKGROUND
[0002] Integrated circuits are made possible by processes which
produce intricately patterned material layers on substrate
surfaces. Producing patterned material on a substrate requires
controlled methods for applying and removing material. For removal,
chemical etching is used for a variety of purposes including
transferring a pattern in photoresist into underlying layers,
thinning layers, or thinning lateral dimensions of features already
present on the surface. Often it is desirable to have an etch
process that etches one material faster than another facilitating,
for example, a pattern transfer process. Such an etch process is
said to be selective to the first material. As a result of the
diversity of materials, circuits, and processes, etch processes
have been developed with a selectivity towards a variety of
materials.
[0003] Etch processes may be termed wet or dry based on the
materials used in the process. A wet HF etch preferentially removes
silicon oxide over other dielectrics and materials. However, wet
processes may have difficulty penetrating some constrained trenches
and also may sometimes deform the remaining material. Dry etches
produced in local plasmas formed within the substrate processing
region can penetrate more constrained trenches and exhibit less
deformation of delicate remaining structures. However, local
plasmas may damage the substrate through the production of electric
arcs as they discharge. Additionally, plasma effluents can damage
chamber components that may require replacement or treatment.
[0004] Thus, there is a need for improved systems and methods that
can be used to produce high quality devices and structures. These
and other needs are addressed by the present technology.
SUMMARY
[0005] Semiconductor systems and methods may include methods of
performing selective etches that include modifying a material on a
semiconductor substrate. The substrate may have at least two
exposed materials on a surface of the semiconductor substrate. The
methods may include forming a low-power plasma within a processing
chamber housing the semiconductor substrate. The low-power plasma
may be a radio-frequency ("RF") plasma, which may be at least
partially formed by an RF bias power operating between about 10 W
and about 100 W in embodiments. The RF bias power may also be
pulsed at a frequency below about 5,000 Hz. The methods may also
include etching one of the at least two exposed materials on the
surface of the semiconductor substrate at a higher etch rate than a
second of the at least two exposed materials on the surface of the
semiconductor substrate.
[0006] In embodiments the modifying operation may include forming a
plasma from a precursor within the processing chamber with the RF
bias power. The precursor may be selected from the group consisting
of oxygen, hydrogen, or helium in embodiments. Additionally, each
of the at least two exposed materials on the surface of the
semiconductor substrate may be selected from the group consisting
of silicon oxide, silicon nitride, silicon carbide, and silicon
oxycarbide.
[0007] For the etching operation, the RF bias power may at least
partially form the low-power plasma and operate at a duty cycle
below about 50%. Also, forming the low-power plasma may further
include utilizing an RF source power below about 100 W. In
embodiments, forming the low-power plasma may also include
utilizing a pulsed DC power. The pulsed DC power may be applied to
a bipolar electrostatic chuck supporting the semiconductor
substrate. In embodiments, the pulsed DC power may be applied to a
conductive ring embedded in a shield ring of a pedestal supporting
the semiconductor substrate or coupled with a showerhead within the
processing chamber.
[0008] The present technology also includes methods of removing
material from a semiconductor substrate. The methods may include
modifying a material on a semiconductor substrate having at least
two exposed materials on a surface of the semiconductor substrate.
The modifying may include forming a plasma from a precursor with an
RF bias power to generate plasma effluents that modify the
material. The methods may also include forming a low-power plasma
within a processing chamber housing the semiconductor substrate.
The low-power plasma may be a radio-frequency (RF) plasma in
embodiments. The low-power plasma may be formed by a pulsed RF bias
power operating at between about 20 W and 50 W at a pulsing
frequency between about 500 Hz and about 2,000 Hz. The pulsed RF
bias power may be operated at a duty cycle of between about 20% and
50% as well. The methods may include operating a DC pulsed power on
an alternating frequency with the RF bias power pulsing. The
methods may further include etching one of the at least two exposed
materials on the surface of the semiconductor substrate at a
selectivity of at least about 20:1 with respect to a second of the
at least two exposed materials on the surface of the semiconductor
substrate.
[0009] In the methods, the modifying operation may include a
chemical modification causing a chemical change to the material on
the semiconductor substrate. The modifying may also include a
physical modification utilizing an inert precursor. In embodiments,
the physical modification may include damaging bonds of the
material on the semiconductor substrate with ions of the inert
precursor. The forming the low-power plasma operation may further
include utilizing an RF source power operating up to about 100
W.
[0010] The present technology also includes substrate processing
chambers including a pedestal configured to support a semiconductor
substrate. The chambers may include an RF bias power electrically
coupled with the pedestal and configured to generate a plasma
within the processing chamber at a power of between about 20 W and
about 50 W in embodiments. The RF bias power may be a pulsing power
configured to pulse at a frequency below about 5,000 Hz. The
substrate processing chambers may further include a DC pulsing
power electrically coupled with the substrate processing chamber
and configured to produce priming particles for the RF bias plasma.
