U.S. patent application number 10/160746 was filed with the patent office on 2002-10-03 for methods for actively controlling rf peak-to-peak voltage in an inductively coupled plasma etching system.
This patent application is currently assigned to LAM RESEARCH CORPORATION. Invention is credited to Nakajima, Shu.
Application Number | 20020139480 10/160746 |
Document ID | / |
Family ID | 24438458 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139480 |
Kind Code |
A1 |
Nakajima, Shu |
October 3, 2002 |
Methods for actively controlling RF peak-to-peak voltage in an
inductively coupled plasma etching system
Abstract
An inductively coupled plasma etching apparatus includes a
chamber and a window for sealing a top opening of the chamber. The
window has an inner surface that is exposed to an internal region
of the chamber. A metal plate, which acts as a Faraday shield, is
disposed above and spaced apart from the window. A coil is disposed
above and spaced apart from the metal plate. The coil is
conductively connected to the metal plate at a connection location
that is configured to generate a peak-to-peak voltage on the metal
plate that optimally reduces sputtering of the inner surface of the
window while substantially simultaneously preventing deposition of
etch byproducts on the inner surface of the window. In another
embodiment, the apparatus includes a controller for externally
applying a peak-to-peak voltage to the metal plate. The controller
includes an oscillation circuit, a matching circuit, an RF
generator, and a feedback control for monitoring the applied
peak-to-peak voltage. Methods for optimizing operation of an
inductively coupled plasma etching apparatus also are
described.
Inventors: |
Nakajima, Shu;
(Kanagawa-ken, JP) |
Correspondence
Address: |
MARTINE & PENILLA, LLP
710 LAKEWAY DRIVE
SUITE 170
SUNNYVALE
CA
94085
US
|
Assignee: |
LAM RESEARCH CORPORATION
FREMONT
CA
|
Family ID: |
24438458 |
Appl. No.: |
10/160746 |
Filed: |
May 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10160746 |
May 30, 2002 |
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09676462 |
Sep 29, 2000 |
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6422173 |
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09676462 |
Sep 29, 2000 |
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09608883 |
Jun 30, 2000 |
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Current U.S.
Class: |
156/345.48 |
Current CPC
Class: |
H01J 37/321
20130101 |
Class at
Publication: |
156/345.48 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A method for optimizing operation of an inductively coupled
plasma etching apparatus, comprising: supplying a chamber for
etching a wafer; attaching a window to a top opening of the
chamber, the window having an outer surface and an inner surface
that is exposed to an inner region of the chamber; placing a coil
over the window; placing a metal plate over the outer surface of
the window, the metal plate being positioned in a spaced apart
relationship between the coil and the outer surface of the window;
connecting the metal plate to a connection location on the coil,
the connection location being between an input terminal and an
output terminal and being optimally selected so as to produce
substantially uniform incident ion energy proximate to the inner
surface of the window, the substantially uniform incident ion
energy being configured to reduce sputtering of the inner surface
of the window while substantially simultaneously preventing
deposition of etch byproducts on the inner surface of the
window.
2. A method for optimizing operation of an inductively coupled
plasma etching apparatus, comprising: supplying a chamber for
etching a wafer; attaching a window to a top opening of the
chamber, the window having an outer surface and an inner surface
that is exposed to an inner region of the chamber; placing a coil
over the window; placing a metal plate over the outer surface of
the window, the metal plate being positioned in a spaced apart
relationship between the coil and the outer surface of the window;
and applying a controlled peak-to-peak voltage to the metal plate
so as to produce substantially uniform incident ion energy
proximate to the inner surface of the window, the substantially
uniform incident ion energy being configured to reduce sputtering
of the inner surface of the window while substantially
simultaneously preventing deposition of etch byproducts on the
inner surface of the window.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 09/676,462, filed Sep. 29, 2000, which is a
continuation-in-part of application Ser. No. 09/608,883, filed Jun.
30, 2000. The disclosures of these applications, from which
priority under 35 U.S.C. .sctn.120 is claimed, are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to semiconductor
fabrication and, more particularly, to methods for controlling the
plasma behavior inside of plasma etching chambers.
[0003] In semiconductor manufacturing processes, etching processes,
insulation film formation, and diffusion processes are repeatedly
carried out. As is well known to those skilled in the art, there
are two types of etching processes: wet etching and dry etching.
Dry etching is typically implemented by using an inductively
coupled plasma etching apparatus such as shown in FIG. 1A.
[0004] In the inductively coupled plasma etching apparatus shown in
FIG. 1A, a reactant gas is first led into chamber 20 through a gas
lead-in port (not shown). High frequency power is then applied from
a power supply (not shown) to coil 17. Semiconductor wafer 11 is
mounted on chuck 19 provided inside chamber 20. Coil 17 is held on
the upper portion of the chamber by spacers 13, which are formed of
an insulating material. In operation, high frequency (RF) current
passing through coil 17 induces an electromagnetic current into
chamber 20, and the electromagnetic current acts on the reactant
gas to generate a plasma.
