U.S. patent application number 15/980621 was filed with the patent office on 2018-09-13 for ion-ion plasma atomic layer etch process and reactor.
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, Yang Yang.
Application Number | 20180261429 15/980621 |
Document ID | / |
Family ID | 56919264 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180261429 |
Kind Code |
A1 |
Collins; Kenneth S. ; et
al. |
September 13, 2018 |
ION-ION PLASMA ATOMIC LAYER ETCH PROCESS AND REACTOR
Abstract
A reactor with an overhead electron beam source is capable of
generating an ion-ion plasma for performing an atomic layer etch
process.
Inventors: |
Collins; Kenneth S.; (San
Jose, CA) ; Ramaswamy; Kartik; (San Jose, CA)
; Carducci; James D.; (Sunnyvale, CA) ; Rauf;
Shahid; (Pleasanton, CA) ; Dorf; Leonid; (San
Jose, CA) ; Yang; Yang; (Los Gatos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
56919264 |
Appl. No.: |
15/980621 |
Filed: |
May 15, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14660531 |
Mar 17, 2015 |
|
|
|
15980621 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/32422 20130101;
H01J 37/32357 20130101; H01J 37/3255 20130101; H01J 37/3233
20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32 |
Claims
1. An electron beam plasma reactor comprising: a plasma chamber
having a side wall, an upper portion, and a lower portion; an upper
electrode in the upper portion of the plasma chamber; a workpiece
support to hold a workpiece in the lower portion of the plasma
chamber with the workpiece facing the upper electrode; a first RF
power source coupled to the upper electrode; a gas supply to
provide gas to the plasma chamber; a vacuum pump coupled to the
chamber to evacuate the chamber; a controller configured to operate
the first RF power source to apply an RF power to upper electrode,
and to operate the gas distributor and vacuum pump, so as to create
a first plasma in an upper portion of the chamber that generates
ions that bombard the upper electrode such that the upper electrode
emits an electron beam toward the workpiece, and such that a
portion of the electron beam impinges gas in the lower portion of
the plasma chamber to generate a second plasma in the lower portion
having a lower electron temperature than the first plasma.
2. The plasma reactor of claim 1, further comprising a bias voltage
generator coupled to workpiece support pedestal.
3. The plasma reactor of claim 1, wherein the upper electrode
comprises one of silicon, carbon, silicon carbide, silicon oxide,
aluminum oxide, yttrium oxide, zirconium oxide.
4. The plasma reactor of claim 1, wherein the RF source power
generator comprises a first RF power generator having a first
frequency and a second RF power generator having a second
frequency.
5. The plasma reactor of claim 4, comprising a folded resonator
coupled between the RF source power generator and the upper
electrode.
6. The plasma reactor of claim 1, comprising a first electromagnet
or permanent magnet adjacent and surrounding the upper portion of
the chamber and a second electromagnet or permanent magnet adjacent
and surrounding the lower portion of the chamber.
7. The plasma reactor of claim 1, comprising a first gas supply to
supply a first gas to the upper portion of the chamber and a second
gas supply to supply a second gas to the lower portion of the
chamber.
8. The plasma reactor of claim 7, wherein the first gas supply is
configured to supply an inert gas to the chamber and the second gas
supply is configured to supply a process gas to the chamber.
9. The plasma reactor of claim 1, further comprising a window in
the side wall in the upper portion of the chamber, a coil antenna
around the window, and an RF generator coupled to the coil
antenna.
10. The plasma reactor of claim 1, wherein the controller is
configured to operate the first RF power source to apply an RF
power to upper electrode, and to operate the gas distributor and
vacuum pump, such that a portion of the electron beam impinges the
workpiece.
11. The plasma reactor of claim 1, wherein the first RF power
source comprises a first RF power supply to apply RF power of a
first frequency and a second RF power supply to apply RF power of a
second frequency.
12. A method of processing a workpiece in an electron beam plasma
reactor, the method comprising: supporting a workpiece in a chamber
of the plasma reactor such that the workpiece faces an upper
electrode; introducing gas into an upper portion of the chamber;
and applying a first RF power to the upper electrode so as to
create a first plasma in an upper portion of the chamber such that
ions of the plasma impact the upper electrode and generate an
electron beam of secondary electrons from the upper electrode
toward the workpiece, wherein a portion of the electron beam
impinges gas in the lower portion of the plasma chamber to generate
a second plasma in the lower portion having a lower electron
temperature than the first plasma.
13. The method of claim 12, wherein introducing gas comprises
supplying a substantially inert gas into the upper portion of the
chamber and supplying a molecular process gas into a lower portion
of the chamber.
14. The method of claim 12, further comprising applying a bias
voltage to the workpiece.
15. The method of claim 12, wherein the upper electrode comprises
one of silicon, carbon, silicon carbide, silicon oxide, aluminum
oxide, yttrium oxide, zirconium oxide.
16. The method of claim 12, comprising applying a first magnetic
field from a first electromagnet or permanent magnet to the upper
portion of the chamber and applying a second magnetic field from a
second electromagnet or permanent magnet to the lower portion of
the chamber.
17. The method of claim 12, wherein applying a first RF power
comprises applying RF power of a first frequency and applying RF
power of a second frequency.
18. The method of claim 12, wherein a portion of the electron beam
impinges the workpiece.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
U.S. application Ser. No. 14/660,531, filed on Mar. 17, 2015, the
entire disclosure of which is incorporated by reference.
BACKGROUND
Technical Field
[0002] The disclosure concerns a plasma reactor for processing a
workpiece such as a semiconductor wafer using an overhead electron
beam source.
Background Discussion
[0003] Plasma sources for processing a workpiece can have an
electron beam source having a beam path that is transverse to the
cylindrical axis of symmetry of the plasma reactor. Such a
transverse arrangement can introduce asymmetries into the
processing, for which special features may be needed in the reactor
to avoid such asymmetries.
[0004] There is a need for a plasma reactor having an electron beam
plasma source in which there are no inherent asymmetries.
SUMMARY
[0005] An electron beam plasma reactor comprises: (1) an upper
plasma chamber comprising: (a) a side wall, (b) a top electrode
support comprising an electrically insulated electrostatic chuck
and thermal control apparatus coupled to said top electrode
support, (c) a top electrode thermally coupled to said top
electrode support and having a top electrode surface, (d) an RF
source power generator coupled to said top electrode or to said top
electrode support or to an interior of said upper chamber, and a
D.C chucking voltage source coupled to said electrically insulated
electrostatic chuck, (e) a gas distributor, and (f) a grid filter
facing said top electrode surface. The electron beam plasma reactor
further comprises: (2) a lower plasma chamber, said grid filter
separating said upper plasma chamber from said lower plasma
chamber, said lower plasma chamber comprising: (a) a vacuum chamber
body surrounding a processing region, and (b) a workpiece support
pedestal comprising an electrically insulated electrostatic chuck
and thermal control apparatus coupled to said workpiece support
pedestal, and having a workpiece support surface facing said grid
filter.
