U.S. patent application number 11/376430 was filed with the patent office on 2006-08-10 for etch chamber with dual frequency biasing sources and a single frequency plasma generating source.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Jin-Yuan Chen, Frank F. Hooshdaran, Dragan V. Podlesnik.
Application Number | 20060175015 11/376430 |
Document ID | / |
Family ID | 31498210 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175015 |
Kind Code |
A1 |
Chen; Jin-Yuan ; et
al. |
August 10, 2006 |
Etch chamber with dual frequency biasing sources and a single
frequency plasma generating source
Abstract
A method and apparatus for selectively controlling a plasma in a
processing chamber during wafer processing. The method includes
providing process gasses into the chamber over a wafer to be
processed, and providing high frequency RF power to a plasma
generating element and igniting the process gases into the plasma.
Modulated RF power is coupled to a biasing element, and wafer
processing is performed according to a particular processing
recipe. The apparatus includes a biasing element disposed in the
chamber and adapted to support a wafer, and a plasma generating
element disposed over the biasing element and wafer. A first power
source is coupled to the plasma generating element, and a second
power source is coupled to the biasing element. A third power
source is coupled to the biasing element, wherein the second and
third power sources provide a modulated signal to the biasing
element.
Inventors: |
Chen; Jin-Yuan; (Union City,
CA) ; Hooshdaran; Frank F.; (Pleasanton, CA) ;
Podlesnik; Dragan V.; (Palo Alto, CA) |
Correspondence
Address: |
Patent Counsel;APPLIED MATERIALS, INC.
P. O. Box 450-A
Santa Clara
CA
95052
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
31498210 |
Appl. No.: |
11/376430 |
Filed: |
March 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10342575 |
Jan 14, 2003 |
|
|
|
11376430 |
Mar 14, 2006 |
|
|
|
60402291 |
Aug 9, 2002 |
|
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|
Current U.S.
Class: |
156/345.44 ;
216/67 |
Current CPC
Class: |
H01J 37/321 20130101;
H01J 37/32706 20130101 |
Class at
Publication: |
156/345.44 ;
216/067 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. A method of processing a workpiece in a plasma reactor having
electrode apparatus for coupling RF power to plasma in said
reactor, said method comprising: simultaneously applying RF power
from three RF sources of three different RF frequencies to said
electrode apparatus; selecting respective power levels of said
three RF sources to select respective characteristics of a plasma
in said reactor.
2. The method of claim 1 wherein said electrode apparatus comprises
a top electrode at a ceiling of the reactor and a bottom electrode
at a wafer support of said reactor, and wherein the step of
applying RF power comprises coupling first and second ones of said
three RF sources to said bottom electrode.
3. The method of claim 2 wherein the step of applying RF power
further comprises coupling a third one of said RF sources to said
electrode apparatus.
4. The method of claim 3 wherein the step of coupling said third
one of said RF sources to said electrode apparatus comprises
coupling said third RF source to said top electrode.
5. The method of claim 1 wherein said respective characteristics
comprise plasma ion density, plasma ion energy and wideness of
energy band of said plasma ion energy.
6. The method of claim 1 wherein the frequencies of said first,
second and third RF sources are VHF, HF and LF frequencies
respectively.
7. The method of claim 6 wherein the step of selecting respective
power levels comprises selecting the power levels of said first,
second and third RF sources within respective predetermined
ranges.
8. A plasma reactor for processing a workpiece, comprising: a
reactor chamber and a wafer support within said chamber; electrode
apparatus for coupling RF power to plasma in said reactor; three RF
sources of three different RF frequencies coupled to said electrode
apparatus.
9. The reactor of claim 8 wherein said three RF sources are
independently controllable.
10. The reactor of claim 8 wherein said electrode apparatus
comprises a top electrode at a ceiling location overlying said
wafer support and a bottom electrode at said wafer support of said
reactor.
11. The reactor of claim 10 wherein said first and second RF
sources are coupled to said bottom electrode.
12. The reactor of claim 11 wherein said third RF sources is
coupled to said top electrode.
13. The reactor of claim 8 further comprising first, second and
third impedance match elements connected between said first, second
and third RF sources, respectively, and said electrode
apparatus.
