U.S. patent application number 15/783983 was filed with the patent office on 2018-02-22 for low electron temperature etch chamber with independent control over plasma density, radical composition ion energy for atomic precision etching.
The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to James D. Carducci, Kenneth S. Collins, Leonid Dorf, Kartik Ramaswamy, Shahid Rauf, Olga Regelman, Hamid Tavassoli, Ying Zhang.
Application Number | 20180053631 15/783983 |
Document ID | / |
Family ID | 58631963 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180053631 |
Kind Code |
A1 |
Dorf; Leonid ; et
al. |
February 22, 2018 |
Low Electron Temperature Etch Chamber with Independent Control Over
Plasma Density, Radical Composition Ion Energy for Atomic Precision
Etching
Abstract
The disclosure concerns a method of operating a plasma reactor
having an electron beam plasma source for independently adjusting
electron beam energy, plasma ion energy and radical population. The
disclosure further concerns an electron beam source for a plasma
reactor having an RF-driven electrode for producing the electron
beam.
Inventors: |
Dorf; Leonid; (San Jose,
CA) ; Collins; Kenneth S.; (San Jose, CA) ;
Rauf; Shahid; (Pleasanton, CA) ; Ramaswamy;
Kartik; (San Jose, CA) ; Carducci; James D.;
(Sunnyvale, CA) ; Tavassoli; Hamid; (Cupertino,
CA) ; Regelman; Olga; (Daly City, CA) ; Zhang;
Ying; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Sant Clara |
CA |
US |
|
|
Family ID: |
58631963 |
Appl. No.: |
15/783983 |
Filed: |
October 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15146133 |
May 4, 2016 |
9799491 |
|
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15783983 |
|
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62247949 |
Oct 29, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 2237/3348 20130101;
H01J 37/32357 20130101; H01J 37/06 20130101; H01J 2237/334
20130101; H01J 37/3233 20130101; H01J 37/32422 20130101; H01J
2237/3174 20130101; H01L 21/3065 20130101; H01J 37/32082 20130101;
H01L 21/31116 20130101; H01J 37/32458 20130101; H01J 37/32532
20130101; H01J 37/3244 20130101; H01J 2237/3151 20130101; H01J
37/32174 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01J 37/06 20060101 H01J037/06 |
Claims
1-8. (canceled)
9. A plasma reactor for processing a workpiece, comprising: an
electron beam gun enclosure having a beam outlet opening at one end
of said enclosure and enclosing an electron emission electrode at
an opposite end of said enclosure, said electron emission electrode
having an electron emission surface facing said beam outlet, said
beam outlet and said electron emission electrode defining a beam
propagation path between them; an RF power source and an RF power
conductor coupled between said RF power source and said electron
emission electrode; and a processing chamber having a beam entry
port aligned with said beam outlet, a workpiece support in said
processing chamber for supporting a workpiece in a plane parallel
with said beam propagation path, and a gas distributor coupled to
said processing chamber.
10. The plasma reactor of claim 9 wherein said RF power source
comprises a first RF power generator and an impedance match coupled
between said first RF power generator and said electron emission
electrode.
11. The plasma reactor of claim 10 wherein said impedance match
comprises a dual frequency impedance match, said power source
further comprising a second RF power generator having a frequency
different from a frequency of said first RF power generator.
12. The plasma reactor of claim 11 wherein said first RF power
generator produces a low frequency and said second RF power
generator produces a high frequency.
13. The plasma reactor of claim 9 further comprising a gas supply
having a feed path into said electron beam gun enclosure.
14. The plasma reactor of claim 13 further comprising an
ion-blocking filter in said beam outlet opening, said ion-blocking
filter permitting flow of electrons through said beam outlet.
15. The plasma reactor of claim 9 further comprising: a backing
plate insulated from said electron gun enclosure and contacting a
back face of said electron emitting electrode; a chiller plate
contacting said backing plate; and wherein said RF power conductor
is connected to said chiller plate.
16. The plasma reactor of claim 15 further comprising an insulator
surrounding an edge of said electron emitting electrode and
disposed between said electron emitting electrode and said electron
gun enclosure.
17. The plasma reactor of claim 9 further comprising a process gas
supply coupled to said gas distributor.
18. The plasma reactor of claim 11 further comprising a remote
plasma source coupled to said processing chamber.
19. The plasma reactor of claim 18 further comprising a bias power
generator coupled to said workpiece support.