[0006] In one embodiment, the reactor further comprises a bias
voltage generator coupled to workpiece support pedestal.
[0007] In one embodiment, said top electrode comprises one of
silicon, carbon, silicon carbide, silicon oxide, aluminum oxide,
yttrium oxide, or zirconium oxide.
[0008] In one embodiment, said RF source power generator comprises
a first RF power generator of a VHF frequency and a second RF power
generator of a below-VHF frequency.
[0009] In one embodiment, said grid filter is conductive, wherein
said grid filter is one of: (a) electrically floating, or (b) at a
fixed potential.
[0010] One embodiment of the plasma reactor further comprises a
folded resonator coupled between said first RF power generator and
said top electrode. In one embodiment, said folded resonator is
coaxial with said side wall.
[0011] In one embodiment, said RF source power generator comprises
a lower VHF frequency generator having a first VHF frequency and a
higher VHF frequency generator having a second VHF frequency
greater than said first VHF frequency.
[0012] In one embodiment, said grid filter comprises first and
second grids facing one another, said plasma reactor further
comprising an acceleration voltage source connected to one of said
first and second grids.
[0013] One embodiment further comprises a first magnet adjacent one
of said upper and lower chambers, each circularly shaped and
disposed at respective axial locations around said chamber. In the
latter embodiment, the reactor further comprises a second magnet,
said first and second magnets being adjacent respective ones of
said upper and lower chambers, said first and second magnets being
circularly shaped and disposed at respective axial locations around
said chamber, wherein said first and second magnets produce one of:
(a) a cusp-shaped field that is predominantly axial in said upper
chamber and predominantly radial in said lower chamber, or (b) an
axial field. In the latter embodiment, the reactor further
comprises a third magnet, wherein said first and second magnets
produce a first cusp-shaped field having a cusp plane at said upper
chamber and said second and third magnet produce a second
cusp-shaped field having a cusp plane at said lower chamber.
[0014] In one embodiment, the reactor further comprises a magnet
having a magnetic field in a transverse direction in said lower
chamber.
[0015] In one embodiment, the reactor further comprises: a window
in said side wall; a coil antenna around said window; and an RF
generator coupled to said coil antenna.
[0016] In one embodiment, the reactor further comprises a remote
plasma source having an output coupled to said chamber.
[0017] In accordance with a further embodiment, a method of
processing a workpiece in an electron beam plasma reactor
comprises: dividing a chamber of said reactor into an upper chamber
and a lower chamber by a grid filter, and supporting a workpiece in
said lower chamber with a surface of said workpiece facing said
grid filter along an axis; supplying a gas into said chamber;
coupling RF source power into said upper chamber or to an electrode
of said upper chamber to generate a plasma including beam electrons
in said upper chamber to produce an electron beam having a beam
propagation direction corresponding to said axis; allowing flow of
at least a portion of said beam electrons from said upper chamber
to said lower chamber while preventing flow of at least a portion
of non-beam electrons and plasma ions from said upper chamber to
said lower chamber; and producing a plasma in said lower chamber
from said electron beam.
[0018] In one embodiment, the method further comprises supplying a
substantially inert gas into said upper chamber and supplying a
molecular process gas into said lower chamber.
[0019] In one embodiment, said generating a plasma comprises
applying RF power to a plasma source electrode underlying a ceiling
of said upper chamber, the method further comprising supporting
said electrode by electrostatically chucking said plasma source
electrode to said ceiling.
[0020] In one embodiment, the method further comprises controlling
a temperature of said plasma source electrode by circulating a
thermally conductive medium inside said ceiling.
[0021] In one embodiment, the method further comprises coupling a
bias voltage to said workpiece.
[0022] In one embodiment, said plasma source electrode comprises
one of silicon, carbon, silicon carbide, silicon oxide, aluminum
oxide, yttrium oxide, or zirconium oxide.
[0023] In one embodiment, said generating a plasma comprises
applying RF source power to a plasma source electrode underlying a
ceiling of said upper chamber, wherein said RF source power
comprises RF power of a first frequency and RF power of a second
frequency.
[0024] In one embodiment, the method further comprises providing a
magnetic field in said chamber from a first magnet comprising
either a permanent magnet or an electromagnet. In one embodiment,
the method further comprises providing a second magnet, said first
and second magnets producing one of a cusp magnetic field or an
axial magnetic field.
[0025] In one embodiment, said generating a plasma further
comprises applying RF source power to a coil antenna around a
window in a sidewall of upper chamber.
[0026] In a yet further embodiment, a method of performing atomic
layer etching using an electron beam plasma source in a process
chamber comprises: dividing said process chamber into upper and
lower chambers by a grid filter, said upper chamber having a
ceiling electrode, and placing a workpiece in said lower chamber
having a surface layer to be etched; furnishing a molecular process
gas to said chamber; (I) performing a passivation process
comprising: (A) performing at least one of: (a) coupling a high
power level of VHF power into said upper chamber or to said ceiling
electrode, or (b) coupling a high level of inductively coupled
power into said upper chamber; and (B) maintaining a bias voltage
on said workpiece at zero or below a threshold for etching said
surface layer of said workpiece to reduce or prevent etching of the
surface layer during the passivation process; (II) performing an
etch process comprising: (A) performing at least one of: (a)
applying to said ceiling electrode a high level of lower frequency
RF power, or (b) reducing or eliminating the power level of at
least one of (1) said VHF power or (2) said inductively coupled
power; and (B) maintaining a bias voltage on said workpiece above a
threshold for etching said surface layer; and (III) repeating said
passivation and etch processes in alternating succession.
[0027] In one embodiment, said furnishing a molecular process gas
to said chamber comprises furnishing said molecular process gas
into said lower chamber. In this latter embodiment, the method may
further comprise furnishing an inert gas into said upper
chamber.
[0028] In one embodiment, said furnishing a molecular process gas
to said chamber comprises furnishing said molecular process gas
into said upper chamber. In this latter embodiment, said
passivation process may further comprise furnishing an inert gas
into said upper chamber.
[0029] In one embodiment, the method further comprises performing
said passivation process for a duration corresponding to
passivation of a selected depth of material of said surface layer.
In one embodiment, said selected depth is one atomic layer.