14. The method of claim 8 wherein the frequencies of said first,
second and third RF sources are VHF, HF and LF frequencies
respectively.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is a continuation of U.S.
application Ser. No. 10/342,575 filed Jan. 14, 2003 by Jin-Yuan
Chen, et al. entitled "ETCH CHAMBER WITH DUAL FREQUENCY BIASING
SOURCES AND A SINGLE FREQUENCY PLASMA GENERATING SOURCE" and
assigned to the present assignee.
FIELD OF THE INVENTION
[0002] Embodiments of the invention generally relate to
semiconductor wafer processing, and more particularly, to etch and
plasma related integrated circuit manufacturing processes and
related hardware.
BACKGROUND OF THE INVENTION
[0003] Semiconductor fabrication wafer process chambers employing
plasma to perform etching and deposition processes utilize various
techniques to control plasma density and acceleration of plasma
components. For example, magnetically-enhanced plasma chambers
employ magnetic fields to increase the density of charged particles
in the plasma, thereby further increasing the rate of
plasma-enhanced deposition and etching processes. Increasing the
process rate is highly advantageous because the cost of fabricating
semiconductor devices is proportional to the time required for
fabrication.
[0004] During a plasma-enhanced process, such as a reactive ion
etch process, material on the wafer is removed in specific areas to
subsequently form the components/features of the devices (e.g.,
transistors, capacitors, conductive lines, vias, and the like) on
the wafer. A mask is formed over areas of the wafer that are to be
protected from the etching process. Uniformity of the etching rate
across the wafer during the entire etch process is very important
for ensuring that features are etched with precision at any
location on the wafer. The uniformity of the etching process is
related to the ability to control the plasma throughout the etch
process. For example, U.S. Pat. No. 6,354,240 includes disposing
magnets around the reactor chamber to provide a magnetic
confinement to sustain a high plasma density in a low pressure
environment.
[0005] However, during "deep trench etching", the wafer may be
exposed to the etchants for a long duration. During these long
etching processes, the etch mask can be completely etched from the
wafer surface to leave the surface unprotected. That is, the deep
trench processes are limited by the selectivity between the
material of the protective mask and the material to be etched,
where the higher the selectivity, the deeper the trench may be
etched.
[0006] Therefore, there is a need in the art for increasing the
selectivity during deep trench etching, such that a sufficient
portion of the masking material remains to cover areas of the wafer
to be protected until the etch process is complete.
SUMMARY OF THE INVENTION
[0007] The present invention provides an etch chamber that is
driven with three RF frequencies: one frequency for establishing
and maintaining a plasma, and two frequencies for biasing a biasing
element (e.g., wafer pedestal). Such triple frequency use provides
improved plasma control that increases the process window for an
etch process. Enhancing control of plasma density and ion energy
improves the coverage of more etching applications and provides a
wider window of processing.
[0008] In particular, the present invention provides an apparatus
for controlling a plasma in a chamber during wafer processing. The
apparatus comprises a biasing element disposed in the chamber and
adapted to support a wafer, and a plasma generating element
disposed proximate the biasing element. A plasma generating (top)
power source is coupled to the plasma generating element, and a
bottom (biasing) power source is coupled to the biasing element to
provide a modulated signal that modulates the plasma.
[0009] A method for selectively controlling a plasma in the
processing chamber during wafer processing comprises providing
process gasses into the chamber over a wafer to be processed, and
providing high frequency RF power to the plasma generating element,
which ignites the process gases into the plasma. A modulated RF
power signal is provided to the biasing element, and wafer
processing is performed according to a particular processing
recipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] So that the manner in which the above recited features of
the invention are attained can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof, which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention, and are therefore, not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0011] FIG. 1 depicts a cross-sectional view of a first embodiment
of a dual frequency bias plasma chamber system;
[0012] FIG. 2 depicts a top cross-sectional view of the plasma
chamber system of FIG. 1;
[0013] FIG. 3 depicts a flow diagram of a method for selectively
controlling a plasma during wafer processing;
[0014] FIG. 4 depicts a cross-sectional view of a second embodiment
of a dual frequency bias plasma chamber system; and
[0015] FIGS. 5A-5D depict graphs of exemplary RF waveforms used in
the present invention.