[0005] The plasma contains various types of radicals and the
chemical reaction of the positive/negative ions is used to etch
semiconductor wafer 11 itself or an insulation film formed on the
wafer. During the etching process, coil 17 carries out a function
that corresponds to that of the primary coil of a transformer while
the plasma in chamber 20 carries out a function that corresponds to
that of the secondary coil of the transformer. The reaction product
generated by the etching process is discarded via exhaust port
15.
[0006] When etching one of the recently developed device materials
(e.g., platinum, ruthenium, and the like), the reaction product
generated may be a nonvolatile substance (e.g., RuO.sub.2). In some
cases, the reaction product may adhere to surface 10a of TCP window
10. If the reaction product is conductive, then the film of
reaction product on surface 10a may electrically shield the
electromagnetic current in the chamber. Consequently, the plasma
does not strike well after several wafers are etched and the
etching process must be discontinued.
[0007] In an effort to avoid this problem, a method for sputtering
the reaction product adhered to surface 10a of TCP window 10 by
using the plasma has been developed. In the inductively coupled
plasma etching apparatus shown in FIG. 1A, however, the
electromagnetic current induced by the RF current generates a
distribution voltage having a standing wave in the vicinity of TCP
window 10. This is problematic because it causes the deposition and
sputtering of the reaction product to become nonuniform.
[0008] FIGS. 1B and 1C illustrate the inherent nonuniformity of the
deposition and sputtering on the TCP window in the inductively
coupled plasma etching apparatus shown in FIG. 1A. In FIG. 1B, coil
17 is indicated by boxes having either an "x" or a ".circle-solid."
therein. The boxes having an "x" therein indicate that the coil
extends into the page. The boxes having a ".circle-solid." therein
indicate that the coil extends out of the page. As shown in FIG.
1B, some portions of surface 10a of TCP window 10 are subjected to
excess sputtering and other portions of the surface are subjected
to excess deposition. Excess sputtering occurs in the regions where
a relatively large amount of energy is added to the ions in the
plasma because the amplitude of the acceleration voltage due to the
standing wave at the location is high. As shown in the graph in the
lower part of FIG. 1C, the amplitude of standing wave 24 is high at
points 24a and 24b, which correspond to ends 17a and 17b,
respectively, of coil 17, as shown in the upper part of FIG. 1C.
Excess deposition occurs in the regions where only a relatively
small amount of energy is added to the ions in the plasma because
the amplitude of the standing wave is low. As shown in the graph in
the lower part of FIG. 1C, the amplitude of standing wave 24 is low
in the region proximate to point 22, which is the node of the
standing wave.
[0009] Nonuniform deposition and sputtering on the TCP window is
undesirable for a number of reasons. Excessive deposition is
undesirable because, as discussed above, the presence of an
electrically conductive film on the surface of the TCP window can
electrically shield the electromagnetic current in the chamber and
thereby disable the etching process. In addition, excessive
deposition often causes particle problems (particles flake off on
the wafer) and, consequently, increases the frequency with which
the chamber must be subjected to dry and wet cleanings. Frequent
cleaning of the chamber is particularly undesirable because it
sacrifices the tool's available up time and thereby reduces
throughput. Excessive sputtering is undesirable because the ion
bombardment can cause erosion of the TCP window, which is typically
made of quartz or alumina. Such erosion not only shortens the
lifetime of the TCP window, but also generates particles, which can
contaminate the wafer and introduce unwanted chemical species into
the process environment. The presence of unwanted chemical species
in the process environment is particularly undesirable because it
leads to poor reproducibility of the process conditions.
[0010] In view of the foregoing, there is a need for an inductively
coupled plasma etching apparatus that prevents substantial
deposition of electrically conductive reaction products on the
surface of the TCP window without causing excess erosion of the TCP
window.
SUMMARY OF THE INVENTION
[0011] Broadly speaking, the present invention provides an
inductively coupled plasma etching apparatus that uniformly adds
energy to the ions in the plasma in the vicinity of a wall of the
chamber in which the plasma is generated.
[0012] In one aspect of the invention, a first type of inductively
coupled plasma etching apparatus is provided. This inductively
coupled plasma etching apparatus includes a chamber and a window
for sealing a top opening of the chamber. The window has an inner
surface that is exposed to an internal region of the chamber. A
metal plate, which acts as a Faraday shield, is disposed above and
spaced apart from the window. A coil is disposed above and spaced
apart from the metal plate. The coil is conductively connected to
the metal plate at a connection location that is configured to
generate a peak-to-peak voltage on the metal plate that optimally
reduces sputtering of the inner surface of the window while
substantially simultaneously preventing deposition of etch
byproducts on the inner surface of the window.