Additionally, the DC pulsing power supply may be configured to
pulse at a frequency to produce priming particles without
developing a plasma sheath.
[0011] In embodiments, the DC pulsing power supply may be
configured to be pulsed on for a duration of 100 microseconds or
less at a duty cycle of less than about 50%. Additionally, in
embodiments the pedestal may be a bipolar electrostatic chuck, and
the DC pulsing power may be applied to electrical ground of the
bipolar electrostatic chuck. In embodiments the DC pulsing power
may be electrically coupled with a conductive ring coupled with the
pedestal, and the conductive ring may be electrically decoupled
from the electrostatic chuck and the RF bias. In embodiments the DC
pulsing power may also be electrically coupled with a conductive
ring embedded in a showerhead within the substrate processing
chamber.
[0012] Such technology may provide numerous benefits over
conventional techniques. For example, the technology may allow
improved selectivity of etching operations due to, for example, the
material modifications. Additionally, the low-power plasmas of the
present technology may produce improved feature profiles over
conventional techniques, and allow improved front end and back end
processing with enhanced plasma control. These and other
embodiments, along with many of their advantages and features, are
described in more detail in conjunction with the below description
and attached figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A further understanding of the nature and advantages of the
disclosed embodiments may be realized by reference to the remaining
portions of the specification and the drawings.
[0014] FIG. 1 illustrates a method of etching a substrate according
to embodiments of the present technology.
[0015] FIG. 2 shows a graph illustrating the additive effects of
material modification and low-power plasma according to embodiments
of the present technology.
[0016] FIG. 3 shows imaging of an etch process performed according
to embodiments of the present technology.
[0017] FIG. 4 shows a chart illustrating etch rates of various
materials with and without treatments according to embodiments of
the present technology.
[0018] FIG. 5 shows a chart illustrating etch rates of silicon
oxycarbide and silicon carbide with and without treatments
according to embodiments of the present technology.
[0019] FIG. 6 shows a partial schematic illustration of a
controller providing DC pulse to an electrostatic chuck according
to embodiments of the present technology.
[0020] FIG. 7 shows a partial schematic illustration of a
controller providing DC pulse to a conductor coupled with a
pedestal structure within a processing chamber according to
embodiments of the present technology.
[0021] FIG. 8 shows a partial schematic illustration of a
controller providing DC pulse to a conductor coupled with a
showerhead of a processing chamber according to embodiments of the
present technology.
[0022] In the appended figures, similar components and/or features
may have the same numerical reference label. Further, various
components of the same type may be distinguished by following the
reference label by a letter that distinguishes among the similar
components and/or features. If only the first numerical reference
label is used in the specification, the description is applicable
to any one of the similar components and/or features having the
same first numerical reference label irrespective of the letter
suffix.
DETAILED DESCRIPTION
[0023] In semiconductor processing, etching may be performed for a
number of reasons. In dry etching, precursors may be flowed through
plasma to produce radical plasma effluents for etching various
semiconductor materials. The plasma effluents include ions directed
to the surface of the substrate and materials to be etched. In
certain etching operations, such as with reactive-ion etching, the
ions are directed to the surface of the materials, and based on the
energy involved can sputter the materials from the surface of the
substrate. Other etching operations are designed with a goal
towards removing one material faster than a second material, often
called a selective etch. In order to enhance selectivity, one
approach may include reducing the sputtering component of an
etching operation. This may be achieved in part by reducing the
plasma power in order to reduce the electron temperature.
Selectivity may become increasingly critical as feature size
reduces. The higher the selectivity, the less material that is
meant to be maintained may be formed as a buffer for the target
dimensions of the final product. Even conventionally higher
selectivities may be unsuitable as feature sizes continue to
reduce. For example, if even a few nanometers is removed from
materials meant to be maintained, device performance may be
negatively impacted.
[0024] Plasma may be produced in a number of ways including, for
example, with a radio-frequency ("RF") bias electrically connected
to a pedestal supporting a substrate. This bias power may be used
in conjunction with or alternatively to an RF source coupled with
portions of the chamber, or may work in conjunction with an
inductively-coupled plasma source, a capactively-coupled plasma
source, a microwave source, or any other plasma source that may
additionally be used to produce plasma effluents. By utilizing a
bias power in lieu of or in addition to a source power,
directionality may be provided to the ions to provide more of an
anisotropic, or orientation dependent etch. However, as ion energy
increases, sputtering may also increase. Because sputtering may be
more material independent, it can reduce selectivity between
materials where only one is desired to be removed. Accordingly, a
goal may be to reduce the plasma power on bias to reduce sputtering
in an attempt to improve selectivity.