[0016] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0017] One application of the present invention provides an
apparatus for performing high aspect ratio deep trench etching. In
particular, a processing chamber is equipped with dual frequency
biasing sources and a single frequency plasma generating source. A
wafer to be processed is secured on a support pedestal in the
chamber. The single frequency plasma generating source is coupled
to a plasma generating element disposed over the wafer to be
processed, while a pair of biasing sources having different
frequencies are coupled to the support pedestal, such that the
support pedestal serves as a biasing element.
[0018] FIG. 1 depicts a cross sectional view of a first embodiment
of a dual frequency bias plasma chamber system 100 of the present
invention. Specifically, FIG. 1 depicts an illustrative chamber
system (system) 100 that can be used in high aspect ratio trench
formation. The system 100 generally comprises a chamber body 102
and a lid assembly 104 that defines an evacuable chamber 106 for
performing substrate processing. In one embodiment, the system 100
is an MxP type etch system available from Applied Materials, Inc.
of Santa Clara, Calif. For a detailed understanding of an MxP type
system, the reader is directed to U.S. Pat. No. 6,403,491, issued
Jun. 11, 2002, the contents of which is incorporated by reference
herein in its entirety. Further, other types of wafer processing
systems are also contemplated, such as an eMAX type system, a
PRODUCER e type system, HOT type system, and an ENABLER type
system, among others, all of which are also available from Applied
Materials, Inc. of Santa Clara, Calif.
[0019] The system 100 further comprises a gas panel 160 coupled to
the chamber 106 via a plurality of gas lines 159 for providing
processing gases, an exhaust stack 164 coupled to the chamber 106
via an exhaust passage 166 for maintaining a vacuum environment and
exhausting undesirable gases and contaminants. Additionally, a
controller 110 is coupled to the various components of the system
100 to facilitate control of the processes (e.g., deposition and
etching processes) within the chamber 106.
[0020] The chamber body 102 includes at least one of sidewall 122
and a chamber bottom 108. In one embodiment, the at least one
sidewall 122 has a polygon shaped (e.g., octagon or substantially
rectangular) outside surface and an annular or cylindrical inner
surface. Furthermore, at least one sidewall 122 may be electrically
grounded. The chamber body 102 may be fabricated from a
non-magnetic metal, such as anodized aluminum, and the like. The
chamber body 102 contains a substrate entry port 132 that is
selectively sealed by a slit valve (not shown) disposed in the
processing platform.
[0021] A lid assembly 104 is disposed over the sidewalls 122 and
defines a processing region 140 within the chamber 106. The lid
assembly 104 generally includes a lid 172 and a plasma generating
element (e.g., source or anode electrode) 174 mounted to the bottom
of the lid 172. The lid 172 may be fabricated from a dielectric
material such as aluminum oxide (Al.sub.2O.sub.3), or a
non-magnetic metal such as anodized aluminum. The plasma generating
element 174 is fabricated from a conductive material such as
aluminum, stainless steel, and the like.
[0022] Further, the plasma generating element 174 is coupled to a
high frequency RF power source 162 via a matching network 161. The
high frequency power source (top power source) 162 provides RF
power in a range between about 100 Watts to 7500 Watts, at a
frequency in the range of about 40-180 MHz, and is used to ignite
and maintain a plasma from a gas mixture in the chamber 106.
[0023] The plasma generating element 174 may be provided with
perforations or slits 176 to serve as a gas diffuser. That is, the
plasma generating element 174 may also serve as a showerhead, which
provides processing gases that, when ignited, forms a plasma in the
processing region 140. The processing gases, (e.g., CF.sub.4, Argon
(Ar), C.sub.4F.sub.8, C.sub.4F.sub.6, C.sub.8F.sub.4, CHF.sub.3,
Cl.sub.2, HBr, NF.sub.3, N.sub.2, He, O.sub.2 and/or combinations
thereof) are provided to the plasma generating element/showerhead
174 from the external gas panel 160 via the gas conduit 159 coupled
therebetween.
[0024] In another embodiment, a gas distribution ring (not shown)
may be coupled to the lid assembly 104 to provide the processing
gases into the chamber 106. The gas distribution ring typically
comprises an annular ring made of aluminum or other suitable
material having a plurality of ports formed therein for receiving
nozzles that are in communication with the gas panel 160.