20. The plasma reactor of claim 19 wherein said first RF power
generator, said second RF power generator, said bias power
generator and said remote plasma source are independently
controllable.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional
Application No. 62/247,949, filed Oct. 29, 2015 entitled LOW
ELECTRON TEMPERATURE ETCH CHAMBER WITH INDEPENDENT CONTROL OVER
PLASMA DENSITY, RADICAL COMPOSITION AND ION ENERGY FOR ATOMIC
PRECISION ETCHING, by Leonid Dorf, et al.
BACKGROUND
Technical Field
[0002] The disclosure concerns a low electron temperature etch
chamber with independent control over plasma density, radical
composition and ion energy for atomic precision etching.
Background Discussion
[0003] Diminishing scale and increasing complexity of
microfabrication processes necessitate the use of novel
ultra-sensitive materials, which in turn requires low-damage plasma
etching with atomic layer precision. This imposes progressively
stringent demands for accurate control over ion energy and radical
composition during plasma processing.
SUMMARY
[0004] A method of processing a workpiece in a processing chamber,
comprises: limiting plasma electron temperature by generating a
plasma in the processing chamber with a sheet electron beam
parallel to a surface of the workpiece; controlling workpiece
potential with respect to plasma in a range between 0 and 25 volts
by applying bias power to a workpiece support in the chamber; and
independently controlling radical population in the plasma by
controlling production rate of a remote plasma source feeding the
processing chamber.
[0005] In one embodiment, the limiting of the plasma electron
temperature is performed so as to limit workpiece potential with
respect to the plasma to not more than a few volts in absence of an
applied bias power.
[0006] In one embodiment, the electron beam energy is limited to a
range (such as from sub-keV to a few keV) so as to limit
dissociation or radical production by the electron beam.
[0007] In one embodiment, the bias power controls the plasma ion
energy to be on an order of or near a bonding energy of a malarial
in the workpiece being etched.
[0008] A related method of processing a workpiece in a processing
chamber comprises: generating a plasma in the processing chamber
while limiting plasma electron temperature by propagating an
electron beam in the processing chamber; controlling a level of
bias power coupled to a workpiece support so as to set plasma ion
energy to be on an order of or near a bonding energy of a material
on the workpiece being etched; and controlling radical population
in the plasma by controlling production rate of a remote plasma
source coupled to the processing chamber. In one optional
embodiment, the electron beam energy is limited to a range (such as
from sub-keV to a few keV) so as to limit dissociation or radical
production by the electron beam.
[0009] A plasma reactor for processing a workpiece comprises: an
electron beam gun enclosure having a beam outlet opening at one end
of the enclosure and enclosing an electron emission electrode at an
opposite end of the enclosure, the electron emission electrode
having an electron emission surface facing the beam outlet, the
beam outlet and the electron emission electrode defining a beam
propagation path between them; an RF power source and an RF power
conductor coupled between the RF power source and the electron
emission electrode; and a processing chamber having a beam entry
port aligned with the beam outlet, a workpiece support in the
processing chamber for supporting a workpiece in a plane parallel
with the beam propagation path, and a gas distributor coupled to
the processing chamber.
[0010] In one embodiment, the RF power source comprises a first RF
power generator and an impedance match coupled between the first RF
power generator and the electron emission electrode. In a further
embodiment, the impedance match comprises a dual frequency
impedance match, the power source further comprising a second RF
power generator having a frequency different from a frequency of
the first RF power generator. In one embodiment, the first RF power
generator produces a low frequency and second RF power generator
produces a high frequency.
[0011] In one embodiment, the plasma reactor further comprises a
gas supply having a feed path to the electron beam gun enclosure.
In one embodiment, the plasma reactor further comprises an
ion-blocking filter in the beam outlet opening, the ion-blocking
filter permitting flow of electrons through the beam outlet.
[0012] In one embodiment, the plasma reactor further comprises: a
backing plate insulated from the electron gun enclosure and
contacting a back face of the electron emitting electrode; a
chiller plate contacting the backing plate; and the RF power
conductor is connected to the chiller plate. In one embodiment, the
plasma reactor further comprises an insulator surrounding an edge
of the electron emitting electrode and disposed between the
electron emitting electrode and the electron gun enclosure.
[0013] In one embodiment, the plasma reactor further comprises a
process gas supply coupled to the gas distributor.
[0014] In one embodiment, the plasma reactor further comprises a
remote plasma source coupled to the processing chamber.
[0015] In one embodiment, the plasma reactor further comprises a
bias power generator coupled to the workpiece support.
[0016] In one embodiment, the first RF power generator, the second
RF power generator, the bias power generator and the remote plasma
source are independently controllable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] So that the manner in which the above recited embodiments of
the invention are attained and can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0018] FIG. 1 illustrates a low damage reactor in accordance with a
first embodiment.