[0030] In one embodiment, said molecular process gas comprises a
passivation species.
[0031] In one embodiment, during said etch process, said reducing
dissociation substantially stops or diminishes passivation of said
surface layer of said workpiece.
[0032] In one embodiment, during said passivation process, said
enhancing dissociation comprises generating an electron beam by ion
bombardment of said ceiling electrode, said electron beam
propagating from said upper chamber to said lower chamber.
[0033] In embodiments, (a) said high level of power of said VHF
power is in a range of 300 to 10,000 Watts; (b) said high level of
inductively coupled power is in a range of 300 to 10,000 Watts; and
(c) said high level of lower frequency RF power is in a range of
300 to 10,000 Watts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] So that the manner in which the exemplary embodiments of the
present 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 appreciated that
certain well known processes are not discussed herein in order to
not obscure the invention.
[0035] FIG. 1 depicts a plasma reactor in accordance with a first
embodiment.
[0036] FIG. 1A depicts a modification of the plasma reactor of FIG.
1 having a pair of grids.
[0037] FIG. 2 depicts a plasma reactor in accordance with a second
embodiment.
[0038] FIG. 3 is a partially cut-away elevational view of a VHF
resonator employed in the embodiment of FIG. 2.
[0039] FIG. 4 is a plan view corresponding to FIG. 3.
[0040] FIG. 5A is an orthographic projection of a second embodiment
of the VHF resonator of FIG. 3.
[0041] FIG. 5B is a plan view corresponding to FIG. 5A.
[0042] FIG. 5C is an enlarged view of a portion of FIG. 5A.
[0043] FIG. 6 depicts an embodiment having a cusp-shaped magnetic
field as a magnetic filter.
[0044] FIG. 7 depicts an embodiment having an axial magnetic field
for confining an electron beam.
[0045] FIG. 8 depicts an embodiment having a transverse magnetic
field as a magnetic filter.
[0046] FIG. 9 depicts an embodiment having an upper cusp-shaped
magnetic field for confining plasma near the ceiling electrode and
a lower cusp-shaped magnetic field as a magnetic filter.
[0047] FIG. 10 is a block diagram depicting a method in accordance
with an embodiment.
[0048] FIG. 11 is a block diagram depicting an atomic layer etch
method in accordance with an embodiment.
[0049] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation. It is to be noted,
however, that the appended drawings illustrate only exemplary
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.
DETAILED DESCRIPTION
[0050] Referring to FIG. 1, an electron beam plasma reactor has a
vacuum chamber body defining a chamber 100 including a side wall
102 of cylindrical shape. The chamber 100 is divided by a grid
filter 104 into an upper chamber 100a and a lower chamber 100b. The
lower chamber 100b is a drift space because of a lack of
substantial electric field therein in the absence of an applied
bias voltage. A ceiling 106 overlies the upper chamber 100a, and
supports an electrode 108. In one embodiment, the electrode 108 is
formed of a process-compatible material such as silicon, carbon,
silicon carbon compound or a silicon-oxide compound. In an
alternative embodiment, the electrode 108 is formed of a metal
oxide such as aluminum oxide, yttrium oxide, or zirconium oxide.
The ceiling 106 and the electrode 108 may be disk-shaped. A bottom
surface of the electrode 108 faces the grid filter 104 and is
exposed to the interior of the upper chamber 100a. In one
embodiment, an insulator or dielectric ring 109 surrounds the
electrode 108.
[0051] A workpiece support pedestal 110 for supporting a workpiece
111 in the lower chamber 100b has a workpiece support surface 110a
facing the grid filter 104 and may be movable in the axial
direction by a lift servo 112. In one embodiment, the workpiece
support pedestal 110 includes an insulating puck 302 forming the
workpiece support surface 110a, a workpiece electrode 304 inside
the insulating puck 302, and a chucking voltage supply 305
connected to the workpiece electrode 304. Additionally, a base
layer 306 underlying the insulating puck 302 has internal passages
308 for circulating a thermal medium (e.g., a liquid) from a
circulation supply 310. The circulation supply 310 may function as
a heat sink or as a heat source.
[0052] An RF power generator 120 having a VHF frequency (e.g., 160
MHz) and a lower frequency RF power generator 122 having a
frequency below the VHF range or below the HF range (e.g., in the
MF or LF range, e.g., 2 MHz) are coupled to the electrode 108
through an impedance match 124 via an RF feed conductor 123. In one
embodiment, the impedance match 124 is adapted to provide an
impedance match at the different frequencies of the RF power
generators 120 and 122, as well as filtering to isolate the power
generators from one another. The output power levels of the RF
generators 120, 122 are independently controlled by a controller
126. As will be described in detail below, power from the RF power
generators 120, 122 is coupled to the electrode 108. In one
embodiment, the ceiling 106 is electrically conductive and is in
electrical contact with the electrode 108, and the power from the
impedance match 124 is conducted through the ceiling 106 to the
electrode 108. In one embodiment, the side wall 102 is formed of
metal and is grounded. In one embodiment, the surface area of
grounded internal surfaces inside the upper chamber 100a is at
least twice the surface area of the electrode 108. In one
embodiment, the grounded internal surfaces inside the chamber 100
may be coated with a process compatible material such as silicon,
carbon, silicon carbon compound or a silicon-oxide compound. In an
alternative embodiment, grounded internal surfaces inside the
chamber 100 may be coated with a material such as aluminum oxide,
yttrium oxide, or zirconium oxide.
[0053] In one embodiment, the RF power generator 120 may be
replaced by two VHF power generators 120a and 120b that are
separately controlled. The VHF generator 120a has an output
frequency in a lower portion (e.g., 30 MHz to 150 MHz) of the VHF
band, while the VHF generator 120b has an output frequency in an
upper portion (e.g., 150 MHz to 300 MHz) of the VHF band. The
controller 126 may govern plasma ion density by selecting the ratio
between the output power levels of the VHF generators 120a and
120b. With the two VHF power generators 120a and 120b, radial
plasma uniformity in the upper chamber 100a can be controlled by
selecting the gap of upper chamber 100a (the distance between the
electrode 108 and the grid filter 104) such that by itself the
lower VHF frequency produces an edge-high radial distribution of
plasma ion density in the upper chamber 100a and by itself the
upper VHF frequency produces a center-high radial distribution of
plasma ion density. With such a selection, the power levels of the
two VHF power generators 120a, 120b are then set to a ratio at
which uniformity of radial distribution of plasma ion density is
optimized.