[0025] A substrate support pedestal 120 is disposed within the
chamber 106 and seated on the chamber bottom 108. A substrate
(i.e., wafer, not shown) undergoing wafer processing is secured on
an upper surface 121 of the substrate support pedestal 120. The
substrate support 120 may be a susceptor, a heater, ceramic body,
or electrostatic chuck on which the substrate is placed during
processing. The substrate support pedestal 120 is adapted to
receive an RF bias signal, such that the substrate support pedestal
serves as a biasing element (e.g., cathode electrode) with respect
to the RF bias signal, as is discussed below in further detail.
[0026] In the embodiment of FIG. 1, the substrate support pedestal
120 comprises an electrostatic chuck 124 coupled to an upper
surface of a cooling plate 126. The cooling plate 126 is then
coupled to an upper surface of the pedestal base 127. The
electrostatic chuck 124 may be fabricated from a dielectric
material e.g., a ceramic such as aluminum nitride (AlN), silicon
oxide (SiO), silicon nitride (SiN), sapphire, boron nitride, or it
can be a plasma sprayed aluminum nitride, or aluminum oxide
material on an anodized aluminum surface, or the like, and is
generally shaped as a thin circular puck.
[0027] Furthermore, the electrostatic chuck 124 may be provided
with one or more chucking electrodes 130. The chucking electrodes
130 are, for example, fabricated from a conductive material, (e.g.,
tungsten). The chucking electrodes 130 are disposed relatively
close to the top surface of the electrostatic chuck 124. In this
way, the chucking electrodes 130 provide the necessary
electrostatic force to the backside of a wafer to retain (i.e.,
chuck) the wafer on the electrostatic chuck 124. The chucking
electrodes 130 may be in any configuration such as a monopolar
configuration, bipolar configuration, zoned chucking configuration,
or any other configuration suitable to retain the wafer to the
chuck 124. The chucking electrodes 130 are connected to a remote
power source, i.e. a high voltage DC (HVDC) power supply 134, which
provides a chucking voltage sufficient to secure the wafer to the
chuck 124.
[0028] The cooling plate 126 assists in regulating the temperature
of the electrostatic chuck 124. Specifically, the cooling plate 126
is fabricated from a material that is a high conductor of RF power,
such as molybdenum, a zirconium alloy (e.g., Zr--Hf), a metal
matrix composite (e.g., Al--Si--SiC), among others. Furthermore,
the materials used to fabricate the cooling plate 126 are selected
from a group of materials that will have a thermal expansion
coefficient value close to the thermal expansion coefficient value
of the electrostatic plate 124. The cooling plate 126 comprises
channels (not shown) formed therein to circulate a coolant to
reduce the thermally conducted heat radiated from the wafer and the
electrostatic chuck 124.
[0029] Additional temperature control may be provided by a heating
element embedded in the electrostatic chuck 124. Moreover, a
backside gas delivery system (not shown) is provided, such that a
gas (e.g., helium) is provided between grooves (not shown), which
are formed in the top surface of the chuck 124, and the backside of
the wafer.
[0030] As discussed above, the substrate support pedestal 120 also
serves as a biasing electrode (e.g., cathode) for biasing the
ionized gases towards the wafer during either a deposition or
etching process. A first bias power supply 150 and a second bias
power supply 154 are coupled in parallel between the substrate
support pedestal 120 and ground via respective matching networks
151 and 155. In one embodiment, the grounded sidewalls 122 and the
plasma generating element 174 together define the anode with
respect to the biasing element (cathode) in the substrate support
pedestal 120.
[0031] In particular, the first biasing power supply 150 provides
RF power in the range of about 10 Watts to 7500 Watts (W), and at a
frequency in the range of about 100 KHz to 6 MHz. The second
biasing power supply 154 provides RF power in the range of about 10
W to 7500 W, at a frequency in the range of about 4 MHz to 60 MHz,
and, for example, at a frequency of 13.56 MHz. As such, the signal
from the first bias power supply 150 amplitude modulates the signal
from the second bias power supply 154. For example, a 13.56 MHz
signal from the second bias power supply 154 is amplitude modulated
with a 2 MHz signal from the first biasing power supply 150. It is
noted that one skilled in the art will appreciate that the power
levels of the first and second biasing power supplies 150 and 154
are related to the size of the workpiece being processed. For
example, a 300 mm wafer requires greater power consumption than a
200 mm wafer during processing.
[0032] In one embodiment, the chucking electrodes 130 may also
function as the biasing element. In particular, the first and
second bias power supplies 150 and 154 are coupled to the chucking
electrode 130, such that the bias signal (e.g., modulated RF
signal) is applied to the electrodes 130 to create a bias voltage.