[0019] FIG. 2 depicts a method of operating the reactor of FIG.
1.
[0020] FIG. 3 illustrates a plasma reactor having an electron beam
source including an RF-driven electron emission electrode.
[0021] FIG. 4 depicts a modification of the embodiment of FIG. 1 in
which the e-beam source is the electron beam source of FIG. 3 that
includes an RF-driven electron emission electrode.
[0022] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. The drawings in the figures are all
schematic and not to scale.
DETAILED DESCRIPTION
Introduction:
[0023] Using an electron sheet beam (e-beam) parallel to the
workpiece surface to produce plasma in a processing chamber
provides an order of magnitude reduction in plasma electron
temperature Te (.about.0.3 eV) and plasma ion energy (Ei less than
a few eV in the absence of applied bias power) compared to
conventional plasma technologies, thus making an electron
beam-generated plasma an ideal candidate for processing features at
5 nm and below. Furthermore, since dissociation is performed only
by high-energy beam electrons and not plasma electrons, and since
the dissociation cross-section drops off considerably at or below
electron beam energies of about 2 keV, the chemical composition of
an electron beam-created plasma can be made radical-poor by
limiting the electron beam energy in accordance with one option.
This allows for independent control over plasma radical composition
by an external radical source, which is another advantage of using
electron beam technology to create plasma.
Low Damage Reactor:
[0024] In a first embodiment depicted in FIG. 1, a low-damage
reactor is provided that enables atomic precision processing (as in
atomic layer etching) and independent control of plasma ion energy
and radical composition of the plasma. The low-damage reactor
includes: a processing chamber 50 including an electrostatic chuck
52 holding a workpiece 54, an electron beam (e-beam) source 56 for
creating a radical-poor, low-electron temperature (Te) plasma in
the processing chamber 50, a remote plasma source 58 for producing
and supplying radicals through an outlet 58a to plasma in the
processing chamber 50, and a bias power generator 60 for creating a
voltage drop (with fine control in 0-50 V range) between the
workpiece 54 and the plasma to accelerate ions over etch-threshold
energies. The outlet 58a may include an ion-blocking grid 90. A
beam outlet 56a of the e-beam source 56 is covered by a filtering
grid 170 that admits electrons forming the electron beam but blocks
ions and other plasma by-products produced within the e-beam source
56.
[0025] The bias power generator 60 may have a bias voltage control
input 60a that provides the fine control in a 0-50 V range. In one
embodiment, the range is 0-25V. The electron beam source 56
includes a beam acceleration voltage control input 62 that controls
the electron energy of the electron beam source 56. The remote
plasma source 58 has a control input 59 for controlling the rate at
which the remote plasma source 58 supplies radicals into the
processing chamber 50. The control input 59 is independent of the
beam acceleration voltage control input 62. The rate at which the
remote plasma source 58 supplies radicals into the processing
chamber 50 and the energy of the electron beam are controlled
independently of one another. The control input 59 may be
implemented in various ways. For example, the control input 59 may
control the power level of an RF generator driving a plasma source
power applicator (not shown) in the remote plasma source 58. As
another possibility, the control input 59 may control a valve at
the outlet 58a between the remote plasma source 58 and the
processing chamber 50. A vacuum pump 66 may be provided for
evacuating the processing chamber 50.
[0026] Because of the ultra-low electron temperature in the
electron-beam generated plasma, the workpiece potential with
respect to the plasma is very low, just a few volts, without an
applied bias. This is much lower than in conventional plasma etch
tools, where it is typically confined to a range above or exceeding
about 15 V. Thus, unlike conventional tools, the low-damage reactor
of FIG. 1 enables precise control of ion energy in the range of
0-25 V by limiting the applied bias power accordingly. In this very
important range, the plasma ion energy is near (e.g., within 10%
of) or on the order of the bond energy of the etched material,
which enables performance of an ultra-low damage etch process. The
etch rate is likewise quite low at such ion energies--just a few
Angstroms per minute--which makes the low damage reactor also
uniquely suitable for atomic precision etching or atomic layer
etching. Another critical advantage enabling precise control over
the etch process is achieved through independent control over the
radical composition governed by the radical production rate of the
remote plasma source 58. As a result, true atomic precision etching
with ultra-low damage and only one to a few atomic layers per
minute etch rates is carried out in the low damage reactor.