[0054] In one embodiment, the ceiling 106 is a support for the
electrode 108 and includes an insulating layer 150 containing a
chucking electrode 152 facing the electrode 108. A D.C. chucking
voltage supply 154 is coupled to the chucking electrode 152 via the
feed conductor 155, for electrostatically clamping the electrode
108 to the ceiling 106. A D.C. blocking capacitor 156 may be
connected in series with the output of the impedance match 124. The
controller 126 may control the D.C. chucking voltage supply 154. In
one embodiment, the RF feed conductor 123 from the impedance match
124 may be connected to the electrode support or ceiling 106 rather
than being directly connected to the electrode 108. In such an
embodiment, RF power from the RF feed conductor 123 may be
capacitively coupled from the electrode support to the electrode
108.
[0055] In one embodiment, upper gas injectors 130 provide process
gas into the upper chamber 100a through a first valve 132. In one
embodiment, lower gas injectors 134 provide process gas into the
lower chamber 100b through a second valve 136. Gas is supplied from
an array of process gas supplies 138 through an array of valves 140
which may include the first and second valves 132 and 136, for
example. In one embodiment, gas species and gas flow rates into the
upper and lower chambers 100a, 100b are independently controllable.
The controller 126 may govern the array of valves 140. In one
embodiment, an inert gas is supplied into the upper chamber 100a
and a process gas is supplied into the lower chamber 100b. The
inert gas flow rate may be selected to substantially prevent
convection or diffusion of gases from the lower 100b into the upper
chamber 100a, providing substantial chemical isolation of the upper
chamber 100a.
[0056] In one embodiment, plasma may be produced in the upper
chamber 100a by various bulk and surface processes, including
energetic ion bombardment of the interior surface of the top
electron-emitting electrode 108. The ion bombardment energy of the
electrode 108 and the plasma density are functions of both RF power
generators 120 and 122. The ion bombardment energy of the electrode
108 may be substantially controlled by the lower frequency power
from the RF power generator 122 and the plasma density in the upper
chamber 100a may be substantially controlled (enhanced) by the VHF
power from the RF power generator 120. Energetic secondary
electrons may be emitted from the interior surface of the electrode
108. The flux of energetic electrons from the emitting surface may
comprise an electron beam, and may have a direction substantially
perpendicular to the interior surface of the electrode 108, and a
beam energy of approximately the ion bombardment energy of the
electrode 108, which typically can range from about 10 eV to 5000
eV. The collision cross-sections for different processes depend
upon the electron energy. At low energies, cross-sections for
excitation (and dissociation in molecular gases) are larger than
for ionization, while at high energies the reverse is true. The RF
power level(s) may be advantageously selected to target various
inelastic electron collision processes.
[0057] In another embodiment having optional RF source generator
174 and coil antenna 172, the plasma density in the upper chamber
100a may be substantially controlled (enhanced) by the RF power
from the RF power generator 174.
[0058] In one embodiment, the grid filter 104 is of a flat disk
shape and may be coaxial with the side wall 102. The grid filter
104 is formed with an array of plural openings 104-1. In one
embodiment, the axial thickness T of the grid filter 104 and the
diameter, d, of the plural openings 104-1 are selected to promote
flow through the grid filter 104 of energetic directed beam
electrons while impeding flow of non-beam (low energy) electrons
and plasma ions through the grid filter 104, and the ratio of grid
filter hole area to total grid filter area may be maximized. The
energetic electron flux (electron beam) may pass through the grid
filter 104 to the lower chamber 100b and may produce a plasma by
various electron impact processes in the lower chamber 100b.
[0059] The plasma produced by the electron beam in the lower
chamber 100b may have different characteristics from the plasma in
the upper chamber 100a. The grid filter 104 may function as a
filter to substantially electrically isolate the upper and lower
chambers 100a, 100b from one another. In one embodiment, the grid
filter 104 is formed of a conductive or semiconductive material,
and may be connected to ground or may be electrically floating. In
another embodiment, the grid filter 104 is formed of a
non-conductive material. In one embodiment, the grid filter 104 may
be coated with a process compatible material such as silicon,
carbon, silicon carbon compound or a silicon-oxide compound. In an
alternative embodiment, grid filter 104 may be coated with a
material such as aluminum oxide, yttrium oxide, or zirconium oxide.
In one embodiment, the plasma produced in the upper chamber 100a
may have high electron density and/or high electron temperature,
and have high energy ions impinging on the electrode 108.
[0060] At least a portion of the electron beam, comprised of the
secondary electron flux emitted from electrode 108 due to energetic
ion bombardment of the electrode surface, propagates through the
grid filter 104 and into the lower chamber 100b, producing a low
electron temperature plasma in the lower chamber 100b, with a
plasma density that depends upon beam energy and flux, as well as
other factors such as pressure and gas composition. The energetic
beam electrons may impinge upon the workpiece 111 or workpiece
support pedestal 110 upon leaving the plasma region of the lower
chamber 100b. The plasma left behind may readily discharge any
resultant surface charge caused by the electron beam flux.
[0061] In one embodiment, an electronegative or electron-attaching
gas such as Chlorine is furnished into the chamber, RF and/or VHF
power is applied to the electrode 108, RF power is optionally
applied to coil antenna 172, RPS power is optionally applied to a
remote plasma source (RPS) 280, a plasma is generated in the upper
chamber 100a and an accelerating voltage is developed on the
electrode 108 with respect to ground and with respect to the
plasma. The resulting energetic ion bombardment of the electrode
108 produces secondary electron emission from electrode surface,
which constitutes an electron beam flux from the electrode surface.
The grid filter 104 allows at least a portion of the electron beam
to propagate through the grid filter 104 and into the lower chamber
100b, while preventing at least a portion of non-beam electrons and
plasma ions from passing through the grid filter 104, producing a
low electron temperature plasma in the lower chamber 100b. The
resultant low electron temperature plasma in the lower chamber 100b
in an electronegative gas such as Chlorine may produce a highly
electronegative plasma, with negative ion densities much higher
than electron densities and approaching densities of positive ions.
Such a plasma is commonly called an ion-ion plasma.
[0062] A substantially axially-directed magnetic field,
substantially parallel to the electron beam, may be optionally used
to help guide the electron beam, improving beam transport through
the upper chamber 100a, the grid filter 104 and/or the lower
chamber 100b. A low frequency bias voltage or arbitrary waveform of
low repetition frequency may be applied to the workpiece support
pedestal 110 (e.g., to the workpiece electrode 304) to selectively
or alternately extract positive and/or negative ions from said
plasma and accelerate those ions at desired energy levels to impact
the surface of the workpiece 111 for etching, cleaning, deposition,
or other materials modification. Radicals produced (a) in the upper
chamber 100a, (b) by the electron beam in the lower chamber 100b,
(c) by the application of bias voltage to the workpiece support
pedestal 110, or (d) by the remote plasma source (RPS) 280, may
convect or diffuse to the workpiece 111 and participate in reaction
on the workpiece surface.