In another embodiment, the first and second bias power supplies 150
and 154 are coupled to the cooling plate 126, which thereby
functions as a biasing element. Alternatively, the first and second
bias power supplies 150 and 154 may be coupled to a base plate (not
shown) disposed below the cooling plate 126, or to another anode
placed within the chuck 124.
[0033] It is noted that the controller 110 may be utilized to
control the bias power supplies 150 and 154, as well as control the
high frequency RF power source 162. In particular, the controller
110 controls the power set points of the bias power supplies 150
and 154 to provide either the bias signal or the modulated signal.
That is, the controller 110 may be used to control the low RF
frequency bias signal (e.g., 2 MHz signal) provided by the first
bias power supply 150, as well as control the intermediate RF
frequency bias signal (e.g., 13.56 MHz signal) provided by the
second bias power supply 154. Moreover, the controller 110 controls
the set point of the high frequency RF signal from the high
frequency RF power source 162. It is noted that a person skilled in
the art will appreciate that the power levels set by the controller
110 for the power sources 150, 154, and 162 are related to the size
of the wafer being processed (e.g., 200 millimeter (mm) and 300 mm
wafers)
[0034] It is noted that the two bias input power signals from the
bias power supplies 150 and 154 are not modulated until after the
formation of the plasma. Specifically, the plasma acts as a
non-linear device, such as a diode, so that the two bias power
supplies 150 and 154 may be modulated in the plasma. The degree of
modulation depends on the plasma condition, biasing signal power
levels, and their respective frequencies.
[0035] Once the biasing signals are modulated in the plasma, the
plasma density and acceleration may be changed in a controlled
manner depending on the modulation scheme. During an etching
process, the selectivity increases such that the protective mask
(e.g., a photoresist mask) has a longer life that allows increased
depth and aspect ratio when etching deep trenches (e.g., vias). The
use of a modulated bias signal provides an increased process window
for many etch processes.
[0036] FIG. 2 depicts a top cross-sectional view of the plasma
chamber system 100 of FIG. 1. In particular, FIG. 2 depicts an
embodiment where the plasma chamber system 100 is magnetically
enhanced using a DC magnetic field in the processing region 140
between the plasma generating element 174 and the biasing element
120. That is, the chamber (also referred to as a reactor) employs
magnetic fields to increase the density of charged particles in the
plasma, thereby further increasing the rate of the plasma enhanced
fabrication process.
[0037] Typically, the direction of the magnetic field is traverse
with respect to the longitudinal axis of the chamber 106, that is,
traverse to an axis extending between the electrodes 120 and 174.
Various arrangements of permanent magnets or electromagnets are
conventionally used to provide such transverse magnetic field. One
such arrangement is a first main pair of coils 182 and 183 disposed
on opposite sides of the cylindrical chamber side wall 122, and a
second main pair of coils 184 and 185 disposed on opposite sides of
the cylindrical chamber side wall 122. Each pair of opposing main
coils 182-185 are connected in series and in phase to a DC power
supply (not shown), such that they produce transverse (adjacent)
magnetic fields, which are additive in the region between the coil
pairs. The traverse magnetic field is represented in FIGS. 1 and 2
by the vector "B" oriented along the negative X-axis. Variations on
the magnetic fields may also be utilized, such as opposed magnetic
fields as used in an etch MxP dielectric chamber, also available
from Applied Materials Inc., of Santa Clara, Calif.
[0038] To facilitate control of the system 100 as described above,
the controller 110 may be one of any form of general-purpose
computer processor that can be used in an industrial setting for
controlling various chambers and sub-processors. In general, the
process controller 110 includes a central processing unit (CPU) 112
in electrical communication with a memory 114 and support circuits
116. The support circuits 116 include various buses, I/O circuitry,
power supplies, clock circuits, cache, among other components.
[0039] The memory 114, or computer-readable medium, may be one or
more of readily available memory such as random access memory (RAM)
read only memory (ROM), floppy disk, hard disk, or any other form
of digital storage that are locally and/or remotely connected.
Software routines are stored in memory 114. The software routines,
when executed by the CPU 112, cause the reactor to perform
processes of the present invention. The software routines may also
be stored and/or executed by a second CPU (not shown) that is
remotely located from the hardware being controlled by the CPU
112.