[0027] In one embodiment, a method of operating the low-damage
reactor chamber is provided, in which the plasma ion energy and the
radical composition of the plasma are independently controlled. The
method is depicted in FIG. 2 and proceeds as follows:
[0028] First, limit plasma electron temperature to not exceed 0.3
eV and plasma ion energy to not exceed a few eV in absence of
applied bias power. This is done by generating in the e-beam source
56 a sheet electron beam parallel to the workpiece surface (block
310 of FIG. 2). This beam creates plasma in the processing chamber
50. Such limiting of the plasma electron temperature helps to
minimize workpiece potential relative to the plasma (i.e., sheath
voltage) to not more than about a few volts without applied
bias.
[0029] Second, control workpiece potential with reference to the
plasma inside the processing chamber 50 by controlling the bias
power generator 60 to set the workpiece potential to a range
between 0 and 25 volts (block 320 of FIG. 2). Alternatively or
equivalently, set the plasma ion energy to near the bonding energy
of the material being etched by controlling the bias power
generator 60.
[0030] Third, as one option that is not necessarily required, limit
electron beam energy to a range between several hundred volts and a
few kilovolts (block 330 of FIG. 2). This has the effect of
minimizing dissociation or radical production by the electron
beam.
[0031] Fourth, independently control radical population in the
plasma by controlling production rate of the remote plasma source
feeding the processing chamber (block 340 of FIG. 2).
E-Beam Source with RF-Driven Electrode
[0032] The challenges of developing an industry-worthy electron
beam plasma source include meeting the following requirements:
1. Process-chemistry compatibility: chemically aggressive and/or
depositing process gas should not affect e-beam source (gun)
operation or render it impossible, as with DC electron beam
sources; conversely, sputtering of the e-beam gun parts should not
adversely affect the process. 2. Capability for operation over a
wide range of process gas chamber pressures. 3. Robustness, i.e.
ability to operate for a long time between the preventive
maintenance events involving parts replacement. 4. High operational
stability and reproducibility. 5. Independent control over density
and energy of beam electrons.
[0033] What is needed is an electron beam source that satisfies the
foregoing criteria.
[0034] FIG. 3 depicts an embodiment of a plasma reactor having an
electron beam (e-beam) plasma source that satisfies the criteria
discussed above. Referring to FIG. 3, an emitting electrode 110 is
mounted on a backing plate 120. The backing plate 120 is mounted on
a chill plate 130. A ceramic spacer 140 and an insulator 150 hold
the emitting electrode 110 in place relative to an electron gun
body 160. The electron gun body 160 may be formed of an
electrically conductive material and be connected to a return
potential or to ground. In the illustrated embodiment, the electron
gun body 160 extends along an e-beam propagation path P and has a
beam outlet opening 160a at a distal end opposite the emitting
electrode 110. A filtering grid 170 is positioned within the beam
outlet opening 160a. A backfill gas feed 180 conducts gas suitable
as an electron source (e.g., Argon) from a gas supply 182 into the
interior of the electron gun body 160. A coolant liquid feed or
conduit 190 conducts coolant from a coolant source 192 to the chill
plate 130. An RF feed 200 conducts RF power to the emitting
electrode 110 through the chill plate 130 and through the backing
plate 120. An insulator 210 surrounds a portion of the RF feed 200.
The electron gun body 160, the emitting electrode 110, the backing
plate 120, the chill plate 130, the ceramic spacer 140, the
insulator 150 and the RF feed 200 together form an e-beam source
assembly 212, which is contained within an RF shield 220. The RF
feed 200 receives RF power through a dual frequency impedance match
230 from RF power generators 242 and 244. In one embodiment, the RF
power generator 242 produces low frequency RF power and the RF
power generator 244 produces high frequency RF power.
[0035] In one modification, the e-beam source assembly 212 of the
embodiment of FIG. 3 may be used as the e-beam source assembly 212
of the embodiment of FIG. 1. Such a modification is depicted in
FIG. 4.
[0036] A process chamber 260 is coupled to the electron gun body
160 through the opening 160a, and has a ceiling gas distributor 270
coupled to a process gas supply 272. An electrostatic chuck 280
within the process chamber 260 supports a workpiece 290 in a plane
parallel to the beam propagation path P.
[0037] An RF plasma discharge is ignited between the emitting
electrode 110 and the electron gun body 160 that serves as an RF
return. Two RF frequencies can be supplied by the RF power
generators 242, 244 including a low frequency such as 2 MHz, and a
HF or VHF frequency such as 60 MHz. This provides independent
control over: (1) the density of plasma (controlled by the level of
the HF or VHF power), which determines the density of the beam
electrons, and (2) the DC self-bias at the emitting electrode 110
(controlled by the level of the low frequency power), which
determines the energy of the beam electrons. Generally, the energy
of the beam electrons may be controlled by controlling the output
power level of the low frequency bias power generator 242.