[0063] In another embodiment, a relatively inert gas such as Helium
or Argon is furnished into the upper chamber 100a, an
electronegative or electron-attaching gas such a Sulfur
Hexafluoride is flowed into the lower chamber 100b, RF and/or VHF
power is applied to the electrode 108, RF power is optionally
applied to coil antenna 172, RPS power is optionally applied to the
RPS 280, a plasma is generated in the upper chamber 100a and an
accelerating voltage is developed on the electrode 108 with respect
to ground and with respect to the plasma. The resulting energetic
ion bombardment of the electrode 108 produces secondary electron
emission from electrode surface, which constitutes an electron beam
flux from the electrode surface. The grid filter 104 allows at
least a portion of the electron beam to propagate through the grid
filter 104 and into the lower chamber 100b, while preventing at
least a portion of non-beam electrons and plasma ions from passing
through the grid filter 104, producing a low electron temperature
plasma in the lower chamber 100b.
[0064] The resultant low electron temperature plasma in the lower
plasma chamber in an electronegative gas such as Sulfur
Hexafluoride may produce a highly electronegative plasma, with
negative ion densities much higher than electron densities and
approaching densities of positive ions, commonly called an ion-ion
plasma. A substantially axially-directed magnetic field,
substantially parallel to the electron beam, may be optionally used
to help guide the electron beam, improving beam transport through
the upper chamber 100a, the grid filter 104 and/or the lower
chamber 100b. A low frequency bias voltage or arbitrary waveform of
low repetition frequency may be applied to the workpiece support
pedestal 110 to selectively or alternately extract positive and/or
negative ions from the plasma and accelerate the ionic species at
desired energy levels to impact the workpiece surface for etching,
cleaning, deposition, or other materials modification. Radicals
produced (a) in the upper chamber 100a, (b) by the electron beam in
the lower chamber 100b, (c) by the application of bias voltage to
the workpiece support pedestal 110, or (d) by the RPS 280 may
convect or diffuse to the workpiece 111 and participate in reaction
on the workpiece surface.
[0065] In one embodiment, the grid filter 104 is a gas distribution
plate, having internal gas passages 105a and gas injection outlets
105b. The internal gas passages 105a may be coupled to the array of
valves 140.
[0066] In one embodiment, an RF bias power generator 142 is coupled
through an impedance match 144 to the workpiece electrode 304 of
the workpiece support pedestal 110. In a further embodiment, a
waveform tailoring processor 147 may be connected between the
output of the impedance match 144 and the workpiece electrode 304.
The waveform tailoring processor 147 changes the waveform produced
by the RF bias power generator 142 to a desired waveform. The ion
energy of plasma near the workpiece 111 is controlled by the
waveform tailoring processor 147. In one embodiment, the waveform
tailoring processor 147 produces a waveform in which the amplitude
is held during a certain portion of each RF cycle at a level
corresponding to a desired ion energy level. The controller 126 may
control the waveform tailoring processor 147.
[0067] In one embodiment, a magnet 160 surrounds the chamber 100.
In one embodiment, the magnet comprises a pair of magnets 160-1,
160-2 adjacent the upper and lower chambers 100a, 100b,
respectively. In one embodiment, the pair of magnets 160-1, 160-2
provides an axial magnetic field suitable for confining an electron
beam that is propagating from the upper chamber 100a to the lower
chamber 100b.
[0068] In one embodiment, a side window 170 in the side wall 102
faces the upper chamber 100a and is formed of a material (e.g.,
quartz or aluminum oxide) through which RF power may be inductively
coupled. An inductive coil antenna 172 surrounds the side window
170 and is driven by an RF power generator 174 through an impedance
match 176. The remote plasma source 280 may introduce plasma
species into the lower chamber 100b.
[0069] In one embodiment, flow of energetic electrons to the
workpiece 111 is blocked by a magnetic field having a predominantly
radial component (i.e., transverse to the electron beam flow
direction) in the region between the grid filter 104 and the
workpiece 111. This magnetic field may be produced by one of the
magnets 160-1 or 160-2, or by another magnet or set of magnets.
[0070] In one embodiment, internal passages 178 for conducting a
thermally conductive liquid or media inside the ceiling 106 are
connected to a thermal media circulation supply 180. The thermal
media circulation supply 180 acts as a heat sink or a heat source.
The mechanical contact between the electrode 108 and the ceiling
106 is sufficient to maintain high thermal conductance between the
electrode 108 and the ceiling 106. In the embodiment of FIG. 1, the
force of the mechanical contact is regulated by the electrostatic
clamping force provided by the D.C. chucking voltage supply
154.
[0071] In one embodiment depicted in FIG. 1A, the grid filter 104
is replaced by two grids, namely an upper grid filter 104A and a
lower grid filter 104B spaced apart from one another. In one
embodiment, the upper and lower grid filters 104A, 104B are
conductive and may be held at different voltages. For example, the
upper grid filter 104A may be grounded while an acceleration
voltage supply 300 may be connected to the lower grid filter
104B.
[0072] In an alternative embodiment, an RF-driven coil antenna 290
may be provided over the ceiling 106.
[0073] FIG. 2 depicts a modification of the embodiment of FIG. 1 in
which the VHF power (from the RF generator 120) and the lower
frequency RF power (from the RF generator 122) are delivered to the
electrode 108 through separate paths. In the embodiment of FIG. 2,
the RF generator 120 is coupled to the electrode 108 through a
folded resonator 195 overlying an edge of the electrode 108. The
lower frequency RF generator 122 is coupled to the electrode 108
via the RF feed conductor 123 through an RF impedance match 194.
The D.C. chucking voltage supply 154 is coupled to the chucking
electrode 152 through the feed conductor 155 extending through a
passage in the ceiling 106.
[0074] One embodiment of the folded resonator 195 of FIG. 2 is now
described with reference to FIGS. 3 and 4. The folded coaxial
resonator 195 includes an inner conductive hollow cylinder 200 that
is coaxial with the ceiling electrode 108. The inner conductive
hollow cylinder 200 has a circular bottom edge 200a electrically
contacting the top surface of the ceiling electrode 108. The folded
coaxial resonator 195 further includes an outer conductive hollow
cylinder 205 having a circular bottom edge 205a contacting the top
surface of a dielectric ring 109 that surrounds the periphery of
the electrode 108. The dielectric ring 109 may consist of an
insulating support ring 109a and an insulating clamp ring 109b
beneath the insulating support ring 109a. The inner and outer
conductive cylinders 200, 205 are of at least approximately the
same axial length, so that their circular top edges 200b, 205b are
at the same height above the ceiling electrode 108. The folded
coaxial resonator 195 also includes a planar conductive annulus 210
resting upon and electrically connecting the circular top edges
200b, 205b of the inner and outer conductive hollow cylinders 200,
205. The folded coaxial resonator 195 further includes a center
conductive hollow cylinder 215 coaxial with the inner and outer
hollow conductive cylinders 200, 205 and located between them.