[0040] The software routines are executed after the wafer is
positioned on the support pedestal 120. The software routines, when
executed by the CPU 112, transform the general-purpose computer
into a specific purpose computer (controller) 110 that controls the
chamber operations such that the etching process is performed in
accordance with the method of the present invention.
[0041] FIG. 3 depicts a flow diagram of a method 300 for
selectively controlling a plasma during wafer processing.
Specifically, the method 300 provides a technique for controlling
plasma density and particle acceleration, which allows for greater
depth and aspect ratios to be achieved on the wafer during deep
trench etching.
[0042] The method 300 starts at step 302, where a substrate is
loaded, moved into an appropriate processing position over the
substrate support pedestal 106. At step 304, a process gas is
introduced into the chamber 106 via the exemplary showerhead of
FIG. 1 or at least one nozzle. The process gas may include Argon
(Ar), CF.sub.4, C.sub.4F.sub.8, C.sub.4F.sub.6, C.sub.8F.sub.4,
CHF.sub.3, Cl.sub.2, HBr, NF.sub.3, N.sub.2, He, O.sub.2 and/or
combinations thereof, and are introduced into the chamber 106 at
rates of between about 1 sccm to about 2000 sccm.
[0043] At step 306, the pressure in the chamber 106 is brought to a
desired processing pressure by adjusting a pumping valve (not
shown) to pump the gas into the chamber 106 at a desired pressure.
In one operational aspect of generating plasma, the pressure may be
between about 1 milliTorr and about 1000 milliTorr.
[0044] Plasma may be generated via application of the source power
by the top power supply 162 between the plasma generating element
174 and ground (e.g., the chamber sidewalls and/or bias element. At
step 308, the top power supply 162 applies the source power between
about 100 Watts and about 7500 Watts, at a frequency of about 40
MHz to about 180 MHz, which ignites the process gas or gases
introduced into the processing region 140 into a plasma. In
particular, the gas mixture (e.g., Ar) is introduced into the
processing region 140 of the chamber 106. Once the pressure in the
chamber reaches a pressure setpoint, the gas is ignited by the RF
signal provided by the RF power source 162 to form the plasma. The
wafer is then chucked to the substrate support pedestal 120, and
then the other processing gases are provided to the chamber 106.
The method 300 proceeds to step 308.
[0045] At step 310, the bias power supplies 150 and 154 are
activated and the biasing element 120 is biased with the modulated
bias signal. Recall that the biasing element may be formed by
coupling the bias power supplies 150 and 154 to the chucking
electrode 130, the cooling plate 126, cathode base plate, among
other components in the substrate support pedestal 120. It is noted
that the order of steps 308 and 310 of method 300 should not be
considered as limiting, but rather, may be performed alternately or
simultaneously.
[0046] In particular, the intermediate RF bias power source 150 and
low RF bias power source 154 are turned on, and the biasing element
120 is biased to between about 10 Watts and about 7500 Watts.
Furthermore, the RF signal from the two bias power sources 150 and
154 provide a modulated signal, such that the intermediate
frequency signal (e.g., 13.56 MHz) is modulated by the low
frequency signal (e.g., 400 KHz to 2 MHz).
[0047] The intermediate frequency RF source (second biasing power
supply) 154 provides a sufficient energy level to accelerate the
ions towards the biasing element 120, such that the particles
bombard the wafer during the etching process. Further, the low
frequency RF bias source 150 provides a wide energy band that
increases the plasma density near the wafer. By increasing the
plasma density, more particles are available for bombarding the
wafer. As such, the modulated RF waveform provided by the bias
power supplies 150 and 154 provides additional control of the
energy used to accelerate the ions, as well as control the plasma
density in the processing region 140.
[0048] At step 312, the wafer processing procedure (e.g., deep
trench etching) is performed according to a particular recipe. The
operation of the plasma process may be monitored by a process
analysis system (not shown) to determine when the wafer processing
has reached an endpoint value and is complete. Once the processing
recipe is completed, at step 314, the plasma generation may be
terminated and the wafer removed from the processing chamber for
further processing, where the method 300 ends.