[0013] In one embodiment, the inductively coupled plasma etching
apparatus further includes a coil input terminal for receiving RF
power and a coil output terminal. In this embodiment, the
connection location is defined between the coil input terminal and
the coil output terminal. In one embodiment, the connection
location is more proximate to the coil output terminal than to the
coil input terminal. In one embodiment, the inductively coupled
plasma etching apparatus further includes an RF generator, a match
circuit network coupled between the RF generator and the coil input
terminal, and a variable capacitor coupled between ground and the
coil output terminal.
[0014] In one embodiment, the inductively coupled plasma etching
apparatus further includes an oscillation circuit coupled to the
metal plate. The oscillation circuit is controllable so that the
peak-to-peak voltage on the metal plate may be adjusted. In one
embodiment, the oscillation circuit includes a variable capacitor
that can be adjusted to control the peak-to-peak voltage along a
harmonic point. In another embodiment, the inductively coupled
plasma etching apparatus further includes a voltage divider circuit
coupled to the metal plate. The voltage divider circuit is
controllable so that the peak-to-peak voltage may be adjusted. In
one embodiment, the voltage divider circuit includes a variable
capacitor that can be adjusted to control the peak-to-peak voltage
along a plot that decreases the peak-to-peak voltage as capacitance
of the variable capacitor increases.
[0015] In one embodiment, the inductively coupled plasma etching
apparatus includes a chamber lid that is configured to have
attached thereto the metal plate and the coil. The chamber lid may
be attached by hinges that enable opening and closing of the
chamber lid. When in a closed position, the chamber lid places the
metal plate proximate to the window in preparation for
operation.
[0016] In another aspect of the invention, a second type of
inductively coupled plasma etching apparatus is provided. This
inductively coupled plasma etching apparatus includes a chamber and
a window for sealing a top opening of the chamber. The window has
an inner surface that is exposed to an internal region of the
chamber. A metal plate, which acts as a Faraday shield, is disposed
above and spaced apart from the window. A coil is disposed above
and spaced apart from the metal plate. The apparatus also includes
a controller for externally applying a peak-to-peak voltage to the
metal plate. The controller includes an oscillation circuit, a
matching circuit, an RF generator, and a feedback control for
monitoring the applied peak-to-peak voltage.
[0017] In one embodiment, the externally applied peak-to-peak
voltage is adjustable so as to reduce sputtering of the inner
surface of the window while substantially simultaneously preventing
deposition of etch byproducts on the inner surface of the window.
In one embodiment, the inductively coupled plasma etching apparatus
further includes a coil input terminal for receiving RF power and a
coil output terminal. In one embodiment, the inductively coupled
plasma etching apparatus further includes an RF generator, a match
circuit network coupled between the RF generator and the coil input
terminal, and a variable capacitor coupled between ground and the
coil output terminal.
[0018] In one embodiment, the metal plate is connected to the
window by dielectric spacers. In one embodiment, the inductively
coupled plasma etching apparatus includes a chamber lid that is
configured to have attached thereto the metal plate and the coil.
The chamber lid may be attached by hinges that enable opening and
closing of the chamber lid. When in a closed position, the chamber
lid places the metal plate proximate to the window in preparation
for operation. When in an open position, the chamber lid places the
metal plate away from the window for visual inspection of the
window and servicing of the chamber.
[0019] In accordance with yet another aspect of the invention, a
first method for optimizing operation of an inductively coupled
plasma etching apparatus is provided. In this method, a chamber for
etching a wafer is supplied. A window is attached to a top opening
of the chamber. The window has an outer surface and an inner
surface that is exposed to an inner region of the chamber. A coil
is placed over the window and a metal plate is placed over the
outer surface of the window. The metal plate is positioned in a
spaced apart relationship between the coil and the outer surface of
the window. The metal plate is conductively connected to a
connection location on the coil. The connection location is between
an input terminal and an output terminal and is optimally selected
so as to produce substantially uniform incident ion energy
proximate to the inner surface of the window. The substantially
uniform incident ion energy is configured to reduce sputtering of
the inner surface of the window while substantially simultaneously
preventing deposition of etch byproducts on the inner surface of
the window.
[0020] In accordance with a still further aspect of the invention,
a second method for optimizing operation of an inductively coupled
plasma etching apparatus is provided. In this method, a chamber for
etching a wafer is supplied. A window is attached to a top opening
of the chamber. The window has an outer surface and an inner
surface that is exposed to an inner region of the chamber. A coil
is placed over the window and a metal plate is placed over the
outer surface of the window. The metal plate is positioned in a
spaced apart relationship between the coil and the outer surface of
the window. A controlled peak-to-peak voltage is applied to the
metal plate so as to produce substantially uniform incident ion
energy proximate to the inner surface of the window. The
substantially uniform incident ion energy is configured to reduce
sputtering of the inner surface of the window while substantially
simultaneously preventing deposition of etch byproducts on the
inner surface of the window.