[0025] Conventional technologies may reduce the plasma power at the
source or the bias, but are limited in the degree to which the bias
power may be reduced both from the perspective of striking a plasma
as well as in producing an etch. In order to strike a plasma, the
power must exceed the breakdown voltage of the fluid from which
plasma is produced. For conventional sputtering and pulsed-etch
operations, glow discharge is often produced around, for example,
500 V and at a power of several thousand Watts in a low current,
medium voltage regime. These power levels, however, will provide
increased ion energy and concomitant sputtering of materials, which
may lead to lower selectivity. If plasma power is lowered to
further reduce sputtering, it may be difficult to generate or
sustain a plasma at all, especially with a pulsed plasma power.
Additionally, if the bias power is reduced too far, although
sputtering may be resolved, overall etching may be reduced to
zero.
[0026] The present technology overcomes many of these issues by
producing a low-power RF plasma that is pulsed. Conventional
so-called low-power plasmas may be produced at up to a few hundred
Watts of source power and at a pulsing frequency in the megahertz
range. These power ranges are unable to produce the selectivities
of the present technology because the sputtering component of these
plamsas is still too pronounced. The present technology, on the
other hand, may produce plasmas at a variety of chamber conditions
with a pulsed RF bias operating below 100 Watts, at a duty cycle
down to about 20%, and at a pulsing frequency down to about 500 Hz.
In this operating regime, sputtering may be reduced or
substantially eliminated and etch selectivies may be produced that
may be up to an order of magnitude improvement over conventional
technologies. The present technology may involve a combination of
enhancing selectivity via material modification and performing a
low-power etch. These processes may enhance overall selectivity by
reducing the amount of materials meant to be maintained both by
reducing the amount etched in relation to other materials, as well
as by reducing any plasma effects that may sputter or impact the
materials negatively.
[0027] Although the following description will routinely identify
etching operations, it is to be understood that the techniques may
be applied more broadly. The system and operating methods may
additionally by applied to deposition, cleaning, or any other
plasma operations that may benefit from a low-power plasma as
described. Accordingly, the description is not intended to limit
the applications only to the examples described throughout the
specification.
[0028] FIG. 1 illustrates a method 100 of etching a substrate
according to embodiments of the present technology. Optional
operations may be performed prior to the noted method operations
including patterning, film formation, or a variety of other known
process operations. The method may include modifying a material on
a semiconductor substrate at operation 110. The substrate may have
at least two exposed materials on a surface of the semiconductor
substrate, and may have three, four, five, six, or more different
materials exposed. Additionally, one or more materials may be
initially covered prior to the selective etching method 100 but
then exposed by the operations, and thus one or more of the exposed
films may be exposed during the etching operation in embodiments.
In embodiments, removal of one or more of these materials may be
sought.
[0029] The method may also include forming a low-power plasma
within a processing chamber housing the semiconductor substrate at
operation 120. The low-power plasma may be a radio-frequency ("RF")
plasma in embodiments, although other plasma formations may
similarly be encompassed. The low-power plasma may be at least
partially formed by an RF bias power operating at between about 10
W and 100 W in embodiments. The RF bias power may be pulsed, and
may be operated at a pulsing frequency below about 5,000 Hz in
embodiments. The method may further include etching one or more of
the at least two exposed materials on the surface of the
semiconductor substrate at operation 130. The etching of one or
more of the at least two exposed materials may be at a higher rate
than a second of the at least two exposed materials on the surface
of the semiconductor substrate in embodiments.
[0030] The modifying operation may be tuned in any number of ways
based on the materials on the surface of the substrate, and may be
based on an identification of properties of the materials and how
they may differ from other materials on the substrate surface. For
example, the modifying operations may initially identify
differences in density, chemical structure, reactive nature, or any
other characteristics between films that may be utilized. The
modification to one or more of the materials may be performed to
enhance or produce differences between the films that may be
exploited in an etching operation. The modification may be
performed in embodiments by exposing the materials to one or more
precursors. In embodiments, the precursors may or may not be
excited prior to interacting with the exposed materials. In
embodiments, the modifying may include forming a plasma from a
precursor within the processing chamber. The plasma may be from
between about 50 W to about 300 W depending on the film being
modified. For example, films exhibiting a higher density may
benefit from a higher plasma power in embodiments. The plasma may
be produced with a source power or a bias power in embodiments, as
well as with a combination of the two in order to generate plasma
effluents that modify one or more of the exposed materials. In
embodiments, the plasma may be formed with an RF bias power.
[0031] The precursor utilized in the operation may include one or
more precursors based on the type of modification being performed.
The precursors may include one or more precursors intended to react
with the materials in one form or another, or may include one or
more precursors intended to physically alter one or more of the
exposed materials. A combination of precursors having either or
both of these effects may also be utilized in embodiments. In
examples, the precursors may be selected from the group of elements
including noble or inert elements, such as helium, neon, argon,
krypton, xenon, and radon. The precursors may also be selected from
halogens including fluorine, chlorine, bromine, iodine, and
astatine, in embodiments. The precursors may also be selected from
the chalcogens including oxygen, as well as a variety of other
reactive and non-reactive precursors including hydrogen, for
example.