Preferably, the radius of the center conductive hollow cylinder 215
may be the geometric mean of the radii of the inner and outer
hollow conductive cylinders 200, 205. The center conductive hollow
cylinder 215 has a circular bottom edge 215a resting on and in
electrical contact with the top surface of the electrode 108.
[0075] A VHF power coupler 220 conducts VHF power from the RF
generator 120 to the center hollow conductive cylinder 215. Thus,
the center hollow conductive cylinder 215 is the RF-fed conductor
of the folded coaxial resonator 195, while the inner and outer
hollow conductive cylinders 200, 205 together with the planar
conducive annulus 210 are analogous to a grounded outer conductor
of a simple coaxial resonator. The electrical connection of the
bottom circular edges 200a, 215a to the ceiling electrode 108
provides the requisite D.C. short, equivalent to the D.C. short at
the end of a simple (unfolded) coaxial tuning stub.
[0076] The VHF power coupler 220 includes an axial conductor 222
extending through a top portion of the hollow inner cylinder 200
from a top end 222a outside of the hollow inner cylinder 200 to a
bottom end 222b inside of the inner cylinder 200. A first spoke
conductor 224a extends radially from the axial conductor bottom end
222b through a hole 226a in the inner cylinder 200 to the center
cylinder 215. As depicted in FIG. 4, there are a plurality of spoke
conductors 224a, 224b, 224c, symmetrically arranged and extending
radially from the axial conductor bottom end 222b, through
respective holes 226a, 226b, 226c in the inner cylinder 200 and to
the center cylinder 215 to which their outer ends are electrically
connected. In the illustrated embodiment, there are three spoke
conductors 224 disposed at 120 degree intervals, although any
suitable number n of spoke conductors 224 may be provided at 360/n
degree intervals.
[0077] In one embodiment, the VHF power coupler 220 is provided as
a coaxial structure in which the axial conductor 222 and each of
the spoke conductors 224 is a coaxial transmission line including a
center conductor that is RF hot, surrounded by a grounded outer
conductor or shield. This coaxial structure is depicted in FIGS. 5A
and 5B, and is compatible with the field-free environment of the
interior of the inner hollow conductive cylinder 200. In the
embodiment of FIGS. 5A and 5B, the axial conductor 222 consists of
a center axial conductor 222-1 connected to the output of the VHF
generator 120, and a grounded outer axial conductor 222-2
surrounding the center axial conductor 222-1. FIG. 5C depicts a
cross-sectional view of the axial conductor 222.
[0078] In the embodiment of FIGS. 5A-5C, each of the spoke
conductors 224a, 224b, 224c embodies a coaxial transmission line
structure. Thus, the spoke conductor 224a consists of a center
spoke conductor 224a-1 and an outer spoke conductor 224a-2
surrounding the center spoke conductor 224a-1. The center spoke
conductor 224a-1 extends radially from the axial center conductor
222-1 and terminates at and is electrically connected to the center
cylinder 215. The center spoke conductor 224a-1 is RF hot by reason
of its connection to the axial center conductor 222-1. The outer
spoke conductor 224a-2 extends from the grounded axial outer
conductor 222-2 and is terminated at (and electrically connected
to) the inner cylinder 200. The center spoke conductor 224a-1
passes through the hole 226a (without contacting the inner
conductive cylinder 200) to contact the center conductive cylinder
215.
[0079] The structure of each of the spoke conductors 224a, 224b,
224c is the same. Thus, the spoke conductor 224b consists of a
center spoke conductor 224b-1 and an outer spoke conductor 224b-2
surrounding the center spoke conductor 224b-1. The center spoke
conductor 224b-1 extends radially from the axial center conductor
222-1 and terminates at the center cylinder 215. The center spoke
conductor 224b-1 is RF hot by reason of its connection to the axial
center conductor 222-1. The outer spoke conductor 224b-2 extends
from the grounded axial outer conductor 222-2 and is terminated at
(and electrically connected to) the inner cylinder 200, while the
center spoke conductor 224b-1 passes through the hole 226b (without
contacting the inner conductive cylinder 200) to contact the center
conductive cylinder 215.
[0080] In like manner, the spoke conductor 224c consists of a
center spoke conductor 224c-1 and an outer spoke conductor 224c-2
surrounding the center spoke conductor 224c-1. The center spoke
conductor 224c-1 extends radially from the axial center conductor
222-1 and terminates at the center cylinder 215. The center spoke
conductor 224c-1 is RF hot by reason of its connection to the axial
center conductor 222-1. The outer spoke conductor 224c-2 extends
from the grounded axial outer conductor 222-2 and is terminated at
(and electrically connected to) the inner cylinder 200, while the
center spoke conductor 224c-1 passes through the hole 226c (without
contacting the inner conductive cylinder 200) to contact the center
conductive cylinder 215.
[0081] The plural spoke center conductors 224a-1, 224b-1 and 224c-1
extend in the radial direction from the axial center conductor
222-1 to electrically contact the center conductive cylinder 215.
The area of this contact defines a circular plane. The axial
location of this circular plane is selected to be such that the
electrical or RF impedance at this location matches the
characteristic impedance of 224a, 224b and 224c, respectively, at
the VHF frequency of the RF generator 120. The characteristic
impedance of the individual spoke conductors 224a, 224b and 224c is
selected such that their total impedance at the junction (222b)
matches the output impedance of the VHF generator 120 at the
frequency of the VHF generator 120.
[0082] FIG. 6 depicts a cusp-shaped magnetic field produced by the
magnets 160-1 and 160-2 in one embodiment. The cusp-shaped magnetic
field is predominantly radial in the lower chamber 100b and
therefore diverts electrons from reaching the workpiece 111. The
cusp-shaped magnetic field is axial in a small region in the
center. In order to avoid leakage of energetic electrons through
the center portion the field due to the predominantly axial form of
the field in the center, a center shield or blocker 400 may be
provided.
[0083] FIG. 7 depicts an axial-shaped magnetic field produced by
the magnets 160-1 and 160-2 in another embodiment. The axial
magnetic field is effective for confining the electron beam along
an axial path.