[0049] In one exemplary embodiment, a deep trench having a width of
about 14 micrometers (.mu.m) and an aspect ratio of at least about
6:1 may be formed in a silicon wafer by providing the modulated
waveform to the plasma during the etch step 312. In particular,
process gases such as NF.sub.3 (at a rate of 80 sccm) and HBr (at a
rate of 400 sccm) are provided to the reactor chamber 106. The flow
ratio of NF.sub.3 to HBr is about 1:5. The pressure in the reaction
chamber 106 is maintained at about 100 to 400 mTorr. The top power
supply 162 applies the source power at about 3000 Watts at a
frequency of about 60 MHz, which ignites the process gases in the
processing region 140 into a plasma. The intermediate RF bias power
source 150 is set to provide power in a range of about 2000 to 3000
Watts at a frequency of 13.56 MHz, while the low RF bias power
source (e.g., first biasing power supply) 154 provides power in a
range of about 2000 to 3000 Watts at a frequency of 2 MHz. The RF
signal from the two bias power sources 150 and 154 provide a RF
signal modulated by about 10 to 80 percent.
[0050] FIGS. 5A-5D depict graphs of exemplary RF waveforms used in
the present invention. FIG. 5A depicts a 2 MHz biasing signal, FIG.
5B depicts a 13.56 MHz biasing signal, and FIG. 5C depicts a
modulated biasing signal. In FIGS. 5A-5C, each waveform graph has a
y-axis representing magnitude of power, and an x-axis representing
frequency. In particular, FIG. 5C shows the resultant amplitude
modulated continuous wave (CW) signal, where the 13.56 MHz RF
signal is modulated by the 2 MHz RF signal.
[0051] FIG. 5D depicts a graph illustrating a modulated pulsed
waveform. In this instance, a square wave is used as a modulating
signal, which produces the modulated signal shown in FIG. 5D, where
the amplitude of the modulated signal varies in strength as a
function of the modulating waveform. The modulated pulsed waveform
graph has a y-axis representing magnitude of power, and an x-axis
representing time. Each pulse represents modulated power having a
pulse peak of about +/-3000 W, and a duty cycle between about 10 to
90 percent. Note that FIG. 5D illustratively shows a 50% duty
cycle, however, one skilled in the art will appreciate that the
duty cycle may vary depending on the particular recipe used to form
the features (e.g., deep trench). The controller 110 controls the
pulsed power to the biasing element 120 based on the particular
processing recipe requirements. The pulses are repeated during
processing to emulate a modulated waveform. It is noted that only
one biasing power source (e.g., 150 or 154) is necessary to provide
the modulated pulsed waveform shown in FIG. 5D.
[0052] At the peak magnitudes (higher energy levels) of the
modulated CW (and pulsed) signal (point A) components of the plasma
(e.g., ions) are accelerated toward the wafer, as compared to when
the magnitude of the modulated CW signal (and modulated pulsed
signal) approaches lower energy levels (point B). Further, the ion
energy increases because of the low and medium frequency used for
the bias power, as well as modulates as the amplitude modulates.
Although the modulation waveforms are shown and discussed in FIGS.
5A-5D as a sine wave and square wave, those skilled in the art will
appreciate that other waveforms may also be modulated onto a
carrier signal.
[0053] FIG. 4 depicts a cross-sectional view of a second embodiment
of a dual frequency bias plasma chamber system 400. This second
embodiment may also be used to practice the invention and is
illustratively an inductively coupled plasma chamber reactor 400,
such as a DPS-DT reactor, available from Applied Materials Inc., of
Santa Clara, Calif. For a detailed description of the exemplary
inductively coupled reactor 400, the reader is directed to U.S.
Pat. Nos. 6,444,085, 6,454,898, 6,444,084, and 6,270,617, which are
incorporated herein by reference in their entirety. In general, any
etch chamber having a plasma source element and a wafer bias
element, where the wafer bias element is capable of being coupled
to a modulated bias power may be utilized. That is, those skilled
in the art will appreciate that other forms of etch chambers may be
used to practice the invention, including chambers with remote
plasma sources, microwave plasma chambers, electron cyclotron
resonance (ECR) plasma chambers, among others.