[0032] As noted above, the modifying operation may include either
or both of a chemical modification or a physical modification. A
chemical modification may cause a chemical change to one or more of
the materials on the semiconductor substrate. The chemical change
may include a reaction such as, for example, producing an oxide of
a material layer in embodiments. The chemical change may also
adjust bonding structures of the materials, or may chemically alter
atoms or molecules of the material, such as, for example, by
removing electrons. The chemical modification may also involve
densifying a material or film that is to be maintained on the
surface of the substrate in relation to an additional material to
be removed. Physical modification may be performed with an inert
precursor that does not react with exposed materials on the
substrate. For example, physical modification may involve damaging
bonds of one or more of the materials on the semiconductor
substrate with ions of the inert precursor. It is to be understood
that the modification may involve a combination of chemical and
physical modification, and individual precursors utilized may cause
an amount of both physical and chemical modification to occur.
[0033] The materials on the surface of the semiconductor substrate
may include a variety of materials used in various semiconductor
processing. The materials may include metals, dielectrics, etch
stop layers, and substrate materials that may include any of a
number of elements commonly understood in semiconductor processing.
For example, the materials may include metals such as copper,
tungsten, titanium, or other metals or metal-containing layers. The
materials may also include silicon-containing materials such as
silicon oxide, silicon nitride, polysilicon, silicon carbide,
silicon oxycarbide, silicon carbonitride, or materials based on
other semiconductor base materials, such as, for example,
gallium.
[0034] In embodiments, the low-power plasma utilized in the etching
operation may be at least partially produced from an RF bias power
electrically coupled with a pedestal on which the substrate is
supported. The bias power may be operated at a power of from about
1 W to about 500 W in embodiments. The bias power may also be
operated from about 10 Watts to about 250 Watts, from about 15
Watts to about 200 Watts, from about 20 Watts to about 150 Watts,
from about 20 Watts to about 100 Watts, or from about 20 Watts to
about 50 Watts in embodiments. The bias power may be operated in
this range which may provide benefits of reducing sputtering, while
still striking a plasma and producing etch results. For example, as
power levels increase, sputtering may increase as well due to
increased ion energy, and so the power level may be maintained
below about 100 Watts in embodiments. On the other hand, the power
level may be maintained above about 20 Watts in embodiments, as
levels below this threshold may have reduced etching capacity or
ability to strike a plasma. These parameters may also be dependent
to a degree on chamber conditions including pressure and
temperature, but may still generate stable plasma under pulsing
conditions utilizing the technology discussed in more detail
below.
[0035] The RF bias power may be operated at a low duty cycle and
pulsing frequency in order to generate the low-power plasma. The
duty cycle may be below about 75% in embodiments, and may be below
about 70%, below about 65%, below about 60%, below about 55%, below
about 50%, below about 45%, below about 40%, below about 35%, below
about 30%, below about 25%, below about 20%, below about 15%, or
below about 10% in embodiments. The RF bias pulsing duty cycle may
also be operated with a duty cycle between about 10% and about 60%,
or between about 20% and 50% in embodiments for similar reasons of
maintaining lower ion energy while still having enough on-time to
generate stable plasma.
[0036] The frequency of pulsing for the RF bias may be below about
10 kHz in embodiments. The frequency of pulsing for the RF bias may
also be below about 9,000 Hz, below about 8,000 Hz, below about
7,000 Hz, below about 6,000 Hz, below about 5,000 Hz, below about
4,500 Hz, below about 4,000 Hz, below about 3,500 Hz, below about
3,000 Hz, below about 2,500 Hz, below about 2,000 Hz, below about
1,500 Hz, below about 1,000 Hz, below about 750 Hz, or below about
500 Hz in embodiments. The pulsing frequency may also be maintained
between about 500 Hz and about 5,000 Hz in embodiments or about 500
Hz and about 2,000 Hz in embodiments. The frequency of the bias
pulsing may affect the dissociation of the plasma precursors, and
thus by adjusting the frequency, the dissociation may be
adjusted.
[0037] In addition to the RF bias power, an RF source power may be
used in embodiments. The RF source power may be used in the etching
operation with a power up to about 1,000 W or less, and may be
operated with a power up to about 500 W, or up to about 100 W in
embodiments. The RF source power may be operated below about 100 W
in embodiments, and may be operated between about 0 W and 100 W in
embodiments. Different precursors may benefit from the addition of
RF source, while other precursors may benefit from the lack of RF
source power. For example, RF source may increase polymer
dissociation, so for certain precursors including, for example
C.sub.4F.sub.8 and C.sub.4F.sub.6, source power may dissociate the
polymer and deposit carbon material on the substrate impeding the
etch operation. Accordingly, using a low or no RF source may
improve etching in some embodiments. In embodiments a variety of
precursors may be utilized in the etching operation depending on
the type of film being etched. Exemplary precursors that may be
used include C.sub.4F.sub.8, C.sub.4F.sub.6, CF.sub.4, Cl.sub.2,
CH.sub.2F.sub.2, O.sub.2, N.sub.2, as well as any other precursors
that may provide etchant characteristics to remove the target
material.