[0021] The apparatus and methods of the present invention provide
numerous advantages. Most notably, the apparatus and methods of the
present invention uniformly prevent the deposition of electrically
conductive reaction products, e.g., RuO.sub.2, on the inner surface
of the upper wall (e.g., TCP window) of a chamber in an inductively
coupled plasma etching system. This increases throughput in the
plasma etching of recently developed device materials, e.g., Ru,
because the plasma etching operation does not have to be stopped to
clean the walls of the chamber after only a few wafers have been
processed. In addition, the apparatus and methods of the present
invention also uniformly prevent sputtering of the inner surface of
the upper wall (e.g., TCP window) of a chamber in an inductively
coupled plasma etching system. This increases the reproducibility
of the process conditions by avoiding the generation of particles
and the introduction of unwanted chemical species into the process
environment.
[0022] It is to be understood that the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are incorporated in and
constitute part of this specification, illustrate exemplary
embodiments of the invention and together with the description
serve to explain the principles of the invention.
[0024] FIG. 1A is a simplified schematic cross-section showing a
prior art inductively coupled plasma etching apparatus.
[0025] FIG. 1B is a simplified schematic diagram that illustrates
the inherent nonuniformity of the deposition and sputtering on the
TCP window in the inductively coupled plasma etching apparatus
shown in FIG. 1A.
[0026] FIG. 1C is a graph that shows the V.sub.pp on the coil in
the inductively coupled plasma etching apparatus shown in FIG. 1A
as a function of coil length.
[0027] FIG. 2A is a simplified schematic cross-section showing an
inductively coupled plasma etching apparatus in accordance with one
embodiment of the present invention.
[0028] FIG. 2B is a simplified schematic cross-section that
illustrates the plasma generation in an inductively coupled plasma
etching apparatus in accordance with one embodiment of the
invention.
[0029] FIG. 2C is a simplified schematic cross-section that
illustrates the uniform window sputtering obtained by an
inductively coupled plasma etching apparatus in accordance with one
embodiment of the invention.
[0030] FIG. 3 is an exploded perspective view of a metal plate,
which acts as a Faraday shield, and the components for holding the
metal plate in place in accordance with one embodiment of the
present invention.
[0031] FIG. 4 is an exploded perspective view of a coil and the
components for holding the coil in place in accordance with one
embodiment of the present invention.
[0032] FIG. 5 is a simplified schematic diagram that shows the
apparatus and the connection locations used in tests conducted to
determine the optimal location at which to connect the Faraday
shield plate to the coil for ruthenium (Ru) etching.
[0033] FIGS. 6A, 6B, and 6C are graphs showing the measured
V.sub.pp as a function of TCP power for the Faraday shield plate,
the coil terminal input, and the coil terminal output,
respectively, for each of connection locations A, B, and C shown in
FIG. 5.
[0034] FIG. 7A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus including an oscillation circuit
to externally control the V.sub.pp of the Faraday shield plate in
accordance with one embodiment of the present invention.
[0035] FIG. 7B is a graph that shows V.sub.pp as a function of
variable capacitor position for the inductively coupled plasma
etching apparatus shown in FIG. 7A.
[0036] FIG. 8A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus including a voltage divider
circuit to externally control the V.sub.pp of the Faraday shield
plate in accordance with another embodiment of the present
invention.
[0037] FIG. 8B is a graph that shows V.sub.pp as a function of
variable capacitor position for the inductively coupled plasma
etching apparatus shown in FIG. 8A.
[0038] FIG. 9A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus in which the Faraday shield plate
is driven by a different frequency in accordance with yet another
embodiment of the present invention.
[0039] FIG. 9B is a graph that shows V.sub.pp as a function of low
frequency RF power for the inductively coupled plasma etching
apparatus shown in FIG. 9A.
[0040] FIG. 10 is a graph that shows the ruthenium etch rate as a
function of the number of wafers processed in a conventional
inductively coupled plasma etching apparatus and an inductively
coupled plasma etching apparatus having a Faraday shield plate that
is coupled to the coil in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Several exemplary embodiments of the invention will now be
described in detail with reference to the accompanying drawings.
FIGS. 1A-1C are discussed above in the "Background of the
Invention" section.
[0042] FIG. 2A is a simplified schematic cross-section showing an
inductively coupled plasma etching apparatus in accordance with one
embodiment of the present invention. As shown in FIG. 2A,
semiconductor wafer 11 is mounted on chuck 19 disposed in chamber
100, which is defined by walls of a housing, proximate to a lower
wall of the housing. Coil 117 is supported on TCP window 10 of
chamber 100 by spacers 13, which may be formed of an insulating
material. TCP window 10 is preferably made of quartz; however,
other materials such as alumina (Al.sub.2O.sub.3), silicon nitride
(Si.sub.3N.sub.4), aluminum nitride (AlN), silicon carbide (SiC),
and silicon (Si) also may be used. The primary role of TCP window
10 is to provide a vacuum seal to chamber 100. In one embodiment,
TCP window 10 is separated from wafer 11 by a distance that is
between about 2 inches and about 8 inches, and more preferably
between about 4 inches and about 5 inches. In operation, a reactant
gas is fed into chamber 100 through a gas lead-in port (not shown).
High frequency power from a power supply (not shown) is applied to
coil 117. The high frequency (RF) current passing through coil 117
induces an electromagnetic current in chamber 100, and the
electromagnetic current acts on the reactant gas to generate a
plasma.
[0043] The plasma contains various types of radicals and the
chemical reaction of the positive/negative ions is used to etch
semiconductor wafer 11 itself or an insulation film formed on the
wafer. During the etching process, coil 117 carries out a function
that corresponds to that of the primary coil of a transformer while
the plasma in chamber 100 carries out a function that corresponds
to that of the secondary coil of the transformer. If the reaction
product generated by the etching process is volatile, then this
reaction product is discarded via exhaust port 15.
[0044] Metal plate 217, which acts as a Faraday shield, is provided
between coil 117 and chamber 100. For ease of reference, metal
plate 217 is also referred to herein as "the Faraday shield plate."
In one embodiment, metal plate 217 is positioned in a spaced apart
relationship between coil 117 and TCP window 10 and is
substantially parallel to the TCP window. The thickness of metal
plate 217 is preferably between about 20 .mu.m and about 10 mm, and
more preferably between about 50 .mu.m and about 5 mm. In one
embodiment, metal plate 217 has a thickness of about 1.5 mm.
Connector 207 electrically connects metal plate 217 to coil 117 at
a predetermined position of the coil and functions to ensure that
the in-plane RF voltage applied to metal plate 217 is uniform.
Because the in-plane RF voltage applied to metal plate 217 is
uniform, energy is uniformly added to the plasma in the vicinity of
TCP window 10. As a result of this uniform energy distribution, the
deposition and sputtering of the reaction product occurs uniformly
so that undesirable accumulation of the reaction product on TCP
window 10 does not occur or is substantially eliminated.
[0045] In one embodiment, connector 207 electrically connects metal
plate 217 to coil 117 at a position so that adequate V.sub.pp
(peak-to-peak voltage) is applied on the metal plate. By uniformly
applying V.sub.pp on metal plate 217, ions in the plasma are
accelerated and uniformly bombard the vacuum side surface of a wall
of the chamber of the inductively coupled plasma etching apparatus
to prevent deposition of the reaction product thereon. In one
embodiment, the inductively coupled plasma etching apparatus is a
TCP 9400 PTX plasma etching apparatus, which is commercially
available from Lam Research Corporation of Fremont, Calif., and the
accelerated ions uniformly bombard the vacuum side surface of the
TCP window to prevent deposition of the reaction product thereon.
In an alternative embodiment, connector 207 electrically connects
metal plate to a conductor extending from an impedance matching box
to the coil.
[0046] FIGS. 2B and 2C illustrate the uniform window sputtering
obtained by an inductively coupled plasma etching apparatus in
accordance with one embodiment of the invention. As shown in FIG.
2B, the application of an appropriate V.sub.pp to metal plate 217
through connector 207, which may be connected to coil 117 at the
optimum location for a particular process, generates magnetic
fields within chamber 100 that are uniform across the surface of
metal plate 217. These uniform magnetic fields in turn induce a
uniform electromagnetic current in chamber 100, and this inductive
current acts on the reactant gas to generate a plasma. Because the
inductive current is uniform across the surface of metal plate 217,
the energy of the incident ions that bombard surface 10a of TCP
window 10 also is uniform, as shown in FIG. 2C.
[0047] FIG. 3 is an exploded perspective view of the metal plate,
which acts as a Faraday shield, and the components for holding the
metal plate in place in accordance with one embodiment of the
invention. As shown in FIG. 3, metal plate 217 is secured to the
underside of attachment frame 201, which is provided with
attachment spacers 13 on a top side thereof, by screws 205.
Attachment frame 201, attachment spacers 13, and screws 205 may be
formed of any suitable insulating material.
[0048] Outer ring 211, inner ring 213, and center disk 215 are
secured to attachment frame 201 by screws 219, which may be formed
of any suitable insulating material. Outer ring 211, inner ring
213, and center disk 215 retain the shape of metal plate 217 during
operation of the inductively coupled plasma etching apparatus. A
plurality of radial slots 221 is formed in metal plate 217. Radial
slots 221 extend transversely to the sections of coil 117 (see FIG.
4) to interrupt an internal induced power generated by electric
current from flowing on metal plate 217, which is a conductor. This
is necessary because electric current flowing on metal plate 217
causes coil 117 (see, e.g., FIGS. 2A and 4) and chamber 100 (see,
e.g., FIG. 2A) to be electrically shielded.
[0049] With continuing reference to FIG. 3, connector 207
electrically connects metal plate 217 and coil 117 (see, e.g.,
FIGS. 2A and 4). Two metal screws 209 are used to make this
connection, with one metal screw connecting metal plate 217 to
connector 207 and the other metal screw connecting coil 117 to
connector 207.
[0050] FIG. 4 is an exploded perspective view of the coil and the
components for holding the coil in place in accordance with one
embodiment of the invention. As shown in FIG. 4, attachment frame
201 and attachment spacers 13 are provided between metal plate 217
and coil 117. The four ends of cross-shaped coil mounting plate 305
are fixed by support spring housings 301 and metal screws 303 to
retain the shape of coil 117. As shown in FIG. 4, coil 117 has
three turns. Coil 117 must have at least one turn, but otherwise
may have any suitable number of turns as may be needed for the
application.
[0051] As discussed above in connection with the description of
FIG. 3, connector 207 electrically connects metal plate 217 to coil
117. As shown in FIG. 4, a U-shaped spacer 309 positions coil
mounting plate 305, coil 117, and metal plate 217. U-shaped spacer
309 is connected to coil 117 by metal screw 307. One metal screw
209 electrically connects connector 207 to coil 117 through
U-shaped spacer 309 and another metal screw 209 electrically
connects connector 207 to metal plate 217 (see FIG. 3). As shown in
FIG. 4, coil 117 is configured so that both the coil input terminal
117a and the coil output terminal 117b are situated proximate to
the center of the coil 117. In particular, coil 117 includes coil
end 117a-1 and coil output terminal 117b. Coil extension 117a-2
connects coil end 117a-1 to coil extension end 117a-3 of coil
extension 117a-4. Coil input terminal 117a is at the other end of
coil extension 117a-4. It will be apparent to those skilled in the
art that the configuration of the coil may be varied from that
shown in FIG. 4 in situations where it is not necessary to have
both the coil input terminal and coil output terminal situated
proximate to the center of the coil 117.
[0052] FIG. 5 is a simplified schematic diagram that shows the
apparatus and the connection locations used in tests conducted to
determine the optimal location at which to connect the Faraday
shield plate to the coil for ruthenium (Ru) etching. As shown in
FIG. 5, RF generator 400, match circuit network 402, and VI probe
412a are coupled to coil input terminal 117a of coil 117. Variable
capacitor 401, which is grounded, and VI probe 412b are coupled to
coil output terminal 117b of coil 117. During testing, metal plate
217, i.e., the Faraday shield plate, was coupled to coil 117 by
connector 207 at locations A, B, and C and V.sub.pp was measured
for each of these connection locations at coil input terminal 117a
and coil output terminal 117b with VI probes 412a and 412b,
respectively. In addition, V.sub.pp of metal plate 217 was measured
for each of connection locations A, B, and C with VI probe 412c. VI
probes 412a, 412b, and 412c are capacitive probes including a metal
probe and a metal, e.g., copper, plate separated by a dielectric
material, e.g., polyimide.
[0053] FIGS. 6A, 6B, and 6C are graphs showing the measured
V.sub.pp as a function of TCP power for metal plate 217, coil input
terminal 117a, and coil output terminal 117b, respectively, for
each of connection locations A, B, and C shown in FIG. 5. As shown
in FIG. 6A, for connection location A (near the output), V.sub.pp
of metal plate 217 decreases significantly as the TCP power
increases. For connection locations B and C, V.sub.pp of metal
plate 217 increases slightly as the TCP power increases. As shown
in FIG. 6B, for each of connection locations A, B, and C, V.sub.pp
at coil input terminal 117a increases significantly as the TCP
power increases. As shown in FIG. 6C, for connection location A,
V.sub.pp at coil output terminal 117b decreases slightly as the TCP
power increases. For connection locations B and C, V.sub.pp at coil
output terminal 117b increases significantly as the TCP power
increases.
[0054] Referring back to FIG. 6A, connection location A yielded a
V.sub.pp of 676 volts at 800 watts for metal plate 217. During
testing, the TCP window remained clean, but there was too much
sputtering. Micromasking of ruthenium was observed with a blasted
quartz window, but was resolved by replacing the blasted quartz
window with a polished window. Connection location B yielded a
V.sub.pp of 464 volts at 800 watts. During testing, no etch
byproduct deposition was observed on the TCP window after the
equivalent of approximately one lot of wafers was subjected to
ruthenium etching. Connection location C yielded a V.sub.pp of 373
volts at 800 watts. During testing, a light deposition was observed
on the TCP window after several wafers were etched. Thus, for a
ruthenium etch process, the foregoing test results demonstrate that
connection location B is superior to connection locations A and
C.
[0055] The Faraday shield plate of the present invention is well
suited for single step etch recipes where the RF peak-to-peak
voltage and the RF matching can be optimized for the specific
etching recipe. Many etching recipes, however, include multiple
etching steps, e.g., the breakthrough step, the bulk etch steps,
and the over etch step, in which the RF power, pressure, and gas
compositions can be substantially different. Consequently, a
certain setting of V.sub.pp on the Faraday shield plate (e.g.,
connection location) for a given etch step may not be optimal in
other etch steps. Further, because the etching chamber impedance
varies for different etch steps, RF tuning to satisfy the various
impedances can be difficult. For an etch recipe that includes
multiple etch steps, each individual etch process can be optimized
by selecting just the right connection point to substantially
eliminate deposition of materials on the quartz window. By way of
example, such optimization can be reached in a manner similar to
that which yielded the selection of connection location B, as
described above with reference to FIG. 5. In that example, the
points A, B, and C were selected to be about 25 mm from the coil
output terminal, about 80 mm from the coil output terminal, and
about 140 mm from the coil output terminal, respectively. Of
course, it will be apparent to those skilled in the art that these
locations can and will change depending on the recipe used to etch
a given material and the combination of matching network element
settings.
[0056] FIG. 7A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus including an oscillation circuit
to externally control the V.sub.pp of the Faraday shield plate in
accordance with one embodiment of the present invention. As shown
in FIG. 7A, RF generator 400 and match circuit network 402 are
coupled to coil input terminal 117a of coil 117. Variable capacitor
401, which is grounded, is coupled to coil output terminal 117b of
coil 117. Metal plate 217 is connected to coil 117 and to shield
box 406, which defines an oscillation circuit including variable
capacitor 408 and inductor 409. Variable capacitor 408 and inductor
409 are grounded. With this configuration, the V.sub.pp of metal
plate 217 can be controlled by adjusting the position of the
variable capacitor of the oscillation circuit. As shown in FIG. 7B,
the maximum V.sub.pp occurs at the harmonic point.
[0057] FIG. 8A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus including a voltage divider
circuit to externally control the V.sub.pp of the Faraday shield
plate in accordance with another embodiment of the present
invention. As shown in FIG. 8A, RF generator 400 and match circuit
network 402 are coupled to coil input terminal 117a of coil 117.
Variable capacitor 401, which is grounded, is coupled to coil
output terminal 117b of coil 117. Metal plate 217 is connected to
coil 117 via voltage divider circuit 416, which includes coupling
capacitor 416a and variable capacitor 416b. Metal plate 217 is
connected to voltage divider circuit 416 such that coupling
capacitor 416a is disposed between coil 117 and the metal plate and
variable capacitor 416b is disposed between the metal plate and
ground. With this configuration, the V.sub.pp of metal plate 217
can be controlled by adjusting the position of the variable
capacitor of the voltage divider circuit. As shown in FIG. 8B,
V.sub.pp is proportional to the divide ratio of the voltage divider
circuit.
[0058] On one hand, the configurations for externally controlling
the V.sub.pp of the Faraday shield plate shown in FIGS. 7A and 8A
are desirable because they are simple and inexpensive. On the other
hand, these configurations may affect TCP matching. In this regard,
the configuration shown in FIG. 7A affects TCP matching to a lesser
extent than does the configuration shown in FIG. 8A.
[0059] FIG. 9A is a simplified schematic diagram of an inductively
coupled plasma etching apparatus in which the Faraday shield plate
is independently driven by a different frequency in accordance with
yet another embodiment of the present invention. As shown in FIG.
9A, RF generator 400 and match circuit network 402 are coupled to
coil input terminal 117a of coil 117. Variable capacitor 401, which
is grounded, is coupled to coil output terminal 117b of coil 117.
Metal plate 217 is coupled to Faraday shield driver 450 at
connection point 462. Faraday shield driver 450 is essentially a
controller that enables monitoring of applied peak-to-peak voltages
at different TCP power settings and on-the-fly adjustments to
achieve the most optimal performance without dependence on the
matching circuitry of coil 117. This is true because no connection
is made between the coil and the metal plate in this exemplary
embodiment. As shown in FIG. 9A, Faraday shield driver 450 includes
matching circuit 452, a 13.56 MHz oscillation circuit that includes
inductor 454 and variable capacitor 456, RF generator 458, and
V.sub.pp feedback loop 460.
[0060] In operation, RF power from RF generator 458, which is
grounded, is applied to metal plate 217. The RF power is preferably
in a range from about 50 KHz to about 50 MHz, and more preferably
in a range from about 100 KHz to just below 13.56 MHz. In one
embodiment, the RF power is about 2 MHz. The 13.56 MHz oscillation
circuit, which is coupled to metal plate 217, acts to "ground" the
metal plate from a 13.56 MHz point of view. Stated differently, the
13.56 MHz oscillation circuit shuts out the interruption from the
RF power applied to metal plate 217 by RF generator 400.
[0061] The V.sub.pp feedback 460 is preferably provided back to RF
generator 458 for comparison with an external V.sub.pp value. Based
on this comparison, adjustments can be made to RF generator 458 so
that the most optimal V.sub.pp level can be applied to the Faraday
shield plate. In a preferred embodiment, the monitoring of the
applied V.sub.pp can be controlled by way of a computer control
station. The computer control station can provide a user with
statistical operational data by way of a text display, a graphical
user interface (GUI), or printouts. Based on this statistical data,
the operator can make further adjustments so as to achieve the most
optimal performance and thus eliminate the deposition of byproducts
on the inner chamber walls such as, for example, the TCP window
inner surface. Accordingly, with the configuration of FIG. 9A, the
V.sub.pp of metal plate 217 can be controlled by adjusting the low
frequency RF power applied to the metal plate. As shown in FIG. 9B,
V.sub.pp increases as the low frequency RF power increases.
Therefore, in this exemplary embodiment, there is no need to have a
fixed connection point to coil 117.
[0062] FIG. 10 is a graph that shows the ruthenium etch rate as a
function of the number of wafers processed in a conventional
inductively coupled plasma etching apparatus and an inductively
coupled plasma etching apparatus having a Faraday shield plate that
is coupled to the coil in accordance with the present invention. As
shown in FIG. 10, in a conventional inductively coupled plasma
etching apparatus, the ruthenium etch rate decreases by about 50%
after 150 wafers have been processed. In contrast, in an
inductively coupled plasma etching apparatus having a Faraday
shield coupled to the coil in accordance with the present
invention, the ruthenium etch rate after 150 wafers have been
processed is substantially the same as the initial etch rate. Thus,
the Faraday shield plate of the present invention provides a highly
reproducible ruthenium etch rate.
[0063] The present invention also provides a method for controlling
an inner surface of a wall defining a chamber in which a plasma is
generated in an inductively coupled plasma etching apparatus. In
this method, a metal plate is provided between a coil for receiving
high frequency (RF) power and the plasma generated in the chamber
such that the metal plate does not contact the coil. The metal
plate has a plurality of metal slits formed therein that extend
transversely to the coil and is electrically connected to the coil,
as described above. A plasma etching operation is conducted in the
inductively coupled plasma etching apparatus. During the plasma
etching operation, the deposition of a reaction product on an inner
surface of a wall positioned between the metal plate and the plasma
and the sputtering of the reaction product from the inner surface
of the wall are substantially uniform so that an amount of the
reaction product sufficient to disable the plasma etching operation
does not accumulate on the inner surface of the wall. In one
embodiment, the wall positioned between the metal plate and the
plasma is an upper wall of the chamber, e.g., a TCP window.
[0064] The present invention further provides methods for
optimizing operation of an inductively coupled plasma etching
apparatus. In these methods, a chamber for etching a wafer is
supplied. A window is attached to a top opening of the chamber. The
window has an outer surface and an inner surface that is exposed to
an inner region of the chamber. A coil is placed over the window
and a metal plate is placed over the outer surface of the window.
The metal plate is positioned in a spaced apart relationship
between the coil and the outer surface of the window. In accordance
with a first optimization method, the metal plate is connected to a
connection location on the coil. The connection location is between
an input terminal and an output terminal and is optimally selected
so as to produce substantially uniform incident ion energy
proximate to the inner surface of the window. The substantially
uniform incident ion energy is configured to reduce sputtering of
the inner surface of the window while substantially simultaneously
preventing deposition of etch byproducts on the inner surface of
the window. In accordance with a second optimization method, a
controlled peak-to-peak voltage is applied to the metal plate so as
to produce substantially uniform incident ion energy proximate to
the inner surface of the window. Again, the substantially uniform
incident ion energy is configured to reduce sputtering of the inner
surface of the window while substantially simultaneously preventing
deposition of etch byproducts on the inner surface of the
window.
[0065] The inductively coupled plasma etching apparatus of the
present invention is well suited for plasma etching of recently
developed device materials (e.g., platinum, ruthenium, and the
like) that generate nonvolatile, electrically conductive reaction
products (e.g., RuO.sub.2). It will be apparent to those skilled in
the art that the inductively coupled plasma etching apparatus of
the present invention also may be used to plasma etch standard
materials such as metal and polysilicon. In the plasma etching of
metal and polysilicon, V.sub.pp is adjusted to realize uniform and
minimum deposition. In this manner, the mean wafer between clean
(MWBC) and the lifetime of the TCP window may be improved.
[0066] It will be apparent to those skilled in the art that the
precise control of V.sub.pp and the resulting balance of sputtering
and deposition on the TCP window provided by the apparatus and
methods of the present invention provide numerous other advantages
including the reduction of problems associated with particles and
contamination, etch profile control (by controlling the etch
sidewall deposition coming from the plasma and the TCP window),
etch selectivity control, and selective etch byproduct deposition.
In the case of selective etch byproduct deposition, this can be
done by tuning V.sub.pp so that materials having certain sticking
coefficients and sputtering yields can be captured on the TCP
window to control etching, provided the surface of the TCP window
is maintained at a relatively constant temperature.
[0067] In summary, the present invention provides an inductively
coupled plasma etching apparatus and methods for optimizing the
operation of an inductively coupled plasma etching apparatus. The
invention has been described herein in terms of several preferred
embodiments. Other embodiments of the invention will be apparent to
those skilled in the art from consideration of the specification
and practice of the invention. For example, the location at which
the Faraday shield plate is connected to the coil may be varied
from the exemplary locations shown and described herein to optimize
a particular etch process. The embodiments and preferred features
described above should be considered exemplary, with the scope of
the invention being defined by the appended claims and their
equivalents.
* * * * *