[0084] FIG. 8 depicts a transverse magnetic field M produced in the
lower chamber 100b by a magnet 161, for diverting electrons from
reaching the workpiece 111. The magnet 161 may be implemented as a
Halbach array, for example. The magnet 161 may be a circular array
of electromagnets so that the transverse magnetic field M may be
electrically rotated about the axis of cylindrical symmetry of the
chamber 100, to enhance process uniformity.
[0085] FIG. 9 depicts a magnetic field including an upper
cusp-shaped magnetic field 500 produced by magnets 160-1 and 160-2
in the upper chamber 100a and a lower cusp-shaped magnetic field
504 produced by magnets 160-2 and 160-3 in the lower chamber 100b.
The upper and lower cusp-shaped magnetic fields 500, 504 have
respective planes of symmetry 506, 508 above and below the grid
filter 104, respectively. The upper cusp-shaped field 500 helps
confine plasma near the electrode 108. The lower cusp-shaped
magnetic field 504 is predominantly radial in the lower chamber
100b and therefore diverts electrons from reaching the workpiece
111. The cusp field is axial in a small region in the center. In
order to avoid leakage of energetic electrons through the center
portion the field due to the predominantly axial form of the field
in the center, a center shield or blocker 400 may be provided in
the lower chamber 100b.
[0086] Any one of the electron beam plasma reactors of FIG. 1, FIG.
1A or FIG. 2 may be employed to carry out the following method of
processing a workpiece in an electron beam plasma reactor.
Referring now to FIG. 10, the grid filter 104 is provided to divide
the chamber 100 into an upper chamber 100a and a lower chamber 100b
(block 610 of FIG. 10), while supporting the workpiece 111 in the
lower chamber 100b facing the grid filter 104. A gas is supplied
into at least one of the upper and lower chambers 100a, 100b (block
612 of FIG. 10). RF source power into the upper chamber 100a or to
the electrode 108 to generate a plasma including beam electrons in
the upper chamber 100a to produce an electron beam having a beam
propagation direction corresponding to the axis of symmetry (block
614 of FIG. 10). The method further includes allowing flow of at
least a portion of the beam electrons from the upper chamber 100a
to the lower chamber 100b through the grid filter 104 (block 616 of
FIG. 10) while preventing flow through the grid filter 104 of at
least a portion of non-beam electrons and plasma ions from the
upper chamber 100a to the lower chamber 100b (block 618 of FIG.
10). The method further includes allowing the electron beam to
produce a plasma in the lower chamber 100b (block 620 of FIG. 10).
The method can further include supplying a substantially inert gas
into the upper chamber 100a and supplying a molecular process gas
into the lower chamber 100b (block 622 of FIG. 10). The method can
further include coupling a bias voltage to the workpiece 111 (block
624 of FIG. 10).
Atomic Layer Etching:
[0087] The reactor of FIG. 1 or FIG. 1A or FIG. 2 may be employed
to perform an atomic layer etch process. In one example, the
workpiece 111 includes a semiconductive bulk layer (e.g.,
monocrystalline Silicon), an overlying layer (e.g., an oxide of
Silicon) and a surface layer (e.g., polycrystalline Silicon), which
may be partially masked. In this process, one of the gas supplies
138 contains a precursor of an etch species (e.g., Argon gas),
while another one of the gas supplies 138 contains a precursor of a
passivation species (e.g., Chlorine gas). The passivation species
is produced by dissociation (in a plasma) of the passivation
precursor species (e.g., the Chlorine gas). Passivation is
performed by exposing the workpiece 111 to the passivation species.
Generally, the surface layer of the workpiece 111 is not readily
etched (or is not susceptible to etching) by the etch species at
the selected energy. Passivation renders the surface layer of the
workpiece susceptible to etching by the etch species. The depth of
the passivated portion of the surface layer is determined by the
time of exposure to the passivation species. In this process, the
time of exposure to the passivation species is set to a duration in
which one atomic layer is passivated. Then, the workpiece 111 is
exposed to the etch species, to remove the one atomic layer.
Thereafter the foregoing sequence is repeated to remove the next
atomic layer. This cycle is repeated until a desired portion (e.g.,
100%) of the surface layer has been removed, one atomic layer at a
time. The process thus consists of alternating phases of
passivation and etching.
[0088] Referring now to FIG. 1, FIG. 1A or FIG. 2, in one
embodiment, an inert gas such as Argon is furnished to the upper
chamber 100a, and a molecular process gas such as Chlorine is
furnished to the lower chamber 100b. As described above with
reference to FIG. 1, the plasma is sustained by various bulk and
surface processes, including energetic ion bombardment of the
electrode 108 by plasma ions. The density of the plasma is
primarily controlled by the power level of the VHF power from the
RF power generator 120 or by the power level of the RF power
generator 174 powering the optional RF coil antenna 172, while the
ion bombardment energy on the electrode 108 and thus the resultant
secondary electron beam energy is primarily controlled by the power
level of the lower frequency power from the RF power generator 122.
During the passivation phase, high power level in a range of 300 to
10,000 Watts of VHF power from the RF power generator 120 (or
optionally from the RF power generator 174 powering the optional RF
coil antenna 172) produces a plasma in the upper chamber 100a.
[0089] The foregoing examples of high power levels are for a
reactor that processes workpieces of 200 mm to 300 mm diameter,
while larger substrates would use higher power levels. The voltage
on the electrode 108, which may be optionally increased by
additional application of RF power from the VHF power generator
120b to the electrode 108, accelerates an electron beam, which
propagates through the grid filter 104 into the lower chamber 100b,
producing a plasma in the lower chamber 100b. The high flux, low
energy, electron beam conditions in the lower chamber 100b enhance
dissociation of at least a portion of molecular Chlorine into
atomic Chlorine radicals, electrons and ions. Due to the low
electron temperature plasma, in the absence of applied workpiece
bias, the ion energy is below the threshold for etching silicon and
passivation of the workpiece surface occurs without significant
etching. Next, in the etching phase, at least one of: (A) a high
level of lower frequency RF power (in a range of 300 to 10,000
Watts) is applied to the electrode 108, or (B) low or no VHF power
is applied to the electrode 108, or (C) low or no RF power is
applied to the coil antenna 172. Low power in this instance is in a
range below 300 Watts. The foregoing example of high power level is
for a reactor that processes workpieces of 200 mm to 300 mm
diameter, while larger substrates would use higher power levels.
The higher voltage on the electrode 108 accelerates a higher energy
electron beam, which propagates through the grid filter 104 into
the lower chamber 100b, producing a plasma in the lower chamber
100b. The high energy electron beam conditions in the lower chamber
100b enhance ionization and reduce dissociation of molecular
Chlorine into atomic Chlorine radicals, electrons and ions. In
addition, Argon neutrals, which have flowed through the grid filter
104 to the lower chamber 100b, may be ionized by beam electrons.
Bias voltage is turned on (applied to the workpiece support
pedestal 110) during the etching phase at a voltage corresponding
to an energy sufficient to etch silicon in the presence of surface
Chlorine passivation species, but insufficient to etch silicon in
the absence of the passivation species, and ionic etchant species
(Argon or Chlorine ions) may be extracted and accelerated into the
workpiece surface, promoting etching. The cycle is then
repeated.
[0090] Alternatively or additionally, the remote plasma source
(RPS) 280 may provide passivation radicals. In an alternative
variation of embodiments described in detail above, Chlorine is
furnished to the upper chamber 100a (and optionally Argon is
furnished into the upper and or lower chambers 100a and 100b), and
Chlorine radicals are generated in the upper chamber 100a by the
application of high power level VHF power from the RF power
generator 120 (or optionally high power level from the RF power
generator 174 powering the optional RF coil antenna 172). The high
VHF power to the electrode 108 or the optional power to the coil
antenna 172 is used during passivation, while lower frequency RF
power to the electrode 108 (at low or no VHF power or coil power)
is used in conjunction with workpiece bias voltage during the
etching phase.
[0091] During the etching phase described above, the RF power
coupled to the electrode 108 may be a low frequency RF power or the
frequency may be of a higher frequency, e.g., VHF.
[0092] A method is provided for performing atomic layer etching
using an electron beam plasma reactor of the type described above
with reference to FIG. 1, 1A or 2. The method is depicted in FIG.
11. Referring to FIG. 11, a grid filter 104 divides the process
chamber 100 into the upper and lower chambers 100a, 100b, and a
workpiece is placed in the lower chamber 100b (block 632 of FIG.
11). A molecular process gas is supplied to the chamber 100 (block
634 of FIG. 11). A passivation process is performed (block 636 of
FIG. 11) and consists of: (A) performing at least one of: (a)
coupling a high power level of VHF power into said upper chamber
100a or to the electrode 108 (block 638 of FIG. 11), or (b)
coupling a high level of inductively coupled power into the upper
chamber 100a (block 640 of FIG. 11); and (B) maintaining a bias
voltage on the workpiece at zero or below a threshold for etching
said surface layer of said workpiece to reduce or prevent etching
of the surface layer during the passivation process (block 642 of
FIG. 11).
[0093] After the passivation process, an etch process is performed
(block 644 of FIG. 11) as follows: (A) performing at least one of:
(a) applying to said ceiling electrode a high level of lower
frequency RF power, (block 646 of FIG. 11) or (b) reducing or
eliminating the power level of at least one of (1) said VHF power
or (2) said inductively coupled power (block 648 of FIG. 11); and
(B) maintaining a bias voltage on said workpiece above a threshold
for etching said surface layer (block 650 of FIG. 11).
[0094] Thereafter, the method consists of repeating the passivation
and etch processes in alternating succession (block 652 of FIG.
11).
[0095] The molecular process gas may be furnished into the lower
chamber 100b. Additionally, the method can further includes
furnishing an inert gas into the upper chamber 100a. Alternatively,
the molecular process gas may be furnished into the upper chamber
100a.
Advantages:
[0096] The cylindrical symmetry of the VHF and RF power flow to the
ceiling and the cylindrical symmetry of the electron beam
distribution over the circular workpiece optimize azimuthal
uniformity in processing. The RF or VHF powered electrode provides
a plasma source for generating the electron beam and does not
require non-insulating surfaces for electrode or ground return. The
electrode 108 may be consumable in certain plasma processes and as
such the support structure, which may include an electrostatic
chuck, allows for fast electrode replacement and chamber
maintenance recovery, while ensuring repeatable electrical and
thermal electrode performance, crucial for process stability. The
grid filter 104 provides separation between the upper and lower
chambers 100a, 100b, enabling control of the workpiece processing
environment in the lower chamber 100b independently of the plasma
source environment of the upper chamber 100a. The upper and lower
gas injectors 130 and 134 enable independent distribution of
different gases or gas species to the upper and lower chambers
100a, 100b. For example, one gas (e.g., a "source" gas)
particularly useful for producing a species desired in the upper
chamber 100a is injected into the upper chamber 100a, while another
gas needed for processing the workpiece 111 (e.g., a "process" gas)
is injected into the lower chamber 100b. Gas may also be injected
through the gas injection outlets 105b of the grid filter 104. For
example, an inert gas may be injected through the gas injection
outlets 105b of the grid filter 104 so as to substantially prevent
process gas in the lower chamber 100b from convecting or diffusing
into the upper chamber 100a. In an embodiment where molecular gas
is provided to the upper chamber 100a, the dissociation of species
in the upper chamber 100a may be enhanced by the application of
higher VHF power to the electrode 108 or by the application of RF
power to the inductive coil antenna 172 without needing to expose
the workpiece 111 to a plasma with high ion density. The electron
beam energy and flux may be adjusted to control relative
dissociation and ionization processes: In an embodiment where inert
gas is flowed into upper chamber 100a and molecular gas is flowed
to lower chamber 100b, RF and/or VHF power to the electrode 108
and/or RF power to the coil antenna 172 may be adjusted to adjust
electron beam energy and flux to the lower chamber 100b for
relative control of dissociation and ionization processes in the
lower chamber 100b. The population of radicals or dissociated
species may be enhanced by the remote plasma source 280. Unlike a
commonly used dc discharge, RF capacitively coupled plasma or
inductively coupled plasma, with which a low electron temperature
plasma may not be produced continuously (may be produced
intermittently during the off-time of a pulsed dc or RF CCP/ICP
discharge), the foregoing embodiments may produce a low electron
temperature plasma continuously, with high uniformity over the
workpiece 111 in the lower chamber 100b. Furthermore, with
electronegative gas, an electron deficient, highly electronegative
"ion-ion" plasma may be produced continuously, with high uniformity
over the workpiece, and with the application of low frequency bias
voltage or low repetition frequency arbitrary voltage waveform
applied to the workpiece support pedestal 110, positive and/or
negative ions may be selectively or alternately extracted from
plasma and accelerated at desired energy levels into workpiece
surface for etching, cleaning, deposition, or other materials
modification processes.
[0097] While the foregoing is directed to embodiments of the
present invention, other and further embodiments may be devised
without departing from the basic scope thereof, and the scope
thereof is determined by the claims that follow.
* * * * *