[0038] The RF bias conditions previously discussed may pose
difficulties in controlling the plasma sheath or maintaining
homogeneity of the sheath in embodiments. However, the conditions
may aid in minimizing sputtering during the etching processes.
Accordingly, the present technology further seeks to gain control
over operating plasmas at low power that may not be assisted by
magnetics or associated components. As pressures and operating
conditions are adjusted for particular processes, plasmas may be
more difficult to strike under these conditions. Plasma generation
or gas discharge may in part depend on priming particles or
creating energized particles as a precursor to breakdown. These
energized particles are generated to accelerate discharge, which
may reduce the needed firing voltage. During a pulsing power
operation such as that previously discussed, including an
additional energy source to produce priming particles and to
maintain electrons in the plasma feedback loop may aid in the
control of plasma generation at low power during a variety of
processing conditions. By providing the additional energy source,
plasma may then be struck at low or lower than normal power levels
such as those described above. The present technology provides
additional sources of energy in embodiments to return energetic
particles back into the plasma priming loop.
[0039] A variety of additional energy sources may be utilized in
the present technology, and in one example may include a pulsed DC
power. The pulsed DC power may be connected to a variety of
locations in the chamber in order to help prime the plasma before
the low-power plasma is struck with the RF bias power. However,
this pulsed DC power is fundamentally different from conventional
DC bias. In some conventional processing, DC bias is applied in the
system, including as a bias on the pedestal. When the DC pulse is
applied, the plasma will form all the way from the bulk and will be
maintained long enough for current to be accommodated in a plasma
sheath at the pedestal. Accordingly, it will collapse down to the
surface of the pedestal creating a sheath with a certain amount of
DC potential. This plasma sheath and potential produces ion
energies for the process and will produce sputtering of the
materials at the surface of the cathode due to high ion energies
associated with the DC plasma. The present technology, however, may
cycle the DC pulse prior to forming a plasma sheath.
[0040] In embodiments of the present technology, the pulsed DC
potential may be initiated to prime the plasma, and then cycled off
to prevent the formation of a high-voltage DC plasma sheath at the
substrate surface. Thus, conventional DC bias maintains the pulse
long enough to develop a sheath, which is at a high voltage and
affects the ion energies. The present technology may utilize the
pulsed DC power to create priming particles to allow a low RF power
to ignite a plasma each time it is pulsed on. The low RF power,
which may be below a typical breakdown voltage, provides lower ion
energies than would be produced in a high-voltage DC plasma sheath,
such as produced by a conventional DC bias. The pulsed DC power of
the present technology instead produces the priming particles that
allow avalanche breakdown and development of the sheath when the RF
bias cycles on, despite the low power of the RF bias. The result is
a plasma sheath at lower ion energies, which may reduce or
substantially reduce sputtering over conventional technologies. By
reducing the sputtering, higher selectivity may be afforded as
previously explained.
[0041] To produce the functionality of the pulsed DC power, the
duty cycle of the pulsed DC power may be very low, and may be
associated with an on time of 1 microsecond to about 100
microseconds in embodiments. In embodiments the on time may be less
than about 75 microseconds, less than about 50 microseconds, less
than about 30 microseconds, less than about 25 microseconds, less
than about 20 microseconds, less than about 15 microseconds, less
than about 10 microseconds, less than about 5 microseconds, or less
than about 1 microsecond.
[0042] In terms of duty cycle, while conventional DC bias may
include a duty cycle of above 50%, above 75%, or above 90% in order
to generate a plasma sheath, the present technology may utilize a
duty cycle of the pulsed DC power that is less than about 50% in
embodiments. The duty cycle of the pulsed DC power may also be less
than about 40%, less than about 30%, less than about 25%, less than
about 20%, less than about 15%, less than about 10%, less than
about 5%, or less than about 1% in embodiments. The DC power may
also be pulsed at a duty cycle between about 1% and about 50%,
between about 1% and about 25%, between about 1% and about 10%, or
any other range between or within these values.
[0043] The pulsed DC power may also be operated on an alternating
or semi-alternating frequency with the RF bias pulsing. For
example, the frequency of the pulsed DC power may be such that it
is in the on cycle while the RF bias is in the off cycle and vice
versa. Depending on the duty cycles of the two powers, either one
of the two powers may be operating at a given time or neither of
the two powers may be operating at a given time. In embodiments
both may also be operating at a given time. By utilizing the
reduced duty cycles of the present technology, a plasma sheath may
not be formed at the substrate surface while the pulsed DC power is
operating. Thus, the pulsed DC power maintains priming particles
available for discharge breakdown and to stabilize the impedance to
improve the operating conditions of the system, while not forming a
sheath or breakdown until the RF power is cycled on. In this way, a
variety of pressure ranges may be accommodated by the present
technology including pressure regimes below about 50 mTorr as well
as pressure regimes up to several hundred mTorr or above. Put
another way, the present technology controls the impedance for glow
discharge breakdown to remove the conventional impedance
limitations of configuration, orientation, pressure, chemistry,
etc.
[0044] The pulsed DC power may be coupled with the system in a
number of ways further described below in relation to the other
figures. For example, and as described in detail below, the pulsed
DC power may be applied to a bipolar electrostatic chuck supporting
the semiconductor substrate. Additionally, the pulsed DC power may
be applied to a conductive ring embedded in or coupled with a
shield ring of a pedestal supporting the semiconductor substrate.
Still further, the pulsed DC power may be applied to a conductive
ring embedded in or connected with a showerhead within the
processing chamber.
[0045] Turning to FIG. 2 is shown a graph illustrating the additive
effects of material modification and low-power plasma according to
embodiments of the present technology. As illustrated, an exemplary
process may include removing an oxide film relative to a carbide
film on the surface of a substrate. As shown by the first bar, a
reactive-ion etching or continuous waveform process may provide a
selectivity below 10:1 for the oxide material with respect to the
carbide material. This may be due in part to the sputtering caused
by the ion process, which is more aggressive to all materials
thereby increasing both etch rates. Moreover, the reactive-ion etch
may also produce rounded corners in the etch profile and may also
etch an underlying layer due to ion bombardment once the desired
film has been removed. Accordingly, a reactive-ion etch may be
unsatisfactory for selective processing and maintaining features of
the substrate.
[0046] As shown in the second bar, by simply utilizing the pulsing
low-power RF bias plasma described above, such as with the pulsed
DC power, selectivity may be improved over the conventional
reactive-ion etch process. The process may also reduce or eliminate
the corner rounding and underlying layer etch produced by
reactive-ion etching. The third bar, however, illustrates the
synergistic benefits of performing a material modification prior to
performing the low-power pulsing. By utilizing both film
modification as well as the low-power plasma RF pulsing process,
selectivity increases by almost an order of magnitude over the
reactive-ion etching process. Additionally, the etch profile is
much improved with reduced corner rounding and underlying layer
etching.
[0047] FIG. 3 illustrates imaging of an etch process performed
according to embodiments of the present technology. As shown in the
image on the left, regions of silicon nitride 305 are disposed
between regions of silicon carbide 310. After a material
modification and low-power RF etching operation as previously
discussed are performed, the silicon carbide sections are removed,
as illustrated in the figure on the right. The layers of silicon
nitride 305 are substantially maintained, and only minimal corner
rounding can be observed. Additionally, silicon oxide layer 315
underlying the silicon carbide sections 310 was exposed during the
etch process, but the film was able to act as an etch stop to the
process, as opposed to a reactive-ion process that would have
etched into the trench due to bombardment of the silicon oxide. The
measured effects illustrate that the present technology was able to
produce an etch selectivity of silicon carbide to silicon nitride
of over 50:1 with minimal corner rounding of the silicon nitride.
The present technology was also able to produce an etch selectivity
of silicon carbide to silicon oxide of over 70:1.
[0048] FIG. 4 shows a chart illustrating etch rates of various
materials with and without a treatment according to embodiments of
the present technology. The present example shows a material
modification that utilized an oxygen precursor in plasma to modify
silicon oxycarbide, silicon oxide, silicon carbide, and silicon
nitride exposed on a substrate surface. A low-power pulsed RF
etching process was performed on similar materials with and without
the oxygen treatment. As illustrated, all four films etched with
low selectivity during the low-power etch process without the
material modification. On the other hand, after the oxygen
treatment, silicon oxycarbide and silicon carbide continued to
etch, while the silicon oxide and silicon nitride films were
essentially maintained and buffered by the oxygen treatment
providing a surface enhancement to those films.
[0049] FIG. 5 shows a chart illustrating etch rates of silicon
oxycarbide and silicon carbide with and without treatments
according to embodiments of the present technology. Although the
oxygen modification performed in the example illustrated in FIG. 4
was successful for the carbon-containing films with respect to
silicon oxide and silicon nitride, the two carbon-containing films
did not have high selectivity with respect to each other. In FIG.
5, a physical modification was performed that exploited the higher
porosity of the silicon oxycarbide film. Silicon oxycarbide is a
more porous film than silicon carbide, and the chemical bonding is
weaker as well. The physical modification of this example included
utilizing a helium precursor in plasma, and then exposing the films
to those plasma effluents. Because helium is inert to the two
films, it did not chemically react with the materials, although the
impact of the helium ions was of a sufficient capacity to damage
the chemical bonds of the silicon oxycarbide. This further weakened
the film, after which a low-power RF pulsing etch was performed. As
illustrated by the figure, the modification followed by the
low-power etch removed the silicon oxycarbide material while
essentially maintaining the silicon carbide.
[0050] The examples illustrated by FIGS. 4 and 5 are exemplary
only, and are not intended to limit the present technology. These
examples merely show the types of material modifications
encompassed by the present technology. One of skill will readily
understand by these examples how the material modifications and
low-power etch operations may be applied to a variety of materials
to enhance selectivity and improve etch profiles. By utilizing the
present technology, greater than 20:1 selectivity may be achieved
for silicon oxycarbide with respect to silicon oxide and silicon
nitride. Greater than 20:1 selectivity may also be achieved for
silicon oxide with respect to silicon oxycarbide, silicon nitride,
and silicon carbide using various material modifications and
etching according to the present technology. Greater than 20:1
selectivity may also be achieve for silicon carbide with respect to
silicon oxide, silicon nitride, and silicon oxycarbide using
various material modifications and etching according to the present
technology. Additionally, greater than 20:1 selectivity may be
achieved for silicon nitride with respect to silicon oxide, silicon
oxycarbide, and silicon carbide using various material
modifications and etching according to the present technology. In
embodiments the selectivity of any of these operations may also be
greater than or about 25:1, greater than or about 30:1, greater
than or about 35:1 , greater than or about 40:1, greater than or
about 45:1, greater than or about 50:1, greater than or about 55:1,
greater than or about 60:1, greater than or about 65:1, greater
than or about 70:1, greater than or about 75:1, greater than or
about 80:1, greater than or about 85:1, greater than or about 90:1,
greater than or about 95:1, or greater than or about 100:1.
[0051] Turning to FIG. 6 is shown a partial schematic illustration
of a controller providing DC pulse to an electrostatic chuck
according to embodiments of the present technology. The system may
be included with a substrate processing chamber according to
embodiments of the present technology. An exemplary chamber may be
the Mesa.TM. Etch System produced by Applied Materials, Inc. of
Santa Clara, Calif. The components may include a pedestal 605
configured to support a semiconductor substrate. The system may
also include a pulsed RF bias power 610 electrically coupled with
the pedestal and configured to generate a plasma as previously
described. The pulsed RF bias power 610 may be configured to
generate a plasma within the processing chamber at a power of
between about 20 W and about 50 W, and the pulsed RF bias power may
be pulsed at a frequency below about 5,000 Hz. The system may also
be configured to operate at any of the other levels previously
described.
[0052] The system may also include a DC pulsing power 615
electrically coupled with the substrate processing chamber. The DC
pulsing power 615 may be as previously described, and configured to
produce priming particles for the RF bias plasma. In embodiments,
the DC pulsing power may be configured to pulse at a frequency to
produce priming particles without developing a plasma sheath. The
DC pulsing power may be operated for any of the times or at any of
the duty cycles previously described, and may be configured to be
pulsed for a duration of 100 microseconds or less at a duty cycle
of less than about 50%. The DC pulsing power may also be configured
to be operated for a pulse duration of less than about 50
microseconds at a duty cycle of less than about 20%. The DC pulsing
power may also be configured to be operated for a pulse duration of
less than about 10 microseconds at a duty cycle of less than about
10% in embodiments.
[0053] As illustrated in FIG. 6, the pedestal 605 may be an
electrostatic chuck. A chamber controller 620 may provide
instructions to the electrostatic chuck controller 625, including
the input/output module 630 for the bipolar electrostatic chuck.
The DC pulsing power 615 may be electrically coupled with
electrical ground of the bipolar electrostatic chuck 630 as
illustrated in the figure. In many processing chambers the
electrodes may be biased to DC voltages, and heavy filtering may be
included at the output of the DC power supplies to block RF power.
Consequently, when the supplies are pulsed as shown in the
configuration, the waveform may begin to be distorted and
attenuated. Accordingly, to overcome this issue, the electrostatic
chuck power may be floated at the voltage of the pulsed DC. Thus,
the electrostatic chuck electrodes are then referenced to the high
voltage of the pulsed DC. Put another way, the electrostatic chuck
power supply may then be floating electrically isolated from the
machine ground, and ground of the electrostatic chuck essentially
may be at high voltage. The electrostatic chuck can then output
positive and negative polarity with respect to the high
voltage.
[0054] Thus, if the pulsed DC is cycled off or grounded, then the
electrostatic chuck electrodes would be referenced to the ground,
plus or minus. However, when the DC is applied or pulsed, then the
electrostatic chuck electrodes would be referenced to the power of
the applied DC power. As a non-limiting example of such a
configuration for the purposes of explanation, and not as a
particular process scenario, if the pulsed DC power operates at 1
kV, and the electrostatic chuck operates at +/-500 volts, when the
DC power supply is cycled on to assist with plasma generation as
previously described, then the electrodes would be at 1500 volts
and 500 volts respectively. A benefit of this configuration may be
that an additional conductor for the pulsed DC power may not be
required inside the chamber. Additionally, in embodiments the DC
and RF pulses may be alternated, and thus the DC and RF supplies
may be decoupled from one another despite that they are each
biasing the same pedestal base.
[0055] An additional coupling option that may be decoupled from the
electrostatic chuck is illustrated in FIG. 7, which shows a partial
schematic illustration of a controller providing DC pulse to a
conductor coupled with a pedestal structure according to
embodiments of the present technology. As illustrated in the
figure, a substrate processing chamber 701 is shown having a
showerhead 703 and a pedestal 705 configured to support a
substrate. The system may include a pulsed RF bias 710 as
previously discussed, as well as a DC power 715 for electrostatic
chucking. An additional DC pulsing unit 720 may be included that
provides pulsed DC power as previously discussed for producing
priming for a plasma ignited by the RF bias. In this example, the
DC pulsing power is electrically coupled with a conductive ring 725
embedded in or coupled with the pedestal. This conductive ring 725
may be decoupled from the electrostatic chuck and from the RF bias
in embodiments. For example, the conductive ring 725 may be
included in a dielectric shield ring, including a quartz shield
ring of the pedestal 705 as shown. The conductive ring may be any
conductive material including a metal or silicon carbide in
embodiments. In this scenario, although an additional conductor is
included in the system, because the conductive ring is decoupled
from the other power supplies, the components do not require
electrical floating with respect to one another.
[0056] Another coupling option that may be decoupled from the
electrostatic chuck is illustrated in FIG. 8, which shows a partial
schematic illustration of a controller providing DC pulse to an
embedded conductor within a showerhead of a processing chamber
according to embodiments of the present technology. As illustrated,
components similar to those discussed with respect to FIG. 7 are
shown, including a substrate processing chamber 701, including
showerhead 703, and pedestal 705, for example. The system similarly
includes a pulsed RF bias 710, a DC power 715 for electrostatic
chucking, and a DC pulsing unit 720. The figure additionally
includes a conductive ring 825 which may be a similar material as
discussed above, but may be coupled with showerhead 703 in
embodiments. This coupling option also decouples the pulsed DC from
the other power supplies.
[0057] The coupling ring may also be included coupled with or
embedded in a chamber wall in embodiments, or other components of
the chamber system. By providing the pulsed DC power with any of
these options or alternative options as would be readily understood
to be similarly encompassed, the system may produce lower power
plasma than conventional systems. By providing energy to produce
energetic particles allowing the low-power, pulsing RF bias to more
easily strike a plasma at lower voltages with lower ion energies,
improved plasma processing may be provided for etching, deposition,
cleaning, or any other process that may benefit from a low-power
plasma.
[0058] In the preceding description, for the purposes of
explanation, numerous details have been set forth in order to
provide an understanding of various embodiments of the present
technology. It will be apparent to one skilled in the art, however,
that certain embodiments may be practiced without some of these
details, or with additional details.
[0059] Having disclosed several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the embodiments. Additionally, a
number of well-known processes and elements have not been described
in order to avoid unnecessarily obscuring the present technology.
Accordingly, the above description should not be taken as limiting
the scope of the technology.
[0060] Where a range of values is provided, it is understood that
each intervening value, to the smallest fraction of the unit of the
lower limit, unless the context clearly dictates otherwise, between
the upper and lower limits of that range is also specifically
disclosed. Any narrower range between any stated values or unstated
intervening values in a stated range and any other stated or
intervening value in that stated range is encompassed. The upper
and lower limits of those smaller ranges may independently be
included or excluded in the range, and each range where either,
neither, or both limits are included in the smaller ranges is also
encompassed within the technology, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included. Where multiple values are
provided in a list, any range encompassing or based on any of those
values is similarly specifically disclosed.
[0061] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural references unless the
context clearly dictates otherwise. Thus, for example, reference to
"a material" includes a plurality of such materials, and reference
to "the precursor" includes reference to one or more precursors and
equivalents thereof known to those skilled in the art, and so
forth.
[0062] Also, the words "comprise(s)", "comprising", "contain(s)",
"containing", "include(s)", and "including", when used in this
specification and in the following claims, are intended to specify
the presence of stated features, integers, components, or
operations, but they do not preclude the presence or addition of
one or more other features, integers, components, operations, acts,
or groups.
* * * * *