[0054] The reactor 400 comprises a process chamber 406 having a
wafer support pedestal 420 within a conductive body (wall) 422, and
a controller 410. The wall 422 is supplied with a dome-shaped
dielectric ceiling 472. Other modifications of the chamber 406 may
have other types of ceilings, e.g., a flat ceiling. Typically, the
wall 422 is coupled to an electrical ground. Above the ceiling 472
is disposed an inductive coil antenna 404. The inductive coil
antenna 404 is coupled to a plasma power source 462, through a
first matching network 461. The inductive coil antenna 404 serves
as a plasma generating element, and is disposed as a spiral shaped
helicoid around the dome ceiling 472. Alternatively, in instances
where the invention is practiced in chamber 100 having a
substantially flat ceiling 472, a stack or other forms of antennas
404 may be provided over the ceiling 472. The plasma power source
462 typically is capable of producing power between about 100 Watts
and about 7500 Watts, at a frequency of about 2 MHz to about 180
MHz, and in one embodiment, at a frequency of about 2 MHz to 13.56
MHz.
[0055] The support pedestal (biasing element) 421, which is
coupled, through a first matching network 451, to a first biasing
power source 450, as well as a second matching network 455, to a
second biasing power source 454. In one embodiment, the first and
second biasing power supplies 150 and 154 are coupled to a chucking
electrode (e.g., monopolar electrode), which is embedded in the
support pedestal (chuck) and functions as the biasing element.
Similar to the first embodiment shown in FIG. 1, the first biasing
power supply 450 provides RF power in the range of about 10 Watts
to 7500 Watts (W), and at a frequency in the range of about 100 KHz
to 6 MHz. The second biasing power supply 454 provides RF power in
the range of about 10 W to 7500 W, at a frequency in the range of
about 10 MHz to 60 MHz relative the ground, and, for example, at a
frequency of 13.56 MHz. As such, the signal from the first bias
power supply 450 amplitude modulates the signal from the second
bias power supply 454. For example, a 13.56 MHz signal from the
second bias power supply 154 is amplitude modulated with a 2 MHz
signal from the first biasing power supply 150, as discussed above
with regard to method 300 of FIG. 3 and illustrated by the
waveforms depicted in FIGS. 5A-5D.
[0056] In operation, a semiconductor wafer 401 is placed on the
pedestal 420 and process gases are supplied from a gas panel 460
through gas entry ports (nozzles) 474 to provide a gaseous mixture
in the processing region 440. The gaseous mixture is ignited into a
plasma in the chamber 406 by applying power from the source 462 to
the antenna 404. The pressure within the interior of the chamber
406 is controlled using a throttle valve 427 and a vacuum pump 464.
The temperature of the chamber wall 422 is controlled using
liquid-containing conduits (not shown) that run through the wall
422.
[0057] The temperature of the wafer 401 is controlled by
stabilizing a temperature of the support pedestal 420. In one
embodiment, helium gas from a source 448 is provided via a gas
conduit 449 to channels formed by the back of the wafer 401 and
grooves (not shown) on the pedestal surface. The helium gas is used
to facilitate heat transfer between the pedestal 420 and the wafer
401.
[0058] To facilitate control of the chamber as described above, the
controller 410 may be one of any form of general-purpose computer
processor that can be used in an industrial setting for controlling
various chambers and sub-processors. The controller 410 comprises a
central processing unit (CPU) 412, a memory 414, and support
circuits 416 for the CPU 412. The controller 410 facilitates
control of the components of the DPS etch process chamber 400 in a
similar manner as discussed for the controller 110 and chamber 106
of FIG. 1.
[0059] Accordingly, an apparatus for controlling a plasma in a
chamber during wafer processing has been shown and discussed above.
The apparatus comprises a biasing element disposed in the chamber
and adapted to support a wafer, and a plasma generating element is
disposed over the biasing element. A first power source is coupled
to the plasma generating element, and a second power source is also
coupled to the biasing element to provide a modulated signal to the
biasing element.
[0060] It is noted that the teachings of the present invention have
been shown and described in two exemplary etching chambers
utilizing a source power supply 162 and 462 to control ion energy
and ion bombardment on the wafers. However, the present invention
is also applicable where no power (i.e., power (W) and frequency
(Hz) both equal zero) is provided from a source power supply, such
as in an eMAX chamber, which is available from Applied Materials
Inc. of Santa Clara, Calif. In this instance, the chamber surface
serves as an RF ground (anode) with respect to the biasing power
supplies 150 and 154, and one of the biasing power supplies may be
utilized to serve as both bias and source power supplies.
[0061] Although various embodiments that incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
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