Independent control over beam electron density can also be achieved
by adding an inductively coupled plasma source to the e-beam source
assembly 212.
[0038] Because the area of the electron gun body 160 is larger than
the area of the emitting electrode 110, the RF-induced DC self-bias
will be much larger at the smaller emitting electrode 110, and can
reach a level appropriate for the electron beam technology. For
example, the self-bias can reach 1-1.5 kV at about 1.5 kW of 2 MHz
power with about 600 W of 60 MHz power, at an internal pressure
within the electron gun body 160 of about 20 mT. The ions
accelerated in the sheath at the emitting electrode 110 bombard the
electrode surface and cause ion-induced secondary electron
emission. These emitted secondary electrons are in turn accelerated
in the same sheath voltage drop as they move away from the
electrode surface, resulting in formation of the electron beam.
Thus, the secondary electron emission coefficient of the emitting
surface of the emitting electrode 110 plays a very significant role
in determining the density of the beam electrons.
[0039] A significant portion of the applied RF power is deposited
into the emitting electrode 110 in the form of heat, due to
constant bombardment by high-energy ions. The chiller plate 130 has
non-conductive cooling fluid running through it, and is coupled
through the backing plate 120 to the emitting electrode 110. The RF
feed 200 is coupled through the chill plate 130 and the backing
plate 120 to the emitting electrode 110. The backing plate 120
serves as an RF plate distributing applied RF power evenly over the
emitting electrode 110.
[0040] The filtering grid 170 has high aspect ratio openings and
prevents leakage of the RF plasma ions and radicals created inside
the electron gun body 160 into the process chamber 260. Further,
the chemically aggressive process gas inside the process chamber
260 is blocked from entering the interior of the electron gun body
160. This gas separation is achieved using the back fill gas feed
180 by backfilling the interior of the electron gun body 160 with
inert gas such as Argon, supplied at a sufficiently high flow rate
to create a considerable gas pressure drop (for example, about 30
mT) across the filtering grid 170. In turn, high-energy electrons
can go through the high aspect ratio openings of the filtering grid
170, due to high directionality of their velocity distribution.
[0041] Backfilling the interior of the electron gun body 160 with
process-independent gas also allows modification of the electrode
emitting surface of the emitting electrode 110 to control secondary
electron emission coefficient by forming, for example, a Silicon
Nitride on the surface. Due to the nature of the plasma discharge,
practically any material (silicon, ceramic, quartz) can be used to
form the emitting surface of the emitting electrode 110 without
affecting general operation of e-beam source assembly 212.
[0042] The material sputtered by the ions off of the emitting
electrode 110 and re-deposited on the other parts of the e-beam
source assembly 212 can be cleaned in-situ by running HF or ICP
plasma only (at much lower self-bias) with appropriate chemistry,
if the emitting surface material is adequately selected. Likewise,
the grounded surface of the electron gun body 160 can be coated
with any process-compatible and not necessarily conductive
material, as long as the capacitance of the coating layer is
sufficiently small. Penetration of the sputtered material into the
process chamber 260 is also considerably restricted by the
filtering grid 170.
Advantages:
[0043] An advantage of using an RF-driven electrode (i.e., the
electrode 110) rather than a DC discharge to create the electron
beam is that electron beam density and electron beam energy are
independently controlled by high frequency power and low frequency
power, respectively, applied to the electrode 110. Further, use of
metals or other conductive materials may be minimized in the
construction of the e-beam source assembly 212, which makes
penetration of any sputtered material through the filtering grid
170 into the process chamber 260 generally less damaging for the
wafer processing.
[0044] Using an electron sheet beam (e-beam) parallel to the
workpiece surface to produce plasma in a processing chamber
provides an order of magnitude reduction in plasma electron
temperature Te (.about.0.3 eV) and plasma ion energy Ei (<2 eV
in the absence of applied bias power) compared to conventional
plasma technologies. This enables the plasma ion energy to be
reduced to near or below the binding energy of the material being
etched (e.g., silicon, silicon oxide, silicon nitride).
Furthermore, since dissociation is performed only by high-energy
beam electrons and not plasma electrons, and since the dissociation
cross-section drops off considerably at or below electron beam
energies of about 2 keV, the chemical composition of an electron
beam-created plasma can be made radical-poor. This allows for
independent control over plasma radical composition by the remote
radical source 58.
[0045] While the foregoing is directed to embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *