U.S. patent application number 11/696327 was filed with the patent office on 2007-08-09 for faraday shield disposed within an inductively coupled plasma etching apparatus.
This patent application is currently assigned to Lam Research Corporation. Invention is credited to Keith Comendant, Robert J. Steger.
Application Number | 20070181257 11/696327 |
Document ID | / |
Family ID | 38056727 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070181257 |
Kind Code |
A1 |
Comendant; Keith ; et
al. |
August 9, 2007 |
Faraday Shield Disposed Within An Inductively Coupled Plasma
Etching apparatus
Abstract
An apparatus and method is provided for positioning and
utilizing a Faraday shield in direct exposure to a plasma within an
inductively coupled plasma etching apparatus. Broadly speaking, the
Faraday shield configuration maintains a condition of an etching
chamber window. At a minimum, positioning the Faraday shield
between the window and the plasma prevents erosion of the window
resulting from plasma sputter and shunts heat generated by an
etching process away from the window.
Inventors: |
Comendant; Keith; (Fremont,
CA) ; Steger; Robert J.; (Los Altos, CA) |
Correspondence
Address: |
MARTINE PENILLA & GENCARELLA, LLP
710 LAKEWAY DRIVE
SUITE 200
SUNNYVALE
CA
94085
US
|
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
38056727 |
Appl. No.: |
11/696327 |
Filed: |
April 4, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10232564 |
Aug 30, 2002 |
7223321 |
|
|
11696327 |
Apr 4, 2007 |
|
|
|
Current U.S.
Class: |
156/345.48 |
Current CPC
Class: |
H01J 37/321 20130101;
H01J 37/32633 20130101 |
Class at
Publication: |
156/345.48 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. A method for making an inductively coupled plasma etching
apparatus, comprising: providing a chamber having an interior
cavity defined by a bottom and side walls, wherein each of the side
walls has a top surface; placing a thermally conductive adapter
plate to interface with the top surface of the side walls so as to
form a seal between the thermally conductive adapter plate and the
side walls, wherein the thermally conductive adapter plate is
defined to have a central opening over the chamber interior cavity;
placing a metal shield to cover the central opening of the
thermally conductive adapter plate and establish a thermal
connection between the metal shield and the thermally conductive
adapter plate, whereby the metal shield is placed to be in direct
exposure to the chamber interior cavity; placing a window above the
metal shield and thermally conductive adapter plate so as to form a
seal between the window and the thermally conductive adapter plate;
and placing a coil above the window.
2. A method for making an inductively coupled plasma etching
apparatus as recited in claim 1, wherein placing the window above
the metal shield is performed such that a distance ranging from
about 0.005 inch to about 0.04 inch exists between the metal shield
and the window.
3. A method for making an inductively coupled plasma etching
apparatus as recited in claim 1, further comprising: coating the
metal shield.
4. A method for making an inductively coupled plasma etching
apparatus as recited in claim 1, wherein placing the metal shield
over the chamber interior cavity is performed such that the metal
shield is electrically isolated from the chamber side walls.
5. A method for making an inductively coupled plasma etching
apparatus as recited in claim 4, further comprising: applying an
electric charge to the metal shield.
6. A method for making an inductively coupled plasma etching
apparatus as recited in claim 1, wherein the metal shield is
defined to include a plurality of slits configured to control a
flow of electrical current through the metal shield.
7. A method for making an inductively coupled plasma etching
apparatus as recited in claim 1, further comprising: placing a
liner proximate to the thermally conductive adapter plate such that
the liner is in direct exposure to the chamber interior cavity.
8. A method for making an inductively coupled plasma etching
apparatus, comprising: providing a chamber defined by a bottom,
side walls, and an upper heat dissipation structure, wherein the
upper heat dissipation structure is defined to include an opening
through which an interior cavity of the chamber is exposed; placing
a thermally conductive metal shield in thermal communication with
the upper heat dissipation structure so as to cover the opening
within the heat dissipation structure, whereby the thermally
conductive metal shield is directly exposed to the chamber interior
cavity; placing a window above the thermally conductive metal
shield so as to form a seal between the window and the upper heat
dissipation structure around the thermally conductive metal shield;
and placing a coil above the window.
9. A method for making an inductively coupled plasma etching
apparatus as recited in claim 8, wherein placing the thermally
conductive metal shield in thermal communication with the upper
heat dissipation structure includes mating a surrounding support
body of the thermally conductive metal shield with a complementary
shaped portion of the upper heat dissipation structure.
10. A method for making an inductively coupled plasma etching
apparatus as recited in claim 9, wherein the surrounding support
body of the thermally conductive metal shield is defined as a ring,
and the complementary shaped portion of the upper heat dissipation
structure is defined as a channel.
11. A method for making an inductively coupled plasma etching
apparatus as recited in claim 9, wherein the surrounding support
body of the thermally conductive metal shield is defined to include
an outer surface contoured to be inserted into and removed from the
upper heat dissipation structure from a direction below the upper
heat dissipation structure.
12. A method for making an inductively coupled plasma etching
apparatus as recited in claim 9, wherein the surrounding support
body of the thermally conductive metal shield is defined to include
an outer surface contoured to be inserted into and removed from the
upper heat dissipation structure from a direction above the upper
heat dissipation structure.
13. A method for making an inductively coupled plasma etching
apparatus as recited in claim 8, wherein the thermally conductive
metal shield is defined to have a thickness ranging from about 0.03
inch to about 1 inch.
14. A method for making an inductively coupled plasma etching
apparatus as recited in claim 8, wherein placing the window above
the thermally conductive metal shield is performed such that a
distance ranging from about 0.005 inch to about 0.04 inch exists
between the thermally conductive metal shield and the window.
15. A method for making an inductively coupled plasma etching
apparatus, comprising: providing a chamber defined by a bottom and
side walls, wherein each of the side walls has a top surface;
forming a chamber top to include a heat dissipation structure and a
metal shield thermally integrated with the heat dissipation
structure, wherein the heat dissipation structure defines a
peripheral portion of the chamber top and the metal shield defines
a central portion of the chamber top such that the metal shield is
substantially planar with a top surface of the heat dissipation
structure; placing the chamber top to interface with the top
surface of the side walls so as to form a seal between the chamber
top and the side walls; placing a window above the chamber top so
as to form a seal between the window and the peripheral portion of
the chamber top; and placing a coil above the window.
16. A method for making an inductively coupled plasma etching
apparatus as recited in claim 15, wherein placing the window above
the chamber top is performed such that a distance ranging from
about 0.005 inch to about 0.04 inch exists between the metal shield
and the window.
17. A method for making an inductively coupled plasma etching
apparatus as recited in claim 15, wherein the metal shield is
defined to include a plurality of slits configured to control a
flow of electrical current through the metal shield.
18. A method for making an inductively coupled plasma etching
apparatus as recited in claim 15, further comprising: placing a
liner proximate to the heat dissipation structure such that the
liner is in direct exposure to an interior cavity of the
chamber.
19. A method for making an inductively coupled plasma etching
apparatus as recited in claim 15, further comprising: coating the
metal shield.
20. A method for making an inductively coupled plasma etching
apparatus as recited in claim 15, wherein the metal shield is
defined to have a thickness ranging from about 0.03 inch to about 1
inch.
Description
CLAIM OF PRIORITY
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/232,564, filed on Aug. 30, 2002, from which
priority under 35 U.S.C. 120 is claimed, which is incorporated
herein by reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to semiconductor
fabrication, and more particularly, to apparatuses and methods for
using a Faraday shield in direct exposure to a plasma within an
inductively coupled plasma etching apparatus.
[0004] 2. Description of the Related Art
[0005] In semiconductor manufacturing, etching processes are
commonly and 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 performed using
an inductively coupled plasma etching apparatus.
[0006] FIG. 1A shows an inductively coupled plasma etching
apparatus 100, in accordance with the prior art. The inductively
coupled plasma etching apparatus 100 includes an etching chamber
structurally defined by chamber walls 101 and a window 111. The
chamber walls 101 are typically fabricated from stainless steel or
aluminum. The window 111 is typically fabricated from quartz. The
chamber walls 101 and the window 111 are configured to form a
chamber internal cavity 102.
[0007] A chuck 117 is positioned within the chamber internal cavity
102 near the bottom inner surface of the etching chamber. The chuck
117 is configured to receive and hold a semiconductor wafer (i.e.,
"wafer") 119 upon which the etching process is performed. The chuck
117 can be electrically charged using an RF power supply 123. The
RF power supply 123 is connected to matching circuitry 121 through
a connection 127. The matching circuitry 121 is connected to the
chuck 117 through a connection 125. In this manner, the RF power
supply 123 is connected to the chuck 117.
[0008] A coil 133 is positioned above the window 111. The coil 133
is fabricated from an electrically conductive material and includes
at least one complete turn. The exemplary coil 133 shown in FIG. 1A
includes three turns. The coil 133 symbols having an "X" indicate
that the coil 133 extends rotationally into the page. Conversely,
the coil 133 symbols having a ".cndot." indicate that the coil 133
extends rotationally out of the page. An RF power supply 141 is
configured to supply RF power to the coil 133. In general, the RF
power supply 141 is connected to matching circuitry 139 through a
connection 145. The matching circuitry 139 is connected to the coil
133 through a connection 143. In this manner, the RF power supply
141 is connected to the coil 133. A Faraday shield 149 is
positioned between the coil 133 and the window 111. The Faraday
shield 149 is maintained in a spaced apart relationship relative to
the coil 133. The Faraday shield 149 is disposed immediately above
the window 111. The coil 133, the Faraday shield 149, and the
window 111 are each configured to be substantially parallel to one
another.
[0009] FIG. 1B shows the basic operating principles of the
inductively coupled plasma etching apparatus 100, in accordance
with the prior art. During operation, a reactant gas flows through
the chamber internal cavity 102 from a gas lead-in port (not shown)
to a gas exhaust port (not shown). High frequency power is then
applied from the RF power supply 141 to the coil 133 to cause an RF
current to flow through the coil 133. The RF current flowing
through the coil 133 generates an electromagnetic field 151 about
the coil 133. The electromagnetic field 151 generates an inductive
current 153 within the chamber internal cavity 102. The inductive
current 153 acts on the reactant gas to generate a plasma 155. High
frequency power is applied from the RF power supply 123 to the
chuck 117 to provide directionality to the plasma 155 such that the
plasma 155 is "pulled" down onto the wafer 119 surface to effect
the etching process. An electrostatic field is also generated
between the coil 133 and the plasma 155. This field is not
necessarily uniform. High voltage gradients can drive the plasma
155 into the window 111 with sufficient energy to erode the window
111, and cause large temperature gradients within the window 111.
The Faraday shield 149 ensures the electrostatic field is more
uniformly distributed across the window 111, thus lessening the
effects of temperature and erosion.
[0010] The plasma 155 contains various types of radicals in the
form of positive and negative ions. The chemical reactions of the
various types of positive and negative ions are used to etch the
wafer 119. During the etching process, the coil 133 performs a
function analogous to that of a primary coil in a transformer,
while the plasma 155 performs a function analogous to that of a
secondary coil in the transformer.
[0011] The reaction products generated by the etching process may
be volatile or non-volatile. The volatile reaction products are
discarded along with used reactant gas through the gas exhaust
port. The non-volatile reaction products, however, typically remain
in the etching chamber. The non-volatile reaction products may
adhere to the chamber walls 101 and the window 111.
[0012] FIG. 1C shows an illustration of a deposition 157 of
non-volatile reaction products on the window 111 in accordance with
the prior art. Adherence of non-volatile reaction products to the
window 111 may interfere with the etching process. Excessive
deposition 157 may result in particles flaking off the window 111
onto the wafer 119, thus interfering with the etching process.
Excessive deposition 157, therefore, requires more frequent
cleaning of the chamber walls 101 and the window 111 which
adversely affects wafer 119 throughput.
[0013] In contrast to the deposition 157 of non-volatile reaction
products on the window 111, plasma 155 sputter can cause erosion of
the window 111. FIG. 1D shows an illustration of window 111 erosion
159 in accordance with the prior art. Such erosion 159 not only
shortens the useful lifetime of the window 111, but also generates
particles which can contaminate the wafer 119 and introduce
unwanted chemical species into the chamber internal cavity 102. The
presence of unwanted species in the chamber internal cavity 102 is
particularly undesirable because it leads to poor reproducibility
of the etching process conditions and resulting wafer 119
characteristics.
[0014] In addition to the deposition 157 and erosion 159 problems
associated with the window 111, selection of the window 111
material is limited by the thermal output of the etching process.
During the etching process, the window 111 is exposed directly to
the plasma 155. Therefore, the window 111 must absorb not only the
heat generated by the bulk plasma 155 but also the heat transferred
to the window 111 from sputtered plasma 155. The thermal properties
of the window 111 must be sufficient to accommodate the thermal
energy absorbed by the window 111 during the etching process. The
thermal properties of the window 111 are primarily defined by the
window 111 material.
[0015] Quartz is commonly used as a window 111 material in the
inductively coupled plasma etching apparatus 100. The primary
benefit associated with quartz is its low coefficient of thermal
expansion. Thus, in the presence of a high temperature gradient
from its center to its edge, the quartz window 111 will not
experience differential thermal expansion leading to cracking and
failure. Quartz, however, has a relatively low tensile strength.
Thus, a large (e.g., .gtoreq.1.75 inch) quartz window 111 thickness
is typically required to span the opening above the chamber
internal cavity 102. The quartz window 111 is relatively expensive
and costly to replace upon failure. Thus, it is desirable to have
more flexibility in using window 111 materials other than
quartz.
[0016] Ceramic has been used as an alternative to quartz for the
window 111 material. Ceramic is more durable, stronger, and less
expensive that quartz. However, ceramic materials have a higher
coefficient of thermal expansion than quartz. Thus, when exposed to
a high thermal output associated with certain etching processes,
the ceramic window 111 is more susceptible to experiencing
differential thermal expansion leading to cracking and failure. For
ceramic window 111 materials to be used in higher thermal output
etching processes, it is necessary to maintain a low temperature
gradient across the ceramic window 111 to prevent cracking and
failure.
[0017] In view of the foregoing, there is a need for an apparatus
and a method to protect the window from deposition of non-volatile
reaction products, erosion due to plasma sputter, and high
temperatures resulting from the heat source associated with the
etching process.
SUMMARY OF THE INVENTION
[0018] Broadly speaking, the present invention fills these needs by
providing an apparatus and method to maintain a condition of an
etching chamber window by configuring a Faraday shield between the
etching chamber window and a plasma. It should be appreciated that
the present invention can be implemented in numerous ways,
including as a process, an apparatus, a system, a device, or a
method. Several embodiments of the present invention are described
below.
[0019] In one embodiment, an apparatus for plasma processing is
disclosed. The apparatus includes a chamber having a substrate
support, surrounding walls, and an upper surface to define a plasma
containment region. A metal shield is disposed within the chamber.
The metal shield is oriented over the substrate support and
proximate to the upper surface of the chamber. The metal shield is
located substantially above the plasma containment region of the
chamber. The metal shield is capable of being in direct contact
with a plasma to be generated in the plasma containment region.
[0020] In another embodiment, a plasma etching apparatus is
disclosed. The plasma etching apparatus includes a chamber having
an interior cavity defined by a bottom and side walls. The side
walls are configured to have a top surface. A plate is configured
to interface with the top surface of the side walls. The plate has
an upper surface and a lower surface. The plate is further
configured to have an opening centrally located above the interior
cavity. A window is configured to interface with the upper surface
of the plate. The window covers the opening centrally located above
the interior cavity. A metal shield is disposed immediately below
the window and inside the chamber. The metal plate is capable of
being exposed directly to a plasma to be generated in the interior
cavity.
[0021] In another embodiment, a method for making an inductively
coupled plasma etching apparatus is disclosed. The method includes
providing a chamber having an interior cavity defined by a bottom,
a top, and side walls. The top is configured to have an opening.
The method further includes placing a metal shield over the chamber
interior cavity such that the metal shield is directly exposed to
the chamber interior cavity. The method also includes placing a
window above the metal shield such that the window creates a seal
around the top opening of the chamber. The metal shield remains
inside the chamber interior cavity and below the window. The method
further includes placing a coil above the window.
[0022] In another embodiment, a method is disclosed for making an
inductively coupled plasma etching apparatus. The method includes
providing a chamber having an interior cavity defined by a bottom
and side walls, wherein each of the side walls has a top surface.
The method also includes placing a thermally conductive adapter
plate to interface with the top surface of the side walls so as to
form a seal between the thermally conductive adapter plate and the
side walls. The thermally conductive adapter plate is defined to
have a central opening over the chamber interior cavity. The method
further includes placing a metal shield to cover the central
opening of the thermally conductive adapter plate. The metal shield
is also placed to establish a thermal connection between the metal
shield and the thermally conductive adapter plate. Thus, the metal
shield is placed to be in direct exposure to the chamber interior
cavity. Additionally, the method includes placing a window above
the metal shield and thermally conductive adapter plate so as to
form a seal between the window and the thermally conductive adapter
plate. A coil is then placed above the window.
[0023] In another embodiment, a method is disclosed for making an
inductively coupled plasma etching apparatus. The method includes
providing a chamber defined by a bottom, side walls, and an upper
heat dissipation structure. The upper heat dissipation structure is
defined to include an opening through which an interior cavity of
the chamber is exposed. The method also includes placing a
thermally conductive metal shield in thermal communication with the
upper heat dissipation structure so as to cover the opening within
the heat dissipation structure. Thus, the thermally conductive
metal shield is directly exposed to the chamber interior cavity.
The method further includes placing a window above the thermally
conductive metal shield so as to form a seal between the window and
the upper heat dissipation structure around the thermally
conductive metal shield. Additionally, the method includes placing
a coil above the window.
[0024] In another embodiment, a method is disclosed for making an
inductively coupled plasma etching apparatus. The method includes
providing a chamber defined by a bottom and side walls, wherein
each of the side walls has a top surface. The method also includes
forming a chamber top to include a heat dissipation structure and a
metal shield thermally integrated with the heat dissipation
structure. The heat dissipation structure defines a peripheral
portion of the chamber top. The metal shield defines a central
portion of the chamber top. Also, the metal shield is substantially
planar with a top surface of the heat dissipation structure. The
method further includes placing the chamber top to interface with
the top surface of the side walls so as to form a seal between the
chamber top and the side walls. Additionally, the method includes
placing a window above the chamber top so as to form a seal between
the window and the peripheral portion of the chamber top. Then, a
coil is placed above the window.
[0025] The advantages of the present invention are numerous. Most
notably, the apparatus and method for configuring a Faraday shield
between the etching chamber window and a plasma avoids the problems
of the prior art by maintaining the condition of the etching
chamber window. The present invention avoids one problem of the
prior art by preventing erosion of the etching chamber window
resulting from plasma sputter. The present invention avoids another
problem of the prior art by shunting heat generated by an etching
process away from the etching chamber window.
[0026] Other aspects and advantages of the invention will become
more apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings in which:
[0028] FIG. 1A shows an inductively coupled plasma etching
apparatus 100, in accordance with the prior art;
[0029] FIG. 1B shows the basic operating principles of the
inductively coupled plasma etching apparatus 100, in accordance
with the prior art;
[0030] FIG. 1C shows an illustration of a deposition 157 of
non-volatile reaction products on the window 111 in accordance with
the prior art;
[0031] FIG. 1D shows an illustration of window 111 erosion 159 in
accordance with the prior art;
[0032] FIG. 2 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 201 that is
integral with the adapter plate 203 in accordance with one
embodiment of the present invention;
[0033] FIG. 3A shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 231 that is
configured to mate with a channel 239 in an adapter plate 233 in
accordance with one embodiment of the present invention;
[0034] FIG. 3B shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 251 that is
configured to mate with a channel 257 in an adapter plate 253 in
accordance with one embodiment of the present invention;
[0035] FIG. 4 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 271 configured
with a radial support body 275 that is contoured to be
bottom-inserted within an adapter plate 273 in accordance with one
embodiment of the present invention;
[0036] FIG. 5 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 291 configured
with a radial support body 295 that is contoured to be top-inserted
within an adapter plate 293 in accordance with one embodiment of
the present invention;
[0037] FIG. 6 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 311 that is
configured to be integral with an adapter plate liner 315 in
accordance with one embodiment of the present invention;
[0038] FIG. 7 shows an illustration of a top view of a Faraday
shield 401 configured within an adapter plate 403 in accordance
with an exemplary embodiment of the present invention;
[0039] FIG. 8 shows an illustration of a top view of a Faraday
shield 407 configured within an adapter plate 403 in accordance
with an exemplary embodiment of the present invention;
[0040] FIG. 9 shows an illustration of a Faraday shield 411 in
accordance with an exemplary embodiment of the present
invention;
[0041] FIG. 10 shows an illustration of a two-part Faraday shield
assembly 419 in accordance with an exemplary embodiment of the
present invention;
[0042] FIG. 11 shows an illustration of an exemplary temperature
distribution across a quartz window directly exposed to the plasma
in accordance with the prior art;
[0043] FIG. 12 shows an illustration of an exemplary temperature
distribution across the quartz window when the Faraday shield is
disposed substantially near the window inside the inductively
coupled plasma etching chamber in accordance with one embodiment of
the present invention;
[0044] FIG. 13 shows an illustration of an exemplary temperature
distribution across a ceramic (e.g., Al.sub.2O.sub.3) window
directly exposed to the plasma in accordance with the prior
art;
[0045] FIG. 14 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.19 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention;
[0046] FIG. 15 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.38 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention;
[0047] FIG. 16 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.56 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention; and
[0048] FIG. 17 shows a flowchart of a method for making an
inductively coupled plasma etching apparatus in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] An invention is disclosed for apparatuses and methods for
positioning and using a Faraday shield in direct exposure to a
plasma within an inductively coupled plasma etching apparatus.
Broadly speaking, the present invention maintains a condition of an
etching chamber window. Configuring the Faraday shield between the
window and the plasma prevents erosion of the window resulting from
plasma sputter and shunts heat generated by an etching process away
from the window. The present invention solves one problem of the
prior art by reducing the window replacement frequency driven by
erosion of the window due to plasma sputter. The present invention
solves another problem of the prior art by allowing the use of a
larger variety of window materials through a relaxation of thermal
performance requirements afforded by the shunting of heat away from
the window.
[0050] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. It will be apparent, however, to one skilled in
the art that the present invention may be practiced without some or
all of these specific details. In other instances, well known
process operations have not been described in detail in order not
to unnecessarily obscure the present invention.
[0051] FIG. 2 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 201 that is
integral with the adapter plate 203 in accordance with one
embodiment of the present invention. The inductively coupled plasma
etching apparatus 100 includes an etching chamber structurally
defined by chamber walls 101, an adapter plate 203, and a window
111. The chamber walls 101 and adapter plate 203 are typically
fabricated from aluminum or stainless steel; however, other
suitable materials may also be used. The window 111 is typically
fabricated from 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) may also be
used. An o-ring 211 is used to provide a vacuum seal between the
window 111 and the adapter plate 203. The window 111 position is
maintained by a bumper 207. A heater 209 is located below the
bumper 207 in a channel provided within the adapter plate 203. The
heater 209 is used to prevent the existence of cold surfaces which
could adversely affect the etching process. The heater 209 is
generally used to maintain the adapter plate 203 temperature within
a range from about 50.degree. C. to about 70.degree. C. However,
during the etching process, adapter plate 203 temperatures may
exceed the heater 209 operational range, thus eliminating the need
to operate the heater 209.
[0052] An adapter plate liner 213 is configured to cover the
adapter plate 203 surface exposed to a chamber internal cavity 102.
The adapter plate liner 213 also extends between the chamber walls
101 and the adapter plate 203. The adapter plate liner 213
thickness is nominally about 0.06 inch. However, the adapter plate
liner 213 thickness may be larger or smaller depending on the
etching chamber configuration and etching process requirements.
Typically, there is a region of free space between the adapter
plate liner 213 and the adapter plate 203. Therefore, an o-ring 217
is used to provide a vacuum seal between the adapter plate liner
213 and the adapter plate 203 at a location between the adapter
plate 203 and the chamber walls 101. An RF gasket 219 is provided
outside of the o-ring 217 to maintain continuity of ground between
the adapter plate liner 213 and the adapter plate 203.
[0053] A chuck 117 is positioned near the bottom inner surface of
the etching chamber. The chuck 117 is configured to receive and
hold a semiconductor wafer (i.e., "wafer") 119 upon which the
etching process is performed. The chuck 117 can be electrically
charged using an RF power supply (not shown). A bucket liner 215 is
configured to form an annular trough surrounding the chuck 117. The
bucket liner 215 is further configured to cover the chamber walls
101 extending upward from the annular trough. The bucket liner 215
also extends between the chamber walls 101 and the adapter plate
203. Typically, there is a region of free space between the bucket
liner 215 and the chamber walls 101. Therefore, an o-ring 221 is
used to provide a vacuum seal between the bucket liner 215 and the
chamber walls 101 at a location between the adapter plate 203 and
the chamber walls 101. An RF gasket 223 is provided outside of the
o-ring 221 to maintain continuity of ground between the bucket
liner 215 and the chamber walls 101.
[0054] A coil 133 composed of an electrically conductive material
and including at least one complete turn is configured above the
window 111. The exemplary coil 133 shown in FIG. 2 includes three
turns. The coil 133 symbols having a ".cndot." indicate that the
coil 133 extends rotationally out of the page. The coil 133 is
configured to be substantially parallel to the window 111.
Additionally, an RF power supply (not shown) is configured to
supply RF power to the coil 133.
[0055] The Faraday shield 201 is positioned immediately below the
window 111 to be directly exposed to the chamber internal cavity
102. The Faraday shield 201 is configured to be substantially
parallel to the window 111. The Faraday shield 201 generally has a
thickness ranging from about 0.03 inch to about 1 inch. A nominal
Faraday shield 201 thickness is about 0.19 inch. The Faraday shield
201 is generally composed of an electrically conductive material
such as aluminum. Hence, the Faraday shield 201 is also referred to
as a metal shield 201. The Faraday shield 201 may also be coated or
anodized with a material compatible with the etching process
environment such as alumina. Depending on the Faraday shield 201
configuration, the coating thickness can range from about 0.002
inch to about 0.01 inch. Numerous other Faraday shield 201 and
coating materials may be used so long as the Faraday shield 201
functionality is not compromised.
[0056] A space 205 exists between the Faraday shield and the window
111. A distance across the space 205 perpendicular to both the
Faraday shield 201 and the window 111 is generally within the range
from about 0.005 inch to 0.04 inch. A nominal perpendicular
distance across the space 205 is about 0.02 inch. As previously
mentioned, the Faraday shield 201 shown in FIG. 2 is an integral
part of the adapter plate 203. Thus, since the adapter plate 203 is
grounded, the Faraday shield 201 is also grounded. In some etching
processes, however, it may be beneficial to have the Faraday shield
201 electrically charged. The Faraday shield 201 is typically
configured to have a plurality of slots oriented to be
perpendicular to the direction of the coil 133 turns. The plurality
of slots are provided to disrupt a flow of electric current induced
by the coil 133 through the Faraday shield 201. A current flowing
through the Faraday shield 201 can electrically shield a plasma
from the coil 133, thus extinguishing the plasma.
[0057] During operation, a reactant gas flows through the etching
chamber from a gas lead-in port 220 to a gas exhaust port (not
shown). High frequency power (i.e., RF power) is then applied from
a power supply (not shown) to the coil 133 to cause an RF current
to flow through the coil 133. The RF current flowing through the
coil 133 generates an electromagnetic field about the coil 133. The
electromagnetic field generates an inductive current within the
etching chamber. The inductive current acts on the reactant gas to
generate the plasma. High frequency power (i.e., RF power) is
applied from a power supply (not shown) to the chuck 117 to provide
directionality to the plasma such that the plasma is "pulled" down
onto the wafer 119 surface to effect the etching process.
[0058] The plasma contains various types of radicals in the form of
positive and negative ions. The chemical reactions of the various
types of positive and negative ions are used to etch the wafer 119.
During the etching process, the coil 133 performs a function
analogous to that of a primary coil in a transformer, while the
plasma performs a function analogous to that of a secondary coil in
the transformer.
[0059] During operation, the Faraday shield 201 ensures that an
electrostatic field generated between the coil 133 and the plasma
is uniformly distributed across the window 111 interior surface.
With the Faraday shield 201 configured below the window 111 and in
direct exposure to the plasma, the Faraday shield intercepts plasma
sputtering toward the window 111, thus preventing window 111
erosion generally caused by plasma sputter. The Faraday shield also
intercepts the heat flux generated by the etching process occurring
in the chamber internal cavity 102. The integral configuration of
the Faraday shield with the adapter plate 203 creates an efficient
thermal conduction path to shunt heat away from the window 111.
Hence, the window 111 temperatures are lowered, and the temperature
gradient across the window surface is substantially decreased.
Configuring the Faraday shield 201 to be inside the chamber
internal cavity 102, below the window 111, and in direct exposure
to the plasma serves to protect the window 111 from etching
by-product deposition, plasma sputter induced erosion, and thermal
stresses caused by large temperature gradients.
[0060] FIG. 3A shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 231 that is
configured to mate with a channel 239 in an adapter plate 233 in
accordance with one embodiment of the present invention. The
Faraday shield 231 characteristics are the same as those previously
described for the Faraday shield 201 shown in FIG. 2 with the
exception of the features described below.
[0061] The Faraday shield 231 includes a surrounding ring 241
configured to mate with the channel 239 provided in the adapter
plate 233. The o-ring 211 provides a vacuum seal between the window
111 and the surrounding ring 241. Similarly, an o-ring 235 provides
a vacuum seal between the adapter plate 233 and the surrounding
ring 241. The Faraday shield 231 and surrounding ring 241 are both
electrically conductive and are grounded to the adapter plate 233
by an RF gasket 237. The Faraday shield 231 and surrounding ring
241 have the beneficial feature of being easy to access and remove
from the adapter plate 233 for routine maintenance or
replacement.
[0062] FIG. 3B shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 251 that is
configured to mate with a channel 257 in an adapter plate 253 in
accordance with one embodiment of the present invention. The
Faraday shield 251 characteristics are the same as those previously
described for the Faraday shield 201 shown in FIG. 2 with the
exception of the features described below.
[0063] The Faraday shield 251 includes a surrounding insulating
ring 255 configured to mate with the channel 257 provided in the
adapter plate 253. The o-ring 211 provides a vacuum seal between
the window 111 and the surrounding insulating ring 255. Similarly,
an o-ring 258 provides a vacuum seal between the adapter plate 253
and the surrounding insulating ring 255. The Faraday shield 251 is
electrically conductive and electrically isolated from the adapter
plate 253 by the surrounding insulating ring 255. An electrical
conductor 261 is connected to the Faraday shield 251 through an
insulated penetration 259 in the bumper 207. A voltage can be
applied to the electrical conductor 261 to electrically charge the
Faraday shield 251. Some etching processes may benefit from the
Faraday shield 251 being electrically charged. The Faraday shield
251 and surrounding insulating ring 255 have the beneficial feature
of being easy to access and remove from the adapter plate 253 for
routine maintenance or replacement.
[0064] FIG. 4 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 271 configured
with a radial support body 275 that is contoured to be
bottom-inserted within an adapter plate 273 in accordance with one
embodiment of the present invention. The Faraday shield 271
characteristics are the same as those previously described for the
Faraday shield 201 shown in FIG. 2 with the exception of the
features described below.
[0065] The Faraday shield 271 includes a radial support body 275
contoured to be bottom-inserted within the adapter plate 273. The
contour of the radial support body 275 mates with a complementary
contour on the adapter plate 273. The o-ring 211 provides a vacuum
seal between the window 111 and the radial support body 275.
Similarly, an o-ring 277 and an o-ring 279 provide a vacuum seal
between the adapter plate 273 and the radial support body 275. An
o-ring 283 provides a vacuum seal between the bucket liner 215 and
the radial support body 275. The Faraday shield 271 and the radial
support body 275 are both electrically conductive and are grounded
to the adapter plate 273 by an RF gasket 281. The radial support
body 275 is further grounded to the bucket liner 215 by an RF
gasket 285. The Faraday shield 271 and the radial support body 275
have the beneficial feature of being easy to access and remove from
the adapter plate 273 for routine maintenance or replacement. Also,
the adapter plate 273 can be removed from the etching apparatus
without removing the Faraday shield 271 and the radial support body
275.
[0066] FIG. 5 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 291 configured
with a radial support body 295 that is contoured to be top-inserted
within an adapter plate 293 in accordance with one embodiment of
the present invention. The Faraday shield 291 characteristics are
the same as those previously described for the Faraday shield 201
shown in FIG. 2 with the exception of the features described
below.
[0067] The Faraday shield 291 includes a radial support body 295
contoured to be top-inserted within the adapter plate 293. The
contour of the radial support body 295 mates with a complementary
contour on the adapter plate 293. The o-ring 211 provides a vacuum
seal between the window 111 and the radial support body 295.
Similarly, an o-ring 297 provides a vacuum seal between the adapter
plate 293 and the radial support body 295. An o-ring 301 provides a
vacuum seal between the bucket liner 215 and the adapter plate 293.
The Faraday shield 291 and the radial support body 295 are both
electrically conductive and are grounded to the adapter plate 293
by an RF gasket 299. Continuity of ground is also provided by an RF
gasket 305 between the adapter plate 293 and the bucket liner 215.
The Faraday shield 291 and the radial support body 295 have the
beneficial feature of being easy to access and remove from the
adapter plate 293 for routine maintenance or replacement. Also, the
Faraday shield 291 and the radial support body 295 can be removed
without removing the adapter plate 293.
[0068] FIG. 6 shows an illustration of an inductively coupled
plasma etching apparatus 100 having a Faraday shield 311 that is
configured to be integral with an adapter plate liner 315 in
accordance with one embodiment of the present invention. The
Faraday shield 311 characteristics are the same as those previously
described for the Faraday shield 201 shown in FIG. 2 with the
exception of the features described below.
[0069] The Faraday shield 311 is integral with the adapter plate
liner 315. An o-ring 317 provides a vacuum seal between the Faraday
shield 311 and adapter plate liner 315 combination and an adapter
plate 313. The Faraday shield 311 and adapter plate liner 315
combination is electrically conductive and is grounded to the
adapter plate 313 by an RF gasket 319. The Faraday shield 311 and
adapter plate liner 315 combination has the beneficial feature of
being easy to access and remove from the adapter plate 313 for
routine maintenance or replacement.
[0070] FIGS. 7-10 show illustrations of a number of alternate
Faraday shield configurations in accordance with exemplary
embodiments of the present invention. The Faraday shield is
composed of an electrically conductive material such as metal.
Since the Faraday shield is exposed to the electromagnetic field
generated by the coil 133, an electric current is capable of being
induced within the Faraday shield. The electric current induced in
the Faraday shield will generally flow in a direction corresponding
to the coil 133 turns. Since the coil 133 is typically turned in a
circular manner, the electric current induced in the Faraday shield
will typically flow in a circular direction about the center of the
coil 133 (i.e., the center of the etching chamber). The presence of
an electric current on the Faraday shield can be detrimental to the
etching process by electrically shielding the plasma from the coil
133. Thus, the electric current on the Faraday shield disrupts the
required electrical communication between the coil 133 and the
plasma. Therefore, it is necessary to disrupt the flow of electric
current on the Faraday shield. A plurality of slots are provided on
the Faraday shield to disrupt the flow of the induced electric
current. The plurality of slots are generally oriented in an
outwardly radiating direction from the center of the chamber.
Hence, the plurality of slots are configured to be perpendicular to
the direction in which the coil 133 is turned.
[0071] FIG. 7 shows an illustration of a top view of a Faraday
shield 401 configured within an adapter plate 403 in accordance
with an exemplary embodiment of the present invention. A plurality
of slots 405 are provided to disrupt the flow of electric current
induced by the coil 133.
[0072] FIG. 8 shows an illustration of a top view of a Faraday
shield 407 configured within an adapter plate 403 in accordance
with an exemplary embodiment of the present invention. A plurality
of slots 409 are provided to disrupt the flow of electric current
induced by the coil 133.
[0073] FIG. 9 shows an illustration of a Faraday shield 411 in
accordance with an exemplary embodiment of the present invention. A
plurality of slots 413 are provided to disrupt the flow of electric
current induced by the coil 133.
[0074] FIG. 10 shows an illustration of a two-part Faraday shield
assembly 419 in accordance with an exemplary embodiment of the
present invention. The two-part Faraday shield assembly 419
includes a dielectric-coated star-pattern insert 415 and a
complementary dielectric-coated receiving member 417. Insertion of
the star-pattern insert 415 into the complementary receiving member
417 results is the creation of a plurality of slots 421. The
plurality of slots 421 disrupt the flow of electric current induced
by the coil 133. Disassembly of the two-part Faraday shield
assembly 419 provides easy access to interior surfaces of the
plurality of slots 421. Access to the interior surfaces of the
plurality of slots 421 is beneficial for applying a coating
material to the Faraday shield assembly 419.
[0075] FIG. 11 shows an illustration of an exemplary temperature
distribution across a quartz window directly exposed to the plasma
in accordance with the prior art. In the example of FIG. 11, the
quartz window is one inch thick. The quartz window temperature
distribution corresponds to a plasma power of 100 W. The maximum
quartz window temperature of 220.degree. C. occurs at a location
161 substantially near the center of the quartz window surface
exposed to the plasma. The minimum quartz window temperature of
100.degree. C. occurs at a location 163 substantially near the edge
of the quartz window surface opposite the plasma. Thus, direct
exposure of the quartz window to the 100 W plasma results in a
temperature difference of 120.degree. C. between the center and the
edge of the quartz window. Also, the temperature gradient is quite
large near the edge of the quartz window. Since quartz has a very
low coefficient of thermal expansion, the quartz window can
withstand the large temperature gradient experienced during the
etching process. However, the quartz window is quite susceptible to
erosion caused by plasma sputter. Therefore, placement of the
Faraday shield below the quartz window is desirable to protect the
window from the erosive effects of the plasma sputter.
[0076] FIG. 12 shows an illustration of an exemplary temperature
distribution across the quartz window when the Faraday shield is
disposed substantially near the window inside the inductively
coupled plasma etching chamber in accordance with one embodiment of
the present invention. As in the example of FIG. 11, the quartz
window in FIG. 12 is one inch thick. Also, the quartz window
temperature distribution corresponds to a plasma power of 100 W. A
maximum quartz window temperature of 90.degree. C. occurs at a
location 501 substantially near the center of the quartz window
surface exposed to the plasma. Similarly, a maximum Faraday shield
temperature of 110.degree. C. occurs at a location 505
substantially near the center of the Faraday shield. A minimum
quartz window temperature of 75.degree. C. occurs at a location 503
substantially near the edge of the quartz window surface opposite
the plasma. Thus, the maximum-to-minimum temperature difference
from the center to the edge of the quartz window is approximately
15.degree. C. with the Faraday shield located below the quartz
window. Also, placement of the Faraday shield below the quartz
window significantly reduces the temperature gradient present from
the center to the edge of the quartz window.
[0077] For the example etching process considered in FIGS. 11 and
12, the presence of the Faraday shield below the quartz window as
opposed to above the quartz window decreases the maximum and
minimum temperatures by about 59% and about 25%, respectively.
Also, the temperature gradient from the center to the edge of the
quartz window is significantly reduced with the Faraday shield
located below the quartz window and inside the etching chamber.
With the decreased temperature gradient afforded by placement of
the Faraday shield below the window, other stronger, more durable,
and less expensive window materials (e.g., ceramic) can be
considered for use in conjunction with higher power, higher
temperature etching processes.
[0078] FIG. 13 shows an illustration of an exemplary temperature
distribution across a ceramic (e.g., Al.sub.2O.sub.3) window
directly exposed to the plasma in accordance with the prior art. In
the example of FIG. 13, the ceramic window is one inch thick. The
ceramic window temperature distribution corresponds to a plasma
power of 100 W. The maximum ceramic window temperature of
110.degree. C. occurs at a location 165 substantially near the
center of the ceramic window surface exposed to the plasma. The
minimum ceramic window temperature of 90.degree. C. occurs at a
location 167 substantially near the edge of the ceramic window
surface opposite the plasma. Thus, direct exposure of the ceramic
window to the 100 W plasma results in a temperature difference of
20.degree. C. between the center and the edge of the ceramic
window. This temperature difference is less than the corresponding
temperature difference of 120.degree. C. for the quartz window due
to the ceramic window's higher thermal conductivity. However, the
ceramic window has a larger coefficient of thermal expansion than
the quartz window. Thus, the presence of a large temperature
gradient across the ceramic window may result in non-uniform
thermal expansion and subsequent failure of the ceramic window.
However, relative to quartz the ceramic window is stronger, more
durable, and less expensive. Therefore, placement of the Faraday
shield below the ceramic window is desirable not only for shielding
the window from direct exposure to the plasma but also for shunting
heat away from the window toward the adapter plate.
[0079] FIG. 14 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.19 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention. As in the example of FIG. 13,
the ceramic window in FIG. 14 is one inch thick. Also, the
temperature distribution corresponds to a plasma power of 100 W. A
maximum Faraday shield temperature of 110.degree. C. occurs at a
location 515 substantially near the center of the Faraday shield.
The temperature distribution from a location 511 near the center of
the ceramic window to a location 513 near the edge of the ceramic
window is approximately constant at 75.degree. C. Thus, placement
of the Faraday shield below the ceramic window results in a
vanishingly small temperature gradient from the center to the edge
of the ceramic window. Such a small temperature gradient allows the
ceramic window to be used in higher power, higher temperature
etching processes without experiencing cracking and failure due to
non-uniform thermal expansion.
[0080] For the example etching process considered in FIGS. 13 and
14, the presence of the Faraday shield below the ceramic window as
opposed to above the ceramic window decreases the maximum and
minimum ceramic window temperatures by about 32% and about 17%,
respectively. Also, the temperature gradient from the center to the
edge of the ceramic window is significantly reduced with the
Faraday shield located below the ceramic window and inside the
etching chamber. In addition to minimizing the temperature gradient
across the ceramic window, it may also be desirable in some etching
processes to reduce the maximum Faraday shield temperature.
[0081] FIG. 15 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.38 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention. As in the examples of FIGS. 13
and 14, the ceramic window in FIG. 15 is one inch thick. Also, the
temperature distribution corresponds to a plasma power of 100 W.
The temperature distribution from a location 517 near the center of
the ceramic window to a location 519 near the edge of the ceramic
window remains approximately constant at 75.degree. C. A maximum
Faraday shield temperature of 90.degree. C. occurs at a location
521 substantially near the center of the Faraday shield. Thus,
increasing the Faraday shield thickness by about a factor of two
from 0.19 inch to 0.38 inch results in approximately a 18% decrease
in maximum Faraday shield temperature. The decrease in temperature
is a result of increased thermal conductance to the adapter plate
as afforded by the thicker Faraday shield.
[0082] FIG. 16 shows an illustration of an exemplary temperature
distribution across the ceramic window when a 0.56 inch thick
Faraday shield is disposed substantially near the window inside the
inductively coupled plasma etching chamber in accordance with one
embodiment of the present invention. As in the examples of FIGS.
13, 14, and 15, the ceramic window in FIG. 16 is one inch thick.
Also, the temperature distribution corresponds to a plasma power of
100 W. The temperature distribution from a location 523 near the
center of the ceramic window to a location 525 near the edge of the
ceramic window remains approximately constant at 75.degree. C. A
maximum Faraday shield temperature of 85.degree. C. occurs at a
location 527 substantially near the center of the Faraday shield.
Thus, increasing the Faraday shield thickness by about a factor of
three from 0.19 inch to 0.56 inch results in approximately a 23%
decrease in maximum Faraday shield temperature. As in the example
of FIG. 15, the decrease in temperature is a result of increased
thermal conductance to the adapter plate as afforded by the thicker
Faraday shield.
[0083] FIG. 17 shows a flowchart of a method for making an
inductively coupled plasma etching apparatus in accordance with one
embodiment of the present invention. The method includes a step 601
for providing a chamber having an interior cavity defined by a
bottom, side walls, and a top having an opening. The method further
includes a step 603 wherein a metal shield to be placed within the
chamber interior cavity is coated, if required by the etching
process parameters. The method also includes a step 605 wherein the
metal shield is electrically isolated, if required by the etching
process parameters. The method includes another step 607 wherein
the metal shield is placed within the chamber interior cavity to
cover the opening in the chamber top. In a step 609 of the method,
a window is placed above the metal shield such that the window
covers the opening in the chamber top and creates a vacuum seal
with the outside of the chamber top. The method also includes a
step 611 wherein a coil is placed above the window such that the
coil and window are substantially parallel to each other.
[0084] While this invention has been described in terms of several
embodiments, it will be appreciated that those skilled in the art
upon reading the preceding specifications and studying the drawings
will realize various alterations, additions, permutations and
equivalents thereof. It is therefore intended that the present
invention includes all such alterations, additions, permutations,
and equivalents as fall within the true spirit and scope of the
invention.
* * * * *